Visible-light-mediated difunctionalization of styrenes: An unprecedented approach to 5-aryl-2-imino-1,3-oxathiolanes

Article abstract of DOI:10.1039/c5gc00642b

The visible-light-induced straightforward synthesis of 5-aryl-2-imino-1,3-oxathiolanes from styrenes and ammonium thiocyanate is reported. The protocol utilizes air (O₂) and visible light as green reagents and eosin Y as an organophotoredox cat

Full text of DOI:10.1039/c5gc00642b

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Visible-light-mediated difunctionalization of styrenes: an unprecedented approach
to 5-aryl-2-imino-1,3-oxathiolanes†
Arvind K . Yadav and Lal Dhar S. Yadav*
Green Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad-211002, India. E-mail: ldsyadav@hotmail.com; Fax: +91
5322460533; Tel:+91 5322500652
†Electronic supplementary information (ESI) available: Experimental details and copies of 1H and 13C spectra for the products, See DIO:
10.1039/c0xx00000x
5
widely applied as a photoredox catalyst in organic synthesis by
several research groups5 including ours.6
Visible-light-induced straightforward synthesis of 5-aryl-2-
10 imino-1,3-oxathiolanes from styrenes and ammonium
thiocyanate is reported. The protocol utilizes air (O2) and
visible light as the greenest reagents and eosin Y as an
organophotoredox catalyst. The reaction involves formation
The 1,3ꢀoxathiole core is present in a variety of pharmaceutical
products7b,e and biologically active compounds.7aꢀd For example,
55 a number of 1,3ꢀoxathiolꢀ2ꢀone derivatives have been studied for
their antibacterial, tuberculostatic and antifungal activities,7cꢀf
whereas some oxathiolones are used as neuroprotective agents.7b
Likewise, 2ꢀaryliminoꢀ1,3ꢀoxathiole derivatives have been found
to exhibit potential pharmaceutical and biochemical activities.7d-g
60 Of these, the compound A is useful agrochemical pesticide and
compound B might possess fungicidal activity (Fig. 1).7,8
of C-S bond followed by
intramolecular
C-O
15 heterocyclization in
temperature.
a
one-pot procedure at room
Introduction
Air, water and light are the frontiers in green chemistry, because
these are the ecoꢀsustainable, clean, cheapest and unending
20 resources. Recently, visibleꢀlightꢀphotoredox catalysis has offered
to synthetic organic chemists a new platform for the construction
of CꢀC and CꢀX (X = N, O, S, P etc.) bonds.1 In this area, the
seminal work reported by the research groups of MacMillan et
al.,2a Yoon et al.2b and Stephenson et al.3 has demonstrated that
25 the use of photocatalysts such as Ru(bpy)3Cl2 (bpy = 2,2’ꢀ
bipyridine) and Ir(dtbbpy)3Cl2 (dtbbpy = 4,4’ꢀdiꢀtert butylꢀ2,2’ꢀ
bipyridine) is capable of initiating powerful transformations,
both for the target oriented and method driven organic synthesis.1
Moreover, the field of visibleꢀlightꢀphotoredox catalysis is
30 attractive because it has capability of dioxygen (air) activation.
Dioxygen is not only green oxidant but also an ideal oxygen
source for the functionalization of organic molecules. Seeking
dioxygen activation by organic molecules is an interesting and
sustainable approach for green synthesis of fine chemicals,
35 especially in the pharmaceutical industry.4 In the photoredox
O
S
S
MeO
O
N
O
S
S
N
N
A
B
65 Fig. 1 Biologically active 2ꢀiminoꢀ1,3ꢀoxathiolanes.
Very few methods are available in the literature for the
synthesis of 2ꢀiminoꢀ1,3ꢀoxathioles.8 Most of them have one or
more limitations such as the use of special or expensive metal
70 catalysts and reagents, unsatisfactory efficiencies, tedious
multistep manipulations and narrow scopes.
