One-Pot Synthesis of O -Aryl Carbamates

Article abstract of DOI:10.1055/s-0035-1560726

A simple, versatile, one-pot procedure for the synthesis of substituted O-aryl carbamates has been developed, and a protocol is henceforth described. N-Substituted carbamoyl chloride is formed in situ and subsequently reacted with a substituted phenol, avoiding the direct manipulation of sensitive reactants. This procedure offers an economical and efficient route to many compounds of interest.

Full text of DOI:10.1055/s-0035-1560726

SYNTHESIS
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
© Georg Thieme Verlag Stuttgart · New York
2016, 48, 43–47
psp
43
S. E. Varjosaari et al.
PSP
Synthesis
One-Pot Synthesis of O-Aryl Carbamates
O
Sami E. Varjosaari
O
R1
Paolo Suating
Marc J. Adler*
OH
O
N
R2
Cl3CO
pyridine, 110 °C, 1–18 h
OCCl3
R1
HN
R2
+
Department of Chemistry & Biochemistry,
Northern Illinois University, 1425 W. Lincoln
Hwy., DeKalb, IL 60115-2828, USA
mjadler@niu.edu
R3
one-pot
versatile
R3
14 examples
up to 99% yield
R1, R2 = Me, Et, OMe, -C2H4OC2H4-
3 = H, 4-NO2, 3-NO2, CHO, Ac, CN, 2,6-Cl2
R
Received: 25.08.2015
Accepted after revision: 24.09.2015
Published online: 27.10.2015
O
O
N
O
N
N
O
O
DOI: 10.1055/s-0035-1560726; Art ID: ss-2015-m0500-psp
N
Abstract A simple, versatile, one-pot procedure for the synthesis of
substituted O-aryl carbamates has been developed, and a protocol is
henceforth described. N-Substituted carbamoyl chloride is formed in
situ and subsequently reacted with a substituted phenol, avoiding the
direct manipulation of sensitive reactants. This procedure offers an
economical and efficient route to many compounds of interest.
1
2
O
N
O
O
S
N
O
N
O
O
S
O
NH
Key words O-aryl carbamates, phenyl carbamates, one-pot, versatile,
safe, high yield
3
4
Figure 1 O-Aryl carbamate-containing active agents: acetylcholines-
terase inhibitors neostigmine (1) and rivastigmine (2), matrix metallo-
proteinase-2 inhibitor 3, and an antifungal agent 4.
O-Aryl carbamates are an important class of molecules
that have a wide range of uses. The pharmaceutical and
medical industries have used them as acetylcholinesterase
inhibitors for the treatment of debilitating neurodegenera-
tive diseases such as Parkinsonism, myasthenia gravis, and
Alzheimer’s disease.1–3 O-Aryl carbamates have also been
investigated as potential prodrugs for antineoplastic and
antifungal drugs (Figure 1).4,5 Additionally, they have been
effectively used as intermediates for the synthesis of a
range of antiviral, anti-infective, and antineoplastic drugs
in the form of semicarbazides.6
The agrochemical industry also has a use for O-aryl car-
bamates in the form of herbicides and insecticides, the dif-
ference being the substitution pattern on the O-aryl ring.7
O-Aryl carbamates have also been used as synthetic inter-
mediates for a variety of reactions using the carbamate
functionality as a directing group (particularly for C–H acti-
vation at the ortho-position of the phenol) with lithium re-
agents,8,9 and more recently rhodium,10 ruthenium,11 and
palladium catalysts.12 They have also proven to be effective
reagents for nickel-catalyzed α-arylation of esters and am-
ides, which can be further reacted to form α-arylcarboxylic
acids and β-arylamines.13
An economical means of synthesizing O-aryl carba-
mates directly from the corresponding amine and phenol
has not been realized.6 Current methods include reaction of
isolated carbamoyl chlorides with a substituted phe-
nol,11,12c,14 reaction of isolated aryl chloroformates with an
amine,10,15 or copper catalyzed oxidative cross-couplings of
formamides and phenols.16 These reactions are limited by
the availability of aryl chloroformates and carbamoyl chlo-
rides, as well as the highly reactive nature of these com-
pounds. In this work, we communicate a simplified one-pot
method for the generation of O-aryl carbamates directly
from widely commercially available amines and phenols.
