JP2019172575A - Production methods of nitrogen-containing heterocyclic compound and squarylium compound - Google Patents

Abstract

To provide a production method of nitrogen-containing heterocyclic compound enabling nitrogen-containing heterocyclic compound to be effectively provided, and a production method of a squarylium compound.SOLUTION: The production method of a nitrogen-containing heterocyclic compound is provided that includes a step of reacting a compound represented by the following formula (1) with an aldehyde compound represented by the following formula (2) in the presence of a hydrogenated boron compound represented by the following formula (3) to obtain a compound represented by the following formula (4). In the formula (1) to the formula (4), Rand Rrepresent each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or a halogeno group, Rrepresents an alkyl group having 1 to 20 carbon atoms, Rrepresents an alkyl group having 1 to 6 carbon atoms, or an acyl group having 2 to 6 carbon atoms, M represents an alkali metal atom, and a ring A represents a 5- to 8-membered nitrogen-containing heterocycle which may have a substituent.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a nitrogen-containing heterocyclic compound and a method for producing a squarylium compound.

The squarylium compound is useful as a dye having an absorption range in the red to near infrared region, and various types of squarylium compounds have been known so far. For example, Patent Documents 1 to 3 disclose a squarylium compound having a structure in which a benzene ring is bonded to both sides of a squarylium skeleton. Particularly, Patent Document 1 discloses a squarylium compound shown below. Patent Document 1 also discloses a method for producing the squarylium compound, using 2,3,3-trimethylindolenine as a starting material, introduction of a group R _x into the nitrogen atom of the indolenine skeleton, and hydrogenation of the indolenine skeleton. The following squarylium compounds are produced through the conversion to the indoline skeleton, introduction of the nitro group into the indoline skeleton, reduction of the nitro group to the amino group, amidation of the amino group, and addition reaction with squaric acid. .

International Publication No. 2014/088063 JP 2012-008532 A Japanese Patent Application Laid-Open No. 2015-086378

  However, the production method of Patent Document 1 has room for improvement in terms of yield, and in particular, there is a method that can be more efficiently produced at the stage of producing a nitrogen-containing heterocyclic compound such as an indoline compound that is a raw material for producing a squarylium compound. Desirable if present.

  This invention is made | formed in view of the said situation, The objective is providing the manufacturing method of a nitrogen-containing heterocyclic compound which can obtain a nitrogen-containing heterocyclic compound efficiently, and the manufacturing method of a squarylium compound. It is in.

  The present inventors have studied various methods for producing a nitrogen-containing heterocyclic compound that can be used as a raw material for producing a squarylium compound. As a result, a nitro group is bonded to a benzene ring, and a compound in which a nitrogen-containing heterocycle is condensed to the benzene ring is introduced into a nitrogen atom constituting the ring structure, thereby producing a squarylium compound. It turned out that the nitrogen-containing heterocyclic compound which can be used as a raw material can be manufactured efficiently. At this time, an aldehyde compound is used as a source of a substituent to be introduced into the nitrogen-containing heterocyclic ring, and this is reacted in the presence of a specific borohydride compound, whereby the substituent is converted into a ring structure of the nitrogen-containing heterocyclic compound. It has been clarified that it can be efficiently introduced into the nitrogen atoms composing

［式（１）〜式（４）中、
Ｒ¹とＲ²はそれぞれ独立して、水素原子、炭素数１〜２０のアルキル基、炭素数１〜２０のアルコキシ基、またはハロゲノ基を表し、
Ｒ³は炭素数１〜２０のアルキル基を表し、
Ｒ⁴は炭素数１〜６のアルキル基または炭素数２〜６のアシル基を表し、
Ｍはアルカリ金属原子を表し、
環Ａは置換基を有していてもよい５員〜８員の含窒素複素環を表す。］
［２］Ｒ³は分岐状アルキル基を表す［１］に記載の含窒素複素環化合物の製造方法。
［３］Ｒ³の分岐状アルキル基は、前記式（２）のアルデヒド化合物のホルミル基のα位、β位またはγ位で分岐している［２］に記載の含窒素複素環化合物の製造方法。
［４］Ｒ¹およびＲ²は水素原子を表す［１］〜［３］のいずれかに記載の含窒素複素環化合物の製造方法。
［５］［１］〜［４］のいずれかに記載の製造方法により前記式（４）で表される含窒素複素環化合物を得る工程を含むことを特徴とするスクアリリウム化合物の製造方法。
［６］前記含窒素複素環化合物に含まれるニトロ基をアミノ基に変換する還元工程と、
前記アミノ基をアミド基に変換するアミド化工程と、
前記アミド化工程で得られた生成物を、スクアリン酸またはその誘導体と反応させて、下記式（５）で表される構造を有するスクアリリウム化合物を得る工程をさらに含む［５］に記載のスクアリリウム化合物の製造方法。

［式（５）中、Ｒ¹〜Ｒ³および環Ａは上記と同じ意味を表し、Ｒ⁶は有機基を表す。］ That is, the present invention includes the following inventions.
[1] A compound represented by the following formula (1) is reacted with an aldehyde compound represented by the following formula (2) in the presence of a borohydride compound represented by the following formula (3). (4) The manufacturing method of the nitrogen-containing heterocyclic compound characterized by including the process of obtaining the compound represented.

[In Formula (1)-Formula (4),
R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or a halogeno group,
R ³ represents an alkyl group having 1 to 20 carbon atoms,
R ⁴ represents an alkyl group having 1 to 6 carbon atoms or an acyl group having 2 to 6 carbon atoms,
M represents an alkali metal atom;
Ring A represents a 5- to 8-membered nitrogen-containing heterocyclic ring which may have a substituent. ]
[2] The method for producing a nitrogen-containing heterocyclic compound according to [1], wherein R ³ represents a branched alkyl group.
[3] Production of the nitrogen-containing heterocyclic compound according to [2], wherein the branched alkyl group of R ³ is branched at the α-position, β-position or γ-position of the formyl group of the aldehyde compound of the formula (2). Method.
[4] The method for producing a nitrogen-containing heterocyclic compound according to any one of [1] to [3], wherein R ¹ and R ² represent a hydrogen atom.
[5] A method for producing a squarylium compound, comprising a step of obtaining the nitrogen-containing heterocyclic compound represented by the formula (4) by the production method according to any one of [1] to [4].
[6] A reduction step of converting a nitro group contained in the nitrogen-containing heterocyclic compound into an amino group;
An amidation step of converting the amino group into an amide group;
The squarylium compound according to [5], further comprising the step of reacting the product obtained in the amidation step with squaric acid or a derivative thereof to obtain a squarylium compound having a structure represented by the following formula (5): Manufacturing method.

