Preparation of trans-4-alkyl-cyanoarylcyclohexanes

In a process for the preparation of a trans-4-alkyl-cyanoarylcyclohexane having the formula:

• ##STR2## in which R is an unbranched or singly branched alkyl radical of 1 to 12 carbon atoms and n is an integer in the range from 0 to 2, from an arylcarboxylic acid of the formula ##STR3## wherein n is the same as in Formula (I) above, in which process (a) an arylcarboxylic acid having the Formula (II) is hydrogenated to produce a mixture of both the corresponding cis and trans isomers of aryl substituted cyclohexa-2,5-diene-4-carboxylic acid having the formula:
• ##STR4## wherein n is the same as in Formula (I) above, (b) the produced mixture of aryl substituted cyclohexadiene carboxylic acid isomers having the Formula (III) is esterified with a lower alkanol whereby a mixture of the corresponding carboxylic acid alkyl ester isomers is produced,
• (c) the resulting mixture of aryl susbstituted cyclohexadiene carboxylic acid alkyl ester isomers is hydrogenated whereby the corresponding cis and trans isomers of 1-aryl substituted cyclohexane-4-carboxylic acid alkyl ester are produced having the formula:
• ##STR5## (d) the aryl substituted cyclohexane-4-carboxylic acid alkyl ester is saponified and the resulting salt is converted to the corresponding free carboxylic acid;
• (e) the resulting free carboxylic acid is reacted with an alkyl metal compound of 1 to 12 carbon atoms per alkyl group whereby chain growth is produced and the carboxylic group is reduced to a carbonyl group,
• (f) the carbonyl group is reduced to form an alkyl group, and
• (g) a cyano group is introduced in the 4'-, the 4"- or the 4'"-position of the aromatic substituent whereby the desired trans-4-alkyl-cyanoarylcyclohexane having the Formula (I) above is produced;
• an improvement in said steps (a) through (c) whereby a trans isomer of said aryl substituted cyclohexane-4-carboxylic acid alkyl ester having the Formula (IV) above substantially free from its cis isomer is produced for treatment in step (d) above, which improvement comprises the steps of
• (a) hydrogenating an arylcarboxylic acid having the Formula (II) above at a temperature below -20.degree. C. with solvated electrons in the presence of a proton donor to produce a mixture of both the corresponding cis and trans isomers of aryl substituted cyclohexa-2,5-diene-4-carboxylic acid having the formula:
• ##STR6## wherein n is the same as in Formula I above;
• (b) esterifying the produced carboxylic acids having the Formula (III) with a lower alkanol whereby a mixture of the corresponding arylcyclohexadiene carboxylic acid alkyl ester isomers is produced,
• (c) hydrogenating the mixed alkyl ester isomers with molecular hydrogen in anhydrous lower alkanol in the presence of a Pd/activated carbon catalyst whereby a mixture of the corresponding cis and trans isomers of 1-aryl substituted cyclohexane-4-carboxylic acid esters is produced having the formula:
• ##STR7## (c') heating said mixture of the cis and trans isomers of the aryl substituted cyclohexane-4-carboxylic acid alkyl esters to its boiling point under reflux under anhydrous conditions under an inert gas in a lower alkanol in the presence of an alkali metal of the group consisting of sodium or potassium whereby the cis alkyl ester present in the isomeric mixture is isomerized to the trans alkyl ester, and recovering said stereo-specifically substantially pure trans isomer of the aryl substituted cyclohexane-4-carboxylic acid alkyl ester.