Anodic co-oxidation of urazole and ferrocenes: First trapping of cyclopentadienols

Article abstract of DOI:10.1039/a702516e

Cyclopentadien-5-ols, the major products resulting from decomposition of some ferrocenium cations by molecular oxygen, are regio- and stereo-selectively trapped by 4-phenyl-1,2,4-triazoline-3,5-dione.

Full text of DOI:10.1039/a702516e

View Online / Journal Homepage / Table of Contents for this issue
Anodic co-oxidation of urazole and ferrocenes: first trapping of
cyclopentadienols
a
a
b
a
Jocelyn Lorans, Fabrice Pierre, Lo ¨ı c Toupet and Claude Moinet*
a
Laboratoire ‘Electrochimie et Organom e´ talliques’, UMR CNRS 6509, Universit e´ de Rennes 1, 35042 Rennes cedex, France
Laboratoire de Physique Cristalline, Universit e´ de Rennes 1, 35042 Rennes cedex, France
b
Cyclopentadien-5-ols, the major products resulting from
(Fig. 1) and 4a from an endo addition. Compound 4a is identical
to the Diels–Alder adduct prepared by a different method using
2 and freshly distillated cyclopentadiene.8
decomposition of some ferrocenium cations by molecular
oxygen, are regio- and stereo-selectively trapped by
4-phenyl-1,2,4-triazoline-3,5-dione.
1,1A-Dialkylated ferrocenium cations 1b and 1d decomposed
more slowly than 1a and gave, after reaction with 2, compounds
1
13
In oxygenated organic solvents, ferrocenium cations are
3b and 3d respectively. The H and C NMR spectra of 3b and
3d and the X-ray analysis of 3b (Fig. 2) indicate a regioselective
exo-addition like that for 3a. After decomposition of mono-
alkylated ferrocenium cation 1c and reaction with 2, a mixture
of 3a and 3d was isolated. Compounds 3a and 3d were
separated by column chromatography. Adduct 4a was not
detected.
1
unstable and can easily be used for generating substituted
cyclopentadienes in the presence of very reactive dienophiles.
The strong dienophilic character of cyclic a-carbonyl azo
compounds is well known.2 These are generally prepared by
chemical oxidation of the corresponding hydrazino compounds
–6
using lead(iv) acetate7 or tert-butyl hypochlorite.
,8
9–11
We
report herein the co-oxidation of ferrocenes and a triazolidine-
dione (urazole) in a flow cell fitted with a graphite felt porous
anode.12 Electrolyses were performed in acidified MeCN (2%
The rate of decomposition of acetylferrocenium 1e and
1,1A-diacetylferrocenium 1f was much faster. Thus 1f gave a
mixture of unidentified products and 1e gave 3a in poor yield
(12%).
2 4
H SO ); solid sodium carbonate and oxygen were added to the
solution of triazolinedione and ferrocenium cations at the outlet
of the cell. Decomposition of ferrocenium cations proceeded via
unexpected cyclopentadien-5-ols as major products which were
trapped in situ with 4-phenyl-1,2,4-triazoline-3,5-dione
Table 1 Composition of mixtures from decomposition of ferrocenium
cations 1 in the presence of 4-phenyl-1,2,4-triazoline-3,5-dione 2
(
Scheme 1). To the best of our knowledge, this reaction has
Substrates (molar ratio)
Products (% yielda)
never been reported before. Theoretical calculations show that
13
the three cyclopentadienol isomers should be very unstable.
Previously, cyclopentadienol has only been postulated as an
intermediate during a thermal retro-Diels–Alder reaction.
Decomposition of ferrocenium cation 1a in the presence of
triazolinedione 2 was complete after 1 h and gave a mixture of
3
1
a + 2 (1:1)
3a (46) + 4a (12)
3a (69) + 4a (14)
3a (80) + 4a (15)
3b (41)
3a (24) + 3d (45)
3d (52)
1a + 2 (1:2)
1a + 2 (1:3)
1b + 2 (1:2)
14
1c + 2 (1:2)
1d + 2 (1:2)
1e + 2 (1:2)
1f + 2 (1:2)
a and 4a. The yield of 3a increased as the molar ratio
3a (12)
—
triazolinedione:ferrocenium cation increased, whereas the
yield of 4a was practically unchanged (Table 1). The H and
1
13
C
NMR spectra of 3a show a regio- and stereo-selective addition.
X-Ray analyses show that 3a results from an exo addition
a
Calculated from initial ferrocene.
R1
R2
N
N
Fe+
+
C(7)
C(4)
O
N
O
C(5)
Ph
O(3)
1
2
C(3)
C(6)
N(3)
O2, solid Na2CO3
MeCN, 25 °C, 1–15 h
R
N(2)
R
O(1)
C(1)
OH
N
N
N
+
C(2)
N
O
O(2)
N
O
N(1)
N
C(13)
Ph
O
4
C(8)
O
Ph
C(12)
3
1
2
a R = R = R = H
1
2
b R = R = R = Me
1
2
C(9)
c R = H, R = Et
1
2
C(11)
d R = R = R = Et
C(10)
1
2
e R = H, R = COMe
1
2
f
R = R = R = COMe
Scheme 1
Fig. 1 X-Ray structure of 3a
Chem. Commun., 1997
1279

