Base-free NiH-catalyzed regio- and stereo-selective hydroacylation of allenes: A new route to synthesis of tetra-substituted olefins

The synthesis of all-carbon tetra-substituted olefins still constitutes a formidable synthetic challenge due to unavoidable issues, including uncontrolled E/Z selectivity. Herein, we report a regio- and stereoselective synthesis of tetra-substituted olefins via Ni-catalyzed hydroacylation of 1,1-disubstituted allenes with a diverse range of aliphatic and aromatic carboxylic anhydrides. NiH catalysis mainly with NˆN or NˆNˆN ligand systems has been utilized for bifunctionalization of various alkenes but is not suitable for allenes. In this work, the unprecedented PˆN ligand-tailored NiH catalysis of allenes in the absence of a base additive has been developed, which shows the opposite regioselectivity to Cu chemistry. The coordination of the extra carbonyl in the anhydride coupling partner to the Ni center makes the challenging intermolecular process more feasible. The chemistry is supported by combined experimental and computational mechanistic studies.