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

In this study, methyl ±12nitrobenzyl4oxo2cyclohexene1carboxylate and methyl ±2nitrobenzyl4oxo2cyclopentene1carboxylate were prepared and subjected to reductive cyclization under dissolving metal conditions. The two reactants showed divergent behavior with the sixring substrate reacting at the ester carbonyl and the fivering substrate closing on the enone double bond. The difference in reactivity is attributed to the conformational flexibility, relative reactivity, and steric environment of C4substituted six and fivemembered cyclic enones. J. Heterocyclic Chem., 2009.