Electrochemical synthesis of 5,6,11,12-tetrahydro-5,6,11,12-tetrakis(ethoxycarbonyl)dibenzo[a,e]cyclo-octene

Abstract

Electrochemical reduction of diethyl αα′-dibromobenzene-1,2-diacetate (1) in dimethylformamide solution at a vitreous carbon electrode results in the formation of diethylbenzene-1,2-diacetate (3)(15% of isolated products), trans,trans-tetrakis(ethoxycarbonyl)dibenzo[a,e]cyclo-octene (6)(16%), dimer (7)(16%), and a polymer (20%) as major products. Formation of benzocyclobutene (5)(7,8-bisethoxycarbonylbicyclo[4.2.0]octa-1,3,5-triene) takes place only to a very small extent (ca. 7% of isolated products). The intermediate formation of αα′-bis(ethoxycarbonyl)-o-quinodimethane, whose behaviour resembles that of a biradical, through the 2e electrochemical reductive elimination of the Br^– ions from (1), is proposed as the key step leading to the products.