ABSTRACT
The competing reactions in Scheme 1 are influenced by the nature of the substrate and the reaction conditions. In dry aprotic solvents, polymerization is common on a preparative scale, whereas on voltammetric time scales reversible dimerization or enhanced chemical stability of the radical anion may be observed. Addition of proton donors may prevent polymerization. However, hydrogenation of the double bond competes with dimerization if the proton donor is sufficiently acidic. The common hydrodimerization pathway (Scheme 1 ), leading to the linear hydrodimer (LHD), is not always followed. When the activating group is a carboxylic acid derivative, including cyano, or a carbonyl group, intramolecular addition leading to a cyclic hydrodimer (CHD) is often favored over the final protonation step.