Compounds
incorporating a 2ꢀiminoꢀ1,3ꢀoxathiolane system are associated
with potential bioactivities.7e,f Moreover, the presence of a free
imino (=NH) group would allow several synthetically important
75 functional group manipulations in 2ꢀiminoꢀ1,3ꢀoxathiolanes. To
the best of our knowledge, the literature records only one method
for the synthesis of 2ꢀiminoꢀ1,3ꢀoxathiolanes bearing a free imino
(=NH) group, which involves conversion of phenacyl bromides
into phenacyl thiocyanates followed by their reduction with
80 NaBH4 and subsequent cyclization (Scheme 1a).8a However, the
most serious drawbacks of this methods are the utilization of
hazardous (highly lachrymator and toxic) phenacyl bromides as
the starting material and the need of a reduction step, which
reduces cost effectiveness and produces additional waste.
chemistry, it has mostly employed as an acceptor to regenerate
PC
photocatalyst (PC) from its radical anion
formed in the
catalytic cycle via excited state (PC*) by single electron transfer
PC
(SET) from a donor. The
completes the catalytic cycle by
).1ꢀ3 The superoxide
O
2
40 formation of the superoxide radical (
O
2
radical (
) formed in the photoredox cycle of Ru(II), Ir(II)
complexes or eosin Y are utilized in situ for the oxidation
purpose in the synthetic process.
However, the utilization of Ru(II) and Ir(II) complexes suffers
45 from disadvantages such as potential toxicity, low sustainability,
high cost and problematic removal of their undesirable traces
from products, especially in the case of drugs and drug
intermediates. Similar to the chemistry of Ru(II) and Ir(II), eosin
Y (EY), a long known dye is an attractive alternative to typical
50 inorganic transition metal photocatalysts, has recently been
85 Thus, the development of a convenient and ecoꢀsustainable
synthesis for 2ꢀiminoꢀ1,3ꢀoxathiolanes will be
contribution to this class of heterocycles. In view of the above
points and our recent research focused on the functionalization of
alkenes6c,9a-d and alkynes,9e,f we report herein a novel synthesis of
a valuable
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2ꢀiminoꢀ1,3ꢀoxathiolanes from styrenes and NH4SCN. The
method is much more advantageous in terms of green and
sustainable chemistry than the available method8a because it: (i)
uses styrenes as the substrate instead highly lachrymator and
toxic phenacyl bromides, (ii) has better atomꢀ and potꢀeconomy
and (iii) utilizes most inexpensive visible light and atmospheric
oxygen as regents (Scheme 1b).
45
Next, the reaction was optimized for an effective solvent
system and source of SCN ion. It was found that CH3CN was the
best among the tested solvents EtOH, DMF, DMSO and CH3CN,
hence it was used throughout the present study (Table 1, entry 1
versus 3ꢀ5). As regards the thiocyanate ion sources, NH4SCN was
5
50 better than KSCN (Table 1, entry 1 versus 13) in terms of the
yield and time.
Previous work:8a
(a)
NH
Table 1 Optimisation of reaction conditions a
.
O
O
NH
S
Br
S
(i) NH4SCN/CH3CN
(ii) NaBH4/MeOH
O
Ar
Ar
Ar
air
eosin Y
(mol%) (O2)
NH
S
NH SCN,
4
solvent, 12-24 h
(b) Present work:
O
air
eosin Y
(O2)
2a
1a
Entry Catalyst (mol%)
Solvent
Time (h)
Yield (%)b
Ar
NH4SCN/CH3CN
eosin Y (2)
rose bengal (2)
eosin Y (2)
eosin Y (2)
eosin Y (2)
eosin Y (1)
eosin Y (3)
eosin Y (2)
eosin Y (2)
ꢀ
CH3CN
CH3CN
EtOH
12
12
12
12
12
12
12
24
24
24
24
24
24
12
12
92
1
Br
Br
72
HO
Br
O
O
2
63
3
Br
DMF
78
4
COOH
DMSO
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
86
5
67
6
eosin Y
catalyst:
