Metal-Free and Visible-Light-Promoted C-3 Thiocyanation of 2-Arylquinolin-4-ones

Article abstract of DOI:10.1002/ejoc.201900349

A C-3 thiocyanation of 2-aryl-quinolin-4-ones in the presence of eosin-Y and visible light has been developed. The methodology allows easy access to a variety of 2-aryl-3-thiocyano-quinolin-4-ones in moderate to high yields. Regioselective para-thiocyanat

Full text of DOI:10.1002/ejoc.201900349

A Journal of
Accepted Article
Title: Metal-free and visible light promoted C-3 thiocyanation of 2-
arylquinolin-4-ones
Authors: Parul Chauhan, Ritu Ritu, Preeti Preeti, Sharvan Kumar, and
Nidhi Jain
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201900349
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10.1002/ejoc.201900349
European Journal of Organic Chemistry
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Metal-free and visible light promoted C-3 thiocyanation of 2-
arylquinolin-4-ones
ParulChauhan,[a] Ritu,[a] Preeti,[a] Sharvan Kumar[a] and Nidhi Jain*[a]
Abstract:A C-3 thiocyanation of 2-aryl-quinolin-4-ones in the
presence of eosin-Y and visible light has been developed. The
methodology allows easy access to a variety of 2-aryl-3-thiocyano-
quinolin-4-ones in moderate to high yields. Regioselectivepara-
thiocyanation of anilines has also been achieved under these
conditions. The reaction is operationally simple, metal-free, requires
air as the oxidant, and proceeds smoothly at room temperature.
photocatalysts.12While Li and co-workers showed
a C-3
thiocyanation of indolesusing rose Bengal.13Hazra and co-
workers demonstrated it on imidazopyridines using eosin-
Y14(Scheme 1).
Introduction
Visible light mediated photocatalysis has emerged as a powerful
tool in organic synthesis, and has opened up new avenues for
medicinal and synthetic chemists.1 Organic dyes such as eosin-
Y and Rose Bengal absorb visible light, and utilize the collected
energy for in situ radical generation and initiating chemical
reactions.2In recent past, eosin-Y has been explored in a variety
of photoredox functionalizations3such as arylation, alkoxylation,
Scheme 1 Visible light mediated thiocyanation of heteroaromatics
2-arylquinolin-4-ones are
a privileged heterocyclic scaffold
ubiquitously found in natural products and pharmaceutical
drugs.15 They possess a broad range of biological activities such
as antimalarial, anticancer, antibacterial, anti-HIV, antioxidant,
and act as xanthine oxidase inhibitors16 (Figure 1).They are also
used in the treatment of various diseases such asurinary tract
infections and pyelonephritis, chronic bronchitis, prostatitis,
pneumonia, and pelvic infections.17
acylation,
trifluoromethylation,
vinylation,
sulfonylation,
phosphenylation, formylation, cascade reaction,4coupling
reaction,5 and scaffold formation.6Sinceeosin-Y is inexpensive,
lesstoxic, easily available, and has strong absorption in the
visible part of the spectrum with feasible redox potential values
for a variety of organic substrates; itis a useful and attractive
photocatalyst in organic synthesis.7
Thiocyano is an important functionality widely found in natural
products; responsible for the diverse pharmacological activities
of
these
compounds
including
antimicrobial
and
antiproliferative.8It is a valuable building block that provides
access to varioussulphur containing scaffolds through synthetic
manipulations.9Overthe past several years, numerous metal-free
and metal-catalyzedapproaches have been developed for the
thiocyanation of aryls and heteroaryls.
Figure 1 Biologically active 2-aryl quinolin-4-ones.
Introduction of thiocyano group into biologically active
heterocycles is less explored, though it appears to hold
immense potential in enhancing their biological properties and
activity. To the best of our knowledge, there is no report on the
thiocyanation of 2-aryl quinolin-4-ones. Challenged by these
limited findings, and continuing our efforts towards C-H
functionalization of biologically useful heterocycles,18we
embarked upon the synthesis of thiocyanatedquinolinones under
photoredox conditions.
Metal-freemethods involve the use of thiocyanate salts in
presence of oxidants10 such as DDQ (2,3-dichloro-5,6-dicyano-
1,4-benzoquinone), K2S2O8 (potassium peroxydisulphate),
selectfluor, CAN (Ceric ammonium nitrate) etc.while the metal-
catalyzed methods11 have been reported with copper and
palladium salts. Recently, there have been a few reports on
visible light mediatedthiocyanation of heterocycles using various
[a]
Dr.Parul Chauhan, Ritu, Preeti, Dr. Shravan Kumar, Prof.Dr.
Nidhi Jain
Department of Chemistry
Results and Discussion
Indian Institute of Technology,New Delhi-110016
Email: njain@chemistry.iitd.ac.in
Homepage: http://chemistry.iitd.ac.in/faculty/jain.html
Our work commenced by investigating the thiocyanation of 2-
phenylquinolin-4-one (1a) with 2 equiv. of NH4SCN using eosin-
Y (5 mol%) as photocatalyst in DMSO under blue LED and open
Supporting information for this article is given via a link at the end of
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10.1002/ejoc.201900349
European Journal of Organic Chemistry
FULL PAPER
air. As desired, thiocyanation took place at the third position, and
after 12 h, 2-phenyl-3-thiocyanatoquinolin-4(1H)-one (2a)was
formed in 76% yield (Table 1, entry 1). Changing the solvent to
acetonitrile turned out to be favourable, and increased the yield
to 91% (Table 1, entry 2). Encouraged by this initial success, we
decided to optimize the reaction conditions further.The amount
of eosin-Y was varied from 1 to 10 mol% (Table 1, entry2
and3).It was found that 5 mol% eosin-Y worked best for the
reaction (Table 1, entry 2) and enabled a 100% conversion.
Reducing the reaction time to 6 h resulted in incomplete
conversion (52% yield) while increasing it to 18 h had no effect
(Table 1, entry 4). Various solvents such as DMA, Toluene,
DCM, DMF, Methanol and THF were screened (Table 1, entries
5-10) but none was found better than CH3CN. Other
with O2 (balloon) did not bring about much change, and 2a was
obtained in 92% yield (Table 1, entry 16). Changing to KSCN
proved detrimental and yield got reduced to 25% only (Table 1,
entry 17).
With the best optimized reaction conditions using 2 equiv.
NH4SCN and 5 mol% eosin-Y in CH3CN under blue LED in
ambient air; the generality of this method was tested further.
Various substituents were taken on phenyl ring of 2-arylquinolin-
4-one (Table 2). Electron-donating methyl and methoxy groups
at para-position of 2-phenyl ring afforded the C-3 thiocyanated
products, 2b and 2c in 78% and 81% yields respectively. The 4-
benzyloxy and 4-phenyl substituted derivatives gave lower yield
of the corresponding products (2d and 2e) probably due to steric
effects. The 4-halo substituted derivatives (Br, Cl and F)
furnished products 2f-2h in 82-94% yields. However, changing
the position of halo- substituent on phenyl ring from para-to
meta- lowered the product yield (Table 2, 2i-2k) indicating a
position dependent substituent effect. Further, 2-aryl ring
substituted with dimethoxy, ethoxymethoxy, bromomethoxy and
trimethoxy substituents also underwent a facile reaction, and
afforded 2l-2o in 83-88% yields.
photocatalysts
such
as
Ru(bpy)3Cl2.6H2O
and
[Ir{dF(CF3)ppy}2(dtbpy)]PF6were also tested but lower product
yields were obtained in either case due to formation of
unidentified side products (Table 1, entries 11 and 12).
Table 1. Optimization of reaction condition. [a]
Notably, the reaction was facile with C2-H quinolone and 2-
methylsubstituted derivative yielding the desired products 2p
and 2qin 85% and 62%respectively.However, substitution with
methyl ester group at 2-position jeopardized the reaction, and
only 24%yield of the product was obtained(Table 2, entry
2r).Presence of phenyl, methyl and hydrogen at 2-position
stabilized the radical intermediates while the stability was
majorly compromised in the presence ofester group.
Further,with substituents on quinolone core, very poor yield of
thiocyanated products was obtained.Quinoline ringsubstituted
with6,7-methylenedioxy and 8 methyl group gave2s and 2tin 10
and 21% yields respectively while with 6-methoxy substitution,
no thiocyanated product was obtained(Table 2, entry 2u).
Entry
Catalyst
Solvent
Yield[b](%)
1
2
eosin-Y
DMSO
CH3CN
CH3CN
CH3CN
DMA
76
eosin-Y
91
3
eosin-Y
32c,48d, 90e
52f, 90g
51
4
eosin-Y
5
eosin-Y
6
eosin-Y
Toluene
DCM
Trace
Trace
30
Table 2 Scope for C-3 thiocyanation of quinolin-4-onesa
7
eosin-Y
8
eosin-Y
DMF
9
eosin-Y
Methanol
THF
Trace
10
10
11
12
13
14h
15i
16j
17k
eosin-Y
Ru(bpy)3Cl2·6H2O
[Ir{dF(CF3)ppy}2(dtbpy)]PF6
-
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
55
62
n.r.
eosin-Y
Trace
n.r.
eosin-Y
eosin-Y
92
eosin-Y
25
[a] Reaction condition: 1a (0.5 mmol), NH4SCN (1.0 mmol, 2.0 equiv.), eosin-Y
(5 mol%), solvent (2 mL), blue LED (10 W), rt, 12 h, air, [b] Isolated yield, [c] 1
mol% eosin-Y, [d] 2 mol% eosin-Y, [e] 10 mol% eosin-Y, [f] reaction after 6 h,
[g] after 18 h, [h] degassed with nitrogen, In dark, [i] junder O2 (balloon), [k]
with KSCN.
aReaction condition: 1 (0.5mmol), NH4SCN (1.0 mmol), Eosin-Y (5 mol%),
CH3CN (2 mL), blue LED, rt, 12 h, air
Control reactions in the absence of photocatalyst, light or air did
not yield any product (Table 1, entries 13-15) indicating that all
these components were critical for the reaction. Replacing air
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10.1002/ejoc.201900349
European Journal of Organic Chemistry
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Next, the present methodology was also tested with some
biologically active heterocycles such as coumarin, uracil and
indazole, no thiocyanated product was observed which clearly
indicate that the present methodology is only selective for
quinolones.We further wished to explore this methodology with
aryl amines as substrates (Table 3). Literature search revealed
that para-selective C-H thiocyanation of arylamineshas been
accomplished under metal free conditions using salts of
thiocyanate in presence of oxidants such as CAN, K2S2O8, DDQ,
H2O2,19 as well as by metal (Fe, Mn, and Cu) assisted
catalysis.11c,20 On applying the optimized reaction condition to
aniline (3a), we observed that thiocyanation occurred exclusively
at its para-position (4a) though the reaction took longer time to
complete (24 h). The conditions were compatible both with
electron donating and electron-withdrawing groups at ortho- and
meta-positions of aniline (Table 3, 4b-4h). While moderate
product yields were obtained in most cases, the reaction failed
with meta-nitro aniline probably due to the strong electron-
withdrawing effect of nitro group (Table 3, 4i). With meta-
dichloroaniline, the para-thiocyanate product, 4j was formed in
48% yield.The reaction of para-chloro aniline with ammonium
thiocyanate was tried under the optimized condition. However,
no ortho-thiocyanated product was formed, and the starting
material was recovered as such demonstrating high para-
selectivity. Similar regioselectivity at the para-position has been
reported earlier.21
existence of quinolone radical; the intensity of which increased
with time up to 6h.
Scheme 2. Control experiments.
Based on previous literature13,14,22 and experimental results, a
plausible mechanism has been proposed in scheme 3. Initially,
an in situ generation of
anion takes place via single electron transfer between EY* (Ered
0.83 V) and SCN
(Eox=0.62V)inthe presence of blue light. A
·SCN radical (A) and EY·- radical
=
-
undergoes radical addition at the C2-C3 double bond of 1 to
generate another radical intermediate B. Oxidation of
intermediate B in the presence of oxygen gives the cationic
intermediateCwhich undergoes deprotonation to give product
2(Scheme 3).
Table 3 Scope with arylaminesa
[a] Reaction condition: 3 (1.0 mmol), NH4SCN (2.0 mmol), Eosin-Y (5 mol%),
CH3CN (2 mL), blue LED, rt, 24 h, air.
To examine the involvement of free-radical species in the
reaction, quenching studies were carried out. Addition of
TEMPO
(2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl
to the
Scheme 3 Plausible mechanism
reaction mixture lowered the yield of the thiocyanated product,
2a in a dose dependent manner. A similar observation was
made with 3a as the substrate (Scheme 2 (i)). The (M+H)+ peak
due to quinolonyl-TEMPO adduct at 363.2451 was seen in the Conclusions
mass spectrum of the reaction mixture (Scheme 2 (ii)). The data
In summary, we report the synthesis of C-3 thiocyanated 2-arylquinolin-
confirmed the reaction to follow a light mediated radical pathway,
and no product formation was seen in dark. The EPR spectra of
the reaction mixture taken at different time intervals exhibited
EPR signal at room temperature with a g value of 2.0040, and a
line width of ∆H = 4.1 G (Scheme 2 (iii)). This g value is
significantly higher than that of a free radical (g = 2.0023), and
suggested a spin orbit coupling with the adjacent 14N nucleus.
Although we could not observe hyperfine splitting due to
presence of oxygen, yet sufficient lifetime of the radical at room
temperature and its g value suggested that the radical species
might be quinolone radical. Further, a time dependent increase
in the intensity of EPR signal from 3 h to 6 h, and then a
decrease in its intensity from 6 h to 9 h also pointed towards the
4(1H)-onesfor the first time. This has been achieved viaphotoredox
reaction using an inexpensive photocatalysteosin-Y, and air as the
terminal oxidant. The methodology allows an efficient, facile, and
regioselective C-3 thiocyanation of 2-arylquinolin-4-ones and para-
thiocyanation of arylamines in good to excellent yields.The reaction is
mild, operationally simple, metal-free and proceeds smoothly under
ambient air and moisture. The 3-thiocyanated quinolone derivatives are
expected to have potent biological activity, and might find useful
application in medicinal chemistry. They may also serve as valuable
building blocks to access other potent molecules after further
transformations.
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10.1002/ejoc.201900349
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d6) δ 5.25 (s,2H), 7.25 (d, J = 8.56 Hz, 2H), 7.34-7.51 (m,6H), 7.62 (d, J =
8.52 Hz, 2H), 7.70 (d, J = 8.2 Hz, 1H), 7.77 (t, J = 6.96 Hz, 1H), 8.19 (d, J
= 8.08 Hz, 1H), 12.50 (s,1H); 13C NMR: (100 MHz, DMSO-d6) δ 69.8
(OCH2), 101.5 (C), 112.3 (C), 115.2 (2×CH), 119.3 (CH), 124.1 (C),
125.5 (CH), 125.7 (CH), 126.4 (C), 128.2 (2×CH), 128.4 (CH), 129.0
(2×CH), 131.2 (2×CH), 133.4 (CH), 137.1 (C), 139.6 (C), 156.1 (C),
160.3 (C), 174.0 (C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd for
C23H16N2NaO2S 407.0825; Found 407.0824.
Experimental Section
1H NMR and 13C NMR spectra were recorded on a 300 MHz (1H
400MHz,13C 75 and 100 MHz) and 400 MHz spectrometer (1H 400 MHz)
using CDCl3 as the solvent andtetramethylsilane (TMS) as the internal
standard at room temperature. Chemical shifts are in δ (ppm) relative to
TMS. Coupling constants (J) are in Hz and splitting patterns are
described as singlet (s), doublet (d), triplet (t), multiplet (m) and broad
(br). Melting points were determined on melting point apparatus and are
uncorrected. High resolution mass spectra (HRMS) were recorded on a
mass spectrometer using electrospray ionization-time-of-flight (ESI-TOF)
reflectron experiments. Reactions were monitored on silica gel TLC
plates (coated with TLC grade silica gel, obtained from Merck). All glass
apparatus was oven dried prior to use. Column chromatography was
performed over silica gel (100-230Mesh) by using glass column. Electron
Paramagnetic Resonance (EPR) spectra were recorded using Bruker
EMX 1444 EPR spectrometer operating at 9.455 GHz.
Diphenylpicrylhydrazyl, DPPH (g = 2.0037) was used for the calibration
of spectrometer. The samples were prepared by taking supernatant
solution from the crude reaction mixture at reported time under inert
atmosphere.All chemicals and reagents were obtained from Aldrich
(USA) and Alfa Aesar (England) and were used without further
purification.
2-([1,1'-biphenyl]-4-yl)-3-thiocyanatoquinolin-4(1H)-one
(2e):Light
pink, Hexane/EtOAc = 77/25, yield 62% (110 mg), mp 200-204°C;FT-IR
(KBr cm-1) 3439, 2151, 1624;1H NMR: (400 MHz, DMSO-d6) δ 7.43-7.56
(m, 4H), 7.71-7.81 (m, 6H), 7.94 (d, J = 8.24 Hz, 2H), 8.22 (d, J = 8.0 Hz,
1H), 12.66(s,1H); 13C NMR: (100 MHz, DMSO-d6) δ 101.7 (C), 112.2 (C),
119.4 (CH), 124.2 (CH), 125.5 (C), 125.8 (CH), 127.2 (2×CH), 127.4
(2×CH), 128.6 (C), 129.6 (2×CH), 130.1 (2×CH), 133.1 (CH), 133.5 (CH),
139.5 (C), 139.7 (C), 142.7 (C), 156.0 (C), 174.0 (C).HRMS (ESI/TOF-Q)
m/z: [M+Na]+Calcd for C22H14N2NaOS 377.0719; Found 377.0716.
