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Electroorganic Synthesis, 54. Enantioselective Cathodic Reduction of 4-Substituted Coumarins with Alkaloids as Catalysts, 1

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

Publisher: John Wiley and Sons
Year: 1993
Tongue: English
Weight: 700 KB
Volume: 1993
Category: Article
ISSN: 0947-3440
DOI: 10.1002/jlac.199319930198

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✦ Synopsis

Abstract

The optical yield in the alkaloid‐catalyzed enantioselective electroreduction of 4‐methylcoumarin (1a) was increased from 17% to 47.4% by systematic variation of the electrolysis conditions. The results are explained by an induction mechanism in which the adsorbed protonated alkaloid acts as a chiral proton donor towards a prochiral carbanion derived from 1a. The preferred configuration of the product and the results obtained by variation of the alkaloid structure allow us to propose a model of the transition state. Furthermore, 4‐phenylcoumarin (1b) and 4‐(trifluoromethyl)coumarin (1c) were reduced with 13.2% and 8.4% ee, respectively.

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✍ Höweler, Udo ;Schoo, Norbert ;Schäfer, Hans-J. 📂 Article 📅 1993 🏛 John Wiley and Sons 🌐 English ⚖ 561 KB

## 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 specie