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Bicyclo[4 (2).4

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of the proton at highest field: 159 Hz]. The configuration
of the acetate groups in relation to the cyclopropane ring
still remains to be clarified. When the diacetate was
treated with ethereal methyllithium at -50°C, a diol of
m.p. 151-152°C (yield 74%) was formed which, according
to the NMR spectrum has structure ( 6 ) . The diol ( 6 )
can be converted by manganese dioxide in benzene almost
quantitatively into a yellow dicarbonyl compound, m. p.
107-108"C, which is stable in absence of light and oxygen
and to which the norcaradiene structure (7) must be
assigned unambiguously on the basis of spectral findings.
19F-NMRspectrum [(CDCl,); CC1,F as external standard]
contained an AB system at 103.5 and 110.8ppm with
3=238 Hz. The presence of a cycloheptatriene is convincingly shown by the coupling constants of the olefinic
protons H'-H''
(see Table 1) and by the absorption of
these protons at relatively low field strengthc7].Furthermore, the I9F-NMR parameters point to this type of
structure, for if the CF, group were part of a cyclopropane
ring the fluorine atoms should not only absorb at higher
field strengths but also should show smaller geminal
coupling['- 'I.
The NMR spectrum of the dicarbonyl compound (in
[D,]acetone) shows an AA'BB' system (H7-H") centered
at '5 = 3.52, a singlet at 3.49 (H3, H4), and an AB system at
7.41 (anti-H")[31 and 9.22 (syn-H") with 3=4.1 Hz. The
coupling constants of the olefinic protons H7-H10[41
(see Table I), on the one hand, and the geminal coupling
of the CH, protons on the other provide a decisive argument in favor of structure (7). The electron spectrum [(in
methanol), h,,,=226
( E = 15400), 271 (2240), 324 (248),
405nm (186)] also supports the structure (7); the IR
spectrum, with a broad carbonyl band at 1665cm-' (in
KBr) is not very revealing.
The electron spectrum of the compound [(in methanol)
h,,,=210 (~=27900),236 (15350), 245 (15100, sh), 318
(2600), 398 (325), 415 nm (300)] indicates, in accord with
structure (Y), stronger conjugation than in the norcaradiene (7). The IR carbonyl absorption [relatively sharp
band at 1658 cm-' (in KBr)] corresponds, as does that
of (7), to that of an ccJ3-unsaturated ketone or of a quinone["'.
Chemical and physicochemical studies of (7) and ( 9 )
are in progress to provide further information about the
quinonoid nature of these dicarbonyl compounds.
Table 1. Chemical shifts (5 values in ppm) and H,H coupling constants
(Hz)of the olefinic protons in (7) and ( 9 ) .
(7) 3.25 [a] 3.88 [a] 3.49
(9) 2.82
I ::;:
6.03 0.83
110.59 10.12
1 ::::
[a] The assignment of H', HIo, and of H8, H9, respectively, is uncertain.
The replacement of the two methylene protons in (7) by
fluorine offers the possibility of shifting the position of
the equilibrium between the norcaradiene and the cycloheptatriene tautomer in favor of the latter [(7)$(1)
versus (S)+(Y)], for, as the thermal behavior of perfluorocyclopropanes shows, ring strain is considerably
increased by geminal fluorine sub~tituents~'~.
11,ll-Di fl uoro - 1,6- methano [1O]ann~lene[~Ireacts with
lead tetraacetate in glacial acetic acid in the same way
as ( 4 ) , although less readily (reflux), yielding a symmetrical cis-1,4-diacetate (m.p. 171-172°C; yield 10%). The
'H-NMR spectrum of the compound confirms the expectation that in this case we are dealing with a cycloheptatriene derivative, and the same applies to the diol [m.p.
175-176 "C (several recrystallizations from ethyl acetate) ;
crude yield 78x1 obtained from the diacetate by means
of methyllithium at - 50°C. Finally, oxidation of the crude
diol with manganese dioxide in acetone afforded the
desired 11,11-difluorobicyclo[4.4.1]undeca-3,6,8,10-tetraene-2,5-dione (9) as a light-sensitive yellow compound of
m.p. 119-120°C (yield 50%).
Received: December 24,1970 [Z 385a IE]
Publication delayed at the authors' request
German version: Angew. Chem. 83,401 (1971)
[I] Reviews: a) E . Vogel in: Aromaticity, Special Publication No. 21,
Chem. SOC.,London 1967, p. 113; b) E . Vogel, Chimia 22, 21 (1968);
c) E. Vogel, Proc. Robert A. Welch Foundation Conferences on Chemical Research, XII. Organic Synthesis, Houston, Texas, 1968, p. 215.