Wherein (5), R ¹ ~R ^3, and ring A are as defined above, R ⁶ represents an organic group. ]

  According to the production method of the present invention, a nitrogen-containing heterocyclic compound and a squarylium compound can be produced efficiently.

  In the method for producing a nitrogen-containing heterocyclic compound of the present invention, a compound represented by the following formula (1) is represented by the following formula (2) in the presence of a borohydride compound represented by the following formula (3). And a step of obtaining a compound represented by the following formula (4).

In Formula (1) to Formula (4), R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or a halogeno group, and R ³ represents an alkyl group having 1 to 20 carbon atoms, R ⁴ represents an alkyl group having 1 to 6 carbon atoms or an acyl group having 2 to 6 carbon atoms, M represents an alkali metal atom, and ring A represents a substituent. It represents a 5-membered to 8-membered nitrogen-containing heterocyclic ring which may have. Hereinafter, the compound represented by Formula (1) and the compound represented by Formula (4) may be referred to as “nitrogen-containing heterocyclic compounds”.

According to the production method of the present invention, the nitrogen atom bonded to the carbon atom of the benzene ring of the nitrogen-containing heterocyclic compound of the formula (1), which forms part of the ring A condensed with the benzene ring The R ³ alkyl group of the aldehyde compound of the formula (2) can be introduced into the atom. At this time, by allowing the borohydride compound represented by the formula (3) to coexist, the compound of the formula (4) can be obtained from the compound of the formula (1) with high yield and high purity. The nitrogen-containing heterocyclic compound of the formula (4) can be suitably used as a raw material for producing a squarylium compound, particularly a raw material for producing a squarylium compound having an absorption peak in the red to near infrared region. Therefore, according to the present invention, it is possible to efficiently produce a squarylium compound.

  In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), the nitro group bonded to the benzene ring functions as a precursor of the amide group when producing the squarylium compound. By converting the nitro group bonded to the benzene ring of the nitrogen-containing heterocyclic compound of the formula (4) to an amide group, the adjacent hydrogen atom of the amide group can be easily extracted, and when reacting with squaric acid, the hydrogen atom The addition reaction with squaric acid tends to proceed smoothly at the bonding position of atoms. In the compound of formula (1), when the nitro group is bonded at the meta position with respect to the amino group constituting a part of the ring A, the nitro group is bonded at the ortho position or the para position. The basicity is increased, and the reaction for synthesizing the compound of the formula (4) from the compound of the above formula (1) can proceed smoothly.

  In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), when the amino group that is bonded to the benzene ring and constitutes a part of the ring A is a squarylium compound, it absorbs in the red to near-infrared region. It functions to shift the peak to the long wavelength side (for example, 685 nm or more). Thereby, the transmittance of light in the red region is increased, and the color of the transmitted light comes closer to the actual one. When the amino group reacts with squaric acid, it facilitates the extraction of the hydrogen atom at the para position, and contributes to the smooth addition reaction with squaric acid at the bonding position of the hydrogen atom.

  In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), when the ring A is a squarylium compound, it functions to sharply form an absorption peak in the red to near infrared region. Thereby, it becomes possible to selectively cut light in a wavelength region corresponding to the absorption peak.

In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), the alkyl groups of R ¹ and R ² are methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t- Butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl Linear or branched alkyl groups such as cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group and the like, Can be mentioned. The alkyl group may have a substituent, and examples of the substituent that the alkyl group has include an aryl group, a heteroaryl group, and a halogeno group. Examples of the alkyl group having a halogeno group include a monohalogenoalkyl group, a dihalogenoalkyl group, an alkyl group having a trihalomethyl unit, and a perhalogenoalkyl group. As a halogeno group, a fluorine atom, a chlorine atom, and a bromine atom are preferable, and a fluorine atom is more preferable. The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 12, even more preferably 1 to 8, even more preferably 1 if it is a linear or branched alkyl group. If it is -6 and it is a cyclic | annular alkyl group, C4-C10 is preferable and 5-8 are more preferable.

For specific examples of the alkyl group contained in the alkoxy group of R ¹ and R ² , refer to the description regarding the alkyl group.

Examples of the halogeno group for R ¹ and R ² include a fluoro group, a chloro group, a bromo group, and an iodo group.

In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), R ¹ is preferably a non-bulky group or atom. Thereby, reaction with the nitrogen-containing heterocyclic compound of Formula (1) and the aldehyde compound of Formula (2) can be advanced smoothly. Specifically, the aldehyde compound of the formula (2) becomes easily accessible to the amino group bonded to the adjacent carbon atom of R ¹ of the nitrogen-containing heterocyclic compound of the formula (1), and the reaction intermediate carbinolamine or The production reaction of iminium ions is likely to proceed smoothly. As a result, it becomes easy to efficiently introduce the group R ³ derived from the aldehyde compound of the formula (2) into the amino group of the nitrogen-containing heterocyclic compound of the formula (1). R ¹ is preferably not an electron-attracting group, whereby the basicity of the nitrogen-containing heterocyclic compound of the formula (1) is suppressed and the reactivity with the aldehyde compound of the formula (2) is increased. it can. From such a viewpoint, R ¹ is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably a hydrogen atom or a methyl group, and further preferably a hydrogen atom.

