Benzophenone vs. Copper/Benzophenone in Light‐Promoted Atom Transfer Radical Additions (ATRAs): Highly Effective Iodoperfluoroalkylation of Alkenes/Alkynes and Mechanistic Studies

Abstract

Iodoperfluooralkylation of terminal alkenesa nd alkynes is effectively photo-promoted by benzophenone 2 (BP) or the photoreducible copper(II) complex 1.I np articular,B Pa t1mol%i n methanol upon3 65 nm irradiationw ith al ow-pressure mercury lamp (type TLC = thin layer chromatography, 6W)r esults in af ast reaction with excellent reactiony ields.C omplex 1 and BP 2 exhibited very similarr eactivity,s uggestingt hat the reactions involving 1 are likely to be governed by the benzophenone photoactivation processes,r athert han copper(I)/(II) redox processes.M echanistic investigations using transient absorption spectroscopy revealed that ad eactivation pathway of the benzophenone triplet( 3 BP*) is via its reactionw ith the methanol solvent. We propose that the generated radicals, in particular CCH 2 OH, play ak ey role in the initiation step formingR f C by reactingw ith R f I, R f C then entering ar adical chain cycle. 1 HNMR studies provided evidence that as ubstantial amount (~7% NMR yield) of the hemiacetal CH 3 OCH 2 OH is formed, i.e., the possible by-product of the reaction between CCH 2 OH and R f I. Finally,D FT calculations indicatet hat at riplet-triplete nergy transfer (TTET) process from 3 BP* to perfluorooctyl iodide (C 8 F 17 I) is unlikely or should be rather slow under the reaction conditions,c onsistent with the transient absorption studies.

Pyrene-based metal–organic framework NU-1000 photocatalysed atom-transfer radical addition for iodoperfluoroalkylation and (Z)-selective perfluoroalkylation of olefins by visible-light irradiation

“…Interestingly, although the (E)geometries of ATRA products were still more favoured, the corresponding ratios of (Z)-/(E)-isomers were higher than most of the reported results in literatures. 20,[69][70][71] These phenomena gave a strong hint of triplet EnT induced enrichment of (Z)alkenes, and the (E)-to (Z)-conversion was conrmed by exposing (E)-isomer of 6b to the reaction condition (Scheme 5). The heavy-atom effect of iodo group of product 6b was believed to facilitate the conversion from (E)-to (Z)-geometry.…”

“…1 ( 5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heptadecauoro-3iodododecyl)benzene (3e). 20 This compound was synthesized according to the GP and isolated by column chromatography as sticky oil (150.9 mg, 89% yield) using petroleum ether/ethyl acetate (100 : 1 v/v) as the eluent system. 1 heptadecauorononyl)-4-(propan-2-ylidene)cyclohex-1-ene (4h 0 ).…”

“…(E/Z)- 5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-Heptadecauoro-3-iodododec-3-en-1-ol (6a). 20 The (E)-and (Z)-stereoisomer of 6a were synthesized according to the GP and puried by column chromatography as white solids (total 117.2 mg, 76% yield) using petroleum ether/ethyl acetate (10 : 1 v/v) as the eluent system. ((E)-isomer, 64.3 mg, 42%) 1 (Z)- (3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-Heptadecauorodec-1en-1-yl)benzene (7b).…”

Intermolecular Iodofluoroalkylation of Unactivated Alkynes and Alkenes Mediated by Manganese Catalysts

“…In particular, atom transfer radical addition (ATRA) reactions of fluoroalkyl halides to alkynes is an effective and atom‐economical methodology, in which new C−C and C−X bonds (X=I, Br) are simultaneously forged in a single operation, thus rapidly generating molecular complexity. In established ATRA reactions of fluoroalkyl halides to alkynes, fluoroalkyl radicals are usually generated by use of radical initiators, such as AIBN, Na 2 S 2 O 4 /NaHCO 3 , Et 3 B/O 2 , SmI 2 , or by use of UV light irradiation . However, these protocols also revealed some drawbacks such as narrow substrate scope, poor selectivity, and harsh reaction conditions.…”

Photo‐Induced Chloride Atom Transfer Radical Addition and Aminocarbonylation Reactions

“…[9] Vicent group researched a ATRA protocol to add perfluoroalkyl iodides to linear alkenes and alkynes catalyzed by copper/benzophenone under the irradiation of UV light. [10] In the ATRA reactions with involved photocatalysts, active organic bromides and iodides are significantly employed as substrates to afford atom transfer adducts and the use of organic chlorides are quite rare, because the chemically inert CÀ Cl bonds are much more difficult to break than CÀ Br bonds and CÀ I bonds. [11] But for synthetic photochemistry towards a CÀ C coupling reaction, the ubiquitious aryl chlorides have been identified as the qualified candidate to release aryl radicals by direct light excitation accompanying the formation of chlorine radicals.…”