Gold-catalyzed intermolecular hydroamination of allenes with sulfonamides

Article abstract of DOI:10.3762/bjoc.9.117

A co-catalyst of (PPh₃)AuCl/AgOTf for the intermolecular hydroamination of allenes with sulfonamides is shown. The reaction proceeded smoothly under mild conditions for differently substituted allenes giving N-allylic sulfonamides in good yields with high regioselectivity and E-selectivity.

Full text of DOI:10.3762/bjoc.9.117

Gold-catalyzed intermolecular hydroamination of
allenes with sulfonamides
Chen Zhang*1, Shao-Qiao Zhang1, Hua-Jun Cai2 and Dong-Mei Cui*2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2013, 9, 1045–1050.
1School of Pharmaceutical Sciences, Zhejiang University, Hangzhou
310058, PR China and 2College of Pharmaceutical Science, Zhejiang
University of Technology, Hangzhou 310014, PR China
doi:10.3762/bjoc.9.117
Received: 30 January 2013
Accepted: 07 May 2013
Published: 29 May 2013
Email:
Chen Zhang* - chenzhang@zju.edu.cn; Dong-Mei Cui* -
cuidongmei@zjut.edu.cn
This article is part of the Thematic Series "Gold catalysis for organic
synthesis II".
* Corresponding author
Guest Editor: F. D. Toste
Keywords:
allene; gold catalysis; hydroamination; N-sulfonyl; selectivity;
© 2013 Zhang et al; licensee Beilstein-Institut.
License and terms: see end of document.
sulfonamide
Abstract
A co-catalyst of (PPh3)AuCl/AgOTf for the intermolecular hydroamination of allenes with sulfonamides is shown. The reaction
proceeded smoothly under mild conditions for differently substituted allenes giving N-allylic sulfonamides in good yields with high
regioselectivity and E-selectivity.
Introduction
Hydroamination of an N–H bond across a C–C unsaturated require extreme and extended reaction conditions. Thus, devel-
bond represents one of the most effective and atom-economical opment of these reactions is still needed. Recently, Yamamoto
methods to prepare amine derivatives [1-5]. In the case of using and co-workers reported the Pd(0)-catalyzed intermolecular
allenes, this reaction can lead to allylamines, which are invalu- hydroamination of allenes with sulfonamides [25]. In this paper,
able precursors for the synthesis of natural products and other we wish to develop a gold(I)-complex-catalyzed addition of
potentially biologically relevant substances [6]. In the literature, sulfonamides as the amine partner to allenes to synthesize
a wide range of catalytic intramolecular hydroaminations of N-allylic sulfonamides with high regio- and stereoselectivity.
allenes are known, but only a small number of intermolecular
hydroamination reactions are reported [7-15]. More recently, Results and Discussion
Au(I), Au(III), Pt(II) and Rh(I) have been used for the intermol- As part of our ongoing studies on metal-catalyzed reactions, we
ecular hydroamination of allenes with secondary alkylamines, have reported the hydroalkoxylation of allenes with alcohols
ammonia, or carboxamide [7,16-24]. Although some of these and hydroamination of alkynes with sulfonamides in the pres-
advances have been efficiently made in hydroamination, many ence of gold catalysts [26-28]. On the basis of these studies, in
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Beilstein J. Org. Chem. 2013, 9, 1045–1050.
an initial experiment, 1-phenyl-1,2-propadiene (1a) (1.5 mmol) yield (Table 2, entry 6). We also used N-substituted sulfon-
was treated with 4-methylbenzenesufonamide (2a) (0.5 mmol) amide 2g as the amine partner. Although drastic conditions are
in the presence of 2 mol % of (PPh3)AuCl and 8 mol % of required, the addition occurred to provide linear adduct 3g in
AgOTf in dioxane at 70 °C efficiently to form linear adduct 3a good yield (Table 2, entry 7). In all cases, the adduct was
in 43% yield (Table 1, entry 1). Different solvents were obtained with high selectivity.
