Altering Copper-Catalyzed A3 Couplings by Mechanochemistry: One-Pot Synthesis of 1,4-Diamino-2-butynes from Aldehydes, Amines, and Calcium Carbide.

The ability of mechanochemistry to alter established chemical selectivity is demonstrated. A copper(I)-catalyzed mechanochemical aldehyde/alkyne/amine coupling using calcium carbide as the acetylene source provides selective access to 1,4-diamino-2-butynes, which contrasts classical approaches that provide propargylamine-type products. Solventless milling conditions were found to be essential to unmask A3  coupling products with new compositions.