Assembly of homoallylamine derivatives through iron-catalyzed three-component sulfonamidoallylation reaction

Article abstract of DOI:10.1002/aoc.3334

An efficient FeCl₃-catalyzed three-component reaction between aldehydes, sulfonamides and allylsilanes has been achieved, which provides a convenient, atom-economic and green way to construct homoallylamine derivatives. In addition, this reaction exhibits excellent syn stereoselectivity with γ-substituted allylsilanes. A practical three-component cascade process to homoallylamine derivatives is reported, which uses cheap and environmentally benign FeCl₃ as catalyst and shows excellent syn stereoselectivity with γ-substituted allylsilanes.

Full text of DOI:10.1002/aoc.3334

Full paper
Received: 28 February 2015
Revised: 15 April 2015
Accepted: 27 April 2015
Published online in Wiley Online Library: 5 July 2015
(wileyonlinelibrary.com) DOI 10.1002/aoc.3334
Assembly of homoallylamine derivatives
through iron-catalyzed three-component
sulfonamidoallylation reaction
Xiaohui Fana,b*, Hong-Bo Zhua, Hao Lva, Kun Guoa, Yong-Hong Guana,
Xiao-Meng Cuia, Bin Ana and Yan-Ling Pua
An efficient FeCl3-catalyzed three-component reaction between aldehydes, sulfonamides and allylsilanes has been achieved,
which provides a convenient, atom-economic and green way to construct homoallylamine derivatives. In addition, this reaction
exhibits excellent syn stereoselectivity with γ-substituted allylsilanes.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: multicomponent reaction; iron; homoallylamine derivatives; sulfonamidoallylation; imine
Introduction
Results and discussion
Imine and iminium ions are reactive building blocks with diverse
applications in organic chemistry for the construction of α-
functionalized amino derivatives and nitrogen-containing
heterocycles.[1] Representative examples of these transformations
are three-component Mannich reactions and Pictet–Spengler
tetrahydroisoquinoline synthesis, which have become powerful
synthetic tools in both the laboratory and industry.[1,2] Although a
significant number of α-amidoalkylation reactions with the imine
or iminium ion serving as an electrophile have been developed in
the past 100 years, the catalytic versions of three-component
amidoallylation reactions using silicon-based nucleophiles for the
synthesis of homoallylic amines are rather limited.[3–6] In general,
these compounds are prepared by addition of a metallic allyl
reagent such as allyl Sn, Sm, In, Zn and B to a prior-prepared imine
species.[7] Obviously, catalytic three-component amidoallylation re-
actions involving in situ formed imines and non-toxic allylsilanes are
much more step- and atom-economical as well as environmentally
benign. However, despite several efficient catalytic systems for such
transformations have been developed in the past decade, most of
them need a relative expensive Lewis acid such as metal triflate
and oxo-rhenium(VII) as the catalyst.[3,4a–c]
Considering that homoallylamines are fundamentally important
building blocks for the synthesis of many natural products, pharma-
ceuticals and useful nitrogen-containing compounds,[8] further ex-
ploration of cheap and environmentally friendly catalysts for this
transformation would be valuable. Very recently, we reported a
two-component procedure for the construction of indene frame-
works, via an iron-catalyzed in situ formed N-sulfonyliminium ion-
initiated intramolecular alkylation.[9] In continuation of our study
of the examination of iron as a promising catalyst in C–C and C–N
bond formation,[10,11] we extended the reaction mentioned above
to a three-component version (Scheme 1). To the best of our know-
ledge, this iron-catalyzed three-component cascade reaction has
not been reported previously. In this paper, we report the results
of our study of this reaction.