screened, and dioxane was found to be the most suitable one
(Table 1, entries 2–4). Decreasing the amount of AgOTf Various allenes were then examined, and aromatic rings of
resulted in lower yields (Table 1, entry 7). We were pleased to phenylallenes with either an electron-donating or an electron-
find that efficient hydroamination was realized at rt and led to a withdrawing group gave good isolated yields of the corres-
91% yield of 3a with good regioselectivity and high E-selec- ponding adducts (Table 3, entries 1 and 2). Whereas hydroami-
tivity (Table 1, entry 6). Other possible isomers could not be nation of the monosubstituted heteroaromatic allene 1d also
detected. As Ag catalysts, other salts were also screened, lead to the conversion into the expected addition product 3j,
AgBF4 was ineffective. With AgSbF6 or AgNTf2, the reaction hydroamination of the monoalkyl-substituted aliphatic allene 1e
took place and gave adducts in 33% and 47% yield (Table 1, formed a 71:29 mixture of linear product (3ka) and branch pro-
entries 8 and 9). The use of the gold alone gave a lower yield, duct (3kb) under the same conditions (Table 3, entry 4).
and the reaction did not proceed in the absence of gold or Furthermore, disubstituted allenes also worked well. Differen-
through the use of TfOH (entries 11–14). Finally, we deter- tially 1,1-disubstituted allene 1f reacted with sulfonamide to
mined the optimal conditions as 5 mol % of (PPh3)AuCl and afford trans-adducts 3l with high selectivity (Table 3, entry 5).
8 mol % of AgOTf in dioxane at rt (Table 1, entry 6).
Single crystals of the compound 3l suitable for X-ray crystallo-
graphic analysis were also obtained (Figure 1). This shows that
To further assess the scope of this process, we first examined 3l is the E isomer, the sulfonamide carbon link being trans to
the hydroamination of 1a with several sulfonamides. Benzene- the phenyl group (Figure 1). As for differentially 1,3- disubsti-
sulfonamides containing p-Br or p-Cl groups on the benzene tuted allene 1g, hydroamination took place with exclusive
ring were tolerated for the reaction, obtaining the corres- attack of sulfonamide at the more electron-rich allene terminus
ponding adducts 3d and 3e in 54 and 72% yields, respectively to afford the corresponding adduct 3m with 68% yield and with
(Table 2, entries 4–5). Under the same reaction conditions, the high E-selectivity (Table 3, entry 6). In addition, hydroamina-
hydroamination of aliphatic sulfonamides took place smoothly tion of trisubstituted allene 1h took place to afford a different
to afford the corresponding N-allylic sulfonamide 3f with 56% product (Table 3, entry 7). Single crystals of the compound 3n
Table 1: Catalytic hydroamination of 1a and 2a.a
Entry
[Au] (mol %)
[Ag] (mol %)
Solvent
Time (h)
Temp. (°C)
Yield (%)b
1
(PPh3)AuCl (2)
(PPh3)AuCl (2)
(PPh3)AuCl (2)
(PPh3)AuCl (2)
(PPh3)AuCl (5)
(PPh3)AuCl (5)
(PPh3)AuCl (5)
(PPh3)AuCl (5)
(PPh3)AuCl (5)
Au(NHC)Cl (5)
0
AgOTf (8)
AgOTf (8)
AgOTf (8)
AgOTf (8)
AgOTf (8)
AgOTf (8)
AgOTf (5)
AgSbF6 (8)
AgNTf2 (8)
AgOTf (8)
0
dioxane
THF
4
70
70
70
70
70
rt
43
28
32
33
59
91
80
33
47
46
0
2
6
3
toluene
(CH2Cl)2
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
8
4
7
5
4
6
16
16
24
24
16
16
16
16
16
7
rt
8
rt
9
rt
10
11
12
13
14
rt
rt
(PPh3)AuCl (5)
0
0
rt
26
0
AgOTf (8)
TfOH (8)
rt
0
rt
0
aAll reactions were performed with 0.8 mmol of 1a, 0.4 mmol of 2a, 0–5 mol % of (PPh3)AuCl, and 0–8 mol % of AgOTf. bIsolated yields.
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Beilstein J. Org. Chem. 2013, 9, 1045–1050.
