ALKYL-SUBSTITUTED BENZO[1,2-D-3,4-D']DIIMIDAZOLES - PREPARATION AND ANNULAR TAUTOMERISM

The treatment of 4-nitro-5-amino-2,1,3-benzothiadiazole (3) with tin/h ydrochloric acid in the presence of a carboxylic acid having a C1-C3 c hain gave the corresponding 2,5-dialkylbenzo[1,2-d:3,4-d']diimidazoles (1). When the amount of tin was reduced to a half, 3 afforded only 5- alkylimidazolo[4,5-d]benzothiadiazoles (2). Unsymmetrical dialkyldiimi dazoles (1) were obtained from 2 in a second step. Annular tautomers d ue to NH-proton exchange of the imidazole rings of 1 and 2 could be ob served in H-1 NMR spectra in DMSO-d(6) at a low concentration (ca. 5 x 10(-4) M).