MICROWAVE ASSISTED ONEPOT SYNTHESIS AND CHARACTERIZATION OF BENZOXAZOLE CONTAINING MULTI SUBSTITUTED 1,2,3-TRIAZOLES

Abstract

Developing a new method for the synthesis of highly functionalized 1,2,3-triazoles encouraged us to test the three-component reactions between 2-(benzo[d]oxazol-2-ylsulfonyl)-1- phenylethanone (14), benzyl bromide and sodium azide with the base under microwave condition. Herein, we would like to describe an efficient method for obtaining 1,4,5-trisubstituted-1,2,3-triazoles (Scheme 1). Our initial investigation was started with one pot [3+2] cycloaddition reaction of benzyl bromide, sodium azide and 2-(benzo[d]oxazol-2-ylsulfonyl)-1-phenylethanone (14) by following the previously reported literature condition24. However, the reaction did not proceed and the desired product 16a was not obtained (Table 1, entry 1). The same reaction was carried out above 80 oC temperature condition by using triethylamine (5 and 10 mol %) (15a) as catalyst the products were obtained in low yield (Table 1, entry 2). Our investigation of 15b, 15c, 15d, 15e and 15f as the catalysts showed that 15d (5 mol %) was optimal (Table 1, entries 3- 7). When the same reaction was carried out under microwave irradiation resulted in the generation of the desired product 16a in an excellent yield (Table 1, entry 8). It was also found that the loadings of catalyst could be increased to 10 mol% almost without affecting the yield of the desired products (Table 1, entry 9). Thus, the combination of 5 mol% of 15d in the presence of DMSO under microwave irradiation was the optimal reaction conditions. The compounds were further confirmed by spectral analysis data