Magnesium bistrifluoromethanesulfonimide catalysed three-component synthesis of protected homoallylic amines

Article abstract of DOI:10.3184/174751911X13056175312712

A one-pot, three-component reaction of an aldehyde, benzyl carbamate and allyltrimethylsilane in the presence of 3 mol% of magnesium bistrifluoromethanesulfonimide at room temperature has been shown to afford the corresponding protected homoallylic amine in high yield.

Full text of DOI:10.3184/174751911X13056175312712

310 RESEARCH PAPER
MAY, 310–312
JOURNAL OF CHEMICAL RESEARCH 2011
Magnesium bistrifluoromethanesulfonimide catalysed three-component
synthesis of protected homoallylic amines
Hongshe Wang* and Weixing Zhao
Shaanxi Key Laboratory for Phytochemistry, Department of Chemistry and Chemical Engineering, Baoji University of Arts and Sciences,
Baoji, Shaanxi 721013, P. R. China
A one-pot, three-component reaction of an aldehyde, benzyl carbamate and allyltrimethylsilane in the presence of
3 mol% of magnesium bistrifluoromethanesulfonimide at room temperature has been shown to afford the
corresponding protected homoallylic amine in high yield.
Keywords: magnesium bistrifluoromethanesulfonimide, three-component reaction, protected homoallylic amines
Homoallylic amines and their derivatives are useful intermedi-
ates in natural product synthesis1,2 and acylated homoallylic
amines have many synthetic applications.3 Homoallylic amines
are commonly prepared by the allylation of aldimines which
had previously been prepared from aldehydes and amines
using allylic nucleophiles such as allyl silanes and allyl organo-
metallics.4–7 To avoid the prior synthesis of aldimines, a direct
one-pot, three-component reaction has been reported for the
synthesis of homoallyl amines in the presence of a catalyst
such as BF3·OEt2,8 phosphomolybdic acid,9 Cu(OTf)2,10
Bi(OTf)3,11 Sc(OTf)312 and I2.13 Although each of the above
methods has its own merits, some of these earlier methods
employed for this one-pot conversion have drawbacks such as
the use of toxic organic solvents, long reaction times and
unsatisfactory yields. Therefore, the development of conve-
nient approaches with mild reaction conditions and high yields
for the preparation of homoallylic amines is still desirable.
In recent years, metal bistrifluoromethanesulfonimides
[M(NTf2)n] have been successfully used for the acetylation of
phenols and alcohols,14 [2+2] cycloadditions of siloxy alkynes
with carbonyl compounds,15 Friedel-Crafts acylation reac-
tions,16 cycloisomerisation of 1,6-dienes17 and aminolysis of
lactones with amines.18 Previously, we have reported the use of
Eu(NTf2)319 and magnesium bistrifluoromethanesulfonimide
[Mg(NTf2)2]20 as efficient catalysts in organic synthesis.
Mg(NTf2)2 is commercially available, cheaper and not sensi-
tive to air, and therefore better suited for catalytic use. Follow-
ing our interest in the catalytic uses of M(NTf2)n, we report a
facile and efficient procedure for the synthesis of protected
homoallylic amines in the presence of 3 mol% of Mg(NTf2)2
at room temperature (Scheme 1).
Table 1 Effect of different amount of Mg(NTf2)2 on the reaction
of benzaldehyde, benzyl carbamate and allyltrimethylsilanea
Entry
Mg(NTf2)2/mol%
Time/min
Yieldb/%
1
2
3
4
5
6
7
0
0.5
1
180
60
25
10
8
Trace
67
85
3
95
5
7
10
95
8
94
5
90
a The reactions were were performed at room temperature in
EtOH.
b Isolated yield.
when 10 mol% of Mg(NTf2)2 was used, but the yield was rela-
tively low. Considering the amount of the catalyst, reaction
time and yield, 3 mol% of Mg(NTf2)2 was found to be the most
effective.
The effect of different solvents on the reaction was then
studied and the results are listed in Table 2. As shown in
Table 2, moderate yields were obtained in dichloromethane,
acetonitrile and toluene. N,N-Dimethylformamide and dimeth-
ylsulfoxide afforded lower yields. After screening different
solvents, ethanol was the solvent of choice. It not only afforded
the product in excellent yield, but also with a higher reaction
rate.
