Study of the stability of carbocations by chlorosulfonyl isocyanate reaction with ethers

Article abstract of DOI:10.1016/S0040-4020(02)00413-1

The stability order of various alkyl, allyl, and benzyl carbocations was investigated using the novel technique for comparing the stability of carbocations in solution developed by using a simple CSI reaction with various ethers. The p-methoxycinnamyl carbocation was the most stable in our reaction system and the next stable carbocation was the p-methoxybenzyl carbocation. The stability of the other carbocations decreased with methacryl, t-butyl, cinnamyl, acryl, benzyl, 2° and allyl carbocations in that order.

Full text of DOI:10.1016/S0040-4020(02)00413-1

TETRAHEDRON
Pergamon
Tetrahedron 58 =2002) 4395±4402
Study of the stability of carbocations by chlorosulfonyl isocyanate
reaction with ethers
Ji Duck Kim,a Gyoonhee Han,b Lak Shin Jeong,c Hyun-Ju Park,a Ok Pyo Zeea
and Young Hoon Junga,p
aCollege of Pharmacy, Sungkyunkwan University, Suwon 440-746, South Korea
bKorea Research Institute of Bioscience and Biotechnology, Taejon 305-333, South Korea
cCollege of Pharmacy, Ewha Womans University, Seoul 120-750, South Korea
Received 13February 2002; accepted 12 April 2002
AbstractÐThe stability order of various alkyl, allyl, and benzyl carbocations was investigated using the novel technique for comparing the
stability of carbocations in solution developed by using a simple CSI reaction with various ethers. The p-methoxycinnamyl carbocation was
the most stable in our reaction system and the next stable carbocation was the p-methoxybenzyl carbocation. The stability of the other
carbocations decreased with methacryl, t-butyl, cinnamyl, acryl, benzyl, 28 and allyl carbocations in that order. q 2002 Elsevier Science Ltd.
All rights reserved.
1. Introduction
cations have been carried out by Olah et al., under superacid
conditions.10
Of all the reaction intermediates, the carbocation is one of
the organic reaction intermediate that has been extensively
studied and perhaps is the most widely understood and used
intermediate in organic synthesis.1 Thus, various techniques
for forming carbocations have been developed. In par-
ticular, in the gas phase, chemical ionization,2 thermal
ionization,3 electron ionization,4 photoionization,5 etc.6
have been developed and, in the solution phase, the ioni-
zation of alkyl halides7 or alcohols8 and their reactions with
Through the above techniques, the order of carbocation
stability has been well studied using various parameters:
thermochemistry =heat of formation, proton af®nity, etc.)11
and relative reaction rate =solvolysis, nucleophilic substi-
tution, hydride transfer, etc.).12 The chemistry of carbo-
cation stability has been used in a number of syntheses13
and applied to the development of novel synthetic
methodologies.14
9
SbF5 produce their corresponding carbocations. Many of
the pioneering studies on the formation of benzylic carbo-
Recently, a novel synthetic method for N-allylcarbamate
Scheme 1.
Keywords: chlorosulfonyl isocyanate; stability of carbocation; ether; carbamate.
Corresponding author. Tel.: 182-31-290-7711; fax: 182-31-290-5403; e-mail: yhjung@skku.ac.kr
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020=02)00413-1

4396
J. D. Kim et al. / Tetrahedron 58 22002) 4395±4402
Table 1. Conversions of cinnamyl ethers to the corresponding carbamate with CSI
Ethers
Products
Yield =%)a ratio
87.5, 2.7:1
1
2
3
4
83.5, 7.0:1
89.8, 8.4:1
85.9, 7.4:1
5
42.9
All the reactions were carried out in CH2Cl2 at 208C.
Isolated yield of pure material.
a
formation from various alkyl allyl ethers using chloro-
sulfonyl isocyanate =CSI) was reported.15 The reaction
mechanism involved an allyl carbocation intermediate16
different from other CSI reactions with alkenes.17 Herein
we report the direct comparison of the stability of carbo-
cations using the CSI reaction developed in this study.
isomers. The cinnamyl methyl ether =1a)20 produced the
terminal carbamate =3a)21 and the internal carbamate
=4a)22 in a 2.7:1 ratio. As the size of the alkyl moiety of
the ethers increased, the formation of the internal
N-protected allylic amine decreased due to the steric
hindrance with the phenyl ring =entries 1±4). However,
for the cinnamyl t-butyl ether =1e),23 the corresponding
allyl carbamate was obtained as a single product =5) rather
than the N-allylcarbamates =entry 5). These results suggest
that the reaction pathways are determined by the stability
of the carbocation obtained during the reaction process.
