The PMR spectroscopic properties (60 MHz) of cycloadducts of diarylnitrilimins towards 1, 2- dihydroisoquinolines mono alkylated at the N-atom or dialkylated at the C1-carbor and N- atoms have been studied. Date allow us to determine the stereochemistry of the cycloaddition reaction which is regio and diastereospecific. Configuration and conformation of the cycloadducts are specified.