To demonstrate the generality of this method, other alde-
hydes were also used to react with benzyl carbamate and
allyltrimethylsilane in the presence of Mg(NTf2)2 (3 mol%) in
In order to establish optimum conditions for the synthesis
of homoallylic amines, different amount of Mg(NTf2)2 and
various solvents were examined. Using the reaction of benzal-
dehyde, benzyl carbamate, and allyltrimethylsilane as a model,
initially we investigated the effect of the amount of Mg(NTf2)2
on the reaction. As shown in Table 1, in the absence of this
catalyst, only a trace amount of the desired product was
produced. However, even 0.5 mol% of Mg(NTf2)2 accelerated
the reaction, although the corresponding product was obtained
in a low yield and at a slow rate. Increasing the amount of
Mg(NTf2)2 not only enhanced the product yield, but also
reduced the reaction time. Rate enhancement was observed
Table 2 Effect of different solvent on the reaction of
benzaldehyde, benzyl carbamate and allyltrimethylsilanea
Entry
Solvent
Time/min
Yieldb/%
1
2
3
4
5
6
CH2Cl2
Toluene
MeCN
EtOH
20
20
15
10
45
45
85
82
88
95
68
56
DMF
DMSO
a
The reactions were carried out in different solvents at room
temperature with 3 mol% of Mg(NTf2)2.
b Isolated yield.
Scheme 1
* Correspondent. E-mail: hongshewang@126.com

JOURNAL OF CHEMICAL RESEARCH 2011 311
Table 3 Synthesis of Cbz-protected homoallylic amines
the method was suitable for the conversion of aliphatic alde-
hydes (Table 3, entries 11-14), but relatively longer times were
required. However, ketones did not yield any products under
the present reaction conditions.
catalysed by Mg(NTf2)2a
Entry Aldehyde
Product
Time Yieldb
/min
/%
The structures of all products were proved on the basis
of their spectral (1H and 13C NMR) data. For example, the 1H
NMR spectrum of CH=CH2 in compound 4a exhibited a
doublet (J = 10.2 Hz) at 4.98 ppm, two doublets (J = 17.2,
1.1 Hz) at 5.12 ppm and a multiplet at 5.55–5.70 ppm. The
1
2
10
95
1
formation of allylic amines was not detected from H NMR
10
15
10
20
15
20
25
10
15
20
20
20
20
94
94
96
89
96
88
84
97
90
86
89
85
89
and 13C NMR spectra. Isomerisation of the double bond in
products had not occured.
In conclusion, Mg(NTf2)2 was found to be an efficient cata-
lyst for the one-pot, three-component reaction of aldehydes,
benzyl carbamate and allyltrimethylsilane at room temperature
to afford the corresponding protected homoallylic amines.
The advantages of this protocol include mild reaction con-
ditions, easy workup, high yields, and the use of non-toxic
organic solvent and a catalytic amount and commercially
available catalyst.
3
4
5
Experimental
Melting points were determined on an XT4A electrothermal appara-
tus equipped with a microscope and are uncorrected. NMR spectra
were recorded on a Bruker Avance 400 spectrometer in CDCl3 with
TMS as an internal standard. IR spectra were recorded on a Nicolet
FTIR-750 spectrometer. Elemental analyses were performed on a
Perkin Elmer 240-C instrument. All solvents were dried by standard
procedures. The benzaldehyde was distilled prior to use. All other
reagents were commercially available products and were used without
further purification.
6
7
8
Synthesis of protected homoallylic amines; general procedure
A mixture of the aldehyde 1 (1 mmol), benzyl carbamate 2 (1 mmol),
allyltrimethylsilane 3 (1.2 mmol) and Mg(NTf2)2 (3 mol%) in absolute
ethanol (2 mL) was stirred at room temperature until the reaction was
complete (monitored by TLC). The reaction mixture was quenched
with saturated NH4Cl solution and the aqueous layer was extracted
twice with EtOAc. The combined organic layer was dried over anhy-
drous Na2SO4 and concentrated under vacuum. The crude product was
purified by column chromatography on silica gel to give the desired
product 4.
