The reaction of amines with benzyl halides under CO2 atmosphere

Article abstract of DOI:10.1002/1522-2675(20011114)84:11<3357::AID-HLCA3357>3.0.CO;2-P

To find a useful, practical, and ecologically safer way to synthesize protected amines, the reactions of amines with benzyl halides under CO₂ atmosphere were systematically examined. For primary amines, the CO₂-inserted products were obtained in higher yields in the presence of DBU as a base, under a high pressure of CO₂, and in a low-polarity solvent (toluene/hexane 1:1). Secondary amines gave only low yields of CO₂-inserted products.

Full text of DOI:10.1002/1522-2675(20011114)84:11<3357::AID-HLCA3357>3.0.CO;2-P

Helvetica Chimica Acta Vol. 84 (2001)
3357
The Reaction of Amines with Benzyl Halides under CO2 Atmosphere
by Min Shi* and Yu-Mei Shen
Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, 354 Fenglin Lu, Shanghai 200032 China (mshi@pub.sioc.ac.cn)
To find a useful, practical, and ecologically safer way to synthesize protected amines, the reactions of
amines with benzyl halides under CO2 atmosphere were systematically examined. For primary amines, the CO2-
inserted products were obtained in higher yields in the presence of DBU as a base, under a high pressure of CO2,
and in a low-polarity solvent (toluene/hexane 1:1). Secondary amines gave only low yields of CO2-inserted
products.
Introduction. Organic carbamates exhibit unique physical and chemical proper-
ties, accommodating a variety of applications in pharmacology (medicinal drugs),
agriculture (pesticides, fungicides, herbicides), and chemical industry (synthetic
intermediates) [1]. Their use as protective groups for the NH2 group in amino acids
in peptide synthesis is also well-known [2]. So far, the protecting reagent most often
used is benzyl carbonochloridate (ZCl), which is prepared from phosgene (COCl2), an
extremely hazardous compound used in many syntheses, and benzyl alcohol. Several
attempts have been made to employ new methodologies in which the toxic phosgene is
replaced with less toxic and less dangerous reagents [3]. One of the many goals of the
−green chemistry movement× intends to replace phosgene by carbon dioxide, a cheap,
benign-nature, and abundant reagent [4]. So far, several reports have appeared dealing
with the synthesis of carbamate esters from amines, CO2, and alkyl halides [5].
Obviously, this synthetic method can be directly applied to protect amino groups if
benzyl carbamates can be produced in high yields. In one of these reports, Yoshida et al.
found that the reaction of carbamate anions with alkyl halides in the presence of
RR'NH as a base gave predominantly N-alkylated products (RR'NR'') and only poor
yields of carbamate esters (RR'NCO2R'') [5a]. This result may be due to the poor
nucleophilicity of the carbamate as compared to the reactivity of the N-atom or to an
unfavorable equilibrium concentration of carbamate in solution. Improvements in the
yields and selectivities of urethane products over amine products via a stabilization of
the carbamate anion by DBU as a base were reported by Hori et al. [5b]. In this case,
however, only reactions with highly reactive electrophiles, i.e., bromides and tosylates,
gave acceptable amounts of urethanes. Calderazzo et al. have also reported the use of
carbamates as nucleophiles in reactions with MeI to give methyl carbamates [6]. These
investigations showed that the use of crown ethers and cryptands in combination with
carbamate anion/potassium cation systems gave good yields of urethanes. A similar
approach has been elucidated by Aresta and Quaranta in recent reports [7]. Recently,
McGhee et al. disclosed that, in the reaction of amines, carbon dioxide, and alkyl
chlorides, the effect of added base on the yield and selectivity of carbamate

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Helvetica Chimica Acta Vol. 84 (2001)
(RNHCO2R') formation was found to be highly important, the use of sterically
hindered guanidine bases giving the best results [8]. However, in our own investigation
of this reaction, we found that, using DBU as a base, similar yields and selectivities of
carbamates (RNHCO2R') could be obtained as well. In the present paper, we report
our results on the synthesis of benzyl carbamates by means of CO2. This reaction is very
simple because it is well known that mixing CO2 with amines leads to alkylammonium
carbamates. Thus, the key step for the formation of benzyl carbamates is the reaction of
alkylammonium carbamates with benzyl halides (Scheme 1). One competitive reaction
is the direct alkylation of the amine with benzyl halides to give the corresponding
secondary or tertiary amine. Thus the selection of solvents and bases, the pressure of
CO2, and the nucleophilicity of the amines themselves can drastically affect the
reaction.
