Cu(I)-catalyzed reaction of diazo compounds with terminal alkynes: a direct synthesis of trisubstituted furans

A method for the synthesis of tri-substituted furans has been developed based on Cu(I)-catalyzed reaction of terminal alkynes with β-keto α-diazoesters. This method for the synthesis of 2,3,5-trisubstituted furans is operationally simple and applicable to wide substrate scope. Moreover, this synthesis employs cheap Cu(MeCN)4PF6 as the catalyst and no additional ligand is needed. Similar reaction has also been applied to ethyl (E)-2-diazo-3-(methoxyimino)butanoate for the synthesis of 2,3,5-trisubstituted N-methoxypyrroles with limited success.