An Efficient Synthesis of Terminal Allenes from Terminal 1-Alkynes

We have developed a modified method for the synthesis of terminal allenes from terminal 1-alkyne: The reaction of 1-alkynes with 1.8 equiv of Cy2NH and 2.5 equiv of paraformaldehyde mediated by CuI (0.5 equiv) in refluxing dioxane may produce terminal allenes in much higher yields than the previously reported protocol and many functional groups such as mesylate, hydroxyl group, ether, amide, etc. may be tolerated.