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Benzenoid versus Annulenoid Aromaticity Synthesis and Properties of Kekulene.

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same conditions neither 1,3-cyclooctadiene nor 1,3,5-cyclooctatriene can be converted in significant amounts into ( 6 ) ,
1,3,6-cyclooctatriene on the other hand reacts smoothly to
give this product; addition of the BuLi-reagent to (2) and
(4) does occur and in the case of (2) bicyclo[3.3.0]oct-2-ene
(8) is formed. This suggests that (1) and BuLi.TMEDA
initially form ( 3 ) . which is transformed into ( 5 ) bv loss of
LiH and TMEDA. Double metalation of ( 5 ) yields the intermediate (6).
H
H
H
H
H
H
Ilal
Procedure
Compound (1) (12m1, 10.6g, 98mmol) is added to
C6H5Nars1(0.31 mol) in olefin-free pentane (150 ml) and
TMEDA (95ml), and the mixture is stirred under reflux for
20 h. A slow current of dry O2 is then passed over the well
stirred mixture at -5°C for ca. 24h. After filtrationr7] the
solution is vacuum distilled, freed from TMEDA with S N
HC1, neutralized, anddried. G C analysis reveals 1.5 % (163mg,
1.5mmol) of (8) and 78.5 % (8 g, 76.9mmol) of (7), based
on quantitatively consumed (1). The remainder of (1) is
present as oligomerization product in the distillation residue.
Received: March 14, 1978 [Z 959 IE
German version: Angew. Chem. 90, 380 (1978)
CAS Registry numbers:
( I ) , 111-78-4; ( 2 ) , 1700-10-3; ( 4 ) , 1871-52-9; IS), 3725-30-2; (7), 629-20-9;
( 8 ) . 5549-09-7
[l] J. Klein, A. Medlik, J. Chem. SOC.Chem. Commun. 2973, 275.
[2] J. J. Bahl, R. B. Bates, W A. Beavers, C . R . Launer, J. Am. Chem.
SOC.99, 6126 (1977).
[ 3 ] R . B. Bates, D. A . McCombs, Tetrahedron Lett. 1969, 977.
[4] Cf. A. W Longer, Adv. Chem. Ser. 230, l(1974).
[5] a) I: J . Kutz, J. Am. Chem. SOC.82, 3784 (1960); b) I: A. Antkowiak
H . Shechler, ibid. 94, 5361 (1972).
161 As recently reported, ( I ) can be transformed into (7), albeit in poor
yield by reaction with potassium and subsequent oxidation: W J. Evans,
A . L . Wuyda, C.-W Chang, W M . Cwirla, J. Am. Chem. Soc. 100, 333
(1978).
[7] Caution! NaOl decomposes spontaneously with evoiution of O 2 on
exposure to water. The filter cake is sensitive to heat and shock when
dry.
[8] J . F. Nobis, L. F . Moormeier, Ind. Eng. Chem. 46, 539 (1954).
Benzenoid versus Annulenoid Aromaticity : Synthesis
and Properties of Kekulene[ ‘I
By Francois Diederich and Heinz A. Staab“]
In 1965, first attempts to prepare the hydrocarbon ( I )
were reportedr2].Then, at the centennial of Kekultf’s benzene
formula, this compound which may be regarded as a “superbenzene” on account of its planar cyclic conjugation and
D6,, symmetry was given the name “kekulene”[2~3].
(1) was
of interest in connection with investigations to experimentally
define benzenoid as against annulenoid aromaticity : on the
one hand, (1) can be formulated as a combination of two
[4n + 2]annulenes-[l Slannulene inside, [30]annulene outside-bridged by radial single bonds (I a), and on the other,
as a regular benzenoid system with a closed circle of angularly
annellated benzene rings ( l b ) . Since ( I ) , in this respect a
representative of a new class of aromatic compounds, has
an intramolecular cavity containing hydrogen atoms it should
be possible to decide by proton resonance whether an annuIenoid diatropism in the macrocyclic system can compete
successfully with ring-current induction within the benzenoid
subunits.
[*] Prof. Dr. H. A. Staab, Dip1.-Chem. F. Diederich
Abteilung Organische Chemie, Max-Planck-Institut fur mediziniscbe
Forschung
Jahnstrasse 29, D-6900 Heidelberg 1 (Germany)
372
H
llbl
In an attempt to synthesize ( I ) via a very involved and
tedious route Vogtle and S t ~ a b [were
~ ] able to show, on the
basis of a mass spectrometric analysis, that the desired compound was probably formed, albeit in minute and unisolable
amounts. Since preparation of (I) via such a route seemed
impossible all further efforts were abandoned 10 years ago.
