High intensity ultrasound-assisted reduction of sterically demanding nitroaromatics

Article abstract of DOI:10.1016/j.tetlet.2005.02.038

Sterically demanding nitroaromatic compounds have been prepared and reduced to their corresponding amines with high intensity ultrasound using hydrazine in the presence of a Raney nickel catalyst. These reactions were dependent on catalyst quality, solven

Full text of DOI:10.1016/j.tetlet.2005.02.038

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 2469–2473
High intensity ultrasound-assisted reduction of sterically
demanding nitroaromatics
Georgios A. Heropoulos,* Spyros Georgakopoulos and Barry R. Steele
Institute of Organic and Pharmaceutical Chemistry, National Hellenic Research Foundation, Vas. Constantinou Avenue 48,
Athens 116 35, Greece
Received 11 January 2005;revised 2 February 2005;accepted 8 February 2005
Abstract—Sterically demanding nitroaromatic compounds have been prepared and reduced to their corresponding amines with high
intensity ultrasound using hydrazine in the presence of a Raney nickel catalyst. These reactions were dependent on catalyst quality,
solvent and ultrasonic amplitude and, in comparison to their silent reactions, proceeded much faster and afforded higher yields.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
of the alkyl groups.7 This is particularly so when using
a nitric acid/sulfuric acid nitration mixture. These com-
plications can be largely avoided using nitric acid in ace-
tic anhydride and we have applied this procedure to
hydrocarbons 1a–7a.
Sterically demanding molecules are of great interest in
many applications where control of the spatial environ-
ment is an important consideration,1–3 while an addi-
tional useful property often associated with the
presence of bulky organic groups is increased lipophilic-
ity, which makes for more amenable handling with or-
ganic solvents.4 We have developed a simple procedure
for the production of certain crowded aromatic mole-
cules using a catalytic system for the clean addition of
ethylene to a series of alkylaromatics,5 and we are now
actively developing the chemistry of these compounds
further.6 We report here the preparation of a series of
nitroaromatics and their reduction to the corresponding
anilines. The latter should be versatile starting materials
for the preparation of other aromatics and, in particu-
lar, of bulky Schiff bases which are currently of great
interest for their potential applications to catalytic pro-
cesses of great industrial importance such as olefin poly-
merisation and metathesis, asymmetric catalysis and
epoxide–carbon dioxide co-polymerisation.2
Fuming nitric acid gave the best results, especially with
the more crowded substrates and side reactions were sig-
nificant only for the nitrations of 4a, 6a and 7a where
cleavage of an alkyl group occurred to an extent of
about 50% (Eqs. 1, 2).8 It seems that two factors com-
bine to make the cleavage of an alkyl group significant:
(1) when this group is ortho or para (or both) to another
alkyl group and (2) when the expected position for nitra-
tion is ortho to an alkyl group. The side reaction can be
minimised if the reaction temperature is kept below
10 ꢁC. The by-products could be readily separated from
the desired product by recrystallisation from hexane.
2. Results and discussion
The nitration of crowded aromatic molecules is often
problematic due to competing electrophilic substitution
Keywords: Bulky molecules;Ultrasound;Nitroaromatics;Reduction;
Nitration;Anilines.
*
Corresponding author. Tel.: +30 2107273873;fax: +30 2107273877;
e-mail: gherop@eie.gr
0040-4039/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.02.038

2470
G. A. Heropoulos et al. / Tetrahedron Letters 46 (2005) 2469–2473
Table 2. Yields of anilines (1c–7c) from reduction of nitroaromatics
(1b–7b)a
The orientation of the nitration was confirmed in all
1
cases by H and 13C NMR measurements. The results
for the nitrations are presented in Table 1.
Starting
material
Product
Heatingb
Ultrasoundc
Yieldd
(%)
Time
(h)
Yieldd
(%)
Time
(min)
1b
2b
3b
4b
5b
7b
1c
2c
3c
4c
5c
7c
97
95
96
91
84
77
2.0
2.5
2.5
2.5
20
96
97
95
93
90
93
5
7
ð1Þ
7
7
10
15
20
a Compound 1c has been reported previously.9,14 NMR data for all
compounds are provided below.
b With N2H4ÆH2O and catalyst Ni (Raney) in methanol with heating
only (45–50 ꢁC).
c With N2H4ÆH2O and catalyst Ni (Raney) in methanol with sonica-
tion. Temperature maintained at 45–50 ꢁC.
d By GC.
