Metal-Free Thiocyanation of Imidazoheterocycles through Visible Light Photoredox Catalysis

Article abstract of DOI:10.1021/acs.joc.5b01369

A visible light mediated, metal-free process for the thiocyanation of imidazoheterocycles has been developed using eosin Y as a photoredox catalyst under ambient air at room temperature. A library of 3-(thiocyanato)imidazo[1,2-a]pyridines with broad funct

Full text of DOI:10.1021/acs.joc.5b01369

Page 1 of 18
The Journal of Organic Chemistry
1
2
3
4
Metal-Free Thiocyanation of Imidazoheterocycles through Visible Light
Photoredox Catalysis
5
6
7
8
9
Shubhanjan Mitra, Monoranjan Ghosh, Subhajit Mishra, and Alakananda Hajra*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Department of Chemistry, VisvaꢀBharati (A Central University), Santiniketan 731235, India
Email: alakananda.hajra@visvaꢀbharati.ac.in
Abstract:
A visible light mediated, metalꢀfree process for the thiocyanation of imidazoheterocycles has
been developed using eosin Y as a photoredox catalyst under ambient air at room temperature. A
library of 3ꢀ(thiocyanato)imidazo[1,2ꢀa]pyridines with broad functionalities have been
synthesized in high yields. This methodology is also applicable for the selenocyanation of
imidazo[1,2ꢀa]pyridine.
Introduction:
Visible light driven photoredox processes have received much attention as a powerful tool to
develop sustainable synthetic processes.1 Metal complexes mainly ruthenium and iridium are
commonly employed as efficient visible light photocatalysts.2 Despite the excellent
photophysical properties of ruthenium and iridium polypyridyl complexes in visible light
photocatalysis, these are expensive and toxic.3 Organic dyes are used as an attractive alternative
to the transition metal complexes in photoredox catalysis.4 These are typically less expensive,
less toxic, and easy to handle.5 Particularly, eosin Y has been widely used as an organoꢀ
photocatalyst in synthetic transformations.6
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 2 of 18
1
2
3
4
5
6
7
8
The thiocyanation reaction is one of the most useful carbonꢀsulfur bondꢀforming reactions.7
Organic thiocyanates usually serve as the synthetic precursors that can be conveniently converted
into various sulfurꢀcontaining derivatives.8 On the other hand, thiocyanates are the building
blocks of many heterocyclic compounds that show wide range of biological activities and also
consist in many natural products.9 Therefore, several methods have been developed for the
thiocyanation of arenes and other heterocycles.10
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In the last few years, much attention has been drawn on the imidazopyridine scaffolds because of
its wide range of biological activities for example, antiviral, antimicrobial, antitumor,
antiinflammatory, antiparasitic, hypnotic, etc.11 Some marketed drugs like alpidem, zolpidem,
necopidem, saripidem, zolimidine, etc. contain this scaffold. This moiety is also very useful in
material sciences.12 Consequently, various methods for the synthesis and functionalization of
imidazoheterocycles have been reported.13 Recently, we have also accounted a number of
efficient methods for the synthesis14 and functionalization15 of imidazo[1,2ꢀa]pyridine
derivatives from readily available starting materials. The pharmacological activity of
imidazopyridine derivatives is reliant on the nature of substituents at different positions.
Incorporation of sulfur functionalities in azaheterocycles could impart marked biological
properties.16 Very recently, Li et al.10f reported a visible light mediated Cꢀ3 thiocyanation of
indole derivatives using rose bengal as the photocatalyst. However, there is no report for the
thiocyanation of imidazo[1,2ꢀa]pyridine derivatives. Based on our experiences on
functionalization of imidazopyridines, we envisaged that the thiocyanation of imidazopyridines
could be carried out following a C(sp2)ꢀH functionalization strategy. Herein, we report a direct
and environmentally benign method for the thiocyanation of imidazopyridines using eosin Y as a
photoredox catalyst under ambient air at room temperature (Scheme 1).
Scheme 1. Thiocyanation of imidazopyridine
Results and Discussion:
We started our investigation taking 2ꢀphenylimidazo[1,2ꢀa]pyridine (1a) as the model substrate
to find a suitable reaction condition as summarized in Table 1. Initially, the reaction was carried
ACS Paragon Plus Environment

Page 3 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
out employing 3 equiv of NH4SCN as the thiocyanating agent and eosin Y (5 mol%) as the
photocatalyst in DMSO under open air in presence of blue LED light. The 2ꢀphenylꢀ3ꢀ
thiocyanatoimidazo[1,2ꢀa]pyridine (2a) was obtained in 59% yield after 3 h (Table 1, entry 1).
Inspired by the initial result, the effect of other solvents such as DMF, CH3CN, THF, methanol,
chloroform were tested (Table 1, entries 2ꢀ6), and best result (93%) was obtained in CH3CN
(Table 1, entry 3). Other photocatalysts like rose bengal and Ru(bpy)3Cl2·6H2O were also tested
(Table 1, entries 7 and 8) but both of them gave lower yields. No formation of product was seen
in absence of any photocatalyst (Table 1, entry 9). Only trace amount of product was formed in
inert atmosphere (Table 1, entry 10). Furthermore, the yield of the reaction was decreased when
2 equiv. of NH4SCN was used (Table 1, entry 11). Moreover, lower amount of the desired
product was obtained on replacing NH4SCN by KSCN (Table 1, entry 12). A decrease in yield
(84%) was obtained when green LED (4W) was used instead of blue LED even after 12 h (Table
1, entry 13). Finally, the optimized reaction conditions were obtained using 3 equiv NH4SCN, 5
mol% of eosin Y in CH3CN under blue LED irradiation in ambient air affording the optimum
93% yield of the desired thiocyanated product within 3 h (Table 1, entry 3).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 1. Optimization of the reaction parametersa
Entry
Photocatalyst
Solvent Oxidant Yield (%)
1
2
3
4
5
6
7
8
9
eosin Y
eosin Y
eosin Y
eosin Y
eosin Y
DMSO
DMF
CH3CN
THF
methanol
chloroform
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
air
air
air
air
air
air
air
air
air
ꢀ
59
62
93
34
11
8
40
21
ꢀ
eosin Y
rose bengal
Ru(bpy)3Cl2·6H2O
ꢀ
10b
11c
12d
eosin Y
eosin Y
eosin Y
trace
71
46
air
air
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 4 of 18
1
2
3
4
5
6
13e
aReaction conditions (unless otherwise specified): 1a (0.5 mmol), NH4SCN (1.5 mmol), photocatalyst
(5 mol%), solvent (2 mL), 3 h, rt.. In inert atmosphere. NH4SCN (2 equiv.) was used. KSCN (1.5
mmol) was used. eReaction performed in green LED (4W) irradiation for 12 h.
