Part I : Palladium-catalyzed radical alkylation of arenes. Part II : Nickel-catalyzed asymmetric hydrogenation of quinoxalines using formic acid
Lim, Li Hui
Date of Issue2017-03-20
School of Physical and Mathematical Sciences
We developed a general procedure for palladium-catalyzed radical alkylation of activated arenes. Electron-deficient benzenes and naphthalene derivatives reacted to give alkylated products in moderate to good yields. The alkyl radicals added to para position of strong electron-withdrawing groups on the arenes. This alkylation method complements with traditional Friedel-Crafts alkylation which reacted well with electron-rich and neutral arenes. We reported asymmetric transfer hydrogenation of 2-substituted quinoxalines using Ni/TangPhos as the catalyst and formic acid as the source of hydrogen. Moderate to good enantioselectivities were obtained depending on the substituents. We also realized a one-pot reductive amination between 1,2-phenylenediamine and substituted glyoxal. The two spontaneously condensed to form quinoxalines. The later was not isolated and subjected to nickel catalyzed asymmetric transfer hydrogenation. We realized a challenging Heck arylation of N-substituted maleimides, which are exceedingly prone to basic hydrolysis. We found a combination of weak base KOAc in ethylene carbonate solvent helped to slow down the ring-opening side reactions of sensitive maleimide to form the Heck product in good yield and with good generality.