Scheme 1
Results and Discussion. We first examined the reaction of benzylamine with
benzyl halides under CO2 atmosphere or in a stainless-steal autoclave with high
pressure of CO2 under various reaction conditions. The results, summarized in Table 1,
show that bases, pressure of CO2, and solvents played a very important role in this
reaction. With Na2CO3 as a base and toluene or MeCN as solvent, no CO2-inserted
product could be obtained even under high pressure of CO2 (Table 1, Entries 1 3)
(amine/halide/Na2CO3 1:1:1). In the presence of other inorganic bases such as K2CO3,
Cs2CO3, Li2CO3, or LiOH in N,N-dimethylformamide (DMF), the CO2-inserted
product 1a was in general obtained in very low yields (Entries 4 10). The tertiary
amine 2a was the major product. The presence of catalytic amounts of phase transfer
catalyst and crown ether ([18]crown-6) or high pressure of CO2 did not improve the
yields of 1a. However, with 1.0 equiv. of DBU (ˆ1,8-diazabicyclo[5.4.0]undec-7-ene)
as a base, the yields of 1a could be increased, but the undesired 2a was still formed,
especially with benzyl bromide as an electrophile (Table 1, Entries 11 15). This result
can be explained by the −hard-and-soft acid/base priciple× (HSAB). As an acid, benzyl
chloride is harder than benzyl bromide. As base, RNHC(O)OÀ is harder than
benzylamine. Thus, 2a was formed predominantly with benzyl bromide as the
electrophile. In low-polarity solvents (toluene or hexane), the reaction yielded ca.
20% of 1a, and the formation of 2a was reduced (Table 1, Entries 16 and 17).
Moreover, in the mixed solvent toluene/hexane 1:1 at room temperature, the yield of
1a reached 44% (Table 1, Entries 18 and 19), and increasing the pressure of CO2 also
improved the yield of 1a. The optimum result, i.e. 87% of 1a, was obtained with
1.0 equiv. of DBU and benzyl chloride as the electrophile at 808 under high pressure of
CO2 (Table 1, Entry 21). The yield of isolated 1a was very close to that obtained in the

Helvetica Chimica Acta Vol. 84 (2001)
3359
Table 1. The Reaction of Benzylamine with Benzyl Halides under CO2 Atmosphere at Room Temperature
CO2
PhCH2NH2 ‡ PhCH2X
!
PhCH2NHCO2CH2Ph ‡ PhCH2N(CH2Ph)2
base; solvent
Entry
PhCH2X
Base
Pressure, CO2/kg/cm2
Solvent
Yield/%a)
1a
2a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Br
Br
Cl
Br
Br
Br
Cl
Br
Br
Br
Cl
Br
Cl
Na2CO3
Na2CO3
Na2CO3
K2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Li2CO3
LiOH
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
1
1
50
1
toluene
MeCN
30
40
35
40
50
60
60
50
46
MeCN
DMFb)
trace
8
13
13
10
3
1
DMF
50
50
50
1
1
1
1
1
1
1
1
1
1
1
50
50
DMF
DMFc)
DMFd)
DMF
DMF
DMF
H2O
DMF/H2O
DMF
DMF
toluene
hexane
toluene/hexane
toluene/hexane
toluene/hexane
toluene/hexanee)
10
6
trace
60
34
30
12
10
1
12
14
13
7
32
37
32
19
24
44
43
55
87
DBU
DBU
a) Yield of isolated product. b) In the presence of [18]crown-6 (0.1 equiv.). c) In the presence of DBU
(0.1 equiv.). d) In the presence of (Bu4N)Br (5 mol-%) as phase-transfer catalyst. e) The reaction was carried
out at 808.
presence of sterically hindered guanidine as base [8]. We believe that DBU in this
reaction acted both as a CO2 carrier and a base (Scheme 1) [9]1).
