Regio- and diastereoselective three-component syntheses of homoallylic amines in aqueous media catalyzed by Bronsted acids

Article abstract of DOI:10.1002/ejoc.200600944

A systematic investigation into the three component allylation reaction of aldehydes, amines, and allyltributylstannanes catalyzed by Brensted acids in aqueous media was reported. The reaction was effective and able to produce homoallylic amines in modera

Full text of DOI:10.1002/ejoc.200600944

FULL PAPER
DOI: 10.1002/ejoc.200600944
Regio- and Diastereoselective Three-Component Syntheses of Homoallylic
Amines in Aqueous Media Catalyzed by Brønsted Acids
Dong-Sheng Deng,[a] Ping Liu,[a] and Jiwen Cai*[a,b]
Keywords: Aqueous media / Allylation / Multicomponent reactions /Amines
A systematic investigation into the three component al-
lylation reaction of aldehydes, amines, and allyltributylstan-
nanes catalyzed by Brønsted acids in aqueous media was re-
ported. The reaction was effective and able to produce homo-
allylic amines in moderate to high yields under mild condi-
tions, with a good scope of substrates. Moreover, the regiose-
lectivity of the reaction favors the formation of the γ-product,
and good diastereoselectivity in favor of the syn isomers
when cinnamyltributylstannane was employed as the al-
lylation reagent was observed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
preliminary result showing that the Brønsted acid/surfac-
tant p-dodecylbenzenesulfonic acid (DBSA) could catalyze
allylation reactions,[9] as well as the facts that in aqueous
media some imines could be stable[10] and organotin rea-
gents could tolerate acidic media to some extent,[11] we car-
ried out an investigation into the Brønsted acid catalyzed
three component allylation reaction in aqueous media. The
regio- and diastereoselectivities of the reactions were also
explored for the first time.
Introduction
Homoallylic amines are important intermediates in the
syntheses of nitrogen-containing compounds such as natu-
ral products and biologically active compounds.[1,2] The
most useful methods for the synthesis of homoallylic
amines are nucleophilic addition reactions of allylic organo-
metallic species to imines and their derivatives, such as acyl-
imines, acyliminium ions, and iminium ions.[3,4] Because any
of the reagents including the imines, the Lewis acids em-
ployed as the catalysts, and the organotin reagents involved
in the reactions could be hygroscopic and decompose in
aqueous media,[5] the syntheses of homoallylic amines are
generally carried out in organic solvents under strictly an-
hydrous conditions.[6]
Recently, organic reactions in aqueous media have at-
tracted intensive attention[7] because water is a cheap and
safe solvent in comparison with conventional organic sol-
vents and has its inherent advantage as an environmental
benign solvent. Consequently, three component syntheses
of homoallylic amines in aqueous media becomes one of
the most challenging projects in organic synthesis. Water-
tolerant allylation of aldimines with allyltributylstannane
and Barbier-type nucleophilic addition of allylic indium
compounds to aldimine in water have been reported,[8] in
which Lewis acids and zero-valent metals were used as cata-
lysts. In comparison with Brønsted acids, zero-valent metals
can be active and their use can lead to a significant amount
of byproducts. Moreover, water-tolerant Lewis acids are ex-
pensive and toxic to the environment. Encouraged by the
Results and Discussion
The three component reaction of allyltributylstannane,
benzaldehyde, and p-chloroaniline catalyzed by -cam-
phorsulfonic acid (CSA) was employed as the model reac-
tion to explore the preliminary results [Equation (1)]. Reac-
tions carried out in pure water, at room temperature for
24 h, afforded the products in 62–74% yield depending on
the loading of the catalyst, with 20 mol-% as the optimal
amount. When 10% (v) THF, acetonitrile, acetone, or etha-
nol was added as a cosolvent, the yield increased to 82–
87%, with THF showing the best result. A series of
Brønsted acids including carboxylic acids and sulfonic acids
have been screened for their catalytic results and sulfonic
acids are shown to be better promoters than carboxylic ac-
ids. Therefore, 20 mol-% CSA in THF/H2O (1:9) was cho-
sen as the reaction media for further experiments.
