SYNTHESIS OF POLYSUBSTITUTED 1,3-CYCLOHEXADIENES FROM BETA-BRANCHED ALPHA,BETA-ALKENALS AND MONOESTERS OF YLIDENEMALONIC ACIDS

3-Methyl- and 3-phenyl-2-butenal react with monoesters of alkylidene-, alkenylidene-, and arylmethylenemalonic acids in the presence of pipe ridine as the catalyst to give esters of 4,6-disubstituted 1,3-cyclohe xadienecarboxylic acids in 23-96 % yields. Under the same conditions c yclohexylideneacetic aldehyde reacts with the monoesters of prenyliden e- and benzylidenemalonic acid to afford mixtures of 1,8a-trans- and 1 ,8a-cis-isomers of 1-substituted alkyl 1,5,6,7,8,8a-hexahydronaphthale ne-2-carboxylates the ratios and configurations of which were determin ed by means of H-1 NMR spectroscopy. In some cases the formation of cy clic dienes is impeded by the competing process of decarboxylation of acidic ylidenemalonates. The derivatives of 4,6-diphenyl-1,3-cyclohexa dienecarboxylic acid were shown to be convenient precursors for the pr eparation of meta-terphenyls.