92
7
tracesc
tracesd
n. d.e
tracesf
58g
62h
92i
8
10 Scheme 1 Synthesis of 5ꢀarylꢀ2ꢀiminoꢀ1,3ꢀoxathiolanes.
9
10
11
12
13
14
Results and discussion
eosin Y (2)
eosin Y (2)
eosin Y (2)
eosin Y (2)
eosin Y (2)
In order to realise our idea and optimise the reaction conditions,
15 the key reaction of styrene (1a) with NH4SCN was performed
using catalytic amount of eosin Y in a solvent under irradiation
with green LEDs [2.50 W, λ = 535 nm] in open air (Table 1). We
were delighted to get the desired product 5ꢀarylꢀ2ꢀiminoꢀ1,3ꢀ
oxathiolanes (2a) in 92% yield (Table 1, entry 1). Then, the
20 control experiments were carried out, which show that eosin Y,
air (O2) and visible light are essential for the reaction, because in
the absence of any of the reagents/reaction parameters either the
product was not detected (n. d.) or formed in the traces (Table 1,
entry 1 versus 8ꢀ10). The optimum amount of eosin Y required
25 for the reaction was 2 mol%. On decreasing the amount of eosin
Y from 2 mol% to 1 mol% the yield was considerably reduced
(Table 1, entry 6), whereas the yield was not enhanced even on
use of 3 mol% of eosin Y (Table 1, entry 7). The use of another
organic photocatalyst like rose bengal (2 mol%) was not so
30 effective as eosin Y (2 mol%) (Table 1, entry 1 versus 2).
Green LEDs [2.50 W, λ = 535 nm] were more effective than
fluorescent light (Table 1, entry 12), which shows that the higher
photocatalytic activity of eosin Y in presence of high intensity
green light. The presence of O2 (air) is also essential for the
35 reaction because only a trace of product formation was detected
under a nitrogen atmosphere (Table 1, entry 8). Notably, the same
result was obtained on using O2 (balloon) instead of an air
atmosphere (Table 1, entry 14). Moreover, the reaction was
quenched with 2,2,6,6ꢀtetramethylpiperidylꢀ1ꢀoxyl (TEMPO) (1.0
40 mmol) in standard state showing that there may be radical
intermediates involved in reaction (Table 1, entry 11).
Furthermore, the reaction did not quench in the presence of
DABCO (1.0 mmol) (Table 1, entry15), which indicates the
involvement of triplet oxygen in the reaction.10
89j
15
a
Reaction conditions: 1a (1.0 mmol), NH4SCN (1.0 mmol), catalyst
(mol%), in 3 mL solvent irradiated using Luxeon Rebel high power green
LEDs [2.50 W, λ = 535 nm] under an air atmosphere at rt for 12ꢀ24 h.
b
c
Isolated yield of the pure product 2a. Reaction was performed under
nitrogen. d Reaction was performed in the dark. Reaction was carried out
e
without catalyst. f Reaction was quenched with 2,2,6,6ꢀtetramethylpiperidylꢀ
g
1ꢀoxyl (TEMPO (1.0 mmol). 18 W CFL (compact fluorescent lamp,
Philips) was used. h KSCN was used as instead of NH4SCN. O2 balloon
i
was used. j The reaction was quenched with DABCO (1.0 mmol).
55
Under the established reaction conditions, we surveyed the
generality and scope of the present protocol across a range of
styrenes incorporating various substituents like Me, MeO, NO2,
Cl, Br, F and Me2N. The reaction worked well in all the cases and
60 afforded products 2 in good to excellent yields (74ꢀ96%).
However, styrenes 1 with an electronꢀdonating group on the
aromatic ring appear to react faster and afford marginally higher
yields in comparison to those bearing an electronꢀwithdrawing
group (Table 2, products 2b, 2c, 2j versus 2d-2i). The reaction
65 did not work to produce 5ꢀalkylꢀ2ꢀiminoꢀ1,3ꢀoxathiolanes in the
case of aliphatic alkenes such as 1ꢀhexene and 1ꢀheptene. This is
probably because of the less stability of the alkyl free radicals
formed after the attack of the thiocyanate radical on the aliphatic
alkenes as compared to the benzyl free radicals formed in the case
70 of styrenes.
2
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a
Table 2 Substrate scope
.
