engleski

New pentacyclic ring system: intramolecular cyclization of o, o'- disubstituted bibenzothiazoles

Efficient methods for preparation of isomeric o, o'-diaminobibenzothiazoles (8a and 11a) and o, o'-diamino-2, 2'-dimethylbibenzothiazoles (8b and 11b), potentially valuable building blocks for construction of hitherto unknown dithiazolo annulated pentacyclic heterocycles, has been developed. The dithiazolo annulated benzo[c]cinnolines 9a, 9b and 12a were prepared from corresponding diamines by oxidation with PhI(OAc)2 in a good yield. The dithiazolo annulated carbazoles 13 and 14 were efficiently prepared from corresponding diamines by thermal cyclization in H3PO4. Unusual course of reduction and product formation of o, o'-dinitrosubstituted bibenzothiazoles 6a and 6b with SnCl2 under acidic conditions was rationalized by DFT quantum-mechanical calculations. It was suggested that cyclic products are formed from dinitroso derivatives and open-shell species immediately following on a reduction path.

benzothiazole; benzo[c]cinnoline; carbazole; reduction; oxidation;

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