Excess substrate is a spectator ligand in a rhodium-catalyzed asymmetric [2 + 2 + 2] cycloaddition of alkenyl isocyanates with tolanes.

ABSTRACT: 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.

SUBMITTER: Oinen ME 

PROVIDER: S-EPMC2777613 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature