Direct Ortho Arylation of 9-(Pyridin-2-yl)-9H-carbazoles Bearing a Removable Directing Group via Palladium(II)-Catalyzed C–H Bond Activation
摘要:
A one-pot synthesis of ortho-arylated 9-(pyridin-2-yl)-9H-carbazoles via C-H bond activation is presented. Silver nitrate and tert-butyl alcohol were found to be the best oxidant and solvent for the process, respectively. The product yields are from modest to excellent, and the reaction showed sufficient functional group tolerance. p-Benzoquinone served as an important ligand for the transmetalation and reductive elimination steps in the catalytic process. The key intermediate of the reaction, a 9-(pyridin-2-yl)-9H-carbazole palladacycle, was isolated, and its structure was unequivocally confirmed by X-ray crystallography. No kinetic isotope effect (k(H)/k(D) = 1.00 +/- 0.17) for the C-H bond activation step was observed. In addition, a Hammett experiment gave a negative rho value, -2.16 +/- 0.02. The directing group, pyridinyl, was demonstrated to be a removable functional group. Finally, a rational catalytic mechanism is presented on the basis of all experimental evidence.
Palladium/Silver Synergistic Catalysis in Direct Aerobic Carbonylation of C(sp<sup>2</sup>)<i>−</i>H Bonds Using DMF as a Carbon Source: Synthesis of Pyrido-Fused Quinazolinones and Phenanthridinones
作者:D. Nageswar Rao、Sk. Rasheed、Parthasarathi Das
DOI:10.1021/acs.orglett.6b01292
日期:2016.7.1
An unprecedented Pd/Ag synergistic catalysis in the direct carbonylation of C(sp2)–H bonds utilizing DMF as the carbon source under oxygen is described and demonstrated in the synthesis of pyrido-fused quinazolinone and phenanthridinone scaffolds. Control experiments indicated that the “C” of the carbonyl group is derived from the methyl group of DMF and “O” originates from oxygen as in the case of