SiO2-TBD as new heterogeneous catalyst for the nef conversion of secondary nitroalkanes under neat conditions

Article abstract of DOI:10.1055/s-2006-947358

Treatment of secondary nitroalkanes with neat silica-supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), at room temperature, allows the direct conversion of the secondary nitro groups to the corresponding keto carbonyls. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-947358

LETTER
1849
SiO -TBD as New Heterogeneous Catalyst for the Nef Conversion of
2
Secondary Nitroalkanes under Neat Conditions
a
a
b
b
a
b
C
R
atalyst for the
N
o
ef Conversio
b
n
of Second
e
a
ry
N
itroalk
r
a
nes to Ballini,* Dennis Fiorini, Raimondo Maggi, Chiara Oro, Alessandro Palmieri, Giovanni Sartori
a
Dipartimento di Scienze Chimiche dell’Università (‘Green Chemistry Group’), Via S. Agostino 1, 62032 Camerino (MC), Italy
Fax +39(0737)402297; E-mail: roberto.ballini@unicam.it
b
Dipartimento di Chimica Organica e Industriale dell’Università (‘Clean Synthetic Methodologies Group’), Parco Area delle Scienze 17°,
3100 Parma, Italy
4
Received 8 March 2006
of the catalyst), no other solid materials have been applied
to catalyze the reaction.
Abstract: Treatment of secondary nitroalkanes with neat silica-
supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), at room tem-
perature, allows the direct conversion of the secondary nitro groups In recent decades solid catalysis has played a crucial role,
to the corresponding keto carbonyls.
not only in the petrochemical and bulk chemical indus-
Key words: reaction, nitroalkanes, ketones, heterogeneous cataly- tries, but also in the preparation of fine chemicals. In fact,
sis, solventless conditions, SiO -TBD
under heterogeneous conditions product isolation is easier
and frequently the reactions show high selectivity; in ad-
dition, the process is simplified and the volume of waste
2
Nitroalkanes are now firmly established as versatile inter- is significantly reduced.10
1
mediates for organic syntheses. Stabilized anions deriv-
During our studies on the functionalization of aliphatic
ing from nitroalkanes have been, for instance, extensively
11
nitro compounds under heterogeneous catalysis, we
2
3
used in the Michael, Henry, and Knoevenagel reac-
found that treatment of secondary nitroalkanes with
4
tions. Starting from primary nitroalkanes, these reactions
neat silica-supported 1,5,7-triazabicyclo[4.4.0]dec-5-ene
afford valuable secondary nitro derivatives which can be
eventually converted into ketones by the Nef reaction.5
The latter transformation was originally carried out under
acidic conditions, e.g. with strong acid such as aqueous
12
(
TBD), at 60 °C, allows the direct conversion of
reagents 1 into the corresponding ketones 2 (Scheme 1).
In spite of the extended reaction times (usually 4 d, see
Table 1) the reaction is very simple and gives satisfactory
to good yields, even with compounds containing an
additional functional group such as nitro esters and nitro
ketones. If primary nitro derivatives are subjected to the
reaction conditions (i.e., 3-phenyl-1-nitropropane and 1-
nitroundecane), a mixture of unidentified products was
6
HCl. To avoid such drastic conditions several variants
have been developed, including oxidative and reductive
5
,6
conditions. However, the above methodologies are not
of general utility since they are often incompatible with
polyfunctionalized substrates.
Recently, an interesting neutral procedure for the conver- obtained.
sion of secondary nitro derivatives into ketones or oximes,
by the use sodium nitrite, was reported. However, dis-
crimination between the formation of the ketone or the
oxime seems to be strongly dependent upon the nature of
the starting nitro compound.
7
SiO2–TBD
NO2
O
60 °C, 3–6 d
R1
R
R1
R
55–88%
1
2
A few years ago our group reported a selective Nef trans- Scheme 1
formation of secondary nitroalkanes into the correspond-
ing ketones under basic conditions, with the help of DBU
Moreover, because the reaction can be performed without
solvent, any tedious work-up is avoided since the crude
mixture can be directly charged onto a chromatographic
column to give the pure ketone 2.
8
as base and acetonitrile as solvent. However, all the
above procedures are usually carried out under homoge-
neous conditions by using an appropriate solvent in which
both the starting materials and the catalyst are soluble and
consequently catalyst recovery and reuse is difficult or
impossible. With the exception of a publication appearing
three decades ago in which the Nef reaction was per-
formed on activated basic silica gel (even if no comment
was made on the heterogeneity of the process and nature
Finally, we faced the problem of recycling: at the end of
the reaction (1a to 2a was chosen as model reaction) the
mixture was extracted with EtOAc, filtered, washed with
EtOAc, then, the catalyst was dried and reused with simi-
9
st
nd
lar yields (reaction 88%; 1 recycle 87%; 2 recycle:
6%). These results are probably due to the gradual depo-
2
sition of tar compounds on the catalyst surface that after
two cycles hampers the access to the catalytic sites.