View Online
3.29 (d, CHOH), 134.00 (d, CNC), 160.34 (s, CNO), 133.73 (s), 126.86 (d),
8
1
1
2
1
28.68 (d), 129.62 (d) (C
724 (CO); HRMS: m/z 271.095 (M ). d
), 3.36 (s, 1 H, OH), 4.63 (t, 2 H, CH), 6.50 (t, 2 H, NCH),
.3–7.5 (m, 5 H, C ); d (75 MHz, CD COCD ) 217.57 (q, CH ), 71.03
H
6 5
). For 3b: mp 213–214 °C; n(CH
2
Cl
2
)/cm
+
H
(300 MHz, CD
3
COCD
3
) 21.40
C(14)
(
s, 3 H, CH
3
7
6
H
5
C
3
3
3
(
d, CH), 90.26 (d, COH), 132.80 (d, CNC), 158.88 (s, CNO), 131.30 (s),
25.67 (d), 128.62 (d), 129.22 (d) (C ). For 3d mp 197–198 °C;
n(CH Cl )/cm21 1725 (CO); HRMS: m/z 285.110 (M
); d (300 MHz,
C(7)
1
6 5
H
O(3)
+
C(6)
2
2
H
CD
.67 (t, 2 H, CH), 6.48 (t, 2 H, NCH), 7.3–7.5 (m, 5 H, C
CD COCD ) 29.29 (q, CH ), 23.98 (t, CH ), 69.89 (d, CH), 93.76 (s,
3
COCD
3
) 20.98 (t, 3 H, CH
3
), 1.71 (q, 2 H, CH
2
), 3.34 (s, 1 H, OH),
4
6 5
H
); d (75 MHz,
C
C(3)
3
3
3
2
C(4)
C(5)
COH), 132.46 (d, CNC), 158.93 (s, CNO), 131.35 (s), 125.70 (d), 128.59 (d),
1
‡
29.21 (d) (C
X-Ray crystal data for 3a: C13
6 5
H ).
N(2)
C(1)
N(3)
O(2)
11 3 3
H N O : MW = 257.25, Orthorhombic,
O(1)
Pbca, a = 11.386(2), b = 12.706(2), c = 16.275(3) Å, V = 2354.4(7) Å
Z = 8, R = 0.030, Rw = 0.029 for 1354 observations and 206 variables. For
3b: C14 : MW = 271.28, monoclinic, P2 /n, a = 16.440(8),
3
,
C(2)
H N
13 3
O
3
1
C(9)
3
b = 8.490(7), c = 9.580(4) Å, b = 105.07(3)°, V = 1291(1) Å , Z = 4,
N(1)
R = 0.036, Rw = 0.034 for 1278 observations and 221 variables.
Data at 294 K were collected on an automatic diffractometer CAD4
Enrar-Nonius with graphite monochromatized Mo-Ka radiation. Atomic
coordinates, bond lengths and angles, and thermal parameters have been
deposited at the Cambridge Crystallographic Data Centre (CCDC). See
Information for Authors, Issue No. 1. Any request to the CCDC for this
material should quote the full literature citation and the reference number
C(10)
C(8)
C(13)
C(11)
1
82/484.
C(12)
References
1
W. P. Fehlhammer and C. Moinet, J. Electroanal. Chem. Interfacial
Electrochem., 1983, 158, 187.
Fig. 2 X-Ray structure of 3b
2
3
E. Fahr and H. Lind, Angew. Chem., Int. Ed. Engl., 1966, 5, 372.
