Synthesis and Evaluation of Novel Dirhodium(II) Carboxylate Catalysts with Atropisomeric Biaryl Backbone

Abstract

Three new dirhodium(II) carboxylate catalysts containing an axially dissymmetric biphenyl or binaphthyl skeleton have been synthesized and characterized.The X-Ray structure of the dirhodium(II) complex incorporating (R)-2'-methoxycarbonyl-6,6'-dimethyl-[1,1'-biphenyl]-2-carboxylate as bridging ligands demonstrates that the four carboxylate ligands are arranged in a C 2symmetry-like conformation.These catalysts have been shown to provide a reasonable level of asymmetric induction in intramolecular C-H insertion of amethoxycarbonyl-a-diazoacetamide.In recent years, a dramatic development in dirhodium(II) complex-catalyzed, asymmetric carbene transformations of a-diazo carbonyl compounds has been recorded in a number of processes, including cyclopropanation, C-H insertion, and rearrangement or cycloaddition via ylide generation. 1In this context, considerable effort continues to be devoted to the design, synthesis, and evaluation of chiral dirhodium(II) catalysts.Unique in their design are chiral bridging ligands bound to the dirhodium(II) core, which constitute one of the most fundamental factors responsible for a high level of chemical reactivity, turnover numbers, regio-, diastereo-and enantioselectivity. 1,2Our efforts in this area have led to the development of dirhodium(II) carboxylate catalysts, which incorporate N-phthaloyl-or N-benzenefused phthaloyl-(S)-amino acids as bridging ligands. 3,4These catalysts mediate intramolecular C-H insertions of a structurally diverse array of diazo carbonyl compounds, 5-10 intermolecular Si-H insertions, 11 intermolecular 1,3-dipolar cycloadditions via the generation of keto-4 or ester-carbonyl ylides, 12 and [2,3] sigmatropic rearrangement via the intramolecular formation of allylic 13 or propargylic oxonium ylides 14 with a maximum of 98%, 74%, 93%, and 79% ee's, respectively.In these reactions, the presence of phthalimido or benzene-fused phthalimido groups in bridging ligands has proven to be