Highly stereoselective reformatsky reactions of 3-(2-Bromopropionyl)-2-oxazolidone derivatives with various aldehydes

The Reformatsky reactions of 3-2-bromopropionyl)-2-oxazolidone derivatives with various aldehydes were investigated to elucidate the effects of substituents in the 2-oxazolidone moieties on their diastereoselectivities. The highest 2,3-syn-diastereoselectivity (2,3-syn:2,3- anti=98:2) could be realized at -78°C by employing sterically crowded 3-(2- bromopropionyl)-4,4-dibutyl-5,5-pentamethylene-2-oxazolidone. While high 2,3-syn-3,4-syn-selectivity (2,3-syn-3,4-syn:2,3-syn-3,4-anti=94:6) was also accomplished by the reaction with di-2-phenylpropanal, application of this reaction to enantioselective synthesis of 2,3-syn-aldols was found to be unrewarding. The observed diastereoselectivities could be accounted for by the chelating transition state models.