NEW CHIRAL C-3-SYMMETRICAL TRIOLS AS LIGANDS FOR VANADIUM AND TITANIUM COMPLEXES

Several new chiral triols 1a-c with C-3 symmetry have been prepared in enantiopure form via a route involving the iterative catalytic asymme tric alkylation of aldehydes by organozinc reagents followed by diaste reoselective hydroboration. Reactions of these chiral triols with tita nates Ti(OR)(4) and vanadates V(O)(OR)3 are reported. The structure of the binuclear vanadium triolato(3-) complex [V(O)C{(OCH-Et)(3)CH}](2) (12a) has been determined by X-ray analysis. A series of model reacti ons was conducted to assess the catalytic properties of the chirally m odified titanium and vanadium secondary alkoxides. The reactions chose n were the addition of diethylzinc and of trimethylsilyl cyanide to be nzaldehyde and the oxidation of geraniol and of ethyl phenyl sulfide w ith tert-butyl hydroperoxide. Only a moderate asymmetric induction was found in some model reactions catalyzed by titanium complexes 11a,b. On the other hand, a very efficient chemoselective oxidation of sulfid es to sulfoxides with tert-butyl hydroperoxide was possible in the pre sence of vanadium complex 12a.