SYNTHESIS OF METHYL-SUBSTITUTED BICYCLO[3.2.0]HEPT-3-EN-6-ONES AND 3,3A,4,6A-TETRAHYDRO-2H-CYCLOPENTA[B]FURAN-2-ONES

Treatment of methyl mono- or bisubstituted 3-hydroxy-6-alkenoic acids in acetic anhydride and potassium acetate give the corresponding bicyc lo[3.2.0]hept-3-en-6-ones in fair to good yields. This reaction appear s to be of general applicability to prepare the methyl derivatives in all the positions of the five membered ring. The synthesis of 4,7,7-tr imethylbicyclo[3.2.0]hept-3-en-6-one (filifolone) by an efficient bicy clization of 3-hydroxy-3-methyl-6-heptenoic acid followed by the gemin al dimethylation of the intermediate 4-methylbicyclo[3.2.0]hept-3-en-6 -one is reported. The latter reaction proved to be a general method wh en performed on bicyclo[3.2.0]hept-3-en-6-ones and on bicyclo[3.2.0]he pt-2-en-6-one. 3,3a,4,6a-Tetrahydro-2H-cyclopenta[b]furan-2-ones, impo rtant starting materials in the synthesis of linear condensed triquina ne sesquiterpenes, have been prepared in an efficient manner by the ea sy bicyclization of 3-hydroxy-6-heptenoic acids, followed by a Baeyer- Villiger oxidation of the bicyclo[3.2.0]hept-3-en-6-one intermediates.