Thieno quinoline formation

Variable results have been reported for the halogenation of thieno[2,3-6]quinoline (123). Initial attack was mainly at the 3-position, but it was difficult to avoid the formation of 2,3-dihalogenated products, even when only 1 mol of halogen was used (predictions are for 2- and 3-substitution [77ZN(B)1331]). Bromine buffered in chloroform gave the 3-monobromo derivative, but analogous chlorination gave a mixture that included some... 

Radical Reactions.—Thiazolyl, pyridyl, and other heteroaryl radicals formed by aprotic diazotization of the corresponding heterocyclic amines substitute homolytically on thiophen with the formation of 2-heteroaryl-thiophens as the main products in 20—50% yield. The results of competitive experiments indicate that the reactivity of thiophen in this reaction at 70—80 °C is slightly higher than that of benzene. The currently accepted mechanism of the decomposition of benzoyl peroxide in thiophen has been criticized on the basis of new experimental results. No free thienyl radicals are involved in the reaction, as demonstrated by scavenging experiments, and the bithienyls formed are probably derived from dimerization of a benzoyloxythiophen radical a-complex, with subsequent loss of benzoic acid. Nitrene insertion into the thiophen ring has been observed in the thermal decomposition of 2-(2-azidobenzyl)thiophen and similar compounds, leading to thieno[3,2-6]quinoline derivatives. ... 

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