Electrochemical reactions. Part VIII. Asymmetric induction during the reduction of coumarins modified by the presence of tertiary amines

Abstract

The electrochemical reduction of coumarin and some substituted coumarins at a mercury cathode in the presence of tertiary amines known to lower the hydrogen overpotential at the pH used has been examined. Coumarin alone yields a dimeric reduction product. In the presence of amines the yield of this dimeric product is decreased and some 3,4-dihydrocoumarin is formed. The dihydrocoumarin is considered to arise from hydrogen transfer between the radical R₃ṄH derived by reduction of the trialkyl ammonium ion and the radical which is the initial product of the reduction of coumarin. Electrochemical reduction of 4-methylcoumarin and 5-methoxy-4-methylcoumarin in the presence of optically active amines affords optically active dihydrocoumarins. The maximum optical yield achieved for 3,4-dihydro-3-methylcoumarin is 17%.