Initial experiments were carried out on the reaction of benzaldehyde
(1a; 1.0 equiv.) with p-toluenesulfonamide (2a; 1.5 equiv.) and
allyltrimethylsilane (3a; 1.3 equiv.) in dichloromethane at room tem-
perature with FeCl3 (5 mol%) as catalyst. To our delight, the reaction
proceeds smoothly to give the sulfonamidoallylation product 4a in
53% yield, which can be markedly improved by increasing the reac-
tion temperature and catalyst loading (Table 1, entries 1–4). Further
investigation of the solvent effect indicates that the nature of the re-
action media significantly affects the reaction (Table 1, entries 5–12),
with dichloromethane being the most suitable solvent. With respect
to substrate loading, a 1:1.5:1.3 ratio of 1a to 2a to 3a gives the best
result. Under these optimized reaction conditions, the desired prod-
uct 4a can be isolated in 94% yield (Table 1, entry 3). On replacing
FeCl3 with FeCl3ꢀ6H2O, the reaction gives a lower yield (77%; Table 1,
entry 13). Other iron salts and Lewis acids prove to be less effective
or ineffective in promoting this transformation (Table 1, entries
14–20). Control experiment indicates that a catalyst is essential for
this reaction (Table 1, entry 21). In addition, several Brønsted acids
(e.g. TfOH and HCl) were also examined for this reaction. Unfortu-
nately, only a trace amount of 4a is observed when using triflic acid
as the catalyst; other Brønsted acids are completely ineffective for
this transformation (Table 1, entry 22).
With the optimized reaction conditions in hand (Table 1, entry 3),
the substrate scope and limitations of this reaction were then inves-
tigated using a series of aldehydes (Table 2). It is found that the
*
Correspondence to: Xiaohui Fan, School of Chemical and Biological Engineering,
Lanzhou Jiaotong University, Lanzhou, 730070, PR China. E-mail: fanxh@mail.
lzjtu.cn
a School of Chemical and Biological Engineering, Lanzhou Jiaotong University,
Lanzhou, 730070, PR China
b Beijing National Laboratory for Molecular Sciences (BNLMS), Beijing, 100190, PR
China
Appl. Organometal. Chem. 2015, 29, 588–592
Copyright © 2015 John Wiley & Sons, Ltd.

Iron-catalyzed three-component sulfonamidoallylation reaction
Table 2. Reactions of 2a and 3a with various aldehydesa
Entry
R1
Time (h) Product Yield (%)b
1
2-MeC6H4
3-MeC6H4
4-MeC6H4
2-MeOC6H4
4-MeOC6H4
4
4
4
5
5
7
5
5
5
5
5
5
5
5
6
6
5
6
5
4
6
4b
4c
4d
4e
4f
91
89
2
3
93
4
96
5
76
Scheme 1. Strategies for iron-catalyzed intramolecular and intermolecular
reactions.
6
3,4-(OCH2O)C6H3
4-FC6H4
4g
4h
4i
67
7
73
8
4-ClC6H4
79
9
3-ClC6H4
4j
83
Table 1. Optimization of reaction conditionsa
10
11
12
13
14
15
16
17
18
19
20
21
2-BrC6H4
4k
4l
75
4-CNC6H4
70
4-CF3C6H4
4m
4n
4o
4p
4q
4r
82
1-Naphthyl
81
2-Naphthyl
86
Entry Catalyst (mol%)
Solvent
CH2Cl2
Temperature (°C) Yield (%)b
(E)-PhCH¼CH
(E)-PhCH¼CBr
(E)-4-MePhCH¼CH
(E)-4-ClPhCH¼CH
(E)-3,4-(OCH2O)PhCH¼CH
(E)-PhCH¼C(CH3)
CH3CH2
85
1
FeCl3 (5)
rt
53
81
94
80
28
89
Trace
64
0
71
2
FeCl3 (5)
CH2Cl2
CH2Cl2
CH2Cl2
MeCN
40
40
40
40
80
60
40
80
80
80
75
40
40
40
40
40
40
40
40
40
40
82
3
FeCl3 (10)
FeCl3 (15)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3 (10)
FeCl3ꢀ6H2O (10)
FeCl2 (10)
4s
4t
72
4
62
82c
5
4u
4v
6
Dichloroethane
THF
’Mess’
7
aReaction conditions: aldehydes (1b–v, 1.0 mmol), TsNH2 (2a, 1.5 mmol),
allyltrimethylsilane (3a, 1.3 mmol), solvent (5.0 ml), in air.
bIsolated yield.
cYield of cyclization product.
8
CH3NO2
DMF
9
10
11
12
13
14
15
16
17
18
19
20
21
22
DMSO
0
Benzene
EtOH
78
Trace
77
31
74
43
0
CH2Cl2
CH2Cl2
yields of 4f and 4 g are presumably due to their lower stability un-
der the iron catalytic conditions (Table 2, entries 5 and 6).10a,12 Note
that when α-alkylated cinnamylaldehyde 1u is subjected to this
reaction, a cyclization product 4u is obtained exclusively without
observation of the sulfonamidoallylation product (Table 2, entry 20).