[a] School of Chemistry & Chemical Engineering, Sun Yat-Sen
University
Guangzhou 510275, China
[b] School of Pharmaceutical Sciences, Sun Yat-Sen University
Guangzhou 510080, China
Allylation of various imines by allyltributylstannane was
investigated and the results are summarized in Table 1. It is
noted that the reactions can proceed smoothly and generate
Fax: +86-2087334718
E-mail: puscjw@mail.sysu.edu.cn
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Three-Component Syntheses of Homoallylic Amines in Aqueous Media
FULL PAPER
Table 1. The catalytic results of CSA on the three component allylation reaction.
Entry
Aldehyde
Amine
Product
Yield [%][a]
1
2
3
4
5
6
7
8
C6H5CHO
C6H5CHO
C6H5CHO
C6H5NH2
1
2
80
86
87
83
86
80
82
88
82
79
80
80
trace
trace
trace
p-CH3C6H4NH2
p-ClC6H4NH2
C6H5NH2
p-ClC6H4NH2
p-ClC6H4NH2
p-CH3C6H4NH2
C6H5NH2
p-ClC6H4NH2
o-ClC6H4NH2
o-ClC6H4NH2
p-ClC6H4NH2
2-C10H7CH2NH2
CH3CH2CH2NH2
C6H5NH2
3
p-CH3C6H4CHO
p-CH3C6H4CHO
p-ClC6H4CHO
p-CH3C6H4CHO
p-NO2C6H4CHO
p-CH3OC6H4CHO
C6H5CHO
p-CH3C6H4CHO
p-BrC6H4CHO
C6H4CHO
4
5
6
7
8
9
9
10
11
12
13
14
15
10
11
12
C6H4CHO
CH3CH2CHO
[a] Isolated yield. All reactions were run for 24 h.
Table 2. The regio- and diastereoselectivity of the allylation reactions.
Entry
Catalysis
Solvent
γ-Product
syn/anti[b]
de
[%]
[%][a]
1
2
3
4
5
6
7
8
CSA
CSA
CSA
CSA
CSA
DBSA
H2O
THF
CH3CN
70
84
83
83
82
80
46
80
62
52
64
62
trace
85
83:17
72:28
71:29
75:25
82:18
90:10
82:18
82:18
77:23
77:23
77:23
77:23
–
66
44
42
50
64
80
64
64
54
54
54
54
–
CH3CH2OH
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
H2O/THF (9:1)
1,5-Nds[c]
CF3SO3H
p-NO2C6H4CO2H
-(+)-tartaric acid
malonic acid
maleic acid
lauric acid
SnCl2·2H2O
AlCl3·6H2O
9
10
11
12
13
14
15
88:12
88:12
76
76
80
[a] Isolated yield. The reactions of Entries 1–12 were run for 24 h and Entries 14 and 15 were run for 8 h. [b] syn/anti Ratio determined
1
by 300 MHz H NMR spectroscopic analysis.[13] syn/anti Isomer is determined by the coupling constant value. Compare δ = 4.58 ppm
(J = 6.9 Hz) with δ = 4.48 ppm (J = 8.1 Hz), the lower coupling constant (J = 6.9 Hz) indicates that the two adjacent H atoms are
located on the same side belonging to the syn isomer. In contrast to the syn isomer, δ = 4.48 ppm (J = 8.1 Hz) is contributed by the anti
isomer. [c] 1,5-Nds = 1,5-naphthalenedisulfonate.
Eur. J. Org. Chem. 2007, 1594–1598
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D.-S. Deng, P. Liu, J.-w. Cai
FULL PAPER
Table 3. The diastereoselectivity of the allylation reactions catalyzed by CSA.
