Nickel-Catalyzed Reductive Cycloisomerization of Enynes with CO.

Carboxylate groups are ubiquitous in bioactive molecules. The syntheses of carboxylates from petroleum feedstock require a series of oxidation reactions. CO represents a cheap and sustainable, preoxidized C1 source. Herein, we describe a simple, selective, and mild procedure for the construction of (hetero)cyclic α,β-unsaturated carboxylic acids from 1,6- and 1,7-enyes and CO. Terminal 1,7-enynes and sterically hindered alkenes experience a change in regioselectivity and form unconjugated carboxylic acids. Mechanistic studies of the reductive cyclization suggest a hydride insertion pathway, explaining the change in regioselectivity caused by steric effects and distinguishing this work from previous reactions involving CO.