Unusual removal of the ethylene ketal protection from 2,3-dichloro-4,4-ethylenedioxycyclopent-2-en-1-one under alkaline conditions. Simple synthesis of naturally occurring cyclopentenedione analogs

A reaction of 2,3-dichloro-4,4-ethylenedioxycyclopent-2-en-1-one with MeONa in MeOH to furnish 2-chloro-3-hydroxycyclopent-2-en-1,4-dione has been studied. The latter under the action of CH₂N₂ has been converted to the corresponding enol ether. This methodology has been used for the synthesis of 4-chloro-5-methoxy-2-cinnamylidenecyclopent-4-en-1,3-diones and related compounds starting from the parent dichlorocyclopentenone.