Attempts by Tenny et
to prepare (11, which they named
‘[I Zlcoronaphene’ apparently were likewise unsuccessful.
Newly developed methods for C...C coupling in macrocyclic
systems, especially by sulfur extrusion from dithia[3.3]phanes,
prompted us now to resume our efforts to synthesize (1).
The first steps of the synthesis followed,with minor modifications, those of the previously reported synthesis of 5,6,8,9-tetrahydrodibenzo[~,j]anthracene‘~~.whose bromomethylation
according to the procedure used for 9,10-dihydrophenanthrend6], led to the bis(bromomethy1)derivative (2j’l in 50%
yield. After conversion of (2) into the bis(mercaptomethy1)
derivative (3)17] [thiourea method; 75 % yield, m.p. 243°C
(corr.)], (2) and (3) were cyclized to 6,7,9,10,23,24,26,27-octahydro- 2,19 - dithia [3.3] (3,ll)dibenzo[a,j] anthracenophaner’]
(4) [dilution apparatus of Vogtle; solutions of (2) and ( 3 )
in benzene (each 5.3 mmol in 3 500 ml) added dropwise and
simultaneously within 72 h into a boiling mixture of lo00 ml
benzene, 1000ml ethanol (95 %) and 4 g potassium hydroxide;
55 % yield]. (#)[’I:
yellowish platelets, m. p. 291 “C (corr.);
‘H-NMR (360 MHz, CDC13): 6=2.70 (s, 16H, H6,7,9,10,23,24,26,27), 3.82 (s, 8H, H-t,3,18,20), 6.73 (dd, 3 = 8
and 1.8Hz, 4H, H-13,17,30,34), 6.91 (s, 2H, H-8,25), 6.94 (d,
J z I . ~ H z , 4H, H-5,11,22,28), 7.40 (d, J = 8 H z , 4H, H14,16,31,33),7.83 (s, 2H, H-15,32).
6
7
8
IZI, X =Br
131. X = SH
141
Irradiation of (4) in trimethyl phosphite (450W Hg highpressure lamp, 2h, under N2) led in 60% yield to
5,6,8,9,21,22,24,25- octahydro[2.2](3.1 1 )dibcn/o[tr.i]anthra cenophane (5)171: colorless needleh. ni. p. 162 464°C. ( 5 ) ,
which had already been obtained in very unsatisfactory yield
(1.5%) from (2) by a Wurtz reaction (phenyllithium, ether/
benzeney41, was dehydrogenated with 2,3-dichloro-5,6Angew. Chem. Int. Ed. Engl. 27 ( I 978) N o . 5
dicyano-1,4-benzoquinone(DDQ) [24 h, boiling benzene, 80 %
yield] to (6)L7]: pale yellow needles, m. p. 490-495°C (dec.);
MS: m/e=608 ( M ' , base peak), 304 (70 %). The rigid steplike
structure of the molecule is confirmed by the absorption
of the methylene bridges and the upfield shift of the adjacent
internal aromatic protons in the 'H-NMR spectrum (360
MHz, CDCI3, 45°C) [S=2.69 and 3.33 (each 'd', J e 9 H z ,
for axial and equatorial H-1,2,17,18, resp.), 5.76 (dd, J = 9
and 2Hz, 4H, H-12,16,28,32), 7.68 and 7.81 (AB, J = 8 H z ,
8H, H-5,9,21,25 and H-6,8,22,24), 7.72 (d, J e 2 H z , H4,10,20,26),8.04 (d, J = 9 H z , 4H, H-13,15,29,31), 8.31 (s, 2H,
H-7,23), 9.56 (s, 2H, H-14,30)][91.All attempts to achieve the
internal ring closure in ( 6 ) and the dehydrogenation to ( I )
have so far remained unsuccessful.
present: short irradiation (10min, 300 W Osram-Ultra-Vitalux
lamp) in benzene in the presence of iodine afforded the octahydro derivative (9)['], the first compound with the carbon
skeleton of kekulene, in 70 % yield: m. p. > 620°C, pale yellow
needles (from nitrobenzene), diflicultly soluble in all solvents.
