The origin of regioselectivity in Cu-catalyzed hydrocarbonylative coupling of alkynes with alkyl halides
In recent years, the versatile reactivity of Cu-catalyzed hydrocarbonylative coupling of alkynes with alkyl halides has drawn a wide range of attention. In this paper, we explored in detail the origin of different regioselectivity for terminal/internal alkynes coupling with primary, secondary and tertiary alkyl halides by using density functional theory (DFT) calculation. The present results reveal that the dominant factor of high Cα-regioselectivity in alkyne insertion is mainly the electron effect for terminal alkyne, in which the higher electron density of terminal carbon making electrophilic attack more favorable. For internal alkyne, such as 1-phenyl-1-hexyne, d orbital in Cu which is able to conjugated with HOMO of the benzene ring plays a dominate role in Cα-selective formation of alkenylcopper. Moreover, we also confirmed that enones was formed by C-C concerted coupling of alkenylcopper with acyl bromide instead of the oxidation addition suggested in the literature. Notably, the origin of regioselectivity of 1,2-reduction over 1,4-reduction is mainly the steric effect, whether for the terminal alkyne or the internal alkyne case.