10.1021/ja0504441.s001 Daniel T. Nowlan Daniel T. Nowlan Daniel A. Singleton Daniel A. Singleton Mechanism and Origin of Enantioselectivity in the Rh<sub>2</sub>(OAc)(DPTI)<sub>3</sub>-Catalyzed Cyclopropenation of Alkynes American Chemical Society 2005 terminal acetylenic carbon cyclopropenation OAc 13 C KIE mechanism isotope effects DPTI Rh 2 canonical variational transition structures tetrabridged rhodium carbenoids tribridged rhodium carbenoid 2005-05-04 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Mechanism_and_Origin_of_Enantioselectivity_in_the_Rh_sub_2_sub_OAc_DPTI_sub_3_sub_Catalyzed_Cyclopropenation_of_Alkynes/3288079 The mechanism of cyclopropenations of alkynes with ethyl diazoacetate catalyzed by Rh<sub>2</sub>(OAc)<sub>4</sub> and Rh<sub>2</sub>(OAc)(DPTI)<sub>3</sub> (<b>1</b>) is studied by a combination of kinetic isotope effects and theoretical calculations. With each catalyst, a significant normal <sup>13</sup>C KIE was observed for the terminal acetylenic carbon, while a very small <sup>13</sup>C 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.