ð2Þ
Raney nickel catalysed hydrazine reduction of nitroaro-
matics is a generally useful procedure,10 and in our
hands gave satisfactory results for the less hindered
nitroaromatics reported here, but highly variable results
for the more hindered compounds, 5b and 7b, which
were of particular interest to us for our further work.11
served for sonochemical reactions in comparison to the
silent ones.11 In comparative experiments methanol was
used as solvent and the temperature was kept between
45 ꢁC and 50 ꢁC (Eq. 3). t-BuOH and toluene were also
tested as solvents but the results were unsatisfactory.
With ethanol no reaction occurred even after 3 h with
heating or 1 h with sonication for compound 7b,
although for 1b–4b, the results were similar for both
methods.
High energy techniques (ultrasound, microwaves) have
found increasing interest in synthetic organic chemistry,
showing good results for reactions that otherwise were
practically impossible, giving pure products in good
yield and in short reaction times.12 Ultrasound tech-
niques have been applied to many reactions involving
metals,13 and we therefore examined the use of high
intensity ultrasound for the reduction of our nitrocom-
pounds. These reactions were dependent on solvent, cat-
alyst quality and ultrasound intensity dependent and, in
comparison to their silent reactions, proceeded much
faster and afforded higher yields (Table 2;due to its
somewhat lower purity, compound 6b was not examined
in this series of experiments). In heterogeneous reactions
the most important action by sonication is erosion,
which implies the removal of impurities and oxide layers
together with pitting of metal surfaces. This procedure is
believed to remove reactive intermediates away from the
metal surface and keep the metal clean and active during
the reaction, thus accounting for the improvements ob-
ð3Þ
Another very important parameter is the catalyst. The
quality of the Raney nickel was found to be very impor-
tant for good yields for the more difficult reductions and
although care was taken to prepare and store it the same
way to maintain consistent reactivity, it was found to
vary from batch to batch. The yields presented in Table
2 are the highest that we observed.
From Table 2 one can see that, for both methods, in the
case of molecules of low steric demand (1b–4b), the
yields are similar although the reaction times differ
greatly, from 5 min with ultrasound to 2 h with heating.
In contrast, for the compounds with the greatest steric
demand, (5b and 7b), not only are the reaction times
very short with ultrasound, but the yields are also
higher.
Table 1. Yields of nitroaromatic compounds (1b–7b)a
Alkylbenzene
Nitrocompound
Yield (isolated)b (%)
1a
2a
3a
4a
5a
6a
7ac
1b
2b
3b
4b
5b
6b
7b
82
95
87
48
62
66b
40
In order to tackle the problem of reproducibility, we
also tried Ni–Al alloy as a catalyst under the same con-
ditions,15 since, if successful, this should have excellent
reproducibility being a commercial product. The results,
however, were very poor (6% for 7c). We also tried a
ꢀgreen chemistryꢁ approach, substituting the organic sol-
vent with water, but no reaction occurred. Using Ni–Al
alloy and hydrazine hydrate with ultrasound (10 min),
we did, however, manage to reduce nitrobenzene itself
to aniline in 65% yield in water and in 82% in methanol.
a Prepared from alkyl-benzenes (1a–7a) with fuming nitric acid in 1:1
v/v acetic anhydride–acetic acid at 10 ꢁC.8 Compound 1b has been
reported previously.9 NMR data for all compounds are provided
below.
b All compounds except for 6b could be obtained in >97% purity by
distillation or recrystallisation. Compound 6b could not be com-
pletely freed of by-products and was obtained with 90% purity.
c CHCl3 was also added to aid dissolution of the starting material.

