Abstract
Reaction of 5-nitro-2-furoyl isothiocyanate (1) and 5-nitro-2-thiofuroyl isocyanate (2), having a strong electron-withdrawing group, with β-aminocrotonates (3a-d) was examined. The products from the reaction of 1 with 3a-d were proved to be isothiazoles (5a-d) from chemica1 and spectral evidences. And of the expected compounds such as 1, 2- and 1, 4-adducts (4 and 6) and pyrimidines (7) were not obtained by these reactions. The isothiazoles were probably formed from 1, 2-addition of 3 to 1 giving 1 : 1 adducts (4), followed by cyclization with loss of hydrogen. In order to examine the role of the nitro group in this reaction, p-nitrobenzoyl and 2-furoyl isothiocyanate (10a and 10b) were treated with 3b under the same conditions, resulting in the formation of pyrimidines (11a and 11b) ; the corresponding isothiazoles (12a and 12b) were obtained in the presence of bromine as an oxidizing agent. Formation of isothiazoles (5a-d) from 1, without oxidizing agents appeared to be specific for nitrofuran derivatives. On the other hand, the products from the reaction of 2 with 3a-c were found to be linear 1;2-adducts (14a-c) from spectral evidinces.
