Nitrite sulphides. Part 10. Intramolecular 1,3-dipolar cycloadditions

Abstract

Intramolecular 1,3-dipolar cycloadditions involving acetylenic and olefinic esters of o-hydroxybenzonitrile sulphide have been examined. The nitrite sulphides were generated by thermal decarboxylation of the corresponding 1,3,4-oxathiazol-2-one. o-Phenylpropiolyloxy and -amido derivatives (1a) and (2a) afforded chromeno[4,3-c]isothiazolone (7a)(70%) and isothiazolo[4,3-c]quinolinone (9a)(81%) respectively. Four products were formed on thermolysis of cinnamate esters (10); o-cyanophenyl cinnamates resulting from desulphuration of the nitrite sulphide; chromenoisothiazolones (7) from Intramolecular cycloaddition followed by dehydrogenation of the resulting 4,5-dihydroisothiazole; chromeno[4,3-b]quinolinones (14); and 4-amino-3-benzylchromenones (15). The last two compounds are believed to be formed by a pathway involving the 2,5-dihydroisothiazole tautomer (17), extrusion ofsulphur, followed by cyclisation or hydrogenation (Scheme 2). α- and β-Methylcinnamate esters (19) and (20) afforded, in addition to nitrite by-products, dihydroisothiazole (21) and 4-amino-3(α-styryl)chromenone (23) respectively.