2-(4-bromophenyl)-3-thiocyanatoquinolin-4(1H)-one (2f):White solid,
Hexane/EtOAc = 70/30,yield 82% (146 mg), mp 190-194°C;FT-IR (KBr
cm-1) 3443, 2159, 1605;1H NMR: (400 MHz, DMSO-d6) δ 7.50 (t, J = 7.16
Hz, 1H), 7.64-7.69 (m, 3H), 7.78 (d, J = 6.88 Hz, 1H), 7.86 (d, J = 7.72
Hz, 2H), 8.20 (d, J = 7.68 Hz, 1H), 12.65 (s, 1H); 13C NMR: (100 MHz,
DMSO-d6) δ106.6 (C), 116.88 (C), 124.2 (CH), 129 (CH), 129.4 (C),
130.4 (CH), 130.5 (C), 136.3 (2×CH), 136.8 (2×CH), 137.9 (CH), 138.3
(C), 144.4 (C), 160.0 (C), 178.7(C).HRMS (ESI/TOF-Q) m/z:
[M+Na]+Calcd for C16H9BrN2NaOS 378.9511; Found 378.9505.
Representative procedure for the synthesis of product 2:A solution
of 2-phenylquinolin-4(1H)-one(1a) (110 mg, 0.5mmol), ammonium
thiocyanate (76 mg, 1.0mmol), and Eosin-Y (16 mg, 5 mol%) were taken
in acetonitrile (2 mL) and stirred under blue LED at RT for 12 h. The
reaction was diluted with water (60 mL), and the aqueous layer was
extracted with ethylacetate (2 × 15 mL). The organic layer was dried over
sodium sulphate (anhydrous) and evaporatedunder reduced pressure to
give the desired product 2a in 91% yield after column chromatography.
2-(4-chlorophenyl)-3-thiocyanatoquinolin-4(1H)-one (2g):White solid,
Hexane/EtOAc = 70/30,yield 94% (146 mg), mp 169-174°C;FT-IR (KBr
cm-1) 3432, 2253, 1652;1H NMR: (400 MHz, DMSO-d6) δ 7.50 (t, J = 7.4
Hz, 1H), 7.68-7.72 (m, 5H), 7.79 (t, J = 7.12 Hz, 1H), 8.20 (d, J = 7.88 Hz,
1H), 12.63 (s, 1H); 13C NMR: (100 MHz, DMSO-d6) δ 101.9 (C), 112.1
(C), 119.4 (CH), 124.3 (C), 125.6 (CH), 125.7 (CH), 129.1 (2×CH), 131.4
(2×CH), 132.8 (C), 133.5 (CH), 135.8 (C), 139.6 (C), 155.2 (C), 173.9
(C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd for C16H9ClN2NaOS
335.0016 ; Found 335.0003.
2-phenyl-3-thiocyanatoquinolin-4(1H)-one
(2a):White
solid,
Hexane/EtOAc = 70/30, yield 91% (126 mg), mp 176-178°C;FT-IR (KBr
cm-1) 3443, 2149, 1626;1H NMR: (400 MHz, DMSO-d6) δ 7.49(t, J= 7.32
Hz, 1H), 7.65-7.68(m,5H), 7.71(d, J=8.2Hz, 1H), 7.79(t, J= 7.44 Hz, 1H),
8.21(d, J=8.0Hz, 1H), 12.62(s,1H); 13C NMR: (100 MHz, DMSO-d6)
δ101.7 (C), 112.2 (C), 119.4 (CH), 124.2 (C), 125.5 (CH), 125.7 (C),
129.0 (2×CH), 129.4 (2×CH), 131.0 (CH), 133.5 (CH), 134.1 (C), 139.6
(C), 156.3 (C), 174.0 (C). HRMS (ESI/TOF-Q) m/z: [M+H]+Calcd for
C16H11N2OS 279.0587 ; Found 279.0576.
2-(4-fluorophenyl)-3-thiocyanatoquinolin-4(1H)-one (2h):White solid,
Hexane/EtOAc = 70/30,yield 86% (127 mg), mp 202-208°C;FT-IR (KBr
cm-1) 3434, 2158, 1605;1H NMR: (400 MHz, DMSO-d6) δ 7.50 (s, 3H),
7.69-7.78 (m, 4H), 8.20 (d, J = 7.36 Hz, 1H), 12.63 (s, 1H); 13C NMR:
(100 MHz, DMSO-d6) δ 102.0 (C), 112.1 (C), 116.2 (d, J = 21.8 Hz,
2×CH), 119.4 (CH), 124.2 (C), 125.7 (d, J = 17.53 Hz, 2×CH), 130.5 (d, J
= 3.12 Hz, C), 132.1 (d, J = 8.79 Hz, 2×CH), 133.5 (CH), 139.6 (C), 155.4
(C), 164.9 (d, J = 246.8 Hz, C-F), 174.0 (C).HRMS (ESI/TOF-Q) m/z:
[M+Na]+Calcd for C16H9FN2NaOS 319.0312; Found 319.0307.
