ja0504441_si_001.pdf (1.67 MB)

Mechanism and Origin of Enantioselectivity in the Rh2(OAc)(DPTI)3-Catalyzed Cyclopropenation of Alkynes

Download (1.67 MB)
journal contribution
posted on 04.05.2005 by Daniel T. Nowlan, Daniel A. Singleton
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.

History

Exports