To clarify the substituent effect on the benzyl chlorides on the reaction, we studied
other benzyl chlorides C6H4CH2Cl (R ˆ F, CF 3, or Me) and MeO2C6H4CH2Cl under
the optimized reaction conditions (Scheme 2, Table 2). For benzyl chlorides having
electron-withdrawing groups (F or CF 3) or a weak electron-donating group (Me) at the
phenyl ring, CO2-inserted products were isolated in similar yields as with benzyl
chloride, along with small amounts of the corresponding secondary amines 3 or tertiary
amines 2 (Table 2). However, in the case of (MeO)2C6H3CH2Cl, only the correspond-
ing tertiary amine 2e was obtained in low yield because the two strong electron-
donating MeO groups disfavor the nucleophilic attack of benzylammonium carbamates
and benzylamine to benzyl halides. These results suggest that the substituents at the
phenyl ring do not affect the electron density at the benzyl CH2 moiety, which
is connected to chloride and is attacked by alkylammonium carbamates
1
)
We also found that 1a was formed in a very low yield even under the conditions reported by Butcher, with
Cs2CO3 as a base [10a]; the major product was the tertiary amine 2a. A careful examination of this reaction
revealed that no so called −cesium ionic effect× could be reproduced under the same conditions. According
to a detailed report by Jung and co-workers [10c], both 3 equiv. of Cs2CO3 and 3 equiv. of Bu4N are required
to give a high yield of 1a in DMF under CO2 atmosphere with bubbling.

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Helvetica Chimica Acta Vol. 84 (2001)
Scheme 2
Table 2. The Reaction of Benzylamine with Benzyl Chlorides under CO2 Atmosphere (50 kg/cm2) at 708
Entry
ArCH2Cl
Series
Yield/%a)
1
2
3
4
1
2
3
o-CF3-C6H4-CH2Cl
p-F-C6H4-CH2Cl
p-Me-C6H4-CH2Cl
-(MeO)2C6H3-CH2Cl
b
c
d
e
67
60
54
7
25
4
15
14
4m,m
a) Yield of isolated product.
À‡
RNHCO2 NH3R, i.e. the formation of carbamates is generally not affected by
substituents at the phenyl ring; however, there is a threshold, since no carbamates are
formed if the phenyl ring bears several strong electron-donating groups. One
interesting finding is that, in the reaction of benzylamine with p-fluorobenzyl chloride
under high CO2 pressure, compound 4b, derived from the further reaction of the CO2-
inserted carbamate with p-fluorobenzyl chloride, was formed in 15% yield (Table 2,
Entry 2). This phenomenon has never been reported so far.
With other primary amines such as propylamine, butylamine, prop-2-enylamine,
cyclohexylamine, or 1-methylbenzylamine, similar tendencies as with benzylamine
were observed: low yields of CO2-inserted products 5 were obtained with K2CO3 or
Cs2CO3 as a base under CO2 atmosphere, and good yields were obtained with DBU as a
base under high CO2 pressure in toluene/hexane 1:1 at 708 (Scheme 3, Table 3).
Especially in the cases of propylamine, butylamine, and prop-2-enylamine, N-
benzylation of the CO2-inserted product occurred to give the corresponding compound
6. The by-products 7 were also observed.
With secondary amines, e.g. diethyl- and dicyclohexylamine, the CO2-inserted
products (e.g. 8 and 10, resp.) were obtained only in trace amounts, along with the
major tertiary amines RRNR' (e.g. 9 and 11, resp.), even under the optimized reaction
conditions (Scheme 4). Especially for diisopropylamine, no reaction occurred because
of its steric hindrance. On the other hand, for a cyclic secondary amine such as
piperidine, due to its high nucleophilicity, the tertiary amine 12 was formed exclusively
under the same reaction conditions (Scheme 4).

Helvetica Chimica Acta Vol. 84 (2001)
3361
Scheme 3
Table 3. The Reaction of Primary Amines with Benzyl Chlorides under CO2 Atmosphere (50 kg/cm2) at 708
Entry
RNH2
Series
Yield/%a)
5
6
7
1
2
3
4
5
Me(CH2)2NH2
Me(CH2)3NH2
CH2ˆCHCH2NH2
cyclo-C6H11
a
b
c
d
e
86
82
84
84
80
4
3
6
4
8
trace
trace
9
trace
PhCH(Me)NH2
a) Yield of isolated product.
