The cycloadduct 1 exists in a mobile equilibrium with isoquinolinium N-phenylimide (2) and CS2. The reaction of 1 with 1-(diethylamino) propyne (3) afforded the 1: 1: 1 products 4 and 5, the latter predominating with higher CS2 concentration. The NMR spectra and an X-ray analysis of 4 clarified the structures. The hindered rotation about the C N bond of the N, N- diethylthiocarboxamide groups is responsible for the temperature-dependent dynamic ...