An efficient three-component synthesis of homoallylic amines catalysed by MgI2 etherate

Article abstract of DOI:10.3184/174751912X13252567769442

A three-component reaction of aldehydes, amines and allyltributylstannane was efficiently carried out to afford the corresponding homoallylic amine derivatives in the presence of 20 mol% of MgI₂ etherate [(MgI ₂?(OEt₂)_n] under mild and neutral reaction conditions in good to excellent yields.

Full text of DOI:10.3184/174751912X13252567769442

JOURNAL OF CHEMICAL RESEARCH 2012
JANUARY, 21–24
RESEARCH PAPER 21
An efficient three-component synthesis of homoallylic amines catalysed
by MgI etherate
2
Yanping Wang, Yingshuai Liu, Shenghui Hu and Xingxian Zhang*
College of Pharmaceutical Sciences, Zhejiang University ofTechnology, Hangzhou, Zhejiang 310032, P. R. China
A three-component reaction of aldehydes, amines and allyltributylstannane was efficiently carried out to afford the
corresponding homoallylic amine derivatives in the presence of 20 mol% of MgI etherate [(MgI •(OEt ) ] under mild
2
2
2 n
and neutral reaction conditions in good to excellent yields.
Keywords: three-component synthesis, allylstannane, homoallylic amine, MgI etherate
2
Homoallylic amines are important building blocks for the
preparation of various nitrogen-containing natural products
analogues of MgI etherate, MgCl etherate, MgBr etherate
2 2 2
and also Mg(ClO ) were compared under analogous reaction
4
2
1
–4
and biologically or synthetically active compounds. In gen-
eral, homoallylic amines are prepared either by the addition of
organometallic reagents to imines or by the nucleophilic addi-
tion of allylsilane or allyltin or allylborane or allylgermane
conditions (20 mol% of catalyst) in the one-pot allylation
reaction of furfuraldehyde and 4-methoxyaniline with allyl-
stannane (Table 1, entries 13–15). MgCl etherate and MgBr2
2
etherate are almost inactive and Mg(ClO ) is less effective in
4
2
5
–7
reagents to imines in the presence of a variety of catalysts.
terms of substrate conversion and yield.
Recently, three-component syntheses of homoallylic amines
starting from aldehyde, amine and allylic metal compounds
Encouraged by the results obtained with the above reaction,
we investigated the one-pot allylation of a variety of aldehydes,
such as aromatic, heteroaromatic, aliphatic and α,β-unsatu-
rated aldehydes, with aniline, 4-methoxyaniline, 4-toluidine,
4-nitroaniline, 4-fluoroaniline and benzylamine. The results
are summarised in Table 2. The good to excellent yields
strongly suggest that MgI •(OEt ) is an efficient Lewis acid
8–10
have been realised. A straightforward synthesis of homoal-
lylic amines involving the nucleophilic addition of allyltin
reagents to imines, which are generated in situ from aldehydes
and amines in the presence of Lewis acid catalysts, has attracted
1
1–15
the attention of synthetic organic chemists.
However, many
2
2 n
of these methods have drawbacks and include the use of strong
Lewis acids, expensive metal triflate or precious metal cata-
lysts, prolonged reaction times, vigorous reaction conditions
or are difficult to handle especially on a large scale. Therefore,
the development of a facile and efficient one-pot synthesis
of homoallylic amines is an active ongoing research area
and there is scope for further improvement towards milder
catalyst for the three-component allylation of aldehydes,
amines and allylstannane. The reaction proved to be general
and could be utilised for a wide range of aldehydes. Specifi-
cally, the reaction proceeds smoothly under very mild condi-
tions at room temperature in a short period. There is no need
to exclude moisture and oxygen from the reaction system.
Moreover, aromatic aldehydes bearing electron-donating and
electron-withdrawing groups in the aromatic ring reacted
smoothly to afford the desired homoallylic amines in good to
excellent yields (Table 2, entries 1–8). Vinyl aldehydes such as
cinnamaldehyde reacted with p-methoxyaniline to afford the
homoallylic amine derivatives in good yield under the present
reaction conditions (Table 2, entry 9). Heteroaromatic alde-
hydes such as furfuraldehyde and 2-thenaldehyde were good
substrates as well (Table 2, entries 10–14). 3-Phenylpropanal
also led to the product 1o with good yield (Table 2, entry 15).