MS: m/e=608 (20%, Mf), 607 (8), 606 (14), 605 (5), 604
(14), 603 (9), 602 (35), 601 (55), 600 (base peak, corresponding
to ( I ) ) and the doubly and triply charged ions therefrom
at m/e= 300 (82) and 200 (7). 'H-NMR (360 MHz, [D,]nitrobenzene/arsenic trichloride, 1 : 3, 685 scans): S = 3.1 1-3.27
(AABB', 16H, H-1,5,10,14 and H-2,4,11,13), 7.26 (s, 2H, H3,12), 7.74 and 7.77 (each s, 4H,H-7,8,16,17 and H-6,9,15,18),
9.19 (s, 2H, H-20,23), 9.67 (s, 4H, H-19,21,22,24).
191
IS/
/6/
Subjection of the bis-sulfonium salt formed on reaction
of the dithiaphane ( 4 ) with methyl fluorosulfonate (in methylene chloride, 95 % yield) to Stevens rearrangement (potassium
tert-butoxide, tetrahydrofuran, 12h, 20"C, under Nz, 60 %
yield), renewed methylation (methyl fluorosulfonate, methylene chloride, 90 % yield) and elimination (potassium tertbutoxide, tetrahydrofuran, 12 h, 20°C, 9 % yield) afforded
5,6,8,9,21,22,24,25- octahydro [2.2] (3,ll)dibenzo [ q j ] anthracenophanediene (7)[']: pale yellow needles, m. p. 472°C (dec.);
'H-NMR (360MHz, CDC13): 6=2.883 (s, 16H, H5,6,8,9,21,22,24,25), 6.575 (dd, J=8.28 and 1.68 Hz, 4H, H12,16,28,32),6.745 (s, 4H, H-1,2,17,18), 7.098 (d, J=1.68Hz,
4H, H-4,10,20,26),7.114 (s, 2H, H-7,23), 7.365 (d, J=8.28Hz,
4H, H-13,15,29,31),7.658 (s, 2H, H-l4,30).-Dehydrogenation
of (7) with DDQ (boiling benzene, 20h, 66%) yielded the
dibenzo[aj]anthracenophanediene (8)[71: yellow needles,
m.p. >52OoC (sub].); MS: M + calc. for C4sHzs 604.2191,
obs. 604.2197; 'H-NMR (360 MHz, [D,]nitrobenzene, 80°C):
6=7.075 (s, 4H, H-1,2,17,18), 7.119 (d, J=8.7Hz, 4H, H12,16,28,32),7.782 (br. s, 4H, H-4,10,20,26), 7.737 and 7.793
(AB, J=8.95Hz, 8H, H-5,9,21,25 and H-6,8,22,24), 8.141 (s,
2H, H-7,23), 8.602 (d, J=8.7Hz, 4H, H-13,15,29,31), 9.742
(s, 2H, H-14,30) [numbering of carbon atoms cf. formula
~ 1 .
171
I81
In contrast to (a), an easy photo-cyclodehydrogenation
was possible with (7) in which two cis-stilbene units are
Angew. Cltem. Int. Ed. Enyl. I7 (1978) No. 5
Because of the low solubility of (9) the dehydrogenation
with DDQ required rather drastic conditions (1,2,4-trichlorobenzene, 100"C, 3d). Kekulene ( I ) was formed in 80 % yield.
With its extreme insolubility in solvents of all kinds, ( I )
is certainly outstanding among hydrocarbons of comparable
molecular weight: for recrystallization, for example, 350ml
I-methylnaphthalene at the boiling point (245"C) dissolved
10mg ( I ), or 100ml boiling 1,2,4-trichlorobenzene (b.p.
214°C) about 1 mg ( I ) . Kekulene (I)['], greenish-yellow microcrystals, m.p. >620"C, can be sublimed at 500°C/10-3
torr. MS: Mf calc. for C48H24 600.1858, obs. 600.1878. In
the mass spectrum, which is extraordinarily poor in fragment
peaks, there appear besides the molecular peak m/e = 600
(100%) the doubly and triply charged molecular ions at
m/e= 300 (43 %) and 200 (7 %); above the molecular peak
and its I3C-peaks with intensities expected for c48 no
further peaks are observed (up to m/e= 2000, temperature
of the ionic source up to 400°C)['01. The complete dehydrogenation of (9) is also shown by the IR spectrum (KBr)
in which the aliphatic v(C-H) absorptions have disappeared;
the spectrum shows only aromatic v(C-H) absorptions (3007
and 3020cm-I) and, in accord with the high molecular
symmetry, is very poor in vibration absorptions.
