One pot photoredox decarboxylation reaction of N-cyano(α-bromo- α-phenyl)methylanilines leading to synthesis of four-membered cyclic carbamates

Article abstract of DOI:10.1002/jhet.1776

A new four-membered cyclic carbamates have been synthesized through solar irradiation of N-cyano(α-bromo-α-phenyl)methylanilines in their aqueous methanolic solution using iodide salt in basic medium. These compounds have been characterized as 3,4-diphenyl-1,3oxazetidin-2-one through their elemental analysis, IR, ¹H-NMR, ¹³C-NMR, and mass spectral studies.

Full text of DOI:10.1002/jhet.1776

850
One Pot Photoredox Decarboxylation Reaction of N-Cyano(a-bromo-a-
phenyl)methylanilines Leading to Synthesis of Four-Membered Cyclic
Carbamates
Vol 51
*
Manpreet Kaur and Baldev Singh
Department of Chemistry, Punjabi University, Patiala, 147002, Punjab, India
*
E-mail: singhbaldev1981@gmail.com
Received February 28, 2012
DOI 10.1002/jhet.1776
Published online 27 November 2013 in Wiley Online Library (wileyonlinelibrary.com).
H
H
CNBr
N
N
Ethanol
Y
Br CN
Y
X
X
KOH ,KI
Yield 68-77%
hv
(sunlight)
X= H, OH, OCH3
Y= H, CH3, OCH3, Cl, NO2
168 hr
O
O
H
N
Y
X
A new four-membered cyclic carbamates have been synthesized through solar irradiation of N-cyano(a-
bromo-a-phenyl)methylanilines in their aqueous methanolic solution using iodide salt in basic medium.
These compounds have been characterized as 3,4-diphenyl-1,3oxazetidin-2-one through their elemental
analysis, IR, 1H-NMR, 13C-NMR, and mass spectral studies.
J. Hetercycl Chem., 51, 850 (2014).
INTRODUCTION
These N-cyano(a-bromo-a-phenyl)methylanilines (I) were
recrystallized and characterized through their melting points
and elemental analysis and were used further for photoirra-
diation. To the methanolic solution of these compounds (I)
were added 2% potassium iodide and 1% aqueous potassium
hydroxide solution, and the reaction mixture was exposed to
direct sunlight in silica glass photoreactor for a period of
1 week(168 h). These N-cyano(a-bromo-a-phenyl)methyla-
nilines (I) undergo reductive photo-decarboxylation to pro-
vide four-membered cyclic carbamates (II) in good yields
(Scheme 1). These carbamates have been characterized
through their elemental analysis, IR, proton magnetic reso-
nance, and high resolution mass spectra.
Carbon–nitrogen containing compounds are of pharmaco-
logical importance and act as antiseptic, antifungal, antican-
cer agent [1,2], and so forth. Carbon–nitrogen bond present
in variety of substrate azomethines, azomethines-N-oxides,
nitrilimine, azomethines ylids, and N-a-cyanoamines and
find great importance in the synthesis of heterocyclic
compounds of different ring size through their cycloaddition
reaction [2–4] and photoredox reaction [5,6]. N-a-Cyanoa-
mines by for the most suitable substrates [7,8] that has also
been employed for the synthesis of several heterocyclic
compounds of pharmacological importance. Earlier from
these laboratories, a novel synthesis of substituted benzoimi-
dazoloquinolines and a novel photoredox reaction of N-a-cy-
ano-a-styryl-methylanilines have also been reported.
In their IR spectra, these carbamates (II) in Scheme 1 dis-
play a broad absorption band in the region 1702–1680cmÀ1
that has been assigned to four-membered cyclic carbamates
function. Another strong absorption band in the region
1650–1570 cmÀ1 has been assigned to aromatic carbon–
carbon double bond stretching, whereas an absorption band
in the region 1286–1244 cmÀ1 has been assigned to
carbon–nitrogen single bond. In all these IR spectra, absorp-
tion band due to nitrile function 2250–2200cmÀ1 is wanting
indicating that cyano group has been transformed to cyclic
RESULTS AND DISCUSSION
For the present study, N-cyano(a-bromo-a-phenyl)methy-
lanilines (I) have been used for the photoredox decarboxyl-
ation reaction employing solar radiation. These compounds
have been prepared by synthesizing azomethines through
the usual condensation reaction of variously substituted aro-
matic aldehyde and variously substituted anilines followed
by the subsequent addition of cyanogen bromide in ethanol.
1
carbamates moiety. In the 400 MHz H-NMR, these four-
membered cyclic carbamates display a multiplet signal in
the region at d 8.7–6.5 (8H—Ar) and a singlet in the region
© 2013 HeteroCorporation

