Chemoselective synthesis of quinoline N‐oxides from 3‐(2‐nitrophenyl)‐3‐hydroxypropanones

Abstract

The reaction of 3-(2-nitrophenyl)-3-hydroxypropanones with Zn/NH 4 Cl gave the corresponding quinoline N-oxides in 80-90% yields. The reaction initiated the reduction of nitro group to afford the corresponding hydroxylamine, which intramolecularly condensed and followed by dehydration to give quinoline N-oxide. Although treatment of 2-nitrochalcone with Zn/NH 4 Cl in EtOH/H 2 O resulted in the formation of quinoline N-oxide in low yield, the reaction of 2-nitrochalcone with Sn/NH 4 Cl in refluxing EtOH/H 2 O afforded quinoline N-oxide in 80% yield.

Diversely Substituted Quinolines via Rhodium-Catalyzed Alkyne Hydroacylation

“…To address this issue we were attracted to the use of o -alkynyl nitro arenes as substrates. The resultant nitro-substituted chalcones are known precursors to quinolines as well as quinoline N -oxides . Pleasingly, both the parent arene and an OMe-variant underwent coupling with aldehyde 2a in 15 min using only 2 mol % catalyst (Scheme ).…”

Visible-Light-Promoted C2 Selective Arylation of Quinoline and Pyridine N-Oxides with Diaryliodonium Tetrafluoroborate

“…3-bromo-2-phenylquinoline N -oxide, 26.7 mg, yield 89%, white solid; 1 H NMR (400 MHz, CDCl 3 ) δ 8.70 (d, J = 8.7 Hz, 1H), 8.08 (s, 1H), 7.81–7.74 (m, 2H), 7.68–7.64 (m, 1H), 7.58–7.47 (m, 5H); 13 C­{ 1 H} NMR (151 MHz, CDCl 3 ) δ 146.3, 141.3, 133.3, 130.6, 129.4, 129.4, 129.3, 129.2, 128.6, 128.2, 127.1, 120.5, 117.2; HRMS (ESI) m / z calcd for C 15 H 11 BrNO + [M + H] + 300.0024, found 300.0023.…”

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

“…2 b : Yellow solid; yield: 52 % (12 mg); m.p. 122–125 °C (lit 127–128 °C); 1 H NMR (400 MHz, CDCl 3 ): δ =2.43 (s, 3 H), 7.33 (d, J =8.1 Hz, 2 H), 7.51 (d, J =8.8 Hz, 1 H), 7.63 (td, J =8.1, 0.9 Hz, 1 H), 7.75 (d, J =8.8 Hz, 1 H), 7.76 −7.81 (m, 1 H), 7.86 (d, J =8.1 Hz, 1 H), 7.90 (d, J =8.1 Hz, 2 H), 8.85 ppm (d, J =8.8 Hz, 1 H); 13 C NMR (100 MHz, CDCl 3 ): δ =21.6, 120.3, 123.4, 125.3, 128.0, 128.4, 129.1, 129.5, 129.6, 130.6, 130.7, 139.8, 142.4, 145.2 ppm; HRMS (ESI): m / z : calcd for C 16 H 13 NNaO: 258.0889 [ M +Na + ]; found: 258.0889.…”

“…2 j : Brownish white solid; yield: 79 % (21 mg); m.p. 164–168 °C (lit 168–169 °C); 1 H NMR (400 MHz, CDCl 3 ): δ =7.42–7.54 (m, 4 H), 7.60–7.63 (m, 2 H), 7.70 (t, J =7.6 Hz, 1 H), 7.80–7.84 (m, 2 H), 7.94 (dd, J =7.6, 3.6 Hz, 2 H), 8.00 (dd, J =6.0, 3.6 Hz, 1 H), 8.88 ppm (d, J =8.7 Hz, 1 H); 13 C NMR (100 MHz, CDCl 3 ): δ =120.6, 124.7, 125.0, 125.5, 125.6, 126.4, 127.0, 127.9, 128.3, 128.8, 128.8, 130.2, 130.3, 130.8, 131.0, 132.3, 133.7, 142.4, 145.9 ppm; HRMS (ESI): m / z : calcd for C 19 H 14 NO: 272.1070 [ M +H + ]; found: 272.1065.…”

“…[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. This encouraged us to develop as imple and convenient method fort he synthesis of quinoline N-oxides under mild conditions of temperature (room temperature), pressure (atmospheric pressure), and low catalystl oading.…”