30 sustainable reagents and eosin Y as an organophotoredox catalyst
NH
S
N
C
S
N
C
S
N
C
S
O
O
O
O
eosin Y air
(2 mol%) (O2), CH3CN
A
O2 (air)
O2
Ar
Ar
Ar
Ar
Ar
NH SCN (1.0 mmol),
rt, 12-18 h
4
ref. 6c,
11c
1
2
C
A
B
NH
S
NH
NH
O2 (air)
O2
+ NH4
O
O
O
EY
S
S
EY
H atom
abstraction
ref. 11e
Photocatalytic
cycle of eosin
Y
O2 + NH3
O
SCN
N
C
S
NH
92%,b,c 12 h
2c:
96%, 12 h
NH
2b:
2a:
94%, 12 h
+
O
OH
NH4
SCN
S
NH
S
NH
S
Ar
O
Ar
Ar
O
O
, air
eosin Y
S
green LEDs
2
1
D
Scheme 2 Plausible mechanism for the formation of 5ꢀarylꢀ2ꢀiminoꢀ1,3ꢀ
oxathiolanes 2.
Cl
Cl
O2N
Cl
2e:
2f:
74%, 18 h
NH
2d:
83%, 14 h
NH
81%, 14 h
35 at room temperature. Thus, it is a superior alternative to the
existing method with respect to green and sustainable chemistry
(better atomꢀ and stepꢀeconomy) for the synthesis of 5ꢀarylꢀ2ꢀ
iminoꢀ1,3ꢀoxathiolanes bearing a free imino (=NH) group.
NH
O
S
O
S
O
S
F
Br
40 Experimental section
NO2
2i:
80%, 16 h
NH
2h:
2g:
85%, 16 h
O
78%, 18 h
General Information: All commercially available reagents were
used without further purification unless otherwise specified by a
reference. Solvents were purified by the usual methods and stored
45 over molecular sieves. All reactions were performed using ovenꢀ
dried glassware. Organic solutions were concentrated using a
Buchi rotary evaporator. Column chromatography was carried out
over silica gel (Merck 100–200 mesh) and TLC was performed
using silica gel GF254 (Merck) plates. IR spectra in KBr were
50 recorded on a PerkinꢀElmer 993 IR spectrophotometer and 1H
(400 MHz), 13C (100 MHz) NMR spectra were recorded on a
Bruker AVII spectrometer in CDCl3 using TMS as internal
reference. All chemical shifts are reported in δ/ppm and coupling
constants (J) in Hertz (Hz). MS (EI) spectra were recorded on
55 double focusing mass spectrometer. Green LEDs (2.50 W, λ =
535 nm) Rebel LED, mounted on a 25 mm cool base was
purchased from commercial supplier Luxeon Star LEDs Quadica
Developments Inc. 47 6th Concession Rd. Brantford, Ontario N
32 5L7 Canada.
NH
S
NH
S
O
O
S
N
N
2j:
95%, 18 h
2k:
2l:
82%, 16 h
89%, 12 h
a Reaction conditions: 1 (1.0 mmol), NH4SCN (1.0 mmol), eosin Y (2
mol%) in CH3CN (3 mL) irradiated using Luxeon Rebel high power
green LEDs [2.50 W, λ = 535 nm] in open air at rt for 12ꢀ18 h. b Isolated
5
c
yield of the product 2. For general procedure and characterization of
compounds see: Experimental section and ESI†.
10
On the basis of our observations and the literature
reports,6c,8a,11 a plausible mechanistic pathway is depicted in
Scheme 2. Eosin Y (EY) on absorption of light goes to its excited
state (EY*). Single electron transfer between
affords SCN and
and EY*
The photoredox cycle of eosin Y is
EY
SCN
•
11a
EY
,
60
15 completed by the aerobic oxidation of
to its ground states
General procedure for the synthesis of 5-aryl-2-imino-1,3-
oxathiolanes (Table 2): A round bottom flask was charged with
styrene 1 (1.0 mmol), eosin Y (2 mol%), NH4SCN (1.0 mmol)
and CH3CN (3 mL) and the contents were stirred in open air
65 under irradiation with Luxeon Rebel high power green LEDs
[2.50 W, λ = 535 nm] at room temperature for 12ꢀ18 h. After the
completion of reaction (as indicated by TLC), it was quenched
with water (5 mL) and extracted with ethyl acetate (3 × 5 mL).
The organic phase was dried over anhydrous magnesium sulfate
70 and concentrated under reduced pressure to yield the crude
product, which was purified by silica gel column chromatography
using a mixture of EtOAcꢀHexane to give the pure product 2 in
high yields (Table 2).
