Enantioselective Diels–Alder Reactions of Cyclohexa-1,3-diene and Chalcones Catalyzed by Intramolecular Silicon–Sulfur Lewis Pairs as Chiral Lewis Acids
作者:Polina Shaykhutdinova、Martin Oestreich
DOI:10.1021/acs.organomet.6b00548
日期:2016.8.22
The stereoselective preparation of diastereomeric dihydrosilepine-derived silicon cations decorated with another binaphthyl unit at the silicon atom is described. A sulfide donor attached to that additional binaphthyl substituent forms an intramolecular Lewis pair with the electron-deficient silicon atom, as verified by Si-29 NMR spectroscopy. Both chiral sulfur-stabilized silicon cations act as catalysts in the difficult Diels Alder reaction of cydohexa-1,3-diene and chalcone derivatives. Both Lewis acids induce enantioselectivity, but the S,S relative configuration is superior to the S,R configuration. With the former diastereomer, enantiomeric excesses of close to 60% are obtained. These values are the highest achieved to date in this seemingly trivial cycloaddition.