Spirocyclizative Remote Arylcarboxylation of Nonactivated Arenes with CO ₂ via Visible-Light-Induced Reductive Dearomatization

Abstract

Visible-light-induced reductive dearomatization of non-activated arenes is a very challenging transformation and remains in its infancy. Herein, we report a novel strategy to achieve a visible-light-induced spirocyclizative remote arylcarboxylation of non-activated arenes including naphthalenyl-and phenyl-bearing aromatics with CO 2 under mild conditions through a radical-polar crossover cascade (RPCC). This reductive dearomatization protocol rapidly delivers a broad range of spirocyclic and valuable carboxylic acid derivatives from readily accessible aromatic precursors with generally good regioselectivity and chemoselectivity.

Visible‐Light‐Induced Arylcarboxylation of Enamides with CO2 and Aryl Iodides to Synthesize α‐Amino Acids

“…To start our investigation, enamide 1 a (Table 1) was employed as the substrate, [12] which reacted with phenyl iodide under 30 W blue LEDs using a commercially available photocatalyst (PC) Ir[(ppy) 2 (dtbbpy)]PF 6 in the presence of an atmospheric pressure of CO 2 at ambient temperature. After extensive investigation of the reaction conditions, the desired product 3 a , which was the methylated product of the carboxylic acid product from the arylcarboxylation reaction for the ease of isolation, was obtained in 74% yield by employing the 4‐CO 2 K‐HE reductant discovered by our group previously [11a] and K 2 CO 3 as the base in DMSO (entry 1). Of note, some minor hydroarylation side product was also observed without desired carboxylation and the remaining unreacted 1 a likely decomposed and could not be recovered.…”

“…Based on the above mechanistic studies, a mechanism was proposed using 1 a and 2 a as the representative substrate (Scheme 5). Upon blue light irradiation, the excited Ir PC* ( A ) is produced and then quenched reductively by 4‐COOK‐HE to afford PC .− ( B ) together with dihydropyridine radical ( C ) and the generation of CO 2 [11a] . Reduction of phenyl iodide 2 a by B produces phenyl radical D which undergoes addition to enamide 1 a , affording the radical intermediate E .…”

Visible-light induced dearomatization reactions

“…This photocatalytic protocol was illustrated effectively in the dearomative arylcarboxylation of nonactivated arenes employing a novel 4-potassium carboxylate Hantzsch ester (4-CO 2 K-HE) as the net reductant by the Li group in 2021, in which a broad range of spirocyclic and valuable carboxylic acid derivatives with good regioselectivity and chemoselectivity was delivered (Scheme 28). 64 In the absence of CO 2 , cyclohexadienes were afforded through spirocyclizative dearomative hydroarylation under similar reductive reaction conditions, as described by the Li group in 2021. 65 In contrast to intramolecular ones, dearomatization reactions based on intermolecular radical addition are still rare.…”

Visible-light-driven regioselective carbocarboxylation of 1,3-dienes with organic halides and CO2

“…16 c Therefore, the development of a novel regioselective carbocarboxylation of 1,3-dienes under mild conditions is highly desirable. 17,18 In line with our continuous efforts in the catalytic utilization of CO 2 for organic synthesis, 5 j ,19 we envisioned that carbocarboxylation of 1,3-dienes could be achieved by using readily available organic halides with CO 2 by harnessing light as the green strategy to promote the reaction.…”