[2] For synthesis of (2) see E . Vogel, W A . Boll, and E . Lohmar,
Angew. Chem. 83, 403 (1971); Angew. Chem. internat. Edit. 10, 399
131 syn and anti refer to the diene part of the molecule.
[4] H. Giinther and H.-H. Hinrichs, Liebigs Ann. Chem. 706, 1 (1967).
[5] R. A. Mitsch and E. W Neuuar, J. Phys. Chem. 70, 546 (1966);
see also H. Giinther, Tetrahedron Lett. 1970, 5173.
161 V: Rautenstrauch, H.-J. Scholl, and E. Vogel, Angew. Chem. 80,
278 (1968); Angew. Chem. internat. Edit. 7, 288 (1968).
[7] The position of the AA'BB'system of the protons H7-HI0 reflects
strong conjugation between the two halves of the molecule, such as is
present only in the cycloheptatriene structure.
[8] References for 19F-NMR parameters of gem-difluorocyclopropanes: a) R. A . Mitsch, J. Amer. Chem. SOC.87, 758 (1965); b) W D.
Phillips, J. Chem. Phys. 25, 949 (1956).
[9] The spectral data for (7) and (9) do not exclude the possibility
that these compounds exist in rapidly established equilibrium with
their cycloheptatriene or norcaradiene tautomers [ ( I ) and (8)
respectively] ; the concentrations of tautomers ( 1 ) and (8), however,
should not exceed 20%. If more than ca. 5% of ( I ) and (8) were
present, the NMR spectra should be temperature-dependent (measurements are in progress).
[lo] We thank Dr. P. Junkes for determination of the I9F-NMR
With potassium tert-butoxide in dimethyl suifoxide, the tricyclic
dicarbonyl compound (7) affords a semiquinone which, according to
its ESR spectrum, has a bicyclic structure: G. A. Russell, ?: Ku, and
J. Lokensgard, J. Amer. Chem. SOC.92,3833 (1970).
By Emanuel Vogel, Walter A . Boll, and Elmar LohmarI']
Structure (9) was proved by the NMR spectra. The 'HNMR spectrum ([ID,]-acetone) contained an AA'BB'
system (H7-H") disturbed by H, F coupling and centered
at ~=2.62,as well as a singlet at 3.38 (H3, H4), whereas the
Angew. Chem. internat. Edit. 1 Vol. 10 (1971) 1 No. 6
Bicyclo[4.4.l]undeca-3,6,8,lO-tetraene-2,5-dione(2), a diketo derivative of 1,6-methano[lO]annulene corresponding
to p-benzoquinone or 1,4-naphthoquinone, defies attempts
at synthesis because, contrary to expectation, it has a
[*] Prof. Dr. E. Vogel, Dr. W.A. Boll, and Dr. E. Lohmar
Institut fur Organische Chemie der Universitat
5 Koln 1, Ziilpicher Strasse 47 (Germany)
higher free energy than its valence isomer with the norcaradiene structure (3)
With bicyclo[4.4.l]undeca3,5,8,10-tetraene-2,7-dione
an isomer of (2), a cycloheptatriene-norcaradiene equilibrium is ruled out. Thus
only a strong tendency of ( I ) to polymerize should stand
in the way of its synthesis.
A route to ( I ) was opened by the known 2,7-dibromo-f,6methano[lO]annulene (4)I3]. For converting (4) into
1,6-methano[lO]annulene-2,7-diol or its keto tautomers
we used a procedure that had already proved its value for
the preparation of 2-hydroxy-1,6-methano[lO]annulene
from 2-bromo-1,6-methano[10]annulene~41;
in this, the
appropriate bromide was converted into the Grignard
reagent and this was treated with tert-butyl perben~oate[~I,
yielding the tert-butyl ether which is readily cleaved by
acid. The dibromide ( 4 ) did not, in the event, react with
magnesium in the desired manner, but the bifunctional
Grignard reagent (5) could be obtained by interchange of
the metal between the dilithium compound, generated
from ( 4 ) with butyllithium in etherL6],and anhydrous
magnesium bromide. When ( 5 ) was treated with ethereal
tert-butyl perbenzoate at O"C, subsequent chromatography
on aluminum oxide followed by distillation afforded the
di-tert-butyl ether (6) as a pale yellow liquid, b.p. 108-110
"C/O.OI torr (yield 50%) [NMR spectrum (in CC1,): ABC
system at z=2.4-3.4 (6H) and singlets at 8.69 (18H) and
10.55 (2H)l. Fission of (6) effected by a catalytic amount
of p-toluenesulfonic acid in benzene at 80°C for 10min
gave a homogeneous colorless substance of composition
C,,H,,O, and m.p. 138-140°C (56% yield), which spectra
made to approach ( I ) by way of the dibromide (8). With
two equivalents of N-bromosuccinimide (NBS) in boiling
carbon tetrachloride, (7) gave a crystalline dibromo substitution product (crude yield ca. 80%);this was obviously
a mixture of the three possible stereoisomeric dibromides
(8) since the NMR spectrum of this product contained two
singlets and an AB system for the cyclopropane protons.