3-thiocyanato-2-(p-tolyl)quinolin-4(1H)-one
(2b):Pink
solid,
Hexane/EtOAc = 70/30, yield 78% (114 mg),mp 184-186°C;FT-IR (KBr
cm-1) 3430, 2254, 1651;1H NMR: (400 MHz, DMSO-d6) δ 2.44 (s, 3H),
7.43-7.50 (m, 3H), 7.55 (d, J = 7.52 Hz, 2H), 7.71 (d, J = 7.92 Hz, 1H),
7.76 (d, J = 6.92 Hz, 1H), 8.19 (d, J = 7.68 Hz, 1H), 12.55 (s, 1H): 13C
NMR: (100 MHz, DMSO-d6) δ 21.4 (CH3), 101.6 (C), 112.2 (C), 119.4
(CH), 124.2 (C), 125.5 (CH), 125.7 (CH), 129.3 (2×CH), 129.5 (2×CH),
131.3 (C), 133.4 (CH), 139.6 (C), 140.9 (C), 156.4 (C), 174.0 (C). HRMS
(ESI/TOF-Q) m/z: [M+H]+Calcd for C17H13N2OS 293.0743; Found
293.0744.
2-(3-bromophenyl)-3-thiocyanatoquinolin-4(1H)-one (2i):Light pink
solid, Hexane/EtOAc = 70/30, yield 72% (128 mg), mp 185-189°C;FT-IR
(KBr cm-1) 3437, 2159, 1602;1H NMR: (400 MHz, DMSO-d6) δ 7.51 (t, J =
7.12 Hz, 1H), 7.60 (t, J = 7.84 Hz, 1H), 7.68-7.70 (m, 2H), 7.77-7.81 (m,
1H), 7.86 (d, J = 8.04 Hz, 1H), 7.95 (s,1H), 8.19-8.21 (dd, J = 8.08 Hz,
1H), 12.66 (s,1H); 13C NMR: (100 MHz, DMSO-d6) 101.9 (C), 112.1 (C),
119.4 (CH), 124.3 (C), 125.7 (CH), 125.7 (CH), 128.3 (CH), 129.2 (CH),
130.9 (CH), 131.0 (CH), 133.6 (CH), 133.6 (CH), 135.9 (C), 139.6 (C),
154.8 (C), 173.9 (C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd for
C16H9BrN2NaOS 378.9511; Found 378.9504.
2-(4-methoxyphenyl)-3-thiocyanatoquinolin-4(1H)-one (2c):Light pink
solid, Hexane/EtOAc = 67/33, yield 81% (125 mg), mp 174-178°C;FT-IR
(KBr cm-1) 3434, 2255, 1642;1H NMR: (400 MHz, DMSO-d6) δ 3.88
(s,1H), 7.19 (d, J = 8.56 Hz, 2H), 7.49 (t, J = 7.0 Hz, 1H), 7.63 (d, J =
8.52 Hz, 2H), 7.72 (d, J = 8.08, 1H), 7.78 (t, J = 7.0 Hz, 1H), 8.19 (d, J =
7.84 Hz, 1H), 12.52 (s,1H); 13C NMR: (100 MHz, DMSO-d6) δ 55.9
(OCH3), 101.61 (C), 112.3 (C), 114.4 (2×CH), 119.4 (CH), 124.1 (C),
125.4 (CH), 125.7 (CH), 126.2 (C), 131.2 (2×CH), 133.4 (CH), 139.6 (C),
156.1 (C), 161.4 (C), 174.0 (C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd
for C17H12N2NaO2S 331.0512; Found 331.0506.
2-(3-chlorophenyl)-3-thiocyanatoquinolin-4(1H)-one (2j):Light pink
solid, Hexane/EtOAc = 70/30, yield 65% (101 mg), mp 172-176°C;FT-IR
(KBr cm-1) 3432, 2254, 1651;1H NMR: (400 MHz, DMSO-d6) δ 7.51 (t, J =
7.52 Hz, 1H), 7.66-7.70 (m, 4H), 7.77-7.83 (m, 2H), 8.20 (d, J = 7.76 Hz,
1H), 12.67 (s, 1H); 13C NMR: (100 MHz, DMSO-d6) δ 101.9 (C), 112.11
(C), 119.5 (CH), 124.3 (C), 125.6 (CH), 125.7 (CH), 128.3 (CH), 129.2
(CH), 130.8 (CH), 133.5 (CH), 133.6 (C), 135.9 (C), 139.6 (C), 154.8 (C),
2-(4-(benzyloxy)phenyl)-3-thiocyanatoquinolin-4(1H)-one (2d):Light
pink solid, Hexane/EtOAc = 70/30, yield 68% (131 mg), mp 205-
208°C;FT-IR (KBr cm-1) 3436, 2152, 1640;1H NMR: (400 MHz, DMSO-
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10.1002/ejoc.201900349
European Journal of Organic Chemistry
FULL PAPER
173.9 (C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd for C16H9ClN2NaOS
2-methyl-3-thiocyanatoquinolin-4(1H)-one (2q): Light pink solid,
Hexane/EtOAc = 70/30, yield 62% (67 mg), mp 172-175°C; FT-IR (KBr
cm-1) 3437, 2156, 1630; 1H NMR: (400 MHz, DMSO-d6) δ 2.68 (s, 3H),
7.43 (t, J = 7.12 Hz, 1H), 7.58 (d, J = 8.24 Hz, 1H), 7.72-7.76 (m, 1H),
8.12 (d, J = 8.04 Hz, 1H), 12.42 (s, 1H); 13C NMR: (100 MHz, DMSO-d6)
δ 20.5 (CH3), 101.4 (C), 112.2 (C), 118.7 (CH), 124.0 (C), 125.2 (CH),
125.8 (CH), 133.3 (C), 139.3 (C), 155.8 (C), 173.6 (C). HRMS (ESI/TOF-
Q) m/z: [M+H]+Calcd for C11H8N2NaOS 239.0250; Found 239.0247.
335.0016; Found 335.0016.