Plausible reaction pathways are shown in Scheme 2. In
path A, the stable allyl carbocation is formed by the
cleavage of the C±O bond at A position followed by
nitrogen anion attack to produce the N-allylcarbamates.
However, when the formation of a more stable alkyl carbo-
cation =R1) rather than an allyl carbocation occurs, the
2. Results and discussion
Our studies are based on the observation that various carba-
mates are formed from cinnamyl alkyl ethers using CSI in
accord with the alkyl moiety of the cinnamyl alkyl ethers
=Scheme 1). These results are summarized in Table 1.
The cinnamyl alkyl ethers were treated with CSI to produce
the corresponding N-allylcarbamates as a mixture of regio-
Scheme 2.

J. D. Kim et al. / Tetrahedron 58 22002) 4395±4402
Table 2. Conversions of benzyl, allyl ethers to the corresponding carbamate with CSI
Ethers Products
4397
Yield =%)a ratio
85.5
1
2
45.7, 1:2.2b
3
4
5
6
7
8
80.8, 1.2:1b
32.7
72.3, 1.1:1
70.1
60.2
46.1, 5.4:1b
All the reactions were carried out in CH2Cl2 at 208C except for entries 1±3= 2788C).
Isolated yield of pure material.
a
b
1
Isomer ratio determined from the H NMR spectrum of the mixture after column chromatography.
reactions proceed through path B thus producing the corre-
sponding allyl carbamates. Speci®cally, a cinnamyl carbo-
cation is more stable than a benzylic carbocation and less
stable than a 38 carbocation.
more stable than the t-butyl carbocation =entry 4).12e,26,27
The benzylic carbocation is less stable than the crotonylic
carbocation =entry 5)27 and more stable than the allylic and
28 carbocations. =entries 6 and 7).27 Furthermore, in the case
Table 3. The CSI reactions with various solvents and temperature
From these studies, a direct method was established
for comparing the stability of various carbocations in the
solution phase. This method was then applied to determine
the stability order of other various carbocations.
Ethers
Products
Solvent
T =8C)
Ratioa
Yield =%)b
1
2
3
4
5
6
7
8
1g
1g
1g
1g
1g
1h
1h
1h
1h
1h
1h
1i
1i
1i
1m
1m
1m
2g13g
2g13g
2g13g
2g13g
2g13g
2h13h
2h13h
2h13h
2h13h
2h13h
2h13h
2i
CH2Cl2
CHCl3
CH2Cl2
CHCl3
Et2O
CH2Cl2
CHCl3
Et2O
CH2Cl2
CHCl3
Et2O
CH2Cl2
CHCl3
Et2O
278
260
20
20
20
278
260
278
20
20
20
20
20
20
20
20
20
1:2.2
1:2.9
1:4.1
1:4.368.4
1:5.6
1.2:1
1.9:1
1.7:1
1.4:1
2.0:1
1.8:1
±
45.7
48.6
67.7
For a comparison of the stability of various carbocations,
the alkyl, allyl, benzyl and p-methoxybenzyl =PMB)
ethers were prepared according to the conventional
methods and treated with CSI in dichloromethane solution
to give the corresponding carbamates depending on the
carbocation stability. These results are summarized in
Table 2.
32.6
80.8
84.5
81.6
80.7
86.1
87.9
32.7
43.1
22.4
46.1
48.8
38.5
9
10
11
12
13
14
15
16
17
2i
2i
±
±
For entry 1, the fact that cinnamyl N-=p-methoxybenzyl)-
carbamate =2f) was obtained as a single product means
that the p-methoxybenzylic carbocation is more stable
than the cinnamyl carbocation. With a similar analogy, the
p-methoxycinnamyl carbocation is more stable than the
p-methoxybenzylic carbocation =entry 2), which is similar
in stability to the methacrylic carbocation =entry 3) and is
2m13m
2m13m
2m13m
CH2Cl2
CHCl3
Et2O
5.4:1
8.4:1
7.6:1
a
Isomer ratio determined from the 1H NMR spectrum of the mixture after
column chromatography.
Isolated yield of pure material.
b

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J. D. Kim et al. / Tetrahedron 58 22002) 4395±4402
additional puri®cation, unless otherwise stated. All
anhydrous solvents were distilled over CaH2 or P2O5 or
Na/benzophenone prior to reaction. All reactions were
performed under an inert atmosphere of nitrogen or argon.
Melting points were measured on a Gallenkamp melting
point apparatus and were not corrected. Nuclear magnetic
resonance spectra =1H and 13C NMR) were recorded on a
Varian Unity Inova 500 MHz spectrometer for CDCl3
solutions and chemical shifts are reported as parts per
million =ppm) relative to, respectively, residual CHCl3 dH
=7.26 ppm) and CDCl3 dC =77.0 ppm) as internal standards.
