Electrophilic Cyclization of N-Alkynyl-2-(organochalcogen)imidazoles: An Alternative Access to Imidazo[2,1-b]chalcogenazoles

We present here a practical synthesis of multifunctional imidazo[2,1-b]chalcogenazoles through electrophilic cyclization of N-alkynyl-2-(organochalcogen)imidazoles. The cyclization reaction proceeded cleanly and smoothly under mild reaction conditions in the presence of air. The methodology was highly regioselective: In a competition between the chalcogen and oxygen atoms, only S-, and Se-heterocycles were obtained. The resulting imidazo[2,1-b]chalcogenazoles proved to be versatile as precursors for the synthesis of more highly functionalized imidazoselenazoles through copper-catalyzed cross-coupling reactions with arene- and alkanethiols, leading to Ullmann-type products in good yields.