Regioselectively switchable alkyne cyclotrimerization catalyzed by a Ni(ii)/bidentate P-ligand/Zn system with ZnI2 as an additive

A simple catalytic system of Ni(PPh3)2Cl2/dppb or dppm/Zn can effect an efficient and regioselectively controlled alkyne cyclotrimerization to form 1,2,4- (with no additive) or 1,3,5-regioisomers (with the use of a ZnI2 additive). This protocol features the advantages of facile manipulation, mild conditions, broad substrate scope, high yields, excellent functional-group tolerance and easily controllable regioselectivity, and demonstrates practical potential for the construction of complicated and well-defined poly-substituted benzene derivatives. The mechanistic studies were carried out preliminarily.