(EY). The in situ generated thiocyanate radical attacks on styrene
1 to form intermediate A,6c which combines with O2 to form a
peroxy radical B,11b which reacts with A to give radical C.6c,11c
The alkoxy radical C is either reduced and protonated with
+
O2
20
/NH4 or abstract hydrogen to form βꢀhydroxythiocyanate
D.11e Extremely fast cyclization of D affords the desired product
2.8a
Conclusion
25
In conclusion, we have disclosed a novel, oneꢀpot procedure
for the synthesis of 5ꢀarylꢀ2ꢀiminoꢀ1,3ꢀoxathiolanes from
styrenes and ammonium thiocyanate. The protocol utilizes
atmospheric oxygen and visible light as the cheapest and ecoꢀ
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The structure of the products was confirmed by comparison of
IR, 1H, 13C NMR and MS spectral data with those reported in the
literature.8a
Characterization data of compounds 2 are summarised below
with relevant references:
Compound 2g:8a IR (KBr): 3417, 1633, 1526, 1434, 1307, ,
1
1087, 785 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 8.26 (d, 1H
60 |4JHH| 2 Hz), 8.23 (dd, 1H |3JHH| 8 Hz, |4JHH| 2 Hz), 7.76 (d, 1H
|3JHH| 8 Hz), 7.60 (t, 1H |3JHH| 8 Hz), 5.73 (s,1H (=NH), 5.68 (dd,
1H, |3JHH| 9 Hz, |3JHH| 6 Hz), 3.75 (dd, 1H |2JHH| 11 Hz, |3JHH| 6
Hz), 3.47 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz); 13C NMR (CDCl3,
100 MHz): δ = 168.8, 148.2, 139.2, 131.5, 130.3, 123.5, 120.6,
5
Compound 2a:8a IR (KBr): 3165, 1693, 1642, 1585, 1490,
1
1284 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 7.37ꢀ7.31 (m, 3H), 65 82.5, 39.7. HRMS (EI): calcd. for C9H8N2O3S 224.0254, found
7.29 (d, 2H |3JHH| 9 Hz), 5.35 (s,1H (=NH), 4.65 (dd, 1H |3JHH| 9
224.0250.
10 Hz, |3JHH| 6 Hz), 3.60 (dd, 1H |2JHH| 11 Hz, |3JHH| 6 Hz), 3.42 (dd,
1H |2JHH| 11 Hz, |3JHH| 9 Hz); 13C NMR (CDCl3, 100 MHz): δ =
168.7, 136.5, 128.7, 128.3, 125.2, 84.0, 39.3. HRMS (EI) calcd.
for C9H9NOS: 179.0405, found 179.0403.
Compound 2h: IR (KBr): 3207, 1634, 1449, 1257, 1040, 831,
1
671 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 7.45 (d, 2H, |3JHH| 9
70 Hz), 7.32 (d, 2H |3JHH| 9 Hz), 5.59 (s,1H (=NH), 5.57 (dd, 1H
|3JHH| 9 Hz, |3JHH| 6 Hz), 3.60 (dd, 1H |2JHH| 11 Hz, |3JHH| 6 Hz),
3.41 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz); 13C NMR (CDCl3, 100
MHz): δ = 168.6, 135.5, 134.7, 129.0, 127.0, 83.4, 39.5. HRMS
(EI): calcd. for C9H8BrNOS 256.9510, found 256.9513.
75
15
Compound 2b: IR (KBr): 3153, 2922, 1687, 1637, 1570,
1
1387, 857, 672 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 7.35 (d,
2H |3JHH| 9 Hz), 7.20 (d, 2H |3JHH| 9 Hz), 5.60 (s,1H (=NH), 5.56
(dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz), 3.60 (dd, 1H |2JHH| 11 Hz, |3JHH
|
6 Hz), 3.43 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz), 2.30 (s, 3H); 13C
Compound 2i: IR (KBr): 3203, 1632, 1057, 825, 750, cmꢀ1;
1H NMR (CDCl3, 400 MHz): δ = 7.42ꢀ7.36 (m, 2H), 7.24ꢀ7.19
(m, 2H), 5.64 (s,1H (=NH), 5.58 (dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz),
3.63 (dd, 1H |2JHH| 11 Hz, |3JHH| 6 Hz), 3.41 (dd, 1H |2JHH| 11 Hz,
80 |3JHH| 9 Hz); 13C NMR (CDCl3, 100 MHz): δ = 168.7, 160.3,
134.9, 127.0, 115.4, 83.2, 39.5. HRMS (EI) calcd. for
C9H8FNOS: 197.0311, found 197.0310.