In situ formation of the carbamoyl chloride followed by
the nucleophilic attack of the aryloxide ion to yield O-aryl
carbamates in good yields allows for a wide variety of sub-
stituents on the O-aryl ring and the nitrogen on the amine
making the synthesis quite versatile (Scheme 1).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 43–47

44
S. E. Varjosaari et al.
PSP
Synthesis
R1
HN
R2
R1, R2 = Me, Et, OMe,
-C2H4OC2H4-
O
O
6
N
Cl
N
Cl3C
CCl3
+
O
O
I
II
5
OH
O
O
R1
R3 = H, 4-NO2, 3-NO2,
O
N
O
O
O
R3
R2
CHO, Ac, CN, 2,6-Cl2
R1
R3
Cl
N
8
R2
III
R3
R3
13
7
9–12
Scheme 1 Reaction route. Reagents and conditions: (I) CH2Cl2, 0 °C, 20 min; (II) 0 °C to r.t., 1 h; (III) pyridine, r.t. to 110 °C, 1–24 h.
The dropwise addition of pyridine to BTC [bis(trichloro-
methyl) carbonate, triphosgene] dissolved in dichlorometh-
ane, to form pyridiniumchlorocarbonyl chloride (5),17 has to
be cooled down to 0 °C in an ice bath as the reaction is high-
ly exothermic and a rise in temperature will release excess
amounts of toxic unreacted phosgene. For similar reasons,
the selected amine 6 needs to be added in small portions
whilst still cooled to 0 °C. After 6 has displaced pyridine to
form the corresponding carbamoyl chloride 7, dichloro-
methane and excess phosgene has to be removed under re-
duced pressure or the reaction will not proceed.
phenyl chloroformate (14) before the addition of 6 (Scheme
2).
An increase in the acidity of the phenol generally results
in higher yields, as noted in comparing 9d to 9a, and 11c to
11b. This suggests that the rate is dependent on the depro-
Table 1 Reaction Scope
No.
Structure
R
Yield (%)a
O
a: H
70b
87b
76b
99b
88
However, care must be taken in removing dichloro-
methane as extended periods under reduced pressure will
remove 7, and hence lower yields significantly.
O
N
O
b: 4-Ac
c: 3-NO2
d: 4-NO2
e: 2,6-Cl2
9
The selected phenol 8 is dissolved in pyridine and sub-
sequently added to 7 and left to stir for a period of time
varying from one hour to one day. Even though the reaction
proceeds at ambient temperature for most of the com-
pounds, running the reaction at 110 °C generally gives
higher yields and shortens the generalized reaction time to
under six hours.18 After workup, the O-aryl carbamates 9–
12 (Table 1) can be easily purified via column chromatogra-
phy or recrystallization.
R
O
O
O
O
O
O
N
N
N
a: 4-CHO
b: 4-Ac
c: 4-NO2
96
92
81
10
11
12
R
R
R
It has been observed that the reaction does not proceed
if attempted in ‘reverse’, that is, the in situ formation of the
a: 2,6-Cl2
b: 4-Ac
c: 4-NO2
99
84
99
OH
R1
O
O
HN
R2
R1
O
O
N
R2
Cl
O
R3
8
6
Cl
N
a: 4-CHO
b: 4-Ac
c: 4-CN
88
92
98
x
III
O
II
R3
R3
5
14
9–12
Scheme 2 Formation of aryl chloroformate followed by addition of an
amine is unsuccessful at forming desired O-aryl carbamates
a Isolated yields.
b Reactions run at r.t..
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 43–47

45
S. E. Varjosaari et al.
PSP
Synthesis
tonation of 8 by pyridine to give the more nucleophilic
phenoxide ion, which goes on to attack 7. In an effort to in-
crease yield, the more basic triethylamine was used in place
of pyridine; unfortunately this reaction did not proceed
even with heating, resulting only in the generation of side-
product 13.
There seems to be no significant correlation between
the identity of 6 and the overall yield of 9–12. Recent relat-
ed work showed similar results,19 indicating that the N,N-
dialkyl substituents on 7 do not have a significant effect on
this reaction.
4-Acetylphenyl Methoxy(methyl)carbamate (9b)
Yield: 0.584 g (1.305 mmol, 87%); clear oil; Rf = 0.2 (3:1 hexanes–
EtOAc).
IR (ATR): 1725, 1681, 1599, 1408, 1357, 1301, 1264, 1216, 1164, 1120,
1015, 958, 867 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 8.01 (d, J = 9 Hz, 2 H), 7.28 (d, J = 9 Hz,
2 H), 3.83 (s, 3 H), 3.32 (s, 3 H), 2.62 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ = 196.9, 154.6, 154.3, 134.5, 129.9,
121.7, 61.9, 35.6, 26.6.
MS (ESI): m/z = 223 [M]+.
