Chemistry of 4-dicyanomethylene-1,2,6-thiadiazines

The chlorine atoms in 3,5-dichloro-4-dicyanomethylene-1,2,6-thiadiazine 1 a re readily displaced by thiophenols in the presence of Hunig's base, the fi rst at -78 degrees C and the second at 20 degrees C to give the orange mono - and bis-arylthio derivatives in high yield (Table 1). Similarly secondary amines give the red mono- and blue bis-amino compounds in high yield (Tabl e 2); piperidine, for example, gives the former at -78 degrees C and the la tter at -30 degrees C. A low limit of reactivity is reached with diisopropy lamine which gives the mono derivative only, in low yield (30%). Reactions with ammonia and with primary amines are complex since the amines formed ca n cyclise onto the adjacent cyano group, aniline giving only a low yield of the pyrrolo[2,3-c][1,2,6]thiadiazine 8. The 4-dicyanomethylene compound 1 is more reactive than the known 4-oxo analogue 2, but can suffer the added complications of cyano group cyclisation and hydrolysis of dicyanomethylene to the keto group. 3,5-Dimorpholino-4-dicyanomethylene-1,2,6-thiadiazine 7 c is oxidized to the sulfoxide 9 with MCPBA or N2O4, and 9 reverts to 7c wi th triphenylphosphine-tetrachloromethane, all in high yield. Thiadiazine 1 undergoes a complex reaction with DMSO at 20 degrees C to give the three fu ro[2,3-c][1,2,6]thiadiazines 10, 11 and (tentatively) 12 which could all ar ise from the initial product 13 of displacement of chlorine by DMSO, by cyc lisation and sulfoxide type rearrangements. Mechanisms are proposed for all new reactions.