Phosphazene superbase P- t-Bu mediated iodoaminocyclization of 2-(1-alkynyl)benzamides is reported. The reaction works under ambient conditions and instantaneously results in the synthesis of isoindolin-1-ones in 65-97% yields, in a regio- and stereoselective manner. The exclusive formation of products with Z-geometry (across the exo C═C bond) has been confirmed through X-ray crystallography. The methodology also provides an easy access to aristolactams, an important class of natural products. This has been successfully demonstrated by synthesizing two aristolactam derivatives (including Cepharanone B).