Investigations in the imidazole series LXXIV. Electrophilic substitution reactions in the pyrrolo[1,2-a]imidazole series

Preparations ofC-Nitroso Compounds

“…Only electron-rich heterocyclic ring systems are subject to electrophilic attack by nitrosating agents: examples include pyrroles, , pyrazoles, antipyrine (2,3-dimethyl-1-phenylpyrazol-5-one), imidazoles, fused benzimidazoles, − 1 H -pyrrolo[1,2-a]imidazoles, , imidazo[2,1-b]thiazoles, − indolizines, , indoles, − 8-thia-1,4-diazacycl[3,3,2]azines, and thiazoles . Nitrosation of four 3,5-diamino-2 H -1,2,6-thiadiazine 1,1-dioxides with sodium nitrite and acetic acid in a DMF/water solution at 0−5 °C gives good yields of the corresponding 4-nitroso derivatives (eq 5; R = CH 2 Ph, CH 2 CH 2 Ph, Bu, Ph) …”