3-Nitrophenyl Methoxy(methyl)carbamate (9c)
In summary, we have developed a versatile one-pot syn-
thesis of O-aryl carbamates with a large scope of substitu-
ents providing high yields. This method is viable for a range
of both phenols and disubstituted amines and does not re-
quire the isolation or handling of sensitive intermediates.
Yield: 0.257 g (1.14 mmol, 76%); clear oil; Rf = 0.1 (3:1 hexanes–
EtOAc).
IR (ATR): 1726, 1526, 1472, 1442, 1410, 1347, 1276, 1219, 1182, 1121,
1024, 816, 735 cm–1
.
1H NMR (500 MHz, CDCl3): δ = 8.14 (dt, J = 1.5, 7.5 Hz, 1 H), 8.09 (t, J =
1.5 Hz, 1 H), 7.59 (t, J = 8 Hz, 1 H), 7.56 (dt, J = 1.5, 8.5 Hz, 1 H), 3.85 (s,
3 H), 3.35 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ =154.0, 151.3, 148.8, 129.9, 128.1,
120.6, 117.4, 61.9, 35.6.
Chemicals were obtained from Sigma-Aldrich and Fisher Scientific.
Column chromatography was performed using silica gel from Mache-
rey-Nagel (60 M, 0.04–0.063 mm). 1H and 13C NMR data were record-
ed in CDCl3 on either a 300 or 500 MHz Bruker Avance III spectrome-
ter at r.t. Chemical shifts are reported relative to residual CHCl3 (δ =
7.24 for 1H, δ = 77.23 for 13C). IR data were acquired using an ATI
Mattson FTIR spectrophotometer on neat samples. MS data were ob-
tained with a Shimadzu GCMS QC2010S spectrometer at 275 °C.
MS (ESI): m/z = 226 [M]+.
4-Nitrophenyl Methoxy(methyl)carbamate (9d)
Yield: 0.681 g (3.0 mmol, 99%); white solid; mp 84–85 °C (heptanes);
Rf = 0.1 (3:1 hexanes–EtOAc).
IR (ATR): 1725, 1612, 1594, 1512, 1468, 1438, 1397, 1343, 1237, 1154,
O-Aryl Carbamates; General Procedure
1109, 1018, 964, 862 cm–1
.
To an oven-dried, argon-flushed 100 mL round-bottom flask was
added BTC (1.5 mmol) and CH2Cl2 (7.5 mL) at 0 °C, and the mixture
was stirred for 5 min. Pyridine (15 mmol) was added dropwise to
form a pale yellow precipitate 5, which redissolved after 20 min of
continuous stirring. The selected amine 6 (1.6 mmol) was added in
small portions and the mixture resulted in a red solution. This was
then left to stir for 1 h at r.t. at which time the solution turned yellow.
CH2Cl2 was removed under reduced pressure to give a sludge 7. The
selected phenol 8 (1.5 mmol) was dissolved in pyridine (2.5 mL) and
added to the sludge. The reaction mixture was then heated at 110 °C
and followed by TLC/GC-MS until completion (1–18 h). The reaction
was quenched with EtOAc (25 mL) and washed with aq 6 M HCl (2 ×
50 mL). The organic layer was dried (Na2SO4) and the EtOAc removed
under reduced pressure to give a crude product 9–12 either as an oil
or a solid, which can then be purified by via column chromatography
(9:1 hexanes–EtOAc) or recrystallization from hot heptanes.
1H NMR (500 MHz, CDCl3): δ = 8.29 (d, J = 15 Hz, 2 H), 7.37 (d, J = 15
Hz, 2 H), 3.84 (s, 3 H), 3.34 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ = 155.7, 153.6, 145.1, 125.2, 122.2, 61.9,
35.6.
MS (ESI): m/z = 226 [M]+.
2,6-Dichlorophenyl Methoxy(methyl)carbamate (9e)
Yield: 0.0330 g (0.132 mmol, 88%); clear oil; Rf = 0.3 (9:1 hexanes–
EtOAc).
IR (ATR): 1734, 1575, 1444, 1408, 1373, 1237, 1183, 1117, 1100, 1069,
1039, 1017, 956, 849, 834, 788, 773, 734, 712, 652, 610 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.38 (d, J = 8.5 Hz, 2 H), 7.16 (dd, J = 7.5,
8.5 Hz, 1 H), 3.88 (s, 3 H), 3.37 (s, 3 H).
13C NMR (75 MHz, CDCl3): δ = 152.5, 143.9, 129.4, 128.6, 127.1, 61.9,
35.6.
