4,5-Diamino-2,1,3-benzothiadiazole

Diamino-2,l,3-benzothiadiazole 82 affords [l,2,5]selenodiazolo[3,4-i ]-2,l,3-benzothiadiazole 83 quantitatively on treatment with selenium oxychloride in refluxing chloroform-pyridine <2004JHC955>. This was an improvement of the previous method using selenium dioxide (62% yield) <1984ZNB485>. 6-Isoprenyl-477-imidazo[4,5-< ]-benzothiadiazolone 84 was obtained when 4,5-diaminobenzothiadiazole was reacted with methyl acetoacetate in xylene at reflux (Scheme 10) <1997H(45)19>. 

Diamino-2,l>3-benzothiadiazole 201 undergoes cyclization on reaction with selected aromatic aldehydes <2004T2953>. Thus, reactions with pyrene-l-carboxaldehyde or naphthalene-1-carboxaldehyde in refluxing toluene produce the corresponding imidazoles 202 in moderate yields, whereas reactions with /i-(Ar,Ar-dimethylamino)benz-aldehyde and /i-[Ar,Ar-di(4-methylphenyl)amino]benzaldehyde under similar conditions gave the corresponding 5-imino derivatives 203 (Scheme 13). 

Isothiazolo[5,4-c]-2,l,3-benzothiadiazole (502) has been prepared by two methods. In the first, 5-nitro-2,l-benzoisothiazole (498) was converted to the nitroamine (499) by treatment with hydroxyl-amine in basic solution this was reduced with iron and acetic acid, and the o-diamino product (500) cyclized to (502) with thionyl chloride. In a second approach, treatment of 5-amino-4-methyl-2,l,3-benzothiadiazole (501) with iV-sulfinylmethanosulfonamide also led to (502). The isothiazolo[4,5-c]-2,l,3-benzothiadiazole (504) has been synthesized from 4-amino-5-methyl-2,l,3-benzothiadiazole (503) by an analogous procedure (Scheme 39) <80JHC537>. 

Synthesis of the benzo[l,2-c 3,4-c ]bis[l,2,5]thiadiazole (509) required cyclization of diamine (508). Nitration of (505) led to 4-nitro-2,1,3-benzothiadiazole (506) in 95% yield. Amination of (506) with hydroxylamine in basic medium led to compound (507), immediately reduced to the diamino derivative (508). Ring closure of (508) with thionyl chloride and pyridine led to the benzo[l,2-c 3,4-c ]bis[l,2,5]thiadiazole (509) in 89% yield. Compound (509) has been successfully used in the synthesis of several fused tetracyclic compounds (Scheme 40) <75JHC829>. 

H-Imidazo[4,5-c][2,l,3]benzothiadiazol-5(6H)-one (104) was synthesised by condensation of 4,5-diamino-2,l,3-benzothiadiazole (103) with urea. Similarly, fusion of (103) with thiourea produced the 5-mercapto derivative (102) <97H19>. 

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