(NHC)NiH-Catalyzed Regiodivergent Cross-Hydroalkenylation of Vinyl Ethers with α-Olefins: Syntheses of 1,2- and 1,3-Disubstituted Allyl Ethers.

Cross-hydroalkenylation of a vinyl ether (1) with an α-olefin (2) was first achieved by a set of [NHC-Ni(allyl)]BAr (NHC=N-heterocyclic carbene) catalysts. Both 1,2- and 1,3-disubstituted allyl ethers were obtained, highly selectively, by using NHCs of different sizes. In contrast, the chemoselectivity (i.e., 1 as acceptor and 2 as donor) was controlled mostly by electronic effects through the catalyst-substrate interaction. Sterically bulkier alkenes (2) were used as preferred donors compared to smaller alkenes. This electronic effect also served as a basis for the first tail-to-head cross-hydroalkenylations of 1 with either a vinyl silane or boronic ester.