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syn syn-1 6 8 17 10 15-Trismethano[18]annulene DicationЧDication of a [4n+2]Annulene.

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experiences when irradiated with the resonance frequency of
the protons of the central CH, bridge.
It follows from a comparison of the chemical shifts of the
corresponding bridge protons in (3) and (2) that the steric
compression of the inner bridge protons and consequently
the relevant H-H distances [1.78A in the case of (2)l2]]
are very similar in the two annulenes. Considering the rigidity
of the carbon skeleton in annulenes of this type, which hardly
permits any notable deviation of the molecule from the C2"
symmetry, this finding enables the molecular architecture of
( 3 ) , especially the curvature (or bending) of its annulene ring
to be derived with a great degree of certainty["]
Fig. I . Electronic spectra of ( I
), (2),
and ( 3 ) in cyclohexane.
That (3) is to be regarded as aromatic is supported
quite impressively by the relationship of its electronic spectrum
to those of its lower homologues ( I ) and (2) (Fig. 1). The
spectra of the three annulenes are remarkably similar in shape
but on progression from [lo]- to [14]- to /18]annulene all of
the bands undergo bathochromic shifts, as theoretically predieted. The NMR spectrum of (3) (Table I), showing a downfield position of the resonances of the annulene protons and an
upfield position of the resonances of the bridge protons, is
indicative of a diamagnetic ring current and, moreover, due to
its absorption pattern, affords evidence that the expected
syn-syn-stereoisomer having C," symmetry is present, and not
the syn,anti-isomer, likewise compatible with the configuration
of (7). This stereochemical result follows independently from
the marked positive nuclear Overhauser effect["] which the
doublet of the inner protons of the two terminal CH, bridges
Table 1. Spectral data of the diester (61, the dialdehyde (7), the divinyl
compound ( I 2 j , and the swi,syn-1,6:8,17: lO,IS-trismethano[ 18lannulene (3).
161
171
NI
Received: September I I , 1978 [Z IIOa IE]
revised: October 17. 1978
German version: Angew. Chem. 90. 9x8 (1978)
UV (dioxane): & = 3 1 7 n m (r=81200), 339 (sh,
68900), 397 (5650); IR (CsI): 1695cm-' (C=O);
'H-NMR (CDC13): 6 = -0.36 and 3.17 (AX system, J=12.9Hz, 2 H , H-17), 3.35 and 4.22 (AX
system, J = 15.9Hz. 2H, H-l6), 3.94 and 4.97 (AX
s y s t e m , J = 1 6 S H z , 2H, H-l3), 6.92 (s, 2H, H-2,
9), 7.20---6.78 (AA'XX' system, 4 H , H-4, 5, 6,
71, 7.45 (s, 2 H , H-l I . 15), 1.29 and 4.22 (t and
9, IOH, 2C2H5).
UV (dioxane): im,,=326nm (c=80900), 334
(81 600), 409 (5300); IR (CsI): 1668cm-' (C=O);
'H-NMR (C2D2CI,): d = -0.22 and 3.27 (AX system, J = l 3 . 2 H z , 2H, H-17), 3.43 and 4.37 (AX
system, J = 1 5 . 3 H z , 2H, H-l6), 3.53 and 4.85(AX
system, J = 1 6 . 2 H z , 2H, H-13). 6.75-7.22
(AA'XX' system and 2s, 8 H , H-2, 4, 5, 6, 7, 9,
I I. 151, 9.22 (s, 2 H , 2CHO).
UV (dioxane): i,,,=228nm
(c=14100), 323
(I13000). 337 (sh, 76600), 406 (5700); IR (Csl):
1606, 1529cm-' (C=C); 'H-NMR (CDCI,):
6 = -0.42 and 3.15 (AX system, J = l 3 . 5 H z , 2H,
H-l7),3.37and4.30(AXsystem, J = I 5 . 6 H z , 2 H ,
H-l6), 3.79 and 4.1 7 (Axsystem, J = 16.2 Hz, 2 H ,
H-13). 5.03 (d, 2H). 5.54 (d, 2 H ) and 6.39 (m,
2 H ) (ABX system of the protons of the vinyl
groups), 6.32 (s, 2 H , H-11, 15), 6.77 (s, 2H, H-2,
9). 6 3 - 7 . 1 7 (AA'XX system, 4H, H-4, 5, 6, 7).
UV (cyclohexane): L,,, = 258 nm (sh, I: = 6300),
349 (195000), 373 (sh, 26500), 422 (8400). 589
(sh, 200). 596 (sh. 218), 605 (229), 614 (sh, 221).
625 (sh, 203), 637 (sh. 151); IR (CsI): 1540cm-'
(C=C); 'H-NMR (CD2C12): 6 = -0.45 and 1.32
(AXsystem,J=13.5Hz,4H,H-19,,,,H-21.,,e.g.
H-l9',"dO,H-2Ien.d, 0.53 (s, 2H, H-20), 6.70-7.70
(AA'XX' system, 8 H , H-2. 3, 4, 5, 1 I. 12, 13,
141, 7.62 (s, 4 H , H-7, 9, 16, 18).