May 2014
Four-Membered Cyclic Carbamates
851
Scheme 1. Classical synthesis of 3,4-diphenyl-1,3-oxazetidin-2-one.
hydrogen. The other aromatic carbons appear in the region
at d 132.9–116.2, whereas signals in the regions at d 59.7–
60.2 have been assigned to carbon of –OCH3 group, and
signal at d 20.6 has been assigned to carbon of CH3 group.
In the high-resolution mass spectra, these carbamates
display M+ and (M-44)+ as the base peak along with other
prominent peaks (Figure 1). The reaction seems to involve
the generation of hydroxide free radical through iodide free
radical in the sunlight that attack the nitrile function to form
hydroxyimino radical and subsequently that is transformed
to amide function, and at the same time, C-bromo gets
hydroxylated that through nucleophilic attack forms four-
membered cyclic carbamates in Scheme 2.
EXPERIMENTAL
at d 13.3–12.7 (1H-phenolic) whereas a sharp singlet in the
region at d 8.8–8.5 (1H-benzylic) (vide experimental).
Benzylic proton merges in aromatic region because it is
deshielded by nitrogen on one side and oxygen on other
side [2]. In their 13C-NMR spectra, these derivatives show
identical pattern, as are presentative case 13C spectrum of
derivative 3,4-diphenyl-1,3-oxazetidin-2-one is described.
A signal in the region at d 162.2–162.9 has been assigned
to carbonyl carbon, whereas signals in the regions at
d 160.3–161.5, 145.1–146.9, and 133.4–136.7 has been
assigned to carbon atom of aromatic ring bearing no
(I) General procedure for the preparation of azomethines.
Various azomethines were prepared by following an identical
procedure as described in literature [2]. Synthesis of o-hydro-
xybenzylidene-p-nitroaniline is described as a presentative case.
Salicylaldehyde 1.22 g (0.01 mol) was mixed with 1.38 g
(0.01 mol) of p-nitroaniline in 10 mL of ethyl alcohol. The
reaction mixture after gentle warming provided the required
azomethines. mp 128–130ꢀC.
(II) General procedure for the preparation of N-cyano(a-
bromo-a-phenyl)methylanilines. To the solution of azomethines
in ethyl alcohol taken in conical flask, an equimolar quantity of
cyanogen bromide 1.06 g (0.01 mol) were added in a good ventilated
Scheme 2. Mechanistic pathway of 3,4-diphenyl-1,3-oxazetidin-2-one.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