Phenyl Methoxy(methyl)carbamate (9a)
MS (ESI): m/z (%) = 249 (100), 251 (64, [M]+).
Yield: 0.420 g (2.31 mmol, 70%); clear oil; Rf = 0.2 (9:1 hexanes–
EtOAc).
4-Formylphenyl Dimethylcarbamate (10a)
IR (ATR): 1721, 1592, 1494, 1458, 1409, 1367, 1206, 1181, 1164, 1121,
1027, 962, 909, 838, 747, 689, 633, 600 cm–1
1H NMR (500 MHz, CDCl3): δ = 7.40 (m, 2 H), 7.25 (tt, J = 1, 7.5 Hz, 1
H), 7.18 (m, 2 H), 3.84 (s, 3 H), 3.32 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ = 155.2, 150.9, 129.4, 125.7, 121.6, 61.8,
35.7.
MS (ESI): m/z = 181 [M]+.
Yield: 0.0278 g (0.144 mmol, 96%); pale yellow oil; Rf = 0.3 (3:1
hexanes–EtOAc).
.
IR (ATR): 2251, 1719, 1696, 1601, 1486, 1446, 1386, 1300, 1212, 1153,
1065, 1011, 912, 859, 795, 728, 648 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 9.99 (s, 1 H), 7.91 (d, J = 8.5 Hz, 2 H),
7.32 (d, J = 8.5 Hz, 2 H), 3.13 (s, 3 H), 3.05 (s, 3 H).
13C NMR (75 MHz, CDCl3): δ = 191.0, 156.4, 153.9, 133.4, 131.1, 122.3,
36.8, 36.5.
MS (ESI): m/z = 193 [M]+.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 43–47

46
S. E. Varjosaari et al.
PSP
Synthesis
4-Acetylphenyl Dimethylcarbamate (10b)
13C NMR (125 MHz, CDCl3): δ = 156.5, 152.8, 144.7, 125.0, 122.2, 42.5,
42.1, 14.26, 13.27.
MS (ESI): m/z = 238 [M]+.
Yield: 0.0286 g (0.138 mmol, 92%); white solid; mp 48–50 °C (hep-
tanes); Rf = 0.2 (3:1 hexanes–EtOAc).
IR (ATR): 1722, 1673, 1597, 1502, 1446, 1410, 1388, 1356, 1267, 1208,
1163, 1116, 1058, 1009, 958, 875, 807, 752, 587 cm–1
.
4-Formylphenyl 4-Morpholinecarboxylate (12a)
1H NMR (300 MHz, CDCl3): δ = 7.99 (d, J = 8.5 Hz, 2 H), 7.24 (d, J = 8.5
Yield: 0.0311 g (0.132 mmol, 88%); pale yellow solid; mp 56–58 °C
(heptanes); Rf = 0.2 (3:1 hexanes–EtOAc).
Hz, 2 H), 3.13 (s, 3 H), 3.05 (s, 3 H), 2.61 (s, 3 H).
13C NMR (75 MHz, CDCl3): δ = 196.9, 155.3, 154.1, 134.1, 129.8, 121.7,
36.8, 36.5, 26.6.
IR (ATR): 1713, 1688, 1599, 1459, 1417, 1364, 1304, 1280, 1207, 1157,
1111, 1062, 994, 915, 859, 848, 806, 794, 647, 614, 573 cm–1
.
1H NMR (500 MHz, CDCl3): δ = 10.01 (s, 1 H), 7.94 (d, J = 8.5 Hz, 2 H),
7.33 (d, J = 8.5 Hz, 2 H), 3.79 (t, J = 4.5 Hz, 4 H), 3.72 (br, 2 H), 3.61 (br,
2 H).
13C NMR (125 MHz, CDCl3): δ = 190.9, 156.0, 152.7, 133.6, 131.2,
122.3, 66.6, 66.5, 44.9, 44.2.
MS (ESI): m/z = 207 [M]+.
4-Nitrophenyl Dimethylcarbamate (10c)
Yield: 0.255 g (1.22 mmol, 81%); white solid; mp 43–44 °C (hep-
tanes); Rf = 0.1 (3:1 hexanes–EtOAc).
MS (ESI): m/z = 235 [M]+.
IR (ATR): 1699, 1612, 1593, 1519, 1447, 1394, 1336, 1282, 1217, 1159,
1109, 1059, 1007, 864, 745 cm–1
.
4-Acetylphenyl 4-Morpholinecarboxylate (12b)
1H NMR (500 MHz, CDCl3): δ = 8.27 (d, J = 9 Hz, 2 H), 7.33 (d, J = 9 Hz,
Yield: 0.0344 g (0.138 mmol, 92%); pale yellow oil; Rf = 0.1 (3:1
2 H), 3.15 (s, 3 H), 3.07 (s, 3 H).
hexanes–EtOAc).
