Pd‐Catalyzed Decarboxylative Cross‐Coupling of 2‐Carboxyazine N‐Oxides with Various (Hetero)aryl Halides

Abstract

Decarboxylative cross-coupling reactions of substituted 2-carboxyazine N-oxides, with a variety of (hetero)aryl halides, by bimetallic Pd(0)/Cu(I) and Pd(0)/Ag(I) catalysis are reported. Two possible pathways, a conventional bimetallic-catalyzed decarboxylative arylation, as well as a protodecarboxylative/direct C-H arylation sequence have been considered. These methods provide the first general decarboxylative arylation methodology for the 2-carboxyazine series.

Experimental and mechanistic analysis of the palladium-catalyzed oxidative C8-selective C–H homocoupling of quinoline N-oxides

“…This result compliments Hoarau’s Ag- and Cu-mediated, Pd/phosphine-catalyzed C2-selective arylation of 2-carboxyquinoline N -oxides. 17 …”

Carbon Nanotube–Ruthenium Hybrids for the Partial Reduction of 2‐Nitrochalcones: Easy Access to Quinoline N‐Oxides

“…The main method for the preparation of quinoline N ‐oxides is the oxidation of quinolines . The direct palladium‐catalyzed arylation of quinoline N ‐oxides to 2‐arylquinoline N ‐oxides was recently reported . Morita–Baylis–Hillman adducts derived from 2‐nitrobenzaldehyde also react in the presence of trifluoroacetic acid to give N ‐oxides via a nitroso intermediate .…”

“…2 i : Yellowish brown solid; yield: 50 % (12 mg); m.p. 204–206 °C (lit 206–208 °C); 1 H NMR (400 MHz, CDCl 3 ): δ =7.50 (d, J =8.4 Hz, 1 H), 7.70 (t, J =7.3 Hz, 1 H), 7.80–7.85 (m, 4 H), 7.91 (d, J =8.0 Hz, 1 H), 8.11 (d, J =8.0 Hz, 2 H), 8.82 ppm (d, J =8.8 Hz, 1 H); 13 C NMR (100 MHz, CDCl 3 ): δ =113.3, 118.6, 120.4, 122.9, 126.5, 128.4, 129.4, 130.1, 130.6, 131.5, 132.3, 137.9, 142.4, 143.6 ppm; HRMS (ESI): m / z : calcd for C 16 H 10 N 2 NaO: 269.0685 [ M +Na + ]; found: 269.0689.…”

“…[23] The direct palladiumcatalyzed arylation of quinoline N-oxides to 2-arylquinoline Noxidesw as recently reported. [24][25][26] Morita-Baylis-Hillman adducts derived from 2-nitrobenzaldehyde also react in the presence of trifluoroacetic acid to give N-oxides via an itroso intermediate. [27] Althought here are reports of reduction-cyclization sequences starting from 2-nitrochalcones and 3-hydroxyketones for the preparation of quinoline N-oxide and its derivatives, [28][29][30][31] applicability of such methods is curtailed owing to the requirement of drastic conditions such as reflux temperatures or excessa mounts of metal catalysts.…”

Recent Developments in Microwave-Assisted Metal-Catalyzed C–H Functionalization of Heteroarenes for Medicinal Chemistry and Material Applications

“…The stepwise methodology was successfully expanded to quinaldic acid N-oxide for the synthesis of the corresponding C-8-arylated compound 36 (Scheme 19), without the presence of a competitive decarboxylative cross-coupling reaction. 37…”