Tautomerism in ketomethylquinolines. Part 2. Further results on 2-ketomethylquinolines

A further series of 2-ketomethylquinolines has been prepared, many with α-substituents. Base-catalysed α-alkylation of unsubstituted ketomethylquinolines was successful in two instances. With excess sodium hydride and iodomethane α,N-dialkylation occurred. α-Bromination gave three new derivatives which were vulnerable to oxidation to 1,2-diketones. The preparation of two pyrroloquinolinones gave model compounds for the enaminone forms of the ketomethylquinolines. Examination of the compounds by IR and NMR spectroscopy has shown that compounds unsubstituted at the α-position and those carrying nitrite or ester groups strongly prefer the enaminone form in solution. The presence of a bromine atom or an alkyl group on the α-carbon gives compounds in which the major or sole tautomer is the ketone.