2-(3-fluorophenyl)-3-thiocyanatoquinolin-4(1H)-one (2k):Light pink
solid, Hexane/EtOAc = 70/30, yield 68% (101 mg), mp 186-188°C;FT-IR
(KBr cm-1) 3440, 2154, 1625;1H NMR: (400 MHz, DMSO-d6) δ 7.49-7.54
(s, 3H), 7.63-7.71 (m, 3H), 7.79 (t, J = 7.36 Hz, 1H), 8.21 (d, J = 7.96 Hz,
1H), 12.67 (s, 1H); 13C NMR: (100 MHz, DMSO-d6) δ 101.9 (C), 112.12
(C), 116.8 (d, J = 23.24 Hz, CH), 119.4 (CH), 124.34 (CH), 125.7 (d, J =
9.28 Hz, CH), 125.8 (d, J = 2.89 Hz, CH), 131.3 (d, J = 8.37 Hz, 2×C),
133.5 (CH), 136.0 (d, J = 8.22 Hz, 2), 139.6 (CH), 154.9 (C), 163.3 (d, J
= 243.6 Hz, C-F), 173.9 (C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd for
C16H9FN2NaOS 319.0312; Found 319.0298.
Methyl 4-oxo-3-thiocyanato-1,4-dihydroquinoline-2-carboxylate (2r):
White solid, Hexane/EtOAc = 80/20, yield 24% (31.2 mg),mp 178-180°C;
FT-IR (KBr cm-1) 3430, 2253, 1655; 1H NMR: (500 MHz, DMSO-d6)δ
4.06 (s, 3H), 7.84 (S, 2H), 8.19 ((d, J = 8.15 Hz, 2H)), 13.0 (s, 1H); 13C
NMR: (100 MHz, DMSO-d6 δ 54.6 (CH3), 111.2 (C), 120.0 (C), 121.39
(CH), 124.6 (C), 125.8 (CH), 126.4 (CH), 131.4 (C), 134.1 (CH), 146.5
(C), 161.9 (C),173.4 (C).HRMS (ESI/TOF-Q) m/z: [M+H]+Calcd for
C12H8N2NaO3S 283.0148; Found 283.0153.
2-(3,4-dimethoxyphenyl)-3-thiocyanatoquinolin-4(1H)-one (2l):White
solid, Hexane/EtOAc = 65/35, yield 88% (149 mg), mp 174-179°C;FT-IR
(KBr cm-1) 3429, 2255, 1648;1H NMR: (400 MHz, DMSO-d6) δ3.84
(S,3H), 3,88 (s,3H), 7.22 (s, 2H), 7.32 (s, 1H), 7.49 (t, J = 7.0 Hz, 1H),
7.72 (s,1H), 7.49 (d, J = 8.08 Hz, 1H), 7.72 (d, J = 8.08 Hz, 1H), 7.78 (t, J
= 7.0 Hz, 1H), 8.20 (d, J = 8.0 Hz, 1H), 12.53 (s, 1H); 13C NMR: (100
MHz, DMSO-d6) δ 56.2 (OCH3), 56.2 (OCH3), 101.5 (C), 111.9 (CH),
112.5 (C), 113.2 (CH), 119.4 (CH), 122.4 (CH), 124.1 (C), 125.4 (C),
125.7 (CH), 126.3 (CH), 133.4 (CH), 139.6 (C), 148.8 (C), 150.9 (C),
156.2 (C), 174.0 (C).HRMS (ESI/TOF-Q) m/z: [M+Na]+Calcd for
C18H14N2NaO3S 361.0617; Found 361.0623.
7-thiocyanato-[1,3]dioxolo[4,5-g]quinolin-8(5H)-one (2s): Pink solid,
DCM/Methaol = 98/2, yield 10% (12.3 mg), mp 194-198°C; FT-IR (KBr
cm-1) 3434, 2255, 1642; 1H NMR: (400 MHz, DMSO-d6) δ 6.20 (s,
2H),7.08 (s, 1H), 7.45 (s, 1H), 8.45 (d, J = 5.44 Hz, 1H), 12.50 (s, 1H);
13C NMR: (125 MHz, DMSO-d6) δ 97.7 (CH2), 101.9 (CH), 102.9 (CH),
112.3 (C), 120.6 (C), 137.2 (C), 142.56 (C), 142.62 (C), 146.83 (CH),
152.37 (C), 172.4 (C).HRMS (ESI/TOF-Q) m/ z: [M+H]+Calcd for
C11H6N2NaO3S 268.9992; Found 268.9992.
2-(3-ethoxy-4-methoxyphenyl)-3-thiocyanatoquinolin-4(1H)-one
(2m):White solid, Hexane/EtOAc = 68/32,yield 83% (146 mg), mp 201-
205°C;FT-IR (KBr cm-1) 3430, 2253, 1655;1H NMR: (400 MHz, DMSO-
d6) δ 1.38(t, J=6.84Hz, 3H), 3.84(s, 3H), 4.11-4.16 (q, J = 6.96 Hz, 2H),
7.19 (s,2H), 7.30 (s, 1H), 7.48 (t, J = 7.24 Hz, 1H), 7.72 (d, J = 8.2Hz,
1H), 7.78 (t, J = 7.12 Hz, 1H), 8.19 (d, J = 8.04 Hz, 1H), 12.51 (s, 1H);
13C NMR: (100 MHz, DMSO-d6) δ 15.1 (CH3), 56.2 (OCH3), 64.4 (OCH2),
101.5(C), 112.5 (C), 112.7 (CH), 113.3 (CH), 119.4 (CH), 122.3 (CH),
124.1 (C), 125.4 (C), 125.7 (CH), 126.2 (CH), 133.4 (CH), 139.6 (C),
148.9 (C), 150.2 (C), 156.2 (C), 174.0 (C). HRMS (ESI/TOF-Q) m/z:
[M+Na]+Calcd for C19H16N2NaO3S 375.0774; Found 375.0772.
