Intramolecular Hydroamination of Alkynes Catalyzed by Pd(PPh₃)₄/Triphenylphosphine under Neutral Conditions

The intramolecular hydroamination of alkynes tethered with amino group 1 in the presence of catalytic amounts of Pd(PPh₃)₄ and PPh₃ in benzene at 100 °C proceeded smoothly without the use of any additional acid source to afford five- and six-membered nitrogen heterocycles 2 in good to excellent yields. A compulsory addition of carboxylic acid as a cocatalyst was not needed, and the reaction could be carried out under essentially neutral conditions.