Construction of contiguous tetrasubstituted carbon stereocenters by intramolecular crossed benzoin reactions catalyzed by N-heterocyclic carbene (NHC) organocatalyst

Bicyclic compounds with two contiguous tetrasubstituted carbon stereocenters at bridgehead positions were synthesized by N-heterocyclic carbene (NHC)-catalyzed intramolecular crossed benzoin reactions of symmetrical compounds. This desymmetrization strategy was applied to asymmetric synthesis with chiral NHC organocatalysts. Transition-state models were proposed to explain the enantioselectivity. A tricyclic compound with three contiguous tetrasubstituted carbon stereocenters was synthesized by a stepwise strategy. The molecular structure and absolute configuration of the (+)-enantiomer of this tricyclic compound were determined by X-ray crystallographic analysis.