Synthesis of α-methylene-γ-lactones involving Baeyer–Villiger oxidation of α-substituted cyclobutanones

Abstract

The previously reported 7-exo-halogeno-7-endo-methylbicyclo[3.2.0]heptan-6-ones (3) and (13) and 7-exo-bromo-7-endo-methylbicyclo[3.2.0]hept-2-en-6-one (1) were converted into the corresponding α-methylene-γ-lactones (31) and (33) in two steps, involving Baeyer–Villiger oxidation and dehydrohalogenation. Similarly, 7-exo-bromo-7-endo-isopropylbicyclo[3.2.0]hept-2-en-6-one (11) gave the isopropylidene-lactone (34), and the bromomethylbicyclo-octanone (5) gave the lactone (32). In contrast, oxidation and dehydrobromination of 7-endo-bromo-7-exo-methylbicyclo[3.2.0]hept-en-6-one (2) and 7-endo-bromo-7-exo-methylbicyclo[3.2.0]heptan-6-one (4) gave the αβ-unsaturated lactones (36) and (35), respectively.