PALLADIUM CATALYZED REACTIONS: REDUCTIVE CYCLIZATION OF NITROARENES, AND OXIDATIVE CARBONYLATION OF ANILINE

Palladium Catalyzed Reactions: Reductive Cyclization of Nitroarenes, and Oxidative Carbonylation of Aniline Abstract: The thesis is divided into two main chapters: reductive cyclization of nitroarenes, and oxidative carbonylation of aniline. The first chapter involves developing a catalytic system for carbazoles synthesis through reductive cyclization of 2-nitrobiphenyls employing phenyl formate as an in-situ source of CO. Thus, the synthetic chemist can avoid handling pressurized CO lines and perform the reaction in a pressure tube, a cheap and readily available tool for any laboratory. Moreover, the developed protocol can tolerate both air and moisture and can be performed using undried and undistilled commercial DMF. Several carbazoles bearing a wide range of substituents were synthesized in good to excellent yields including some with valuable pharmaceutical or thermo/electrical applications. The reaction could be performed on the grams scale affording carbazole in a very good yield (85%) without the need for chromatographic purification, making our synthetic strategy even more attractive and economically advantageous. The second chapter deals with the palladium/iodide couple which is the most investigated catalytic system for the oxidative carbonylation of amines to give ureas or carbamates. In reinvestigating it, we found that the most prominent role of iodide is to etch the stainless steel of the autoclave employed in most of previous works, releasing in solution small amounts of iron salts. The latter are much better promoters than iodide itself. Iron and iodide have a complex interplay and, depending on relative ratios, can even deactivate each other. The presence of a halide is beneficial, but chloride is better than iodide in this respect. The ideal Fe/Pd ratio is around 10, but even an equimolar amount of iron with respect to palladium (0.02 mol% with respect to aniline, corresponding to 12 ppm Fe with respect to the whole solution) is sufficient to boost the activity of the catalytic system. Such small amount may also come from Fe(CO)5 impurities present in the CO gas when stored in steel tanks. The role of the solvent has also been investigated. It was found that the reason for the better selectivity in some cases is at least in part due to a hydrolysis of the solvent itself, which removes the coproduced water.