GB1578192A

GB1578192A - 2,5 - dimethyl-tetrahydrofuran - 4 - ones - 3 - carboxylic acid compounds

Info

Publication number: GB1578192A
Application number: GB2786677A
Authority: GB
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1976-07-27
Filing date: 1977-07-04
Publication date: 1980-11-05
Also published as: NL7708021A; FR2359835A2; CH631450A5

Abstract

Novel 2,5-dimethyl-3-carbobenzyloxytetrahydrofuran-4-one is prepared by reaction of a lactic acid ester with a crotonic acid ester in the presence of a strong base. Excess lactic acid ester or a solvent which is inert under the reaction conditions is employed. When using an alkyl crotonate, the 2,5-dimethyl-3-carbalkoxytetrahydro-furan-4-one obtained is reacted with benzyl alcohol. The 2,5-dimethyl-3-carbobenzyloxytetrahydrofuran-4-one obtained can be converted by hydrogenation in the presence of noble metal catalysts into the novel 2,5-dimethyl-3-carboxytetrahydrofuran-4-one. The novel compounds obtained have interesting olfactory properties.

Description

(54) 2,5-DIMETHYL-TETRAHYDROFURAN-4-ONE-3-CARBOXYLIC ACID COMPOUNDS (71) We, BASF AKTIENGESELLSCHAFT, a German Joint Stock Company of 6700 Ludwigshafen, Federal Republic of Germany, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following Statement: Our earlier but copending British Patent application No. 907/77 (Serial No. 1578191), hereinafter referred to as the parent patent application discloses and claims 2,5-dimethyl-3carbalkoxy-tetrahydrofuran-4-ones of the general formula (I):

where R is alkyl of one to six carbon atoms, which compounds are proposed for use as scents and as intermediates.

According to the present invention there is provided a compound of the formula (I) above where R is phenylalkyl of 1 to 6 carbon atoms in the alkyl, especially

or -H. These compounds have interesting olfactory properties.

2,5-dimethyl-3-carbobenzyloxy-tetrahydrofuran-4-one has a spicy, tarry scent reminiscent of birch tar oil and may therefore be used as a scent with a leathery, woody or chypre-type note.

2,5-dimethyl-3-carboxy-tetrahydrofuran-4-one has an odour of bread and pastry.

The compounds of the present invention are also of great interest as intermediates for a synthesis of the much sought-after perfume and flavor material 4-oxo-3-hydroxy-2,5dimethyl-4,5-dihydrofuran because 2,5-dimethyl-3-carbobenzoxy-tetrahydrofuran-4-one when reacted with hydrogen in the presence of a conventional hydrogenation catalyst, especially a precious metal catalyst such as palladium or platinum on a carrier such as carbon, calcium, carbonate, silicon dioxide or alumina, in a solvent such as ethyl acetate or dioxane can be converted with a very good yield into 3-carboxy-2,5 dimethyltetrahydrofuran-4-one, from which in a simple manner by oximation with aqueous nitrous acid, an ester of nitrous acid or nitrosyl chloride, 3-oximino-2,5dimethyltetrahydrofuran-4-one can be prepared and this in turn can be converted into 4-oxo-3-hydroxy-2,5-dimethyl-4,5-dihydrofuran by splitting the oximino group, for example by hydrolysis with aqueous acids, by the action of oxidizing agents such as nitrous acid, or by transoximation with a reactive carbonyl compound such as formaldehyde.

The 2,5-dimethyl-3-carbobenzyloxytetrahydrofuran-4-one may be obtained under the reaction conditions described in the parent patent application by reaction of benzyl crotonate with benzyl lactate at a temperature of from -20 C to 1200C, but also in a conventional manner by reaction of a 2,5-dimethyl-3-carbalkoxy-tetrahydrofuran-4-one with benzyl alcohol at a temperature of from 50 to 2500C and preferably at from 1500 to 200"C. The other phenyl alkyl esters may be obtained in an analogous manner.

Accordingly, the invention provides a process for the preparation of a 2,5-dimethyl-3carbophenylalkoxy-tetrahydrofuran-4-one which comprises reacting a lactic ester of the general formula (II):

where R' is alkyl of one to six carbon atoms optionally substituted by phenyl with a phenylalkyl crotonate of one to six carbon atoms in the alkyl moiety in the presence of approximately molar amounts of a strong base, in an excess of the lactic acid ester or in a solvent which is inert under the reaction conditions, at a temperature of from -20"C to + 1200C, and/or by reacting a 2,5-dimethyl-3-carbalkoxytetrahydrofuran-4-one of the general formula (Ia):

where R' is alkyl of one to six carbon atoms with a phenyl-substituted alkanol of 1 to 6 carbon atoms in the alkyl moiety at a temperature of from 50 to 2500C.

2, 5-Dimethyl.3-carboxytetrahydrofuran-4-one may be prepared by a conventional method by hydrolysis of one of the alkyl esters described in the parent patent application with an alkali such as sodium bicarbonate, sodium hydroxide or potassium hydroxide in aqueous solution or suspension, followed by acidification and concentration.

