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Diastereoselective Desymmetrization Of Meso Bis(Phenylsulfonyl) Polycyclic Alkenes Promoted By C2 Symmetric Chiral Diolates: Direct Access To Optically Pure Ketals And Ketones

Sergio Cossu, Paola Peluso

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 Csp 2 react with the enantiopure nucleophile which has been used in stoichiometric amount. The stereoselective process leads to the formation of optically pure α-phenylsulfonylsubstituted polycyclic ketals, which are valuable intermediate in the synthesis of polycyclic α-phenyl sulfonylketones and ketones. The kinetic resolution of a racemic mixture of a tolylsulfonylsubstituted polycyclic alkene is also reported.