A new synthesis of (±) allethrolone, starting from 3-methyl-1,2,4-cyclopentanetrione, is described. The key intermediate for this synthesis is 2-methyl-3,5,5-triethoxy-2-cyclopentene-1-one. Starting from this compound, allethrin, the ester of allethrolone and chrysanthemic acid, has been obtained in an overall yield of 52%. The method has a general applicability in the synthesis of cyclopentenolones