Methyl
8-methyl-4-oxo-3-thiocyanato-1,4-dihydroquinoline-2-
carboxylate (2t): White solid, Hexane/EtOAc = 80/20, yield21% (28 mg),
mp 165-168°C; FT-IR (KBr cm-1) 3436, 2150, 1630; 1H NMR: (400 MHz,
DMSO-d6) δ 2.75 (s, 3H),4.01 (s, 3H), 7.71-7.74 (m, 2H), 7.91 (s, 1H),
10.11 (s, 1H);13C NMR: (125 MHz, DMSO-d6) δ 18.3 (CH3), 53.7 (CH3),
115.9 (C), 119.1 (CH), 130.2 (CH), 131.2 (CH), 138.6 (2×C), 145.6 (C),
154.4 (C), 163.9 (C), 165.4 (CH), 179.8 (C).HRMS (ESI/TOF-Q) m/z:
[M+H]+Calcd for C13H11N2O3S 275.0485; Found 275.0474.
Representative procedure for the synthesis of product 4:A solution
of aniline 3a (93 mg, 1.0 mmol), ammonium thiocyanate (152 mg,
2.0mmol), and Eosin-Y (16 mg, 5 mol%) were taken in acetonitrile (2 mL)
and stirred under blue LED at RT for 24 h. The reaction was diluted with
water (60 mL), and the aqueous layer was extracted with ethylacetate (2
× 15 mL). The organic layer was dried over sodium sulphate (anhydrous)
and evaporatedunder reduced pressure to give the desired product 4a in
85% yield after column chromatography.
2-(3-bromo-4-methoxyphenyl)-3-thiocyanatoquinolin-4(1H)-one
(2n):White solid, Hexane/EtOAc = 70/30, yield 85% (164 mg), mp 160-
164°C;FT-IR (KBr cm-1) 3432, 2151, 1601;1H NMR: (400 MHz, DMSO-
d6) δ 3.98 (s, 3H), 7.37 (d, J = 8.56 Hz, 1H), 7.50 (t, J = 7.6 Hz, 1H), 7.70
(d, J = 8.36 Hz, 2H), 7.79 (t, J = 1.48 Hz, 1H), 7.98 (d, J = 1.48 Hz, 1H),
8.20 (d, J = 8.0 Hz, 1H), 12.57 (s,1H); 13C NMR: (100 MHz, DMSO-d6) δ
57.1 (OCH3), 101.9 (C), 110.9 (C), 112.2 (C), 112.5 (CH), 119.4 (CH),
124.2 (C), 125.5 (CH), 125.7 (CH), 127.4 (C), 130.8 (CH), 133.4 (CH),
133.8 (CH), 139.6 (C), 154.7 (C), 157.4 (C), 174.0 (C).HRMS (ESI/TOF-
Q) m/z: [M+Na]+Calcd for C17H11BrN2NaO2S 408.9617; Found 408.9601.
4-thiocyanatoaniline (4a)23:Yellow solid, Hexane/EtOAc = 98/2,yield
85% (127 mg), mp 45-48°C;1H NMR: (400 MHz, CDCl3) δ 3.97 (s, 2H),
6.66 (d, J = 8.72 Hz, 2H), 7.35 (d, J = 8.72 Hz, 2H); 13C NMR: (100 MHz,
CDCl3) δ 109.5 (C), 112.4 (C), 116.0 (2×CH), 134.4 (2×CH), 148.8 (C).
3-thiocyanato-2-(3,4,5-trimethoxyphenyl)quinolin-4(1H)-one
2-methyl-4-thiocyanatoaniline (4b)23:Yellow solid, Hexane/EtOAc
=
(2o):Light pink solid, Hexane/EtOAc = 60/40, yield 84% (154 mg), mp
215-223°C;FT-IR (KBr cm-1) 3438, 2154, 1628;1H NMR: (400 MHz,
DMSO-d6) δ 3.77 (s, 3H), 3.86 (s, 6H), 7.04 (s, 2H), 7.50 (t, J = 7.4 Hz,
1H), 7.71 (d, J = 8.24 Hz, 1H), 7.79 (t, J = 7.40 Hz, 1H), 8.21 (d, J = 8.04
Hz, 1H), 12.58 (s, 1H); 13C NMR: (100 MHz, DMSO-d6) δ 56.7 (2×OCH3),
60.6 (OCH3), 101.6 (C), 107.2 (2×CH), 112.5 (C), 119.4 (CH), 124.2 (C),
125.5 (CH), 125.7 (CH), 129.4 (C), 133.4 (CH), 139.4 (CH), 139.5 (C),
153.3 (2×C), 156.2 (C), 173.9 (C).HRMS (ESI/TOF-Q) m/z:
[M+Na]+Calcd for C19H16N2NaO4S 391.0723; Found 391.0718.
98/2, yield 68% (112 mg), mp 68-70°C;1H NMR: (400 MHz, CDCl3) δ
2.15 (s, 3H), 3.88 (s, 2H), 6.66 (d, J = 8.16 Hz, 1H), 7.23-7.27 (m, 2H);
13C NMR: (100 MHz, CDCl3) δ 17.2 (CH3), 109.4 (C), 112.5 (C), 115.7
(CH), 123.8 (C), 132.1 (CH), 135.0 (CH), 147.0 (C).
2-iodo-4-thiocyanatoaniline (4c)24:Pale brown solid, Hexane/EtOAc =
98/2, yield 71% (195 mg), mp 140-142°C;1H NMR: (400 MHz, CDCl3) δ
4.43 (s, 2H), 6.73 (d, J = 8.44 Hz, 1H), 7.35-7.37 (m, 1H). 7.85 (s, 1H);
13C NMR: (100 MHz, CDCl3) δ 83.4 (C), 110.7 (C), 111.6 (C), 115.0 (CH),
134.1 (CH), 143.0 (CH), 149.0 (C).
