Intramolecular nitrilimine cycloadditions to the thiophene and the furan rings

The dipolarophilic behavior of furan and thiophene rings have been exploited in the intramol. cycloaddns. of nitrilimines. These labile intermediates were generated from the corresponding hydrazonoyl chlorides by treatment with silver carbonate. The extent of formation of tricyclic cycloadducts was strongly dependent on the substitution pattern of the heteroarom. ring, thus reflecting the HOMO-dipole controlled nature of the cycloaddn.