In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), R ² is preferably a non-bulky group or atom. Thereby, the reactivity at the time of making it react with squaric acid can be improved. Specifically, when the derivative obtained by converting the nitro group of the nitrogen-containing heterocyclic compound of the formula (4) into an amide group is reacted with squaric acid, the carbon atom between the amide group and the group R ² (the carbon atom) Hydrogen atom is bound to) squaric acid, and the reaction with squaric acid is likely to proceed. R ² is also preferably not an electron-attracting group, thereby suppressing a decrease in basicity of the nitrogen-containing heterocyclic compound of formula (1) and increasing the reactivity with the aldehyde compound of formula (2). Can do. From such a viewpoint, R ² is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably a hydrogen atom or a methyl group, and further preferably a hydrogen atom.

  In the nitrogen-containing heterocyclic compounds of the formulas (1) and (4), the 5- to 8-membered nitrogen-containing heterocyclic ring of the ring A essentially has a nitrogen atom as a ring constituent atom, and further has a carbon atom. It is preferable. Ring A may be an aromatic heterocycle or a non-aromatic heterocycle.

  Ring A may have only one nitrogen atom as a ring-constituting atom, or may have two or more. Ring A may have a hetero atom other than a nitrogen atom (for example, an oxygen atom or a sulfur atom) as a ring constituent atom. Examples of the nitrogen-containing heterocycle of ring A include pyrrolidine ring, piperidine ring, hexamethyleneimine ring, heptamethyleneimine ring, morpholine ring, thiomorpholine ring, piperazine ring and the like. From the viewpoint of ease of production and availability of the nitrogen-containing heterocyclic compound of formula (1), it is preferable that the ring A and the nitrogen-containing heterocyclic ring have only one nitrogen atom as a ring constituent atom. The ring-constituting atoms are preferably composed of carbon atoms. Ring A is preferably a non-aromatic nitrogen-containing heterocyclic ring, and a carbon atom and a nitrogen atom or carbon atoms are bonded to each other by a single bond except for a carbon-carbon bond condensed with a benzene ring. More preferably.

  Ring A has 5 to 8 members, preferably 6 or less members. Thereby, when it is set as a squarylium compound, the absorption peak of a red-near infrared region can be made sharp, and the inclination of the inclination part by the side of the short wavelength of the said absorption peak can be made absorption. . Therefore, the boundary between the transmission wavelength region and the absorption wavelength region is sharply formed, and light in the wavelength region corresponding to the absorption peak can be selectively cut.

Ring A of the nitrogen-containing heterocyclic compound of formula (1) may have a substituent. Ring A of the nitrogen-containing heterocyclic compound of formula (4) may have a substituent in addition to R ³ . Examples of the substituent that the ring A may have include an alkyl group, an alkoxy group, an aryl group, an aralkyl group, and a halogeno group. For specific examples of the alkyl group, the alkoxy group and the halogeno group which the ring A may have, the description regarding these groups of R ¹ and R ² is referred to. Examples of the aryl group that ring A may have include a phenyl group, a biphenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a pyrenyl group, and an indenyl group. 6-20 are preferable and, as for carbon number of an aryl group, More preferably, it is 6-12. Examples of the aralkyl group that ring A may have include a benzyl group, a phenethyl group, a phenylpropyl group, a phenylbutyl group, a phenylpentyl group, and a naphthylmethyl group. 7-25 are preferable and, as for carbon number of an aralkyl group, 7-15 are more preferable. Among these, as a substituent which the ring A may have, a C1-C3 alkyl group is preferable. Ring A also preferably has no substituent.

  Preferred examples of the nitrogen-containing heterocyclic compound represented by formula (1) and formula (4) include nitrogen-containing heterocyclic compounds represented by the following formula (1-1) and formula (4-1), respectively.

In Formula (1-1) and Formula (4-1), R ^{1 to} R ³ are as described above. R ⁵ represents a hydrogen atom or a substituent bonded to a carbon atom constituting a nitrogen-containing heterocycle condensed to a benzene ring, and n represents an integer of 1 to 4. Several R < ⁵ > may mutually be same or different. Examples of the substituent for R ⁵ include the alkyl group, alkoxy group, aryl group, aralkyl group, and halogeno group described above. R ⁵ is preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

The aldehyde compound of the formula (2) is used for introducing the group R ³ into the amino group of the nitrogen-containing heterocyclic compound of the formula (1). By using the nitrogen-containing heterocyclic compound of the formula (4) having the group R ³ introduced as a raw material for producing the squarylium compound, it becomes easy to obtain a squarylium compound having excellent solubility in organic solvents and resins. Since such a squarylium compound can be contained in an organic solvent or resin at a high concentration, it becomes easy to effectively exhibit the light absorption characteristics derived from the squarylium.

For specific examples of the R ³ alkyl group of the aldehyde compound of the formula (2), reference is made to the description regarding the alkyl groups of R ¹ and R ² above. As the alkyl group for R ³ , branched alkyl is preferably used, whereby the solubility of the squarylium compound in an organic solvent or resin can be effectively enhanced. In this case, the carbon number of the branched alkyl group of R ³ is 3 or more. On the other hand, the upper limit of the carbon number of the branched alkyl group represented by R ³ is preferably 20 or less, more preferably 12 or less, still more preferably 8 or less, and even more preferably 6 or less.

As the branched alkyl group for R ³ , an alkyl group branched at the α-position, β-position or γ-position of the formyl group of the aldehyde compound of the formula (2) is preferably used. Examples of the aldehyde compound having a branched alkyl group include 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, 2-methylpentanal, 3-methylpentanal, 4-methylpentanal, 2,3-dimethylbutanal, 2-methylhexanal, 3-methylhexanal, 4-methylhexanal, 5-methylhexanal, 2-ethylpentanal, 3-ethylpentanal, 2,3-dimethylpentanal, 2, Examples include 4-dimethylpentanal, 3,4-dimethylpentanal, 2-ethyl-3-methylbutanal, and the like.

By the addition reaction of the nitrogen-containing heterocyclic compound of formula (1) and the aldehyde compound of formula (2), an iminium ion is generated as a reaction intermediate, and the iminium ion is converted by the borohydride compound of formula (3). By reduction, a nitrogen-containing heterocyclic compound of the formula (4) in which an alkyl group R ³ is introduced into the amino group of the nitrogen-containing heterocyclic compound of the formula (1) is obtained. At this time, by using the borohydride compound of formula (3), which has a lower reducing power than sodium borohydride, the reduction reaction of the aldehyde compound of formula (2) is suppressed, and iminium ions are selectively reduced. It becomes possible to do.