13C NMR (125 MHz, CDCl3): δ = 156.4, 153.5, 144.8, 125.6, 125.2, 36.8,
IR (ATR): 1718, 1681, 1599, 1505, 1409, 1359, 1301, 1266, 1203, 1164,
26.6.
1114, 1057, 1014, 989, 959, 855, 802, 749, 589 cm–1
.
MS (ESI): m/z = 210 [M]+.
1H NMR (500 MHz, CDCl3): δ = 8.01 (d, J = 9 Hz, 2 H), 7.24 (d, J = 9 Hz,
2 H), 3.78 (t, J = 5 Hz, 4 H), 3.71 (br, 2 H), 3.61 (br, 2 H), 2.62 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ = 196.9, 154.9, 152.9, 134.3, 129.9,
121.7, 66.6, 66.5, 44.9, 44.2, 26.6.
MS (ESI): m/z = 249 [M]+.
2,6-Dichlorophenyl Diethylcarbamate (11a)
Yield: 0.0389 g (0.148 mmol, 99%); clear oil; Rf = 0.4 (9:1 hexanes–
EtOAc).
IR (ATR): 1727, 1574, 1444, 1414, 1381, 1314, 1272, 1237, 1218, 1147,
1097, 1069, 1035, 952, 936, 786, 771, 746, 707 cm–1
.
4-Cyanophenyl 4-Morpholinecarboxylate (12c)
1H NMR (300 MHz, CDCl3): δ = 7.35 (d, J = 8.0 Hz, 2 H), 7.11 (t, J = 8.0
Hz, 1 H), 3.53 (q, J = 7.0 Hz, 2 H), 3.43 (q, J = 7.0 Hz, 2 H), 1.35 (t, J = 7.0
Hz, 3 H), 1.24 (t, J = 7.0 Hz, 3 H).
Yield: 0.0341 g (0.147 mmol, 98%); white solid; mp 132–134 °C (hep-
tanes); Rf = 0.2 (3:1 hexanes–EtOAc).
13C NMR (75 MHz, CDCl3): δ = 151.8, 144.7, 129.7, 128.5, 126.5, 42.7,
42.3, 14.2, 13.3.
IR (ATR): 2852, 2229, 1709, 1602, 1501, 1446, 1416, 1279, 1245, 1205,
1164, 1116, 1057, 1015, 990, 881, 855, 803, 749, 554 cm–1
.
1H NMR (300 MHz, CDCl3): δ = 7.69 (d, J = 9 Hz, 2 H), 7.27 (d, J = 9 Hz,
2 H), 3.77 (t, J = 4.5 Hz, 4 H), 3.68 (br, 2 H), 3.59 (br, 2 H).
MS (ESI): m/z (%) = 261 (100), 263 (64, [M]+).
4-Acetylphenyl Diethylcarbamate (11b)
13C NMR (75 MHz, CDCl3): δ = 154.6, 152.4, 133.6, 122.6, 118.3, 109.2,
66.4, 44.9, 44.2.
Yield: 0.0296 g (0.126 mmol, 84%); clear oil; Rf = 0.4 (3:1 hexanes–
MS (ESI): m/z = 232 [M]+.
EtOAc).
IR (ATR): 1716, 1681, 1599, 1506, 1473, 1417, 1359, 1264, 1206, 1149,
1098, 1077, 1039, 1014, 956, 864, 807, 781, 752, 589 cm–1
.
Acknowledgment
1H NMR (500 MHz CDCl3): δ = 7.99 (d, J = 8.5 Hz, 2 H), 7.25 (d, J = 8.5
Hz, 2 H), 3.47 (q, J = 7, 7.5 Hz, 2 H), 3.42 (q, J = 7, 7.5 Hz, 2 H), 2.62 (s, 3
H), 1.29 (t, J = 7 Hz, 3 H), 1.24 (t, J = 7 Hz, 3 H).
13C NMR (125 MHz, CDCl3): δ = 197.0, 155.4, 153.4, 133.9, 129.8,
121.7, 42.4, 42.0, 26.6, 14.3, 13.3.
The authors would like to thank the NIU Division of Research and
Graduate Studies (Research & Artistry Opportunity Grant) and the
NIU Department of Chemistry & Biochemistry for funding.
MS (ESI): m/z = 235 [M]+.
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 43–47

47
S. E. Varjosaari et al.
PSP
Synthesis
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