Ring contraction of 1,2,6-thiadiazines to 1,2,5-thiadiazoles: synthesis of 2-substituted 4-amino-2,3-dihydro-3-oxo-1,2,5-thiadiazole 1,1-dioxides

Abstract

Nitrosation of 2-substituted 2,3,5,6-tetrahydro-3,5-dioxo-1,2,6-thiadiazine 1,1-dioxides (2a–d) yielded the corresponding 4-hydroxyimino derivatives (3a–d), which by mild acid treatment were converted into 2-substituted 4-amino-2,3-dihydro-3-oxo-1,2,5-thiadiazole 1,1-dioxides (4a–d). A tentative mechanism is proposed. 2,6-Disubstituted 2,3,5,6-tetrahydro-3,5-dioxo-1,2,6-thiadiazine 1,1-dioxide (2e) also yielded the corresponding 4-hydroxyimino derivative (3e), but this compound does not react following the same pattern and under acid treatment, only the corresponding N,N′-disubstituted sulphamide (1e) was obtained.