Abstract: A three-step, cyclopentenone synthesis scheme, involving the cyclopropanation of enol derivatives with diazomethyl ketones, the liberation of y-dicarbonyl compounds on acid hydrolysis of the resultant (3-oxycyclopropyl ketones, and intramolecular aldol condensation of the I, 4-diketo systems, is described. Its application to the synthesis of a prostanoid intermediate (5), a spiro [4S] decenone model (9), and an acorane intermediate (16) from ...