The Self-condensation of Cyclohexanone and Methylcyclohexanones under Very High Pressure

The self-condensation of cyclohexanone (1) and its methyl substituted derivatives was investigated under pressure of 20-50 kbar and temperature of 160-300 C without solvent and catalyst. It was found that (1) yielded 2-cyclohexenylcyclohexanone (2), 2-cyclohexylidenecyclohexanone (3), 2, 6-dicyclohexenylcyclohexanone (4) and dodecahydrotriphenylene (5). (5) was a main product at high pressure and high temperature. While 2, 2'-methyl-(2methylcyclohexenyl)-cyclohexanone (7) was obtained from 2-methylcyclohexanone (6). The reactivity of 2, 6-dimethylcy clohexanone was also examined and no product was obtained under pressure of 20-50 kbar and below the temperature of 250 C.This condensation seems to occur in liquid state and to proceed through a series of aldol condensation followed by dehydrations. This scheme was confirmed from pressure effects, but the mechanism of this condensation cannot be explained merely by pressure dependence of auto-protolysis.