In general, both aromatic, heteroaromatic, aliphatic, and α,β-
unsaturated aldehydes underwent the conversion smoothly in a
short period whereas ketones did not yield any product even
1
6
reaction conditions. In the coutinuation of our research, we
here describe a simple and efficient protocol for the one-pot
synthesis of homoallylic amines catalysed by MgI etherate
2
(
(
MgI •(OEt ) ) under mild and neutral reaction conditions
Scheme 1).
2 2 n
Results and discussion
We initiated our studies by carrying out the allylation of equi-
molar amounts of furfuraldehyde and 4-methoxyaniline with
allylstannane using freshly prepared MgI etherate in CH Cl
2
2
2
at room temperature. It was demonstrated that the amounts of
MgI etherate catalyst have effects on the yield of addition
2
products. The optimal condition is using 20 mol% of MgI2
etherate to give the desired homoallylic amines in excellent
yield (Table 1, entry 4). Of various untreated solvents screened,
excellent yield was obtained in the non-coordinating reaction
medium CH Cl . Moderate yield was given using MeCN as
after the reaction times in the presence of MgI etherate were
2
prolonged. This is due to the lower reactivity of ketimines,
4
compared to aldimines, towards allylstannanes. In addition,
we have also observed electronic effects: the reactivity of
aromatic amines with electron-donating substituents (i.e. OMe,
Me) is much better than that of aromatic amines with electron-
2
2
solvent (Table 1, entry 7), and very low yields were provided
in nonpolar solvents, such as benzene or toluene (Table 1,
entries 8 and 9). Almost no reaction was observed in coordina-
withdrawing substituents (i.e. NO ) (Table 2, entries 2, 3
2
and 8).
tive polar solvents, such as Et O, DMF and THF (Table 1,
entries 10–12). To examine the halide anion effect, halogen
The one-pot allylation of chiral aldehydes, 4-methoxyani-
line with allylstannane catalysed by MgI •(OEt ) was also
2
2
2 n
2
Scheme 1 MgI etherate-catalysed three-component allylation.
*
Correspondent. E-mail: zhangxx@ zjut.edu.cn

2
2
JOURNAL OF CHEMICAL RESEARCH 2012
Table
1
Three-component allylation of furfuraldehyde,
Table 2 One-pot three-component synthesis of homoallylic
a
p-methoxyaniline with allyltributylstannane under different
2 2 n
amines catalysed by MgI •(OEt )
reaction conditionsa
Entry
Aldehyde
Amine
Time Prod- Yield
Entry Catalyst
Solvent
Loadings/mol%b
Yield/%c
b
/h
uct
/%
1
2
3
4
5
6
7
8
9
MgI
MgI
MgI
MgI
MgI
MgI
MgI
MgI
MgI
MgI
MgI
MgI
2
2
2
2
2
2
2
2
2
2
2
2
CH
CH
CH
CH
CH
CH
CH
2
2
2
2
2
2
3
Cl
Cl
Cl
Cl
Cl
Cl
2
2
2
2
2
2
5
10
15
20
50
100
20
20
20
20
20
20
20
20
20
16
43
1
2
2
1
3
4
2
1
1
2
2
1
1
2
1
2
2
2
2
1a
92
44
98
96
1b
1c
1d
1e
1f
98
88
89
93
92
97
96
91
96
98
90
92
86
81
82c
84d
88
CN
72
Toluene
Benzene
9
3
10
1
0
1
2
3
4
5
Et
2
O
Trace
Trace
Trace
55
1
1
1
1
1
THF
4
DMF
Mg(ClO
MgBr
MgCl
4
)
2
CH
CH
CH
2
2
2
Cl
Cl
Cl
2
2
2
2
15
Trace
5
2
a
The reaction was carried out by addition of furfuraldehyde
6
(
0.5 mmol), p-methoxyaniline (0.5 mmol) with allyltributylstan-
nane (0.6 mmol) in the named solvent at room temperature.
b
Relative to furfuraldehyde.