eosin Y
CH3CN
air
84
b
c
d
7
8
9
With the optimized reaction conditions in hand, we then varied imidazo[1,2ꢀa]pyridines to show
the generality of this methodology. As shown in Scheme 2, first we varied the substituents in Cꢀ2
position of the imidazo[1,2ꢀa]pyridines. Imidazopyridine moiety having ꢀMe and ꢀOMe
substituted phenyl rings at Cꢀ2 position produced the Cꢀ3 thiocyanated products in excellent
yields (2b and 2c). 3ꢀNO2 Phenyl substituted imidazopyridine furnished the product in excellent
yield (2d). Halogens are also well tolerated under the present reaction conditions (2e and 2f).
Imidazopyridines bearing ꢀCN and ꢀOH functionalities also afforded the desired products in
moderate to good yields (2g and 2h). It is notable that the marketed drug zolimidine reacted well
to give the thiocyanated product which might show better bioactivity (2i). Naphthyl substituted
subtrate also worked well (2j). Moreover, heteroaryl substituted imidazopyridine was tested (2k).
In addition, ꢀCF3 as well as aliphatic substituted imidazopyridines were found to very effective
for thiocyanation (2l and 2m). Interestingly, 2,3ꢀunsubstituted imidazopyridine regioselectively
produced the Cꢀ3 thiocyanated product in moderate yield (2n).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 2. Scope of substrates: Variation of C-2 substituents on the imidazo[1,2 -
a]pyridinesa
ACS Paragon Plus Environment

Page 5 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
aReaction conditions: Imidazo[1,2ꢀa]pyridines 1 (0.5 mmol), NH4SCN (1.5 mmol), eosin Y (5 mol%),
CH3CN (2 mL), blue LED, 3 h, rt, ambient air.
Next, we turned our attention to other imidazopyridines bearing substituents on the pyridine
rings as shown in Scheme 3. Methyl substituted imidazopyridines gave the product with good
yields (2o and 2p). Imidazopyridine having other substituents like ꢀCN, ꢀCl and ꢀBr furnished the
desired thiocyanated products in moderate yields (2qꢀ2s).
Scheme 3. Scope of substrates: variation of substituents on pyridine ringa
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 6 of 18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
aReaction conditions: Imidazo[1,2ꢀa]pyridines 1 (0.5 mmol) , NH4SCN (1.5 mmol), eosin Y (5 mol%),
CH3CN (2 mL), blue LED, 3 h, rt, ambient air.
The present protocol is also applicable to other imidazoheterocycles like imidazo[2,1ꢀb]thiazole
and benzo[d]imidazo[2,1ꢀb]thiazole (Scheme 4). To our delight, the corresponding monoꢀ
thiocyanated products were obtained with excellent yields. The structure of 4b was confirmed by
Xꢀray analysis.17 However, other simple imidazoles like imidazole, Nꢀmethylimidazole and 1,2
dimethylimidazole were unreacted under the present reaction conditions.
Scheme 4. Thiocyanation of imidazoheterocycles
S
N
S
N
NH4SCN (3 equiv.)
eosin Y (5 mol%)
N
N
CH3CN
blue LED (425 nm)
3 h, ambient air
NCS
3
4
S
N
S
N
N
N
NCS
4a, 84%
NCS
4b, 89%
The gramꢀscale reaction was also performed in usual laboratory setup (Scheme 5). The reaction
afforded the thiocyanated derivative in excellent yield (89%). This result clearly demonstrated
the practical applicability of this protocol for the thiocyanation of imidazopyridines.
Scheme 5. Gram-scale reactiona
ACS Paragon Plus Environment

Page 7 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
aReaction conditions: Imidazo[1,2ꢀa]pyridine 1a (6 mmol), NH4SCN (18 mmol), eosin Y (5 mol%),
CH3CN (20 mL), blue LED, 3 h, rt, ambient air.
Furthermore, the scope of the reaction was extended for selenocyanation of imidazopyridines
(Scheme 6). Intriguingly, the selenocyanated product 5a was obtained in moderate yield. The
SCN group of the imidazopyridine was also converted to SCF3 (6a) which is a key functionality
of many agrochemical and pharmaceutical products.18
Scheme 6. Selenocyanation and trifluoromethylthiolation of imidazo[1,2-a]pyridine
Few controlled experiments were performed to get a better understanding on the probable
mechanistic path, as shown in Scheme 7. The thiocyanation reaction did not proceed in presence
of radical scavenger TEMPO (entry 1) which indicates that the reaction possibly proceeds
through a radical pathway. The reaction was also carried out in dark (entry 2). But the reaction
did not proceed at all which strongly supports the radical mechanism. Furthermore, the reaction
was performed in presence of DABCO (entry 3). The reaction proceeded with equal ease thereby
indicates that singlet oxygen is not involved in the reaction.6g
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 8 of 18
1
2
Scheme 7. Controlled experiments
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
On the basis of the controlled experiments shown in Scheme 7, and the literature reports,6a,b,10f
a
plausible mechanistic path has been outlined in Scheme 8. Initially, eosin Y is being
photoexcited in presence of blue LED light. The thiocyanate anion is being oxidized to
thiocyanate radical by SET mechanism from anion to photoactivated eosin Y via a reductive
quenching cycle. The resulting thiocyanate radical interacts with 1a to produce the radical
intermediate B. Subsequently, B is oxidized to the intermediate C which affords the product 2a
via deprotonation. Aerobic oxygen probably plays a crucial role to complete the photoredox
cycle by oxidation of the eosin Y radical anion to the ground state.