852
M. Kaur and B. Singh
Vol 51
Figure 1. Mass fragmentation of 4-(2-Hydroxyphenyl)-3-(4-nitrophenyl)-,3-oxazetidin-2-one.
hood. The flask was tightly corked and shaken intermittently for half an
hour. The reaction mixture was kept for overnight period. Usual work
up of the reaction mixture provided the crystalline product that was
recrystallised from benzene/petroleum ether. mp 160–162ꢀC.
Table 2
Characterization data of 3,4-diphenyl-1,3-oxazetidin-2-one.
mp
(ꢀC)
Yield
(III) General procedure for the preparation of 3,4-diphenyl-
Time
(h)
1,3-oxazetidin-2-ones.
To the solution of an appropriate N-
Entry
X
Y
(%)
cyano(a-bromo-a-phenyl)methylaniline in ethanol (200 mL) was
added 2% KI and 1% aqueous KOH in 250mL conical silica
glass flask. The reaction mixture was stirred with nitrogen gas to
expel out any dissolved oxygen, and the reaction mixture was
exposed to direct sunlight for a period of 1 week. The usual work
up of the reaction mixture provided the corresponding 3,4-
diphenyl-1,3-oxazetidin-2-one as white crystalline solids. These
carbamates have been characterized through elemental analysis,
IR, NMR, and high resolution mass spectral data. All the four-
membered cyclic carbamates (S4 to B4) were prepared by
following aforementioned similar procedure (Table 1 and Table 2).
4-(2-Hydroxyphenyl)-3-(4-nitrophenyl)-1,3-oxazetidin-2-one
(S4). mp: 196–198ꢀC; IR (KBr Pellets) n:
S4
S5
S2
A5
A4
A1
B4
2-OH
2-OH
2-OH
4-OCH3
4-OCH3
4-OCH3
4-H
4-NO2
4-Cl
4-CH3
4-Cl
4-NO2
4-H
4-NO2
163
160
157
153
162
156
155
196–198
197–199
187–189
236–238
203–205
188–190
227–229
77
72
74
68
68
69
72
12.7 (s, 1H, OH), 8.6 (s, 1H, —CH—); 13C-NMR (CDCl3) d: 116.2,
118.3, 119.1, 129.8, 132.5, 132.8, 136.4, 145.7, 160.3, 162.9; MS: Molec-
ular ion peak m/z 286; Anal. Calcd for: C14H10N2O5: C, 58.74; H, 3.49; N,
9.79. Found: C, 59.08; H, 4.39; N, 10.5; Percentage yield = 77%.
3-(4-Chlorophenyl)-4-(2-hydroxyphenyl)-1,3-oxazetidin-2-one
(S5). mp: 197–199ꢀC; IR (KBr Pellets) n:
1690, (C—N) 1271, (C═C) 1586–1566, (—NO2) 1566–1340, (—OH)
3481–3069 cmÀ1
;
1H-NMR (400 MHz, CDCl3) d: 8.2–6.5 (m, 8H, Ar),
1690, (C—N) 1271, (C═C) 1584–1566, (—OH) 3084–2979 cmÀ1 1H-
;
NMR (400 MHz, CDCl3) d: 7.8–6.5 (m, 8H, Ar), 13.1 (s, 1H, —OH),
8.5 (s, 1H, —CH—); 13C-NMR (CDCl3) d: 117.3, 119.0, 119.2, 122.5,
129.5, 132.4, 132.6, 133.4, 146.9, 161.1, 162.9; MS: Molecular ion peak
m/z 275; Anal. Calcd for: C14H10NO3Cl: C, 61.09; H,3.63; N, 5.09.
Found: C, 62.27; H, 3.97; N, 5.8; Percentage yield = 72%.
Table 1
Characterization data of azomethines and N-cyano(a-bromo-a-phenyl)
methylanilines.
mp of
mp of N-cyano(a-bromo-a-phenyl)
4-(2-Hydroxyphenyl)-3-p-tolyl-1,3-oxazetidin-2-one (S2).
187–189ꢀC; IR (KBr Pellets) n:
mp:
Entry
X
Y
azomethines
methylanilines
S4
2-OH
4-
128–130
160–162
NO2
4-Cl
4-
CH3
4-Cl
1700–1690, (C—N) 1281, (C═C) 1597–1568, (—OH) 3051–2857cmÀ1
;
S5
S2
2-OH
2-OH
100–102
98–100
145–147
127–129
1H-NMR (400MHz, CDCl3) d: 7.6–6.7 (m, 8H, Ar), 13.3 (s, 1H, —OH),
8.5 (s, 1H, —CH—), 2.4 (s, 3H, —CH3); 13C-NMR (CDCl3) d: 20.6,
116.4, 118.7, 119.0, 129.7, 132.2, 132.6, 136.3, 145.1, 160.4, 162.0; MS:
Molecular ion peak m/z 255; Anal. Calcd for: C15H13NO3: C, 70.58; H,
5.09; N, 5.49. Found: C, 69.09; H, 5.97; N, 6.09; Percentage yield = 74%.
3-(4-Chlorophenyl)-4-(4-methoxyphenyl)-1,3-oxazetidin-2-one
(A5). mp: 236–238ꢀC; IR (KBr Pellets) n:
A5
A4
A1
B4
4-
OCH3
4-
OCH3
4-
85–87
79–80
60–62
40–45
150–152
145–147
146–148
190–192
4-
NO2
4-H
OCH3
4-H
4-
NO2
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

