Four betaines derived from imidazo[4,5‐a], imidazo[5,4‐a] and thiazolo[5,4‐a]acridine have been prepared in a six step procedure starting from 2‐chlorobenzimidazoles and benzothiazoles. The 1H and 13C nmr has been used to characterize the compounds, particularly the orientation of the step leading to the formation of the acridinone ring. The uv‐visible spectra of one betaine (wave numbers v in cm−1) shows a linear dependence with Reichardt's ET parameter and a high sensitivity to solvent effects.
Compounds 2‐azido‐6H‐thiazolo[5,4‐a]acridin‐11‐one 3 and 2‐azido‐6‐butylthiazolo[5,4‐a]acridin‐11‐one 4 have been prepared for the first time. The azido/tetrazole equilibria of the most soluble compound 4 has been studied in six solvents. The resulting tautomeric equilibrium constants have been compared with those of 2‐azido‐4,5‐dimethylthiazole 1 and 2‐azidobenzothiazole 2. The rather insoluble NH derivative 3 when dissolved in DMSO contains 66% of tetrazole 3b while the corresponding anion (obtained by adding sodium hydride) is all in the tetrazole 13b form.
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