Scheme 8. Probable mechanism
ACS Paragon Plus Environment

Page 9 of 18
The Journal of Organic Chemistry
1
2
Conclusions:
3
4
5
6
7
8
9
In summary, we have developed a visible light driven eosin Y catalyzed protocol for the Cꢀ3
thiocyanation of imidazoheterocycles at room temperature. The present method shows broad
substrates scope applicability and a wide range of functional groups tolerance. Most importantly,
this method is scalable and air is used as the sole green oxidant. To the best of our knowledge,
this is the first report for the Cꢀ3 thiocyanation of imidazopyridines. This transformation is also
applicable for the selenocyanation of imidazopyridine. We believe this protocol will gain much
importance in organic synthesis, medicinal chemistry and material science as a powerful and
economical route for the thiocyanation and selenocyanation of imidazoheterocycles.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental Section:
General Information: All reactions were carried out in oven dried 10 mL round bottom flasks
in open air. All solvents were dried and distilled before use. Commercial reagents were used
without further purification unless otherwise noted. All the imidazoheterocycles were
synthesized following the literature procedures.14a,d 1H, 13C{1H} and 19F NMR spectra were
recorded using CDCl3 and DMSOꢀd6 solution at ambient temperature on a spectrometer
13
operating at 400 MHz for 1H and protonꢀdecoupled C{1H} NMR spectra were recorded at 100
19
1
13
MHz and 376 MHz for F NMR. The chemical shifts of all H and C{1H} NMR spectra are
referenced to the residual signal of CDCl3 (δ 7.26 ppm for the 1H NMR spectra and δ 77.16 ppm
13
1
for the C{1H} NMR spectra) and DMSOꢀd6 (δ 2.50 ppm for the H NMR spectra and δ 39.50
ppm for the 13C{1H} NMR spectra). Coupling constant J was given in Hz. The following
abbreviations were used to describe peak splitting patterns when appropriate: s = singlet, d =
doublet, t = triplet, m = multiplet. TLC was monitored with aluminum backed silica gel 60
(HF254) plates (0.25 mm) using various organic solvent mixtures. Column chromatography was
performed with silica gel (60–120 mesh). Xꢀray single crystal data were collected using a
chargeꢀcoupled device (CCD) area detector.
Typical experimental procedure for the synthesis of 2-Phenyl-3-thiocyanatoimidazo[1,2-
a]pyridine (2a) (Table 2): An oven dried 5 mL round bottom flask was charged with 2ꢀ
phenylimidazo[1,2ꢀa]pyridine (1a) (0.5 mmol, 97 mg), ammonium thiocyanate (1.5 mmol, 114
mg), eosin Y (5 mol %, 17 mg) in CH3CN (2 mL) and the reaction mixture was stirred under
blue LED irradiation for 3 h under ambient air. The progress of the reaction was monitored by
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 10 of 18
1
2
3
4
5
6
7
8
TLC. After completion of the reaction, the reaction mixture was extracted with ethyl acetate. The
organic phase was dried over anhydrous Na2SO4 and concentrated under reduced pressure to get
the crude residue which was purified by column chromatography on silica gel (60–120 mesh)
using petroleum ether : ethyl acetate = 9:1 as an eluent to afford the pure thiocyanated product
(2a) (117 mg, 93%) as a red solid.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2-Phenyl-3-thiocyanatoimidazo[1,2-a]pyridine (2a): Red solid (117 mg, 93%), mp 110ꢀ112
1
oC. IR (KBr): 3070, 2349, 1639, 1452 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.47ꢀ8.46 (m, 1H),
8.06ꢀ8.04 (m, 2H), 7.81ꢀ7.79 (m, 1H), 7.54ꢀ7.50 (m, 4H), 7.15 (s, 1H). 13C{1H} NMR (100 MHz,
CDCl3): δ 153.1, 148.0, 131.9, 129.6, 128.9, 128.9, 128.2, 124.5, 118.4, 114.6, 108.2, 94.9.
HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H10N3S: 252.0595; found: 252.0591.
3-Thiocyanato-2-(p-tolyl)imidazo[1,2-a]pyridine (2b): Red solid (112 mg, 85%), mp 99ꢀ101
oC. IR (KBr): 3068, 2357, 1648, 1445 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.47 (s, 1H), 7.97 (d,
J = 7.6 Hz, 2H), 7.84ꢀ7.83 (m, 1H), 7.51 (s, 1H), 7.34 (d, J = 7.2 Hz, 2H), 7.17 (s, 1H), 2.44 (s,
3H). 13C{1H} NMR (100 MHz, CDCl3): δ 152.1, 147.2, 140.1, 129.6, 128.8, 128.2, 124.6, 117.9,
114.9, 108.1, 95.1, 21.5. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C15H12N3S: 266.0752; found:
266.0745.