In conclusion, we systematically examined the reaction of amines with benzyl
halides under high CO2 pressure and found that, in low-polarity solvent and in the
presence of DBU as a base, the CO2-inserted products can be obtained in high yields
from primary amines. This reaction procedure, with CO2 as a cheap, benign-nature and
abundant reagent, can be used for the protection of primary amines, thus replacing
benzyl carbonochloridate (ZCl), which is usually prepared from hazardous phosgene
(COCl2).
We thank the State Key Project of Basic Research (Project 973) (No. G2000048007) and the National
Natural Science Foundation of China for financial support. We also thank the Inoue Photochirogenesis Project
(ERATO, JST) for chemical reagents.
Experimental Part
General. Org. solvents were dried by standard methods when necessary. Commercially obtained reagents
were used without further purification. TLC Monitoring: Huanghai GF254 silica gel coated plates. Flash column
Chromatography (FC): 200 300 mesh silca gel. M.p.s: Yanagimoto micro-melting-point apparatus; uncorrect-
.
ed. IR Spectra: Perkin-Elmer 983 spectrometer in cmÀ1 1H-NMR Spectra: Bruker AM-300 spectrometer;
CDCl3 solns.; d in ppm with SiMe4 as internal standard (ˆ0 ppm), J in Hz. 13C-NMR Spectra: data only for CO2-
inserted products. MS: HP-5989 instrument (EI) or Finnigan MA ‡ mass spectrometer (HR). Some of the solid
compounds reported in this paper gave satisfactory CHN microanalyses with a Carlo-Erba 1106 analyzer.
Reaction of Amines with Benzyl Chlorides under CO2 Atmosphere: General Procedure 1 (G.P. 1). CO2 Gas
was bubbled into a stirred suspension of benzylamine (300 mg, 2.80 mmol) and DBU (426 mg, 2.80 mmol) in
toluene/hexane 1 :1 (10 ml) at r.t. for 1 h. Benzyl chloride (354 mg, 2.80 mmol) was added in 1 portion, and CO2
gas was further passed through the mixture. The mixture was stirred at r.t. for 72 h. After evaporation, the
residue was purified by CC (silica gel, petroleum ether/AcOEt 1:5) to give 1a (290 mg, 43%) and 2a (78 mg,
14%) as white solids.

3362
Helvetica Chimica Acta Vol. 84 (2001)
Scheme 4
Reaction of Amines with Benzyl Chlorides under High CO2 Pressure: General Procedure 2 (G.P. 2).
Benzylamine (300 mg, 2.80 mmol), DBU (426 mg, 2.80 mmol), benzyl chloride (354 mg, 2.80 mmol), anh.
toluene/petroleum ether 1:1 (10 ml), and a magnetic stirring bar were placed in the 50-ml glass liner of a
stainless-steel autoclave under a N2 purge. After the autoclave was purged several times with CO2, it was
pressurized with CO2 (40 atm), sealed, and stirred at r.t. for 24 h. After release of the pressure, the solvent was
evaporated and the residue purified by CC (silica gel, petroleum ether/AcOEt 1:4) to give 1a and 2a.
Benzylcarbamic Acid Benzyl Ester (1a) [10c]. According to the G.P. 2: white solid (587 mg, 87%). M.p.
60 628. IR (CHCl3): 1687 (CˆO). 1H-NMR: 4.39 (d, J ˆ 5.8, CH2); 5.04 (s, NH); 5.14 (s, CH2); 7.26 7.37 (m,
10 arom. H). 13C-NMR: 45.19; 66.89; 127.53; 128.14; 128.53; 128.69; 136.51; 138.40; 156.40 (CˆO). EI-MS: 287
.
‡
(M ). Anal. calc. for C15H15NO2 (241.2851): C 74.67, H 6.27, N 5.81; found: C 74.67, H 6.29, N 5.69.
Tribenzylamine (2a) [11]. According to G.P. 2: white solid (39 mg, 7%). M.p. 85 888. IR (CHCl3): 1601
.
‡
‡
(CˆC). 1H-NMR: 3.55 (s, 1 CH2); 7.22 7.42 (m, 5 arom. H). EI-MS: 287 (M ). HR-MS: 287.1668 (C21H21N ,
‡
M ; calc. 287.1674).
