Some substitution reactions of thieno[3,2-f]quinoline

Abstract

Mononitration, monobromination, and Friedel–Crafts acylation of thieno[3,2-f]quinoline occurred in the 2-position; dibromination in concentrated sulphuric acid gave the 1,2-dibromo-derivative. The Hunsdiecker reaction of thieno[3,2-f]quinoline-2-carboxylic acid gave a mixture of 1,2,5-tribromothieno[3,2-f]quinoline and 5-bromothieno[3,2-f]quinoline-2-carboxylic acid in addition to unchanged starting material. Bromination of sodium thieno[3,2-f]quinoline-2-carboxylate gave the 5-bromo-acid. N-methylthieno[3,2-f]quinolinium hydrogen sulphate was oxidised to N-methylthieno[3,2-f]quinolin-7-one, which, on treatment with phosphorus pentachloride, gave 7-chlorothieno[3,2-f]quinoline. However, the methosulphate reacted with aqueous potassium cyanide to give 6,9-dihydro-N-methylthieno[3,2-f]quinoline-9-carbonitrile which when oxidised with iodine in pyridine yielded 9-cyano-N-methylthieno[3,2-f]quinolinium iodide. Demethylation gave thieno [3,2-f]quinoline-9-carbonitrile. The Reissert compound derived from thieno[3,2-f]quinoline reacted with phosphorus pentachloride to yield thieno[3,2-f]quinoline-7-carbonitrile, which on hydrolysis with concentrated hydrochloric acid yielded the 7-carboxylic acid. This was methylated with diazomethane to give methyl thieno[3,2-f]quinoline-7-carboxylate. The assignment of these structures has been confirmed whenever possible by conversion of the compounds into known compounds and comparison with authentic samples, or is derived from a study of the relevant 1H n.m.r. spectra.