Entry
Aldehyde
Amine
Product
Yield[a]
[%]
syn/anti[b]
de
[%]
1
2
3
4
5
6
7
C6H5CHO
C6H5CHO
p-CH3C6H4CHO
p-BrC6H4CHO
p-CH3C6H4CHO
p-CH3C6H4CHO
p-CH3C6H4CHO
p-CH3C6H4NH2
p-ClC6H4NH2
p-ClC6H4NH2
p-CH3C6H4NH2
p-CH3C6H4NH2
C6H5NH2
13
14
15
16
17
18
19
80
82
80
76
81
79
78
81:19
82:18
84:16
89:11
88:12
88:12
76:24
62
64
68
78
76
76
52
o-ClC6H4NH2
1
[a] Isolated yield. All reactions were run for 24 h. [b] syn/anti Ratio determined by 300 MHz H NMR spectroscopic analysis.[13]
Scheme 1. A plausible mechanism for the Brønsted acid catalyzed imine allylation reaction.
good yields with substrates bearing both electron-with- Scheme 1. The γ-syn addition probably occurs via acyclic
drawing and electron-donating groups on the phenyl rings antiperiplanar transition state B, which results from the in-
of benzaldehyde and aniline (Table 1, Entries 1–12). As for teraction of cinnamyltributylstannane with A, because of
aliphatic amines or aldehydes, the allylation reaction did the steric hindrance between the p-chlorobenzyl group and
not proceed (Table 1, Entries 13–15).
the phenyl group in antiperiplanar transition state C, as
With the use of cinnamyltributylstannane as the al- shown in Scheme 1.[12]
lylation reagent, the regio- and diastereoselectivities were
studied and the results are summarized in Table 2. The reac-
tions produced only the γ-isomers. When sulfonic acids
were used as the catalysts, moderate to good diastereoselec-
tivity for the syn isomer was obtained (Table 2, Entries 5–
8), with DBSA showing the best result (Table 2, Entry 6). In
the case of the CSA-catalyzed reactions in different media
(Table 2, Entries 1–5), the best selectivity was observed in
pure water. When Lewis acids were used as the promoters
(Table 2, Entries 14, 15), good diastereoselectivity for the
syn isomer was obtained. However, 50 mol-% of the catalyst
was needed to achieve effective results.
Conclusions
In summary, we present here the first systematic investi-
gation into three component allylation reactions catalyzed
by Brønsted acids in aqueous media. The reaction proved
to be effective to produce homoallylic amines in moderate
to high yields under mild conditions, with good substrate
scopes. Moreover, the reactions have regioselectivity favor-
ing the γ-products, as well as good diastereoselectivity fav-
oring the syn isomers when cinnamyltributylstannane was
employed as the allylation reagent.
Finally, the diastereoselectivity of the allylation of varied
imines by cinnamyltributylstannane, catalyzed by CSA, was
investigated and the results are summarized in Table 3. The
reactions afforded 100% γ-products with the syn isomers as
the major isomers. A plausible mechanism for the Brønsted
Experimental Section
General Remarks: All reagents are commercially available and used
acid catalyzed imine allylation reaction is illustrated in as received. 1H-NMR and 13C-NMR spectra were recorded with a
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Eur. J. Org. Chem. 2007, 1594–1598

Three-Component Syntheses of Homoallylic Amines in Aqueous Media
FULL PAPER
Varian UNITY/NOVA 300 MHz spectrometer with CDCl3 as the
solvent at room temperature. Chemical shifts were given in δ rela-
tive to tetramethylsilane, and expressed in ppm. Coupling constants
(J) are given in Hz. Mass spectra were measured with a SHIM-
ADZU LCMS-2010A.