Benzylcarbamic Acid 2-(Trifluoromethyl)benzyl Ester (1b). According to the G.P. 2: colorless oil (581 mg,
67%). IR (CHCl3): 1703 (CˆO). 1H-NMR: 4.39 (d, J ˆ 5.8, 1 CH2); 5.17 (s, NH); 5.19 (s, 1 CH2); 7.25 7.63 (m,
9 arom. H). 13C-NMR: 45.19; 65.86; 124.56 (q, J(C,F) ˆ 3.8); 124.84 (q, J(C,F) ˆ 3.8); 127.13; 127.58; 127.94 (q,
J(C,F) ˆ 145.2); 128.32 (q, J(C,F) ˆ 145.2); 128.70; 128.98; 131.13; 137.64; 138.24; 156.11 (CˆO). EI-MS: 310
‡
2
.
‡
‡
(MH ). HR-MS: 309.0996 (C16H14F3NO , M ; calc. 309.0977)

Helvetica Chimica Acta Vol. 84 (2001)
3363
Benzyl[2-(trifluoromethyl)benzyl]amine (3b). According to G.P. 2: colorless oil (138 mg, 25%). IR
.
‡
1
(CHCl3): 1601 (CˆC). H-NMR: 3.84 (s, CH2); 3.89 (s, CH2); 7.26 7.67 (m, 4 arom. H). EI-MS: 265 (M ).
‡
‡
HR-MS: 265.1071 (C15H14F3N , M ; calc. 265.1078)
Benzylcarbamic Acid 4-Fluorobenzyl Ester (1c). According to the G.P. 2: white solid (437 mg, 60%). M.p.
45 488. IR (CHCl3): 1714 (CˆO). 1H-NMR: 4.39 (d, J ˆ 6.0, 1 CH2); 5.0 (s, NH); 5.10 (s, 1 CH2); 7.25 7.50 (m,
9 arom. H). 13C-NMR: 45.17; 66.12; 127.02; 127.54; 128.14; 128.43; 129.66 (d, J(C,F) ˆ 6.0); 130.09 (d, J(C,F) ˆ
‡
2
‡
6.0); 138.33; 156.29 (CˆO); 162.55 (d, J(C,F) ˆ 225.9). EI-MS: 260 (MH ). HR-MS: 259.1014 (C15H14FNO ,
‡
M ; calc. 259.1009).
Benzyl[bis(4-fluorobenzyl)]amine (2c). According to G.P. 2: colorless oil (41 mg, 4%). IR (CHCl3): 1600
(CˆC). 1H-NMR: 3.49 (s, 1 CH2); 3.52 (s, 1 CH2); 6.96 7.02 (m, 4 arom. H); 7.29 7.35 (m, 8 arom. H). EI-MS:
.
‡
‡
‡
323 (M ). HR-MS: 323.1476 (C21H19F2N , M ; calc. 323.1486).
Benzyl(4-fluorobenzyl)carbamic Acid 4-Fluorobenzyl Ester (4c). According to G.P. 2: colorless oil
(136 mg, 15%). IR (CHCl3): 1696 (CˆO). 1H-NMR: 4.41 (br. s, 2 CH2); 5.19 (s, 1 CH2); 7.0 7.50 (m, 13 arom.
H). 13C-NMR: 49.21; 66.12; 66.86; 127.53; 127.54; 128.11; 128.66; 129.84; 129.95; 130.06; 132.40 (d, J(C,F) ˆ 6.2);
.
‡
133.07 (d, J(C,F) ˆ 6.2); 137.15; 156.54 (CˆO); 162.35 (d, J(C,F) ˆ 245.6). EI-MS: 368 (MH ). HR-MS:
‡
2
‡
259.1396 (C22H19F2NO ), M ; calc. 367.1384).
Benzyl Carbamic Acid 4-Methylbenzyl Ester (1d). According to G.P. 2: white solid (386 mg, 54%). M.p.
