A new entry to enantioselective synthesis of α-methylene-β-hydroxy ketones by the chalcogeno-Baylis-Hillman reaction

Abstract

Chiral hydroxy chalcogenides in the presence of TiCl4 achieved the asymmetric version of the chalcogeno-Baylis-Hillman reaction. The reaction proceeded under atmospheric pressure for 1 h. 10-Methylthioisoborneol (9) achieved the best enantioselectivity. A methoxy derivative 10 of 10- methylthioisoborneol resulted in lower selectivity than that obtained by 10- methylthiolsoborneol (9). A hydroxyl group is required to perform good asymmetric induction. The asymmetric chalcogeno-Baylis-Hillman reaction with a C2 symmetric bidentate ligand-TiCl4 complex was also examined. Diol ligands gave the adduct in low to good yields with low or no enantiomeric excess. The adduct was also obtained in low to high yields with low or no enantiomeric excess using bisoxazoline ligands.