Condensed Systems incorporating 4- Thiadiazoles

A general synthetic route to N-bridgehead condensed heterocyclic structures incorporating a 1,2,4-thiadiazole ring consists of the interaction of an a-amino-heterocyclic compound with chlorothioformyl chloride (84) or ethyldithiocarbonyl chloride (85). The reaction is widely applicable, as shown. 

2-Aminothiazoles (86) react with chlorothioformyl chloride (84) to give tars, from which 2H-thiazolo[3,2-l ][l,2,4]thiadiaz(d-2-one (87) is isolable in 3% yield the use of ethyldithiocarbonyl chloride (85) raises the yields to 25%.  

More favourable results are obtained in analogous syntheses, which afford the following types of compounds 6H-[l,3,4]thiadiazolo[3,2-b]-[l,2,4]thiadiazol-6-ones (10—53%) (88) 2H-[l,2,4]thiadiazolo[2,3-a]pyridin-2-ones (48%) (89) 2JFf-[I,2,4]thiadiazolo[2,3-b]pyridazin-2-ones (90), and 5,6-dihydro-2H-[l,2,4]thiadiazolo[3,2-b]thiazin-2-one (91). The i.r. spectra 

The interaction of chlorothioformyl chloride and comparable heterocyclic methylureas (92) proceeds partly with identical results. Loss of methyl isocyanate from (92) yields the parent amine (93) and thence the condensed bicyclic products (97), as described immediately above. Simultaneous direct condensation of the urea (92) affords, by way of the hypothetical intermediate (94), the fused thiatriazepinediones (96) as well as 1,2,4-thiadiazoli-dinediones (95), generally in moderate yields. The observations on record are too varied to be adequately summarized examples of the structures obtained are 2H-thiazolo[3,2-b][l,2,4,6]thiatriazepine-2,4(3H)-diones (98) and 2-(thiazol-2-yl)-4-methyH,2,4-thiadiazolidine-3,5-diones (99).  

Representatives of the l,2,4-thiadiazolo[3,2-b]thiazole (101), 1,2,4-thia-diazolo[2,3-a]pyridine (102), and l,2,4-thiadiazolo[2,3-a]pyrimidine (103) ring-system are accessible in high yield by the action of bromine in chloroform on the appropriate heterocyclic thiourea, e.g. (100).  

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Condensed ring systems incorporating 1,2,4-thiadiazole are formed when a heterocyclic compound (178) functioning as the amidine is condensed with chlorothioformyl chloride (179) or ethyldithiocarbonyl chloride (180) the scope of this synthesis is very wide indeed. 

The condensation of sulphamide and diethyl oxalate produces 3,4-dihydroxy-1,2,5-thiadiazole 1,1-dioxide as the dipotassium salt in high yield. The free acid (177) is an excellent precursor for the preparation of other functional derivatives, and for building up fused ring systems incorporating the 1,2,5-thiadiazole 1,1-dioxide structure (see below). The two isomeric benzothiadiazole acetoximes (178) and (179) undergo the Beckmann reaction, resulting in the fission of their carbocyclic ring. This provides an effective synthesis of novel ajS-unsaturated 1,2,5-thiadiazoles (180 X = COaH, Y = CR=CHCN X =... 

Benzo[l,2-c 3,4-c 5,6-c ]tris[l,2,5]thiadiazole.—Four related condensed tetracyclic ring systems incorporating 1,2,5-thiadiazole (202 X = S, Se, CH, or CH=CH) are accessible from a common starting material, benzo[l,2-c 3,4-c ]-bis[l,2,5]thiadiazole (200), which is converted into the diamine (201) and variously cyclized to (202). The condensation of (201) and 9,10-phenanthrene-quinone in boiling acetic acid similarly yields the heptacyclic ring system dibenzo-[a,c]bis[l,2,5]thiadiazolo[3,4-/r.3, 4V]phenazine. 2... 

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