Accordingly, the invention also provides a process for the production of 2,5-dimethyl-3carboxy-tetrahydrofuran-4-one wherein a corresponding 3-carbalkoxy tetrahydrofuran-4one in which the alkyl moiety has 1 to 6 carbon atoms is saponified in aqueous solution or suspension, or alternatively and more advantageously by reaction of the corresponding phenylalkyl (e.g. benzyl) ester with hydrogen in the presence of a conventional hydrogenation catalyst, especially one of the precious metal catalysts palladium or platinum on a carrier such as carbon, calcium carbonate, silica or alumina in a solvent such as ethyl acetate or dioxane.

The invention is illustrated by the following Examples.

EXAMPLE 1 40 g of 2,5-dimethyl-3-carboethoxytetrahydrofuran-4-one is heated with 200 ml of benzyl alcohol to 1800 to 2000C. Methanol formed is distilled off. The excess benzyl alcohol is then distilled off at subatmospheric pressure and the residue is fractionated. 45 g (equivalent to 78% of theory) of 2,5-dimethyl-carbobenzyloxy-tetrahydrofuran-4-one is obtained; it has a boiling point of 102"C at 0.02 mm Hg and a refractive index n25 = 1.5070.

EXAMPLE 2 20 g of the benzyl ester obtained according to Example 1 is reacted with hydrogen in 100 ml of ethyl acetate in the presence of 1 g of 10% Pd on carbon at atmospheric pressure.

2,280 ml of H2 is absorbed. The solvent is distilled off at subatmospheric pressure.

2,5-dimethyl-3-carboxytetrahydrofuran-4-one is obtained as a colourless oil which solidifies to crystals having a melting point of 55" to 570C; spectroscopic data confirm the structure.

The yield is quantitative.

EXAMPLE 3 Manufacture of 4-oxo-3-hydroxy-2,5-dimethyl-4,5-dihydrofuran (a) Preparation of 3-oximino-2,5-d itnethyl-tetrahyd rofuran-4-one 15.8 g of 4-oxo-3-carboxy-2,5-dimethyl-tetrahydrofuran are dissolved in 80 ml of ethanol and 15 g of ethyl nitrite are added. A slow stream of HC1 is passed in whilst cooling with ice.

On warming to 20"C, evolution of gas occurs, accompanied by a slight exo-thermicity.

When evolution of gas has ceased (which is the case after about 1 hour), the mixture is concentrated, the residue is taken up in ether and the ether solution is washed neutral with aqueous NaNCO3 solution, dried and concentrated under reduced pressure. 13.5 g of 4-oxo-3-oximino-2,5-dimethyl-tetrahyrofuran (corresponding to a crude yield of 94% of theory) remain.

(b) Scission of the 3-oximino compound with aqueous acids 10 g of 4-oxo-3-oximino-2,5-dimethyl-tetrahydrofuran and 50 ml of 10% strength H2SO4 are heated at 800C and the hydrolysis is followed by thin layer chromatography. The oxime has been converted after 3 hours. In its place, 4-oxo-3-hydroxy-2,5-dimethyl-4,5dihydrofuran has been formed, as established by isolating the product and comparing the chromatographic and spectroscopic data with those of a comparative substance.

(c) Scission of the 3-oximino compound by trans-oximation with reactive carbonyl compounds 10 g of 4-oxo-3-oximino-2,5-dimethyl-tetrahydrofuran are stirred with 50 ml of a 40% strength formaldehyde solution and 30 ml of 20% strength sulfuric acid for 24 hours at room temperature. Subsequent examination by thin layer chromatography shows that the oxime has been completely converted to 4-oxo-3-hydroxy-2 ,5-dimethyl-4,5-dihydrofuran.

WHAT WE CLAIM IS: 1. A 2,5-dimethyl-tetahydrofuran-4-one-3-carboxylic acid compound of the general formula (I):

where R is phenylalkyl of 1 to 6 carbon atoms in the alkyl or hydrogen.

2. 2,5-Dimethyl-3-carbobenzyloxy-tetrahydrofuran-4-one.

3. 2,5-Dimethyl-3-carboxy-tetrahydrofuran-4-one.

4. A process for the manufacture of a 2,5-dimethyl-3-carbo-phenylalkoxytetrahydrofuran-4-one as claimed in claim 1 which comprises reacting a lactic ester of the general formula (II):

where R' is alkyl of one to six carbon atoms optionally substituted by phenyl with a phenylalkyl crotonate of one to six carbon atoms in the alkyl moiety in the presence of approximately molar amounts of a strong base, in an excess of the lactic acid ester or in solvent which is inert under the reaction conditions, at a temprature of from -20 C to +1200C, and/or by reacting a 2,5-dimethyl-3-carbalkoxytetrahydrofuran-4-one of the general formula (Ia)

where R' is alkyl of one to six carbon atoms with a phenyl-substituted alkanol of 1 to 6 carbon atoms in the alkyl moiety at a temperature of from 50 to 250"C.