Table 2: Hydroamination of 1a with sulfonamide 2.a
Entry
1
Sulfonamide
TsNH2
2
Product
3
Yield (%)b
91
2a
3a
2
3
PhSO2NH2
2b
2c
3b
3c
76
60
o-Me-C6H4SO2NH2
4
5
p-Br-C6H4SO2NH2
p-Cl-C6H4SO2NH2
2d
2e
3d
3e
54
72
6
MeSO2NH2
2f
3f
56
79
7c
n-BuNHTs
2g
3g
aThe reactions were performed with 0.8 mmol of allene 1a, 0.4 mmol of 2, 5 mol % of (Ph3P)AuCl and 8 mol % of AgOTf in 2 mL of dioxane at rt for
16 h. bIsolated yield. cAt 100 °C for 8 h.
Table 3: Hydroamination of allenes 1 with 2a.a
Entry
1
Allene
1
Product
3
Yield (%)
82
1b
3h
2
3
1c
1d
3i
3j
72
60
3ka
3kb
4
5
1e
1f
48
67
3l
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Beilstein J. Org. Chem. 2013, 9, 1045–1050.
Table 3: Hydroamination of allenes 1 with 2a.a (continued)
6
1g
1h
3m
3n
68
31
7
aThe reactions were performed with 0.8 mmol of allene 1, 0.4 mmol of 2a, 5 mol % of (Ph3P)AuCl and 8 mol % of AgOTf in 2 mL of dioxane at rt for
16 h. bIsolated yield. c3ka/3kb = 71:29.
suitable for X-ray crystallographic analysis were also obtained The proposed mechanism of the gold-catalyzed hydroaamina-
(Figure 2). This showed that 3n is the E isomer, the sulfon- tion of allenes is shown in Scheme 1 [2,7,29-36]. The gold
amide being trans to the diphenylmethyl groups (Figure 2). cation coordinated with allene to form cationic Au(I)-allene
complex A, and this leads to cationic gold(I) complex B. The
sulfonamide attacks at the less-substituted terminus of inter-
mediate B to form C. Protonolysis of the Au–C bond of B
yields the allylic sulfonamide 3, regenerating the gold complex.
On the other hand, in comparison with phenyl-substituted
allenes, for alkyl-substituted allene 1e, a mixture of 3ka and
3kb was produced; although the details are unclear, perhaps due
to electronic factors, the addition of sulfonamide also occurred
at the more-hindered position of intermediate B to give 3ka and
3kb.
Figure 1: The X-ray structure of 3l.
Scheme 1: Proposed mechanism for the hydroamination of allenes.
Conclusion
In conclusion, we have successfully employed (PPh3)AuCl/
AgOTf catalyzed intermolecular hydroamination of allenes with
sulfonamides to produce N-allylic sulfonamide. This reaction
takes place under mild conditions with effective and high regio-
and stereoselectivity. Monosubstituted, 1,1- and 1,3-disubsti-
tuted, and trisubstituted allenes were well tolerated in the reac-
Figure 2: The X-ray structure of 3n.
tion.
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Beilstein J. Org. Chem. 2013, 9, 1045–1050.
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Experimental
General Information: Unless otherwise noted, materials were
obtained from commercial suppliers and used without further
purification. Allenes were prepared by procedures in the litera-
ture [37-39]. Thin-layer chromatography (TLC) was performed
on glass plates coated with silica gel 60 F254 and visualized by
UV light (254 nm). Column chromatography was performed
with silica gel (mesh 300–400). Infrared (IR) spectra were
obtained on a 370 FTIR spectrometer; absorptions are reported
in cm−1. Mass spectra were obtained in the electron impact (EI)
mode, and high-resolution mass spectra were measured on a
high-resolution mass spectrometer (GCT Premier).
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General Procedure: To a mixture of sulfonamide (0.4 mmol),
PPh3AuCl (0.02 mmol), and AgOTf (0.032 mmol) in anhy-
drous 1,4-dioxane (2 mL) was added allene (0.8 mmol). The
mixture was then sealed and stirred at room temperature until
the starting sulfonamide was consumed as judged by TLC. The
mixture was quenched with a saturated solution of NaHCO3 and
then extracted with ethyl acetate (3 × 20 mL). The organic layer
was washed with brine, dried over Na2SO4 and concentrated in
vacuo. The residue was purified by column chromatography
(silica gel) to yield the product in an analytically pure form.
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Supporting Information
Supporting Information File 1
Analytical and spectroscopic data for compounds 3a–3j,
3ka, 3kb and 3l–3n.
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We thank the Hangzhou Natural Science Foundation (No.
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