G. A. Heropoulos et al. / Tetrahedron Letters 46 (2005) 2469–2473
2471
Table 3. Product yield dependence on ultrasound intensity
1H, CH), 7.27 (d, J = 8.9 Hz, 2H, CH), 8.12 (d,
J = 8.9 Hz, 2H, CH); 13C NMR (75 MHz, CDCl3): d
12.0, 29.0, 49.7, 123.5, 128.5, 146.3, 154.0;HR-MS
(EI) m/z calcd for C11H15NO2: 193.1103. Found
193.1099;IR (cm ꢀ1) 1516 (vs), 1346 (vs).
a
Yield (%)
Product
Sonication
time (min)
Yield
ratio
Ab
Bc
1c
2c
3c
4c
5c
7c
5
7
21
17
18
15
13
7
96
97
95
93
90
93
1:4.5
1:5.7
1:5.3
1:6.2
1:6.9
1:13.3
7
3.2. 1,2-Di(1-ethylpropyl)-4-nitrobenzene, 2b
7
10
15
1H NMR (300 MHz, CDCl3) d 0.76 (m, 12H, CH3), 1.54
(m, 4H, CH2), 1.69 (m, 4H, CH2), 2.88 (m, 2H, CH), 7.29
(d, J = 8.7 Hz, 1H, CH), 7.96 (d, J = 8.7 Hz, 1H, CH),
8.00 (s, 1H, CH); 13C NMR (75 MHz, CDCl3): d 12.3,
29.2, 41.5, 41.9, 112.6, 113.3, 126.7, 134.6, 143.6, 145.2;
HR-MS (EI) m/z calcd for C16H25NO2: 263.1885. Found
263.1882;IR (cm ꢀ1) 1516 (vs), 1351 (vs).
a By GC.
b Ultrasound intensity 30% of maximum, temperature 45–50 ꢁC.
c Ultrasound intensity 90% of maximum, temperature 45–50 ꢁC.
Ammonium chloride in water has been used as an alter-
native to hydrazine hydrate but under our conditions it
gave only a low yield (8% aniline).16 Although not suit-
able for our substrates, water has many advantages as a
solvent and so we also examined its possible use for less
demanding substrates. Indeed 1-nitronaphthalene was
reduced using a catalytic amount of Raney nickel and
an excess of hydrazine hydrate to the corresponding
amine in water with high intensity ultrasound in a 97%
yield.
3.3. 2,4-Di(1-ethylpropyl)-1-nitrobenzene, 3b
Mp 27 ꢁC; 1H NMR (300 MHz, CDCl3) d 0.76 (m, 12H,
CH3), 1.58 (m, 4H, CH2), 1.71 (m, 4H, CH2), 2.38 (m,
1H, CH), 3.02 (m, 1H, CH), 7.06 (d, J = 8.9 Hz, 1H,
CH), 7.09 (s, 1H, CH), 7.63 (d, J = 8.9 Hz, 1H, CH);
13C NMR (75 MHz, CDCl3): d 11.7, 11.9, 28.9, 42.1,
49.7, 123.7, 125.5, 127.4, 139.5, 149.6, 150.7;HR-MS
(EI) m/z calcd for C16H25NO2: 263.1885. Found
263.1881;IR (cm ꢀ1) 1526 (vs), 1366 (vs).
Another parameter that was considered was the intensity
of sonication, although at this point it must be men-
tioned that the measurement of the absorbed acoustic
power in a liquid is something that has not yet been
defined.17 Experiments performed with different typical
intensities (30% and 90% of the max), but under other-
wise identical conditions, led to markedly different reac-
tion yields. A complete comparison of the results is listed
in Table 3. Although the intensities are in 1:3 ratios (30%
and 90%, respectively), the corresponding yields are in
ratios between 1:4.6 for the least crowded (1c) and
1:13.3 for the most bulky (7c). It is clear that the higher
intensity influences all the reactions and this beneficial ef-
fect is most evident for the most crowded molecules.
3.4. 1,4-Di(1-ethylpropyl)-2-nitrobenzene, 4b
Mp 42 ꢁC; 1H NMR (300 MHz, CDCl3) d 0.75 (t,
J = 8.9 Hz, 6H, CH3), 0.80 (t, J = 8.9 Hz, 6H, CH3),
1.55 (m, 4H, CH2), 1.70 (m, 4H, CH2), 2.37 (m, 1H,
CH), 2.89 (m, 1H, CH), 7.27 (s, 1H, CH), 7.28 (d,
J = 2.3 Hz, 1H, CH), 7.40 (d, J = 2.3 Hz, 1H, CH);
13C NMR (75 MHz, CDCl3): d 11.9, 28.9, 29.0, 42.2,
49.0, 65.0, 122.3, 127.6, 131.6, 136.9, 144.7, 151.6;HR-
MS (EI) m/z calcd for C16H25NO2: 263.1885. Found
263.1880;IR (cm ꢀ1) 1526 (vs),1356 (vs).
