Enantioselective cathodic reduction of 4-substituted coumarins with alkaloids as catalysts, 2. AM1 and force-field study of the transition-state model

✍ Scribed by Höweler, Udo ;Schoo, Norbert ;Schäfer, Hans-J.

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 561 KB
• Volume: 1993
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199319930199

✦ Synopsis

Abstract

The experimental data presented in Part 1 of this series lead to a refined model for the transition state of the alkaloid‐induced enantioselective electroreduction of 4‐methylcoumarin. This model is based on a zwitterionic complex formed by the protonated alkaloid and the reduced species of the coumarin. The complex is studied by a combination of quantum chemical and molecular mechanics methods. The reactant geometries and their charge distributions are determined by the semiempirical AM1 method. The MOBY force field is used for a complete conformational analysis and optimization of the complexes. In agreement with experiment, an optical induction is found for yohimbine while its isomer rauwolscine shows no stereoselectivity. An upper limit for the distance between the reactants in the zwitterionic complex is determined and criteria for improved inductors are developed.