Transition metal-free photochemical C–F activation for the preparation of difluorinated-oxindole derivatives

Abstract

The development of strategies for single and selective C–F bond activation represents an important avenue to overcome limitations in the synthesis of valuable fluorine-containing compounds.

Visible-light-mediated C–F bond cleavage for the synthesis of polyfluorinated compounds

“…Based on experimental observation and literature precedents, 10 a ,14,15 we propose a tentative reaction mechanism depicted in Scheme 2. Initially, upon blue LED irradiation, the excited-state [Ir III ]* is quenched by DABCO ( E p OX = +0.69 V vs. SCE (standard calomel electrode) in MeCN) to give reduced [Ir II ] and the radical cation of DABCO.…”

“…10 a Although the selective cleavage of single C–F bonds in the trifluoromethyl (CF 3 ) group is progressing rapidly in the synthesis of difluoroalkyl compounds, the combination of C–F and C–F bond cleavage in visible-light-induced cross-coupling reactions remains elusive. 14 Herein, we developed visible-light-mediated C–F and C–F bond cleavage for the synthesis of polyfluorinated compounds (Scheme 1b).…”

Photocatalytic defluorocarboxylation using formate salts as both a reductant and a carbon dioxide source

“…DMSO, besides acting as a solvent, may also oxidize thiols to generate disulfide, which forms thiyl radicals under visible light conditions, thus facilitating the efficiency of the entire catalytic cycle. 20 Other alkali metal formates such as HCOOLi, HCOONa, and HCOOCs also promoted this transformation with comparable efficiency (Table 1, entry 11). Other bases, like KOH and NaOH or even common organic bases like Et 3 N and DMAP were also successful in performing the reactions, affording the desired products in moderate to good yields, except for the cases of pyridine and morpholine (Table 1, entries 12 and 13).…”

Recent Developments on Photochemical Synthesis of 1,n‐Dicarbonyls

“…Like the ability of bromodifluoroacetates to undergo radical formation, [82] fluorosulfonyldifluorocarbonyls can also be used as radical precursors for the synthesis of 1,4-dicarbonyl synthesis as reported by Xi and co-workers. Their methodology enables the generation of difluoro containing 1,4-dicarbonyls from styrenes 33 using fluorosulfonyldifluoroacetate 62 as an α-carbonyl difluoromethyl radical progenitor, and DMSO as a solvent cum oxidant (Scheme 46).…”