K₂S₂O₈-Mediated Selective Trifluoromethylacylation and Trifluoromethylarylation of Alkenes under Transition-Metal-Free Conditions: Synthetic Scope and Mechanistic Studies

Abstract

A practical and efficient method for selective intramolecular radical trifluoromethylacylation and -arylation of alkenes with inexpensive CF3SO2Na and K2S2O8 in aqueous media has been developed, respectively, affording the highly chemoselective synthesis of CF3-functionalized chroman-4-ones and chromanes in satisfactory yields. Control experiments and DFT calculations indicate that the CF3SO2Na/K2S2O8 system is capable of trifluoromethylating the substrate of alkenes without a transition metal catalyst and the oxidation of CF3SO2Na to ·CF3 by K2S2O8 is involved in the rate-determining step.

Visible‐Light‐Induced Difluoroacetylation of O‐(Allyloxy)Aryl‐Aldehydes: Access to Difluoroacetylated Chroman‐4‐ones

“…In 2018, Zhao group reported a silver‐catalyzed alkyl radical‐trigged cascade cyclization reaction to provide 1,5‐dicarbonyl‐containing chroman‐4‐ones (Scheme c) . Very recently, Tang group described a K 2 S 2 O 8 ‐mediated radical cascade reaction for the synthesis of CF 3 ‐containing chroman‐4‐ones from 2‐(allyloxy)arylaldehydes and CF 3 SO 2 Na (Scheme d) . Despite this progress, it is highly desired to develop milder and more efficient method for the synthesis of functionalized chroman‐4‐ones.…”

Radical Reactions for the Synthesis of 3‐Substituted Chroman‐4‐ones

“…Therefore, the development of efficient synthetic methods for the incorporation of F‐containing groups into the valuable scaffolds has drawn huge attention in the past decades . As mentioned above, Tang et al have realized the synthesis of CF 3 ‐functionalized chroman‐4‐ones 17 . Similarly, the difluoromethylene (CF 2 ) is also an attractive and unique function group.…”

“…Similarly, potassium persulfate (K 2 S 2 O 8 ) as an inexpensive and easily available inorganic oxidant has been widely used in oxidative transformations . In 2018, Tang and Chang's group reported a practical and efficient method for selective intramolecular radical trifluoromethylacylation of alkenes 16 with inexpensive CF 3 SO 2 Na and K 2 S 2 O 8 to synthesize CF 3 ‐functionalized chroman‐4‐ones 17 (Scheme ) . The generation of trifluoromethyl radical ( · CF 3 ) from CF 3 SO 2 Na by the oxidation of K 2 S 2 O 8 was involved in the rate‐determining step.…”

Metal-free synthesis of phosphinoylchroman-4-ones via a radical phosphinoylation–cyclization cascade mediated by K2S2O8

“…Besides, chroman-4-one derivatives were also constructed via intramolecular oxa-Michael additions of 2'-hydroxychalcones [9,10], or through condensation cyclization reactions of o-hydroxyacetophenones with ketones/aldehydes [11,12], in addition to other alternative transformations [13,14]. Moreover, radical cascade cyclizations of o-allyloxybenzaldehydes by employing appropriate radical precursors through visible-light promoted systems [15,16], transition-metal-catalyzed systems [17,18], or transition-metal-free systems [19,20], have emerged as a powerful strategy for the synthesis of diversely functionalized chroman-4-one derivatives.…”