Abstract
An oxidation system comprising phenyliodine(III) diacetate (PIDA) and iodosobenzene with inorganic bromide, i.e., sodium bromide, in an organic solvent led to the direct introduction of carboxylic acids into benzylic C–H bonds under mild conditions. The unique radical species, generated by the homolytic cleavage of the labile I(III)–Br bond of the in situ-formed bromo-λ3-iodane, initiated benzylic carboxylation with a high degree of selectivity for the secondary benzylic position.
Highlights
The oxidative activation of a C(sp3)–H bond in organic molecules to directly install various functional groups and new carbon–carbon networks is a topic of interest for researchers engaged in modern synthetic chemistry [1,2,3,4,5,6,7,8]
Based on our previous research and general interest in the unique reactivity of hypervalent iodine(III)–Br bonds [53,54,55,56], we report the results of our extensive study and optimization of our radical C–H activation strategy for the intermolecular oxidative coupling between the benzylic secondary C–H bond and the O–H group of carboxylic acids (Scheme 1)
Significant advances for realizing such transformations have been made over the last decade, strategies that do not utilize a directing group to facilitate the activation of the benzylic C(sp3)–H bond are rare [21,57,58,59,60,61,62]
Summary
The oxidative activation of a C(sp3)–H bond in organic molecules to directly install various functional groups and new carbon–carbon networks is a topic of interest for researchers engaged in modern synthetic chemistry [1,2,3,4,5,6,7,8]. A radical C–H activation strategy, using nonaqueous hypervalent iodine(III)/inorganic bromide systems that can work in organic solvents, was developed for the novel synthesis of lactones via the intramolecular oxidative cyclization of aryl carboxylic acids at the benzyl carbon under transition-metal-free conditions [52].
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