Resonance patterns are reported with the notations s
=singlet), d =doublet), t =triplet), q =quartet), and m =multi-
plet). In addition, the notation br is used to indicate a broad
signal. Coupling constants =J) are reported in hertz =Hz). IR
spectra were recorded on a Nicolet 205 Infrared spectro-
photometer and are reported as cm21. Thin layer chroma-
tography was carried out using plates coated with Kieselgel
60F254 =Merck). For ¯ash column chromatography, E.
Merck Kieselgel 60 =230±400 mesh) was used. Elemental
analyses were performed with an the EA 1110 analyzer, and
high-resolution mass spectra =HRMS) were recorded on a
JEOL, JMS-AX505WA spectrometer using the chemical
ionization =CI) method.
Figure 1.
of entry 8, we found that a 28 carbocation is more stable than
an allylic carbocation.3a,27
However, for entries 2, 3, and 8, the mixture of 2 and 3 was
formed and the chemical yield for entry 4 was very poor.
Therefore, we investigated these reactions by varying the
solvents and temperature to increase the ratio of the isomers
and optimize the yield. Especially, we chose chloroform and
ether =Et2O), which might stabilize the carbocations rather
than dichloromethane. These results are summarized in
Table 3.
4.2. General procedure for the preparation of ethers
From Table 3, we found that chloroform and ether =Et2O)
provided an increased ratio of 2 and 3 compared to dichloro-
methane, and the ratio of the regioisomers was increased in
accord with the temperature increase. The results of entries
6±11 provided information that the p-methoxybenzylic
carbocation is more stable than the methacrylic carbocation.
For the p-methoxybenzyl t-butyl ether =1i), the chemical
yield was slightly increased in the chloroform solution.
To a solution of alcohol =5 mmol) in THF =28 ml) and DMF
=7 ml) was added NaH =7.5 mmol, 60% in mineral oil) and
alkyl halide =7.5 mmol). The reaction mixture was stirred at
room temperature for 15 h, quenched with H2O =20 ml),
then extracted with EtOAc =20 ml). The organic layer was
washed with H2O and brine, dried over MgSO4 and con-
centrated in vacuo. The residue was puri®ed by column
chromatography =n-Hex/EtOAc) to afford ether.
From the results of Tables 1±3, the stability of the carbo-
cations is as follows =Fig. 1).
4.2.1. 1-%But-2-enyloxy)-3-phenylprop-2-ene %1d). 1H
NMR =500 MHz, CDCl3): d 1.74=dd, 3H, Jˆ6.5, 1.5 Hz),
3.98=dd, 2H, Jˆ6.5, 1.5 Hz), 4.15=d, 2H, Jˆ6 Hz), 5.65=dtq,
1H, Jˆ13, 6.5, 1.5 Hz), 5.77=dtq, 1H, Jˆ13, 6.5, 1.5 Hz),
6.31=dt, 1H, Jˆ16, 6 Hz), 6.62=d, 1H, Jˆ16 Hz), 7.23±
7.41=m, 5H); 13C NMR =125 MHz, CDCl3): d 18.53,
71.22, 71.63, 126.93, 127.18, 128.19, 128.32, 129.24,
130.52, 133.03, 137.49; IR =neat): 3029, 2859, 1660,
1453, 1358, 1098 cm21; HRMS =CI) calcd for C13H16O±H
=M2H)1 187.1123. Found: 187.1118.
The p-methoxycinnamyl carbocation is the most stable in
our reaction system and the next stable carbocation is the
p-methoxybenzyl carbocation. The stability of the other
carbocations decreases with methacryl, t-butyl, cinnamyl,
acryl, benzyl, 28 and allyl carbocations in that order.28 For
reference,27 thermodynamic data in the gas phase for
various carbocations suggests that the stability order of
the carbocations is similar to that obtained under our
reaction conditions except for the benzyl carbocation,
which is more stable than the acryl carbocation.
4.2.2. 1-p-Methoxybenzyloxy-3-phenylprop-2-ene %1f).
1H NMR =500 MHz, CDCl3): d 3.78=s, 3H), 4.15=d, 2H,
Jˆ6 Hz), 4.49=s, 2H), 6.32=dt, 1H, Jˆ16, 6 Hz), 6.60=d,
1H, Jˆ16 Hz), 6.88=dd, 2H, Jˆ6.5, 2 Hz), 7.22±7.39=m,
7H); 13C NMR =125 MHz, CDCl3): d 55.97, 71.19, 72.55,
114.56, 126.97, 127.20, 128.35, 129.26, 130.14, 131.10,
133.14, 137.50, 159.97; IR =CH2Cl2): 3027, 2923, 2866,
1607, 1485, 1347, 1254, 1074 cm21; mp: 38±408C =n-
Hex); Anal. Calcd for C17H18O2: C, 80.28; H, 7.13.
