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

Abstract

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.