Divergent reactivity in tandem reduction–Michael ring closures of five‐ and six‐membered cyclic enones

Abstract magnified image In this study, methyl (±)‐1‐(2‐nitrobenzyl)‐4‐oxo‐2‐cyclohexene‐1‐carboxylate and methyl (±)‐(2‐nitrobenzyl)‐4‐oxo‐2‐cyclopentene‐1‐carboxylate were prepared and subjected to reductive cyclization under dissolving metal conditions. The two reactants showed divergent behavior with the six‐ring substrate reacting at the ester carbonyl and the five‐ring substrate closing on the enone double bond. The difference in reactivity is attributed to the conformational flexibility, relative reactivity, and steric environment of C4‐substituted six‐ and five‐membered cyclic enones. J. Heterocyclic Chem., (2009).