N-Benzyloxycarbonyl-1-phenylbut-3-enylamine (4a): M.p. 68–
69 °C (lit.12 67–68 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.31–2.50 (m,
2H), 4.60–4.83 (m, 1H), 4.90–4.96 (m, 3H), 4.98 (d, J = 10.2 Hz, 1H),
5.12 (dd, J = 17.2, 1.1 Hz, 1H), 5.55–5.70 (m, 1H), 7.11–7.20
(m, 5H), 7.20–7.31 (m, 5H). 13C NMR (CDCl3, 100 MHz) δ: 41.2,
54.6, 66.8, 118.6, 126.6, 127.3, 128.2, 128.4, 128.7, 133, 136.1, 142.2,
155.9. IR (KBr) ν: 3051, 1712, 1427, 1260, 745 cm−1. Anal. Calcd
for C18H19NO2: C, 76.87, H, 6.76; N, 4.98. Found: C, 76.80; H, 6.80;
N, 4.91%.
N-Benzyloxycarbonyl-1-(4-methylphenyl)but-3-enylamine (4b):
M.p. 62–63 °C (lit.21 62–64 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.37
(s, 3H), 2.46–2.56 (m, 2H), 4.60–4.71 (m, 1H), 4.98–5.15 (m, 5H),
5.60–5.65 (m, 1H), 7.01–7.18 (m, 4H), 7.29–7.45 (m, 5H). 13C NMR
(CDCl3, 100 MHz) δ: 21.6, 40.6, 54.8, 67.5, 100.2, 118.3, 126.8,
128.4, 128.8, 129.0, 134.2, 136.6, 137.1, 156.8. IR (KBr) ν: 3357,
1690, 1522, 1455, 1266 cm−1. Anal. Calcd for C19H21NO2: C, 77.29;
H, 7.12; N, 4.75. Found: C, 77.36; H, 7.07; N, 4.83%.
N-Benzyloxycarbonyl-1-(4-methoxyphenyl)but-3-enylamine (4c):
M.p. 71–72 °C (lit.12 70–71 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.50–
2.58 (m, 2H), 3.76 (s, 3H), 4.71–4.80 (m, 1H), 5.04–5.21 (m, 5H),
5.55–5.76 (m, 1H), 6.83 (d, J = 8.6 Hz, 2H), 7.17 (d, J = 7.8 Hz, 2H),
7.31–7.40 (m, 5H). 13C NMR (CDCl3, 100 MHz) δ: 40.9, 53.5, 55.0,
86.6, 113.8, 118.5, 127.3, 128.0, 128.3, 133.6, 136.4, 155.6, 158.9. IR
(KBr) ν: 3053, 1717, 1501, 1429, 1264, 735 cm−1. Anal. Calcd for
C19H21NO3: C, 73.29; H, 6.80; N, 4.50. Found: C, 73.21; H, 6.73;
N, 4.58%.
9
10
11
12
13
14
a The reactions were conducted in the presence of 3 mol% of
Mg(NTf2)2 at room temperature in EtOH.
b Isolated yield.
ethanol at room temperature. The results are summarised
in Table 3. As shown in Table 3, in all cases, aromatic and
aliphatic aldehydes afforded the desired products smoothly.
Aromatic aldehydes containing both electron-donating and
electron-withdrawing groups on the aromatic ring worked well
(Table 3, entries 1–8). The three-component reactions derived
from an α,β-unsaturated aldehyde such as cinnamaldehyde
(Table 3, entry 9) and a sterically-hindered aldehyde such as
2-naphthaldehyde (Table 3, entry 10) also afforded the cor-
responding homoallyllic amines in high yields. Additionally,
N-Benzyloxycarbonyl-1-(2-methoxyphenyl)but-3-enylamine (4d):
M.p. 90–91 °C (lit.3 90–91 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.52–
2.59 (m, 2H), 3.86 (s, 3H), 4.92–5.17 (m, 5H), 5.64–5.71 (m, 2H),
6.88–6.93 (m, 2H), 7.18–7.33 (m, 7H). 13C NMR (CDCl3, 100 MHz)
δ: 40.1, 52.9, 55.8, 66.7, 111.0, 117.1, 120.7, 128.1, 128.3, 128.4,

312 JOURNAL OF CHEMICAL RESEARCH 2011
128.5, 129.8, 134.4, 136.8, 155.8, 157.2. IR (KBr) ν: 3330, 1688,
1602, 1537, 1490 cm−1. Anal. Calcd for C19H21NO3: C, 73.29; H, 6.80;
N, 4.50. Found: C, 73.24; H, 6.70; N, 4.57%.
