Direct C−H Radical Alkylation of 1,4‐Quinones

Abstract

1,4-Quinones display unique redox and biological properties and have multiple applications in a wide array of fields, including health. Synthesis of diversely substituted quinonebased compounds remains difficult and usually consists of multiple step sequences. Interest in direct CÀ H radical alkylation of 1,4-quinones has thus continuously grown over this last decade. These reactions involve addition of carbon-centered radicals generated from radical precursors through decarbox-ylative alkylation, hydrogen-atom abstraction, or by carbonhalogen bond reduction. Recent progresses in radical chemistry, including photoredox catalysis, have provided useful tools for quinone functionalization. This Minireview describes the recent progress with these methodologies, including the new promising three-component cascade reactions involving quinones and alkenes, allowing for the preparation of complex substituted 1,4-quinones in a single step.

Formal Glycosylation of Quinones with exo-Glycals Enabled by Iron-Mediated Oxidative Radical–Polar Crossover

“…Studies have been motivated by the widespread biological activity of these compounds and their interest as dye molecules , but also by the synthetic challenges associated with the unique electrochemical properties of the 1,4-quinone scaffold. However, despite the recent progress in the field, many of the methods reported so far suffer from limited substrate scope, regioselectivity issues, and/or harsh reaction conditions . In 2019, the group of Liu reported a Fe­(III)-mediated C–H radical alkylation of 1,4-quinones using an excess of simple olefins and NaBH 4 as the hydride source enabling the generation of a putative Fe–H complex for the HAT process (Scheme a).…”

“…With the objective of developing a convergent, step-economical access to the benzoxocin core found in C , O -fused glycosyl arenes such as serjanione A or nogalamycin, we envisioned the direct incorporation of phenol groups via the addition of MHAT-generated pseudoanomeric radicals onto 1,4-quinones. The development of efficient methods for the radical alkylation of 1,4-quinones has been a very active area in the past several years . Studies have been motivated by the widespread biological activity of these compounds and their interest as dye molecules , but also by the synthetic challenges associated with the unique electrochemical properties of the 1,4-quinone scaffold.…”

“…The development of efficient methods for the radical alkylation of 1,4-quinones has been a very active area in the past several years. 22 Studies have been motivated by the widespread biological activity of these compounds and their interest as dye molecules 23,24 but also by the synthetic challenges associated with the unique electrochemical properties of the 1,4-quinone scaffold. However, despite the recent progress in the field, many of the methods reported so far suffer from limited substrate scope, regioselectivity issues, and/ or harsh reaction conditions.…”

Organophotoredox-catalyzed cyanoalkylation of 1,4-quinones

“…Based on the above control experiments and precedented literature, 9,12 a plausible mechanism for this visible-light promoted metal- and oxidant-free cyanoalkylation of 1,4-quinones is proposed (Scheme 4). A single electron reduction of the cyclobutanone oxime ester 2 by the excited photocatalyst (RB*) generates the iminyl radical A .…”

Quinone-based conjugated polymer cathodes synthesized via direct arylation for high performance Li-organic batteries

“…Direct arylation polymerization (DAP) involves the C-C formation from the cross-coupling reaction between aromatic halides and aromatics with active C-H bonds, which provides a relatively facile and low-cost synthetic method for the preparation of conjugated polymers. 16,17 In the field of rechargeable batteries, DAP was mainly employed to synthesize conductive polymer binders for LIBs. [18][19][20][21][22] Recently, Byon and coworkers used DAP to synthesize a pyridinium-based negolyte for redox flow batteries.…”