4-Methyl-N-(4-chlorophenyl)-α-2-phenyl-2-propenylbenzenemethan-
amine (15): Light yellow liquid. Yield: 277 mg (80%) (syn/anti =
84:16). syn isomer: 1H NMR (300 MHz, CDCl3): δ = 7.35–6.95 (m,
12 H, ArH), 6.38–6.33 (m, 2 H, ArH), 6.06–5.94 (m, 1 H, CH),
5.12 (d, J = 10.2 Hz, 1 H, CH), 4.98 (d, J = 16.8 Hz, 1 H, CH),
4.55 (d, J = 7.2 Hz, 1 H, CH), 3.71 (t, J = 7.8 Hz, 1 H, CH), 2.35
Typical Experimental Procedure for the Allylation Reactions of Im-
ines: The aromatic aldehyde (123 µL, 1.2 mmol) and aromatic
amine (127 mg, 1 mmol) were mixed in degassed water (4.5 mL) for
30 min at room temperature. CSA (46 mg, 0.2 mmol), THF
(0.5 mL), and allyltributylstannane (466 µL, 1.5 mmol) were added
into the mixture, and the reaction was left to stir for 24 h, monitor-
ing by TLC. The mixture was then quenched with saturated
NaHCO3 solution and extracted into ethyl acetate (3ϫ20 mL). The
combined organic layers were treated by KF. The resulting solution
was filtered to remove the resin and the filtrate was washed with
brine, dried with anhydrous MgSO4, and the solvent removed in
vacuo to yield the crude product. Purification by silica gel
chromatography 100–200 mesh ZCX II (typical eluent: hexane/
ethyl acetate, 12:1, v/v) gave the homoallylic amine. The spectro-
scopic characteristics of known products 1–6, 8–10, and 14 are in
agreement with the published data.[13,14] Spectral data of some se-
lected compounds is given below.
1
(s, 3 H, CH3) ppm. anti isomer: H NMR (300 MHz, CDCl3): δ =
7.35–6.95 (m, 2 H, ArH), 6.44–6.41 (m, 0.4 H, ArH), 6.25–6.13 (m,
0.2 H, CH), 5.30–5.25 (m, 0.4 H, CH2), 4.46 (d, J = 8.1 Hz, 0.2 H,
CH), 3.61–3.55 (m, 0.2 H, CH), 2.28 (s, 0.6 H, CH3) ppm.
4-Bromo-N-(4-methylphenyl)-α-2-phenyl-2-propenylbenzenemethan-
amine (16): Light yellow liquid. Yield: 305 mg (78%) (syn/anti =
89:11). syn isomer: 1H NMR (300 MHz, CDCl3): δ = 7.37–6.94 (m,
9 H, ArH), 6.83 (d, J = 7.8 Hz, 2 H, ArH), 6.30 (d, J = 7.8 Hz, 2
H, ArH), 6.00–5.88 (m, 1 H, CH), 5.12 (d, J = 10.2 Hz, 1 H, CH),
4.98 (d, J = 16.8 Hz, 1 H, CH), 4.52 (d, J = 6.9 Hz, 1 H, CH), 3.64
1
(t, J = 7.8 Hz, 1 H, CH), 2.16 (s, 3 H, CH3) ppm. anti isomer: H
NMR (300 MHz, CDCl3): δ = 7.37–6.94 (m, 1 H, ArH), 6.86 (d, J
= 8.7 Hz, 0.2 H, ArH), 6.38–6.34 (m, 0.2 H, ArH), 6.21–6.09 (m,
0.1 H, CH), 5.28–5.20 (m, 0.2 H, CH2), 4.46 (d, J = 8.1 Hz, 0.1 H,
CH), 3.51–3.45 (m, 0.1 H, CH), 2.18 (s, 0.3 H, CH3) ppm.
4-Methyl-N-(4-methylphenyl)-α-2-phenyl-2-propenylbenzenemethan-
amine (17): Light yellow liquid. Yield: 265 mg (81%) (syn/anti =
88:12). syn isomer:1H NMR (300 MHz, CDCl3): δ = 7.33–6.96 (m,
9 H, ArH), 6.83 (d, J = 8.1 Hz, 2 H, ArH), 6.35 (d, J = 8.4 Hz, 2
H, ArH), 6.04–5.91 (m, 1 H, CH), 5.08 (d, J = 10.2 Hz, 1 H, CH),
4.96 (d, J = 17.1 Hz, 1 H, CH), 4.54 (d, J = 7.2 Hz, 1 H, CH), 3.71
(t, J = 7.8 Hz, 1 H, CH), 2.32 (s, 3 H, CH3), 2.16 (s, 3 H, CH3)
4-Methyl-N-(4-methylphenyl)-α-2-propenylbenzenemethanamine (7):
Light yellow liquid. Yield: 206 mg (82%). 1H NMR (300 MHz,
CDCl3): δ = 7.26 (d, J = 7.8 Hz, 2 H, ArH), 7.20 (d, J = 8.1 Hz, 2
H, ArH), 6.90 (d, J = 8.1 Hz, 2 H, ArH), 6.44 (d, J = 8.4 Hz, 2 H,
ArH), 5.72–5.85 (m, 1 H, CH), 5.13–5.22 (m, 2 H, CH2), 4.34 (q,
J = 5.1 Hz, 1 H, CH), 2.45–2.64 (m, 2 H, CH2), 2.35 (s, 3 H, CH3),
2.21 (s, 3 H, CH3) ppm. 13C NMR (75 MHz, CDCl3): δ = = 145.1,
140.7, 136.6, 135.0, 129.7 129.4, 126.8, 126.4, 118.3, 113.9, 57.6,
43.6, 21.4, 20.7 ppm. MS (ESI): m/z = 252 [M + H]+.