72 748. IR (CHCl3): 1682 (CˆO). 1H-NMR: 2.35 (s, Me); 4.38 (d, J ˆ 6.0, 1 CH2); 5.10 (s, NH); 5.10 (s, 1 CH2);
7.25 7.63 (m, 9 arom. H). 13C-NMR: 21.19; 45.17; 66.86; 127.51; 128.31; 128.68; 129.22; 133.48; 138.00; 138.44;
‡
2
.
‡
‡
156.47 (CˆO). EI-MS: 255 (M ). HR-MS: 255.1257 (C16H17NO , M ; calc. 255.1259).
Benzyl(4-methylbenzyl)amine (3d). According to G.P. 2: colorless oil (82 mg, 14%). IR (CHCl3): 1602
(CˆC). 1H-NMR: 2.36 (s, Me); 3.78 (s, 1 CH2); 3.81 (s, 1 CH2); 5.10 (s, 1 CH2); 7.14 7.40 (m, 9 arom. H). EI-
‡
‡
‡
MS: 210 ([ M À H ). HR-MS: 211.1348 (C15H17N , M ; calc. 211.1361).
Benzylbis(3,5-dimethoxybenzyl)amine (2e). According to G.P. 2: colorless oil (81 mg, 7%). IR (CHCl3):
1602 (CˆC). 1H-NMR: 3.58 (s, 2 CH2); 3.64 (s, 1 CH2); 3.84 (s, 4 MeO); 6.40 (s, 2 arom. H); 6.68 (s, 4 arom. H);
‡
4
‡
‡
7.14 7.50 (m, 5 arom. H). EI-MS: 408 (MH ). HR-MS: 407.2101 (C25H29NO , M ; calc. 407.2097).
Propylcarbamic Acid Benzyl Ester (5a). According to G.P. 2: colorless solid (456 mg, 86%). M.p. 42 448.
1
IR (CHCl3): 1700 (CˆO). H-NMR: 0.92 (t, J ˆ 7.5, Me); 1.51 (quint, J ˆ 7.5, 1 CH2); 3.16 (q, J ˆ 7.5, 1 CH2);
4.77 (s, NH); 5.09 (s, 1 CH2); 7.26 7.36 (m, 5 arom. H). 13C-NMR: 11.17; 23.16; 42.76; 128.05; 128.08; 128.47;
.
‡
136.62; 156.41 (CˆO). EI-MS: 193 (M ). Anal. calc. for C11H15NO2: C 68.37, H 7.82, N 7.25; found: C 68.45, H
7.89, N 7.39.
Benzyl(propyl)carbamic Acid Benzyl Ester (6a). According to G.P. 2: colorless oil (28 mg, 4%). IR
(CHCl3): 1696 (CˆO). 1H-NMR: 0.83 (t, J ˆ 7.5, Me); 1.37 1.68 (m, 1 CH2); 3.15 3.28 (m, 1 CH2); 4.50 (s,
1 CH2); 5.17 (s, 1 CH2); 7.13 7.45 (m, 10 arom. H). 13C-NMR: 11.20; 21.33; 47.91; 50.17; 67.10; 127.22; 127.76;
.
‡
127.86; 128.42; 128.49; 128.52; 136.45; 137.98; 156.41 (CˆO). EI-MS: 254 ([ M À 29] ). HR-MS: 283.1587
‡
2
‡
(C18H21NO , M ; calc. 283.1572).
Dibenzylpropylamine (7a). According to G.P. 2: colorless oil (25 mg, 4%). IR (CHCl3): 1602 (CˆC).
1H-NMR: 0.92 (t, J ˆ 7.5, Me); 1.51 (quint, J ˆ 7.5, 1 CH2); 3.16 (q, J ˆ 7.5, 1 CH2); 3.54 (s, 2 CH2); 7.0 7.46 (m,
.
‡
‡
‡
10 arom. H). EI-MS: 239 (M ). HR-MS: 239.1667 (C17H21N , M ; calc. 239.1674).
Butylcarbamic Acid Benzyl Ester (5b) [12]. According to G.P. 2: colorless oil (476 mg, 82%). IR (CHCl3):
1701 (CˆO). 1H-NMR: 0.91 (t, J ˆ 7.3, Me); 1.27 1.37 (m, 1 CH2); 1.38 1.52 (m, 1 CH2); 3.15 3.22 (m,
1 CH2); 4.77 (s, NH); 5.09 (s, 1 CH2); 7.26 7.36 (m, 5 arom. H). 13C-NMR: 13.68; 19.85; 32.02; 40.80; 66.54;
‡
2
.
