PALLADIUM(0)-CATALYZED ASYMMETRIC CYCLOADDITION OF VINYLOXIRANES WITHHETEROCUMULENES USING CHIRAL PHOSPHINE-LIGANDS - AN EFFECTIVE ROUTE TO HIGHLY ENANTIOSELECTIVE VINYLOXAZOLIDINE DERIVATIVES

Cycloaddition reaction of 2-vinyloxiranes with carbodiimides using Pd- 2(dba)(3) . CHCl3, and TolBINAP as the chiral ligand, in THF at ambien t temperature, afforded 4-vinyl-1,3-oxazolidin-2-imines in 70-99% yiel d and in up to 95% ee. The stereoselectivity is strongly influenced by the structure of the chiral phosphine ligands and substrates, as well as by the reaction conditions. The enantiodetermination step is assum ed to be nucleophilic attack of a nitrogen nucleophile on a pi-allyl p alladium intermediate. Reaction of 2-vinyloxiranes with isocyanates us ing the same catalyst system afforded 4-vinyl-1,3-oxazolidin-2-ones in high yield but in no greater than 50% ee.