Conjugate addition of triallylaluminum to α,β-unsaturated nitroalkenes to produce 4,5-unsaturated nitroalkenes

Article abstract of DOI:10.1080/00397910600978184

The reaction of aryl substituted α,β-unsaturated nitroalkenes 1a-g with triallylaluminum 2 in ether solution at 0°C generated low to high yields of 4,5-unsaturated nitroalkenes 3a-g after adding the nitronate to an ice-cold solution of dilute hydrobromic

Full text of DOI:10.1080/00397910600978184

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Conjugate Addition of Triallylaluminum to
α,β‐Unsaturated Nitroalkenes to Produce
4,5‐Unsaturated Nitroalkenes
Kao‐Hsien Shen a , Ju‐Tsung Liu a , Yih‐Ru Wu a & Ching‐Fa Yao a
a Department of Chemistry , National Taiwan Normal University , Taipei,
Taiwan, China
Published online: 05 Oct 2007.
To cite this article: Kao‐Hsien Shen , Ju‐Tsung Liu , Yih‐Ru Wu & Ching‐Fa Yao (2007) Conjugate Addition
of Triallylaluminum to α,β‐Unsaturated Nitroalkenes to Produce 4,5‐Unsaturated Nitroalkenes, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 37:20,
3677-3687, DOI: 10.1080/00397910600978184
To link to this article: http://dx.doi.org/10.1080/00397910600978184
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Synthetic Communicationsw, 37: 3677–3687, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600978184
Conjugate Addition of Triallylaluminum to
a,b-Unsaturated Nitroalkenes to Produce
4,5-Unsaturated Nitroalkenes
Kao-Hsien Shen, Ju-Tsung Liu, Yih-Ru Wu, and
Ching-Fa Yao
Department of Chemistry, National Taiwan Normal University, Taipei,
Taiwan, China
Abstract: The reaction of aryl substituted a,b-unsaturated nitroalkenes 1a–g with
triallylaluminum 2 in ether solution at 08C generated low to high yields of 4,5-unsatu-
rated nitroalkenes 3a–g after adding the nitronate to an ice-cold solution of dilute
hydrobromic acid. The yields of products 3h–j were increased substantially when
the alkyl substituted a,b-unsaturated nitroalkene 1h and the highly hindered a,b-unsa-
turated nitroalkenes 1i and 1j reacted with 2 in the presence of aluminum chloride. The
most important thing is triallylaluminum was prepared from allyl bromide and pure
elemental Al, not from Grignard reagent.
Keywords: conjugate addition, triallylaluminum, a,b-unsaturated nitroalkenes,
4,5-unsaturated nitroalkenes
INTRODUCTION
Nitroalkenes are one of the more useful intermediates in organic synthesis and
can be used as starting materials for the synthesis of a variety of compounds.[1]
Reactions of nitroalkenes with allyl organometallic reagents such as allyl
Grignard reagents,[2] allylsamarium bromides,[3] allylzinc reagents,[4]
allyltin and allylsilanes,[5] or organoaluminum Et2AlR2MgX (R ¼ allyl,
Received in R.O.C. March 12, 2006
Address correspondence to Ching-Fa Yao, Department of Chemistry, National
Taiwan Normal University 88, Sec. 4, Tingchow Road, Taipei, Taiwan, China.
E-mail: cheyaocf@scc.ntnu.edu.tw
3677

3678
K.-H. Shen et al.
phenyl, or benzyl)[6] result in the formation of the 1,4-addition products, and
the reaction mechanism was proposed to involve an ionic reaction.
Although the reaction of nitroalkene with allyl Grignard reagent in tetra-
hydrofuran (THF) at 2788C has been reported by Barboni et al. excellent
yields were obtained only when an aromatic nucleus was present in the
b-position; aliphatic substituent in that position, such as 1-nitrohex-1-ene or
1-nitrocyclohexene, leads to an intractable mixture.[2] Similarly, reactions of
a,b-unsaturated nitroalkenes in hexane solution with either trialkylaluminum
R3Al (R ¼ Et or i-Bu) or a trialkylaluminum etherate R3Al OEt2 (R ¼ Et, i-Bu
or Ph)[6a] at 08C or a tetraorganoalanate such as [R3AlR0]M (R0 ¼ allyl or
phenyl, M ¼ MgX or Li) or [R2AlR20 ]MgX (R0 ¼ allyl, phenyl, or
benzyl)[6b] to generate the conjugate addition products have also been
reported by Pecunioso. However, surprisingly, only the unreacted nitroalkene
was recovered when 1-nitrocyclohexene was reacted with triisobutylalumi-
num or diethylallylaluminum in diethyl ether.[6b]
Our group also reported that the Michael addition of a Grignard or an
organolithium reagent to b-nitrostyrenes generated high yields of nitroalkanes
when the nitronate was added to an ice-cold and dilute hydrochloric acid solu-
tion.[7a,b] Similarly, triethylaluminum or diethylaluminum chloride also reacts
with b-nitrostyrenes in ether solution to generate chlorooximes and alkenes.