This result is consistent with our previous study in which α-alkylated
cinnamylaldehyde was found to be favorable for intramolecular
alkylation.[9] In addition, aromatic and cinnamic ketones such as
acetophenone and (E)-4-phenylbut-3-en-2-one are also found to be
unsuitable substrates for this reaction, which might be attributed to
the lower electrophilicity of ketone.
To learn about the effect of silyl reagents, we next examined the
reaction of 1a and 2a with other silyl nucleophiles (Table 3). The
substituents of the allylsilanes have obvious influences on the reac-
tion outcomes. With the β-substituted allylsilane 3d, the reaction
can be accomplished at room temperature with a full conversion
of 1a; while the reactions of γ-substituted allylsilanes 3b and 3c pro-
ceed slowly at 40 °C to give the corresponding homoallylamines 4w
and 4x in excellent syn diastereoselectivity, accompanied by a small
amount of unreacted 1a. Based on previous experimental and the-
oretical studies,[13] this higher stereoselectivity can probably be ex-
plained by the hypothesis that the reaction may take place through
antiperiplanar transition states 5a and 5b (Fig. 1). The γ-substituted
allylsilane prefers to react with the imine through transition state 5a
to produce the syn product, in which the steric interaction between
the imine substituent and the vinyl substituent of the allylsilane is
reduced; on the contrary, disfavored transition state 5b will lead
to the anti isomer. More bulky phenyl-substituted allylsilane 3c
Fe(NO3)3ꢀ9H2O (10) CH2Cl2
Fe(ClO4)3ꢀH2O (10) CH2Cl2
Fe(acac)3 (10)
TiCl4 (10)
ZnCl2 (10)
CuI (10)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
0
64
0
—
0
TfOH (10)
Trace
aReaction conditions: benzaldehyde (1a, 1.0 mmol), TsNH2 (2a,
1.5 mmol), allyltrimethylsilane (3a, 1.3 mmol), solvent (5.0 ml), in air.
bIsolated yield.
optimized reaction conditions show good substrate compatibility
with a wide variety of aromatic and allylic aldehydes, providing
the corresponding homoallylamine derivatives in good to excellent
yields (Table 2, entries 1–19). Aliphatic aldehydes such as propanal
do not undergo this transformation even under harsh reaction con-
ditions (Table 2, entry 21), which results in an intractable mixture.
Functional groups, e.g. aromatic methoxy, C¼C double bond,
cyano and acetal, tolerate the reaction conditions very well (Table 2,
entries 5, 6, 11 and 15). With respect to the electronic effect, the
substituents on the phenyl ring of benzylic aldehydes have an ob-
vious influence on the product yields. Overall, the reaction is facili-
tated with electron-rich substrates which bear an electron-donating
group on the phenyl ring (Table 2, entries 1–4). The relatively lower
Appl. Organometal. Chem. 2015, 29, 588–592
Copyright © 2015 John Wiley & Sons, Ltd.
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X. Fan et al.
Table 3. Reactions of 1a and 2a with various silyl nucleophilesa
Table 4. Examination of other amine sourcesa
Entry
1
R
Time
(h)
Product
Yield
(%)b
Entry
R
Time (h)
Product
Yield (%)b
1
2
3
4
5
6
PhSO2 (2b)
4
4
4b′
4c′
4d′
4e′
4f′
91
90
87
72
0
(E)-CH3CH¼CHCH2 3b
24
4w
4x
81c
2-MePhSO2 (2c)
4-ClPhSO2 (2d)
4
CH3SO2 (2e)
4
2
(E)-PhCH¼CHCH2
3c
24
61
PhCH2OCO (Cbz, 2f)
(CH3)3COCO (Boc, 2 g)
12
12
4g′
0
aReaction conditions: benzaldehyde (1a, 1.0 mmol), RNH2 (2b–g,
1.5 mmol), allyltrimethylsilane (3a, 1.3 mmol), solvent (5.0 ml), in air.
bIsolated yield.