3.5. 1,3,5,-Tri(1-ethylpropyl)-2-nitrobenzene, 5b
All the compounds reported here have been character-
1
ised by H and 13C NMR and gave spectra consistent
Mp 38 ꢁC; 1H NMR (300 MHz, CDCl3) d 0.73 (t,
J = 7.5 Hz, 18H, CH3), 1.52 (m, 6H, CH2), 1.67 (m,
6H, CH2), 2.26 (m, 3H, CH), 6.84 (s, 2H, CH); 13C
NMR (75 MHz, CDCl3): d 11.7, 11.9, 29.1, 29.3, 43.6,
49.6, 123.6, 135.9, 147.4, 151.9;HR-MS (EI) m/z caꢀlc1d
with the proposed structures.
In conclusion, we have synthesised a series of bulky
nitroaromatic compounds, which were reduced to the
corresponding anilines using hydrazine hydrate in the
presence of Raney nickel as catalyst with the assistance
of high intensity ultrasound. Parameters such as the
catalyst and solvent were examined. It has been
demonstrated that the application of high intensity
ultrasound is very beneficial for these reductions to pro-
ceed in good yield and in short reaction times in com-
parison with classical methods. Further development
of the chemistry of these compounds is in progress.
for C21H35NO2: 333.2668. Found 333.2664;IR (cm
1526 (vs), 1381 (vs).
)
3.6. 1,2,4,-Tri(1-ethylpropyl)-5-nitrobenzene, 6b
1H NMR (300 MHz, CDCl3) d 0.80 (m, 18H, CH3), 1.56
(m, 6H, CH2), 1.70 (m, 6H, CH2), 2.85 (m, 2H, CH),
3.03 (m, 1H, CH), 7.09 (s, 1H, CH), 7.49 (s, 1H, CH);
13C NMR (75 MHz, CDCl3): d 11.8, 28.9, 41.8, 121.4,
125.5, 136.4, 143.2, 149.3;HR-MS (EI) m/z calcd for
C21H35NO2: 333.2668. Found 333.2663;IR (cm
1521 (vs), 1345 (vs).
ꢀ1
)
3. Data for all compounds
3.1. 1-(1-Ethylpropyl)-4-nitrobenzene, 1b
3.7. 1,2,4,5-Tetra(1-ethylpropyl)-3-nitrobenzene, 7b
1H NMR (300 MHz, CDCl3) d 0.72 (t, J = 7.5 Hz, 6H,
CH3), 1.52 (m, 2H, CH2), 1.70 (m, 2H, CH2), 2.43 (m,
Mp 157 ꢁC; 1H NMR (300 MHz, CDCl3) d 0.81 (m,
24H, CH3), 1.52 (m, 4H, CH2), 1.71 (m, 12H, CH2),

2472
G. A. Heropoulos et al. / Tetrahedron Letters 46 (2005) 2469–2473
2.20 (m, 2H, CH), 2.91 (m, 2H, CH), 7.08 (s, 1H, CH);
13C NMR (75 MHz, CDCl3): d 12.0, 12.9, 28.1, 29.0,
42.3, 45.8, 126.9, 129.7, 144.2, 156.3;HR-MS (EI) m/z
calcd for C26H45NO2: 403.3450. Found 403.3446;IR
(cmꢀ1) 1526 (vs), 1381 (vs).
3.13. 2,3,5,6-Tetra(1-ethylpropyl)phenylamine, 7c
Mp 70 ꢁC; 1H NMR (300 MHz, CDCl3) d 0.78 (t,
J = 7.3 Hz, 12H, CH3), 0.87 (t, J = 7.3 Hz, 12H, CH3),
1.58 (m, 8H, CH2), 1.79 (m, 8H, CH2), 2.79 (m, 2H,
CH), 3.00 (m, 2H, CH), 3.47 (s, 2H, NH2), 6.38 (s,
1H, CH); 13C NMR (75 MHz, CDCl3): d 12.0, 13.4,
26.2, 28.8, 41.1, 42.7, 125.3, 141.5, 143.6;HR-MS (EI)
m/z calcd for C26H47N: 373.3708. Found 373.3703;IR
(cmꢀ1) 3500 (m), 3424 (w).
