Photoredox/Copper Dual-Catalyzed Benzylic C–H Esterification via Radical-Polar Crossover

Abstract

Herein, we report a distinctive photoredox/copper dual-catalyzed esterification of benzylic C–H bonds through the combination of photoredox-mediated hydrogen atom transfer and Cu­(II)-mediated radical-polar crossover. This methodology demonstrates a high functional group tolerance (>40 examples) and moderate to good yields with structurally diverse benzylic C–H substrates. Notably, stoichiometric amounts of carboxylic acids are used as coupling partners, which allows the synthesis of structurally diverse benzylic esters and the late-stage functionalization of pharmaceuticals.

Oxidative Trifluoroacetoxylation of 1°, 2°, and 3° Benzylic C(sp3)–H Bond Donors Using N-Trifluoroacetoxyquinuclidinium Salts under Photoredox Catalysis

“…Remarkably, in a number of cases benzylic trifluoroacetates were the only efficient benzylic electrophiles while analogous and more common benzylic derivatives such as halides, mesylates, tosylates, benzoates, or acetates failed. , Typically, synthetic access to various types of benzylic trifluoroacetates is limited to the acylation of the corresponding benzylic alcohols . The oxidative esterification of C–H bond donors has emerged as an efficient alternative method for the preparation of arene- and alkanecarboxylic acid-derived benzylic esters. , Still, there are only a few reports of efficient oxidative benzylic C–H trifluoroacetoxylation. In one report, PhI­(O 2 CCF 3 ) 2 serves as a trifluoroacetoxylation reagent under photochemical (400 nm) conditions (Scheme a) .…”

Direct benzylic C–H difluoroalkylation with difluoroenoxysilanes by transition metal-free photoredox catalysis

“…11 Among multiple accesses to carbocations from C(sp 3 )–H bonds, 12 the combined principle of hydrogen atom transfer (HAT) with oxidative radical-polar crossover (ORPC) promoted by visible light photoredox catalysis offers a mild and versatile approach. 8 b ,13 Based on our interest in difluoroalkylation 7 b ,14 and C–H functionalization, 15 we herein report a direct benzylic C–H difluoroalkylation with difluoroenoxysilanes by photoredox catalysis via a HAT-ORPC pathway (Scheme 1c). In comparison with transition metal photocatalysts, commonly used in the late-stage difluoroalkylation of organic substrates, 16 transition metal-free photocatalysts are typically low cost, of low toxicity, and easily handled, which show great advantages in environmental friendliness, combined with the green oxidant of air 17 and mild reaction conditions.…”

Coordination in functional traits of Populus euphratica leaves under salt stress

“…P. euphratica is a tree species with an extremely strong adaption to growth under an adverse environment where it can persist for decades and centuries (Si et al, 2014). Increases in soil salinization could further inhibit tree growth and increase the risk of plant mortality; however, plants change their functional traits to adapt to the environment (Zhang C. et al, 2022).…”

“…Leaf functional traits are key to the understanding of tree internal coordination and adaptation mechanisms to the environment; thus, coordination of leaf functional traits plays a critical role in realizing the physiological, ecological, and survival strategies of plants (Derroire et al, 2018;Zhang C. et al, 2022). Recent studies on tree response processes in the environment highlight the importance of hydraulic functional integrity for tree survival and that hydraulic failure can lead to tree mortality across multiple tree taxa (Adams et al, 2017;Powers et al, 2020).…”