REGIOSELECTIVE AND ENANTIOSELECTIVE SYNTHESIS OF PLANARLY CHIRAL CYCLOPENTADIENYLMANGANESE TRICARBONYL COMPLEXES VIA 2-CYMANTRENYL-1,3-DIOXOLANES

With the aim of finding suitable models for the asymmetric synthesis o f planarly chiral metallocenes developed by us recently, metalation of three chiral cyclic acetals, (4R,5R)-2-cymantrenyl-4,5-dimethyl-, (2R ,4R)-2-cymantrenyl-4-phenyl-, and (2S,4R)-2-cymantrenyl-4-phenyl-1,3-d ioxolanes (4-6), has been studied. While the reaction of 4 with n-BuLi appeared to be nonstereoselective, the corresponding reactions of 5 a nd 6 were diastereoselective and provided, upon the quenching of the l ithiated intermediates with electophiles, enantiomeric chiral 1,2-disu bstituted cymantrenes with ee values of 44 and 84%, respectively. Lith iation of 2-cymantrenyl-1,3-dioxolane is a convenient and regioselecti ve method for the synthesis of 1,2-disubstituted derivatives of cymant rene.