May 2014
Four-Membered Cyclic Carbamates
853
1690, (C—N) 1285, (C═C) 1582–1573 , (—OCH3) 1171–1015 cmÀ1
;
3-(4-Nitrophenyl)-4-phenyl-1,3-oxazetidin-2-one (B4). mp:
227–229ꢀC; IR (KBr Pellets) n:
1H-NMR (400 MHz, CDCl3) d: 8.6–7.2 (m, 8H, Ar), 8.8 (s, 1H, —
CH—), 3.8 (s, 3H, —OCH3 ); 13C-NMR (CDCl3): d 60.2, 116.2,
118.3, 119.5, 129.3, 132.7, 132.2, 136.7, 145.7, 160.7, 162.2; MS: Mo-
lecular ion peak m/z 289; Anal. Calcd for: C15H12NO3Cl: C, 62.28; H,
4.15; N, 4.84. Found: C, 63.09; H, 4.89; N, 4.31; Percentage
yield = 69%.
1689, (C—N) 1244, (C═C) 1650–1570, (—NO2) 1527–1332 cmÀ1 1H-
;
NMR (400 MHz, CDCl3) d: 7.8–6.6 (m, 8H, Ar), 8.6 (s, 1H, —CH—);
13C-NMR (CDCl3) d: 117.2,119.3, 119.4, 122.8, 129.6, 132.4, 132.8,
133.4, 146.3, 161.5, 162.7; MS: Molecular ion peak m/z 270; Anal. Calcd
for: C14H10N2O4: C, 62.22; H, 3.70; N, 10.37. Found: C, 62.97; H, 4.25;
N, 10.9; Percentage yield = 72%.
4-(4-Methoxyphenyl)-3-(4-nitrophenyl)-1,3-oxazetidin-2-one
(A4). mp:203–205ꢀC; IR (KBr Pellets) n:
1702, (C—N) 1283, (C═C) 1581–1553, (—OCH3) 1175–1022, (NO2)
1553–1331 cmÀ1 1H-NMR (400 MHz, CDCl3) d: 8.7–7.1 (m, 8H, Ar),
;
Acknowledgment. The author wish to thank NIPER (Mohali), SAIF
(PU) for spectral studies.
8.8 (s, 1H, —CH—), 3.9 (s, 3H, —OCH3); 13C-NMR (CDCl3) d: 59.7,
117.2, 119.1, 119.7, 122.7, 129.8, 132.3, 132.9, 133.7, 146.6, 161.4,
162.8; MS: Molecular ion peak m/z 300; Anal. Calcd for: C15H12 N2O5:
C, 60.00; H, 4.00; N, 9.33. Found: C, 59.06; H, 4.73; N, 9.87; Percentage
yield = 68%.
REFERENCES AND NOTES
4-(4-Methoxyphenyl)-3-phenyl-1,3-oxazetindin-2-one (A1).
mp:
188–190ꢀC; IR (KBr Pellets) n:
[1] Shreenivas, M.T.; Chetan, B.P.; Bhat, A.R. Journal of Pharma-
ceutical Sciences & Technology 2009, 1, 88.
[2] Layer, R.W. Chem Rev 1963, 63, 489.
[3] Singal, K. K.; Singh, B.; Rehalia, K. S. Indian J Chem 1988,
27B, 643.
[4] Singal, K. K.; Singh, B.; Raj, Baldev. Synthetic Commun 1999,
29, 911.
1680, (C—N) 1286, (C═C) 1570–1580, (—OCH3) 1172–1012 cmÀ1
;
1H-NMR (400 MHz, CDCl3) d: 8.5–6.9 (m, 8H, Ar) , 8.7 (s, 1H, —
CH—), 3.8 (s, 3H, —OCH3); 13C-NMR (CDCl3) d: 59.8, 116.9,
119.2, 119.6, 122.4, 129.4, 132.7, 132.6, 133.9, 146.8, 161.3, 162.9;
MS: Molecular ion peak m/z 255; Anal. Calcd for: C15H13NO3: C,
70.58; H, 5.09; N, 5.49. Found: C, 69.87; H, 5.23; N, 5.89; Percentage
yield = 69%.
[5] Singal, K. K.; Singh, B. Synthetic Commun 1985, 15, 829.
[6] Singal, K. K.; Singh, B. Chemica Acta Turcita 1998, 26, 1.
[7] Shah, S.; Singh, B. Tetrahedron Lett 2012, 53, 151.
[8] Kumar, V. Synlett 2005, 10, 1638.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet