New Methods Of C-S Bond Formation From Aryl Thiols

Sulfur is one of the most important elements in nature. Sulfur-containing organiccompounds play important roles in the pharmaceuticals, agricultural chemicals andmaterials science. The C-S bond formation is one of the most exciting research topicsin organic chemistry and has been attracted sustained attention. The construction ofC-S bond under mild reaction conditions from cheap and readily avilable materials isbecoming focus of study. Many efficient methods for the C-S bond formation havebeen developed in the past decades. We investigated a variety of C-S bond formationreactions involving arylthiols, which can be reacted with aryl ketones,cyclohexanones and acetylenes. Detailed research was described as follows:1. A series of2-arylsulfanylphenols were synthesized by iodine-catalyzedtransformation based on C-S bond formation from benzenethiols and cyclohexanones.The C-S bond formation, dehydrogenation and tautomerization were realized inone-pot without any metal-catalyst and cyclohexanones were used as phenol source.Catalytic amount of iodine was used as catalyst and molecule oxygen was used ashydrogen acceptor in this transformation. This method can afford an efficient andenvironmentally benign approach for2-arylsulfanylphenols from readily availablematerials. In addition,2-arylsulfanylphenols were also could be prepared frombenzenesulfonohydrazides and cyclohexanones using stoichiometric amounts ofiodine as additive under similar conditions in good yields.2. The construction of C-S bond reaction for phenothiazine formation wasreported from cyclohexanones and2-aminobenzenethiols. Cyclohexanones were usedas aryl source by condensation, tautomerization, cyclization and dehydrogenationtransformation. The combination use of catalytic amount of benzyl phenyl sulfone andKI significantly improved the reaction yields using molecular oxygen as hydrogenacceptor in the absence of transition-metals. It will provide a novel, convenient andenvironmentally benign method for the synthesis of phenothiazines.3. A facile synthesis of2-aryl benzothiazoles via C-S bond formation reactionusing molecular oxygen as oxidant under metal-free conditions have beensuccessfully developed. DMSO played an important role in this transformation.Functional groups such as methyl, methoxy, fluoro, chloro, bromo and nitro were allwell tolerated under the optimized reaction conditions. Since aryl ketones are cheap,readily available starting materials, this method afforded an efficient alternative route for the rapid synthesis of2-aryl benzothiazoles.4. An efficient anti-Markovnikov hydrothiolation from acetylenes and arylthiolsunder transition-metal-free conditions is described. The choice of base and solventsignificantly affected the reaction selectivity. When potassium phosphate was used asbase in NMP, the Z-vinyl sulfides were formed in good yields and high regio-andstereoselectivity. Whereas E-vinyl sulfides were the major products when the reactionwas carried out in neat without any additive in good yields.