Cascade One‐Pot Synthesis of Orange‐Red‐Fluorescent Polycyclic Cinnolino[2,3‐f]phenanthridin‐9‐ium Salts by Palladium(II)‐Catalyzed C−H Bond Activation of 2‐Azobiaryl Compounds and Alkenes

Abstract

Quaternary ammonium salts were synthesized in moderate to good yields through double oxidative C−H bond activation on azobenzenes. The mechanism of the highly regioselective reaction of 2‐azobiaryls with alkenes to give orange‐red‐fluorescent cinnolino[2,3‐f]phenanthridin‐9‐ium salts and 15H‐cinnolino[2,3‐f]phenanthridin‐9‐ium‐10‐ide is proposed to involve ortho C−H olefination of the 2‐azobiaryl compound with the alkene, intramolecular aza‐Michael addition, concerted metalation–deprotonation (CMD), reductive elimination, and oxidation.

Rhodium-Catalyzed Oxidative Annulation of 2- or 7-Arylindoles with Alkenes/Alkynes Using Molecular Oxygen as the Sole Oxidant Enabled by Quaternary Ammonium Salt

“…Without n -Bu 4 NOAc, 4a was not obtained at all, and nor was the C-H olefinated product ( 3a ) formed. Quaternary ammonium salts have always been considered to be an effective catalyst for Michael reactions [ 74 , 75 , 76 , 77 , 78 , 79 ]. As one can see from Figure 2 , the intramolecular aza-Michael reaction of ortho -alkenylated-2-phenyl-1 H -indole could indeed be improved by the addition of n -Bu 4 NOAc.…”

Transition Metal‐Catalyzed Intermolecular Cascade C−H Activation/Annulation Processes for the Synthesis of Polycycles

“…More recently, Chuang's group developed a palladium‐catalyzed double oxidative C−H bond activation of azobenzenes and alkenes for the construction of orange‐red‐fluorescent cinnolino[2,3‐ f ]phenanthridin‐9‐ium salts and 15 H ‐cinnolino[2,3‐ f ]phenanthridin‐9‐ium‐10‐ide (Scheme 44). [84] Interestingly, the reaction could tolerate electron rich styrene, giving the desired product in 45 % yield. However, it was not compatible with strongly electron‐deficient alkenes, such as acrylonitrile and phenyl vinyl sulfone.…”

Ligand-Controlled Csp2–H versus Csp3–H Bond Formation in Cycloplatinated Complexes: A Joint Experimental and Theoretical Mechanistic Investigation

“…The main components of these energy sources are alkanes, which are also the raw materials of the chemical industry. There has been and continues to be much interest to functionalize alkanes through selective C–H bond activation to obtain more valuable organic chemicals under mild conditions. − There are many reports on C–H bond activation using transition-metal complexes. − In this area, homogeneous catalytic systems bearing late transition metals such as palladium − and platinum − are particularly important. The study of direct C–H bond activation is often difficult, and as a result, C–H alkane activation is often investigated through the protonolysis of M–C bonds (i.e., the microscopic reverse of the activation step) in organometallic compounds such as methylplatinum­(II) complexes. − …”