‡
‡
128.03; 128.48; 136.70; 156.41 (CˆO). EI-MS: 208 (MH ). HR-MS: 207.1273 (C12H17NO , M ; calc. 207.1259).
Benzyl(butyl)carbamic Acid Benzyl Ester (6b). According to G.P. 2: colorless oil (25 mg, 3%). IR (CHCl3):
1695 (CˆO). 1H-NMR: 0.83 0.91 (m, 2 Me); 1.27 1.38 (m, 2 CH2); 1.39 1.58 (m, 2 CH2); 3.15 3.28 (m,
2 CH2); 4.50 (s, 1 CH2); 5.17 (s, 1 CH2); 7.13 7.45 (m, 10 arom. H). 13C-NMR: 13.80; 19.98; 30.10; 30.26; 45.98;
46.96; 50.17; 67.14; 127.25; 127.81; 127.89; 128.44; 128.52; 138.02; 156.41 (CˆO). EI-MS: 207 ([ M À 90] ]. HR-
‡
‡
2
‡
MS: 297.1719 (C19H23NO , M ; calc. 297.1729).
Butyldibenzylamine (7b) [13]. According to G.P. 2: colorless oil (36 mg, 8%). IR (CHCl 3): 1602 (CˆC).
1H-NMR: 0.91 (t, J ˆ 7.3, Me); 1.27 1.37 (m, 1 CH2); 1.38 1.52 (m, 1 CH2); 3.15 3.22 (m, 1 CH2); 5.09 (s,
‡
‡
‡
2 CH2); 7.26 7.36 (m, 10 arom. H). EI-MS: 163 ([ M À 90] ]. HR-MS: 163.1347 (C11H17N ; M ; calc. 163.1361).
Prop-2-enylcarbamic Acid Benzyl Ester (5c). According to G.P. 2: colorless oil (452 mg, 84%). IR (CHCl3):
1701 (CˆO). 1H-NMR: 3.80 (s, 1 CH2); 5.10 (s, 1 CH2); 5.06 5.20 (m, 1 CH2); 5.73 5.93 (m, 1 H); 7.26 7.36
(m, 5 arom. H). 13C-NMR: 43.28; 66.52; 115.74; 127.92; 128.26; 128.32; 134.37; 136.39; 156.21 (CˆO). EI-MS:
‡
‡
‡
192 (MH ). HR-MS: 191.0954 (C11H14NO , M ; calc. 191.0946).
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Benzyl(prop-2-enyl)carbamic Acid Benzyl Ester (6c). According to G.P. 2: colorless oil (47 mg, 6%). IR
(CHCl3): 1700 (CˆO). 1H-NMR: 3.80 (s, 1 CH2); 4.53 (s, 1 CH2); 5.10 (s, 1 CH2); 5.06 5.20 (m, 1 CH2); 5.73
5.93 (m, 1 H); 7.26 7.36 (m, 10 arom. H). 13C-NMR: 49.03; 67.05; 67.25; 117.45; 127.29; 127.74; 127.96; 128.05;
‡
2
‡
‡
128.45; 128.48; 133.15; 137.53; 156.41 (CˆO). EI-MS: 282 (MH ). HR-MS: 281.1429 (C18H19NO , M ; calc.
281.1416).
Cyclohexylcarbamic Acid Benzyl Ester (5d) [12]. According to G.P. 2: colorless solid (522 mg, 84%). M.p.
80 838. IR (CHCl3): 1701 (CˆO). 1H-NMR: 1.0 1.25 (m, 3 H); 1.27 1.52 (m, 1 CH2); 1.52 1.80 (m, 3 H,
CH2); 1.81 2.0 (m, 2 H, CH2); 3.40 3.60 (m, CH); 4.65 (s, NH); 5.09 (s, 2 H, CH2); 7.26 7.36 (m, 5 arom. H).
‡
13C-NMR: 24.78; 25.50; 33.41; 49.91; 66.48; 128.05; 128.13; 128.52; 136.74; 156.41 (CˆO). EI-MS: 234 (MH ).
