The strategic use of para-quinone methides to access synthetically challenging and chemoselective α,α'-diarylmethyl N-glycosides from unprotected carbohydrate amines

Tropylium Salt-Promoted Vinylogous Aza-Michael Addition of Carbamates to para-Quinone Methides: Elaboration to Diastereomerically Pure α,α'-Diarylmethyl Carbamates

Carbocation catalysis is emerging as an important subarea of Lewis acid catalysis. Some stable and isolable carbocations have been successfully utilized as Lewis acid catalysts and promoters in many synthetic transformations. In this manuscript, we report a tropylium cation-promoted vinylogous aza-Michael addition of carbamates to para-quinone methides (QMs) to access a wide range of unsymmetrical α,α'-diarylmethyl carbamates. This mild protocol was effective for the vinylogous conjugate addition of (-)-menthyl carbamate to p-QMs, and the respective diastereomerically pure α,α'-diarylmethyl carbamate derivatives could be obtained in excellent yields and diastereoselectivities (up to >20:1 de).

Synthesis of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline through nucleophilic addition of organozinc reagents to N,O-acetals

A new approach to access 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline has been developed through nucleophilic addition of organozinc reagents to N,O-acetals. A number of substituted organozinc reagents were amenable for this transformation, and the desired products were obtained with excellent yields. Moreover, Sc(OTf)3 proved to be an effective catalyst for the formation of 1-benzylisoindoline and 1-benzyl-tetrahydroisoquinoline using such nucleophilic addition.