FORMAL DESYMMETRIZATION BY A MITSUNOBU TRICK - ENANTIOMERICALLY PURE CIS-3,4-DIHYDROXYPYRROLINE N-OXIDES FOR THE ENANTIODIVERGENT SYNTHESISOF TRIHYDROXYINDOLIZIDINES

A protocol is presented for a completely enantioselective format desym metrization of C-s-symmetric diols by monoprotection of the correspond ing enantiopure C-2 diols, followed by an inversion of configuration b y a Mitsunobu reaction (''Mitsunobu trick''). Its application to the u nprecedented synthesis of enantiopure cis-3,4-dihydroxypyrroline N-oxi des, employed in the enantiodivergent synthesis of two selectively pro tected 1,2,7-trihydroxyindolizidines, is also reported.