Recent Advances in Sulfur-Containing Heterocycle Formation via Direct C-H Sulfuration with Elemental Sulfur

The synthesis of sulfur heterocycles via the construction of C-S bonds has received considerable attention due to their biological value and extensive pharmaceutical application. While diverse sulfurating agents have been developed over the past few decades, in this regard, elemental sulfur, with advantages of low toxicity, odorless nature and chemical stability, has great potential for the construction of diverse sulfur heterocycles through its direct incorporation into the target molecules in a concise way. Direct functionalization of inert C-H bonds can shorten the number of reaction steps and minimize the amount of waste formed. Hence, heteroannulations via direct C-H sulfuration is considered to be an attractive strategy for the synthesis of sulfur heterocycles. In the last few years, a vast array of concise systems have been reported for the synthesis of some valuable sulfur heterocycles such as thiophenes, thienoindoles, thienothiazoles, thiazoles, benzothiazoles, and thiadiazoles through direct C-H sulfuration/annulations with elemental sulfur. These are discussed in detail in this review. Introduction Thiophenes Thienoindoles Thienothiazoles Other Fused Thiophenes Thiazoles Benzothiazoles Thiadiazoles Others Summary and Outlook