A facile synthesis of a series of 1-alkoxyisoquinolines and (2H)-isoquinolones by an intramolecular 6-endo-dig cyclization of ortho-alkynylbenzonitriles in the presence of a catalytic amount of hydrido (dimethylphosphinous acid-κP)[hydrogen bis (dimethylphosphinito-κP)] platinum (II) in various alcohols at 65–90° C is described for the first time.