Synthesis Of Sulfur Compounds Based On Sp ~ 2C-H Functionalization

Seeking mild and efficient methods for the synthesis of sulfur-containing compounds is of fundamental and immense importance in organic chemistry, because sulfur-containing framworks widely exist in natural products, biological molecules and organic materials and they are also found in numerous clinically important drugs, such as clopidogrel, zileuton, arzoxifene, raloxifene, seroquel, riluzole and actos ect.The conventional methods for the synthesis of these sulfur-containing compounds are always limited by the uneasily available precursors or the harsh reactions. As a consequence, seeking mild and selective approaches for the construction of sulfur-containing compounds is still a high ongoing interest.Over the past few decades, direct thiolation of sp~2C-H bonds has emerged as an efficient and highly selective method for constructing of sulfur-containing compounds. However, in the field of C-S bond formation by sp~2C-H functionalization reactions, more wide and success approachs need the participate of Pd, Rh, Ru and other heavy metal catalysts. Although these methods have some advantages, but there are also some significant drawbacks, for example: the presence of trace metal residues of drugs harm to human health; heavy metal catalysts are generally expensive, toxic; the use of ligands also make the reaction system more complicated.Recently, there are increasing demands in metal-free or low-cost and low toxicity Cu/Fe transformations owing to that trace-metal impurities might be avoided in the target molecules. We herein carried out a number of new explorations of sp~2C-H bond activation reaction to extend new synthetic methods of sulfur-containing compounds.This dissertation is made up of four chapters:(1) Metal-free iodine-catalyzed direct sp~2C-H arylthiation of commercially available anilines or anisole compounds with thiols efficiently approach to diaryl sulfides. This method has advantages of environmental friendly, low cost and high yields, thus it has good application prospects.(2) Intermolecular cyclization of alkynes and aromatic disulfides/thiols leading to benzothiophenes under metal-free conditions. This method takes inexpensive and easy available TEAB or I2 as catalyst, K2S2O8 or DTBP as the oxidant, and provides a simple, green and efficient synthetic method for the synthesis of benzothiophenes.(3) Catalyst-free regioselective C?3 thiocyanation of imidazopyridines takes K2S2O8 as the oxidant under room temperature. The reaction without participation of metal catalysts and has high atom economy.(4) Copper-catalyzed synthesis of benzo[b]thiophene/imidazo[1,2-a]pyridines or benzo[d]imidazo[5,1-b]thiazoles under mild conditions. This method via intramolecular oxidative addition, reductive elimination efficiently and build a class of sulfur-containing heterocycles.We herein offer several approachs for the synthesis of useful diverse sulfur-containing compounds. Almost all of the corresponding target products were obtained in moderate to good yields. These experiments of synthesis of sulfur-containing compounds compared with traditional method, possesses the advantages of efficient, practical, economic and green, will cause the widespread attention in the field of organic chemistry and pharmaceutical chemistry.