Electronic and Steric Effects Control Regioselectivity in Alkyne Migratory Insertion during Ni-Catalyzed Indenone Synthesis

Abstract

Many useful transition-metal-catalyzed reactions depend on the migratory insertion of an alkyne into a metal–carbon bond. Steric effects, electronic effects, and coordinating directing groups have all been shown to control product distributions in reactions in which this is the regioselectivity-determining step. This study describes how both steric and electronic parameters influence regioselectivity within a previously disclosed Ni-catalyzed indenone synthesis reaction. Steric repulsion determines the overall sense of regioselectivity, and to some extent the magnitude, while electronic effects can also significantly alter the magnitude of the observed regioselectivity. The relationship between alkyne insertion regioselectivity and the electronic character of the migrating aryl group is demonstrated via comparisons with established electronic substituent constants (σ+ values). These observations will aid in the understanding and development of other regioselective alkyne carbofunctionalization reactions.

P,N Ligand in Ni-Catalyzed Cross-Coupling Reactions: A Promising Tool for π-Functionalization

“…The arylnickel­(II) complex undergoes syn -migratory insertion into alkyne, leading to the formation of a nucleophilic alkenyl-Ni­(II) intermediate. In this step, regioselectivity is often governed by the electronic environment and the directing effect of electrophiles . Due to the resonance-stabilized benzylic nickel intermediate, unsymmetric internal alkyl-arylacetylenes are preferred substrates, displaying excellent selectivity.…”