SOME NOVEL ASPECTS OF REGIOSELECTIVITY IN 1,3 DIPOLAR CYCLOADDITIONS OF 4H-1-BENZOPYRAN-4-THIONE

Article abstract of DOI:10.1016/S0040-4020(01)89803-3

4H-1-Benzopyran-4-thione (1) reacted smoothly with nitrilimines (3a-e) to afford regioselective cycloadducts (4a-e) in good yields.In contrast,benzonitrile oxide (6) and aldonitrones (7a-d) reacted preferentially at the thione function.The unstable cycloadduct (8) or (9) ruptured to give as isolable products chromone (10) and phenyl isothiocyanate (11) and the thioamides (12a-d).This indirectly proves the site of attack of the dipole at the thione group.