Stereoselective intermolecular [2+2]-photocycloaddition reactions and their application in synthesis

Stereoselective intermolecular [2+2]-photocycloaddition reactions of alkenes and Paterno-Buchi reactions are reviewed. For both reactions the regioselectivity and the simple diastereoselectivity which are relevant to the formation of a single product isomer are explained based on representative examples. In the subsequent sections the facial diastereoselectivity induced by the respective reaction partner is treated. Particular emphasis is given on synthetic applications of the cyclobutanes and oxetanes obtained by the photochemical key step. Consecutive reactions are discussed and the potential use of the four-membered ring intermediates is highlighted.