PHOTOCHEMICALLY MEDIATED RING CONTRACTION OF PYRAZOLIDIN-3-ONES TO BETA-LACTAMS

Synthetic routes to beta-lactams have conventionally followed either a one-bond cyclization or two-bond cycloaddition strategy.1 Virtually a ll possible variations of these two constructions have been realized2 and several, notably N-C4 cyclization3 and chlorosulfonylisocyanate cy cloaddition,4 have adapted well to the synthesis of therapeutically im portant beta-lactam antibiotics. In contrast, ring contraction approac hes to 2-azetidinones have received relatively little attention and no ne has been applied to the synthesis of a clinically useful beta-lacta m.