7
1g
1h
1i
c
Isolated yield by silica gel flash chromatography.
8
investigated (Table 2, entries 16 and 17). Gratifyingly, the
allylation was carried out in good yield with high stereoselec-
tivity in the presence of an acid sensitive acetonide or a Boc
9
1
7
group which do not survive under strongly acidic conditions.
We found that the allylation of acid sensitive D-glyceralde-
hyde acetonide without affecting the acetonide grouping exclu-
sively afforded the 1,2-anti homoallylic amine 1p determined
by H NMR analysis in 82% yield (Table 2, entry 16). Further-
more, this method is also useful for the selective allylation of
10
11
1j
1
1k
1l
Boc-L-phenylalaninal to afford a mixture of diastereoisomers
1
1
1
2
3
4
1
q with an anti:syn ratio of 93:7 ratio and with retention of the
Boc group (Table 2, entry 17).
1m
1n
1o
1p
1q
It is noteworthy that no homoallylic alcohol was observed in
the one-pot allylation of aldehydes, amines and allyltributyl-
stannane under the same reaction conditions. This is attributed
to the rapid formation and activation of imines in the presence
of MgI etherate The unique reactivity of MgI etherate is
attributed to the dissociative character of the iodide counterion
and a more Lewis acidic cationic [MgI] species as a result
of Lewis base activation of the Lewis acid. We propose the
following plausible mechanism for this one-pot allylation
reaction (Scheme 2), which suggests that the aldehyde rapidly
reacts first with the amine to form imine 2 by formation of
2
.
2
15
+
1
8
16
17
an oxonium salt with MgI etherate due to the latter’s high
oxophilic character. The in situ formed imine 2 is activated
2
a
Reactions were run in a mixture of aldehyde (0.5 mmol),
amine (0.5 mmol), allyltributylstannane (0.6 mmol) and
by coordination with MgI etherate. The cationic character of
2
2
2 2 2
0 mol % of MgI etherate in CH Cl at room temperature.
this more Lewis acidic Mg(II) coordination with peripheral
ethereal ligands results from the dissociation of iodide ion in
accordance with the coordination of the Lewis basic imine
group. Thus the activated imine 3 undergoes nucleophilic
addition by allyltributylstannane to afford the corresponding
derivative of homoallylic amine 1. In this process, the catalyst
b
Isolated yields by silica gel flash chromatography.
Only anti-configuration homoallylic amine was obtained.
The product was obtained as a mixture of anti and syn
c
d
product in a 93:7 ratio.
with allyltributylstannane. This magnesium-catalysed allylation
has advantages of simplicity, efficiency, mild reaction condi-
tions and high yields, which make it a useful and attractive
process for the synthesis of homoallylic amines. Further inves-
tigation is in progress in our laboratories to study regio- and
stereoselectivity, and to attempt the preparation of chiral units
which might function as important synthetic targets relevant to
drugs and natural products.
MgI etherate plays a vital role in the activation of the carbonyl
2
group to form the imine and in the activation of the imine to
react with allylating agent as shown in Scheme 2.
We have demonstrated that the unique catalytic reactivity
of MgI etherate in the three component allylation of various
2
aldehydes, including aromatic aldehydes, heteroaromatic
aldehydes, vinyl aldehydes and aliphatic aldehydes and amines

JOURNAL OF CHEMICAL RESEARCH 2012 23
Scheme 2 The proposed mechanism of MgI
2
2
•(OEt )
n
-catalysed allylation of aldehydes, amines and allyltributylstannane.
