Stereochemistry and mechanistic study of intramolecular Pd-II-catalyzed oxypalladation and 1,3-chirality-transfer reactions

Pd-II-catalyzed cyclizations of chiral epsilon-, xi-, and eta-hydroxy-alpha,beta-unsaturated alcohols are described. The reactions took place stereospecifically to give chiral 2,5-disubstituted tetrahydrofurans, 2,6-disubstituted tetrahydropyrans, and 2,7-disubstituted oxepanes, respectively. The chirality of the carbon center of the chiral allylic alcohol is transferred stereospecifically to the carbon center of the newly generated oxacyclic ring. A plausible reaction mechanism involves 1) chiral-allylic-alcohol-induced syn facioselective formation of a Pd pi-complex, 2) syn oxypalladation, and 3) syn elimination of PdCl(OH), which provide a rational account for the stereochemical results.