Photochemical preparation of cyclopropanes from cyclobutanones

A general method for the preparation of cyclopropanes is reported. Triplet- photosensitized reactions of a series of cyclobutanones give cyclopropanes as the major product. Part 1 describes the synthesis of substituted cyclobu tanones used in this study. In Part 2, the photo-reactions of cyclobutanone s are reported. Triplet-sensitized reactions of cyclobutanones using aceton e as a sensitizer give cyclopropanes as the major non-polar products. The e xtent of photodecarbonylation seems to be dependent on alpha-substitution. Electron-donating groups promote decarbonylation while electron-withdrawing groups favour cycloelimination.