The unprecedented eco-friendly Pt-catalyzed 5-endo-dig cycloisomerization of readily available α-amino ynones is reported under microwave irradiation in PEG-3400 as reaction matrix. The corresponding pure pyrrolin-4-ones were obtained in excellent yields (80-98%) directly after a straightforward precipitation-filtration workup, thus avoiding any chromatographic purification. The catalytic system was recycled and the chiral purity of all the products was also investigated.