Excess Substrate is a Spectator Ligand in a Rhodium-Catalyzed Asymmetric [2 + 2 + 2] Cycloaddition of Alkenyl Isocyanates with Tolanes
作者:Mark Emil Oinen、Robert T. Yu、Tomislav Rovis
DOI:10.1021/ol9020805
日期:2009.11.5
Excess substrate has been identified as an unintended spectator ligand affecting enantioselectivity in the [2 + 2 + 2] cycloaddition of alkenyl isocyanates with tolanes. Replacement of excess substrate with an exogenous additive affords products with consistent and higher ee's. The increase in enantioselectivity is the result of a change in composition of a proposed rhodium(III) intermediate on the catalytic cycle. The net result is a rational probe of a short-lived rhodium(III) intermediate and gives insight that may have applications in many rhodium-catalyzed reactions.