N-Benzyloxycarbonyl-1-heptylbut-3-enylamine (4l): M.p. 50–51 °C
(lit.12 51–52 °C). 1H NMR (CDCl3, 400 MHz) δ: 0.86 (t, J = 6.3 Hz,
3H), 1.20–1.45 (m, 12H), 2.02–2.30 (m, 2H), 3.51–3.80 (m, 1H),
4.41–4.60 (m, 1H), 5.01–5.16 (m, 4H), 5.70–5.85 (m, 1H), 7.29–7.41
(m, 5H). 13C NMR (CDCl3, 100 MHz) δ: 14.6, 22.2, 25.4, 29.0, 29.5,
31.7, 34.9, 39.4, 50.5, 66.6, 117.8, 128.4, 128.6, 134.3, 136.9, 156.1.
IR (KBr) ν: 3057, 1713, 1500, 1436, 1264, 736 cm−1. Anal. Calcd
for C19H29NO2: C, 75.21; H, 9.63; N, 4.62. Found: C, 75.16; H, 9.55;
N, 4.66%.
N-Benzyloxycarbonyl-1-(4-bromophenyl)but-3-enylamine ( 4e):
M.p. 86–87 °C (lit.12 87–88 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.40–
2.58 (m, 2H), 4.66–4.89 (m, 1H), 4.91–5.24 (m, 5H), 5.50–5.68 (m,
1H), 7.16 (d, J = 7.6 Hz, 2H), 7.22–7.45 (m, 5H), 7.40 (d, J = 8.2 Hz,
2H). 13C NMR (CDCl3, 100 MHz) δ: 40.6, 53.9, 66.6, 118.9, 121.7,
127.9, 128.2, 128.5, 131.0, 133.2, 136.2, 141.4, 155.5. IR (KBr) ν:
3051, 1711, 1599, 1416, 1261, 745 cm−1.Anal. Calcd for C18H18BrNO2:
C, 60.01; H, 5.03; N, 3.89. Found: C, 60.05; H, 5.10; N, 3.80%.
N-Benzyloxycarbonyl-1-(3-chlorophenyl)but-3-enylamine ( 4f):
M.p. 62–63 °C (lit.12 62–63 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.30–
2.51 (m, 2H), 4.61–4.79 (m, 1H), 4.88–5.18 (m, 3H), 5.21 (d, J =
10.2 Hz, 1H), 5.25 (dd, J = 17.2, 1.4 Hz, 1H), 5.56–5.66 (m, 1H), 7.03
(d, J = 6.3 Hz, 1H), 7.11–7.48 (m, 8H). 13C NMR (CDCl3, 100 MHz)
δ: 40.5, 53.7, 66.2, 119.3, 124.9, 126.0, 127.1, 128.0, 128.8, 129.3,
133.6, 134.8, 136.6, 155.1. IR (KBr) ν: 3051, 1717, 1505, 1260, 737,
708 cm−1. Anal. Calcd for C18H18ClNO2: C, 68.46; H, 5.74; N, 4.43.
Found: C, 68.51; H, 5.66; N, 4.52.
N-Benzyloxycarbonyl-1-isopropylbut-3-enylamine (4m): Oil.12 1H
NMR (CDCl3, 400 MHz) δ: 0.85 (d, J = 6.8 Hz, 3H), 0.96 (d, J =
6.8 Hz, 3H), 1.66–1.79 (m, 1H), 2.06–2.13 (m, 1H), 2.20–2.35 (m,
1H), 3.50–3.64 (m, 1H), 4.55–4.70 (m, 1H), 5.01–5.18 (m, 4H), 5.73–
5.80 (m, 1H), 7.29–7.42 (m, 5H). 13C NMR (CDCl3, 100 MHz)
δ: 17.9, 19.0, 31.8, 36.5, 55.9, 66.3, 117.8, 128.1, 128.3, 128.5, 134.4,
136.9, 156.6. IR (neat) ν: 3077, 1695, 1537, 1246, 736 cm−1. Anal.
Calcd for C15H21NO2: C, 72.84; H, 8.56; N, 5.66. Found: C, 72.95;
H, 8.50; N, 5.61%.