1
ppm. anti isomer: H NMR (300 MHz, CDCl3): δ = 7.33–6.96 (m,
1 H, ArH), 6.87 (d, J = 8.7 Hz, 0.2 H, ArH), 6.38–6.35 (m, 0.2 H,
ArH), 6.21–6.09 (m, 0.1 H, CH), 5.28–5.20 (m, 2 H, CH2), 4.40 (d,
J = 8.1 Hz, 0.1 H, CH), 3.51–3.45 (m, 0.1 H, CH), 3.35 (s, 0.3 H,
CH3), 2.18 (s, 0.3 H, CH3) ppm.
4-Methyl-N-(2-chlorophenyl)-α-2-propenylbenzenemethanamine
(11): Light yellow liquid. Yield: 217 mg (80 %). 1H NMR
(300 MHz, CDCl3): δ = 7.20 (d, J = 8.1 Hz, 3 H, ArH), 7.11 (d, J
= 8.1 Hz, 2 H, ArH), 6.94–7.03 (m, 1 H, ArH), 6.61 (d, J = 0.9 Hz,
1 H, ArH), 6.50 (s, 1 H, ArH), 6.34–6.37 (m, 1 H, ArH), 5.66–5.83
(m, 1 H, CH), 5.12–5.20 (m, 2 H, CH2), 4.33 (q, J = 5.7 Hz, 1 H,
CH), 2.45–2.66 (m, 2 H, CH2), 2.33 (s, 3 H, CH3) ppm. 13C NMR
(75 MHz, CDCl3): δ = 143.3, 140.0, 136.8, 134.4, 129.5, 129.1,
127.7, 126.3, 119.5, 118.7, 117.3, 112.8, 57.1, 43.6, 21.4 ppm. MS
(ESI): m/z = 272 [M + H]+.
4-Methyl-N-phenyl-α-2-phenyl-2-propenylbenzenemethanamine (18):
Light yellow liquid. Yield: 247 mg (79%) (syn/anti = 84:16). syn
isomer: 1H NMR (300 MHz, CDCl3): δ = 7.32–6.97 (m, 11 H,
ArH), 6.63–6.57 (m, 1 H, ArH), 6.42 (d, J = 8.4 Hz, 2 H, ArH),
6.05–5.93 (m, 1 H, CH), 5.09 (d, J = 10.2 Hz, 1 H, CH), 4.98 (d,
J = 16.8 Hz, 1 H, CH), 4.57 (d, J = 6.9 Hz, 1 H, CH), 3.70 (t, J =
1
7.8 Hz, 1 H, CH), 2.32 (s, 3 H, CH3) ppm. anti isomer: H NMR
(300 MHz, CDCl3): δ = 7.32–6.97 (m, 2 H, ArH), 6.65–6.62 (m,
0.2 H, ArH), 6.49 (d, J = 7.8 Hz, 0.4 H, ArH), 6.26–6.12 (m, 0.2
H, CH), 5.28–5.18 (m, 0.4 H, CH2), 4.46 (d, J = 8.1 Hz, 0.2 H,
CH), 3.59–3.51 (m, 0.2 H, CH), 2.26 (s, 0.6 H, CH3) ppm.
