One-step construction of indolo[2,1-a]isoquinolines using solid calcium carbide as an alternative to gaseous acetylene

An efficient method for the synthesis of indolo[2,1-a]isoquinolines using calcium carbide as an alkyne source, 2-(2-bromophenyl)-1H-indoles as starting materials, and copper as a catalyst is described. The target products are synthesized via Sonogashira cross-coupling/nucleophilic addition tandem reactions. The advantages of this protocol include the use of inexpensive and easy-to-handle solid alkyne source instead of flammable and explosive gaseous acetylene, cheap and readily available raw materials, wide range of substrates, and simple reaction procedure. The method can also be extended to gram scale. In addition, the desired product can also be obtained by one-pot three-component reaction of phenylhydrazine hydrochlorides, o-bromoacetophenones and calcium carbide.