3.8. 4-(1-Ethylpropyl)phenylamine, 1c
1H NMR (300 MHz, CDCl3) d 0.87 (t, J = 7.3 Hz,
3H, CH3), 0.88 (t, J = 7.3 Hz, 3H, CH3), 1.59 (m, 2H,
CH2), 1.72 (m, 2H, CH2), 2.28 (m, 1H, CH), 3.59 (s,
2H, NH2), 6.71 (d, J = 7.2 Hz, 2H, CH), 7.00 (d,
J = 7.2 Hz, 2H, CH); 13C NMR (75 MHz, CDCl3): d
12.3, 29.5, 48.9, 115.3, 128.6, 135.9, 144.3;HR-MS
(EI) m/z calcd for C11H17N: 163.1361. Found
163.1359;IR (cm ꢀ1) 3440 (m), 3354 (m), 3219 (w).
Acknowledgments
This work was supported by the Greek General Secre-
tariat of Research and Technology. We would like to
thank Dr. A. Nikolopoulos for advice and assistance
in setting up the ultrasonic apparatus.
3.9. 3,4-Di(1-ethylpropyl)phenylamine, 2c
1H NMR (300 MHz, CDCl3) d 0.83 (m, 12H, CH3), 1.53
(m, 4H, CH2), 1.65 (m, 4H, CH2), 2.74 (m, 2H, CH),
3.45 (br s, 2H, NH2), 6.52 (m, 2H, CH), 6.95 (m, 1H,
CH); 13C NMR (75 MHz, CDCl3): d 12.3, 29.2, 41.4,
41.9, 112.6, 113.2, 126.6, 134.6, 143.6, 145.2;HR-MS
(EI) m/z calcd for C16H27N: 233.2143. Found
233.2140;IR (cm ꢀ1) 3450 (m), 3359 (m), 3219 (w).
References and notes
1. Tokitoh, N.;Okazaki, R. Coord. Chem. Rev. 2000, 210,
251–277;Power, P. P. Chem. Commun. 2003, 2091–2101;
Toyota, K.;Kawasaki, S.;Yoshifuji, M. J. Org. Chem.
2004, 69, 5065–5070;Weidenbruch, M. Organometallics
2003, 22, 4348–4360;Kobayashi, K.;Takagi, N.;Nagase,
S. Organometallics 2001, 20, 234–236;Dutan, C.;Shah, S.;
Smith, R. C.;Choua, S.;Berclaz, T.;Geoffroy, M.;
Protasiewicz, J. D. Inorg. Chem. 2003, 42, 6241–6251;Hu,
Y. H.;Su, M. D. Chem. Phys. Lett. 2003, 378, 289–298.
2. Catsoulacos, D. P.;Steele, B. R.;Heropoulos, G. A.;
Micha-Screttas, M.;Screttas, C. G. Tetrahedron Lett.
2003, 44, 4575–4578;Connor, E. F.;Younkin, T. R.;
Henderson, J. I.;Waltman, A. W.;Grubbs, R. H. Chem.
Commun. 2003, 2272–2273;Gonsalvi, L.;Gaunt, J. A.;
Adams, H.;Castro, A.;Sunley, G. J.;Haynes, A.
Organometallics 2003, 22, 1047–1054;Dove, A. P.;Gib-
son, V. C.;Hormnirun, P.;Marshall, E. L.;Segal, J. A.;
White, A. J. P.;Williams, D. J. Dalton Trans. 2003, 3088–
3097;Jenkins, J. C.;Brookhart, M. J. Am. Chem. Soc.
2004, 126, 5827–5842;Roder, J. C.;Meyer, F.;Kaifer, E.;
Pritzkow, H. Eur. J. Inorg. Chem. 2004, 1646–1660;
Krajete, A.;Steiner, G.;Kopacka, H.;Ongania, H. K.;
Wurst, K.;Kristen, M. O.;Preishuber-Pflugl, P.;Bildstein,
B. Eur. J. Inorg. Chem. 2004, 1740–1752;Axenov, K. V.;
Kotov, V. V.;Klinga, M.;Leskela, M.;Repo, T. Eur. J.
