Highly regio-, chemo- and diastereoselective synthesis of oxa-bridged spirocycles: A novel observation of reverse selectivity

The reverse regio- and diastereoselectivities are observed between the reactions involving 5- and 6-membered-ring cyclic carbonyl ylide dipoles with (alpha)-methylene ketones. A mild catalytic route to synthesize spirocyclic systems with high regio-, chemo- and diastereoselectivities is described.