Cu-Catalyzed Three-Component Synthesis of 1,3-Benzoselena- and -tellurazoles

Significance

Reported is an efficient method for the synthesis of 2-heteroatom-substituted 1,3-benzoselenazoles via copper catalysis starting from 2-halo phenylisocyanides. The yields of products vary widely but are generally very good. The substitution on the aryl ring was not studied, perhaps owing to the unavailability of arylisocyanides but a variety of different amines were tested. Phenyl bromo and iodo isocyanates can both be used but in one case (n-BuNH₂ as nucleophile), for the bromo isocyanate, no conversion was observed; using the iodo variant, a 71% yield of product was obtained. A mechanism for the reaction was suggested on the basis of a selenourea isolated, when conducting the reactions in the absence of CuI. CuI is suggested to stabilize an intermediate complex and to facilitate the elimination of the halogen through oxidative addition. Modification of the conditions was required for the synthesis of benzotellurazoles.