The proposed reaction mechanism involves an ionic 1,4-conjugate addition
to produce chlorooxime and the free-radical substitution of the nitro group
to yield an alkene.[7b]
We recently reported that triallylaluminum reacts with aldehydes, ketones,
aldimines, and ketimines in excellent yields.[8] Herein, we report on the allylation
of a,b-unsaturated nitroalkene with triallylaluminum. To the best of our
knowledge, reactions of the a,b-unsaturated nitroalkene 1 and triallylaluminum
2 have not been reported. Based on the previous study, we predict that triallyla-
luminum might function as an allyl organometallic reagent[2–5] and that an
organoaluminum reagent such as trialkylaluminum,[6a,7a] dialkylaluminum
chloride,[7c] or triphenylaluminum[6a] would react with a,b-unsaturated nitroalk-
enes to generate different products. The most significant feature of this reaction
concerns the preparation of the triallylalumium reagent, from allyl bromide and
pure elemental Al,[9,10] as opposed to earlier reports in which the allylaluminum
was prepared from alkylaluminum and allylmagnesium.[11]
RESULTS AND DISCUSSION
In general, the allylaluminum reagents were prepared by coupling commer-
cially available aluminum chloride (Me2AlCl) with the appropriate
Grignard or organolithium reagent.[10] In this article, the triallylaluminum
reagent 2 was first prepared by reacting allyl bromide and elemental
aluminum in ether under reflux conditions according to literature procedures
(Scheme 1).[9,10]

Triallylaluminum to a,b-Unsaturated Nitroalkenes
3679
Scheme 1.
Scheme 2.
When triallylaluminum 2 was rapidly added to the b-nitrostyrene 1a
dissolved in ether solution at 08C under nitrogen, the yellow color of 1a
disappeared immediately. A quantitative yield of 1-nitro-2-phenylpent-4-ene
3a was observed after workup of the reaction, and the crude mixture was
checked by NMR and purified by flash-column chromatography (Scheme 2,
and entry 1 of Table 1).[11]
Table 1. Reaction of nitroalkene 1 and triallylaluminum 2 to generate 4,5-unsaturated
nitroalkenes 3
AlCl3
(eq)
Time
(min)
Yield
(%)
Entry
1
R1
R2
R3
3
1
2
1a
1a
1b
1c
1d
1e
1f
Ph
Ph
H
H
H
H
H
H
H
H
H
H
H
H
–
–
–
–
–
–
–
–
–
1
3
–
3
–
3
2
2
2
2
2
2
5
5
2
2
2
2
2
5
5
3a
3a
3b
3c
3d
3e
3f
100
38a
100
100
94
H
3
4-MeOC6H4
2-MeOC6H4
H
4
H
5
4-CIC6H4
2-thienyl
Ph
H
6
H
100
41
7
Me
Ph
H
8
1g
1h
1h
1h
1i
Ph
Bu
3g
3h
3h
3i
26
65
9
10
11
12
13
14
15
Bu
Bu
H
70
H
81
R1 þ R3 ¼ 2(CH2)4 2 , R2 ¼ H
3i
61b
70b
55c
81d
1i
R1 þ R3 ¼ 2(CH2)4 2 , R2 ¼ H
3i
1j
Et
Et
Et
Et
H
H
3j
1j
3j
aTwo equivalents of benzoyl peroxide were added to the solution before 2 was
added.
bTwo diastereomers were observed in the crude 1H-NMR but inseparable after the
flash column purification.
c37% of nitroalkene 3j and 18% of nitrone 4j were isolated.
d43% of 3j and 38% of 4j were isolated.

3680
K.-H. Shen et al.