20 NMR (CDCl3, 100 MHz): δ = 168.9, 136.8, 136.3, 128.6, 125.5,
84.1, 39.2, 21.1. HRMS (EI): calcd. for C10H11NOS 193.0561,
found 193.0559.
Compound 2c: IR (KBr): 3146, 2920, 1683, 1639, 1509,
25 1463, 1259, 1173, 1025, 830 cmꢀ1; 1H NMR (CDCl3, 400 MHz):
δ = 7.30 (d, 2H |3JHH| 9 Hz), 6.98 (d, 2H |3JHH| 9 Hz), 5.64 (s,1H
(=NH), 5.56 (dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz), 3.79 (s, 3H), 3.61
Compound 2j: IR (KBr): 3421, 3141, 2952, 1639, 1354,
(dd, 1H |2JHH| 11 Hz, |3JHH| 6 Hz), 3.43 (dd, 1H |2JHH| 11 Hz, |3JHH
|
85 1059, 853, 776 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 7.24 (d,
1
9 Hz); 13C NMR (CDCl3, 100 MHz): δ = 168.7, 159.2, 132.7,
30 127.4, 125.3, 84.2, 55.7, 39.4. HRMS (EI) calcd. for
C10H11NO2S: 209.0510, found 209.0513.
2H |3JHH| 9 Hz), 6.76 (d, 2H |3JHH| 9 Hz), 5.63 (s,1H (=NH), 5.57
(dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz), 3.60 (dd, 1H |2JHH| 11 Hz, |3JHH
|
6 Hz), 3.43 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz), 3.06 (s, 6H); 13C
NMR (CDCl3, 100 MHz): δ = 168.1, 149.3, 134.9, 129.2, 127.0,
Compound 2d:8a IR (KBr): 3204, 1637, 1057, 832, 670 cmꢀ1; 90 83.3, 40.2, 38.6. HRMS (EI) calcd. for C11H14N2OS: 222.0827,
1H NMR (CDCl3, 400 MHz): δ = 7.40 (d, 2H |3JHH| 9 Hz), 7.33
35 (d, 2H |3JHH| 9 Hz), 5.65 (s,1H (=NH), 5.57 (dd, 1H |3JHH| 9 Hz,
|3JHH| 6 Hz), 3.62 (dd, 1H |2JHH| 11 Hz, |3JHH| 6 Hz), 3.40 (dd, 1H
|2JHH| 11Hz, |3JHH| 9 Hz); 13C NMR (CDCl3, 100 MHz): δ = 168.7,
found 222.0825.
Compound 2k: IR (KBr): 3146, 1674, 1043, 910, 874, 776
1
cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 8.01ꢀ7.92 (m, 2H), 7.68ꢀ
135.3, 134.7, 129.2, 127.1, 83.3, 39.7. HRMS (EI) calcd. for 95 7.50 (m, 2H), 7.47 (s, 1H), 7.33ꢀ7.27 (m, 2H), 5.52 (s,1H (=NH),
C9H8ClNOS: 213.0015, found 213.0017.
5.47 (dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz), 3.65 (dd, 1H |2JHH| 11 Hz,
|3JHH| 6 Hz), 3.43 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz); 13C NMR
(CDCl3, 100 MHz): δ = 168.3, 135.4, 134.9, 129.0, 128.3, 127.6,
127.2, 126.7, 126.3, 125.6, 123.8, 83.4, 39.2. HRMS (EI) calcd.
40
Compound 2e:8a IR (KBr): 3334, 1636, 1563, 1032, 837, 676
1
cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 7.50 (d, 1H |4JHH| 2 Hz),
7.48 (d, 1H |3JHH| 8 Hz), 7.26 (dd, 1H, |3JHH| 8 Hz, |4JHH| 2 Hz), 100 for C13H11NOS: 229.0561, found 229.0564.