Found: C, 80.28; H, 7.20.
3. Conclusion
In conclusion, a novel technique was developed to compare
directly the stability of carbocations in the solution phase
using a CSI reaction and to establish the stability order of
the various carbocations. We are actively pursuing further
investigation of the stability of the other interesting
carbocations using CSI reactions.
4. Experimental
4.1. General
4.2.3. 1-p-Methoxybenzyloxy-3-p-methoxyphenylprop-2-
ene %1g). 1H NMR =500 MHz, CDCl3): d 3.82=s, 3H),
3.83=s, 3H), 4.15=d, 2H, Jˆ6 Hz), 4.51=s, 2H), 6.20=dt,
1H, Jˆ16, 6 Hz), 6.57=d, 1H, Jˆ16 Hz), 6.85±6.91=m,
4H), 7.27±7.35=m, 4H); 13C NMR =125 MHz, CDCl3): d
Commercially available reagents were used without

J. D. Kim et al. / Tetrahedron 58 22002) 4395±4402
4399
55.98, 56.01, 71.39, 72.43, 114.52, 114.57, 124.60, 128.38,
130.15, 130.24, 131.14, 132.90, 159.90, 159.98; IR
=CH2Cl2): 2938, 2845, 1668, 1582, 1513, 1464, 1303,
1250, 1179, 1031 cm21; mp: 46±478C =n-Hex); Anal.
Calcd for C18H20NO3: C, 76.03; H, 7.09. Found: C, 76.21;
H, 7.09.
Jˆ7 Hz), 5.01±5.10=br,1H), 5.24=dd, 1H, Jˆ10, 1.5 Hz),
5.25=dd, 1H, Jˆ17, 1.5 Hz), 5.33±5.37=br, 1H), 6.01=ddd,
1H, Jˆ17, 10, 5 Hz), 7.22±7.37=m, 5H); 13C NMR =125
MHz, CDCl3): d 15.30, 57.64, 61.72, 116.37, 127.73,
128.34, 129.32, 138.45, 141.52, 156.54; IR =neat): 3321,
2979, 1702, 1517, 1347, 1252, 1058 cm21; HRMS =CI)
Calcd for C12H15NO21H =M1H)1 206.1181. Found:
206.1185.
4.2.4. 1-p-Methoxybenzyloxy-3-methylbut-2-ene %1h). 1H
NMR =500 MHz, CDCl3): d 1.67=s, 3H), 1.77=s, 3H), 3.80=s,
3H), 3.99=d, 2H, Jˆ7 Hz), 4.45=s, 2H), 5.42=t, 1H, Jˆ7 Hz),
6.88=dd, 2H, Jˆ8, 1.5 Hz), 7.28=dd, 2H, Jˆ8, 1.5 Hz); 13C
NMR =125 MHz, CDCl3): d 18.76, 26.52, 55.93, 67.00,
72.42, 114.44, 121.93, 130.11, 131.40, 137.71, 159.84; IR
=neat): 2925, 2864, 1607, 1511, 1447, 1371, 1249,
1061 cm21; HRMS =CI) Calcd for C13H18O21H =M1H)1
207.1485. Found: 207.1389.
4.3.3. Benzyl N-%3-phenylprop-2-enyl)carbamate %3c). 1H
NMR =500 MHz, CDCl3): d 3.99=dd, 2H, Jˆ6, 4.5 Hz),
4.88±4.97=br, 1H), 5.15=s, 2H), 6.17=dt, 1H, Jˆ16, 6 Hz),
6.53=d, 1H, Jˆ16 Hz), 7.23±7.39=m, 10H); 13C NMR =125
MHz, CDCl3): d 43.88, 67.54, 126.52, 127.11, 128.41,
128.85, 129.10, 129.25, 129.29, 132.49, 137.25, 156.98;
IR =KBr): 3319, 2832, 1686, 1543, 1451, 1261, 1248,
1138 cm21; mp: 62±638C =n-Hex); Anal. Calcd for
C17H17NO2: C, 76.38; H, 6.41; N, 5.24. Found: C, 76.52;
H, 6.46; N, 5.22.
4.2.5. 1-Benzyloxybut-2-ene %1j). 1H NMR =500 MHz,
CDCl3): d 1.77=dd, 3H, Jˆ6.5, 1.5 Hz), 4.01=dd, 2H, Jˆ6,
1.5 Hz), 4.55=s, 2H), 5.69=dtq, 1H, Jˆ13, 6.5, 1.5 Hz),
5.78=dtq, 1H, Jˆ13, 6.5, 1.5 Hz), 7.31±7.40=m, 5H); 13C
NMR =125 MHz, CDCl3): d 18.58, 71.66, 72.65, 128.28,
128.32, 128.52, 130.40, 139.22; IR =neat): 2926, 2858,
1602, 1452, 1363, 1291, 1233, 1091 cm21; HRMS =CI)
Calcd for C11H14O±H =M2H)1 161.0967. Found:
161.0963.
1
4.3.4. Benzyl N-%1-phenylallyl)carbamate %4c). H NMR
=500 MHz, CDCl3): d 5.12=s, 2H), 5.15=dd, 1H, Jˆ5.5,
5 Hz), 5.24=dd, 1H, Jˆ9.5, 1.5 Hz), 5.25=dd, 1H, Jˆ18,
1.5 Hz), 5.33±5.40=br, 1H), 6.01=ddd, 1H, Jˆ18, 9.5,
5.5 Hz), 7.21±7.38=m, 10H); 13C NMR =125 MHz,
CDCl3): d 57.81, 67.65, 116.54, 126.79, 127.74, 128.42,
128.87, 129.23, 129.46, 137.06, 138.27, 141.32, 156.25;
IR =CH2Cl2): 3322, 3045, 2934, 1707, 1515, 1242,
1042 cm21; mp: 46±478C =n-Hex); HRMS =CI) Calcd for
C17H17NO21H =M1H)1 268.1337. Found: 268.1343.
4.2.6. Benzyl i-propyl ether %1l). 1H NMR =500 MHz,
CDCl3): d 1.27=d, 6H, Jˆ5.5 Hz), 3.73=q, 1H, Jˆ5.5 Hz),
4.56=s, 2H), 7.25±7.41=m, 5H); 13C NMR =125 MHz,
CDCl3): d 22.88, 70.78, 71.67, 128.09, 128.27, 129.07,
139.88; IR =neat): 2963, 2871, 1601, 1463, 1362,
1097 cm21; HRMS =CI) Calcd for C10H14O±H =M2H)1
149.0967. Found: 149.0959.
4.3.5. But-2-enyl N-%3-phenylprop-2-enyl)carbamate
%3d). 1H NMR =500 MHz, CDCl3): d 1.72=d, 3H, Jˆ
6.5 Hz), 3.91±3.99=br, 2H), 4.52=d, 2H, Jˆ5.5 Hz), 4.93±
5.02=br, 1H), 5.61=dt, 1H, Jˆ15, 5.5 Hz), 5.77=dq, 1H, Jˆ
15, 6.5 Hz), 6.18=dt, 1H, Jˆ16, 6 Hz), 6.51=d, 1H, Jˆ
16 Hz), 7.22±7.36=m, 5H); 13C NMR =125 MHz, CDCl3):
d 18.51, 43.79, 66.43, 126.41, 126.68, 127.09, 128.37,
129.28, 131.67, 132.30, 137.29, 157.09; IR =neat): 3340,
4.3. General procedure for the reaction of ether with CSI
A suspension of Na2CO3 =6.75 mmol) in anhydrous CH2Cl2
=12 ml) was adjusted to 20 or 2788C, then CSI =4.5 mmol)
and ether =3mmol) was added under N 2. The reaction
mixture was stirred at 20 or 2788C, quenched with H2O
=10 ml) when the reaction was completed =TLC monitor-
ing), then extracted with EtOAc =10 ml£2). The organic
layer was added to an aqueous solution of Na2SO3 =25%)
and KOH =10%), and the reaction mixture was stirred at
room temperature for overnight. The organic layer was
washed with H2O and brine, dried over MgSO4 and con-
centrated in vacuo. The residue was puri®ed by column
chromatography =n-Hex/EtOAc) to afford carbamate.
3034, 2937, 1706, 1524, 1383, 1250, 1121, 1066 cm21
;
HRMS =CI) Calcd for C14H17NO21H =M1H)1 232.1337.
Found: 232.1335.
4.3.6. But-2-enyl N-%1-phenylallyl)carbamate %4d). 1H
NMR =500 MHz, CDCl3): d 1.72=d, 3H, Jˆ6.5 Hz),
4.52=d, 2H, Jˆ5.5 Hz), 4.95±5.05=br, 1H), 5.24=dd, 1H,
Jˆ10, 1.5 Hz), 5.25=dd, 1H, Jˆ17, 1.5 Hz), 5.36±5.40=br,
1H), 5.59=dt, 1H, Jˆ15, 5.5 Hz), 5.78=dq, 1H, Jˆ15,
6.5 Hz), 6.00=ddd, 1H, Jˆ17, 10, 5.5 Hz), 7.26±7.37=m,
5H); 13C NMR =125 MHz, CDCl3): d 18.49, 57.69, 66.53,
116.42, 126.29, 127.73, 128.36, 129.42, 131.85, 138.36,
141.42, 156.28; IR =CH2Cl2): 3319, 3038, 2939, 1703,
1518, 1321, 1247, 1096 cm21; mp: 53±558C =n-Hex);
HRMS =CI) Calcd for C14H17NO21H =M1H)1 232.1337.
Found: 232.1331.
1
4.3.1. Ethyl N-%3-phenylprop-2-enyl)carbamate %3b). H
NMR =500 MHz, CDCl3): d 1.26 =t, 3H, Jˆ7 Hz), 3.87=dd,
2H, Jˆ6, 4.5 Hz), 4.15=q, 2H, Jˆ7 Hz), 4.82±4.92=br, 1H),
6.17±6.23=dt, 1H, Jˆ16, 6 Hz), 6.52=d, 1H, Jˆ16 Hz),
7.22±7.37=m, 5H); 13C NMR =125 MHz, CDCl3): d 15.38,
43.74, 61.63, 126.78, 127.08, 128.36, 129.28, 132.26,
137.31, 157.31; IR =KBr): 3299, 2983, 2935, 1695, 1661,
1539, 1497, 1377, 1253, 1135 cm21; mp: 52±538C =n-Hex);
Anal. Calcd for C12H15NO2: C, 70.22; H, 7.37; N, 6.82.
Found: C, 70.04; H, 7.39; N, 6.69.
4.3.7. 3-Phenylprop-2-enyloxycarbonylamine %5). 1H
NMR =500 MHz, CDCl3): d 4.73=d, 2H, Jˆ6.5 Hz), 4.73±
4.78=br, 2H), 6.30=dt, 1H, Jˆ16, 6.5 Hz), 6.60=d, 1H,
Jˆ16 Hz), 7.25±7.40=m, 5H); 13C NMR =125 MHz,
CDCl3): d 66.39, 124.24, 127.31, 128.73, 129.30, 134.58,
136.85, 157.32; IR =CH2Cl2): 3398, 3250, 3187, 2925,
1670, 1561, 1411, 1316, 1050 cm21; mp: 118±1208C
1
4.3.2. Ethyl N-%1-phenylallyl)carbamate %4b). H NMR
=500 MHz, CDCl3): d 1.24=t, 3H, Jˆ7 Hz), 4.12=q, 2H,

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J. D. Kim et al. / Tetrahedron 58 22002) 4395±4402
=EtOAc/n-Hex); Anal. Calcd for C10H11NO2: C, 67.78; H,
6.26; N, 7.90. Found: C, 67.51; H, 6.63; N, 7.82.
4.25=d, 2H, Jˆ5 Hz), 4.75±4.83=br, 1H), 6.86=dd, 2H, Jˆ
8, 2 Hz), 7.21=dd, 2H, Jˆ8, 2 Hz); 13C NMR =125 MHz,
CDCl3): d 29.13, 44.87, 55.99, 80.03, 114.68, 129.57,
131.71, 156.55, 159.59; IR =neat): 3332, 3051, 2937,
1705, 1543, 1255, 1130, 1019 cm21; HRMS =CI) Calcd
for C13H19NO31H =M1H)1 238.1443. Found: 238.1436.
4.3.8. 3-Phenylprop-2-enyl N-%p-methoxybenzyl)carba-
mate %2f). H NMR =500 MHz, CDCl3): d 3.79=s, 3H),
1
4.33=d, 2H, Jˆ5.5 Hz), 4.76=d, 2H, Jˆ6.5 Hz), 4.97±
5.03=br, 1H), 6.30=dt, 1H, Jˆ16, 6.5 Hz), 6.64=d, 1H,
Jˆ16 Hz), 6.87=dd, 2H, Jˆ7, 2 Hz), 7.22±7.40=m, 7H);
13C NMR =125 MHz, CDCl3): d 45.13, 55.99, 66.23,
114.74, 124.62, 127.30, 128.67, 129.29, 129.65, 131.26,
134.33, 137.03, 156.98, 159.72; IR =CH2Cl2): 3332, 2917,
1718, 1692, 1543, 1513, 1437, 1274, 1251 cm21; mp: 1048C
=EtOAc/n-Hex); Anal. Calcd for C18H19NO3: C, 72.71; H,
6.44; N, 4.71. Found: C, 72.73; H, 6.41; N, 4.55.
4.3.12. Benzyl N-%but-2-enyl)carbamate %3j) and benzyl
N-%1-methylallyl)carbamate %4j). Benzyl N-2but-2-enyl)-
carbamate =3j). H NMR =500 MHz, CDCl3): d 1.68=d,
1
3H, Jˆ6.5 Hz), 3.70±3.79=br, 2H), 4.76±4.85=br, 1H),
5.09=s, 2H), 5.48=dq, 1H, Jˆ15, 6,5 Hz), 5.61=dt, 1H, Jˆ
15, 6.5 Hz), 7.30±7.40=m, 5H); 13C NMR =125 MHz,
CDCl3): d 18.35, 43.71, 67.39, 127.85, 128.81, 129.23,
140.41, 156.92.
4.3.9. 3-p-Methoxyphenylprop-2-enyl N-%p-methoxyben-
zyl)carbamate %2g) and p-methoxybenzyl N-%3-p-meth-
oxybenzylprop-2-enyl)carbamate %3g). 3-p-Methoxy-
phenylprop-2-enyl N-2p-methoxybenzyl)carbamate =2g).
1H NMR =500 MHz, CDCl3): d 3.79=s, 3H), 3.80=s, 3H),
4.31=d, 2H, Jˆ6 Hz), 4.73=d, 2H, Jˆ6 Hz), 4.97±5.03=br,
1H), 6.16=dt, 1H, Jˆ16, 6 Hz), 6.61=d, 1H, Jˆ16 Hz), 6.85±
6.90=m, 4H), 7.20±7.34=m, 4H); 13C NMR =125 MHz,
CDCl3): d 45.34, 55.99, 66.50, 114.50, 114.64, 122.91,
128.53, 129.59, 129.84, 131.05, 134.18, 157.01, 160.02,
160.24.
Benzyl N-21-methylallyl)carbamate =4j). 1H NMR =500
MHz, CDCl3): d 1.24=d, 3H, Jˆ6.5 Hz), 4.28±4.36=br,
1H), 4.70±4.78=br, 1H), 5.11=s, 2H), 5.12=dd, 1H, Jˆ
10 Hz, 1.5 Hz), 5.15=dd, 1H, Jˆ17, 1.5 Hz), 5.84=ddd, 1H,
Jˆ17, 10, 5.5 Hz), 7.30±7.40=m, 5H); 13C NMR =125 MHz,
CDCl3): d 21.35, 49.39, 67.36, 114.69, 127.85, 128.81,
129.23, 137.26, 140.41, 156.30; IR =neat): 3410, 3331,
3033, 2971, 2937, 1769, 1729, 1691, 1531, 1454, 1334,
1293, 1241, 1134, 1053 cm21; HRMS =CI) Calcd for
C12H15NO21H =M1H)1 206.1181. Found: 206.1178.
p-Methoxybenzyl N-23-p-methoxybenzylprop-2-enyl)carba-
mate =3g). H NMR =500 MHz, CDCl3): d 3.80=s, 3H),
4.3.13. Allyl N-benzylcarbamate %2k). 1H NMR
=500 MHz, CDCl3): d 4.39=d, 2H, Jˆ5.5 Hz), 4.60=d, 2H,
Jˆ5.5 Hz), 5.02±5.08=br, 1H), 5.23=dd, 1H, Jˆ10.5,
1.5 Hz), 5.32=dd, 1H, Jˆ17, 1.5 Hz), 5.94=ddt, 1H, Jˆ17,
10.5, 5.5 Hz), 7.27±7.36=m, 5H); 13C NMR =125 MHz,
CDCl3): d 45.73, 66.35, 118.36, 128.13, 128.22, 129.33,
133.67, 139.34, 157.15; IR =neat): 3334, 3052, 2933,
1707, 1529, 1252, 1136, 1013 cm21; HRMS =CI) Calcd
for C11H13NO21H =M1H)1 192.1024. Found: 192.1031.
1
3.81=s, 3H), 3.94=dd, 2H, Jˆ6 Hz, 5.5 Hz), 4.78±4.86=br,
1H), 5.06=s, 2H), 6.05=dt, 1H, Jˆ16, 6 Hz), 6.45=d, 1H,
Jˆ16 Hz), 6.83±6.86=m, 4H), 7.20±7.34=m, 4H); 13C
NMR =125 MHz, CDCl3): d 43.92, 55.96, 67.31, 114.71,
114.76, 124.25, 128.26, 129.39, 130.03, 130.68, 132.07,
157.01, 160.24, 160.29; IR =CH2Cl2): 3315, 2929, 1690,
1609, 1547, 1512, 1450, 1246, 1177, 1031 cm21; HRMS
=CI) Calcd for C19H21NO41H =M1H)1 328.1549. Found:
328.1546.