The alkyl group contained in the R ⁴ alkyl group and acyl group of the borohydride compound of formula (3) may be linear, branched or cyclic, but is linear or branched. It is preferable. In the alkyl group, part or all of the hydrogen atoms may be replaced with halogen atoms. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a pentyl group, and a hexyl group. The alkyl group for R ⁴ preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and still more preferably a methyl group or an ethyl group. The acyl group for R ⁴ preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms, and still more preferably an acetyl group or a propionyl group. As R ⁴ , an acyl group is more preferable than an alkyl group, and an acetyl group is particularly preferable from the viewpoint of ease of production and availability.

  Examples of the M alkali metal atom of the borohydride compound of the formula (3) include lithium, sodium, potassium, rubidium, and cesium. Among these, lithium, sodium or potassium is preferable, and sodium is more preferable. In the borohydride compound of the formula (3), the alkali metal atom of M is usually present in the form of a cation.

  Examples of the borohydride compound of the formula (3) include sodium triacetoxyborohydride, sodium trimethoxyborohydride, sodium tris (1,1,1,3,3,3-hexafluoroisopropoxy) borohydride and the like. It is done.

  The above reaction is preferably performed in the presence of a Bronsted acid such as a carboxylic acid or a sulfonic acid from the viewpoint of allowing the reaction to proceed more rapidly. As the carboxylic acid, a saturated fatty acid having 1 to 6 carbon atoms is preferably used. As the sulfonic acid, it is preferable to use a compound in which a saturated fatty acid having 1 to 5 carbon atoms is bonded to a sulfo group. Among these, it is preferable to use carboxylic acid from the viewpoint of easy purification after the reaction. As the carboxylic acid, it is particularly preferable to use acetic acid, propionic acid or butyric acid.

  The above reaction is preferably performed in a solvent. Solvents that can be used include aliphatic hydrocarbons such as hexane, toluene, heptane, octane, decane, cyclohexane, and cyclooctane; aromatic hydrocarbons such as benzene, toluene, and xylene; dichloromethane, chloroform, 1,2-dichloroethane Halogenated hydrocarbons such as: ethers such as diethyl ether, tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, and methyl tertiary butyl ether; nitriles such as acetonitrile, propionitrile, acrylonitrile, butyronitrile, and the like. These solvents may use only 1 type and may use 2 or more types together.

  The amount of the nitrogen-containing heterocyclic compound of the formula (1) and the aldehyde compound of the formula (2) used is 0.8% of the aldehyde compound of the formula (2) with respect to 1 mol of the nitrogen-containing heterocyclic compound of the formula (1). It is preferably at least mol, more preferably at least 1.0 mol, more preferably at least 1.2 mol, more preferably at most 4.0 mol, even more preferably at most 3.0 mol, further at most 2.5 mol. preferable. The amount of the borohydride compound of formula (3) used is preferably 0.8 mol or more, more preferably 1.0 mol or more, relative to 1 mol of the nitrogen-containing heterocyclic compound of formula (1), 1.2 It is more preferably at least mol, more preferably at most 4.0 mol, even more preferably at most 3.0 mol, further preferably at most 2.5 mol.

  When the above reaction is carried out in the presence of carboxylic acid or sulfonic acid, the amount of carboxylic acid or sulfonic acid used (the total amount of use when both carboxylic acid or sulfonic acid is used) is the amount of formula (1). 0.7 mol or more is preferable, 0.8 mol or more is more preferable, 0.9 mol or more is more preferable, 1.6 mol or less is preferable, and 1.4 mol or less is preferable with respect to 1 mol of the nitrogen heterocyclic compound. Is more preferable, and 1.2 mol or less is still more preferable.

  The total concentration of the nitrogen-containing heterocyclic compound of the formula (1), the aldehyde compound of the formula (2) and the borohydride compound of the formula (3) in the reaction solution is preferably 10 g / L or more, for example, 50 g / L or more. More preferably, 100 g / L or more is further preferable, 800 g / L or less is preferable, 700 g / L or less is more preferable, and 600 g / L or less is more preferable.

  The reaction temperature at the time of performing the above reaction is, for example, preferably -80 ° C or higher, more preferably -40 ° C or higher, further preferably -20 ° C or higher, more preferably 100 ° C or lower, more preferably 80 ° C or lower, 50 ° C. The following is more preferable. What is necessary is just to adjust reaction time suitably according to the progress of reaction, for example, 0.5 hours or more are preferable, 1 hour or more are more preferable, 24 hours or less are preferable, and 12 hours or less are more preferable. The above reaction is preferably performed in an inert gas (for example, nitrogen gas or argon gas) atmosphere.

  By reacting as described above, the nitrogen-containing heterocyclic compound of the formula (4) can be produced from the nitrogen-containing heterocyclic compound of the formula (1). According to the production method of the present invention, the yield in producing the nitrogen-containing heterocyclic compound of the formula (4) from the nitrogen-containing heterocyclic compound of the formula (1) can be set to 90% or more, for example. The yield can be 95% or more, 97% or more, 98% or more, or 99% or more. Moreover, there are very few by-products, and the nitrogen-containing heterocyclic compound of Formula (4) can be obtained with high purity. For this reason, it is possible to simplify the purification operation after the reaction. Examples of the purification operation include solid-liquid separation, washing, extraction, solvent distillation, and drying.

  The nitrogen-containing heterocyclic compound of the formula (4) obtained as described above can be suitably used as a raw material for producing a squarylium compound. Since the nitrogen-containing heterocyclic compound of the formula (1) is easily available or easy to produce, the squarylium compound can be efficiently produced by using the compound as a starting material. As nitrogen-containing heterocyclic compounds of the formula (1), 7-nitro-1,2,3,4-tetrahydroquinoline, 6-nitroindoline and the like are commercially available.

