JPS607629B2 - Method for producing r-pyrone derivative - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel method for producing y-pyrone derivatives, particularly y-pyrone derivatives represented by the general formula (in which R4 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms). This invention relates to a new and improved method for producing derivatives.

The y-pyrone derivative represented by the above formula (1) is generally a substance useful as a fragrance ingredient, but especially 3-oxy-2-methyl-y-pyrone where R4 is a hydrogen atom and 3-oxy-2-ethyl where R4 is a methyl group. -y-pyrone is an important flavoring substance known under the names maltol or ethylmaltol, respectively. These y-pyrone derivatives can also be obtained by extraction from natural products containing them, but in recent years attempts have been made to produce them by synthetic methods using various hexoses as raw materials.

For example, regarding the production of maltol,
As disclosed in Publication No. 9181, R5 represents an ether residue or a phosphoric acid residue, and
6, R7 each represents a hydrogen atom, an ester residue or jointly a ketal residue, and R8 represents a hydrogen atom, a methyl group or an esterified hydroxymethyl group), especially when R8 is methyl A method is known in which a group derivative is heated with an acid or an alkali.

However, this method has the disadvantage of a low yield of the target maltol, as well as a low reaction yield when synthesizing the above-mentioned hexose derivatives, which serve as intermediate raw materials, from starting materials such as glucose, making the product expensive. There was a problem. Furthermore, there was a problem that ethyl maltol could not be obtained by this method. The present inventors have conducted extensive research into an advantageous method that solves the problems of the conventional methods described above and can easily synthesize the y-pyrone derivative represented by the formula (1) above in good yield using inexpensive intermediate raw materials. As a result, the present invention was completed, which is based on the general formula (in which R1, R2, and R3 each have 1 to 4 carbon atoms).
an alkyl group, R4 is a hydrogen atom or has 1 to 3 carbon atoms
6-deoxy-hexose-4-ulose (6-deoxy-4-ketoaldohexose) or a derivative thereof represented by the general formula (representing an alkyl group of The present invention relates to a method for producing a pyrone derivative represented by (R4 is the same as above), particularly a method for producing maltol in which R4 is a hydrogen atom and ethylmaltol in which R4 is a methyl group.

The method of the present invention will be explained in more detail below.

6-deoxy- represented by the general formula (b) used as a raw material
Hexose-4-ulose or its derivatives can be easily synthesized by conventionally known methods using inexpensive hexoses such as glucose or mannose as starting materials, but R1, R2, and R3 are all ether residues, In particular, since it is an alkyl group having 1 to 4 carbon atoms, it has a 6 times greater protective effect during reduction or alkylation reactions than when it is an ester residue, and therefore has a high synthesis yield. Therefore, it has the characteristic that it can be obtained at an extremely low cost. As mentioned above, R1, R2, and R3 are all alkyl groups having 1 to 4 carbon atoms, that is, groups selected from methyl, ethyl, propyl, and butyl groups, but this is difficult to synthesize. In this respect, a methyl group is preferable, and long-chain alkyl groups having 5 or more carbon atoms or other substituted alkyl groups will only increase the difficulty in synthesis and no particular effect will be obtained.

Next, -R4 is selected from a hydrogen atom or a lower alkyl group having 1 to 3 carbon atoms depending on the type of the target product, but in either case, the target product can be provided under almost the same reaction conditions.

As mentioned above, especially when this is a hydrogen atom or a ethyl group, the product becomes maltol or ethylmaltol, which has high industrial value. All of the raw materials for the method of the present invention explained above have a relatively high solubility in hot water, so they can be easily added to water containing an acid as a catalyst, dissolved, and continued heating. can get the desired object.

