Oinen Mark Emil, Yu Robert T, Rovis Tomislav
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523, USA.
Org Lett. 2009 Nov 5;11(21):4934-7. doi: 10.1021/ol9020805.
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.
过量底物已被确定为一种意外的旁观配体，它会影响异氰酸烯酯与二苯乙炔的[2 + 2 + 2]环加成反应中的对映选择性。用外源添加剂替代过量底物可得到对映体过量值（ee值）一致且更高的产物。对映选择性的提高是催化循环中所提出的铑（III）中间体组成变化的结果。最终结果是对一种短寿命铑（III）中间体进行了合理的探究，并提供了可能在许多铑催化反应中具有应用价值的见解。
