Substrate Expansion of Aryl Iodides
Under optimal conditions, the authors explored the substrate range of organic iodides. Overall, a variety of aryl iodides with electron-donating or electron-absorbing substituents were able to carry out the reaction without difficulty, yielding a range of corresponding products in high yields (81-99%) (Fig. 4 top). For comparison, the reaction can also be carried out at room temperature, albeit in slightly reduced yield (4aa-4ad). The cross-coupling reaction exhibits good functional group
compatibility, with a wide range of functional groups including methoxy, tert-butyl, phenyl, fluorine atoms, chlorine atoms, trifluoromethyl, trifluoromethoxy, aldehydes, ketones, esters, and cyano groups being tolerated (4aa-4aq). The o-methoxy/phenyl and m-trifluoromethoxy substituted aryl iodides (4ao-4aq) were also converted smoothly. These results indicate that the large variations in electronic properties and site resistance factors do not affect the efficiency of the reaction. The method is also applicable to aryl iodides containing cyclopropane or silyl substituents in yields of 95-99% after purification by simple column chromatography. In particular, the reaction was
characterized by excellent chemoselectivity when using halogenimetic substituents (OAc, OTf, 3ag-3ah), thus allowing subsequent functional group transformations. However, when the substrate 1-iodo-4-nitrobenzene (3ai) was cross-coupled, the reaction did not yield the target product, possibly due to the incompatibility of the nitro group with the reductive coupling conditions. Notably, many heteroaryl iodides are well tolerated in this cross-coupling system and can provide the various target thioether products in moderate to excellent yields. Heteroaromatics of different structures including carbazole, benzofuran, indole, quinoline, thiophene, pyrazole, and pyridine (4ar-4ba) indicate that this reductive coupling reaction has good compatibility with different heteroaromatics.
（Substrate range of (hetero)aryl halides
（Substrate expansion of (hetero)aryl bromides/chlorides
Furthermore, this interesting nickel-catalyzed reductive coupling strategy can be applied to various aryl/heteroaryl bromides (in Figure 4), showing good reactivity and compatibility with electron-donating or electron-withdrawing substituents such as methoxy (4bb), fluoro (4bg), trifluoromethyl (4bc), acetyl (4bd), ketocarbonyl (4bh), esteryl (4be), and cyano (4bf). In addition, this strategy developed by the authors is also well tolerated to bromides of heteroaromatic hydrocarbons such as benzofuran (4bi), indole (4bj), benzothiophene (4bk), quinoline (4bl), pyrazine (4bm), pyridine (4bn) and pyrimidine (4bo). Notably, 4bp was also obtained in 28% yield for the relatively less active 2-chloropyrimidine substrate.However, the more challenging common aryl chloride substrate (4bq-4br), failed to achieve the desired cross-coupling reaction with the current reaction system.