3d,e
4e
CH2¼C(CH3)CH2
3d
3e
18
24
4y
4z
69
0
Phenylethynyl
5d
Propargyl
3f
2
4a′
’Mess’
With the aim of understanding the mechanism, several control
experiments were conducted (Scheme 2). First, prior-prepared
aldimine 5c was reacted with allyltrimethylsilane under the optimal
conditions in air. After 3 h, 95% yield of allylation product 4a is ob-
tained; without FeCl3, the reaction does not occur. In the presence
of Brønsted acids (e.g. TfOH and HCl, 10 mol%), most of 5c is
decomposed into 1a without the formation of 4a. Interestingly,
upon the reaction of 5c with allyltrimethylsilane under the catalysis
of FeCl3, we also find that part of 5c is decomposed into 1a and 2a at
the beginning of the reaction; however, they disappear when the re-
action is finished (monitored using TLC, 3 h). Second, on conducting
the model reaction under argon atmosphere with 10 mol% FeCl3,
only 37% yield of 4a is obtained after 8 h at 40 °C, which can be
markedly improved to 91% yield when a small amount of water is
added (15 μl, 4 h). Third, a three-component reaction was carried
out involving 1a with allyltrimethylsilane for 1 h under the catalysis
of FeCl3, then TsNH2 was added. Under these reaction conditions,
only a trace amount of 4a is observed without the formation
of homoallylic alcohol. Fourth, reaction of 1a (1.0 equiv.) with 2a
(1.5 equiv.) for 1 h under the catalysis of 10 mol% FeCl3 affords
34% yield of aldimine 5c along with unreacted 1a and 2a. These
experiments reveal that this reaction involves the equilibrium forma-
tion of a sulfonylimine, which, rather than homoallylic alcohol, func-
tions as the intermediate;10a,14 the addition of an allyltrimethylsilane
shifts the equilibrium towards the formation of a homoallylamine
derivative; and the reaction is assisted by both FeCl3 and water.[15]
Based on the above results, a tentative reaction pathway is
proposed, as shown in Scheme 3. The first step is the nucleo-
philic addition of a sulfonamide to the carbonyl group of the
aReaction conditions: benzaldehyde (1a, 1.0 mmol), TsNH2 (2a,
1.5 mmol), allylsilanes (3b–f, 1.3 mmol), solvent (5.0 ml), in air.
bIsolated yield.
cMixture of syn and anti isomers; syn/anti = 10:1.
dRoom temperature.
eR1=R.
undergoes this reaction exclusively through transition state 5a that
results in the formation of the syn diastereomer solely. To our disap-
pointment, alkynylsilane 3e and propargylsilane 3 f fail to give the
desired products. Compound 3e remains intact under the
employed reaction conditions, while use of 3 f leads to an intracta-
ble mixture with full consumption of 1a and 3 f.
To further investigate the generality of this reaction, several other
sulfonamides and carbamates such as benzenesulfonamide (2b),
2-methylbenzenesulfonamide (2c), 4-chlorobenzenesulfonamide
(2d), methanesulfonamide (2e), benzyl carbamate (2f) and tert-
butyl carbamate (2 g) were examined in this reaction (Table 4).
Under the optimal reaction conditions, 2b–e react smoothly with
1a and 3a to give the corresponding sulfonamidoallylation products
4b′–e′in good to excellent yields. However, 2f and 2gare found to be
unsuitable reaction partners: no reactions are observed even under
harsh reaction conditions.
Finally, removal of the tosyl group was tested. Product 4a was
successfully detosylated under reductive conditions (Na/naphtha-
lene) to afford the deprotection homoallylamine in 64% yield.
Figure 1. Antiperiplanar transition states (TSs) 5a and 5b.
Scheme 2. Control experiments.
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Iron-catalyzed three-component sulfonamidoallylation reaction
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added sulfonamide (1.5 equiv.) and FeCl3 (10 mol%, 98% purity;
purchased from Alfa Aesar). The resulting mixture was stirred at
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with ethyl acetate (3× 5 ml). The combined organic layer was
washed with brine, dried over Na2SO4 and concentrated. The crude
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corresponding product. Note that when allyltrimethylsilane was
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Acknowledgments
We thank the National Natural Science Foundation of China
(21162013) and Gansu Provincial Science and Technology Depart-
ment (project no. 1204WCGA017) for financial support and Prof.
Zhi-Xiang Yu for helpful discussions.
Appl. Organometal. Chem. 2015, 29, 588–592
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