CYCLOADDITION REACTIONS OF 4,6-DIPHENYLTHIENO[3,4-c]-1,2,5-OXADIAZOLE AND -1,2,5-THIADIAZOLE WITH 6,6-DIPHENYLFULVENE AND TROPONE

Abstract 4,6-Diphenylthieno[3,4-c]-1,2,5-oxadiazole (1) reacts as a thiocarbonyl ylide with 6,6-diphenylfulvene to give the exo-[4 + 2] adduct via a stereoselective and regiospecific cycloaddition. The exo-adduct undergoes thermal cleavage of the oxadiazole ring to nitrile and nitrile oxide moieties which can be trapped as 1,3-cycloadducts to the fulvene and dimethyl acetylenedicarboxylate. The reaction of 4,6-diphenylthieno[3,4-c]-1,2,5-thiadiazole (2) with the fulvene affords a mixture of analogous exo- and endo-adducts which are subject to a retro-cycloaddition reaction. On the other hand, 1 reacts with tropone to give the corresponding [4 + 6] adduct which is susceptible to a retro-cycloaddition reaction. However, 2 did not react with tropone.