Synthesis of Functionalized Chiral (Racemic) Cyclobutanones

Chiral (racemic) cyclobutanones, produced by the photochemical reaction between chiral ene carbamates and chromium alkoxycarbene complexes, were functionalized in several ways. Enolization/O-alkylation produced enol ethers and esters that underwent facile ring opening to produce electron-rich dienes. Epoxidation of the silyl enol ether followed by epoxide opening produced α-(silyloxy)cyclobutanones. α-Bromination (NBS) of the cyclobutanones followed by Baeyer−Villiger oxidation led to α-bromobutyrolactones that could be converted to butenolides. By using α-stannyl ene carbamates as substrates for the photochemical cycloaddition, β-stannyl cyclobutanones were produced.