Reaktion von Phenyldiazomethan mit 1,3‐Thiazol‐5(4 H )‐thionen: Basenkatalysierte Ring‐Öffnung des Primäradduktes

Reaction of Phenyldiazomethane with 1,3‐Thiazole‐5(4 H )‐thiones: Base‐Catalyzed Ring Opening of the Primary Adduct Reaction of 1,3‐thiazole‐5(4 H )‐thiones 1 and phenyldiazomethane ( 2a ) in toluene at room temperature yields the thiiranes trans ‐ and cis ‐1,4‐dithia‐6‐azaspiro[2.4]hept‐5‐enes ( trans ‐ and cis ‐ 4 ; Scheme 2 ). With Ph 3 P in THF at 70°, these thiiranes are transformed stereospecifically into ( E )‐ and ( Z )‐5‐benzylidene‐4,5‐dihydro‐1,3‐thiazoles 5 , respectively. In the presence of DBU, 1 and 2a react to give 1,3,4‐thiadiazole derivatives 6 or 7 via base‐catalyzed ring opening of the primary cycloadduct ( Scheme 3 ). In the case of 2‐(alkylthio)‐substituted 1,3‐thiazole‐5(4 H )‐thiones 1c and 1d , this ring opening proceeds by elimination of the corresponding alkylthiolate, yielding isothiocyanate 7 . The structures of ( Z )‐ 5c and 6b have been established by X‐ray crystallography.