Microwave-initiated hydroamination of 2-ethoxypropenal with secondary amines

Reactions of 2-ethoxyprop-2-enal with cycloaliphatic secondary amines (morpholine, piperidine, pyrrolidine) follow 1,4- or 1,2-addition pattern with subsequent condensation of the adduct with the initial amine to produce isomeric 2-ethoxyprop-2-ene-1,1-diamines and 2-ethoxyprop-1-ene-1,3-diamines. These reactions are accelerated by a factor of 15–30 under microwave irradiation and in the presence of water. The regioselectivity of primary nucleophilic attack varies over a wide range, depending on the amine basicity and reactant ratio. The reaction of 2-ethoxyprop-2-enal with pyrrolidine and water at a ratio of 1: 10: 10 was characterized by increased regioselectivity of 1,4-addition (up to 75%). Unlike cycloaliphatic amines, 2-ethoxyprop-2-enal reacted with N-methylaniline under microwave irradiation at a lower rate to give 2-ethoxy-N 1,N 1,N 3-trimethyl-N 1,N 1,N 3-triphenylpropane-1,1,3-triamine.