Equilibrations of 3-methoxycarbonylcycloalkenones

Abstract

Conditions of acid and base catalysis under which 3-methoxycarbonylcycloalk-2-enones and -3-enones with ring sizes 7–10 could be interconverted have been investigated. The use of 1,5-diazabicyclo[4.3.0]non-5-ene as a basic catalyst is recommended, to overcome problems associated with Michael additions. For each ring size, more of the Δ³-isomer was obtained than in the unsubstituted series. Only the cis- and trans-3-methoxycarbonyl cyclodec-3-enones were available as starting materials in the ten-membered series, but these were efficiently equilibrated without detectable formation of Δ²-isomers. A possible explanation of the methoxycarbonyl substituent effect is offered.