The electronic spectrum of ( I )
molar solution in
1,2,4-trichlorobenzene)shows the following absorptions: h,,,
388 nm (1gE 4.22), 347 (sh, 4.74), 326 (4.93). Solutions of ( I )
exhibit intense green fluorescence; in 1,2,4-trichlorobenzene a
fluorescence emission is observed from about 400 to 550nm
with maxima at 420 and 435 nm (excitation at 365 nm). Under
the same conditions a phosphorescence emission is observed
around 590 nm with a half life of 0.6 s at - 196OCrl'1.
The extreme insolubility of ( I ) made the recording of a
'H-NMR spectrum extraordinarily difficult. In the first usable
spectra (80MHz) of a saturated solution of ( 1 ) in [D3]-1,3,5trichlorobenzene at 215°C after about 50000 scans three
signals were observed reproducibly at F = 7.94, 8.37 and 10.45
in the intensity ratio of 2: 1 : 1[Iz1. According to these results,
there is no signal shifted strongly upfield as would be expected for the internal protons in the case of a synchronous
induction of diamagnetic ring-currents in a double annulene
system. On the contrary, intensity ratios and comparison with
the 'H-NMR data of compounds ( 5 ) to ( 9 ) lead to the
373
assignment of the signal at 6 = 7.94 to the twelve equivalent
protons H-1,2,4,5,7,8..., of the absorption at 6 = 8.37 to the
second group of equivalent external protons H-3,6,9,12,15,18
and of the signal at 6=10.45 to the six internal protons
H-19,20,21,22,23,24[numbering as in ( 9 ) ] .The peculiar downfield shift just of the internal protons of (1) is taken as a strong
experimental argument against the dominance of an annulenoid ring-current in the macrocyclic system and in favor of
a strong coupling between the inner and outer perimeters
according to the benzenoid formulation ( I b). This result is
inconsistent with calculations of the diamagnetic anisotropy
for ( I ) using the semi-classical approach of P a ~ l i n g [ ' ~ "it] ;
agrees qualitatively, however, with more recent MO calculations['31.
Received: March 2, 1978 [Z 954a I E ]
German version: Angew. Chem. 90,383 (1978)
CAS Registry numbers:
( I ) , 15123-47-4; (2), 66183-91-3; ( 3 ) , 66183-90-2; ( 4 ) , 66183-89-9; (j),
19576-05-7;(61,661 83-88-8; (7), 66183-87-7;(S), 21273-84-7; (9), 66183-86-6
Conjugation in Macrocyclic Systems, Part 27.-Part 26: li. E. Meissner,
A. Gender, H.A. Staub, Tetrahedron 1977, 3.
H.A. Staab, Plenary Lecture at the Annual Meeting, Gesellschaft Deutscher Chemiker (Kekul6 Centennial) in Bonn on 14.9.1965.
The naming of ( I ) as a polycyclic system according to the IUPAC
rules on nomenclature leads to an extraordinarily complicated name
which does not give any direct information about structure and symmetry of the molecule (see also [4]).
F . Mgtle, H. A. Staab, Chem. Ber. 101, 2709 (1968).
K. Burri, @! Jenny, Helv. Chim. Acta 50, 1978, 2542 (1967); W Jenny,
R. Paioni, Chimia 22, 248 (1968); 23, 41 (1969); Helv. Chim. Acta
53, 141 (1970); P . Baumgarfner, R. Paioni, W Jenny, ibid. 54, 266 (1971).
H. A. Sraab, M . Haeuei, Chem. Ber. 106, 2190 (1973); cf. also J . u.
Braun, Ber. Dtsch. Chem. Ges. 70, 979 (1937).
Elemental analyses, molecular weights and spectroscopic data are in
agreement with the structures mentioned.
For the 'phane-nomenclature' cf. F. M g t l e , P. Neumann, Tetrahedron
26, 5847 (1970).
Cf. the results obtained for the sterically similar [2.2](2,7)naphthaIenophane: J . R . Dauy, J . A. Reiss, Aust. J. Chem. 29, 163 (1976).
We thank Dr. W Otting, Max-Planck-lnstitut fur medizinische Forschung Heidelberg, for the recording of the mass spectra, which for
most of the compounds mentioned here was very difficult.