2-(4-Methoxyphenyl)-3-thiocyanatoimidazo[1,2-a]pyridine (2c): Yellow solid (115 mg, 82%),
mp 102ꢀ104 oC. IR (KBr): 3081, 2352, 1627, 1459 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.44 (d,
J = 6.8 Hz, 1H), 8.02 (d, J = 8.8 Hz, 2H), 7.80 (d, J = 8.8 Hz, 1H), 7.48 (t, J = 8.0 Hz, 1H), 7.14
13
(t, J = 6.8 Hz, 1H), 7.05 (d, J = 8.8 Hz, 2H), 3.88 (s, 3H). C{1H} NMR (100 MHz, CDCl3): δ
160.9, 152.4, 147.5, 130.3, 128.5, 124.5, 123.8, 117.8, 114.6, 114.3, 108.1, 94.2, 55.5. HRMS
(ESIꢀTOF) m/z: [M+H]+ Calcd for C15H12N3OS: 282.0701; found: 282.0696.
2-(3-Nitrophenyl)-3-thiocyanatoimidazo[1,2-a]pyridine (2d): Red solid (127 mg, 86%), mp
o
1
128ꢀ130 C. IR (KBr): 3076, 2355, 1620, 1441, 1340, 1275 cmꢀ1. H NMR (400 MHz, DMSOꢀ
d6): δ 8.97ꢀ8.93 (m, 1H), 8.86ꢀ8.78 (m, 1H), 5.57 (d, J = 9.2 Hz, 1H), 8.36ꢀ8.31 (m, 1H), 7.94ꢀ
13
7.85 (m, 2H), 7.67ꢀ7.63 (m, 1H), 7.42ꢀ7.32 (m, 1H). C{1H} NMR (100 MHz, DMSOꢀd6): δ
148.0, 146.7, 134.1, 132.2, 130.5, 128.8, 125.5, 123.7, 122.4, 120.8, 117.5, 115.0, 110.0, 99.1.
HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H9N4O2S: 297.0446; found: 297.0443.
2-(4-Chlorophenyl)-3-thiocyanatoimidazo[1,2-a]pyridine (2e): White solid (112 mg, 78%),
mp 109ꢀ111 oC. IR (KBr): 3041, 2359, 1635, 1475, 1278, 814 cmꢀ1. 1H NMR (400 MHz, DMSOꢀ
ACS Paragon Plus Environment

Page 11 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
7
d6): δ 8.81 (d, J = 6.0 Hz, 1H), 8.09 (d, J = 7.6 Hz, 2H), 7.87 (d, J = 8.0 Hz, 1H), 7.72ꢀ7.65 (m,
13
3H), 7.39ꢀ7.38 (m, 1H). C{1H} NMR (100 MHz, DMSOꢀd6): δ 147.3, 145.5, 134.4, 129.9,
129.9, 129.7, 128.9, 125.7, 116.5, 115.5, 109.8, 99.2. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for
C14H9ClN3S: 286.0206; found: 286.0201.
8
9
2-(4-Fluorophenyl)-3-thiocyanatoimidazo[1,2-a]pyridine (2f): Red solid (118 mg, 88%), mp
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
1
86ꢀ88 C. IR (KBr): 3061, 2343, 1634, 1464, 1340 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.44ꢀ
8.42 (m, 1H), 8.05ꢀ8.02 (m, 2H), 7.76 (d, J = 8.4 Hz, 1H), 7.50ꢀ7.46 (m, 1H), 7.21ꢀ7.13 (m, 3H).
13C{1H} NMR (100 MHz, CDCl3): δ 163.6 (d, JCꢀF = 249 Hz), 151.1, 147.3, 130.8 (d, JCꢀF = 9
Hz), 128.8, 127.4, 124.5, 117.8, 115.9 (d, JCꢀF = 22 Hz), 114.9, 107.9, 95.2. 19F NMR (376 MHz,
CDCl3) δ −110.6. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H9FN3S: 270.0501; found:
270.0494.
4-(3-Thiocyanatoimidazo[1,2-a]pyridin-2-yl)benzonitrile (2g): Red solid (92 mg, 67%), mp
142ꢀ144 oC. IR (KBr): 3076, 2360, 2221, 1463 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.49 (d, J =
6.8 Hz, 1H), 8.22 (d, J = 8.0 Hz, 2H), 7.83ꢀ7.79 (m, 3H), 7.56ꢀ7.52 (m, 1H), 7.22ꢀ7.19 (m, 1H).
13C{1H} NMR (100 MHz, CDCl3): δ 150.7, 148.1, 136.4, 132.6, 129.3, 128.7, 124.6, 118.7,
118.6, 115.2, 113.0, 107.5, 96.1. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C15H9N4S:
277.0548; found: 277.0547.
2-(3-Thiocyanatoimidazo[1,2-a]pyridin-2-yl)phenol (2h): Yellow solid (94 mg, 71%), mp
113ꢀ115 oC. IR (KBr): 3686, 3049, 2389, 1604, 1454 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.50ꢀ
8.34 (m, 2H), 7.72ꢀ7.52 (m, 2H), 7.36ꢀ7.32 (m, 1H), 7.21ꢀ7.20 (m, 1H), 7.07ꢀ6.97 (m, 2H).
13C{1H} NMR (100 MHz, CDCl3): δ 158.5, 150.7, 145.8, 131.6, 129.0, 127.9, 124.2, 119.3,
118.2, 117.4, 115.2, 114.8, 107.6, 93.6. HRMSꢀEI m/z: [M]+ Calcd for C14H9N3OS: 267.0466;
found: 267.0466.