~-
Angrw. C h r m . I n t . Ed. Engl. 17 (1978) No. 12
.-
~
E . h g d , J . Sombroek, W Wugemurin, Angew. Chem. 87, 591 (1975);
Angew. Chem. Int. Ed. Engl. 14, 564 (1975).
[2] R. Drstro, 7: Piluti, M . Simonettu, Acta Crystallogr. 8 3 3 , 940 (1977).
[3] a) F . Sondheimer, Acc. Chem. Res. 5 , 81 (1972); b) M. N u k u g o w ,
Pure Appl. Chem. 44, 885 (1975); c) V Boekrlheidr, ihid 4 4 , 751 (1975);
and literature cited therein.
[4] E . Vogel, H . M . Deger, J . Palm, A . Wugner, J . Leu, Angew. Chem.
and Angew. Chem. Int. Ed. Engl., in press.
[5] 7: Pilati, M . Simonrtru, Acta Crystallogr. 8 3 3 , 851 (1977).
[6] R. B. Woodwnl, R . Hoffniuriri, Angew. Chem. K l , 797 (1969); Angew.
Chem. Int. Ed. Engl. X, 781 (1969); R . Huisgrn, Chim. Ind. (Milan)
51,963 (1969).-The cyclizations of (a), (/Oj,and ( 1 2 ) to the corresponding dihydro[18]annulenes, interpreted here as disrotatory 18x-electrocyclic processes, can be alternatively explained in terms of a 6rr-electrocyclic process (cycloheptatriene-norcaradieneisornerization) followed
by a number of Cope rearrangements equal to the number of bridges.
171 G. Kobrich, H . f i u p p , K . Florr, W Drischel. Chem. Ber. 99, 689 (1966).
[X] I t could be shown by thermolysis of the p$-dideuteriovinylchlorovinyl
compound that the cyclization of ( 1 0 ) does not proceed uiu an acetylene
intermediate. This finding warrants mention, since in the meantime
it has been found that the ethynylvinyl compound also gives (31 on
thermolysis (unpublished experiments in collaboration with M. Huneit):
cf. also the benzene synthesis by thermal cyclization of 1,3-hexadien-5yne described by H. Hopfand H . Musso, Angew. Chem. 81, 704 (1969);
Angew. Chem. Int. Ed. Engl. 8, 680 (1969).
191 Other solvents have proved less suitable; on recrystallization of the
NMR-spectroscopically pure annulene ( 3 ) from toluene ( - 20°C)
cu. 50 "/, of the substance remains in the mother liquor.
[lo] C . E. Burhers, 7: SchurJtr, Chem. Rev. 71, 617 (1971).
[I 11 An X-ray structure analysis ofcompound (3 j has so far been impossible
due to the state of the crystals (thin, flaky platelets).
[I]
syn,syn-l,6 :€417 :10,15-Trismethano[ 18Jannulene
DicationDication of a [4n+ 21Annulene
By Hans M. Deger, Klaus Miillen, and Emanuel Vogel[']
The dications of polycyclic arenes, which can be regarded
as 4 n n electron systems, have been known for some
time"*21. Annulene dications have also been described
on a number of
however, in this case, all the
species studied-with
exception of the hexachlorobenzene
dicati~n[~I-have been aromatic (4 n 2)n-electron systems
derived from [4n]annulenes. The formal structural relationship between syn,syn-1,6:8,17: 10,15-trismethano[18]annulene
(1)['1and naphthacene ( 3 ) , which is oxidized to ( 4 ) in superacid
would suggest [4n+ Zlannulene ( I ) as being
a possible candidate for the formation of a potentially antiaromatic dication.
+
[*] Prof. Dr. E. Vogel, Dr. H. M. Deger
Institut fur Organische Chemie der Universitit
Greinstrasse 4, D-5000 Koln 41 (Germany)
Priv.-Doz. Dr. K. Mullen
Laboratorium fur Organische Chemie der Eidgenossischen Technischen
Hochschule
Universitatstrasse 16, CH-8092 Zurich (Switzerland)
957
downfield than those of (1 ). In contrast there is essentially
no difference between the spectra of ( 2 ) and ( 1 ) as regards
the resonance positions of the annulene protons. This is understandable if one assumes that an upfield shift of the annulene
protons due to the ring current in (2) is compensated by
the influence of the positive charge.
,28
I21
111
-
'0333;'
I41
131
Addition of ( I ) in dichloromethane to a solution of fluorosulfonic acid in SOzCIF cooled to -80°C leads to a violet
reaction mixture whose color changes irreversibly to olivegreen on warming to 0°C. The NMR spectra of this solution,
which can be stored for weeks in a sealed tube at -2O"C,
show that the dication (2) is indeed presentl6-'I.