  The present invention also provides a method for producing a squarylium compound comprising the step of obtaining the nitrogen-containing heterocyclic compound of formula (4) from the nitrogen-containing heterocyclic compound of formula (1) as described above. The method for producing the squarylium compound from the nitrogen-containing heterocyclic compound of the formula (4) is not particularly limited, but a reduction step of converting a nitro group contained in the nitrogen-containing heterocyclic compound of the formula (4) into an amino group, A production method including an amidation step for converting a group into an amide group and a step of reacting the product obtained in the amidation step with squaric acid or a derivative thereof to obtain a squarylium compound is suitably shown. Thus, by converting the nitro group of the compound of formula (4) to an amide group and reacting with squaric acid or a derivative thereof, a squarylium compound into which a nitrogen-containing heterocyclic structure derived from the compound of formula (4) is introduced is obtained. It can be obtained in high yield. Hereinafter, each process is demonstrated in order.

  In the reduction step, as shown in the following reaction formula, the nitro group of the compound of formula (4) is reduced to obtain the compound represented by formula (6). Hereinafter, the compound of the formula (4) may be referred to as “nitro compound”, and the compound of the formula (6) may be referred to as “amino compound”.

  In the reduction step, the nitro group of the nitro compound of formula (4) can be reduced to an amino group by using (1) a metal + acid reduction method, (2) a catalytic reduction method, or (3) a metal hydride compound. Reduction methods that have been used. In addition to this, a method of reducing a nitro group to an amino group in the presence of phthalocyanine iron (II) and an iron sulfate catalyst may also be mentioned.

  In the reduction method (1), iron, zinc, tin (for example, tin chloride) or the like is used as a metal, hydrochloric acid, acetic acid, ammonium chloride or the like is used as an acid, and the nitro group is converted to an amino group by acting as a reducing agent. To convert to Examples of the combination of metal and acid include iron / hydrochloric acid, tin / hydrochloric acid, zinc / acetic acid, iron / ammonium chloride, tin chloride / hydrochloric acid and the like.

  The reduction method (2) is a method in which a nitro group is reduced to an amino group with hydrogen in the presence of a catalyst. As the catalyst, Pd, Pt, Ni, Os, or the like is used. These metals that function as a catalytically active component are preferably supported on a carrier such as activated carbon, a carbon-ethylenediamine complex, fibroin, or polyethyleneimine. As a hydrogen source, hydrogen gas, hydrazine, ammonium formate, or the like can be used.

  The reduction method (3) is a method of reducing a nitro group to an amino group using a metal hydride compound. Examples of metal hydride compounds include aluminum hydride compounds such as lithium aluminum hydride, diisobutylaluminum hydride, sodium bis (2-methoxyethoxy) aluminum hydride; sodium borohydride, lithium triethylborohydride, zinc borohydride, etc. Borohydride compounds; tin hydride compounds such as tributyltin hydride; transition metal hydride compounds and the like.

  Among the above reduction methods, it is a metal hydride compound because it is relatively safe during the reaction and can efficiently produce the amino compound of formula (6) by reducing the nitro compound of formula (4). It is preferable to employ a method of reduction using a borohydride compound. More preferably, the nitro group is reduced using a borohydride compound in the presence of a metal salt. In this case, a metal boride is generated from the borohydride compound and the metal salt, and this acts as a reduction catalyst, realizing efficient reduction of the nitro group. As the metal salt, nickel chloride, cobalt chloride, copper chloride, tin chloride, nickel sulfate, nickel acetate and the like can be used, and nickel chloride is particularly preferably used.

The nitro group reduction reaction using a borohydride compound and a metal salt is preferably performed in an alcohol such as methanol or ethanol. Thereby, a highly active metal boride (for example, Ni ₂ B) is easily formed.

  The amount of the borohydride compound used is preferably 1 mol or more with respect to 1 mol of the nitro compound of the formula (4) from the viewpoint of increasing the reduction yield of the nitro group of the nitro compound of the formula (4). The above is more preferable, and 4 mol or more is more preferable. On the other hand, if the amount of borohydride compound used is too large, the amount of borohydride compound that does not contribute to the reduction reaction of the nitro group increases, and there is a concern that an undesirable side reaction may occur. The amount is preferably 25 mol or less, more preferably 20 mol or less, still more preferably 15 mol or less, relative to 1 mol of the nitro compound of formula (4). The amount of the metal salt used is preferably 0.05 mol or more, preferably 0.1 mol or more, preferably 0.5 mol or less, more preferably 0.4 mol or less, relative to 1 mol of the borohydride compound. .

  What is necessary is just to set the reaction temperature of the reduction reaction of the nitro compound of Formula (4) in a reduction | restoration process suitably according to reaction conditions, for example, between -80 degreeC-60 degreeC. The reaction time is not particularly limited, and may be appropriately adjusted according to the progress of the reaction. For example, 0.5 hour or more is preferable, 1 hour or more is more preferable, 24 hours or less is preferable, and 12 hours or less is more preferable. . The reduction step is preferably performed in an inert gas (for example, nitrogen gas or argon gas) atmosphere.

Following the reduction step, an amidation step is performed. In the amidation step, the amino group of formula (6) obtained in the reduction step is reacted with an organic carboxylic acid or a derivative thereof to convert the amino group into an amide group. An organic carboxylic acid or derivative thereof has an organic group bonded to a carboxyl group or derivative thereof. Examples of the carboxylic acid or derivative thereof include carboxylic acid, carboxylic acid anhydride, carboxylic acid halide, and carboxylic acid ester. Among these, it is preferable to use a carboxylic acid halide from the viewpoint of excellent reactivity with an amino group. In this case, as shown in the following reaction formula, the amidation step is carried out by reacting the amino compound represented by the formula (6) with the carboxylic acid halide represented by the formula (8) to express the formula (7). The compound to be obtained is obtained. In the following formulas (7) and (8), R ⁶ represents an organic group, and X represents a halogeno group. Hereinafter, the compound of the formula (7) may be referred to as “amide compound”.

