Efficient synthesis of 4-oxo-4,5-dihydrothieno[3,2-]quinoline-2-carboxylic acid derivatives from aniline

The first reported synthesis of potential kinase inhibitors, 4-oxo-4,5-dihydrothieno[3,2-]quinoline-2-carboxylic acid derivatives starting from aniline is described. This efficient high yielding sequence was carried out in six steps without any chromatographic purification. A tandem nucleophilic aromatic substitution/cyclization reaction was used as a key step in the sequence. The versatile intermediate 2-carboxylic acid was used as a suitable precursor to access the functionalization of the C-ring, by convergent analog synthesis of several novel derivatives.