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Catalytic reductive [4 + 1]-cycloadditions of vinylidenes and dienes

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Science  22 Feb 2019:
Vol. 363, Issue 6429, pp. 857-862
DOI: 10.1126/science.aau0364

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Five-membered rings for two nickels

The Diels-Alder reaction is widely used to make six-membered rings by adding four-carbon dienes to two-carbon alkenes. It would seem straightforward to likewise access five-membered rings from dienes and one-carbon sources, or carbenes, but that does not tend to work. Instead, the carbene adds to just half of the diene to form a cyclopropane. Zhou and Uyeda now show that a catalyst with two nickel centers can steer this reaction toward the cyclopentyl products (see the Perspective by Johnson and Weix). A chiral version of the catalyst rendered the reaction enantioselective in intramolecular cases.

Science, this issue p. 857; see also p. 819

Abstract

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 + 1]-cycloaddition reactions of 1,3-dienes. The C1 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 C2-symmetric chiral ligand that stabilizes a metal-metal bond.

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