  In the carboxylic acid halide of formula (8), examples of the halogeno group for X include a fluoro group, a chloro group, a bromo group, and an iodo group. Of these, a chloro group is preferred. Therefore, it is preferable to use a carboxylic acid chloride as the carboxylic acid halide.

Preferred examples of the organic group R ⁶ of the carboxylic acid halide of the formula (8) and the amide compound of the formula (7) include an alkyl group, an aryl group, and an aralkyl group. By reacting the amide compound of the formula (7) into which these groups have been introduced with squaric acid or a derivative thereof, a squarylium compound excellent in solubility in an organic solvent or a resin can be easily obtained. Thereby, the squarylium compound can be contained at a high concentration in the organic solvent or the resin, and the light absorption characteristics derived from the squarylium compound can be effectively exhibited.

The alkyl group for R ⁶ may be linear, branched, or cyclic (alicyclic). For specific examples of the alkyl group of R ⁶ , refer to the description of the alkyl groups of R ¹ and R ² above. However, the alkyl group of R ⁶ may have more than 20 carbon atoms. The number of carbon atoms of the alkyl group of R ⁶ is preferably 5 or more, more preferably 6 or more, from the viewpoint of increasing the solubility of the squarylium compound obtained from the amide compound of formula (7) in an organic solvent or resin. 7 or more is more preferable, 8 or more is further more preferable, 30 or less is preferable, 25 or less is more preferable, 20 or less is further preferable, and 18 or less is still more preferable. From the same viewpoint, the alkyl group of R ⁶ is preferably linear or branched. Furthermore, from the viewpoint of enhancing the heat resistance of the squarylium compound, the alkyl group of R ⁶ is more preferably linear. In this case, it is possible to suppress the decomposition of the squarylium compound, for example, when the squarylium compound is blended with the resin to be heat-molded or heat-cured, and the squarylium compound is present in a high concentration even in the resin cured product that has undergone the heat treatment. It becomes possible. As the linear alkyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n- Examples include tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group and the like.

  From the viewpoint of increasing the yield of the amide compound of the formula (7), the amount of the carboxylic acid halide used is preferably 1.0 mol or more and 1.2 mol or more with respect to 1 mol of the amino compound of the formula (6). More preferably, 1.5 mol or more is more preferable, 3.0 mol or less is preferable, 2.5 mol or less is more preferable, and 2.0 mol or less is further preferable.

  The reaction of the amino compound of formula (6) with the carboxylic acid halide of formula (8) is carried out in the presence of a low nucleophilic base such as triethylamine, N, N-diisopropylethylamine, pyridine, diazabicycloundecene, etc. Is preferred. By coexisting a low nucleophilic base, the reaction between the base and the carboxylic acid halide is suppressed, while the acid produced by the reaction of the amino compound of the formula (6) with the carboxylic acid halide of the formula (8) is neutralized. Can be summed. The amount of the low nucleophilic base used is preferably 0.9 mol or more, more preferably 1.0 mol or more, still more preferably 1.2 mol or more, and 3.0 mol per 1 mol of carboxylic acid halide. The following is preferable, 2.5 mol or less is more preferable, and 2.0 mol or less is more preferable.

  The reaction in the amidation step is preferably performed in a solvent. Solvents that can be used include aliphatic hydrocarbons such as hexane, toluene, heptane, octane, decane, cyclohexane, and cyclooctane; aromatic hydrocarbons such as benzene, toluene, and xylene; dichloromethane, chloroform, 1,2-dichloroethane And halogenated hydrocarbons such as diethyl ether, tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, and methyl tertiary butyl ether. These solvents may use only 1 type and may use 2 or more types together.

  What is necessary is just to set reaction temperature with the carboxylic acid halide of Formula (8) of the amino compound of Formula (6) suitably according to reaction conditions, for example, what is necessary is just to set between -20 degreeC-60 degreeC. The reaction time is not particularly limited, and may be set as appropriate according to the progress of the reaction. For example, it is preferably 1 hour or longer, more preferably 2 hours or longer, 48 hours or shorter, more preferably 24 hours or shorter. The reaction is preferably performed in an inert gas (for example, nitrogen gas or argon gas) atmosphere.

  Following the amidation step, a squarylium production step is performed in which the amide compound of the formula (7) is reacted with squaric acid or a derivative thereof to obtain the squarylium compound of the following formula (5). As the squaric acid derivative, squaric acid ester, squaric acid amide, squaric acid salt and the like can be used. Hereinafter, squaric acid or a derivative thereof is simply referred to as “squaric acid”.

  The amount of squaric acid used is preferably 0.3 mol or more, more preferably 0.4 mol or more, still more preferably 0.45 mol or more, relative to 1 mol of the amide compound of the formula (7), and 1.0 mol Mol or less is preferable, 0.8 mol or less is more preferable, and 0.7 mol or less is more preferable.

  The reaction between the amide compound of formula (7) and squaric acid is preferably carried out in a solvent. Solvents that can be used include aliphatic hydrocarbons such as hexane, toluene, heptane, octane, decane, cyclohexane, and cyclooctane; aromatic hydrocarbons such as benzene, toluene, and xylene; dichloromethane, chloroform, 1,2-dichloroethane Halogenated hydrocarbons such as: ethers such as diethyl ether, tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, and methyl tertiary butyl ether; alcohols such as methanol, ethanol, propanol, and butanol. These solvents may use only 1 type and may use 2 or more types together.

  What is necessary is just to set suitably the reaction temperature of the amide compound of Formula (7), and squaric acid according to reaction conditions, for example, between 50 degreeC-180 degreeC. The reaction is preferably performed under reflux. The reaction time is not particularly limited and may be appropriately set according to the progress of the reaction. For example, 0.5 hour or more is preferable, 1 hour or more is more preferable, 24 hours or less is preferable, and 12 hours or less is more preferable. . The reaction is preferably performed in an inert gas (for example, nitrogen gas or argon gas) atmosphere.

  By reacting as described above, the squarylium compound represented by the formula (5) can be obtained. The obtained squarylium compound may be appropriately purified by known purification means such as filtration, silica gel column chromatography, alumina column chromatography, sublimation, recrystallization, and crystallization as necessary.