Inorg. Chem. 2004, 695–706;van der Vlugt, J. T.;Hewat,
A. C.;Neto, S.;Sablong, R.;Mills, A. M.;Lutz, M.;Spek,
A. L.;Muller, C.;Vogt, D. Adv. Synth. Catal. 2004, 346,
993–1003.
3. Groysman, S.;Segal, S.;Goldberg, I.;Kol, M.;Goldsch-
midt, Z. Inorg. Chem. Commun. 2004, 7, 938–941;Ham-
ilton, C. W.;Laitar, D. S.;Sadighi, J. P. Chem. Commun.
2004, 1628–1629;Roder, J. C.;Meyer, F.;Kaifer, E.;
Pritzkow, H. Eur. J. Inorg. Chem. 2004, 1646–1660;
Volꢁeva, V. B.;Karmilov, A. Y.;Belostotskaya, I. S.;
Komissarova, N. L.;Prokof ꢁev, A. I. Polym. Sci. A 2004,
46, 264–269;Shivanyuk, A.;Saadioui, M.;Broda, F.;
Thondorf, I.;Vysotsky, M. O.;Rissanen, K.;Kolehmai-
nen, E.;Bohmer, V. Chem. Eur. J. 2004, 10, 2138–2148.
4. Siraki, A. G.;Chan, T. S.;O ꢁBrien, P. J. Toxicol. Sci.
2004, 81, 148–159;Seifert, S.;Kunstler, J. U.;Schiller, E.;
Pietzsch, H. J.;Pawelke, B.;Bergmann, R.;Spies, H.
Bioconjugate Chem. 2004, 15, 856–863;Durand, G.;
Polidori, A.;Ouari, O.;Tordo, P.;Geromel, V.;Rustin,
P.;Pucci, B. J. Med. Chem. 2003, 46, 5230–5237;Kara-
3.10. 2,4-Di(1-ethylpropyl)phenylamine, 3c
1H NMR (300 MHz, CDCl3) d 0.82 (m, 12H, CH3), 1.6
(m, 8H, CH2), 2.16 (m, 1H, CH), 2.49 (m, 1H, CH),
3.07 (br s, 2H, NH2), 6.65 (d, J = 7.5 Hz, 1H, CH),
6.76 (d, J = 7.5 Hz, 1H, CH), 7.04 (d, J = 7.5 Hz, 1H,
CH); 13C NMR (75 MHz, CDCl3): d 11.9, 12.2, 27.6,
29.2, 41.9, 49.0, 123.1, 126.5, 129.5, 136.1, 142.1,
146.4;HR-MS (EI) m/z calcd for C16H27N: 233.2143.
Found 233.2138;IR (cm ꢀ1) 3465 (m), 3374 (m), 3219
(w).
3.11. 2,5-Di(1-ethylpropyl)phenylamine, 4c
1H NMR (300 MHz, CDCl3) d 0.83 (t, J = 7.3 Hz, 6H,
CH3), 0.87 (t, J = 7.3 Hz, 6H, CH3), 1.69 (m, 8H,
CH2), 2.22 (m, 1H, CH), 2.47 (m, 1H, CH), 3.65 (br s,
2H, NH2), 6.49 (s, 1H, CH), 6.60 (d, J = 7.7 Hz, 1H,
CH), 6.98 (d, J = 7.7 Hz, 1H, CH); 13C NMR
(75 MHz, CDCl3): d 12.0, 12.3, 27.9, 29.3, 41.8, 49.4,
115.6, 118.8, 126.5, 127.4, 143.8, 144.0;HR-MS (EI)
m/z calcd for C16H27N: 233.2143. Found 233.2139;IR
(cmꢀ1) 3470 (m), 3379 (m), 3219 (w).
3.12. 2,4,6-Tri(1-ethylpropyl)phenylamine, 5c
1H NMR (300 MHz, CDCl3) d 0.73 (t, J = 7.3 Hz, 6H,
CH3), 0.81 (t, J = 7.3 Hz, 12H, CH3), 1.61 (m, 12H,
CH2), 2.16 (m, 1H, CH), 2.50 (m, 2H, CH), 3.39 (br s,
2H, NH2) 6.61 (s, 2H, CH); 13C NMR (75 MHz,
CDCl3): d 11.8, 12.1, 27.8, 42.2, 49.2, 123.3, 129.6,
135.1, 139.9;HR-MS (EI) m/z calcd for C21H37N:
303.2926. Found 303.2922;IR (cm ꢀ1) 3480 (m), 3394
(w), 3219 (vw).