2
1
Experimental
For product purification by flash column chromatography, silica gel
200–300 mesh) and light petroleum ether (PE, b.p. 60–90 °C) were
4-(4′-Nitro-phenyl)-4-(N-4′-methyl-phenyl)aminobut-1-ene (1h):
Yellowish oil; δ 2.18 (s, 3H), 2.48–2.52 (m, 1H), 2.59–2.63 (m, 1H),
H
4
.12 (br s, 1H,), 4.45 (dd, 1H, J = 5.0, 8.5 Hz), 5.18–5.21 (m, 2H),
5.70–5.78 (m, 1H), 6.38 (dd, 2H, J = 3.0, 10.0 Hz), 6.89 (d, 2H, J =
.5 Hz),7.48 (t, 1H, J = 8.0 Hz), 7.71 (d, 1H, J = 7.5 Hz), 8.09 (dd, 1H,
J = 1.0, 7.0 Hz), 8.24 (t, 1H, J = 2.0 Hz).
-Phenyl-4-(N-4′-methoxy-phenyl)amino-1,5-hexadiene (1i): Pale
yellowish oil; δ 2.43–2.50 (m, 2H), 3.73 (s, 3H) 5.14–5.20 (m, 2H),
(
1
used. All solvents were commercially available. H NMR spectra
were taken on a BrukerAM-500 spectrometer with TMS as an internal
8
13
standard and CDCl as solvent. C NMR spectral measurements were
3
19
6
performed at 125 MHz using TMS as an internal standard. HRMS was
determined on a GCT Premier spectrometer.
H
5
.81–5.89 (m, 1H), 6.19 (dd, 1H, J = 6.0, 15.5 Hz), 6.57–6.64 (m,
Synthesis of homoallylamines; general procedure
3H), 6.75 (dd, 2H, J = 2.5, 6.5 Hz), 7.19–7.36 (m, 5H).
4-(2′-Furan)-4-(N-phenyl)aminobut-1-ene (1j): Yellowish oil;
21
MgI etherate (0.1 mmol) was added to a stirred solution of aldehyde
2
(
0.5 mmol) and amine (0.5 mmol) in CH Cl (5 mL) at room tempera-
δ 2.64–2.67 (m, 2H), 3.98 (br s, 1H), 4.55 (t, 1H, J = 6.5 Hz), 5.12–
H
2
2
ture. After stirring for 10 min, a solution of allylstannane (0.6 mmol)
in CH Cl (2 mL) was added dropwise using a syringe. The resulting
5.19 (m, 2H), 5.71–5.79 (m, 1H), 6.16 (d, 1H, J = 3.5 Hz), 6.28
(dd, 1H, J = 1.5, 3.0 Hz), 6.60 (dd, 2H, J = 1.0, 8.5 Hz), 6.70 (t, 1H,
J = 7.5 Hz), 7.14 (dd, 2H, J = 7.0, 9.0 Hz), 7.34 (s, 1H).
2
2
homogeneous mixture was stirred at room temperature for 2.0 h and
quenched with 1.0 M aq. HCl. Extractive workup with ethyl acetate
and chromatographic purification of the crude product on silica gel
gave the desired homoallylic amine.
23
4-(2′-Furan)-4-(N-4′-methoxy-phenyl)aminobut-1-ene (1k): Yello-
wish oil; δ 2.62 –2.65 (m, 2H), 3.72 (s, 3H), 3.74 (br s, 1H), 4.46
H
(t, 1H, J = 6.0 Hz), 5.11–5.17 (m, 2H), 5.72–5.78 (m, 1H), 6.14
(
d, 1H, J = 3.0 Hz), 6.27 (dd, 1H, J = 2.0, 3.0 Hz), 6.56–6.59 (m, 2H),
Spectroscopic data
6.72–6.74 (m, 2H), 7.34 (s, 1H).
