Abstract
Many nickel-catalyzed transformations via a hetero-nickelacycle have been reported, in which two different key reaction steps to generate a hetero-nickelacycle from nickel(0) species have been proposed. One proposed reaction is oxidative cyclization of two π-components with nickel(0) complex to give five-membered hetero-nickelacycles. The other type of reaction to generate a hetero-nickelacycle is the oxidative addition of cyclopropyl ketones and cyclopropyl imines to give six-membered hetero-nickelacycles, which has also been proposed as an important key step in nickel-catalyzed [3+2] cycloaddition reactions to give cyclopentane derivatives. We report here oxidative cyclization reactions of carbon-carbon unsaturated compounds and aldehyde, ketone or imine with nickel(0). These reactions have been proposed as an important key step in multicomponent-coupling reactions as well as [2+2+2] cycloaddition reactions. Oxidative addition of a cyclopropyl ketone to nickel(0) to give a dihydronickelapyran and its role in a catalytic reaction is also discussed in this paper.
