Department of Applied Chemistry, College of Materials and Energy, South China Agricultural University, Guangzhou 510642, China.
Org Biomol Chem. 2019 Feb 20;17(8):2279-2286. doi: 10.1039/c8ob03191f.
Dialkyl azo compounds were found to be effective alkyl radical sources for direct alkyl sulfuration with imidazopyridines using elemental sulfur under metal-free conditions. Iodine, an inexpensive and mild reagent, could promote alkyl sulfuration. A variety of quaternary cyanoalkyl radicals were successfully coupled with elemental sulfur. A subsequent C-H sulfuration of imidazopyridines afforded a diverse array of imidazopyridine derivatives bearing cyanoalkylthio groups. The cyano group could be modified and further underwent condensation with 2-aminothiazole to afford an interesting heterocyclic amide. Control experiments showed that iodine could greatly suppress the self-coupling of cyanoalkyl radicals, thus making the sulfuration proceed smoothly.
二烷基偶氮化合物被发现是在无金属条件下，使用元素硫将咪唑并吡啶直接烷基化磺化的有效烷基自由基源。碘是一种廉价且温和的试剂，能够促进烷基磺化反应。各种季碳氰烷基自由基与元素硫成功偶联。随后，咪唑并吡啶的 C-H 磺化反应得到了一系列含有氰烷基硫基团的咪唑并吡啶衍生物。氰基可以被修饰，并且进一步与 2-氨基噻唑缩合，得到有趣的杂环酰胺。控制实验表明，碘可以大大抑制氰烷基自由基的自身偶联，从而使磺化反应顺利进行。