5.65 (s,1H (=NH), 5.54 (dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz), 3.68 (dd,
45 1H |2JHH| 11 Hz, |3JHH| 6 Hz), 3.42 (dd, 1H |2JHH| 11 Hz, |3JHH| 9
Hz); 13C NMR (CDCl3, 100 MHz): δ = 168.5, 137.0, 133.2,
132.0, 130.8, 127.7, 124.6, 82.3, 39.4. HRMS (EI) calcd. for
C9H7Cl2NOS: 246.9625, found 246.9628.
Compound 2l: IR (KBr): 3203, 3040, 1642, 1053, 828, 728,
1
700 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 8.30 (s, 1H), 7.73ꢀ
7.68 (m, 1H), 7.46ꢀ7.40 (m, 2H), 5.42 (s,1H (=NH), 5.35 (dd, 1H
105 |3JHH| 9 Hz, |3JHH| 6 Hz), 3.61 (dd, 1H |2JHH| 11 Hz, |3JHH| 6 Hz),
3.40 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz); 13C NMR (CDCl3, 100
MHz): δ = 168.4, 145.3, 142.7, 138.3, 132.1, 123.0, 83.5, 39.6.
HRMS (EI) calcd. for C8H8N2OS: 180.0357, found 180.0354.
50
Compound 2f:8a IR (KBr): 3340, 1664, 1595, 1541, 1405,
1
1337, 1081, 781 cmꢀ1; H NMR (CDCl3, 400 MHz): δ = 8.22 (d,
2H |3JHH| 9 Hz), 7.57 (d, 2H |3JHH| 9 Hz), 5.71 (s,1H (=NH), 5.69
(dd, 1H |3JHH| 9 Hz, |3JHH| 6 Hz), 3.74 (dd, 1H |2JHH| 11 Hz, |3JHH
|
110 Aknowledgements
6 Hz), 3.41 (dd, 1H |2JHH| 11 Hz, |3JHH| 9 Hz); 13C NMR (CDCl3,
We sincerely thank the SAIF, Punjab University, Chandigarh,
for providing spectra. One of us (A.K.Y.) is grateful to the CSIR,
New Delhi, for the award of a Senior Research Fellowship.
55 100 MHz): δ = 168.6, 148.2, 144.0, 126.3, 124.0, 82.4, 39.2.
HRMS (EI): calcd. for C9H8N2O3S 224.0256, found 224.0253.
4
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(a) A. K. Yadav and L. D. S. Yadav, Tetrahedron Lett., 2014,
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DOI: 10.1039/C5GC00642B
Graphical Abstract:
Visible-light-mediated difunctionalization of styrenes: an unprecedented approach
to 5-aryl-2-imino-1,3-oxathiolanes
5
Arvind K. Yadav and Lal Dhar S. Yadav*
A mild and efficient method for the synthesis of 5ꢀarylꢀ2ꢀiminoꢀ1,3ꢀoxathiolanes from styrenes and
10 NH4SCN is developed. The protocol utilizes visible light and air as the ecoꢀsustainable and cheapest
reagents.
NH
O
air
eosin Y
S
(2 mol%) (O2)
Ar
Ar
NH4SCN, CH3CN, rt, 12-18 h
yield: 74-96%,
12 examples
15
20
25
30
6
| Journal Name, [year], [vol], 00–00
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Dynamic Article Links ►
View Article Online
DOI: 10.1039/C5GC00642B
Cite this: DOI: 10.1039/c0xx00000x
www.rsc.org/xxxxxx
ARTICLE TYPE
Graphical Abstract:
Visible-light-mediated difunctionalization of styrenes: an unprecedented approach
to 5-aryl-2-imino-1,3-oxathiolanes
5
Arvind K. Yadav and Lal Dhar S. Yadav*
A mild and efficient method for the synthesis of 5ꢀarylꢀ2ꢀiminoꢀ1,3ꢀoxathiolanes from styrenes and
NH4SCN is developed. The protocol utilizes visible light and air as the ecoꢀsustainable and cheapest
10 reagents.
NH
S
O
air
(O2)
eosin Y
2 mol%
Ar
Ar
NH4SCN, CH3CN, rt, 12-18 h
yield: 74-96%,
12 examples
15
20
25
30
35
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1