One-Pot Synthesis of 1,3-Disubstituted Allenes from 1-Alkynes, Aldehydes, and Morpholine

ZnI2 has been identified as the catalyst for the one-step synthesis of allenes from terminal alkynes and aldehydes with morpholine as the base in toluene. The reaction is believed to proceed via the intermediacy of propargylic amines, which was converted to allenes by a sequential hydride transfer and β-elimination process. The reaction is applicable for both aromatic and aliphatic aldehydes. Functionalities such as halide, hydroxyl, or amine may be tolerated.