Professor Wu Jie's research group of Fudan University realized the visible light catalyzed synthesis of alkylsulfonyl compounds by the three-component reaction of alkyltrifluorobotassium, sulfur dioxide and alkene

DABCO (SO 2) 2 and sulfite have been widely used in the synthesis of sulfonyl compounds as substitutes for sulfur dioxide DABCO · (SO 2) 2 can react with aryldiazo tetrafluoroborate under mild conditions to produce arylsulfonyl radicals, and then synthesize a variety of sulfonyl compounds However, due to the instability of alkyl diazo tetrafluoroborate, the application of this method is limited Therefore, the development of alkylsulfonyl radicals involved in organic reactions has a certain challenge Recently, Professor Wu Jie's research group of Fudan University reported for the first time a method (scheme 1) for the synthesis of alkylsulfonyl compounds by the three-component reaction of potassium alkyltrifluorobborate, DABCO · (SO 2) 2 and olefins The reaction conditions of this method are mild, and the insertion reaction of sulfur dioxide can be realized at room temperature and visible light Alkyl radical and alkylsulfonyl radical are the key intermediates of the reaction Relevant research results were published in org Lett (DOI: 10.1021/acs.orglett.8b01385) (source: org Lett.) firstly, the reaction conditions were screened by using 4-vinylpyridine (1a), cyclopentyltrifluoroaborate (2a), DABCO · (SO2) 2 as substrates (Table 1) It is found that the target molecule 3A can be obtained in 92% yield by using 5 mol% MES ACR + as photocatalyst and blue LED as light source in the reaction of dichloroethane at room temperature for 24 hours The use of iridium as photocatalyst or the reaction in dark can not promote the reaction (source: org Lett.) next, the author investigated the substrate applicability of the reaction (scheme2) Potassium trifluoroaborate substituted by cyclohexyl, tert butyl, n-butyl and allyl can react with 4-vinylpyridine and DABCO · (SO 2) 2, and the corresponding target product can be obtained in excellent yield Then, the reactions of different olefins were studied Under the standard conditions, sensitive sensory energy groups such as halogen, hydroxyl, ester, ketone carbonyl and nitro can be compatible with the reaction conditions In addition, a gram scale preparation of compound 3K was realized (source: Org Lett.) then, the author further expanded the scope of application of this method Compound 4 with complex structure can react smoothly with cyclopentyl potassium trifluoroaborate (2a) and DABCO · (SO2) 2, and target molecule 5 can be obtained in 51% yield The experimental results further prove the universality of the reaction (scheme 3) (source: org Lett.) later, the author studied the reaction mechanism (scheme4) The formation of the target product was inhibited by the addition of tempo in the reaction system The adduct of tempo cyclopentane can be detected by gas chromatography, which proves the existence of alkyl radical intermediate in the system It was found that (E) - 1-phenyl-3-p-toluenylinone 1K and sodium cyclopentane sulfonate 7 can only obtain compound 3K in 6% yield under blue LED irradiation and in the presence of MES ACR +, and the reaction can not be carried out without light or photocatalyst It is proved that the key intermediate of the reaction may be sulfonyl radical rather than corresponding sulfonate (source: org Lett.) based on the above results, the author proposed the possible mechanism of the reaction (scheme5): under the visible light irradiation, the photocatalyst MES ACR reached the excited state of mes-acr + *; the species can oxidize the potassium alkyltrifluoborate 2 to the alkyl radical, at the same time, it can be reduced to the MES ACR by itself; after the combination of the alkyl radical and sulfur dioxide with alkene 1 Free radical intermediate B was produced; B was further reduced by MES ACR to anion intermediate C; finally C protonated to target product 3 (source: org Lett.) conclusion: Professor Wu Jie's research group of Fudan University reported for the first time the method of synthesizing alkylsulfonyl compounds by photocatalysis of three-component reaction of potassium alkyltrifluoborate, DABCO · (SO 2) 2 and alkene The method has mild conditions, and the insertion of sulfur dioxide can be realized at room temperature and visible light Alkyl radical and sulfonyl radical are the key intermediates of the reaction.