5. A process for the production of 2,5-dimethyl-3-carboxy-tetrahydrofuran-4-one wherein a corresponding 3-carbalkoxy-tetrahydro-furan-4-one in which the alkyl moiety has 1 to 6 carbon atoms is saponified in aqueous solution or suspension, or the corresponding phenylalkyl ester as claimed in claim 1 is reacted with hydrogen in the presence of a hydrogenation catalyst.

6. A process as claimed in claim 5 wherein the phenylalkyl ester is reacted with hydrogen in the presence of a platinum or palladium catalyst.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

On warming to 20"C, evolution of gas occurs, accompanied by a slight exo-thermicity.

When evolution of gas has ceased (which is the case after about 1 hour), the mixture is concentrated, the residue is taken up in ether and the ether solution is washed neutral with aqueous NaNCO3 solution, dried and concentrated under reduced pressure. 13.5 g of 4-oxo-3-oximino-2,5-dimethyl-tetrahyrofuran (corresponding to a crude yield of 94% of theory) remain.

(b) Scission of the 3-oximino compound with aqueous acids

10 g of 4-oxo-3-oximino-2,5-dimethyl-tetrahydrofuran and 50 ml of 10% strength H2SO4 are heated at 800C and the hydrolysis is followed by thin layer chromatography. The oxime has been converted after 3 hours. In its place, 4-oxo-3-hydroxy-2,5-dimethyl-4,5dihydrofuran has been formed, as established by isolating the product and comparing the chromatographic and spectroscopic data with those of a comparative substance.

(c) Scission of the 3-oximino compound by trans-oximation with reactive carbonyl compounds

10 g of 4-oxo-3-oximino-2,5-dimethyl-tetrahydrofuran are stirred with 50 ml of a 40% strength formaldehyde solution and 30 ml of 20% strength sulfuric acid for 24 hours at room temperature. Subsequent examination by thin layer chromatography shows that the oxime has been completely converted to 4-oxo-3-hydroxy-2 ,5-dimethyl-4,5-dihydrofuran.

WHAT WE CLAIM IS: 1. A 2,5-dimethyl-tetahydrofuran-4-one-3-carboxylic acid compound of the general formula (I):

where R is phenylalkyl of 1 to 6 carbon atoms in the alkyl or hydrogen.
2. 2,5-Dimethyl-3-carbobenzyloxy-tetrahydrofuran-4-one.
3. 2,5-Dimethyl-3-carboxy-tetrahydrofuran-4-one.
4. A process for the manufacture of a 2,5-dimethyl-3-carbo-phenylalkoxytetrahydrofuran-4-one as claimed in claim 1 which comprises reacting a lactic ester of the general formula (II):

where R' is alkyl of one to six carbon atoms optionally substituted by phenyl with a phenylalkyl crotonate of one to six carbon atoms in the alkyl moiety in the presence of approximately molar amounts of a strong base, in an excess of the lactic acid ester or in solvent which is inert under the reaction conditions, at a temprature of from -20 C to +1200C, and/or by reacting a 2,5-dimethyl-3-carbalkoxytetrahydrofuran-4-one of the general formula (Ia)

where R' is alkyl of one to six carbon atoms with a phenyl-substituted alkanol of 1 to 6 carbon atoms in the alkyl moiety at a temperature of from 50 to 250"C.
5. A process for the production of 2,5-dimethyl-3-carboxy-tetrahydrofuran-4-one wherein a corresponding 3-carbalkoxy-tetrahydro-furan-4-one in which the alkyl moiety has 1 to 6 carbon atoms is saponified in aqueous solution or suspension, or the corresponding phenylalkyl ester as claimed in claim 1 is reacted with hydrogen in the presence of a hydrogenation catalyst.
6. A process as claimed in claim 5 wherein the phenylalkyl ester is reacted with hydrogen in the presence of a platinum or palladium catalyst.
7. A process as claimed in claim 4 or 6 wherein any phenylalkyl moiety present is

benzyl.
8. A process as claimed in claim 4 or 5, carried out substantially as described in either of the foregoing Examples 1 and 2.
9. A compound as claimed in claim 1 when manufactured by a process as claimed in any of claims 4 to 8.
10. A process for the manufacture of 4-oxo-3-hydroxy-2 ,5-dimethyl-4 ,5-dihydrofuran, wherein 2,5-dimethyl-3-carboxy-tetra-hydrofuran-4-one is reacted with nitrous acid, a nitrous acid ester or nitrosyl chloride to form 3-oximino-2,5-dimethyl-tetrahydrofuran-4one, which is then converted into the 4-oxo-3-hydroxy-2,5-dimethyl-4,5-dihydrofuran by splitting the oximino group.
11. A process as claimed in claim 10 carried out substantially as described in the foregoing Example 3(a) followed by 3(b) or by 3(c).
12. 3-Oximino-2 ,5-dimethyltetrahydrofuran-4-one when obtained by reaction of 2,5dimethyl-3-carboxy-tetrahydrofuran-4-one with nitrous acid, a nitrous acid ester or nitrosyl chloride.
13. 4-Oxo-3-hydroxy-2,5-dimethyl-4,5-dihydrofuran when manufactured by a process as claimed in claim 10 or 11.
14. An odorous composition containing a compound as claimed in claim 1, 2, 3 or 13 as an odoriferous constituent.