Synthesis 2-Substituted Benzazoles By Catalytic Aeroic Oxidative Cyclization

Benzoazoles and their derivatives as very important structural motifs in hetero-cyclic compounds, are commonly encountered groups in natural products, pharma-ceuticals, agrochemicals, and other effect chemicals, and new methods for their preparation are in still demand.In this paper, a series of simple and efficient method for TEMPO-based catalytic aerobic oxidative cyclizing synthesis of 2-substituted benzazoles compounds using chemical stable activated aryl primary alcohols bearing carbon-carbon double bond or O or N or S heteroatoms, and o-arylamines as raw materials via stepwise one-pot reaction were developed.Initial experiment showed that nontoxic, inexpensive and readily available TEMPO/Fe(NO3)3 catalyst system can efficiently and rapidly catalyze aerobic oxidation of activated aryl primary alcohols to aryl aldehydes in acetonitrile by pure O2 at elevated temperature, then 2-substituted benzimidazoles wer obtained in high yields followed by oxidative cyclized with o-phenylenediamines. Additionly, o-aminothiophenol not o-aminophenol also efficiently underwent the reaction, affording the corresponding 2-arylbenzothiazoles.Moreover, TEMPO/copper salts catalyst systems were investigated to catalytic oxidative synthesis of 2-substituted benzazoles compounds. The effects of various conditions (such as copper salts compounds, solvents, the amounts of the catalyst, and temperature) on the oxidative cyclization were studied. Under optimized condition, similarily, TEMPO/CuCl2 could also rapidly catalyze activated aryl primary alcohols to aryl aldehydes by molecular oxygen at elevated temperature, then 2-aryl-benzoxazoles,2-arylbenzimidazoles and 2-arylbenzimidazoles were obtained in high yields, followed by oxidative cyclized with oaminophenol, o-phenylenediamines and o-aminothiophenol using stepwise one-pot reaction, respectively. In conclusion, those newly developed procedures for 2-substituted benzazoles exhibited many advantages; green, economy, high yield, relatively mild reaction conditions and easily industrial production.