The Dowd–Beckwith ring expansion: a theoretical study

UB3LYP/6-311++G(d,p) and ROMP2/6-311++G(d,p)//UB3LYP/6-311++G(d,p) calculations including the effect of benzene solvent through the PCM-UAHF method render a concerted mechanism without fragmentation as the most favourable one for the Dowd–Beckwith radical ring expansion of the bromomethyl adduct of methyl cyclopentanone-2-carboxylate to yield methyl cyclohexanone-3-carboxylate. The corresponding concerted TS is a bicyclic alcoxy radical.