Asymmetric Olefin Isomerization via Phase-Transfer-Catalyzed [1,3]-Hydrogen Transfer for Access to Axially Chiral Furan-Benzimidazoles.

An efficient catalytic asymmetric olefin isomerization of axially chiral methylene dihydrofuran-benzimidazoles via kinetic resolution is reported. Under mild phase-transfer catalysis, axially chiral furan-benzimidazole compounds and recovered methylene dihydrofuran-benzimidazoles were obtained in high ee. The combination of the kinetic resolution and TBD-catalyzed isomerization of recovered dihydrofuran-benzimidazoles provided access to both enantiomers of furan-benzimidazoles. Deuterium-labeling experiments reveal intramolecular [1,3]-H transfer mechanism. The utility of this method was demonstrated by scale-up synthesis and functionalization of the products.