3-thiocyanatoquinolin-4(1H)-one (2p): Light pink solid, Hexane/EtOAc
= 70/30, yield 85% (86 mg), mp 182-184°C; FT-IR (KBr cm-1) 3438, 2151,
1618; 1H NMR: (400 MHz, DMSO-d6) δ 7.47 (t, J = 7.2 Hz, 1H), 7.64 (d, J
= 8.16 Hz, 1H), 7.76 (t, J = 7.04 Hz, 1H), 8.16 (d, J = 7.84 Hz, 1H), 8.59
(d, J = 6.28 Hz, 1H), 12.64 (s, 1H); 13C NMR: (100 MHz, DMSO-d6)
δ102.7 (C), 112.3 (C), 119.4 (CH), 125.0 (C), 125.5 (CH), 125.6 (CH),
133.3 (CH), 140.05 (C), 144.7 (CH), 173.7 (C). HRMS (ESI/TOF-Q) m/z:
[M+H]+Calcd for C10H6N2NaOS 225.0094; Found 225.0093.
2-bromo-4-thiocyanatoaniline (4d)23:Yellow solid, Hexane/EtOAc
=
98/2, yield 65% (149 mg), mp 56-59°C;1H NMR: (400 MHz, CDCl3) δ
4.43 (s, 2H), 6.75 (d, J = 8.4 Hz, 1H), 7.30-7.32 (m, 1H). 7.64 (d, J = 1.12
Hz, 1H); 13C NMR: (100 MHz, CDCl3) δ 109.2 (C), 110.2(C), 111.7 (C),
116.2 (CH), 133.2 (CH), 136.9 (CH), 146.4 (C).
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900349
European Journal of Organic Chemistry
FULL PAPER
2-chloro-4-thiocyanatoaniline (4e)23:Yellow solid, Hexane/EtOAc
=
Green Chem.2014, 16, 2418-2421; c) D. Sun, K. Yin, R. Zhang, Chem.
Commun.2018,54, 1335-1338.
98/2, yield 62% (115 mg), mp 50-52°C;1H NMR: (400 MHz, CDCl3) δ
4.32 (s, 2H), 6.69 (d, J = 8.4 Hz, 1H), 7.19-7.21 (m, 1H). 7.42 (d, J = 1.28
Hz, 1H); 13C NMR: (100 MHz, CDCl3) δ 110.0 (C), 111.6 (C), 116.4 (CH),
119.7 (C), 132.6 (CH), 133.8 (C), 145.3 (C).
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3-bromo-4-thiocyanatoaniline (4f)25:Brown solid, Hexane/EtOAc
=
98/2,yield 52% (119 mg), mp 62-65°C;1H NMR: (400 MHz, CDCl3) δ 4.04
(s, 2H), 6.60-6.63 (dd, J = 8.52, 2.48 Hz, 1H), 6.94 (d, J = 2.48 Hz, 1H),
7.45 (d, J = 8.52 Hz, 1H); 13C NMR: (100 MHz, CDCl3) δ 111.0 (C), 111.2
(C), 115.1 (CH), 127.5 (C), 134.9 (CH), 149.7 (C).
3-chloro-4-thiocyanatoaniline (4g)26:Yellow solid, Hexane/EtOAc
=
98/2, yield 50% (92 mg), mp 75-77°C;1H NMR: (400 MHz, CDCl3) δ 4.05
(s, 2H), 6.57-6.59 (m, 1H), 6.77 (d, J = 1.68 Hz, 1H), 7.42 (d, J = 8.44 Hz,
1H); 13C NMR: (100 MHz, CDCl3) δ 108.9 (C), 110.9 (C), 114.5 (C),
116.1 (CH), 135.2 (CH), 137.7 (C), 149.8 (C).
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3-fluoro-4-thiocyanatoaniline (4h)27:Yellow solid, Hexane/EtOAc = 98/2,
yield 45% (76 mg), mp 60-62°C;1H NMR: (400 MHz, CDCl3) δ 4.04 (s,
2H), 6.56-6.59 (dd, J = 8.52, 2.52 Hz, 1H), 6.78 (d, J = 2.52 Hz, 1H), 7.43
(d, J = 8.52 Hz, 1H); 13C NMR: (100 MHz, CDCl3) δ 108.8 (C), 110.9 (C),
114.4 (CH), 116.1 (CH), 135.2 (CH), 137.7 (C), 149.8 (C).
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3,5-dichloro-4-thiocyanatoaniline (4j)27:Yellow solid, Hexane/EtOAc =
98/2, yield 48% (105 mg), mp 165-167°C;1H NMR: (400 MHz, CDCl3) δ
4.04 (s, 2H), 6.56-6.59 (dd, J = 8.52, 2.52 Hz, 1H), 6.78 (d, J = 2.52 Hz,
1H), 7.43 (d, J = 8.52 Hz, 1H); 13C NMR: (100 MHz, CDCl3) δ 108.8 (C),
110.9 (C), 114.4 (CH), 116.1 (CH), 135.2 (CH), 137.7 (C), 149.8 (C).
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Acknowledgments
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The authors thank FIRP-IIT Delhi, DST (INT/HUN/P-11/2016) for
financially supporting this work; and DST-FIST for funding the
ESI-HRMS facility at IIT Delhi. Parul Chauhan thanks CSIR,
Delhi for RA fellowship and Ritu thanks DST for inspire
fellowship.
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Keywords:Visible light, quinolone, thiocyanation, eosin-Y,
anilines.
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Entry for the Table of Contents
FULL PAPER
A
visible
light
mediated
of
Quinolone thiocyanation*
regioselectivethiocyanation
Parul Chauhan, Ritu,Preeti,Sharvan
Kumar, and Nidhi Jain*
quinolones and anilines has been
accomplished with ammonium
thiocyanate in the presence
ofeosin-Y under blue LED. The
reaction conditions are mild, metal-
free, economical, and moderate to
high product yields are obtained.
Page No. – Page No.
Metal-free and visible light promoted
C-3 thiocyanation of 2-arylquinolin-4-
ones
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