Fluoroboric acid adsorbed on silica-gel(HBF4-SiO2)as a new,highly efficient and reusable heterogeneous catalyst for thia-Michael addition to alpha,beta-unsaturated carbonyl compounds

摘要

Fluoroboric acid adsorbed on silica-gel(HBF4-SiO2)has been found to be a new and highly efficient heterogeneous catalyst for thia-Michael addition to alpha,beta-unsaturated carbonyl compounds under solvent-free conditions.In the case of 1,3-diaryl-2-propenones,the reactions are best carried out in MeOH.The rate of thia-Michael addition was dependent on the steric hindrance at the beta-carbon of the alpha,beta-unsaturated carbonyl substrate as well as surrounding the thiol moiety and was exploited for selective thia-Michael addition during intermolecular competition between two enones with a common thiol and between two aryl/alkyl thiols for a common enone.The methodology finds application for one-pot syntheses of 2,3-dihydro-1,5-benzothiazepines.