Chemistry of 3,5‐Dichloro‐4H‐1,2,6‐thiadiazine‐4‐thione.

Thionation of 3,5‐dichloro‐4H‐1,2,6‐thiadiazin‐4‐one with P2S5 affords 3,5‐dichloro‐4H‐1,2,6‐thiadiazine‐4‐thione (17 %) and 4,5‐dichlorothieno[2,3‐c:5,4‐c′]bis([1,2,6]thiadiazine) (13 %) that forms via an isolable but highly reactive 1,2‐dithiine intermediate. An independent synthesis of the 4,5‐dichlorothieno[2,3‐c:5,4‐c′]bis([1,2,6]thiadiazine) was attempted via (2E,5E)‐2,5‐bis[(chlorothio)imino]‐2,5‐dihydrothiophene‐3,4‐dicarbonitrile, the chemistry of which was briefly investigated. Thiadiazine‐4‐thione reacts with diazoacetate and dimethylsulfonium dicyanomethylide to form the expected ylidenes, and undergoes a Diels‐Alder reaction with 2,3‐butadiene to give a spirocyclic 3,6‐dihydro‐2H‐thiopyran. Treating the thione with Ph3P (1 equiv) affords {3,4‐dicyano‐5‐[(triphenyl‐λ5‐phosphaneylidene)amino]thien‐2‐yl}carbonimidoyl dicyanide and 2‐[(3,5‐dichloro‐4H‐1,2,6‐thiadiazin‐4‐ylidene)amino]‐5‐[(triphenyl‐λ5‐phosphaneylidene)amino]thiophene‐3,4‐dicarbonitrile, the structure of which was supported by X‐ray crystallography. The reaction mechanism as well as independent syntheses of both products were investigated. [ABSTRACT FROM AUTHOR]