4-(2′-Thiophene)-4-(N-phenyl)aminobut-1-ene (1l): Pale yellowish
19
8
4
-Phenyl-4-(N-phenyl) aminobut-1-ene (1a): Pale yellowish oil;
δ 2.60–2.65 (m, 1H), 2.71–2.75 (m, 1H), 4.29 (br s, 1H), 4.50–4.53
oil; δ 2.64–2.68 (m, 2H), 4.12 (br s, 1H), 4.71 (t, 1H, J = 7.5 Hz),
H
H
(
m, 1H), 5.26–5.33 (m, 2H), 5.85–5.92 (m, 1H), 6.63 (d, 2H, J =
5.15–5.21 (m, 2H), 5.76–5.83 (m, 1H), 6.60 (d, 2H, J = 7.5 Hz),
7
1
.5 Hz), 6.78 (t, 1H, J = 7.5 Hz), 7.19–7.22 (m, 2H), 7.35–7.37 (m,
6.68–6.71 (m, 1H), 6.93–6.98 (m, 2H), 7.11–7.17 (m, 3H).
4-(2′-Thiophene)-4-(N-4′-fluoro-phenyl)aminobut-1-ene (1m): Yello-
2
1
H), 7.42–7.50 (m, 4H).
19
4-Phenyl-4-(N-4′-methoxy-phenyl)aminobut-1-ene(1b): Paleyello-
wish oil; δ 2.60–2.70 (m, 2H), 4.06 (br s, 1H), 4.31 (t, 1H,
H
wish oil; δ 2.48–2.52 (m, 1H), 2.58–2.61 (m, 1H), 3.68 (s, 3H),
J = 6.0 Hz), 5.16–5.21 (m, 2H), 5.77–5.83 (m, 1H), 6.52–6.54 (m,
2H), 6.81–6.84 (m, 2H), 6.93–6.96 (m, 2H), 7.17 (dd, 2H, J = 1.5,
5.0 Hz).
H
4.30 (dd, 1H, J = 5.0, 8.0 Hz), 5.12–5.19 (m, 2H), 5.71–5.78 (m, 1H),
6.46 (d, 2H, J = 8.5 Hz), 6.67 (dd, 2H, J = 2.5, 7.0 Hz), 7.24–7.27 (m,
1H), 7.31 (t, 2H, J = 7.5 Hz), 7.35 (d, 2H, J = 7.0 Hz).
24
4-(2′-Thiophene)-4-(N-benzyl)aminobut-1-ene (1n): Pale yello-
20
4
-Phenyl-4-(N-4′-nitro-phenyl)aminobut-1-ene (1c): Colourless
wish oil; δ 2.52–2.55 (m, 2H), 3.62 (d, 1H, J = 13.0 Hz), 3.81 (d, 1H,
H
oil; δ 2.55–2.60 (m, 1H), 2.65–2.69 (m, 1H), 4.50–4.54 (m, 1H), 4.91
J = 13.5 Hz), 4.02 (t, 1H, J = 7.0 Hz), 5.05–5.12 (m, 2H), 5.67–5.76
(m, 1H), 6.97 (t, 1H, J = 3.0, 5.0 Hz), 7.24–7.26 (m, 2H), 7.29–7.33
(m, 4H).
H
(
(
d, 1H, J = 4.5 Hz), 5.20–5.26 (m, 2H), 5.71–5.77 (m, 1H), 6.45
d, 2H, J = 9.0 Hz), 7.26–7.30 (m, 3H), 7.34–7.37 (m, 2H), 7.99 (d,
25
2
H, J = 9.5 Hz).
-Phenyl-4-(N-benzyl)aminobut-1-ene (1d): Pale yellowish oil;
δ 2.43–2.44 (m, 2H), 3.53 (d, 1H, J = 13.0 Hz), 3.67–3.71 (m, 2H),
6-Phenyl-4-(N-4′-methoxy-phenyl)aminohex-1-ene (1o):
Pale
19
4
yellowish oil; δ 1.77–1.90 (m, 2H), 2.32 (t, 2H, J = 6.5 Hz), 2.70–
H
H
2.76 (m, 2H), 3.34–3.39 (m, 1H), 3.75 (s, 3H), 5.05–5.10 (m, 2H),
5.76–5.84 (m, 1H), 6.55 (d, 2H, J = 8.5 Hz), 6.76 (dd, 2H, J = 2.0,
6.5 Hz), 7.16–7.20 (m, 3H), 7.26–7.29 (m, 2H).
5
.02–5.09 (m, 2H), 5.66–5.74 (m, 1H), 7.23–7.37 (m, 10H).
2
1
4
-(3′-Methoxy-phenyl)-4-(N-phenyl)aminobut-1-ene (1e): Pale
yellowish oil; δ 2.45–2.51 (m, 1H), 2.58–2.62 (m, 1H) 3.78 (s, 3H),
4-(2,2-Dimethyl-[1,3]dioxolanyl)-4-(N-4′-methoxy-phenyl)aminobut-1-
H
4
5
6
7
.14 (br s, 1H), 4.34 (dd, 1H, J = 5.0, 8.0 Hz), 5.13–5.20 (m, 2H),
.72–5.80 (m, 1H), 6.50 (d, 2H, J = 8.0 Hz), 6.64 (t, 1H, J = 7.5 Hz),
.77 (dd, 1H, J = 2.0, 8.0 Hz), 6.92–6.96 (m, 2H), 7.06–7.09 (m, 2H),
.22–7.25 (m, 1H).
ene (1p): Colourless oil; δ 1.35 (s, 3H), 1.45 (s, 3H), 2.31–2.37
H
(m, 1H), 2.40–2.45 (m, 1H), 3.32 (br s, 1H), 3.40–3.43 (m, 1H), 3.74
(s, 3H), 3.86–3.88 (m, 1H), 4.04–4.06 (m, 2H), 5.08–5.12 (m, 2H)
5.82–5.88 (m, 1H), 6.60 (d, 2H, J = 9.0 Hz). 6.76 (dd, 2H, J = 2.0,
22
4
-(4′-Methoxy-phenyl)-4-(N-phenyl)aminobut-1-ene (1f): Yello-
7.0 Hz); δ 152.41, 141.57, 134.29, 118.22, 115.42, 114.91, 109.36,
C
wish oil; δ 2.48–2.52 (m, 1H), 2.58–2.61 (m, 1H), 3.78 (s, 3H,), 4.12
77.57, 77.25, 77.00, 76.75, 67.29, 56.50, 55.76, 35.34, 26.77, 25.22;
H
+
(
5
br s, 1H), 4.33 (dd, 1H, J = 5.0, 8.0 Hz), 5.12–5.19 (m, 2H), 5.71–
.80 (m, 1H), 6.48–6.50 (m, 2H), 6.62–6.65 (m, 1H), 6.86 (ddd, 2H,
J = 2.5, 5.0, 10.0 Hz), 7.05–7.09 (m, 2H), 7.27 (ddd, 2H, J = 2.0, 5.0,
0.0 Hz).
-(4′-Nitro-phenyl)-4-(N-phenyl)aminobut-1-ene (1g): Pale yello-
m/z (EI): 277 ([M] , 28), 236 (27), 176 (100), 160 (33), 134 (70);
+
HRMS (EI) Calcd for C H NO : 277.1678; found for [M] :
16
23
3
277.1675.
1
[1-Benzyl-2-(4-methoxy-phenylamino)-pent-4-enyl]-carbamic acid
21
4
tert-butyl ester (1q):Yellowish oil; δ 1.35 (s, 9H), 2.23–2.28 (m, 1H),
H
wish oil; δ 2.47–2.53 (m, 1H), 2.60–2.66 (m, 1H), 4.21 (br s, 1H),
2.34–2.37 (m, 1H), 2.66–2.80 (m, 1H), 2.90–3.04 (m, 1H), 3.36–3.39
(m, 2H), 3.75 (s, 3H), 4.12 (br s, 1H), 4.51 (br s, 1H), 5.04–5.10 (m,
2H) 5.77–5.80 (m, 1H), 6.58 (d, J = 2.0, 8.5 Hz), 6.75–6.77 (m, 2H),
H
4.48 (dd, 1H, J = 5.0, 8.0 Hz), 5.19–5.23 (m, 2H), 5.69–5.77 (m, 1H),
6.43 (dd, 2H, J = 0.5, 8.5 Hz), 6.67–6.70 (m, 1H), 7.06–7.10 (m, 2H),
7.54 (ddd, 2H, J = 2.5, 4.0, 9.5 Hz), 8.17–8.20 (m, 2H).
7.16–7.29 (m, 5H); δ 28.24, 37.03, 38.66, 53.96, 55.77, 56.64, 79.36,
C

2
4
JOURNAL OF CHEMICAL RESEARCH 2012
1
1
1
14.95, 115.02, 117.61, 126.30, 128.36, 129.19, 134.86, 138.19,
42.00, 152.23, 155.85; m/z (EI): 396 ([M] , 8), 355 (15), 299 (39),
8
9
T. Gastner, H. Ishitani, R. Akiyama and S. Kobayashi, Angew. Chem., Int.
Ed., 2001, 40, 1896.
T. Akiyama, J. Iwai, Y. Onuma and H. Kagoshima, Chem. Commun., 1999,
+
76 (100), 134 (49); HRMS (ESI) Calcd for C H N O : 397.2491;
24
33
2
3
+
2191.
found for [M+H] : 397.2478.
1
1
1
0
1
2
M. Billet, P. Klotz and A. Mann, Tetrahedron Lett., 2001, 42, 631.
T. Akiyama and Y. Onuma, J. Chem. Soc., Perkin Trans., 1 2002, 1157.
Y. Yuan, F. Chen and D.B. Zhao, Appl. Organomet. Chem., 2009, 23, 485.
We acknowledge financial support from the Zhejiang Province
Natural Science Foundation of China (Project Y4100692).
13 A.V. Narsaiah, J.K. Kumar and P. Narsimha, Synthesis, 2010, 1609.
1
4
J.S. Yadav, B.V.S. Reddy, A.K. Raju and D. Gnaneshwar, Adv. Synth.
Catal., 2002, 344, 938.
P. Tirupathi and S.S. Kim, Tetrahedron, 2009, 65, 5168.
X.-X. Zhang, Synlett, 2008, 65.
Received 11 November 2011; accepted 20 December 2011
Paper 1100979 doi: 10.3184/174751912X13252567769442
Published online: 31 January 2012
1
1
5
6
17 B.M. Choudary, C. Sridhar and C.V.R. Sekhar, Synlett, 2002, 1694.
1
1
8
9
S.E. Denmark and R.A. Stavenger, Acc. Chem. Res., 2000, 33, 432.
C. Bellucci, P.G. Cozzi and A. Umani-Ronchi, Tetrahedron.Lett., 1995, 36,
References
1
2
3
7
289.
Y. Yamamoto and M. Schmid, J. Chem. Soc., Chem. Comm., 1989, 1310.
J.C.A. Hunt, P. Laurent and C.J. Moody, Chem. Comm., 2000, 177.
F.-X. Felpin, S. Girard, G.R. Vo-Thanh, J. Robins, J. Villieras and
J. Lebreton, J. Org. Chem., 2001, 66, 6305.
R. Bloch, Chem. Rev., 1998, 98, 1407.
S. Yamasaki, K. Fujii, R. Wada, M. Kanai and M. Shibasaki, J. Am. Chem.
Soc., 2002, 124, 6536.
20
21
22
Z.F. Xie, G.L. Li, G. Zhao and J.D.Wang, Chin. J. Chem., 2009, 27, 925.
L. Li and G. Zhao, Org. Lett., 2006, 8, 633.
M.C. Law, T.W. Cheung, K. Wong and T. H Chan, J Org. Chem., 2007, 72,
9
23.
D.K.Wang, Y.G. Zhou, Y. Tang, X.L. Hou and L.X. Dai, J. Org. Chem.,
999, 64, 4233.
4
5
2
3
1
6
7
T.H. Chan and W. Lu, Tetrahedron Lett., 1998, 39, 8605.
T. Akiyama, J. Iwai, Y. Onuma and H. Kagoshima, Chem. Commun., 1999,
24 K.H. Shen and C.F. Yao, J. Org. Chem., 2006, 71, 3980.
25 I. Shibata, K. Nose, K. Sakamoto, M. Yasuda and A. Baba, J. Org. Chem.,
2004, 69, 2185.
2
191.