A Binaphthyl-Based Scaffold for a Chiral Dirhodium(II) Biscarboxylate Ligand with α-Quaternary Carbon Centers

Abstract

A chiral dirhodium(II) paddlewheel complex has been synthesized from biscarboxylate ligands derived from BINOL, and the resulting complex has been used in enantioselective carbene/alkyne cascade reactions. The ligand design was guided by requirements of α,α-dimethyl substituted carboxylates and bidentate ligands to ensure high levels of catalytic activity. Previously disclosed chiral complexes lack these features, resulting in low product yields. The design successfully replicated or exceeded the yields of the unusually effective achiral catalyst for the cascade reaction, Rh2(esp)2, which often shows unique reactivity. Promising enantioselectivity was observed for aldehyde-derived hydrazone substrates (29–96% ee), showing that the new scaffold has significant potential.