Anal. calc. for C15H15NO2 (233.3062): C 72.07, H 8.21, N 6.00; found: C 72.09, H 8.02, N 5.76.
(a-Methylbenzyl)carbamic Acid Benzyl Ester (5e). According to G.P. 2: colorless oil (571 mg, 80%). IR
(CHCl3): 1714 (CˆO). 1H-NMR: 1.48 (d, J ˆ 6.9, Me); 4.85 4.88 (m, CH); 5.02 (s, NH); 5.05 (d, J ˆ 12.3, 1 H);
5.12 (d, J ˆ 12.3, 1 H); 7.20 7.46 (m, 10 arom. H). 13C-NMR: 22.51; 50.81; 66.76; 125.94; 127.36; 128.11; 128.52;
‡
2
‡
‡
128.67; 136.51; 155.57 (CˆO). EI-MS: 256 (MH ). HR-MS: 255.1243 (C16H17NO , M ; calc. 255.1259).
(a-Methylbenzyl)dibenzylamine (7e). According to G.P. 2: colorless oil (76 mg, 9%). IR (CHCl3): 1602
(CˆC). 1H-NMR: 1.42 (d, J ˆ 6.9, Me); 3.68 (d, J ˆ 13.8, CH); 3.78 (d, J ˆ 13.8, CH); 3.92 (q, J ˆ 6.7, CH); 7.20
‡
‡
‡
7.50 (m, 10 arom. H). EI-MS: 302 (MH ). HR-MS: 301.1832 (C22H23N ; M ; calc. 301.1830).
Diethylcarbamic Acid Benzyl Ester (8). According to G.P. 2: colorless oil (6 mg, 1%). IR (CHCl3): 1700
(CˆO). 1H-NMR: 1.07 (t, J ˆ 7.2, 2 Me); 2.52 (q, J ˆ 7.2, 2 CH2); 5.12 (s, 1 CH2); 7.13 7.50 (m, 5 arom. H). EI-
‡
2
‡
‡
MS: 207 (M ). HR-MS: 207.1250 (C12H17NO , M ; calc. 207.1259).
Benzyldiethylamine (9) [14]. According to G.P. 2: colorless oil (59 mg, 10%). IR (CHCl3): 1602 (CˆC).
1H-NMR: 1.02 (t, J ˆ 7.4, 2 Me); 2.51 (q, J ˆ 7.3, 2 CH2); 3.57 (s, 1 CH2); 7.14 7.40 (m, 5 arom. H). EI-MS: 210
‡
‡
‡
([M À H] ). HR-MS: 163.1358 (C11H17N ; M ; calc. 163.1361).
Dicyclohexylcarbamic Acid Benzyl Ester (10). According to G.P. 2: colorless oil (9 mg, 1%). IR (CHCl3):
1
1719 (CˆC). H-NMR: 1.17 1.40 (m, 5 CH2); 1.40 1.78 (m, 5 CH2); 4.20 4.22 (m, 2 CH2); 5.37 (s, 1 CH2);
‡
‡
‡
7.26 7.58 (m, 5 arom. H). EI-MS: 316 (MH ). HR-MS: 315.2197 (C20H29O2N , M ; calc. 315.2198).
Benzyldicyclohexylamine (11). According to G.P. 2: colorless oil (61 mg, 8%). IR (CHCl3): 1602 (CˆC).
1H-NMR: 0.82 1.50 (m, 6 CH2); 1.51 2.01 (m, 4 CH2); 2.47 2.65 (m, 2 CH); 3.75 (s, 1 CH2); 7.14 7.40 (m,
‡
‡
‡
5 arom. H). EI-MS: 272 (MH ). HR-MS: 271.2292 (C19H29N ; M ; calc. 271.2300).
N-Benzylpiperidine (12) [15]. According to G.P. 2: colorless oil (441 mg, 90%). IR (CHCl3): 1602 (CˆC).
1H-NMR: 1.23 1.51 (m, 1 CH2); 1.52 1.73 (m, 2 CH2); 2.30 2.48 (m, 2 CH2); 7.20 7.40 (m, 5 arom. H). EI-
‡
‡
‡
MS: 175 (M ). HR-MS: 175.1364 (C12H17N , M ; calc. 175.1361).
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Received March 27, 2001