The main supporting evidence for the existence of (2) is
afforded by the seven-line I3C-NMR spectrum (Fig. l), from
which it follows that the CZvsymmetry of the starting material
is retained in the product. The downfield shift of the center
of the ring carbon signals observed during conversion of (1)
into (2) is 17.7 ppm and thus corresponds to the value expected
owing to the deshielding effect of the two positive charges
in (2). Since the shifts of the signals of the C atoms 7, 9,
16, and 18 are most pronounced, it may be assumed-by
analogy with the situation in the naphthacene dication ( 4 )
and in agreement with M O calculations-that a build up
of charge occurs at these positions.
C-7.6.16 18
137.0 '
C-3.4.12,13
' 126.5
1'
C-1.6.10.15
107.0
7
c-20
c-19.21
26.7
14.1
5
'
'a
I
121
3
OCH,
151
Chemical evidence for the existence of (2) was provided
by the isolation of a solvolysis product: on treatment of a
solution of (2) in dichloromethane at -80°C with methanol
and subsequent chromatography of the mixture on silica gel
(dichloromethane/ether/hexane, 1 : 1 :2) a dihydrodimethoxy
derivative of ( f ) is obtained [bright yellow rhombohedra,
m. p. 205-206°C (methanol/ethyl acetate); yield 13 %I, which
according to the spectra has the structure ( 5 ) with cis arrangement of the methoxy groups[*] ['H-NMR (CDC13): 6=0.00
and 3.75 (AX system, J = 12Hz, 2H, H-19), 1.09 and 4.25
(AX system, J = 15 Hz, 2H, H-21), 3.75 and 4.22 (AX system,
J = 1 2 H z , 2H, H-20), 3.98 (s, 2H, H-7, 18), 5.70-5.84 and
6.18-6.37 (AA'XX' system, 4H, H-2, 3, 4, 5), 6.05 (s, 2H,
H-9,16),6.18-6.37and6.67-6.82(AAfXX'system,4H,
H-11,
12, 13, 14), 3.37 (s, 6H, 2OCH,)].
It is conceivable that the oxidation of [4n+2]annulenes
to dications is not restricted to the example described here,
but is a general reaction for higher [4n + 2lannulenes.
Received: September I I , 1978 [Z 1 IOb IE]
German version: Angew. Chem. YO. 990 (1978)
I
W l j Aalhersherg, G. J . Hoijrink, E. L. Mackor. W P. Weijland, J. Chem.
Soc. 1959.3055.
[2] For more recent I3C-NMR spectroscopic studies on such dications, see:
a) D. A. Forsyth, G. A. Olah, J . Am. Chem. Soc. 98, 4086 (1976); b)
K . Mullen, Helv. Chim. Acta 59, 1357 (1976).
J . F . M . Orh, D. M . Sniifli, U . Prange. G. SchrBder. Angew. Chem.
85. 352 (1973); Angew. Chem. Int. Ed. Engl. 12, 327 (1973); G. A . Olah.
J . M . Bollinger, A. M . White, J . Am. Chem. Soc. 91, 3667 (1969); G.
A. Olah, J . S . Sraral, G. Liurtg. L. A. Puquetfr, W P. Mrleqa, M . J .
Curmodj, ihid. YY, 3349 (1977).
E. Wussrriiiuii, R. S. Hutfoii, K J . Kuck, E. A . Chuiiilross, J . Am. Chem.
Soc. 96, I965 ( I 974).
W Wugestuiiii. M. lyodu, H. M . Deger, J . Sontbroek, E. Vogel. Angew.
Chem. 90, 988 (1978); Angew. Chem. Int. Ed. Engl. 17, 956 (1978).
The mechanism of the oxidation of ( I ) to (2) is still an open question.
We are currently carrying out investigations in an attempt to elucidate
whether a cr-complex is initially formed or whether the reaction proceeds
riu a radical cation. The reaction of ( I ) with antimony pentafluoride
in SOZCIF, which also leads to ( 2 ) , might involve a radical cation
mechanism.
As already found by P. Wururr and S. Wirisreiii, under the conditions
employed for the generation of (2) from ( I ), 1,6-methano[IO]annulene
affords a stable 0-complex, cf. J. Am. Chem. Soc. 91, 7785 (1969).
From the spectra it is not certain which configuration the methoxy
groups assume with respect to the C H z bridges. An X-ray structure
analysis is expected to resolve this problem.
[I]
1B
I
100
-6
i0
i
TMS
Fig. 1. Schematic representation of the "C-NMR spectra of ( I ) and ( 2 ) .
In agreement with the expectation that the dication (2) (as
a 4 nn-electron system) exhibits a paramagnetic ring current,
the resonances of the bridge protons in the 'H-NMR spectrum
of (2) [(S0,C1F/CD,C1,/FS03H, - 10°C): 6=4.35 and 7.58
(AX system, J=14.4Hz, 4 H , H-19, 21), 6.07 (s, 4H, H-7,
9, 16, 18), 7.01-7.35 (AA'XX" system, 8H, H-2, 3, 4, 5, 11,
12, 13, 14), 8.25 (s, 2H, H-20)] appear considerably further
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A i i g w . Chrm. lttr. Ed. Engl. 17 (1978) N o . 12
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