Rh2(OAc)(DPTI)3催化炔烃环丙烷化反应中对映选择性的机理与起源

Mechanism and origin of enantioselectivity in the Rh2(OAc)(DPTI)3-catalyzed cyclopropenation of alkynes.

作者信息

Nowlan Daniel T, Singleton Daniel A

机构信息

Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842, USA.

出版信息

J Am Chem Soc. 2005 May 4;127(17):6190-1. doi: 10.1021/ja0504441.

DOI:10.1021/ja0504441

PMID:15853322

Abstract

The mechanism of cyclopropenations of alkynes with ethyl diazoacetate catalyzed by Rh2(OAc)4 and Rh2(OAc)(DPTI)3 (1) is studied by a combination of kinetic isotope effects and theoretical calculations. With each catalyst, a significant normal 13C KIE was observed for the terminal acetylenic carbon, while a very small 13C KIE was observed at the internal acetylenic carbon. These isotope effects are predicted well from canonical variational transition structures for cyclopropenations with intact tetrabridged rhodium carbenoids. A viable mechanism based on the recently proposed importance of a [2 + 2] cycloaddition on a tribridged rhodium carbenoid could not be identified. An explanation for the enantioselectivity with DPTI ligands is described.

摘要

通过动力学同位素效应和理论计算相结合的方法，研究了由Rh2(OAc)4和Rh2(OAc)(DPTI)3（1）催化的乙炔与重氮乙酸乙酯的环丙烯化反应机理。对于每种催化剂，在末端炔碳处观察到显著的正常13C动力学同位素效应（KIE），而在内侧炔碳处观察到非常小的13C KIE。这些同位素效应可以通过具有完整四桥连铑卡宾的环丙烯化反应的正则变分过渡结构很好地预测。基于最近提出的三桥连铑卡宾上[2 + 2]环加成重要性的可行机理尚未得到确认。文中描述了对使用DPTI配体时对映选择性的一种解释。