Enantioselective Protonation of Enol Silanes by Protonated Chiral Sulfinamides

Significance

Jacobsen and co-workers developed a protocol for the asymmetric protonation of aryl-substituted cyclic enol silanes. The catalyst system is based on a chiral sulfinamide A as the source of enantioinduction, an achiral sulfonic acid B as co-catalyst and 2,6-di-tert-butylphenol as stoichiometric proton source. A screening of bifunctional sulfinamide/urea catalysts as well as simple ureas, sulfinamides and bifunctional sulfonamide/urea catalysts revealed that the simple sulfinamide motif is sufficient and necessary to achieve enantioinduction as well as conversion. While the use of other sulfonic acids as co-catalysts led to equally good conversion, B was found to be best in terms of enantioselectivity.