N-Benzyloxycarbonyl-1-cyclohexylbut-3-enylamine (4n): M.p. 64–
1
66 °C (lit.3 64–65 °C). H NMR (CDCl3, 400 MHz) δ: 0.98–1.27
N-Benzyloxycarbonyl-1-(2-chlorophenyl)but-3-enylamine ( 4g):
M.p. 65–66 °C (lit.3 64–65 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.33–
2.58 (m, 2H), 5.05–5.24 (m, 6H), 5.62–5.71 (m, 1H), 7.14–7.38 (m,
9H). 13C NMR (CDCl3, 100 MHz) δ: 39.0, 52.1, 67.3, 118.9, 127.3,
127.5, 128.3, 128.5, 128.6, 130.5, 132.7, 133.5, 136.9, 139.4, 155.8.
IR (KBr) ν: 3320, 1689, 1544, 1433cm−1.Anal. Calcd for C18H18ClNO2:
C, 68.46; H, 5.74; N, 4.43. Found: C, 68.54; H, 5.69; N, 4.49%.
N-Benzyloxycarbonyl-1-(4-nitrophenyl)but-3-enylamine (4h): M.p.
86–88 °C (lit.12 88–89 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.33–2.55
(m, 2H), 4.70–4.88 (m, 1H), 4.94–5.29 (m, 5H), 5.40–5.65 (m, 1H),
6.97–7.34 (m, 5H), 7.37 (d, J = 7.6 Hz, 2H), 8.16 (d, J = 7.8 Hz, 2H).
13C NMR (CDCl3, 100 MHz) δ: 40.3, 54.7, 67.1, 119.6, 123.4, 127.3,
128.2, 128.3, 128.5, 132.9, 147.0, 149.6, 155.1. IR (KBr) ν: 3044,
2300, 1711, 1516, 1263, 737 cm−1. Anal. Calcd for C18H18N2O4:
C, 66.25; H, 5.56; N, 8.58. Found: C, 66.21; H, 5.50; N, 8.63%.
N-Benzyloxycarbonyl-1-(2-phenylethenyl)but-3-enylamine (4i):
M.p. 71–72 °C (lit.3 72–74 °C). 1H NMR (CDCl3, 400 MHz) δ: 2.40–
2.48 (m, 2H), 4.41–4.57 (m, 1H), 4.80–4.85 (m, 1H), 5.11–5.15
(m, 2H), 5.18 (d, J = 10.2 Hz, 1H), 5.23 (dd, J = 17.2, 1.1 Hz, 1H),
5.70–5.85 (m, 1H), 6.12 (dd, J = 15.9, 6.0 Hz, 1H), 6.63 (d, J = 15.9
Hz, 1H), 7.24–7.30 (m, 10H). 13C NMR (CDCl3, 100 MHz) δ: 40.1,
52.6, 66.2, 118.9, 126.4, 127.2, 128.0, 128.4, 128.5, 128.7, 129.4,
130.9, 133.3, 136.9, 136.9,155.8. IR (KBr) ν: 3053, 3028, 2917, 1716,
1638, 1602, 1505, 1318, 1264, 968, 746, 693 cm−1. Anal. Calcd for
C20H21NO2: C, 78.18; H, 6.84; N, 4.56. Found: C, 78.11; H, 6.80;
N, 4.67%.
(m, 6H), 1.56–1.78 (m, 5H), 2.18–2.30 (m, 2H), 3.56–3.68 (m, 1H),
4.48–4.63(m, 1H), 5.01–5.11 (m, 4H), 5.70–5.79 (m, 1H), 7.28–7.40
(m, 5H). 13C NMR (CDCl3, 100 MHz) δ: 26.1, 26.2, 26.4, 28.8, 36.5,
39.4, 41.1, 55.0, 66.8, 117.7, 128.5, 128.4, 134.3, 136.6,156.3. IR
(KBr) ν: 3436, 2930, 2853, 1724, 1506, 1446, 1342, 1214 cm−1. Anal.
Calcd for C18H25NO2: C, 75.26; H, 8.71; N, 4.88. Found: C, 75.32;
H, 8.67; N, 4.81%.
This work was financially supported by the Educational
Committee of Shaanxi Province (Nos. 09JK332, 09JS066,
2010JS069) and the Science Research Foundation of Baoji
University of Arts and Sciences (No. ZK1053).
Received 9 March 2011; accepted 26 April 2011
Paper 1100611 doi: 10.3184/174751911X13056175312712
Published online: 1 June 2011
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C20H23NO2: C, 77.67; H, 7.44; N, 4.53. Found: C, 77.74; H, 7.49;
N, 4.50%.
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