Isothiazoles. Part VI.1 Cycloaddition of azides to isothiazole dioxides: Synthesis of thiadiazabicyclo[3.1.0]hexene derivatives and their thermal rearrangement to thiazete dioxides, 1,2,6-thiadiazine dioxides and pyrazoles

3-Diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxide (1) was made to react with arylalkyl-and arylazides 2. Cycloadducts 3, which could be isolated in some cases, afforded N-arylalkyl-or N-aryl-thiadiazabicyclo[3.1.0]hexene derivatives 4 through N2-elimination. Thermal rearrangements of N-aryl-and N-β-phenylethyl substituted compounds 4b-e, produced derivatives of 1,2-thiazete 1,1-dioxide 5, 1,2,6-thiadiazine 1,1-dioxide 6 and pyrazole 7. The reaction can be optimized to afford compounds 6 in synthetically useful yield. In the case of N-benzyl-thiadiazabicyclo[3.1.0]hexene derivative 4a the different substitution on the aziridine nitrogen produced a different reaction course, affording the thiadiazine derivative 6a and the pyrimidine derivative 8. Copyright © 1996 Elsevier Science Ltd.