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

Article abstract of DOI:10.1246/cl.1980.1031

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.