Research Seminar by Dr. Hemanta Kumar Kisan | Shiv Nadar University
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Research Seminar by Dr. Hemanta Kumar Kisan

Research Seminar by Dr. Hemanta Kumar Kisan from Department of Chemistry, Utkal University, Bhubaneswar.

Seminar Title: Mechanistic Investigation on the Origin Parallel Kinetic Resolution of rac-Aziridines Using Chiral Bimetallic Catalyst.

Event Date: 
Friday, June 14, 2019 -
11:0012:00

Mechanistic Investigation on the Origin Parallel Kinetic Resolution of rac-Aziridines Using a Chiral Lanthanum−Yttrium Bimetallic Catalyst

Hemanta Kumar Kisan

Department of Chemistry, Utkal University, Bhubaneswar Odisha 751004, India

Email: hemantkisna12@gmail.com

Abstract

In asymmetric catalysis, the domain of parallel kinetic resolution thrives to separate both enantiomers from a racemic mixture. In an exciting recent demonstration, a rac-cis-2,3-substituted chiral N-benzoyl aziridine was converted into enantiomerically pure (ee > 98%) products through a ring-opening reaction in near-quantitative yields from both the enantiomers (~48%). When the rac-aziridine is reacted with dimethyl malonate in the presence of a lanthanum-yttrium hetero-bimetallic chiral Schiff base as the catalyst, high degree of regio- and enantio-selectivities could be accomplished.1,2 Through a comprehensive computational investigation, herein we delineate the origin of regio-divergent and enantioselective formation of -amino ester derivatives. The Gibbs free energy of the transition state for ring-opening at the propyl substituted C2 carbon is found to be 7.2 kcal/mol lower in energy than that at the ethyl substituted C3 carbon in the case of (2R,3S) enantiomer of the parent aziridine. Reversal of the regio-chemical preference is noted for enantiomeric (2S,3R)-aziridine, where the ring-opening occurs at the ethyl substituted C3 carbon. The La-Y chiral Schiff base catalyst has been found to first ‘recognize’ both the enantiomers of the rac-aziridine rather indiscriminately. The key to high regio-selectivity in the addition of lanthanum-bound malonate to the aziridine anchored on to the yttrium center is traced to a unique geometric disposition of the latter in the stereocontrolling ring opening.

Keywords: Parallel kinetic resolution, Regioselectivity, Enantioselectivity, Transition states, Density functional theory

References:

(1) Xu, Y.; Kaneko, K.; Kanai, M.; Shibasaki, M.; Matsunaga, S. J. Am. Chem. Soc. 2014, 136, 9190.

(2) Kisan, H. K.; Sunoj, R. B. ACS Catal. 2018, 8, 7633.

Friday 14, Jun 2019
11:00 AM - 12:00 PM
D-330

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