Visible‐Light‐Induced Vicinal Dichlorination of Alkenes through LMCT Excitation of CuCl₂

Abstract

This work demonstrates photoredox vicinal dichlorination of alkenes, based on the homolysis of CuCl2 in response to irradiation with visible light. This catalysis proceeds via a ligand to metal charge transfer process and provides an exciting opportunity for the synthesis of 1,2‐dichloride compounds using an inexpensive, low‐molecular‐weight chlorine source. This new process exhibits a wide substrate scope, excellent functional group tolerance, extraordinarily mild conditions and does not require external ligands. Mechanistic studies show that the ready formation of chlorine atom radicals is responsible for the facile formation of C−Cl bonds in this synthetic process.

A cross-dehydrogenative C(sp3)−H heteroarylation via photo-induced catalytic chlorine radical generation

“…However, the C-O cleavage was still inevitable with tetrahydrofuran (THF) and methanol (19)(20)(21)(22), possibly due to the relatively high ring strain and oxidation potential of the alcoholic oxygen atom. Reactions with tetrahydropyran (THP) and its analogues proceeded smoothly and gave good yields of the products 23-26. α-C(sp 3 )-H functionalisation of amine derivatives, for example, amides, sulfonamide and phosphoramide, were all successful (27)(28)(29)(30)(31)(32)(33). Interestingly, the HAT of the N-methyl group of N,N-dimethylformamide (DMF) is more favourable than the formyl one and the alkylated heteroarene 29 was obtained as the major product.…”

“…Nevertheless, the unfavourable chloride-to-chlorine oxidation (E = 1.36 V vs NHE) 23 and untamed reactivity of Cl• compared with other halide analogues 17,18,[24][25][26] make chlorine radical-promoted alkylation rarely explored. In this endeavour, few strategies have been disclosed for the efficient usage of Cl•, including (a) the direct singleelectron transfer (SET) from Cl − to photocatalyst under photothermal conditions [27][28][29][30] ; (b) the ligand-to-metal charge transfer (LMCT), which has been employed for the coupling of alkanes and organohalides by metallophotoredox catalysis [31][32][33][34][35][36] ; (c) the photolysis of in situ generated Cl 2 via electrooxidation of HCl 37 ; (d) the bimolecular homolytic substitution (S H 2) between chloroborate and an oxy radical for the alkane borylation 38 . These pioneering examples demonstrate the potential of Cl − to realise the HAT process via Cl• intermediate (Fig.…”

Light‐Induced Vicinal Dichlorination of Alkenes Using FeCl3 as the Dichlorination Reagent

“…Noticeably, (2‐chloroethene‐1,1‐diyl)dibenzene 3 a (38 % yield) could also be detected when 1,1‐diphenylethylene was added into the standard reaction system (Scheme 2c and Figure S3). The above results suggested the possible formation of a chlorine radical [10,13a,17] or the occurrence of Cl‐atom transfer between substrate/trapping agent and excited FeCl 3 [11c,e,18] . This again proved that the proton or excess C−H bonds of methylene in solvents or substrates can capture free radical intermediates and resulted in low selectivity and yield.…”

“…Nevertheless, the application of photoexcited LMCT in the dichlorination of alkenes is still relatively limited. In 2020, Wan and co‐workers successfully enhanced the photocatalytic activity for dichlorination of alkenes with CuCl 2 as dichlorination reagent (Scheme 1a) via LMCT mechanism [10] . However, the unsafe additive HCl was also needed.…”

Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

“…80,81 Our working hypothesis is inspired by recent reports demonstrating the generation of alkoxy radicals via photoinduced LMCT excitation of Ce(IV)-OR complexes. [66][67][68][69][70][82][83][84][85][86][87][88][89] As shown in Scheme 2, anodically generated Ce(IV) could coordinate with MeOH to afford transient Ce(IV)-OMe, which can undergo homolysis via photoinduced LMCT to give transient MeO•. Governed by the polarity-matching effect, HAT to electrophilic MeO• from the more hydridic Si-H in preference to a C-H bond allows the selective generation of silyl radicals.…”