Commercially available liquid enol ethers and acetates as gaseous alkyne equivalents in cationic Rh(I)/BINAP-catalyzed chemo- and regioselective formal cross-alkyne cyclotrimerizations

A cationic rhodium(I)/BINAP complex catalyzes partial intramolecular [2+2+2] cycloadditions of 1,6- and 1,7-diynes with enol ethers or a ketene acetal giving substituted benzenes in good yields. The same catalyst also catalyzes complete intermolecular [2+2+2] cycloadditions of two different monoynes with enol acetates giving tri- and tetrasubstituted benzenes in good yields with complete regioselectivity. Commercially available liquid enol ethers and acetates can be used as versatile equivalents for gaseous alkynes in the present rhodium-catalyzed formal cross-alkyne cyclotrimerizations. (C) 2009 Elsevier Ltd. All rights reserved.