2-(4-(Methylsulfonyl)phenyl)-3-thiocyanatoimidazo[1,2-a]pyridine (2i): White solid (126 mg,
77%), mp 162ꢀ164 oC. IR (KBr): 3037, 2391, 1643, 1413, 1299, 1149 cmꢀ1. 1H NMR (400 MHz,
DMSOꢀd6): δ 8.82 (d, J = 6.4 Hz, 1H), 8.36 (d, J = 8.4 Hz, 2H), 8.15 (d, J = 8.0 Hz, 2H), 7.91 (d,
J = 8.8 Hz, 1H), 7.70 (t, J = 8.0 Hz, 1H), 7.38 (t, J = 6.8 Hz, 1H), 3.32 (s, 3H). 13C{1H} NMR
(100 MHz, DMSOꢀd6): δ 147.9, 146.7, 141.5, 136.8, 129.9, 129.4, 127.9, 126.1, 117.6, 115.8,
110.4, 100.4, 43.8. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C15H12N3O2S2: 330.0371; found:
330.0391.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 12 of 18
1
2
3
4
5
6
7
8
2-(Naphthalen-1-yl)-3-thiocyanatoimidazo[1,2-a]pyridine (2j): Yellow solid (119 mg, 79%)
o
1
mp 118ꢀ120 C. IR (KBr): 3051, 2351, 1494 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.47 (d, J =
6.4 Hz, 1H), 8.04ꢀ7.98 (m, 2H), 7.94ꢀ7.86 (m, 2H), 7.69 (d, J = 6.4Hz, 1H), 7.63ꢀ7.59 (m, 1H),
7.53ꢀ7.51 (m, 3H), 7.19ꢀ7.16 (m, 1H). 13C{1H} NMR (100 MHz, CDCl3): δ 153.1, 147.6, 133.7,
131.7, 130.1, 129.2, 128.7, 128.5, 128.4, 127.0, 126.3, 125.7, 125.1, 124.6, 118.2, 114.9, 108.1,
98.1. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C18H12N3S: 302.0752; found: 302.0747.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3-Thiocyanato-2-(thiophen-2-yl)imidazo[1,2-a]pyridine (2k): Yellow solid (90 mg, 70%), mp
o
1
108ꢀ110 C. IR (KBr): 3074, 2354, 1643, 1488 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.42ꢀ8.40
(m, 1H), 7.97ꢀ7.96 (m, 1H), 7.75ꢀ7.72 (m, 1H), 7.51ꢀ7.50 (m, 1H), 7.48ꢀ7.44 (m, 1H), 7.22ꢀ7.20
13
(m, 1H), 7.14ꢀ7.10 (m, 1H). C{1H} NMR (100 MHz, CDCl3): δ 148.1, 148.0, 134.8, 128.4,
128.3, 128.2, 127.9, 124.3, 118.1, 114.6, 107.6, 93.3. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for
C12H8N3S2: 258.0160; found: 258.0153.
3-Thiocyanato-2-(trifluoromethyl)imidazo[1,2-a]pyridine (2l): Red solid (81 mg, 67%), mp
o
1
92ꢀ94 C. IR (KBr): 3043, 2397, 2165, 1529 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.48 (d, J =
6.8 Hz, 1H), 7.87 (d, J = 8.8 Hz, 1H), 7.63ꢀ7.59 (m, 1H), 7.32ꢀ7.28 (m, 1H). 13C{1H} NMR (100
MHz, CDCl3): δ 147.2, 142.1 (q, JCꢀF = 76 Hz), 129.3, 124.5, 120.5 (q, JCꢀF = 268 Hz), 116.3,
113.9, 106.4, 98.7. 19F NMR (376 MHz, CDCl3) δ −61.3. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd
for C9H5F3N3S: 244.0156; found: 244.0150.
2-Isobutyl-3-thiocyanatoimidazo[1,2-a]pyridine (2m): Yellow liquid (80 mg, 69%), IR (KBr):
1
3071, 2362, 1430 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.90 (d, J = 6.8 Hz, 1H), 7.97ꢀ7.90 (m,
2H), 7.56ꢀ7.53 (m, 1H), 2.83 (d, J = 7.2 Hz, 2H), 2.26ꢀ2.19 (m, 1H), 0.97 (d, J = 6.8 Hz, 6H).
13C{1H} NMR (100 MHz, DMSOꢀd6): δ 147.6, 142.6, 132.6, 126.7, 116.8, 114.0, 109.4, 103.1,
34.3, 28.2, 22.1. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C12H14N3S: 232.0908; found:
232.0905.
3-Thiocyanatoimidazo[1,2-a]pyridine (2n): Yellow liquid (47 mg, 54%). IR (KBr): 3058,
2344, 1449 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.41 (d, J = 6.4 Hz, 1H), 8.02 (s, 1H), 7.76 (d, J
13
= 9.2 Hz, 1H), 7.46 (t, J = 7.6 Hz, 1H), 7.14 (t, J = 6.8 Hz, 1H). C{1H} NMR (100 MHz,
CDCl3): δ 149.0, 143.2, 127.6, 124.2, 118.7, 114.7, 107.9, 99.0. HRMS (ESIꢀTOF) m/z: [M+H]+
Calcd for C8H6N3S: 176.0282; found: 176.0276.
ACS Paragon Plus Environment

Page 13 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
7
8
8-Methyl-2-phenyl-3-thiocyanatoimidazo[1,2-a]pyridine (2o): Red solid (98 mg, 74%), mp
o
1
98ꢀ100 C. IR (KBr): 3051, 2358, 1629, 1456 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.32 (d, J =
6.8 Hz, 1H), 8.06ꢀ8.04 (m, 2H), 7.55ꢀ7.51(m, 2H), 7.49ꢀ7.45 (m, 1H), 7.27ꢀ7.25 (m, 1H), 7.04 (t,
J = 6.8 Hz, 1H), 2.70 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ 152.4, 148.0, 132.0, 129.4,
129.0, 128.8, 128.5, 127.1, 122.2, 114.6, 108.2, 95.2, 16.8. HRMS (ESIꢀTOF) m/z: [M+H]+
Calcd for C15H12N3S: 266.0752; found: 266.0744.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7-Methyl-2-phenyl-3-thiocyanatoimidazo[1,2-a]pyridine (2p): Brown solid (94 mg, 71%), mp
104ꢀ106 oC. IR (KBr): 3078, 2348, 1654, 1431 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.31 (d, J =
6.8 Hz, 1H), 8.03 (d, J = 7.2 Hz, 2H), 7.54ꢀ7.47 (m, 3H), 7.46ꢀ7.44 (m, 1H), 6.95 (d, J = 6.8 Hz,
1H), 2.48 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3): δ 153.0, 148.3, 139.8, 132.0, 129.4, 128.8,
128.8, 123.6, 117.1, 116.8, 108.3, 93.9, 21.5. HRMS (ESIꢀTOF): Calcd for C15H11N3S ([M+H])+:
266.0752; found: 266.0749.
