Palladium-katalysierte kinetische Racematspaltung allylischer Carbonate mit S-Nukleophilen und enantioselektive Umlagerung allylischer O-Sulfinate : asymmetrische Synthese von allylischern Sulfiden und Sulfonen

The palladium(0) catalyzed reactions of symmetrically disubstituted racemic allylic carbonates, being either cyclic or acyclic, with 2-pyrimidinethiol in the presence of N,N'-(1R,2R)-1,2-cyclohexanediyl-bis[2-(diphenylphosphino)-benzamide] BPA as ligand proceed with excellent levels of enantio-selectivity in both kinetic resolution and substitution. While the kinetic resolution allows for the synthesis of enantiomerically highly enriched cyclic and acyclic allylic alcohols up to 99% ee, the substitution provides for an asymmetric synthesis of enantiomerically highly enriched allylic sulfides up to 99% ee. The reaction of the enantiopure cyclohexenyl carbonate with 2-pyrimidinethiol in the presence of BPA was shown to exhibit, under the conditions used, an overall pseudo-zero order kinetics in regard to the allylic substrate. In accordance with previous observations the faster reacting enantiomer of the substrate and the preferentially formed substitution product have the same absolute configuration. According to experiments with racemic and enantioenriched cyclohexenyl carbonate and 2-pyrimidinethiol the ee value of the substitution product is independent of the chirality of the substrate, that is, no "memory effect" is operating. However, a "memory effect" seems to operate in the case of the reaction of the cyclopentenyl esters with 2-pyrimidinethiol. The second part described the asymmetric synthesis of cyclic and acyclic allylic S-aryl and S-alkyl sulfones through a highly selective palladium(0)-catalyzed 1,3-rearrangement of racemic allylic sulfinates. Treatment of racemic cyclic and acyclic allylic S-tolyl- and S-tert-butylsulfinates with Pd2(dba)3.CHCl3 as precatalyst and BPA as ligand for the palladium atom afforded the corresponding allylic S-tolyl- and S-tert-butylsulfones of up to 99% ee. The racemic allylic sulfinates were obtained from the corresponding racemic alcohols and racemic tolylsulfinyl chloride and racemic tert-butylsulfinyl chloride. Rearrangement of the racemic tert-butylsulfinic acid 2-cyclooct-1-enyl ester with Pd2(dba)3.CHCl3 and BPA was accompanied by a highly selective kinetic resolution of the substrate and gave at 50% conversion the (R)-configured sulfinate as mixture of the SS and RS diastereomers of 92% ee and 85% ee and the (S)-configured 3-tert-butylsulfonyl cyclooctene sulfone with 98% ee in almost quantitative yields