Nitration of cyclic vinylsilanes with acetyl nitrate: Effect of silyl moiety and ring size

Article abstract of DOI:10.1039/a902388g

Reaction of AcONO₂ with common ring vinylsilanes gives the corresponding α,β-unsaturated 1-nitrocycloalkenes, and with medium and large ring vinylsilanes it produces novel 1,1-dinitro 2-nitrates.

Full text of DOI:10.1039/a902388g

Nitration of cyclic vinylsilanes with acetyl nitrate: effect of silyl moiety and
ring size
Govindagouda S. Patil and Gopalpur Nagendrappa*
Department of Chemistry, Bangalore University, Bangalore 560001, India. E-mail: nagendrappa@mailcity.com
Received (in Cambridge, UK) 25th March 1999, Accepted 4th May 1999
Reaction of AcONO
2
with common ring vinylsilanes gives
the powerful influence of silicon in directing this transforma-
tion. The apparently different results from the medium and large
ring vinylsilanes 4 and 5 can also be attributed to control by the
silicon moiety.
the corresponding a,b-unsaturated 1-nitrocycloalkenes, and
with medium and large ring vinylsilanes it produces novel
1,1-dinitro 2-nitrates.
2
All the results of AcONO reaction with the cyclic vinyl-
The reaction of AcONO
2
with olefins leads to a plethora of
silanes 1–5 can be rationalized by a mechanistic scheme
involving the initial formation of a [2 + 2] cycloaddition
intermediate 12–16 (Scheme 2), following the proposal of
products, which include isomeric nitro acetates, nitro nitrates
and nitroalkenes.1 However, the desired a,b-unsaturated
nitroalkenes are obtained at best as only very minor products or
,2
Borisenko et al. who based it on theoretical calculation and
3
1
not at all. The results have been rationalized by proposing an
experimental results of AcONO
2
reaction with cycloalkenes.
oxazetidine intermediate, a [2 + 2] cycloadduct of a nitryl cation
with an olefin.1 Because of the well-known propensity of
4
vinylsilanes to undergo regiospecific electrophilic substitution,
–OAc
SiMe3
+
N
a
b
5
we considered that they could be nitrated to the synthetically
NO2
O
6
path a
versatile a,b-unsaturated nitroalkenes. This has now been
(
)n
( )n
n = 1–3
realized in the case of common ring vinylsilanes. However, the
medium and large ring vinylsilanes give different but interesting
and novel products.
O
a
1
2–16 (n = 1–4, 8)
6–8
path b n = 4, 8
The nitration procedure is very simple. The cyclic vinylsilane
NO2
+
N
+
N
O
+
O
–OAc
(
2.5 mmol) in CH
2
Cl
2
(2 ml) at 215 °C was treated dropwise
–
NO2
7
(
)n
with AcONO
2
(5 mmol). After stirring the mixture for about
(
(
)n
O
O
half an hour (the disappearance of the vinylsilanes was
monitored by GC), water was added and the mixture worked up
in the usual manner. The products were purified by silica gel
chromatography [2% EtOAc–light petroleum (bp 60–65 °C)].
For the present study, a series of 1-trimethylsilylcycloalkenes
consisting of three common rings (1–3), one medium ring (4)
and one large ring (5, a 1:1 mixture of cis and trans isomers)
NO2
O
–
)n
+
N
O
17
