Cathodically initiated cyclodimerization of trimethyl aconitate

Trimethyl aconitate (2) affords, by reduction in dimethylformamide–Et4NBr at a mercury cathode in 75% yield and high stereoselectivity, pentamethyl-1-(2-methoxy-2-oxoethyl)-1,2,3,4,5-cyclopentane pentacarboxylate (6). The product structure, the substoichiometric current consumption and cyclovoltammetry indicate that product formation occurs by means of a base that is electrogenerated from 2. The base induces a catalytic cycle of two successive Michael additions, where 2 acts as an acceptor and its conjugated base 2d as a donor. X-ray structure analysis of the main diastereomer of 6 and quantum chemical calculations show that the most stable out of 16 diastereomers is formed as the main product. This indicates that the cathodically initiated tandem-Michael addition is controlled thermodynamically. In the presence of an excess of dimethyl maleate, 2 undergoes a cathodic heterocoupling to afford hexamethyl cyclopentane hexacarboxylate (8).