4-Bromo-N-(4-chlorophenyl)-α-2-propenylbenzenemethanamine (12):
Light yellow liquid. Yield: 268 mg (80 %). 1H NMR (300 MHz,
CDCl3): δ = 7.44 (d, J = 8.4 Hz, 2 H, ArH), 7.20 (d, J = 8.4 Hz, 2
H, ArH), 7.02 (d, J = 8.7 Hz, 2 H, ArH), 6.37 (d, J = 8.7 Hz, 2 H,
ArH), 5.66–5.79 (m, 1 H, CH), 5.16–5.22 (m, 2 H, CH2), 4.31 (q,
J = 5.1 Hz, 1 H, CH), 2.42–2.64 (m, 2 H, CH2) ppm. 13C NMR
(75 MHz, CDCl3): δ = 145.4, 142.0, 134.0, 131.9, 129.1, 128.2,
122.7, 121.1, 119.1, 114.9, 57.2, 43.3 ppm. MS (ESI): m/z = 336 [M
+ H]+.
4-Methyl-N-(2-chlorophenyl)-α-2-phenyl-2-propenylbenzenemethan-
amine (19): Light yellow liquid. Yield: 270 mg (78%) (syn/anti =
76:24). syn isomer: δ = 7.36–6.96 (m, 7 H, ArH), 6.92–6.87 (m, 2
H, ArH), 6.57–6.49 (m, 2 H, ArH), 6.48–6.31 (m, 2 H, ArH), 6.14–
6.01 (m, 1 H, CH), 5.16 (d, J = 10.2 Hz, 1 H, CH), 5.09 (d, J =
16.8 Hz, 1 H, CH), 4.61 (d, J = 6.6 Hz, 1 H, CH), 3.79 (t, J =
1
7.8 Hz, 1 H, CH), 2.32 (s, 3 H, CH3) ppm. anti isomer: H NMR
N-(4-Methylphenyl)-α-2-phenyl-2-propenyl-benzenemethanamine
(13): Light yellow liquid. Yield: 250 mg (80%) (syn/anti = 81:19).
syn isomer: H NMR (300 MHz, CDCl3): δ = 7.31–6.98 (m, 10 H,
(300 MHz, CDCl3): δ = 7.36–6.96 (m, 2 H, ArH), 6.92–6.87 (m,
0.5 H, ArH), 6.57–6.49 (m, 0.5 H, ArH), 6.42–6.31 (m, 0.5 H,
ArH), 6.28–6.17 (m, 0.2 H, CH), 5.32–5.23 (m, 0.5 H, CH2), 4.52
(d, J = 7.8 Hz, 0.2 H, CH), 3.65 (t, J = 8.4 Hz, 0.2 H, CH), 2.27
(s, 0.7 H, CH3) ppm.
1
ArH), 6.82 (d, J = 7.8 Hz, 2 H, ArH), 6.33 (d, J = 8.4 Hz, 2 H,
ArH), 6.03–5.91 (m, 1 H, CH), 5.06 (d, J = 10.2 Hz, 1 H, CH),
4.95 (d, J = 16.8 Hz, 1 H, CH), 4.56 (d, J = 7.2 Hz, 1 H, CH), 3.70
1
(t, J = 7.8 Hz, 1 H, CH), 2.15 (s, 3 H, CH3) ppm. anti isomer: H
Acknowledgments
NMR (300 MHz, CDCl3): δ = 7.31–6.98 (m, 2 H, ArH), 6.86 (d, J
= 8.7 Hz, 0.4 H, ArH), 6.41 (d, J = 8.4 Hz, 0.4 H, ArH), 6.23–6.12
(m, 0.2 H, CH), 5.27–5.18 (m, 0.4 H, CH2), 4.46 (d, J = 8.1 Hz,
0.2 H, CH), 3.58–3.51 (m, 0.2 H, CH), 2.17 (s, 3 H, CH3) ppm.
We are grateful for the financial support of the Natural Science
Foundation of Guangdong (Grant No. 04105493).
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FULL PAPER
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Received: October 30, 2006
Published Online: February 2, 2007
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