PALLADIUM(II)-CATALYZED ASYMMETRIC ACETALIZATION OF ALKENES

The terminal olefinic carbon of N-methacryloyl-2-oxazolidinones is smoothly acetalized by alcohols in the presence of PdCl2 catalyst. The use of 4(S)-isopropyl-, phenyl-, and tert-butyl-2-oxazolidinones as the chiral auxiliary resulted in the formation of the corresponding (2'S)-acetals in 61, 80, and 95% de, respectively. Reductive removal of the auxiliary with LiAlH4 followed by deacetalization produced (R)-3-hydroxy-2-methylpropanal. The enantiomer of this compound, derived from 4(R)substituted oxazolidinones, served as a building block for synthesizing a 1 beta-methylcarbapenem precursor in high enantiomeric excess. In the acetalization of 3',3'-dideuteriated methacryloyl-4-isopropyloxaiolidinone with MeOH, one D-atom on the terminal olefinic carbon stereoselectively migrated to the chiral center in the product acetal. On the basis of this 1,2-hydride migration and the conformational preference of the methacryloyl moiety, the reaction pathway and the mechanism of the diastereoselection are discussed.