OAc
NO2
8
was employed. The three common ring vinylsilanes 1–3 gave,
AcONO2
Nef
reaction
in moderate to good isolated yields, the corresponding 1-ni-
trocycloalkenes 6–8 (Scheme 1), which were identical to
authentic compounds.3 No other products were detected in any
of these cases.
18
9, 10
Scheme 2
11
,5
SiMe3
AcONO2
15 °C
NO2
NO2
NO2
O
In the present case, the regiospecificity is presumed to arise
4
(
)n
(
)n
+
(
)n
+ ( )n
from the well-known b-silicon effect which directs the
–
+
ONO2
ONO2
electrophile NO2 to attack the a position. Since the loss of
1
n = 1
n = 2
n = 3
n = 4
n = 8
6 n = 1 (50%)
7 n = 2 (73%)
8 n = 3 (70%)
—
—
—
—
—
silicon is more rapid than that of a b-proton in the b-elimination
reactions of b-silicon-containing substrates, the further trans-
formation of 12–16 is guided by this process. The b-elimination
in 12–16 to the nitroolefinic products 6–8 occurs if silicon and
the b-leaving group (C–O bond) attain the antiperiplanar
geometry,10 which is achieved when the carbocycles in 12–16
have the required conformation (e.g. cyclohexane in the chair
2
3
4
5
—
—
—
9 n = 4 (75%)
10 n = 8 (56%) 11 n = 8 (32%)
—
Scheme 1
1
-Trimethylsilylcyclooctene 4 produced a single solid prod-
uct, which was identified as 2,2-dinitrocyclooctyl nitrate 9.
-Trimethylsilylcyclododecene 5 (a 1:1 mixture of cis and
trans isomers) gave a 2:1 mixture of the dinitro nitrate 10 and
the keto nitrate 11 (Scheme 1), which were separated by
repeated fractional crystallization from light petroleum (bp
form with a-C–SiMe and b-C–O bonds being axial-axial
3
1
trans). All the intermediates 12–16 from the vinylsilanes 1–5
can accommodate this conformational demand, but only those
(12–14, n = 1–3) from the common ring vinylsilanes eventually
lead to the 1-nitrocycloalkenes 6–8 (Scheme 2, path a). In the
case of medium and large rings, the more rapid changes in their
6
0–65 °C). Compounds 9–11 were characterized by their
9
10
spectral and elemental analysis data. The expected 1-ni-
trocycloalkenes were not detected in either of these cases. This
is in stark contrast to the results of nitration of cyclooctene,
which was found to behave like the common ring cycloalk-
enes.1
conformations and transannular interactions probably dimin-
ish the life-time of the crucial conformation in which silicon and
the leaving group are antiparallel to such an extent that the
intermediate takes a different route to give the observed
products (Scheme 2, path b).
The smooth conversion of the cyclic vinylsilanes 1–3 to the
corresponding 1-nitrocycloalkenes 6–8 as the sole products is
strikingly dissimilar to the complex results obtained in the
We verified and confirmed that 9 is not formed from 4 via
1-nitrocyclooctene 18. When 18, prepared by a literature
procedure,11 was treated with AcONO
under conditions
identical to those used for the nitration of 4, the starting
2
1
nitration of their unsilylated analogues. This clearly underlines
Chem. Commun., 1999, 1079–1080
1079

