An efficient cyclotrimerization of terminal alkynes in poly( ethylene glycol)-400 (PEG-400) has been developed. In the presence of PdC12 (0.04 mol), CuC12 ( 1 mmol) and PEG-400 ( 1.5 g), a variety of terminal alkynes ( 1 retool) underwent cyclotrimerization smoothly and formed regio-selectively the corresponding benzene derivates with good yield. It is worth while to note that the reaction was conducted under environment friendly conditio...