Diastereoselective desymmetrization of meso bis(phenylsulfonyl) polycyclic alkenes promoted by C2 symmetric chiral diolates: direct accessto optically pure ketals and ketones

The desymmetrization of meso 1,2-bis(phenylsulfonyl) substituted bridged polycyclic alkenes promoted by C2 symmetric chiral diolates is reported. The phenylsulfonyl group exerts an electronwithdrawing effect onto the C-C double bond, making the alkenylic function a good Michael acceptor: enantiotopic Csp2 react with the enantiopure nucleophile which has been used in stoichiometric amount. The stereoselective process leadsto the formation of optically pure a-phenylsulfonylsubstituted polycyclic ketals, which are valuable intermediate in the synthesisof polycyclic a-phenylsulfonylketones and ketones.The kinetic resolution of a racemic mixture of a tolylsulfonulsubstituted polycyclic alkene is also reported.