nitrocycloalkene 18 was recovered intact. We presume that the
formation of 10 from 5 follows a similar route.
Additional evidence for this mechanistic scheme is the fact
that no 1,2-nitro acetate, 1,2-nitro nitrate or transannular
products are produced from any of the cyclic vinylsilanes 1–5,
unlike the reported results of the nitration of cycloalkenes under
similar conditions.1
The formation of the keto nitrate 11 is likely to be due to a
Nef-type transformation12 of a possible intermediate 17, which
can also give the dinitro nitrate.
Our work demonstrates that nitration of cyclic vinylsilanes
can be accomplished, though the nature of the products is
dependent on the ring size, in that the common rings give the
Wierschke, J. Chandrasekhar and W. L. Jorgensen, J. Am. Chem. Soc.,
985, 107, 1496; J. S. Panek, Comprehensive Organic Synthesis, ed.
B. M. Trost, Pergamon, London, 1991, vol. 1, part 1, p. 579; I. Fleming,
A. Barbero and D. Walter, Chem. Rev., 1997, 97, 2063.
An unsuccessful attempt to nitrate cyclic vinylsilanes has been
previously reported, but without revealing the details: E. J. Corey and H.
Estreicher, Tetrahedron Lett., 1980, 21, 1113.
See for example, M. Ayerbe, A. Arrieta and F. P. Cossio, J. Org. Chem.,
1998, 63, 1795; S. E. Denmark and J. A. Dixon, J. Org. Chem.,1997, 62,
7086; E. Dumez, J. Rodriguez and J.-P. Dulcere, Chem. Commun.,
1997, 1831; S. E. Denmark and A. Thorarensen, Chem. Rev.,1996, 96,
1
5
6
1
37.
AcONO
AR Grade, Merck) to Ac
G. Nagendrappa, Synthesis, 1980, 704.
Selected data for 9: mp 56–58 °C; nmax/cm2 1652, 1595, 1564;
(CDCl ) 6.19 (dd, J 7.6 and 1.4, 1H), 2.94–2.63 (m, 2H), 2.45–2.30
m, 1H), 2.12–1.99 (m, 1H), 1.89–1.77 (m, 4H), 1.59–1.44 (m, 4H);
7
2
was prepared by adding 0.375 g of conc. HNO
3
(1.40 density,
2
O (5 ml, distilled over P ); see ref. 1.
2 5
O
8
9
1
-nitrocycloalkenes and rings larger than seven-membered
1
rings will produce novel dinitro nitrates.
d
H
3
The authors thank the DST and the CSIR, New Delhi, for
financial support of this work and a fellowship to GSP. Some of
the equipment used in this work was donated by the Alexander
von Humboldt Foundation, Germany.
(
d (CDCl ) 121.5 (s), 78.7 (d), 32.3 (t), 30.6 (t), 25.9 (t), 25.8 (t), 24.8 (t),
C
3
+
21.8 (t); d
O
(CDCl
3
) 596.3, 445.2, 352.9; m/z 264 (1%, M + 1), 171 (3),
+
95 (37), 81 (34), 67 (37), 55 (72), 46 (100, NO
2
), 41 (67) (Found: C,
3
1
d
1
6.73; H, 5.03; N, 16.01. C
5.96%). For 10: mp 80–82 °C; nmax/cm
(CDCl ) 6.08 (d, J 9.9, 1H), 2.58–2.39 (m, 2H), 2.03–1.83 (m, 1H),
.60–1.28 (m, 17H); d (CDCl ) 120.4, 74.9, 32.5, 26.6, 25.6, 25.0, 22.3,
22.1, 22.0, 21.8, 21.6, 19.6 (Found: C, 45.11; H, 6.81; N, 12.83.
requires: C, 45.14; H, 6.63; N, 13.16%). For 11: mp.
8 13 3 7
H N O requires: C, 36.51; H, 4.98; N,
2
1
1667, 1595, 1569;
H
3
Notes and references
C
3
1
2
3
A. A. Borisenko, A. V. Nikulin, S. Wolfe, N. S. Zefirov and N. V. Zyk,
J. Am. Chem. Soc., 1984, 106, 1074 and references cited therein.
G. A. Olah, R. Malhotra and S. C. Narang, Nitration:Methods and
Mechanisms, VCH, New York, 1989.
For some of the procedures for the preparation of 1-nitroalkenes, see
J. R. Hwu, K.-L. Chen and S. Ananthan, J. Chem. Soc., Chem.
Commun., 1994, 1425; S. E. Denmark and L. R. Marcin, J. Org. Chem.,
12 21 3 7
C H N O
2
1
89–91 °C; nmax/cm 1729, 1652, 1636; d
2.81–2.71 (m, 1H), 2.50–2.40 (m, 1H), 2.14–1.85 (m, 3H), 1.64–0.88
(CDCl ) 204.3, 85.5, 34.8, 26.2, 26.1, 25.9, 23.7, 22.6,
H 3
(CDCl ) 5.29 (q, J 3.3, 1H),
(m, 15H); d
C
3
22.2, 21.8, 21.0, 19.2 (Found: C, 59.05; H, 8.85; N, 5.38.C12
requires: C, 59.24; H, 8.70; N, 5.76%).
H21NO
4
1
993, 58, 3850; A. Kamimura, T. Kawai and A. Kaji, J. Chem. Soc.,
10 E. L. Eliel and S. H. Wilen, Stereochemistry of Organic Compounds,
Wiley, New York, 1994, ch. 11, pp. 762–771.
11 W. K. Seifert, Org. Synth., 1988, Coll. Vol. 6, 837.
12 J. R. Hwu and B. A. Gilbert, J. Am. Chem. Soc., 1991, 113, 5917 and
references cited therein.
Chem. Commun., 1987, 1550; E. J. Corey and H. Estreicher, J. Am.
Chem. Soc., 1978, 100, 6294; R. Ballini and C. Palestini, Tetrahedron
Lett., 1994, 35, 5731; R. S. Varma, R. Dahiya and S. Kumar,
Tetrahedron Lett., 1997, 38, 5131.
4
B. Chiavarino, M. E. Crostoni and S. Fornarini, J. Am. Chem. Soc.,
1998, 120, 1523; J. B. Lambert, Tetrahedron, 1990, 46, 2677; S. G.
Communication 9/02388G
1080
Chem. Commun., 1999, 1079–1080