A tentative mechanism for this five-component reaction is proposed in Scheme 2. The reaction of primary amine 1, formaldehyde 2, and arylboronic acid 3 afforded a secondary amine 6via the PBM reaction,8,9,11 which was detected by GC-MS throughout the reaction. The secondary amine 6 might further react with formaldehyde 2 to produce an iminium intermediate B. The copper acetylide intermediate, generated from alkyne 4 and Cu(OAc)2, reacted with iminium B to give the corresponding propargylamine 5 and regenerated the copper catalyst for further reactions.5,7 Thus, this five-component reaction involved a MCR2 of PBM and A3-coupling reactions.