Esterification of the Primary Benzylic C–H Bonds with Carboxylic Acids Catalyzed by Ionic Iron(III) Complexes Containing an Imidazolinium Cation

Abstract

The first iron-catalyzed esterification of the primary benzylic C-H bonds with carboxylic acids using di-tert-butyl peroxide as an oxidant is achieved by novel ionic iron(III) complexes containing an imidazolinium cation. The use of well-defined, air-stable, and available iron(III) complex in a 5 mol % loading and readily available starting materials with a broad generality and outstanding sterically hindered tolerance renders this methodology a useful alternative to other protocols that are typically employed for the synthesis of benzyl esters.

Recent progress in catalytic acyloxylation of C(sp3)‐H bonds

“…Sun with coworkers reported the iron(III) catalyzed esterification of primary benzylic C(sp 3 )‐H bonds with carboxylic acids. [ 102 ] With DTBP as oxidant, iron(III) complex with imidazolium derived countercation mediated coupling of a number of benzylic hydrocarbons with aromatic or aliphatic carboxylic acids of the type 159 , in up to 99 % yields (Scheme 25). The authors postulated that the mechanism of this iron‐catalyzed acyloxylation might involve radical species.…”

Recent Advances in the Synthesis of Carboxylic Acid Esters

“…under O 2 (1 atm) afforded the corresponding esters via benzylic C-H bond activation (Scheme 10) [118]. Other interesting examples of this approach have been extensively studied [119][120][121][122][123][124][125].…”

Chemo- and regioselective benzylic C(sp3)–H oxidation bridging the gap between hetero- and homogeneous copper catalysis

“…The chemo- and regioselective transformation in a pool of vulnerable C‒H bonds in nondirected fashion through the judicious choice of the catalytic system is a prime research area ( Khake and Chatani, 2020 ; Lerchen et al., 2018 ). In the past, copper ( Rout et al., 2012 ), iron ( Lu et al., 2017 ), palladium-catalyzed ( Ju et al., 2013 ), or metal-free ( Feng et al., 2012 ) intermolecular acetoxylation of benzylic C‒H bonds have been reported where the reaction proceeds through the formation of a putative metal-carboxylate or acyloxy radical species. The Stahl group and others reported copper-catalyzed intermolecular benzylic C‒H functionalization for the synthesis of pharmacophores from feedstock chemicals ( Chi et al., 2019 ; Hu et al., 2020a ; Liu et al., 2020 ; Vasilopoulos et al., 2017 ; Wang et al., 2019 ).…”