2-Phenyl-3-thiocyanatoimidazo[1,2-a]pyridine-6-carbonitrile (2q): Red solid (84 mg, 61%),
o
1
mp 132ꢀ134 C. IR (KBr): 3062, 2351, 2237, 1629, 1429 cmꢀ1. H NMR (400 MHz, CDCl3): δ
8.85 (s, 1H), 8.07ꢀ8.04 (m, 2H), 7.83 (d, J = 8.4 Hz, 1H), 7.58ꢀ7.49 (m, 4H). 13C{1H} NMR (100
MHz, CDCl3): δ 154.9, 147.3, 130.8, 130.3, 130.2, 129.0, 128.9, 128.1, 119.3, 115.7, 107.1,
100.9, 97.4. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C15H9N4S: 277.0548; found: 277.0543.
6-Chloro-2-phenyl-3-thiocyanatoimidazo[1,2-a]pyridine (2r): Yellow solid (93 mg, 65%), mp
o
1
101ꢀ103 C. IR (KBr): 3049, 2346, 1645, 1431 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.48 (s,
1H), 8.09ꢀ8.02 (m, 2H), 7.71 (d, J = 9.6 Hz, 1H), 7.56ꢀ7.51 (m, 2H), 7.50ꢀ7.46 (m, 1H), 7.45ꢀ
7.42 (m, 1H). 13C{1H} NMR (100 MHz, CDCl3): δ 153.7, 146.4, 131.6, 129.8, 129.6, 128.9,
128.8, 123.1, 122.5, 118.7, 107.7, 95.8. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H9ClN3S:
286.0206; found: 286.0204.
6-Bromo-2-phenyl-3-thiocyanatoimidazo[1,2-a]pyridine (2s): Brown solid (112 mg, 68%),
mp 128ꢀ130 oC. IR (KBr): 3022, 2341, 2158, 1479 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.56 (s,
13
1H), 8.03 (d, J = 7.2 Hz, 2H), 7.65 (d, J = 9.2 Hz, 1H), 7.52ꢀ7.45 (m, 4H). C{1H} NMR (100
MHz, CDCl3): δ 153.4, 146.3, 131.7, 131.4, 129.8, 128.9, 128.8, 124.7, 118.9, 109.4, 107.8,
95.6. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H9BrN3S: 329.9701; found: 329.9692.
6-Phenyl-5-thiocyanatoimidazo[2,1-b]thiazole (4a): White solid (108 mg, 84%), mp 124ꢀ126
oC. IR (KBr): 3120, 2354, 2158, 1438 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 7.96 (d, J = 7.2 Hz,
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 14 of 18
1
2
3
4
5
6
2H), 7.66ꢀ7.65 (m, 1H), 7.51ꢀ7.48 (m, 2H), 7.45ꢀ7.41 (m, 1H), 7.06 (s, 1H). 13C{1H} NMR (100
MHz, CDCl3): δ 154.5, 153.4, 132.1, 129.2, 128.8, 128.2, 117.8, 114.8, 108.5, 95.9. HRMS
(ESIꢀTOF) m/z: [M+H]+ Calcd for C12H8N3S2 ([M+H])+: 258.0160; found: 258.0155.
7
8
9
2-Phenyl-3-thiocyanatobenzo[d]imidazo[2,1-b]thiazole (4b): White solid (137 mg, 89%), mp
152ꢀ154 oC. IR (KBr): 3070, 2352, 2156, 1479 cmꢀ1. 1H NMR (400 MHz, CDCl3): δ 8.47 (d, J =
8.4 Hz, 1H), 7.99ꢀ7.97 (m, 2H), 7.77 (d, J = 7.6 Hz, 1H), 7.59ꢀ7.55 (m, 1H), 7.54ꢀ7.50 (m, 2H),
7.47ꢀ7.42 (m, 2H). 13C{1H} NMR (100 MHz, CDCl3): δ 155.6, 152.8, 132.9, 131.8, 130.2,
129.3, 128.8, 128.5, 127.0, 125.8, 124.6, 113.9, 108.9, 98.1. HRMS (ESIꢀTOF) m/z: [M+H]+
Calcd for C16H10N3S2 ([M+H])+: 308.0316; found: 308.0313.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2-Phenyl-3-selenocyanatoimidazo[1,2-a]pyridine (5a): Yellow solid (76 mg, 51%), mp 135ꢀ
o
1
137 C. IR (KBr): 3066, 2513, 1645 cmꢀ1. H NMR (400 MHz, CDCl3): δ 8.66ꢀ8.46 (m, 1H),
8.01ꢀ7.97 (m, 2H), 7.79ꢀ7.76 (m, 1H), 7.55ꢀ7.45 (m, 4H), 7.16ꢀ7.11 (m, 1H). 13C{1H} NMR (100
MHz, CDCl3): δ 129.7, 129.4, 129.3, 129.1, 128.8, 128.6, 128.0, 126.9, 125.6, 118.2, 114.5,