4.3.14. i-Propyl N-benzylcarbamate %2l). 1H NMR
=500 MHz, CDCl3): d 1.24=d, 6H, Jˆ6 Hz), 4.37=d, 2H,
Jˆ5.5 Hz), 4.96=q, 1H, Jˆ6 Hz), 4.91±5.00=br, 1H),
7.27±7.36=m, 5H); 13C NMR =125 MHz, CDCl3): d 22.90,
45.62, 68.91, 128.06, 128.15, 129.31, 139.54, 157.12; IR
4.3.10. 3-Methylbut-2-enyl N-%p-methoxybenzyl)carba-
mate %2h) and p-methoxybenzyl N-%3-methylbut-2-enyl)-
carbamate %3h). 3-Methylbut-2-enyl N-2p-methoxy-
benzyl)carbamate =2h). 1H NMR =500 MHz, CDCl3): d
1.72=s, 3H), 1.76=s, 3H), 3.79=s, 3H), 4.30=d, 2H, Jˆ
5.5 Hz), 4.59=d, 2H, Jˆ7 Hz), 4.93±4.98=br, 1H), 5.34=t,
1H, Jˆ7 Hz), 6.86=dd, 2H, Jˆ8, 1.5 Hz), 7.22=dd, 2H, Jˆ
8, 1.5 Hz); 13C NMR =125 MHz, CDCl3): d 18.72, 26.48,
45.28, 55.97, 62.50, 114.70, 119.84, 129.47, 131.38, 157.33,
159.66.
=neat): 3334, 2959, 1701, 1526, 1363, 1257, 1129 cm21
;
HRMS =CI) Calcd for C11H15NO21H =M1H)1 194.1181.
Found: 194.1187.
4.3.15. Allyl N-i-propylcarbamate %2m) and i-propyl
N-allylcarbamate %3m). Allyl N-i-propylcarbamate =2m).
1H NMR =500 MHz, CDCl3): d 1.16=d, 6H, Jˆ6.5 Hz),
3.82=q, 1H, Jˆ6.5 Hz), 4.50±4.60=br, 3H), 5.20=dd, 1H,
Jˆ10.5, 1.5 Hz), 5.30=dd, 1H, Jˆ17, 1.5 Hz), 5.92=ddt,
1H, Jˆ17, 10.5, 5.5 Hz); 13C NMR =125 MHz, CDCl3): d
23.59, 43.64, 65.82, 110.03, 133.75, 156.11.
1
p-Methoxybenzyl N-23-methlbut-2-enyl)carbamate =3h). H
NMR =500 MHz, CDCl3): d 1.66=s, 3H), 1.71=s, 3H),
3.77=d, 2H, Jˆ5.5 Hz), 3.81=s, 3H), 4.60±4.64=br, 1H),
5.03=s, 2H), 5.18=t, 1H, Jˆ5.5 Hz), 6.88=dd, 2H, Jˆ7.5,
1.5 Hz), 7.30=dd, 2H, Jˆ7.5, 1.5 Hz); 13C NMR =125
MHz, CDCl3): d 18.52, 26.30, 39.64, 55.99, 67.12,
114.58, 121.22, 129.58, 130.67, 157.31, 160.20; IR
=CH2Cl2): 3334, 2963, 2932, 1700, 1613, 1515, 1465,
1301, 1245, 1178, 1134, 1036 cm21; HRMS =CI) Calcd
for C14H19NO31H =M1H)1 250.1443. Found: 250.1443.
i-Propyl N-allylcarbamate =3m). 1H NMR =500 MHz,
CDCl3): d 1.23=d, 6H, Jˆ6 Hz), 3.74±3.82=br, 2H), 4.62±
4.70=br, 1H), 4.93=q, 1H, Jˆ6 Hz), 5.14=dd, 1H, Jˆ10,
1.5 Hz), 5.18=dd, 1H, Jˆ15.5, 1.5 Hz), 5.65=ddt, 1H,
Jˆ15.5, 10, 5 Hz); 13C NMR =125 MHz, CDCl3): d 22.81,
43.97, 68.68, 116.41, 135.46, 156.89; IR =neat): 3337,
3328, 2964, 1704, 1700, 1529, 1354, 1260, 1248, 1135,
1089 cm21; HRMS =CI) Calcd for C7H13NO21H =M1H)1
144.1014. Found: 144.1022.
1
4.3.11. t-Butyl N-%p-methoxybenzyl)carbamate %2i). H
NMR =500 MHz, CDCl3): d 1.47=s, 9H), 3.80=s, 3H),

J. D. Kim et al. / Tetrahedron 58 22002) 4395±4402
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Acknowledgements
The authors wish to acknowledge the ®nancial support of
the Korea Research Foundation made in the program year of
1998.
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