As the squarylium compound of the formula (5), those in which R ³ and R ⁶ are both alkyl groups (particularly alkyl groups having 3 or more carbon atoms) are preferred. Such squarylium compounds are excellent in solubility in organic solvents and resins. Therefore, it becomes possible to contain the squarylium compound in the resin composition at a high concentration, and even when the optical filter is formed from the resin composition, even if the thickness is formed thin, it is derived from the squarylium compound. Light in the near infrared region can be suitably absorbed. Moreover, when using a squarylium compound for a security ink etc., a squarylium compound can be contained in high concentration in an ink, and the coloring property of an ink can be improved.

In the squarylium compound of the formula (5), R ³ is more preferably a branched alkyl group from the viewpoint of enhancing solubility in an organic solvent or a resin. For example, when R ³ is a linear alkyl group, a visible light region squarylium compound in a resin cured product (e.g., a wavelength range of 500 nm to 600 nm) where there may exhibit new absorption peak, R ³ is If it is a branched alkyl group, such a concern becomes unnecessary and it can permeate | transmit the light of visible region with high transmittance | permeability also in resin cured material. On the other hand, R ⁶ is preferably a linear alkyl group, which tends to increase the heat resistance of the squarylium compound. Therefore, it is possible to suppress the decomposition of the squarylium compound such as when the resin is blended with the squarylium compound and thermoformed or heat cured, and the squarylium compound must be present in a high concentration even in the cured resin after heat treatment. Is possible. The preferred carbon number of the alkyl group of R ³ and R ⁶ is as described above.

  The squarylium compound of formula (5) can be mixed with a resin component to form a resin composition. The resin composition thus obtained can be applied to a substrate, for example, to form a resin layer, or to form a resin molded body such as a film. It can be suitably applied to various types of optical sensors. Resin moldings also include near-infrared absorbing films and near-infrared absorbing plates that block heat rays for energy saving, solar cell materials that use visible light and near-infrared light, plasma display panels (PDP), and specific wavelengths for CCDs. Application to an absorption filter or the like is also possible.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, and is implemented with appropriate modifications within a range that can meet the purpose described above and below. Any of these may be included in the technical scope of the present invention.

(1) Synthesis of Nitrogen-containing Heterocyclic Compound (1-1) Synthesis Example 1: Synthesis of Nitrogen-containing Heterocyclic Compound A A 3 L 4-neck flat bottom flask attached to an ice bath was subjected to nitrogen flow (flow rate: 100 mL / min). 510 g of acetonitrile, 24.64 g (0.4104 mol) of acetic acid, 73.12 g (0.4104 mol) of 7-nitro-1,2,3,4-tetrahydroquinoline, 191.33 g (0.9028 mol) of sodium triacetoxyborohydride In this order, the mixture was stirred for about 30 minutes with two paddle blades. Next, 65.10 g (0.9028 mol) of isobutyraldehyde and 510 g of acetonitrile were added over about 1 hour using a feed pump, and then stirred for another 2 hours to obtain a reaction solution. The internal temperature during these operations was always maintained at 0 ° C to 10 ° C. Into a 5 L 4-neck flat bottom flask, under a nitrogen flow (flow rate: 100 mL / min), 1500 g of sodium hydroxide aqueous solution with a concentration of 1 mol / L and 1500 g of toluene were added, and the whole amount of the reaction solution obtained earlier was added thereto, Stir for about 30 minutes. Thereafter, the stirring was stopped and the mixture was allowed to stand for about 15 minutes. Then, the phases were separated, and the organic phase was extracted using a feed pump. To the extracted organic phase, 1500 g of a 3% by weight aqueous sodium chloride solution was added and stirred for about 30 minutes. Then, stirring was stopped and it was left still for about 15 minutes, and the organic phase was extracted using the feed pump. This operation was repeated a total of 2 times. The solvent was distilled off from the obtained organic phase using a rotary evaporator under the conditions of a bath temperature of 60 ° C. and an internal pressure of about 27 kPa. The concentrated liquid after the distillation was dried overnight with stirring under conditions of a bath temperature of 60 ° C. and an internal pressure of about 3 kPa, whereby a nitrogen-containing heterocyclic compound A (1-isobutyl-7-nitro represented by the following formula (4A) 95.87 g of (-1,2,3,4-tetrahydroquinoline) was obtained. The yield of nitrogen-containing heterocyclic compound A with respect to 7-nitro-1,2,3,4-tetrahydroquinoline was 99.7 mol%.

  0.01 g of nitrogen-containing heterocyclic compound A was dissolved in 3 g of acetonitrile, and the resulting liquid was analyzed using high performance liquid chromatography. At this time, a mixed solvent of acetonitrile and phosphoric acid aqueous solution (acetonitrile: 0.1 mass% phosphoric acid aqueous solution = 70: 30 (volume basis)) was used as a developing solvent, and Inertsil ODS- manufactured by GL Science Co., Ltd. was used as a separation column. 3 (silica gel particle diameter: 5 μm, inner diameter 3.0 mm × length 250 mm) was used. When the purity was calculated from the peak area of the nitrogen-containing heterocyclic compound A, the HPLC purity was 99.2%.

(1-2) Synthesis Example 2: Synthesis of Nitrogen-containing Heterocyclic Compound B In Synthesis Example 1, except that 2-methylbutyraldehyde was used instead of isobutyraldehyde, the following formula was used. The nitrogen-containing heterocyclic compound B (1- (2-methylbutyl) -7-nitro-1,2,3,4-tetrahydroquinoline) shown in (4B) was obtained. The yield of nitrogen-containing heterocyclic compound B with respect to 7-nitro-1,2,3,4-tetrahydroquinoline was 99.3 mol%, and the HPLC purity was 99.1%.

