Synthesis of Methyl Substituted Bicyclohept-3-en-6-ones and 3,3a,4,6a-Tetrahydro-2H-cyclopentafuran-2-ones.

Article abstract of DOI:10.1016/S0040-4020(01)90491-0

Treatment of methyl mono- or bisubstituted 3-hydroxy-6-alkenoic acids in acetic anhydride and potassium acetate give the corresponding bicyclo<3.2.0>hept-3-en-6-ones in fair to good yields.This reaction appears 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-trimethylbicyclo<3.2.0>hept-3-en-6-one (filifolone) by an efficient bicyclization of 3-hydroxy-3-methyl-6-heptenoic acid followed by the geminal 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 when performed on bicyclo<3.2.0>hept-3-en-6-ones and on bicyclo<3.2.0>hept-2-en-6-one. 3,3a,4,6a-Tetrahydro-2H-cyclopentafuran-2-ones, important starting materials in the synthesis of linear condensed triquinane sesquiterpenes, have been prepared in an efficient manner by the easy 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.