However, only 38% of 3a but no 1-phenyl-1,4-pentadiene (PhCH55CH-
CH2-CH55CH2) were isolated when 2 equiv of benzoyl peroxide, a free-
radical initiator, were added to the solution (entry 2). This indicates that 1a
can only react with 2 via an ionic 1,4-conjugate addition because the
presence of benzoyl peroxide had no effect on the reaction. The decrease in
3a can be explained by the assumption that benzoyl peroxide also can react
with or destroy the aluminum reagent. Similarly, high yields (94–100%) of
3b–e were observed when b-nitrostyrenes 1b–e were reacted with 2, respect-
ively (entries 3–6). All of these results are consistent with the literature
reports that aryl substituted b-nitrostyrenes react with allylic metals to
generate high yields of the conjugate addition products.[2]
The reactions are very sensitive to steric effects. When the hindered
nitroalkene 1-nitro-2-phenylpropene 1f[12a–c] or 1,1-diphenyl-2-nitroethene
1 g[13] was reacted with 2, only 41% of 3f or 26% of 3g (entries 7 and 8)
were isolated, and the yields are much lower compared to the yields of
3a–e (entries 1–6). A possible explanation for this is that the substitution
of the hydrogen atom by a methyl or phenyl group dramatically increases
the steric hindrance between the nitroalkene and 2, thus retarding the
conjugate addition to some degree.
Not only the mono- or di-aryl substituted b-nitrostyrenes 1a–g but also
the b-alkyl substituted 1-nitrohex-1-ene 1h reacts with 2 as described pre-
viously. However, 3h was isolated in only 65% yield (entry 9), but the
yield was increased to 70% when 1 equiv of aluminum chloride AlCl3 was
added (entry 10). Although the possibility of the formation other organoalumi-
num
compounds
such
as
(CH255CHCH2)xAlClyBr3-x-y
or
(CH255CHCH2)xAlClyBr4-x-y cannot be excluded after adding AlCl3, the
presence of AlCl3 was found to improve and increase the product yields sub-
stantially. Surprising, the yield of 3h increased to 81% when 3 equiv of AlCl3
were added to the solution under similar conditions (entry 11). Similarly, a
61% yield of two inseparable diastereomers 3i was also isolated when a,b-
disubstituted nitroalkenes such as 1-nitrocyclohexene 1i were reacted with 2
under similar conditions (entry 12), and the yield increased to 70% in the
presence of 3 equiv of AlCl3, as described previously (entry 13). Compared
to b-nitrostyrenes 1a–e, which always generate high yields of product, the
use of b-alkyl substituted 1-nitrohex-1-ene 1h leads to a lower yield of 3h
in the absence of AlCl3 because polymers and/or intractable products may
have been formed during reaction. A possible explanation for this is that trial-
lylaluminum reagent 2 not only functions as a nucleophile but also as a Lewis
acid to form a complex or coordinates with the aryl group and/or the oxygen
atom of the nitro group of b-nitrostyrenes of 1a–e to stabilize the transition
state or intermediate, thus retarding the formation of side reaction products,
such as polymers. In the case of the a,b-disubstituted nitroalkene 1i, the
generation of a slightly lower yield of 3i than 3h indicates that the presence
of the disubstituted group at the a-position and b-position increases the
steric hindrance, as described previously. However, the reactions of both 1h

Triallylaluminum to a,b-Unsaturated Nitroalkenes
3681
and 1i were improved by the addition the Lewis acid AlCl3. Compared to the use
of the allyl Grignard reagent to react with 1h or 1i to generate intractable reaction
mixtures,[2] the use of 2 leads to much better results in the presence of AlCl3.
In addition to the nitroalkenes 1a–i, other highly hindered nitroalkenes
such as 2-ethyl-1-nitrobutene 1j[13a,b] were also studied. For example, 55%
of the final products including 37% of the expected product nitroalkene 3j
and 18% of the unexpected product nitrone [Et2C(CH2CH55CH2)-
CHN(O)CH2CH55CH2] 4j were isolated (entry 14). Surprisingly, the yield
dramatically increased to 81%, including 43% of 3j and 38% of 4j, when 3
equiv of AlCl3 were added (entry 15). Compared to the a-monosubstituted,
b-monosubstituted, or a,b-disubstituted nitroalkenes that have been
reported in the literature,[2–7] substrate 1j also reacted rapidly with 2 to
generate moderate yields of product in both the absence or presence of
AlCl3, but the yield was higher in the presence of AlCl3.
Based on these results, we conclude that 2 reacts with a,b-unsaturated
nitroalkene 1 to undergo a 1,4-conjugate addition, similar to other allyl orga-
nometallic reagents. Compared to the allyl Grignard reagent[2] or a tetraorga-
noalanate R3AlR0M (R0 ¼ allyl or phenyl) or R2AlR20 MgX (R0 ¼ allyl,
phenyl),[6] the use of 2 has certain advantages. First, the use of an allyl
Grignard reagent to react with 1h and 1i at 2788C gave an intractable
reaction mixture whereas the use of 2 generated 65% or 81% of 3h and
61% or 70% of 3i at 08C in the absence or presence of AlCl3. Second, no
product was generated and only the unreacted nitroalkene was recovered
when triisobutylaluminum or diethylallylaluminum was reacted with 1i in
diethyl ether, and the use of Et2AlR2MgX (R ¼ allyl) requires 30 min to
complete the reaction at room temperature, whereas the use of 2 requires
only 2 min. Third, the preparation of the triallylalumium reagent 2 from
aluminum metal and allyl bromide under reflux is a much simpler
procedure compared to the formation of Et2AlR2MgX (R ¼ allyl) from
Et2AlCl and RMgCl (R ¼ allyl) at 08C and then at 2158C. Fourth, 2 is a trior-
ganoalane, and Et2AlR2MgX is a tetraorganoalanate, but 2 can also react with
a,b-unsaturated nitro olefins to undergo exclusively conjugate addition, which
is different from the allyl Grignard reagent, which can also undergo 1,2- and/
or 1,4-additions in some cases.
Finally, the proposed mechanism for the generation of nitroalkane 3a,
which was obtained from the reaction of b-nitrostyrene 1a and triallylalumi-
nium reagent 2 under a nitrogen atmosphere, is shown as Scheme 3. First, the
1,4-addition occurs to yield the intermediate nitronate I, and then I can
obtain the proton from the dilute aqueous HBr solution to produce the final
product.
Triallylaluminum reagent 2, compared to other organometallic reagents,
has some advantages: (1) short reaction time, (2) easy preparation, (3) opera-
tionally simple procedure, and (4) broadest substrate scope. For example, the
allylzinc reagents always need longer reaction times (0.5–4.5 h) to complete
the reaction.[4] Similarly, the preparation of allylsamarium reagents needs

3682
K.-H. Shen et al.
Scheme 3.
expensive samarium metal, and the reaction time is longer.[3] The use of
allyltin reagents in the presence of Lewis acid needs to undergo a 1.4-
addition reaction. Even though mercuric chloride (about 0.4 mol%) was
used in the preparation of triallylaluminum reagent, care has been taken to
avoid the toxicity of allylmercury reagents.
CONCLUSION
In summary, a simple, convenient, and efficient method for preparing the 4,5-
unsaturated nitroalkene 3 using a,b-unsaturated nitroalkene 1 and triallylalu-
mium 2 in the absence or presence of AlCl3 in ether under nitrogen at 08C is
described. The short reaction time and the simplicity of the procedures make
this method one of the most efficient for the synthesis of this class of
compounds. The most significant feature of this reaction concerns the prep-
aration of triallylalumium, from allyl bromide and pure elemental Al,[9,10]
unlike previous procedures in which alkylaluminum and allylmagnesium
chloride were used.[11]
EXPERIMENTAL
General
All reactions were performed in oven-dried glassware under nitrogen. 1H and
1
13C NMR spectra were recorded with a Bruker EX 400 FT NMR. H NMR

Triallylaluminum to a,b-Unsaturated Nitroalkenes
3683
chemical shifts are expressed in parts per million downfield from tetramethyl-
C
silane with reference to internal residual CHCl3 (d ¼ 7.26 ppm) in CDCl3. 13
NMR chemical shifts are expressed in parts per million downfield from CDCl3
as an internal standard (d ¼ 77.0 ppm) in CDCl3. GC-MS data were acquired
using a HP 5890 GC/HP 5973 MSD mass spectrometer. Mass spectra were
obtained on a Jeol JMS-D300 spectrometer. High-resolution mass spectra
(HRMS) were obtained on a Jeol JMS-HX 110 spectrometer.
Starting Materials
trans-b-Nitrostyrene 1a and analogues 1b–h were prepared according to
literature procedures with minor modifications. 1-Nitro-cyclohexene 1j was
purchased from Aldrich Chemical Co. and was used without purification.
The Formation of Triallylaluminum 2[9,10]
A dry 250-mL flask fitted with a mechanical stirrer is assembled with a
vacuum seal, a dropping funnel, and a reflux condenser to which a nitrogen
inlet and an oil bubbler are attached. The flask is charged with aluminum
granules (2.7 g, 0.1 mol), mercuric chloride (0.1 g), and iodine (0.1 g), and
then the apparatus is thoroughly flushed with dry nitrogen. Ether (65 mL)
and allyl bromide (freshly distilled, 10 mL) are added successively via the
dropping funnel. The rest of allyl bromide (25 mL) is slowly added at rate
sufficient to maintain a gentle reflux. The mixture is stirred for 5–6 h under
refluxing conditions until the aluminum metal reacted completely.
Typical Experimental Procedures for the Preparation 3a from the
Reaction of b-Nitrostyrene 1a and Triallylaluminum Reagent 2
Triallylaluminun reagent 2 (0.85 mmol, 0.5 M ꢀ 1.7 mL) was added rapidly
to a stirred solution of b-nitrostyrene 1a (1 mmol) in ether (2 mL) at 08C
under nitrogen. The yellow color of 1a disappeared immediately.
After stirring for 2 min, the nitronates solution was added to an ice-cold
and dilute hydrochloric acid solution at the same temperature. The solution
was extracted with diethyl ether (25 mL ꢀ 3), and the ether solution was
dried over MgSO4, filtered, and evaporated to give an oily mixture. Quantitat-
ive yield of 1-nitro-2-phenylpent-4-ene 3a was obtained after the crude
1
mixture was checked by H NMR, and the mixture was purified by flash-
column chromatography using hexane–ethyl acetate as the eluent to obtain
the pure products. All spectral data are consistent with the literature
reports. Spectral data 3a,[3] 3b,[3] 3d,[3] 3e[4], and 3i[6b] are consistent with
the literature.

3684
K.-H. Shen et al.
1-Nitro-2-phenylpent-4-ene (3a)[3]
Colorless oil, 1H NMR (400 MHz, CDCl3) d 7.32 (d, J ¼ 7.20 Hz, 2H), 7.25
(tt, J ¼ 7.20, 2.08 Hz, 1H), 7.32 (dd, J ¼ 7.20, 2.08 Hz, 2H), 5.71–5.60
(m, 1H), 5.09–5.03 (m, 2H), 4.62 (dd, J ¼ 12.10, 6.84 Hz, 1H), 4.54 (dd,
J ¼ 12.10, 8.44 Hz, 1H), 3.56 (quint, J ¼ 7.36 Hz, 1H), 2.52–2.39 (m, 2H).
13C NMR (100 MHz, CDCl3) d 139.15, 134.12, 128.81, 127.56, 127.35,
118.09, 79.80, 43.69, 37.58. MS m/z (relative intensity) 191 (Mþ, tr), 143
(18), 129 (21), 104 (100), 91 (47).
1-Nitro-2-(4-methoxyphenyl)pent-4-ene (3b)[3]
Colorless oil, 1H NMR (400 MHz, CDCl3): the pattern of the aromatic protons
is AA0XX0 and is simplified as d 7.13 (dt, J ¼ 8.72, 2.96 Hz, 2H), 6.88 (dt,
J ¼ 8.72, 2.96 Hz, 2H), and the other protons are 5.73–5.63 (m, 1H), 5.11–
5.05 (m, 2H), 4.61 (dd, J ¼ 12.10, 6.76 Hz, 1H), 4.51 (dd, J ¼ 12.10,
8.60 Hz, 1H), 3.79 (s, 3H), 3.53 (quint, J ¼ 7.36 Hz, 1H), 2.49–2.40
(m, 2H). 13C NMR (100 MHz, CDCl3) d 158.83, 134.29, 131.01, 128.34,
117.90, 114.14, 80.06, 55.07, 42.98, 37.60. MS m/z (relative intensity) 221
(Mþ, 8), 180 (11), 134 (100), 121 (14), 91 (15).
1-Nitro-2-(2-methoxyphenyl)pent-4-ene (3c)
Colorless oil, 1H NMR (400 MHz, CDCl3) d 7.26 (td, J ¼ 8.04, 1.60 Hz, 1H),
7.12 (dd, J ¼ 7.48, 1.60 Hz, 1H), 6.94 (dd, J ¼ 7.48, 1.60 Hz, 1H), 6.90
(td, J ¼ 8.04, 1.60 Hz, 1H), 5.74–5.64 (m, 1H), 5.10-5.02 (m, 2H), 4.69
(dd, J ¼ 12.30, 7.52 Hz, 1H), 4.63 (dd, J ¼ 12.30, 7.04 Hz, 1H), 3.87
(quint, J ¼ 7.32 Hz, 1H), 3.86 (s, 3H), 2.62–2.47 (m, 2H). 13C NMR
(100 MHz, CDCl3) d 157.27, 134.96, 128.76, 128.59, 127.03, 120.71,
117.54, 110.96, 78.46, 55.32, 39.15, 35.81. MS m/z (relative intensity) 221
(Mþ, 20), 180 (22), 134 (100), 119 (55), 91 (54). HRMS calcd. for
C12H15NO3 (Mþ) 221.1052, found 221.1054.
1-Nitro-2-(4-chlorophenyl)pent-4-ene (3d)[3]
Colorless oil, 1H NMR (400 MHz, CDCl3): the pattern of the aromatic protons
is AA0XX0 and is simplified as d 7.29 (dt, J ¼ 8.48, 2.64 Hz, 2H), 7.11 (dt,
J ¼ 8.48, 2.64 Hz, 2H), and the other protons are 5.67–5.55 (m, 1H), 5.07–
5.03 (m, 2H), 4.61 (dd, J ¼ 12.60, 6.48 Hz, 1H), 4.52 (dd, J ¼ 12.60,
8.92 Hz, 1H), 3.54 (quint, J ¼ 7.24 Hz, 1H), 2.44–2.39 (m, 2H). 13C NMR
(100 MHz, CDCl3) d 137.66, 133.72, 133.34, 128.98, 128.75, 118.44, 79.54,
43.10, 37.46. MS m/z (relative intensity) 225 (Mþ, tr), 178 (18), 141 (35),
138 (100), 125 (30), 103 (20).

Triallylaluminum to a,b-Unsaturated Nitroalkenes
2-(1-Nitropent-4-en-2-yl)thiophene (3e)[4]
3685
Colorless oil, 1H NMR (400 MHz, CDCl3) d 7.22 (dd, J ¼ 5.12, 1.08 Hz, 1H),
6.94 (dd, J ¼ 5.12, 3.44 Hz, 1H), 6.87 (dd, J ¼ 3.44, 1.08 Hz, 1H), 5.78–5.67
(m, 1H), 5.17–5.10 (m, 2H), 4.63 (dd, J ¼ 12.50, 6.68 Hz, 1H), 4.53 (dd,
J ¼ 12.50, 8.16 Hz, 1H), 3.91 (quint, J ¼ 7.44 Hz, 1H), 2.58–2.44 (m, 2H).
13C NMR (100 MHz, CDCl3) d 142.14, 133.65, 126.95, 125.26, 124.51,
118.72, 80.19, 39.13, 38.50. MS m/z (relative intensity) 197 (Mþ, tr), 150
(25), 110 (100), 97 (23).
1-Nitro-2-methyl-2-phenylpent-4-ene (3f)
1
Colorless oil, H NMR (400 MHz, CDCl3) d 7.47–7.34 (m, 4H), 7.28 (tt,
J ¼ 7.00, 1.60 Hz, 1H), 5.59–5.48 (m, 1H), 5.14–5.08 (m, 2H), 4.63
(d, J ¼ 11.12 Hz, 1H), 4.59 (d, J ¼ 11.12 Hz, 1H), 2.71 (dd, J ¼ 13.92,
6.40 Hz, 1H), 2.51 (dd, J ¼ 13.92, 8.04 Hz, 1H), 1.56 (s, 3H). 13C NMR
(100 MHz, CDCl3) d 142.17, 132.75, 128.69, 127.17, 126.11, 119.41, 85.28,
44.21, 42.11, 22.75. MS m/z (relative intensity) 205 (Mþ, tr), 164 (21), 118
(92), 117 (100), 91 (32). HRMS calcd. for C12H15 [(M-NO2)þ] 159.1174,
found 159.1164.
1-Nitro-2,2-diphenylpent-4-ene (3g)
Colorless oil, 1H NMR (400 MHz, CDCl3) d 7.33 (tt, J ¼ 8.32, 1.80 Hz, 4H),
7.27 (tt, J ¼ 7.20, 2.08 Hz, 2H), 7.12 (dt, J ¼ 7.20, 1.80 Hz, 4H), 5.16 (s, 2H),
5.19–5.10 (m, 1H), 3.19 (d, J ¼ 6.24 Hz, 2H). 13C NMR (100 MHz, CDCl3) d
143.50, 132.75, 128.39, 127.48, 127.11, 120.43, 81.75, 50.25, 41.10. MS m/z
(relative intensity) 267 (Mþ, tr), 226 (61), 180 (100), 165 (43). HRMS calcd.
for C17H17NO2 (Mþ) 267.1259, found 267.1265.
1-Allyl-2-nitrohexane (3h)
1
Colorless oil, H NMR (400 MHz, CDCl3) d 5.86–5.66 (m, 1H), 5.13-5.09
(m, 2H), 4.34 (dd, J ¼ 12.00, 6.80 Hz, 1H), 4.28 (dd, J ¼ 12.00, 8.40 Hz,
1H), 2.35–2.07 (m, 3H), 1.45–1.20 (m, 6H), 0.94 (t, J ¼ 6.76 Hz, 3H). 13C
NMR (100 MHz, CDCl3) d 134.36, 118.24, 79.01, 37.05, 35.52, 30.74,
28.44, 22.62, 13.89. MS m/z (relative intensity) 171 (Mþ, tr), 110 (31), 81
(75), 67(82), 55(100), 41(90). HRMS calcd. for C9H17 [(M-NO2)þ]
125.1330, found 125.1329.
1-Allyl-2-nitrocyclohexane (3i)[6b]
Colorless oil; two isomers were observed by NMR after workup of the
reaction, and these two isomers were inseparable even after the mixture was
purified by column chromatography and then by HPLC. The 1H NMR

3686
K.-H. Shen et al.
1
spectral data of the mixture of these two isomers are H NMR (400 MHz,
CDCl3) d 5.77–5.66 (m, 1H), 5.12–5.01 (m, 2H), 4.63 (quint, J = 3.84 Hz,
0.84H), 4.25 (td, J = 11.20, 4.04 Hz, 0.16H), 2.32–0.80 (m, 11H). 13C
NMR (100 MHz, CDCl3) d 135.37, 134.16, 117.80, 117.22, 90.41, 85.84,
40.26, 38.66, 36.92, 33.78, 31.94, 29.42, 27.51, 26.66, 24.69, 24.37, 22.18,
21.93. MS m/z (relative intensity) 169 (Mþ, tr), 107 (26), 93 (36), 81 (100),
79 (56), 67 (55), 41 (43).
1-Nitro-2,2-diethylpent-4-ene (3j)
1
Colorless oil, H NMR (400 MHz, CDCl3) d 5.85–5.75 (m, 1H), 5.19–5.15
(m, 2H), 4.28 (s, 2H), 2.12 (d, J ¼ 7.60 Hz, 2H), 1.36 (q, J ¼ 7.40 Hz, 4H),
0.91 (t, J ¼ 7.40 Hz, 6H). 13C NMR (100 MHz, CDCl3) d 132.62, 119.33,
80.11, 41.11, 38.04, 26.30, 7.22. MS m/z (relative intensity) 171 (Mþ, tr),
110 (53), 95 (41), 83 (73), 55 (100), 41 (46). HRMS calcd. for C9H17 [(M-
NO2)þ] 125.1330, found 125.1329.
C-(3-Ethyl-hex-1-ene)-N-allylnitrone (4j)
Colorless oil, 1H NMR (400 MHz, CDCl3) d 6.35 (s, 1H), 6.12–6.02 (m, 1H),
5.75–5.65 (m, 1H), 5.43-5.37 (m, 2H), 5.11–5.02 (m, 2H), 4.37
(d, J ¼ 6.64 Hz, 2H), 2.50 (d, J ¼ 7.48 Hz, 2H), 1.83–1.67 (m, 4H), 0.81
(t, J ¼ 7.60 Hz, 6H). 13C NMR (100 MHz, CDCl3) d 143.25, 134.46,
130.73, 121.31, 117.45, 69.51, 43.33, 36.60, 25.41, 8.28. MS m/z (relative
intensity) 195 (Mþ, tr), 105 (16), 91 (100), 77 (12), 69 (13), 55 (15). HRMS
calcd. for C12H21NO (Mþ) 195.1623, found 195.1622.
ACKNOWLEDGMENTS
Financial support by National Taiwan Normal University ORD 93-C and
National Science Council of the Republic of China is gratefully acknowl-
edged. We also thank Professor Milton S. Feather for helpful discussions
during the preparation of the manuscript.
REFERENCES
1. (a) Corey, E. J.; Estreicher, H. J. Am. Chem. Soc. 1978, 100, 6294; (b) Seebach, D.;
Colvin, E. W.; Weller, T. Chimia 1979, 33, 1; (c) Barrett, A. G. M.;
Graboski, G. G. Chem. Rev. 1986, 86, 751; (d) Rosini, G.; Ballini, R. Synthesis
1988, 833; (e) Nitroalkanes and Nitroalkenes in Synthesis Tetrahedron 1990,
46, 7313; (f) Barrett, A. G. M. Chem. Soc. Rev. 1991, 20, 95; (g) Ono, N. The
Nitro Group in Organic Synthesis; Wiley-vch: New York, 2001; (h) Padwa, A.;
Pearson, W. H. Synthetic Applications of 1,3-Dipolar Cycloaddition Chemistry
Toward Heterocycles and Natural Products; John Wiley & Sons: NJ, 2003.

Triallylaluminum to a,b-Unsaturated Nitroalkenes
3687
2. Barboni, L.; Bartoli, G.; Marcantoni, E.; Petrini, M.; Dalpozzo, R. J. Chem. Soc.,
Perkin Trans. 1 1990, 2133.
3. Bao, W.; Zheng, Y.; Zhang, Y. J. Chem. Res., Synop. 1999, 732.
4. Kumar, H. M. S.; Reddy, B. V. S.; Reddy, P. T.; Yadav, J. B. Tetrahedron Lett.
1999, 40, 5387.
5. (a) Ochiai, M.; Arimoto, J.; Jujita, E. Tetrahedron Lett. 1981, 22, 1115;
(b) Uno, H.; Fujiki, S.; Suzuki, S. Bull. Chem. Soc. Jpn. 1986, 59, 1267;
(c) Yamamoto, Y.; Nishii, S. J. Org. Chem. 1988, 53, 3597.
6. (a) Pecunioso, A.; Menicagli, R. J. Org. Chem. 1988, 53, 45; (b) Pecunioso, A.;
Menicagli, R. J. Org. Chem. 1989, 54, 2391; (c) Menicagli, R.; Malanga, C.;
Guagnano, V. Tetrahedron Lett. 1992, 33, 2867.
7. (a) Yao, C.-F.; Chen, W.-C.; Lin, Y.-M. Tetrahedron Lett. 1996, 37, 6339;
(b) Yao, C.-F.; Kao, K.-S.; Liu, J.-T.; Chu, C.-M.; Wang, Y.; Chen, W.-C.;
Lin, Y.-M.; Yan, M.-C.; Liu, J.-Y.; Chuang, C.-M.; Shiue, J.-L. Tetrahedron
1998, 54, 791; (c) Chu, C.-M.; Liu, J.-T.; Lin, W.-W.; Yao, C.-F. J. Chem. Soc.,
Perkin Trans. 1 1999, 47.
8. Shen, K.-H.; Yao, C.-F. J. Org. Chem. 2006, 71, 3980.
9. Triallylaluminum 2 was prepared according to the procedures in the following;
Komiya, S. Synthesis of Organometallic Compounds; John Wiley & Sons:
New York, 1997.
10. The concentration of triallylaluminum 2 was determined by the following
methods; (a) Gilman, H.; Haubein, A. H. J. Am. Chem. Soc. 1944, 66, 1515;
(b) Bergbreiter, D. E.; Pendergrass, E. J. Org. Chem. 1981, 46, 219;
(c) Bowen, M. E.; Aavula, B. R.; Mash, E. A. J. Org. Chem. 2002, 67, 9087.
11. (a) Paley, R. S.; Snow, S. R. Tetrahedron Lett. 1990, 31, 5853; (b) Rainier, J. D.;
Cox, J. M. Org. Lett. 2000, 2, 2707; (c) Allwein, S. P.; Cox, J. M.; Howard, B. E.;
Johnson, H. W. B.; Rainier, J. D. Tetrahedron 2002, 58, 1997.
12. (a) Lin, W.-W.; Jang, Y.-J.; Wang, Y.; Liu, J.-T.; Hu, S.-R.; Wang, L.-Y.;
Yao, C.-F. J. Org. Chem. 2001, 66, 1984; (b) Jang, Y.-J.; Lin, W.-W.;
Shih, Y.-K.; Liu, J.-T.; Hwang, M.-H.; Yao, C.-F. Tetrahedron 2003, 59, 4979;
(c) Ohta, H.; Kobayashi, N.; Ozaki, K. J. Org. Chem. 1989, 54, 1802.
13. Bordwell, F. G.; Garbish, E. W. J. J. Org. Chem. 1962, 27, 3049.