The Liebeskind–Srogl Cross-Coupling Reaction as a Crucial Step in the Synthesis of New Squaramide-Based Antituberculosis Agents

The synthesis of an extensive series of new squaramides with high potential in treating drug-resistant tuberculosis employing the Liebeskind–Srogl cross-coupling reaction is presented. Using the protocol given and various substrates, we assessed the scope and limitations of our methodology and prepared an extensive range of desired compounds. Moreover, 1H NMR spectra in solution show the presence of two rotational conformers (rotamers) in special cases. The results of antimycobacterial activity demonstrate the highly selective substrate specificity of the tested squaramides, requiring an efficient and widely applicable synthetic approach needed for the discovery of lead compounds. Our synthetic strategy confirms the versatility of squaramides that can be easily transformed into diverse functionalized molecules.