Enantioselective Synthesis of Inherently Chiral Tetraphenylene Analogues Enabled by NHC-Catalyzed Benzoin Condensation.

Herein, we report an enantioselective N-heterocyclic carbene (NHC)-catalyzed intramolecular benzoin reaction of bisaldehydes featuring a 1,1':2',1''-terphenyl linkage to afford eight-membered α-hydroxy ketones in which six of the eight ring atoms are benzene carbons. The benzene-rich framework is conformationally inflexible and thus inherently chiral, adopting a saddle-shaped conformation. A variety of heteroaromatic- and naphthalene-embedded tetraphenylene analogues were prepared enantioselectively by routine transformations of the α-hydroxy ketone moiety. Density functional theory (DFT) calculations elucidate the reaction mechanism and provide insights into the origin of the stereoselectivity.