K. MacKenzie, in The Chemistry of the Hydrazo, Azo and Azoxy
Groups, ed. S. Patai, Wiley, New York, 1975, ch. 11.
G. Bianchi, C. De Micheli and R. Gandolfi, in The Chemistry of the
Double Bonded Functional Groups, ed. S. Patai, Wiley, New York,
Decomposition of ferrocenium cation is probably initiated
via radical coupling with molecular oxygen as previously
suggested. After rearrangement and chemical evolution, cleav-
age of the iron and the formed cyclopentadienol ligand takes
place, whereas only limited decomplexation of the second
ligand (in case of 1a) leads to free cyclopentadiene. To support
this hypothesis, we note that the oxygen decomposition of
ferrocenium cations in MeCN gave a brown precipitate
4
1
1
977, part 1, ch. 6.
5
6
M. Quinteiro, C. Seoane and J. L. Soto, Heterocycles, 1978, 9, 1771.
C. J. Moody, Azo Dicarbonyl Compounds Advances in Heterocyclic
Chemistry, Academic Press Inc., 1982, vol. 30.
7 R. A. Clement, J. Org. Chem., 1960, 25, 1724; 1962, 27, 1115.
8 R. C. Cookson, S. S. H. Gilani and I. D. R. Stevens, Tetrahedron Lett.,
1
962, 14, 615; J. Chem. Soc., C,1967, 1905.
characterised as an iron salt; elemental analyses of this salt
showed the presence of one cyclopentadienyl ligand.15
9 E. F. Ullman and E. A. Barktus, Chem. Ind., 1962, 93.
0 T. J. Kealy, J. Am. Chem. Soc., 1962, 84, 966.
1 J. Sau e¨ r and B. Schr o¨ der, Angew. Chem., Int. Ed. Engl., 1965, 4, 711.
2 C. Moinet and E. Raoult, Bull. Soc. Chim. Fr., 1991, 214.
1
1
1
Footnotes
*
†
E-mail: claude.moinet@univ-rennes1.fr
Selected data for 3a, 3b and 3d. Satisfactory elemental analyses were
13 F. Turecek, J. Org. Chem., 1986, 51, 1563.
14 K. Alder and F. H. Flock, Chem. Ber., 1956, 1732.
15 C. Moinet, unpublished results.
2
1
obtained for these new compounds. For 3a: mp 214 °C; n(CH
1
2
Cl
2
)/cm
) 24.15
+
726 (CO); HRMS: m/z 241.084 (M ); d
H
(300 MHz, CD
3
COCD
3
(
7
dt, 1 H, CHOH), 4.80 (m, 2 H, CH), 5.65 (d, 1 H, OH), 6.53 (t, 2 H, NCH),
Received in Cambridge, UK, 14th April 1997; Com.
7/02516E
.35–7.51 (m, 5 H, C ); d (75 MHz, CD COCD ) 269.14 (d, CH),
6
H
5
C
3
3
1280
Chem. Commun., 1997