SYNLETT 2006, No. 12, pp 1849–1850
0
1
.0
8
.2
0
0
6
Advanced online publication: 24.07.2006
DOI: 10.1055/s-2006-947358; Art ID: D07206ST
©
Georg Thieme Verlag Stuttgart · New York

1
850
R. Ballini et al.
LETTER
Table 1 Ketones 2 Prepared from Secondary Nitroalkanes 1
R1
Yield (%) of 2
a
Reaction times (d)
Entry
R
a
b
c
d
e
f
Ph(CH2)3
n-C H
n-Pr
88
63
74
62
60
55
56
77
4
8
4
4
3
4
8
5
(CH ) COO(CH ) Me
5
11
11
2 4
2 14
n-C H
(CH ) COMe
5
2 2
n-C H
n-C H
1
9
39
10 21
n-Pr
Et
(CH ) COOMe
2
2
(CH ) CO(CH ) Me
2
2
2 2
g
MeCO(CH2)2
(CH ) COOMe
2 2
h
n-C H
Me
9
19
a
Yield of pure isolated product.
General Procedure for the Nef Conversion
Green Chem. 2003, 5, 475. (f) Ballini, R.; Bosica, G.;
Fiorini, D.; Palmieri, A. Synthesis 2004, 1938.
Secondary nitro compound 1 (0.5 mmol) was added to the catalyst
0.75 mmol, 1.36 g), then the mixture was stirred and warmed at
0 °C for the appropriate time (Table 1). At the end of the reaction,
(
6
(12) Selected Analytical Data for Compounds 2a–e.
–
1 1
Compound 2a: oil. IR: 1714, 698 cm . H NMR (CDCl ):
3
the mixture was directly charged onto flash chromatography
column (eluting with EtOAc–cyclohexane), furnishing the pure
ketone 2.12
d = 0.92 (t, 3 H, J = 7.3 Hz), 1.51–1.70 (m, 2 H), 1.84–2.01
(m, 2 H), 2.37 (t, 2 H, J = 7.3 Hz), 2.42 (t, 2 H, J = 7.3 Hz),
13
2.64 (t, 2 H, J = 7.5 Hz), 7.15–7.37 (m, 5 H). C NMR
(
1
CDCl ): d = 13.8, 17.3, 25.2, 35.1, 41.9, 44.8, 125.9, 128.4,
3
+
28.5, 141.6, 211.0. MS (EI, 70eV): m/z (%) = 190 [M ],
Acknowledgment
175, 147, 129, 115, 104 (100), 91, 77, 71, 65, 58, 51, 43, 29.
Anal. Calcd for C H O (190.28): C, 82.06; H, 9.53. Found:
1
3
18
This work was supported by the University of Camerino, and by
MIUR-Italy.
C, 82.34; H, 9.71.
Compound 2b: oil. IR: 1732, 1702, 1192 cm . H NMR
CDCl ): d = 0.84–0.89 (m, 6 H), 1.23–1.38 (m, 30 H), 1.50–
–
1 1
(
3
1
.68 (m, 8 H), 2.25–2.33 (m, 2 H), 2.34–2.44 (m, 4 H), 4.03
References and Notes
1
3
(
t, 2 H, J = 6.7 Hz). C NMR (CDCl ): d = 14.2, 14.3, 22.7,
3
(
1) (a) Rosini, G.; Ballini, R. Synthesis 1988, 833. (b) Rosini,
G.; Ballini, R.; Petrini, M.; Marotta, E.; Righi, P. Org. Prep.
Proced. Int. 1990, 22, 707. (c) Ballini, R. Synlett 1999,
22.9, 23.5, 24.0, 24.7, 26.1, 28.9, 29.1, 29.5, 29.6, 29.7, 29.8,
29.9, 30.0, 31.8, 32.1, 34.1, 34.3, 42.5, 43.1, 64.8, 64.9,
+
173.7, 211.1. MS (EI, 70eV): m/z (%) = 424 [M ], 354, 197,
1009. (d) Ono, N. The Nitro Group in Organic Synthesis; J.
168, 145, 127, 113, 83, 57, 43 (100), 29. Anal. Calcd for
C H O (424.70): C, 76.36; H, 12.34. Found: C, 76.26; H,
Wiley: New York, 2001.
2
7
52
3
(
(
2) Ballini, R.; Bosica, G.; Fiorini, D.; Palmieri, A.; Petrini, M.
Chem. Rev. 2005, 105, 933.