Potassium iodide''] in acetone dehalogenated the dibromide
mixture to the desired bicycIo[4.4.1]undeca-3,5,8,lO-tetraene-2,7-dione ( I ) which was obtained as yellowishorange crystals (from acetone), m. p. 147-148 "C (yield CU.
50%), after chromatography on silica gel.
Proof of the structure of ( I ) was provided by the NMR
spectrum. This showed only an ABC system at z= 3.0-3.8,
assigned to the six vinylic protons, [chemical shifts and
coupling constants determined by analysis : z3+8=3.71,
z4,,=3.11, ~,,,,-,=3.75; 5,,,=11.52 Hz, J,.,= -0.06 Hz,
and J4,5=5.22 Hz (positional numerals as in formula
plus a singlet at ~ = 6 . 8 3arising from the CH,bridge protons, and it thus has the form expected from the
C, symmetry of ( I ) . Further the UV and IR spectra are
in accord with structure ( I ) [hmax(in cyclohexane)= 244
(~=3750,sh), 342 (7300), 431nm (1600); carbonyl or
double-bond bands (in KBr) at 1625,1635, and 1645 cm- '1.
The physical and spectroscopic properties determined so
far for ( I ) leave it open whether this compound can be
described as a quinone. The chemical behavior appears
to justify such a description, for treating ( I ) with zinc
and acetic anhydride in the presence of pyridine leads
readily to reductive acetylation that affords the aromatic
2,7-diacetoxy-1,6-methano[lO]annulene ( 9 ) of m. p.
130-131 "C; this product is identical with that obtained
by acid-catalyzed reaction of (6) with acetic anhydride.
Received: March 12,1971 [ Z 385b IEJ
German version: Angew. Chem. 83,403 (1971)
showed conclusively to be the diketone (7) with cyclopropane structure [NMR (in CDCI,): AB system with
triplet splitting of each line at ~=3.1-4.2 (4H), quartet at
7.0 {4H), and singlet at 8.33 (2H); UV (in cyclohexane):
h,,,=214 (~=20500),331 nm (150); IR (in KBr): carbonyl
band at I 650 cm- '1. 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone did not dehydrogenate (7), so an attempt was
[I] E. Vogel, E . Lohmar, W A. Boll, B. Sohngfn, K. Miillen, and H .
Giinther, Angew. Chem. 83, 401 (1971); Angew. Chem. internat. Edit.
10,398 (1971).
[2] To the best of our knowledge, the 1,5-naphthoquinoneanalogous
to ( I ) is unknown.
[3] E. Vogel and W A. Boll, Angew. Chem. 76, 784 (1964); Angew.
Chem. internat. Edit. 3,642 (1964); E. Vugel, W A . Boll, and M . Biskup,
Tetrahedron Lett. 1966, 1569.
[4] W A. Boll, Angew. Chem. 78, 755 (1966); Angew. Chem. internat.
Edit. 5, 744 (1966); E . Vogel and W A. Boll, unpublished work.
[S] S.-0. Lawesson and N.C.Yang, J. Amer. Chem. SOC.
81,4230 (1959).
[6] E. Vugel in: Aromaticity, Special Publication No. 21, Chem. SOC.,
London 1967, p. 113.
171 When sodium iodide is used, (1) is accompanied by an iodinecontaining product, presumably the diiodide corresponding to (8) ;
when kept, this product decomposes to ( I ) in an apparently reversible
[S] We thank If. Schmickler for analysis of the ABC system.
Angew. Chem. internal. Edit. / VoL 10 (1971) / No. 6
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