Full Papers
doi.org/10.1002/ejoc.202100420
gel (100–200 mesh) or neutral alumina. Analytical grade solvents
for the column chromatography were used as received.
General procedure for the synthesis of alkenylazaarenes (3aa–3az
and 3ba, 3ca, 3do, 3fa, 7aa–7fa) as exemplified for 3ah.
Method A. To a two way 50 mL round-bottom flask equipped with a
stirring bar and condenser (attached with an air balloon on the top)
was added 2-methylquinoline 1a (0.20 g, 1.40 mmol), (4-tolyl)
methanol 2h (0.20 g, 1.68 mmol), and CsOH.H2O (0.21 g,
°
1.39 mmol) in toluene (3 mL) and the mixture was heated at 110 C
Scheme 6. Reaction with secondary alcohol.
under stirring. The reaction was continued for 24 h and on
completion (as monitored by TLC), the solvent was removed
completely under the reduced pressure. The residue thus obtained
was triturated with H2O (10 mL) to furnish 3ah as a yellow solid
product that was filtered and dried in vacuum.
quinolone 16 in 32% yield together with the recovery of
starting material (58%) (Scheme 7).[19]
Method B. For the products where solid was not obtained, the
residue was extracted with H2O (25 mL) and EtOAc (3×20 mL). The
combined organic layers was washed with brine (20 mL), dried over
anhydrous Na2SO4, filtered and evaporated to furnish the crude
product. Purification by silica gel column chromatography using
hexanes/ EtOAc (9:1, v/v) as the eluent, to yield the product.
Conclusion
In summary, we have developed a base-mediated facile,
practical and atom-efficient method for preparing the alkenyl
azaarenes and 2-aminoquinolines utilizing (substitutedaryl)
methanols or substituted (2-aminophenyl)methanols, respec-
tively. The protocol scores over the reported methodologies as
it does not requires the use of a metal catalyst or ligand and is
tenable in the presence of air only. Comparatively, the
CsOH.H2O was found more efficient than KOH, speculatively
due to Cesium effect.[20] This method tolerates wide range
methyl azaarenes and arylmethanols. The protocol was success-
fully extended for the synthesis of 2-aminoquinolines from (2-
aminophenyl)methanol and phenylacetonitriles via aerobic
oxidative cyclocondensation.
General procedure for the synthesis of 2-Styrylquinoxalines (5a–5z)
as exemplified by the synthesis of 5a.
To a round-bottom flask fitted with condenser (having an air
balloon) was added 2-methyl quinoxaline 4 (0.20 g, 1.39 mmol),
phenyl methanol 2a (0.18 g, 1.66 mmol), and CsOH. H2O (0.21 g,
°
1.39 mmol) in toluene (3 mL) was heated at 100 C. The reaction
progress was monitored by TLC. After completion, the solvent was
removed under vacuum and the residue was directly adsorbed on
silica. Purification by column chromatography on silica gel using
hexanes/ EtOAc (9:1, v/v) as eluent afforded the product 5a.
General procedure for the synthesis of 3-Phenylquinolin-2-amines
(10aa–10am, 10ba–10bk, 10ca–10ha, 14) as exemplified for
10aa.
A round-bottom flask equipped with a stirring bar, condenser
(attached with an air balloon on the top) was charged with 2-
(aminophenyl)methanol 8a (0.20 g, 1.62 mmol), phenylacetonitrile
9a (0.23 g, 1.94 mmol), and the base (CsOH.H2O: 0.24 g or KOH:
Experimental Section
General Information- Unless otherwise stated, all reactions were
performed in non-dry glassware under an air atmosphere and were
monitored by analytical thin layer chromatography (TLC). TLC was
performed on pre-coated silica gel plates. After elution, plate was
visualized under UV illumination at 254 nm for UV active materials.
Further visualization was achieved either via Iodine or KMnO4
solution. The melting points were recorded on a hot stage
apparatus and are uncorrected. IR spectra were recorded using a
FTIR spectrophotometer. 1H NMR and 13C NMR spectra were
recorded on 400 or 500 MHz NMR spectrometers with CDCl3 or
DMSO-d6 as solvent, using TMS as an internal standard (chemical
°
0.090 g, 1.62 mmol) in toluene (6 mL) and heated at 90 C for 24 h
under vigorous stirring. On completion, the solvent was removed
from the reaction mixture and the residue was directly adsorbed on
neutral alumina for column chromatography. Purification using
hexanes/ EtOAc (7:3, v/v) as eluent afforded the product 10aa as a
white solid.
Acknowledgements
1
shifts in δ). Peak multiplicities of H-NMR signals were designated
as s (singlet), brs (broad singlet), d (doublet), dd (doublet of
The authors DJD and AG gratefully acknowledge the financial
support from CSIR, New Delhi, in the form of fellowships. The
authors acknowledge the SAIF, CDRI for providing the spectro-
scopic data. This is CDRI Communication no 10233.
doublet),
t (triplet), q (quartet), m (multiplet) etc. Coupling
constants (J) are in Hz. The ESI-MS and HRMS were recorded on
triple quadrupole Mass spectrometer and orbitrap velos pro mass
spectrometer. Column chromatography was performed using silica
Conflict of Interest
The authors declare no conflict of interest.
Scheme 7. Utility of 2-aminoquinoline.
Eur. J. Org. Chem. 2021, 2746–2751
2750
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