98.9. HRMS (ESIꢀTOF) m/z: [M+H]+ Calcd for C14H10N3Se: 300.0040; found: 300.0034.
2-(p-Tolyl)-3-((trifluoromethyl)thio)imidazo[1,2-a]pyridine (6a):18b White solid (63 mg,
1
48%), H NMR (400 MHz, CDCl3): δ 8.51 (d, J = 6.8 Hz, 1H), 8.06 (d, J = 8.4 Hz, 2H), 7.72ꢀ
13
7.70 (m, 1H), 7.42ꢀ7.38 (m, 1H), 7.31ꢀ7.29 (m, 2H), 7.03ꢀ6.99 (m, 1H), 2.42 (s, 3H). C{1H}
NMR (100 MHz, CDCl3): δ 154.3, 148.1, 139.2, 129.8, 129.3, 128.7 (q, JCꢀF = 313 Hz), 128.6,
127.8, 124.6, 117.9, 113.7, 98.7, 21.5. 19F NMR (376 MHz, CDCl3) δ −43.23.
Acknowledgment
A.H. acknowledges the financial support from CSIR, New Delhi (Grant No. 02(0168)/13/EMRꢀ
II). S. M. thanks CSIR, and M.G. and S. M. thank UGC for their fellowship.
1
Supporting information:Scanned copies of H and 13C NMR spectra of the synthesized
compounds, CIF file for compound 4b are available as supporting information. This material is
available free of charge via the Internet at http://pubs.acs.org.
References:
(1) (a) Hari, D. P.; König, B. Angew. Chem., Int. Ed. 2013, 52, 4734. (b) Narayanam, J. M. R.;
Stephenson, C. R. J. Chem. Soc. Rev. 2011, 40, 102. (c) Zeitler, K. Angew. Chem., Int. Ed. 2009,
ACS Paragon Plus Environment

Page 15 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
7
48, 9785. (d) Shi, L.; Xia, W. Chem. Soc. Rev. 2012, 41, 7687. (e) Hering, T.; Hari, D. P.; König,
B. J. Org. Chem. 2012, 77, 10347. (f) Rueping, M.; Vila, C.; Bootwicha, T. ACS Catal. 2013, 3,
1676. (g) Skubi, K. L.; Yoon, T. P. Nature 2014, 515, 45. (h) Xu, Z.; Gao, L.; Wang, L.; Gong,
M.; Wang, W.; Yuan, R. ACS Catal. 2015, 5, 45.
8
9
(2) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C. Chem. Rev. 2013, 113, 5322.
(3) Ravelli, D.; Fagnoni, M.; Albini, A. Chem. Soc. Rev. 2013, 42, 97.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(4) (a) Huang, L.; Zhao, J. Chem. Commun. 2013, 49, 3751. (b) Guo, S.; Zhang, H.; Huang, L.;
Guo, Z.; Xiong, G.; Zhao, J. Chem. Commun. 2013, 49, 8689. (c) Zhao, J.; Wu, W.; Sun, J.;
Guo, S. Chem. Soc. Rev. 2013, 42, 5323.
(5) (a) Nicewicz, D. A.; Nguyen, T. M. ACS Catal. 2013, 4, 355. (b) Ravelli, D.; Fagnoni, M.
ChemCatChem 2012, 4, 169. (c) Cantillo, D.; de Frutos, O.; Rincón, J. A.; Mateos, C.; Kappe, C.
O. Org. Lett. 2014, 16, 896.
(6) (a) Hari, D. P.; König, B. Chem. Commun. 2014, 50, 6688. (b) Kundu, D.; Ahammed, S.;
Ranu, B. C. Org. Lett. 2014, 16, 1814. (c) Hari, D. P.; Schroll, P.; König, B. J. Am. Chem. Soc.
2012, 134, 2958. (d) Majek, M.; von Wangelin, A. J. Chem. Commun. 2013, 49, 5507. (e) Yang,
D.ꢀT.; Meng, Q.ꢀY.; Zhong, J.ꢀJ.; Xiang, M.; Liu, Q.; Wu, L.ꢀZ. Eur. J. Org. Chem. 2013, 7528.
(f) Meng, Q.ꢀY.; Zhong, J.ꢀJ.; Liu, Q.; Gao, X.ꢀW.; Zhang, H.ꢀH.; Lei, T.; Li, Z.ꢀJ.; Feng, K.;
Chen, B.; Tung, C.ꢀH.; Wu, L.ꢀZ. J. Am. Chem. Soc. 2013, 135, 19052. (g) Keshari, T.; Yadav,
V. K.; Srivastava, V. P.; Yadav, L. D. S. Green Chem. 2014, 16, 3986.
(7) Guy, R. G. In the Chemistry of Cyanates and their Thio Derivatives; Patai, S. (Ed.), John
Wiley & Sons: New York, 1977, part 2, 819.
(8) (a) Nguyen, T.; Rubinstein, M.; Wakselman, C. J. Org. Chem. 1981, 46, 1938. (b) Zhang, Z.
H.; Liebeskind, L. S. Org. Lett. 2006, 8, 4331. (c) Riemschneider, R. J. Am. Chem. Soc. 1956,
78, 844. (d) Lee, Y. T.; Choi, S. Y.; Chung, Y. K. Tetrahedron Lett. 2007, 48, 5673 and
references cited therein.
(9) (a) Patil, A. D.; Freyer, A. J.; Reichwein, R.; Carte, B.; Killmer, L. B.; Faucette, L.; Johnson,
R. K.; Faulkner, D. J. Tetrahedron Lett. 1997, 38, 363. (b) Hill, H. A. O. Chemistry and
Biochemistry of Thiocyanic Acid and Its Derivatives; Newman, A. A. (Ed.), Academic Press:
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 16 of 18
1
2
3
4
5
6
London, 1975. (c) Dutta, S.; Abe, H.; Aoyagi, S.; Kibayashi, C.; Gates, K. S. J. Am. Chem. Soc.
