Preparation of Thietane Derivatives through Domino Photochemical Norrish Type II/Thia-Paternò-Büchi Reactions.

This work describes straightforward access to a large collection of thietane derivatives through an innovative two-step domino photochemical reaction involving a Norrish type II fragmentation and a thia-Paternò-Büchi reaction. Starting from stable phenacyl sulfides, unprecedented thiocarbonyl intermediates were generated in situ and reacted with diverse electron-deficient alkene partners to form a thietane core. The rules governing the regio- and diastereoselectivity of this [2+2] photocycloaddition have been rationalized and fully controlled for many substrates.