The acids used in this case are inorganic acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and perchloric acid, as well as relatively highly water-soluble organic acids such as trifluoroacetic acid, chloroacetic acid, toluenesulfonic acid, and methanesulfonic acid. In addition, strongly acidic or weakly acidic ion exchange resins may also be used.
The amount of acid used should be adjusted as appropriate depending on conditions such as the type of acid used, the type of raw materials, and the desired reaction rate.
Generally, for water-soluble acids, the concentration in the reaction solution is 1 to 2.
In the case of ion-exchanged dark fat, it may be in the range of 0.2 to 0.3 equivalents based on the number of moles of raw materials in the reaction solution. It is preferable for the concentration of the raw materials in the reaction solution to be as high as possible in terms of production efficiency, but this is limited by the solubility of each raw material in water, so it is determined by considering the solubility at the reaction temperature in each case. do it.
Regarding the reaction temperature, although the reaction in the method of the present invention proceeds even at room temperature, it is desirable to heat it for the purpose of obtaining a sufficient reaction rate and sufficient raw material concentration.
20 CO, for example by heating under reflux.

At temperatures above the above-mentioned temperature range, the yield actually decreases due to an increase in side reactions. Although the reaction time varies depending on the conditions described above, approximately 0.5 to 1 Hatadera is sufficient, and the target product can be crystallized by simply cooling the solution after the reaction is completed. After extraction with an organic solvent such as, the target product may be precipitated by evaporating the solvent, and it is not difficult to achieve a crude yield of 90% or more.

The crude product obtained here can be made into a pure product by repeating recrystallization from an aqueous solution if necessary, and the target product can be identified by performing elemental analysis, infrared absorption spectrum analysis, NMR analysis, etc. on the pure product. It can be confirmed. Next, examples of the present invention will be given.

Example 1 Methyl 6-deoxy-2,3-di-0-methyl-1D-xylohexos-4-uropyra/side
1 61 deo Masuichi 2・3-di-01 methyl
- Q - ○ - xylo - hexos -
4 - mountain opyranoside) (formula (m) tRI=
R2 = R3 = methyl group, R4 = H) 8.00 g was added to 100 m of a 5% sulfuric acid aqueous solution, heated to dissolve at 90 p.m., and heated and stirred at the same temperature for 6 hours.

The product was extracted from the reaction solution using chloroform, and the obtained chloroform solution was washed with brine and dehydrated, and then the chloroform was evaporated to obtain about 4.54 cm of white needle-like crystals. Regarding this product purified by recrystallization, NM
When the R spectrum was compared with a standard product, it was confirmed that it was maltol. Note that the above crude yield corresponds to about 90% of the theoretical amount. Example 2 Methyl 6-deoxy-2,3-di0-methyl-Q-D-lyxo-hexos-4-uropyranoside (me ratio y1 6-deo
Fence-2・31di-01methyl-Q-D
- lyxo - hexos - 4 - shout opy
ranoside) 6.00 evening and Amberlight IR
- 12 females (acid type, strongly acidic ion exchange fat manufactured by Rohm and Haas, trade name) about 60' in pure water 100 kites [
After heating to dissolve the mannopyranoside derivative, heating was performed for 6 hours with stirring.

Next, the ion exchange resin was removed by filtration, and extraction and separation using chloroform was performed in the same manner as in Example 1 to obtain 3.18 g of a crude product. This was also confirmed to be maltol, and the crude yield corresponded to about 86% of the theoretical value. Example 3 Methyl 6-deoxy-2,3-di○-methyl-6-C-methyl-Q-○-xylo-hexos-4-uropyranoside was heated to 100 ml of a 5% aqueous solution of trifluoroacetic acid. The mixture was heated under reflux for 4 hours while stirring.

Claims (1)

[Claims] 1 General formula▲ Numerical formula, chemical formula, table, etc.▼ (In the formula, R^1, R^2, R^3 are each an alkyl group having 1 to 4 carbon atoms, and R^4 is A general formula characterized by heating 6-deoxy-hexose-4-ulose (representing a hydrogen atom or an alkyl group having 1 to 3 carbon atoms) or a derivative thereof in the presence of an acid ▲Mathematical formula, chemical formula, There are tables, etc. ▼ Method for producing a γ-pyrone derivative represented by (R^4 in the formula is the same as above). 2. The manufacturing method according to claim 1, wherein R^1, R^2, and R^3 are all methyl groups. 3. The manufacturing method according to claim 1 or 2, wherein R^4 is a hydrogen atom. 4. The manufacturing method according to claim 1 or 2, wherein R^4 is a methyl group.