Highly selective synthesis of tetra-substituted furans and cyclopropenes: copper(I)-catalyzed formal cycloadditions of internal aryl alkynes and diazoacetates.

A convenient Cu(I)-catalyzed cycloaddition of electron rich internal aryl alkynes and diazoacetates was discovered for the chemoselective and regioselective synthesis of tetra-substituted furans and cyclopropenes in moderate isolated yields (18-67%), and alkyne conversion (29-73%).