3) (a) Rosini, G. In Comprehensive Organic Synthesis, Vol. 2;
Trost, B. M., Ed.; Pergamon: Oxford, 1991, 321.
12.25.
–
1 1
Compound 2c: oil. IR: 1715 cm . H NMR (CDCl ):
d = 0.90 (t, 3 H, J = 6.6 Hz), 1.20–1.39 (m, 4 H), 1.51–1.67
(m, 2 H), 2.20 (s, 3 H), 2.46 (t, 2 H, J = 7.5 Hz), 2.64–2.76
(m, 4 H). C NMR (CDCl ): d = 13.9, 23.5, 25.4, 30.0, 31.4,
36.0, 36.9, 42.8, 207.3, 209.7. MS (EI, 70eV): m/z 170 [M ],
127, 114, 99, 43. Anal. Calcd for C H O (170.25): C,
70.55; H, 10.66. Found: C, 70.81; H, 10.84.
3
1
3
(
b) Luzzio, F. A. Tetrahedron 2001, 57, 915.
3
+
(4) Carey, F. A.; Sundberg, R. J. In Advanced Organic
Chemistry, 4th ed., Part B; Plenum: New York, 2001, 100.
(5) (a) Pinnick, H. W. Org. React. 1990, 38, 655. (b) Ballini,
R.; Petrini, M. Tetrahedron 2004, 60, 1017.
(
1
0
18
2
–
1 1
Compound 2d: oil. IR: 1701 cm . H NMR (CDCl ):
3
6) (a) Seebach, D.; Colvin, E. W.; Lehr, F.; Weller, T. Chimia
d = 0.88 (t, 6 H, J = 6.6 Hz), 1.20–1.34 (m, 46 H), 1.52–1.62
1
3
1979, 33, 1. (b) Noland, W. E. Chem. Rev. 1955, 55, 137.
(m, 4 H), 2.37 (t, 4 H, J = 7.4 Hz). C NMR (CDCl ): d =
3
(
c) Pinnick, H. W. Org. React. 1990, 38, 655.
14.3, 22.9, 24.1, 29.4, 29.50, 29.53, 29.58, 29.6, 29.7, 29.8,
29.84, 29.88, 29.92, 32.1, 32.2, 43.0, 212.0. MS (EI, 70eV):
(
(
(
7) Gissot, A.; N’Gouela, S.; Matt, C.; Wagner, A.;
Mioskowski, C. J. Org. Chem. 2004, 69, 8997.
8) Ballini, R.; Bosica, G.; Fiorini, D.; Petrini, M. Tetrahedron
Lett. 2002, 43, 5233.
+
m/z (%) = 436 [M ], 296, 207, 185, 170 (100), 97, 71, 57, 41.
Anal. Calcd for C H O (436.80): C, 82.49; H, 13.85.
Found: C, 82.81; H, 14.22.
Compound 2e: oil. IR: 1728, 1705, 1190 cm . H NMR
(CDCl ): d = 0.90 (t, 3 H, J = 7.2 Hz), 1.56–1.68 (m, 2 H),
2.42 (t, 2 H, J = 7.2 Hz), 2.57 (t, 2 H, J = 6.5 Hz), 2.71 (t, 2
H, J = 6.5 Hz), 3.66 (s, 3 H). C NMR (CDCl ): d = 13.9,
17.5, 27.9, 37.2, 44.9, 52.0, 173.5, 209.2. MS (EI, 70eV):
3
0
60
–
1 1
9) Keinan, E.; Mazur, Y. J. Am. Chem. Soc. 1977, 99, 3861.
(
(
10) Clark, J. H. Acc. Chem. Res. 2002, 35, 791.
3
11) See, for example: (a) Ballini, R.; Bosica, G.; Parrini, M.
Tetrahedron Lett. 1998, 39, 7963. (b) Ballini, R.; Bigi, F.;
Gogni, E.; Maggi, R.; Sartori, G. J. Catal. 2000, 191, 348.
1
3
3
+
(
2
c) Ballini, R.; Bosica, G.; Fiorini, D. Tetrahedron Lett.
001, 42, 8471. (d) Ballini, R.; Bosica, G.; Livi, D.;
Palmieri, A.; Maggi, R.; Sartori, G. Tetrahedron Lett. 2003,
4, 2271. (e) Ballini, R.; Fiorini, D.; Gil, M. V.; Palmieri, A.
m/z (%) = 158 [M ], 130, 127, 115 (100), 98, 87, 71, 43.
Anal. Calcd for C H O (158.20): C, 60.74; H, 8.92. Found:
C, 60.49; H, 9.10.
8
14
3
4
Synlett 2006, No. 12, 1849–1850 © Thieme Stuttgart · New York