G. A. Heropoulos et al. / Tetrahedron Letters 46 (2005) 2469–2473
2473
nikolopoulos, G.;Batis, C.;Pitsikalis, M.;Hadjichristidis,
N. Macromol. Chem. Phys. 2003, 204, 831–840;Blum, P.;
Mohr, G. J.;Matern, K.;Reichert, J.;Spichiger-Keller, U.
E. Anal. Chim. Acta 2001, 432, 269–275.
11. Sonication experiments were carried out in a 250 mL
sonochemical reaction vessel fitted with a thermometer, a
reflux condenser and probe (length 254 mm, diameter
13 mm) and controlled by a 400 W ultrasonic processor
Sonics & Materials. This processor allows the ultrasonic
vibrations at the probe (titanium alloy) tip to be set at 90%
and 30% amplitude. The system was operated in the non-
pulse mode. In a typical reaction 0.403 g (1.0 mmol) of 7b
and 1.0 mL of N2H4ÆH2O and a catalytic amount (ca.
0.15 mmol) of Raney nickel were sonicated in 30 mL of
absolute MeOH at 45–50 ꢁC for 15 min. CH2Cl2 was added
after sonication and the whole reaction mixture was filtered
through Celite. The filtrate was washed three times with
30 mL of water, dried over Na2SO4 and evaporated. The
product was analysed by GC and GC-MS;The compar-
ative silent, thermal reactions were carried out using the
same quantities of materials at 40–50 ꢁC for the times
indicated in Table 2. Work-up and analysis as above.
12. Mason, T.;Lorimer, J. Applied Sonochemistry: Uses
of Power Ultrasound in Chemistry and Processing;
Wiley, 2002.
5. Steele, B. R.;Screttas, C. G. J. Am. Chem. Soc. 2000, 122,
2391–2392.
6. Steele, B. R.;Micha-Screttas, M.;Screttas, C. G. Tetra-
hedron Lett. 2004, 45, 9537–9540;Steele, B. R.;Micha-
Screttas, M.;Screttas, C. G. Appl. Organomet. Chem.
2002, 16, 501–505.
7. Nightingale, D. V. Chem. Rev. 1947, 40, 117–140;Saleh, S.
A.;Tashtoush, H. I. Tetrahedron 1998, 54, 14157–14177.
8. In a typical reaction 17.9 g (50 mmol) of 7a was added to a
mixture of 10 mL Ac2O and 50 mL CHCl3 in a flask
cooled by an ice bath. To this mixture was added a
mixture of 10 mL Ac2O and 3 mL HNO3 (100%) prepared
below 10 ꢁC and the reaction mixture was stirred over-
night at room temperature. The reaction mixture was
neutralised with 10% NaOH, extracted with (3 · 100 mL
CH2Cl2), dried over Na2SO4 and evaporated. The product
was recrystallised from hexane. Yield 9.3 g 7b (46%, mp
157 ꢁC). The other nitrocompounds were prepared in a
similar way.
13. Luche, J. L.;Cintas, P. In Active Metals;Fu rstner, A.,
¨
Ed.;VCH: Weinheim, 1996;pp 133–190.
14. Cram, D. J. J. Am. Chem. Soc. 1952, 74, 2152–2159.
15. Keefer, L. K. Chem. Rev. 1989, 89, 459–502.
16. Bhaumik, K.;Akamanchi, K. Can. J. Chem. 2003, 81,
197–198.
9. Huston, R. C.;Kaye, I. A. J. Am. Chem. Soc. 1942, 64,
1576–1580.
10. Furst, A.;Berlo, R. C.;Hooton, S. Chem. Rev. 1965, 65,
51–68;Gowda, S.;Gowda, D. C. Tetrahedron 2002, 58,
2211–2213;Yuste, F.;Saldana, M.;Walls, F. Tetrahedron
Lett. 1982, 23, 147–148.
17. Margulis, M. A.;Margulis, I. M. Russ. J. Phys. Chem.
2003, 77, 1183–1190.