Mechanistic Features of Allylic Hydrogen Abstraction by Alkoxy Radicals

Article abstract of DOI:10.1021/jo00144a024

A TS(excit) of angular H abstraction from allylbenzene in the course of the allylic acetoxylation reaction was previously invoked to explain a temperature-independent primary KIE; k_H/k_D = 2.90.This reaction geometry is now fully supported by the finding of inverse α-secondary deuterium isotope effects at both ends of the double bond in allylbenzene; (k_H/k_D)_α^C1 = 0.977 and (k_H/k_D)_α^C2 = 0.985.In keeping with these results an unsymmetrically structured, bridged radical intermediate, formed by the interaction of t-BuO with the allylic double bond, steers the reaction course.Such a complex is recognized to be unusual since most of the verified cases of radical bridging involve heteroatom centers capable of octet expansion.A discussion is also given of the factors determining the relative influence of benzene and double bond participation in the H-abstraction reactions of allylbenzene, which possesses both of these activating functions.