(1-3) Synthesis Example 3 (Comparative Example): Synthesis of nitrogen-containing heterocyclic compound A In a 300 mL four-necked flask, 5 g of dimethylformamide, 2.2 g of potassium carbonate, 7-nitro-1,2,3,4- Tetrahydroquinoline (1.43 g, 0.008 mol) and 1-iodo-2-methylpropane (2 g) were added, and the mixture was allowed to react at 80 ° C. for 48 hours while stirring with a stirring blade under nitrogen flow (10 mL / min) , 7-nitro-1,2,3,4-tetrahydroquinoline remained about 30%. This reaction solution was added to a beaker containing 50 mL of a 1 mol / L sodium hydroxide aqueous solution and 50 mL of toluene while stirring. After stirring for about 30 minutes, the organic phase was extracted with a separatory funnel. After distilling off the solvent of this organic phase with an evaporator, 0.5 g of nitrogen-containing heterocyclic compound A was isolated using silica gel column chromatography (developing solvent: chloroform). The yield based on 7-nitro-1,2,3,4-tetrahydroquinoline was 27.2 mol%, and the HPLC purity was 95.8%.

(2) Synthesis example 4: Synthesis of squarylium compound A 4.69 g (0.02 mol) of the nitrogen-containing heterocyclic compound A obtained in synthesis example 1, 70 g of methanol, nickel chloride hexahydrate in a 300 mL four-necked flask 9.51 g (0.04 mol) of the product was supplied, and the internal temperature was adjusted to 0 to 10 ° C. in an ice bath while stirring using a magnetic stirrer under nitrogen flow (flow rate: 10 mL / min). While maintaining the temperature in the flask at 0 ° C. to 10 ° C., 3.78 g (0.10 mol) of sodium borohydride was added little by little over about 2 hours, and stirring was continued for about 2 hours. The obtained reaction solution was poured into 300 g of ion exchange water little by little to perform a quenching operation, 200 g of ethyl acetate was added and stirred for about 30 minutes, and the organic phase was extracted with a separatory funnel. To the organic phase, 200 g of a 10% strength by weight aqueous sodium chloride solution was added and stirred for about 30 minutes, and the organic phase was extracted with a separatory funnel. An operation of adding 200 g of ion exchanged water to the obtained organic phase, stirring for about 30 minutes, and extracting the organic phase with a separatory funnel was performed twice. The obtained organic phase was concentrated and dried overnight using a rotary evaporator or the like to obtain 3.56 g of a brown liquid intermediate A (7-amino-1-isobutyl-1,2,3,4-tetrahydroquinoline). It was. The yield of intermediate A based on nitrogen-containing heterocyclic compound A was 87.1 mol%.

  Next, 2.92 g (0.0143 mol) of intermediate A and 50 g of tetrahydrofuran were placed in a 100 mL three-necked flask, and triethylamine was stirred with a magnetic stirrer under a nitrogen flow (flow rate: 5 mL / min). 4.34 g (0.0429 mol) and 7.86 g (0.0286 mol) of palmitoyl chloride were added and reacted at room temperature for 12 hours. After completion of the reaction, 50 g of methanol was added to the resulting reaction solution, and then 50 g of water was added little by little. After confirming the precipitation of yellow particles in the reaction solution, filtration under reduced pressure was performed. The cake was rinsed with 50 g of an aqueous methanol solution having a concentration of 50% by mass, and then dried at 60 ° C. for 12 hours using a vacuum drier. Intermediate B (7-hexadecylamide-1-isobutyl-1,2,3,4) -Tetrahydroquinoline) 5.91 g was obtained. The yield of intermediate B with respect to intermediate A was 95.3 mol%.

  Next, 2.81 g (0.0064 mol) of Intermediate B, 0.36 g (0.0032 mmol) of squaric acid, 20 g of 1-butanol, and 20 g of toluene were placed in a 300 mL two-necked flask under nitrogen flow (10 mL / min). ), The mixture was stirred using a magnetic stirrer, and the reaction was carried out for 3 hours under reflux conditions while removing the eluted water using a Dean Stark apparatus. After completion of the reaction, the mixture was cooled to room temperature, and the precipitate was filtered off. The precipitate separated by filtration was washed with methanol, and only the precipitate was filtered again, and the resulting cake was dried at 60 ° C. for 12 hours using a vacuum dryer to obtain 2.4 g of squarylium compound A. The yield based on squaric acid was 79.4 mol%.

  The nitrogen-containing heterocyclic compound obtained by the production method of the present invention can be suitably used as a raw material for producing a squarylium compound. The squarylium compound can be used for a near-infrared absorbing film, a near-infrared absorbing plate, a security ink, and the like by utilizing the property of absorbing light in the near-infrared region.

Claims (6)

A compound represented by the following formula (1) is reacted with an aldehyde compound represented by the following formula (2) in the presence of a borohydride compound represented by the following formula (3) to give the following formula (4): A method for producing a nitrogen-containing heterocyclic compound, comprising a step of obtaining a compound represented by the formula:

[In Formula (1)-Formula (4),
R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or a halogeno group,
R ³ represents an alkyl group having 1 to 20 carbon atoms,
R ⁴ represents an alkyl group having 1 to 6 carbon atoms or an acyl group having 2 to 6 carbon atoms,
M represents an alkali metal atom;
Ring A represents a 5- to 8-membered nitrogen-containing heterocyclic ring which may have a substituent. ] The method for producing a nitrogen-containing heterocyclic compound according to claim 1, wherein R ³ represents a branched alkyl group. The method for producing a nitrogen-containing heterocyclic compound according to claim 2, wherein the branched alkyl group of R ³ is branched at the α-position, β-position or γ-position of the formyl group of the aldehyde compound of the formula (2). The method for producing a nitrogen-containing heterocyclic compound according to claim ^1, wherein R ¹ and R ² each represent a hydrogen atom.   A method for producing a squarylium compound, comprising the step of obtaining the nitrogen-containing heterocyclic compound represented by the formula (4) by the production method according to claim 1. A reduction step of converting a nitro group contained in the nitrogen-containing heterocyclic compound into an amino group;
An amidation step of converting the amino group into an amide group;
The squarylium compound according to claim 5, further comprising a step of reacting the product obtained in the amidation step with squaric acid or a derivative thereof to obtain a squarylium compound having a structure represented by the following formula (5). Manufacturing method.

Wherein (5), R ¹ ~R ^3, and ring A are as defined above, R ⁶ represents an organic group. ]