CH636611A5 - PROCEDURE FOR THE PREPARATION OF REPLACED DIHYDROPHURANS. - Google Patents

Description

The present invention relates to a new process for the preparation of substituted dihydrofurans of formula (I)

I HAVE

i.e. 2,5-dialkyl-4-hydroxy-2,3-dihydrofuran-3-oni, in which the two R are methyl radicals or in which one of the R is a methyl radical and the other is a starting ethyl radical from compounds of formula

CH, CH-CO-CO-CH-R

I I <«>

OH OH

wherein R represents a methyl or ethyl radical.

The process for preparing said substituted dihydrofurans of formula (I) is characterized in claim 1 above.

Formula I products possess valid organoleptic properties and are therefore of considerable interest to the food, pharmaceutical and perfume industries.

The products of formula II are obtainable with known economic methods (see for example L. Re and G. Ohloff, US Patent 3 576 014 of Lirmenich & Cie .; L. Re and V. Caciagli, Ger. Offen, n. 2 426 051 of Snamprogetti SpA).

Previously the best method for obtaining the compounds of formula I was based on the cyclization of the precursors of formula II by means of mineral or organic acids, or acidic buffers, soluble in the reaction medium.

The method object of the present invention offers the following advantages compared to the previous method:

(1) The cyclization agent, which must be used in large quantities with respect to the dioneion with both methods, can be recovered by simple filtration and reused.

(2) The isolation of the furan derivative from the reaction mixture is operationally simpler, as it does not involve the continuous extraction of the product from the aqueous phase with ethyl ether (as in the previous method) and can be carried out by simple evaporation, after filtration from the resin of the aqueous filtrate, followed by extraction of the product from the residue with a suitable solvent (preferably carbon tetrachloride) and evaporation of said solvent.

(3) The furan derivatives isolated from the reaction mixture do not require further purification (purity: 95%), while, for the preparation according to the previous method of the derivative I in which the two R are methyl radicals, a sublimation purification must be done follow the isolation of the reaction raw product.

More precisely, for the preparation of the derivatives of formula I, the starting dioldione of formula II is reacted in a mixture of water with a hydrophilic solvent (such as methanol, ethanol, dioxane, etc.) or, preferably, in pure water with a cation exchange resin (such as Am-berlite IR 122, IR 124, IR 112, IR 200 or IR 120, preferably with the latter) at a temperature between 50 and 150 ° C (preferably at 100 ° C and in a inert atmosphere (e.g. nitrogen).

In the case of the dioldione of formula II wherein R represents an ethyl radical, the cyclization provides a mixture of the two isomers 2-ethyl-5-methyl-2,3-dihydrofuran-3-one and 5-ethyl - 2-methyl- 2,3-dihydrofuran-3-one, in a ratio of approx. 2: 1, which can be used as such in the food, pharmaceutical and perfume industries.

The operational particularities will however be more evident from the examination of the following examples:

Example 1

Preparation 2,5-dimethyl-4-hydroxy-2,3-dihydrofuran-3-one

To 1,040 g of crude 2,5-dihydroxyhexan-3,4-dione dissolved in 20 cc of water, 4.75 g of Amberlite IR 120 resin are added and the mixture heated under reflux under stirring in a nitrogen atmosphere for 4 hours. After filtering the resin, the aqueous solution is neutralized with NaOH 2N and dried under vacuum at room temperature.

The oily residue obtained is extracted with three successive portions of 10 ml of carbon tetrachloride. After removal of the solvent under vacuum at room temperature, a residue of 0.327 g (yield, 32% from hexin-diol) of 2,5-dimethyl-4-hydroxy-2,3-dihydrofuran-3-one oily is obtained which crystallizes spontaneously, gas chromatographic purity of 95% (gc analyzes were performed with a Hewlett-Packard Model 7620-A instrument equipped with a heat-conducting detector. Column 6 ft X 1 / g in., of 4% SE 30 on Chromosorb G silanized (60-80 mesh); 170 ° C for 6 ', then 170) 230 ° C (30 ° C / min) with 8 ml / min of helium, using n-eicosane as internal standard), mp 60-70 ° C, mass and nmr spectra according to literature (J.O. R.odm et al. J. Food Science, 30, 280 [1965]).

Example 2

Preparation of 2-ethyl-5-methyl-4-hydroxy-2,3-dihydrofuran-3 - one and 5-ethyl-2-methyl-4-hydroxy-2,3-dihydrofuran-3-one

At 1,139 g of crude 2,5-dihydroxyheptan-3,4-dione (prepared from 3-heptin-2,5-diol), dissolved in 20 cc of ven5 water

I

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3

636611

4.75 g of Amberlite IR 120 resin are added and the mixture is heated under reflux in a nitrogen atmosphere for 6 hours. After filtering the resin, the aqueous solution is neutralized with NaOH 2N and dried under vacuum at room temperature. The oily residue obtained is extracted with three successive portions of 10 ml of carbon tetrachloride. After removal of the solvent under vacuum at room temperature, an oily residue of 0.325 g is obtained

(yield, 29% from heptindiol), consisting of a mixture of 2-ethyl-5-methyl-4-hydroxy-2,3-dihydrofuran-3-one- and 5-ethyl-2-me-tyl-4- hydroxy-2,3-dihydrofuran-3-one (—2: 1), gas chromatographic purity of 94% (gc conditions as for 2-5-5-dimethyl-4-hydroxy-2,3-dihydrofuran -3-one), eg 62-65 ° C / 0.015 mm'Hg, mass spectra and nmr according to the literature.

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Claims (3)

636611 2. Process according to claim 1, characterized in that the reaction is carried out at temperatures between 50 and 150 ° C, in an inert atmosphere. 2 CLAIMS 1. Procedure for the preparation of substituted dihydrofurans of formula (I) I HAVE wherein R and Rx are methyl radicals or where one of the two aforementioned radicals is a methyl radical while the other is an ethyl radical, by cyclization of compounds of formula (II) R - CH - C - C - CH - R, OH O 0 OH where R and Rj have the already known meanings, characterized in that the cyclization reaction is carried out in the presence of a catalyst constituted by cation exchange resins, insoluble in the reaction medium. 3. Process according to claim 2, characterized in that the reaction is carried out in an aqueous or aqueous-alcoholic solution.