Synthesis of Fused 1,2,4-Dithiazines and 1,2,3,5-Trithiazepines

Reacting (Z)-N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-1H-pyrazol-5-amines 5 with Et2NH and then with concd H2SO4 gives 5H-pyrazolo[3,4-e][1,2,4]dithiazine-3-carbonitriles 7 in good yields (74-85%) and 6H-pyrazolo[3,4-f][1,2,3,5]trithiazepine-4-carbonitriles 9 as minor products (0-6%). Furthermore, the 1,3-dimethylpyrazole analogue 5a was transformed into the dithiazine 7a in two discrete steps, allowing the isolation of a disulfide intermediate (Z)-2-[(diethylamino)disulfan-yl]-2-[(1H-pyrazol-5-yl)imino]acetonitrile (8a). The one-pot, two-step reaction also worked with electron-rich hydroxy- and methoxy-substituted anilines. Thermolysis of the pyrazolo[3,4-e][1,2,4]dithiazines 7 gave the ring-contracted 1H-pyrazolo[3,4-d]thiazole-5-carbonitriles 6 (94-100%). With active sulfur, 1,3-dimethyl-5H-pyrazolo[3,4-e][1,2,4]dithiazine-3-carbonitrile (7a) gave 1,3-dimethyl-6H-pyrazolo[3,4-f][1,2,3,5]trithiazepine-4-carbonitrile (9a), but on prolonged reaction times, it gave 5,7-dimethyl-5H-[1,2,3]dithiazolo[4,5-b]pyrazolo[3,4-e][1,4]thiazine (13). Finally, in the absence of acid, heating a solution of (Z)-2-[(diethylamino)disulfanyl]-2-[(1,3-dimethyl-1H-pyrazol-5-yl)imino]acetonitrile (8a) gave 4,6,10,12-tetramethyl-6H-pyrazolo[3,4-f]pyrazolo[3',4':4,5]pyrimido[6,1-d][1,2,3,5]trithiazepine-8,12b(10H)-dicarbonitrile (19) (67%).