Photocyclisation des (oxo-3)-butyl glycopyranosides

3-Oxo butyl glycopyranosides undergo Norrish type II photocyclization giving hydroxyspiroketals. The influence of the anomeric configuration and of different substituents at C-2 has been studied. The favored photocyclization of various β-glycosides occurs with retention of configuration and is interpreted in terms of the greater stability of the radical formed by abstraction of the axial anomeric hydrogen atom.