Fluoroboric Acid Adsorbed on Silica‐Gel (HBF4—SiO2) as a New, Highly Efficient and Reusable Heterogeneous Catalyst for thia‐Michael Addition to α,β‐Unsaturated Carbonyl Compounds.

TLDR: Fluoroboric acid adsorbed on silica-gel has been found to be a new and highly efficient heterogeneous catalyst for thia-Michael addition to α,β-unsaturated carbonyl compounds under solvent-free conditions as discussed by the authors.

Abstract: Fluoroboric acid adsorbed on silica-gel (HBF 4 –SiO 2 ) has been found to be a new and highly efficient heterogeneous catalyst for thia-Michael addition to α,β-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 β-carbon of the α,β-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.