Studies on a new reducing agent

Abstract

The reductive Pauson-Khand reaction is the analogous formation of cyclopentenones from alkyne, via its hexacarbonyldicobalt complex, an alkene and carbon monoxide. We discovered that bicyclopentanones were formed form enynes using $Co_2(CO)_8$ or $Co_4(CO)_12$ and $H_2O$ in DME. Although the exact identifying of the reaction mechanism remains unspecified, we speculated that an in situ 1,4-reduction of the intermediate bicyclopentenone form the Pauson-Khand reaction by the $HCo(CO)_4$, that is presumably generated from the reaction of residual cobalt carbonyl complexes with $H_2O$, is responsible for bicyclopentanone formation. With the same method, reduction of various functional groups such as alpha,beta-unsaturated carbonyl compounds, alpha-heterosubstituted ketones and aromatic nitro compounds can be accomplished. This reagent for these reductions is extremely clean with little byproduct formation, provides remarkable selectivity and affords the desired products in good to high yields. However, attempted reductive N-O bond cleavage of 2-isoxazolines was not successful and gave various products in low yields depending on the structure of the reactants.