2005, 127, 15004. (d) Pham, A. T.; Ichiba, T.; Yoshida, W. Y.; Scheuer, P. J.; Uchida, T.;
Tanaka, J.ꢀI.; Higa, T. Tetrahedron Lett. 1991, 32, 4843.
7
8
9
(10) (a) Zhu, D.; Chang, D.; Shi, L. Chem. Commun. 2015, 51, 7180. (b) Grant, M. S.; Snyder,
H. R. J. Am. Chem. Soc. 1960, 82, 2742. (c) Toste, F. D.; Stefano, V. D.; Still, I. W. J. Synth.
Commun. 1995, 25, 1277. (d) Yadav, J. S.; Reddy, B. V. S.; Murali Krishna, B. B. Synthesis
2008, 3779. (e) Bhalerao, D. S.; Akamanchi, K. G. Synlett 2007, 2952. (f) Fan, W.; Yang, Q.;
Xu, F.; Li, P. J. Org. Chem. 2014, 79, 10588.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(11) EnguehardꢀGueiffier, C.; Gueiffier, A. Mini Rev. Med. Chem. 2007, 7, 888.
(12) (a) Stasyuk, A. J.; Banasiewicz, M.; Cyrański, M. K.; Gryko, D. T. J. Org. Chem. 2012, 77,
5552. (b) Shao, N.; Pang, G.ꢀX.; Yan, C.ꢀ X.; Shi, G.ꢀF.; Cheng, Y. J. Org. Chem. 2011, 76,
7458.
(13) (a) Bagdi, A. K.; Santra, S.; Monir, K.; Hajra, A. Chem. Commun. 2015, 51, 1555. (b)
Pericherla, K.; Kaswan, P.; Pandey, K.; Kumar, A. Synthesis 2015, 47, 887. (c) Koubachi, J.;
Kazzouli, S. E.; Bousmina, M.; Guillaumet, G. Eur. J. Org. Chem. 2014, 5119. (d) He, C.; Hao,
J.; Xu, H.; Mo, Y.; Liu, H.; Han, J.; Lei, A. Chem. Commun. 2012, 48, 11073. (e) Wang, H.;
Wang, Y.; Liang, D.; Liu, L.; Zhang, J.; Zhu, Q. Angew. Chem., Int. Ed. 2011, 50, 5678. (f)
Chernyak, N.; Gevorgyan, V. Angew. Chem., Int. Ed. 2010, 49, 2743. (g) Zeng, J.; Tan, Y. J.;
Leow, M. L.; Liu, X.ꢀW. Org. Lett. 2012, 14, 4386. (h) Ravi, C.; Mohan, D. C.; Adimurthy, S.
Org. Lett. 2014, 16, 2978.(i) Cao, H.; Liu, X.; Zhao, L.; Cen, J.; Lin, J.; Zhu, Q.; Fu, M. Org.
Lett. 2014, 16, 146. (j) Yan, R.ꢀL.; Yan, H.; Ma, C.; Ren, Z.ꢀY.; Gao, X.ꢀA.; Huang, G.ꢀS.;
Liang, Y.ꢀM. J. Org. Chem. 2012, 77, 2024.
(14) (a) Mishra, S.; Monir, K.; Mitra, S.; Hajra, A. Org. Lett. 2014, 16, 6084. (b) Monir, K.;
Bagdi, A. K.; Ghosh, M.; Hajra, A. Org. Lett. 2014, 16, 4630. (c) Monir, K.; Bagdi, A. K.;
Mishra, S.; Majee, A.; Hajra, A. Adv. Synth. Catal. 2014, 356, 1105. (d) Bagdi, A. K.; Rahman,
M.; Santra, S.; Majee, A.; Hajra, A. Adv. Synth. Catal. 2013, 355, 1741. (e) Santra, S.; Bagdi, A.
K., Majee, A.; Hajra, A. Adv. Synth. Catal. 2013, 355, 1065.
ACS Paragon Plus Environment

Page 17 of 18
The Journal of Organic Chemistry
1
2
3
4
5
6
(15) (a) Monir, K.; Bagdi, A. K.; Ghosh, M.; Hajra, A. J. Org. Chem. 2015, 80, 1332. (b) Ghosh,
M.; Naskar, A.; Mitra, S.; Hajra, A. Eur. J. Org. Chem. 2015, 715. (c) Bagdi, A. K.; Mitra, S.;
Ghosh, M.; Hajra, A. Org. Biomol. Chem. 2015, 13, 3314.
7
8
9
(16) (a) Gueiffier, A.; Mavel, S.; Lhassani, M.; Elhakmoui, A.; Snoeck, R.; Andrei, G.;
Chavignon, O.; Teulade, J.ꢀC.; Witvrouw, M.; Balzarini, J.; De Clercq, E.; Chapat, J.ꢀP. J. Med.
Chem. 1998, 41, 5108. (b) Véron, J.ꢀB.; Allouchi, H.; EnguehardꢀGueiffier, C.; Snoeck, R.;
Andrei, G.; De Clercq, E.; Gueiffier, A. Bioorg. Med. Chem. 2008, 16, 9536.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(17) Further information can be found in the CIF file. This crystal was deposited in the
Cambridge Crystallographic Data Centre and assigned as CCDC 1052831.
(18) (a) Matheis, C.; Wang, M.; Krause, T.; Gooßen, L. J. Synlett 2015, 26, 1628. (b) Wang, Q.;
Qi, Z.; Xie, F.; Li, X. Adv. Synth. Catal. 2015, 357, 355.
ACS Paragon Plus Environment

The Journal of Organic Chemistry
Page 18 of 18
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment