Novel synthesis of alkenes via triethylaluminum-induced free radical reactions of alkyl iodides and β-nitrostyrenes

Article abstract of DOI:10.1016/S0040-4039(01)00519-6

Reactions of (E)-β-nitrostyrenes 1 with triethylaluminum (Et₃Al) 2 and alkyl iodide (RI) 3, 4, or 5 in the presence of benzoyl peroxide in diethyl ether solution at room temperature to give 60-100% of the different (E)-alkenes 6, 7, or 8. Under

Full text of DOI:10.1016/S0040-4039(01)00519-6

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 3613–3615
Novel synthesis of alkenes via triethylaluminum-induced free
radical reactions of alkyl iodides and b-nitrostyrenes
Jing-Yuan Liu, Ju-Tsung Liu and Ching-Fa Yao*
Department of Chemistry, National Taiwan Normal University 88, Sec. 4, Tingchow Road, 116 Taipei, Taiwan, ROC
Received 22 February 2001; revised 19 March 2001; accepted 23 March 2001
Abstract—Reactions of (E)-b-nitrostyrenes 1 with triethylaluminum (Et3Al) 2 and alkyl iodide (RI) 3, 4, or 5 in the presence of
benzoyl peroxide in diethyl ether solution at room temperature to give 60–100% of the different (E)-alkenes 6, 7, or 8. Under
similar conditions, 95% of 1-adamantyl-2-(4-methoxyphenyl)ethene 10 or 80% of 1-(4-oxoadamantyl)-2-(4-methoxyphenyl)ethene
12 also can be easily prepared by using 1-iodoadamantane 9 or 5-iodo-2-adamantanone 11 and 2. © 2001 Elsevier Science Ltd.
All rights reserved.
Nitro olefins are useful intermediates in organic synthe-
sis and are important structural units which can be used
as starting materials for many classes of compounds.1
Reactions of b-nitrostyrenes with dialkylzinc or
organozinc halides,2 t-BuHgX/KI,3 organomanganese,4
Reactions of trialkylaluminum or triorganoaluminum–
ether complexes with a,b-unsaturated nitroalkenes to
generate high yields of 1,4-alkylated products have been
reported by Pecunioso and Menicagli.8 Our previous
study also found that medium to high yields of alkenes
and/or hydroximoyl chloride can be generated when
(E)-b-nitrostyrenes 1 reacts with triethylaluminum or
diethylaluminum chloride in a diethyl ether solution
under refluxing conditions in the presence of a trace of
oxygen in the nitrogen or by photolysis in the presence
of benzoyl peroxide as a radical initiator or in the
presence of MgCl2 as the Lewis acid after the solution
was worked-up with ice-cold concentrated hydrochloric
trialkylgallium,5
organoborane,6
and
Grignard
reagents,7 respectively, to generate alkenes and/or
nitroalkanes or halooximes have been reported. All
these results indicate that b-nitrostyrenes can react with
different organometallic reagents to generate different
products under different conditions and workup proce-
dures and the reaction mechanism is proposed to be a
free radical and/or an ionic reaction.1–7
Ar
H
R
Ar
H
RI
Et3Al
+
+
H
H
NO2
3, 4, 5
7
6, 7, 8
1
2
(1)
6
8
a: Ar = Ph, R = i-Pr
a: Ar = Ph, R = c-C6H11
a: Ar = Ph, R = t-Bu
b: Ar = 4-MeOC6H4, R = c-C6H11
b: Ar = 4-MeOC6H4, R = t-Bu
c: Ar = 4-ClC6H4, R = t-Bu
b: Ar = 4-MeOC6H4, R = i-Pr
c: Ar = 4-ClC6H4, R = i-Pr
d: Ar = 2-thienyl, R = i-Pr
c: Ar = 4-ClC6H4, R = c-C6H11
d: Ar = 2-thienyl, R = c-C6H11
e: Ar = 2-furyl, R = c-C6H11
d: Ar = 2-thienyl, R = t-Bu
e: Ar = 2-furyl, R = t-Bu
e: Ar = 2-furyl, R = i-Pr
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00519-6

3614
J.-Y. Liu et al. / Tetrahedron Letters 42 (2001) 3613–3615
acid.9a The mechanism of the generation of the alkenes
is proposed to be free radical substitution1–6 and the
generation of the hydroximoyl chloride is proposed to
be ionic reaction that is similar to literature proposed.7,8
Table 1. Reaction of (E)-b-nitrostyrenes 1 (1 equiv.) with
RI (6–20 equiv.), Et3Al (2–6 equiv.), and benzoyl peroxide
(2 equiv.) in diethyl ether at room temperature
Entry
1
RI (equiv.)
Product
Yield (%)a
Triethylborane10,11 and diethylzinc2a,11d,e,12 not only can
be served as one of the methods for the generation of
radical species but also can be used as an effective
radical initiator to generate different radicals by reac-
tion of triethylborane or diethylzinc with alkyl halides
in the presence of tin hydride under mild conditions.
On the basis of literature reports,9 we wish to report an
effective method by combining our previous study9a
and the literature method,9b to synthesize different alke-
nes by reaction of b-nitrostyrenes with different radi-
cals, prepared from alkyl iodides and triethylaluminum
in the presence of benzoyl peroxide as a radical initia-
tor, in diethyl ether solution at room temperature.
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
1a
1b
1c
1d
1e
3 (20)
3 (20)
3 (20)
3 (20)
3 (20)
4 (20)
4 (20)
4 (20)
4 (20)
4 (20)
5 (6)
6a
6b
6c
6d
6e
7a
7b
7c
7d
7e
8a
8b
8c
8d
8e
96
99
100
98
100
99
99
97
98
90
79
72
60
77
70
9
10
11
12
13
14
15
5 (6)
5 (6)
5 (6)
5 (6)
At room temperature, (E)-b-nitrostyrenes 1a–e (a: Ar=
Ph, b: Ar=4-MeOC6H4, c: Ar=4-ClC6H4, d: Ar=2-
thienyl, e: Ar=2-furyl) reacted with triethylaluminum 2
and alkyl iodides RI such as isopropyl iodide 3, cyclo-
hexyl iodide 4, or tert-butyl iodide 5 in diethyl ether
solution in the presence of benzoyl peroxide at room
temperature to generate 60–100% of 1-aryl-2-alkyl-
ethenes 6, 7, or 8 within 1.5–2 h (Eq. (1) and Table 1).
All spectral data indicate that the alkenes have (E)
configuration (Jtrans=16.0–16.2 Hz for vinyl hydrogen)
after the mixture was purified by flash column chro-
matography and most of the spectral data of the known
products are also consistent with literature reports.2,8
Gas chromatography and proton NMR analysis of the
crude mixture also found that only the (E) isomer and
none of the (Z) isomer could be detected.
a NMR yields.
the corresponding Heck-type coupling product (E)-1-
adamantyl-2-arylethene in Similarly,
15–41%.14
Yamataka and coworkers have also reported that both
(Z)- and (E)-1-adamantyl-2-arylethene mixture can be
prepared from the Wittig reaction of substituted ben-
zaldehydes with (1-adamantylmethylidene)triphenyl-
phosphorane.15 After observation of Eq. (1) and Table
1, we applied this method to prepare similar product by
reaction of 1b with 1-iodoadamantane 9 and 2 under
similar conditions. To our surprise, not only high yields
(95%) of the expected products 1-adamantyl-2-(4-
methoxyphenyl)arylethene 10 but also only the trans
isomer was generated at room temperature (Eq. (2)).
This result indicates that adamantyl radical can also be
generated by using 9 and 2 at room temperature in the
presence of benzoyl peroxide. Similarly, 12 can also be
isolated in 80% yield when 5-iodo-2-adamantone 11
was reacted with 1b and 2 under similar conditions (Eq.
(3)).
Tashtoush and Sustmann have reported that alkyl radi-
cals including 1-adamantyl radical and aryl radical can
be generated by the reduction of alkyl or aryl halides
with (ethylenediamine)chromium(II) complexes in dry
dimethylformamide.13 Bra¨se et al. also have reported
the palladium–catalyzed reaction of 1-bromoadaman-
tane with styrene and donor-substituted styrenes give
In conclusion, our study found that the triethylalu-
minum can serve as an initiator to induce radical
MeO
H
+
Et3Al
+
H
NO2
(2)
(3)
I
OMe
10 (95%)
1b
2
9
O
MeO
O
H
+
Et3Al
+
H
NO2
I
OMe
12 (80%)
1b
2
11

J.-Y. Liu et al. / Tetrahedron Letters 42 (2001) 3613–3615
3615
reactions to prepare (E)-alkenes by using (E)-b-
nitrostyrenes, alkyl iodide RI, and triethylaluminum in
the presence of benzoyl peroxide in diethyl ether solu-
tion at room temperature. Further study about the
reaction mechanism and the application of this method-
ology to synthesize other compounds will be reported in
the future.
Buckley, G. D.; Ellery, E. J. J. Chem. Soc. 1947, 1497; (d)
Ashwood, M. S.; Bell, L. A.; Houghton, P. G.; Wright, S.
H. B. Synthesis 1988, 379; (e) Yao, C.-F.; Chen, W.-W.;
Lin, Y.-M. Tetrahedron Lett. 1996, 37, 6399; (f) Yao,
C.-F.; Kao, K.-H.; Liu, J.-T.; Chu, C.-M.; Wang, Y.;
Chen, W.-C.; Lin, Y.-M.; Lin, W.-W.; Yan, M.-C.; Liu,
J.-Y.; Chuang, M.-C.; Shiue, J.-L. Tetrahedron 1998, 54,
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C.-F. Tetrahedron 1999, 55, 7115.
Acknowledgements
8. (a) Pecunioso, A.; Menicagli, R. Tetrahedron 1987, 43,
5411; (b) Pecunioso, A.; Menicagli, R. J. Org. Chem.
1988, 53, 45; (c) Pecunioso, A.; Menicagli, R. J. Org.
Chem. 1989, 54, 2391.
9. (a) Chu, C.-M.; Liu, J.-T.; Lin, W.-W.; Yao, C.-F. J.
Chem. Soc., Perkin Trans. 1 1999, 47; (b) Maruoka, K.;
Sano, H.; Fukutani, Y.; Yamamoto, H. Chem. Lett.
1985, 1689.
Financial support of this work by the National Science
Council of the Republic of China is gratefully
acknowledged.
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