I). Schweitzer, unpublished.
We thank Professor J . Dabrowski and D. Griebel of our Department
for the great erfort made by them in overcoming the unusual technical
difficulties in the 'H-NMR-measurements of ( I ) .
a) R. McWeeny, Proc. Phys. Soc. London A 6 4 , 261, 921 (1951); c t
also L. Pauling, J. Chem. Phys. 4, 673 (1936); b) G. Ege, H. Fischer,
Tetrahedron 23, 149 (1967); G. Ege, H . Vogler, Theor. Chim. Acta
26, 55 (1972).
Attempts to Synthesize Zwitterionic Donor-Acceptor
Cyclophanes: The Diastereomeric 12,15Bis(dirnethylarnino)-[2](2,5)-p-benzoquinono[2]paracyclophanes[
By Renate Reimann and Heinz A . Staabr]
Previous investigations of charge-transfer interactions in
donor-acceptor cyclophanes[21led to the question of the existence of 'paracyclophane-zwitterions' in which, as a consequence of an especially low ionization potential of the donor
or a high electron affinity of the acceptor, an electron transfer
[*] Prof. Dr. H. A. Staab, DipLChem. R. Reimann
Abteilung Organische Chemie, Max-Planck-Institut fur medizinische
Forschung
Jahnstrasse 29, D-6900 Heidelberg 1 (Germany)
314
from donor to acceptor occurs already in the ground state
of the molecule. Such paracyclophanes for which the radical
cation and the radical anion components would be fixed in
close proximity and definite orientation were of interest regarding the interaction between the radical electrons: strong
coupling should lead to a singlet (or a triplet?) ground state
of the molecule, whereas with weak transanular interaction
the single radical ion units of such a molecule should exist
in doublet spin states. Furthermore, we wondered whether
a zwitterionic structure of donor-acceptor cyclophanes would
result in a crystal structure comprising stacked cyclophane
moieties where the stacking axis is perpendicular or nearly
perpendicular to the cyclophane planes and, therefore, the
radical cation side of one cyclophane directly faces the radical
anion side of the neighboring molecule. For such lattice structures peculiar anisotropic crystal properties (e. g., changes in
electrical conductivity) might be expected.
As an effort aimed in this direction we synthesized the
donor-acceptor cyclophanes ( 1 ) and (2) in which p-benzoquinone as acceptor is combined in pseudo-ortho and pseudogeminal orientations with the especially strong donor
N,N,N,N'-tetramethyl-p-phenylene diamine (TMPD). The
zwitterions (1 a ) and ( 2 a ) corresponding to (1) and (2),
respectively, would include as components the semiquinone
radical anion and the 'Wurster's Blue' radical cation, both
of which are known as relatively stable radical ions. Although,
in intermolecular CT complexes of TMPD, the formation
of radical ions apparently requires acceptors with higher electron affinity (e.g., chloranil)r31.due to the specific interactions
in [2.2]paracyclophanes, no definite conclusions could be
drawn regarding the stability of the zwitterions ( l a ) and
( 2 a ) as against ( 1 ) and (2).
/la/
1Zal
For the syntheses of (1 ) and ( 2 ) , after the failure of more
direct synthetic routes, we had to adopt the multi-step course
starting from the diastereomeric 4,7-dimethoxy-12,15-dimethoxycarbonyl[2.2]paracyclophanes (3) and ( 4 ) which had
already been synthesized as donor-acceptor cyclophanes previously"].
Hydrolysis of (3) (potassium hydroxide, methanol; 24 h,
97 % yield) afforded the dicarboxylic acid (5)r41 (dec. > 320°C),
which on reaction with sulfinyl chloride (chloroform/dimethylformamide; 85 % yield) gave thedichloride (7)[41 (m.p. 152°C).
Treatment of (7) with sodium azide in acetone/water afforded
the diazide (9)C41 (dec. > 9 0 T , 85 % yield). Subsequent Curtius
reaction of (9) (boiling toluene, 2 h) led to the diamino derivative which, on account of its extraordinary instability, without
further purification and characterization was methylated with
methyl iodide/potassium carbonate (methanol, 2 0 T , under
argon) to pseudo-ortho-4,7-dimethoxy-12,15-bis(dimethylamino)[2.2]paracyclophane (11)14] (colorless crystals, m.p.
98 "C, overall yield 3 1 %).
Angew. Chem. Int. Ed. Engl. 17 (1978) No. 5
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