Science. Feb 22, 2019, Vol. 363 Issue 6429, p857, 6 p.
Ring formation (Chemistry) -- Research, Diels-Alder reaction -- Research, Chemistry, Organic -- Research, and Chemical research
Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze [4 + l]-cycloaddition reactions of 1, 3-dienes. The Ci partner is a vinylidene equivalent generated from the reductive activation of a 1, 1-dichloroalkene in the presence of stoichiometric zinc. Intermolecular and intramolecular variants of the reaction are described, and high levels of asymmetric induction are achieved in the intramolecular cycloadditions using a [C.sub.2]-symmetric chiral ligand that stabilizes a metal-metal bond.