Synthesis, structure, and properties of twofold bridged sesquinorbornenes

Article abstract of DOI:10.1002/(SICI)1099-0690(199809)1998:9<1759::AID-EJOC1759>3.0.CO;2-I

The twofold bridged sesquinorbornenes 2 and 6 were prepared using sequential [4 + 2] cycloadditions of benzoquinone with 1,5-dihydropentalenes 1 and 5. These syntheses were improved using dilution conditions or a more reactive substituted benzoquinone. Results from semiempirical and ab initio DFT calculations indicated remarkably high pyramidalization angles (φ = 46-47°) for the central C-C double-bond atoms. The chemical reactivity with triplet and singlet oxygen, dimethyldioxirane and N-methyl-1,2,4-triazoline-3,5-dione supports these structural assignments.

Full text of DOI:10.1002/(SICI)1099-0690(199809)1998:9<1759::AID-EJOC1759>3.0.CO;2-I

FULL PAPER
Synthesis, Structure, and Properties of Twofold Bridged Sesquinorbornenes
Axel G. Griesbeck*a, Thomas Deufelc, Georg Hohlneicherb, Rupert Rebentischb, and Jörg Steinwaschera
Institut für Organische Chemie der Universität zu Kölna,
Greinstraße 4, D-50939 Köln, Germany
Fax: (internat) ϩ 49(0)221/470-3083
E-mail: griesbeck@uni-koeln.de
Institut für Physikalische Chemie der Universität zu Kölnb,
Luxemburgstraße 116, D-50939 Köln, Germany
Institut für Organische Chemie der Universität Würzburgc,
Am Hubland, D-90737 Würzburg, Germany
Received April 23, 1998
Keywords: Alkenes / Cycloadditions / Cage compounds / Ab initio calculations / Double-bond pyramidalization
The twofold bridged sesquinorbornenes
prepared using sequential [4 2] cycloadditions of central C–C double-bond atoms. The chemical reactivity
benzoquinone with 1,5-dihydropentalenes 1 and 5. These with triplet and singlet oxygen, dimethyldioxirane and N-
syntheses were improved using dilution conditions or a more methyl-1,2,4-triazoline-3,5-dione supports these structural
reactive substituted benzoquinone. Results from assignments.
semiempirical and ab initio DFT calculations indicated
2
and
6
were
remarkably high pyramidalization angles (␾ = 46–47°) for the
+
The structural properties and the chemical reactivity of ments and studies on the chemical reactivity as well as
syn-sesquinorbornes have been studied intensively[1] in the theoretical investigations with these molecules.
last decades. Especially the symmetric deformation of the
Figure 1. Pyramidalization angle ␾
central CϪC double bond is a remarkable property which
leads to an increased reactivity in comparison with nor-
bornenes. One out of several parameters which are used to
describe the out-of-plane deformation is the pyramidali-
zation angle ␾ as defined by Borden[2] (cos ␾ ϭ Ϫcos
(RCC)/[cos 0.5(RCR)], see Figure 1). Several syn-sesquinor-
bornes have been described with ␾ values up to 25°.[3]
Much higher pyramidalization angles have been determined
A sequence of inter- and intramolecular Diels-Alder re-
actions of the dihydropentalene 1[13] with 1 equivalent of p-
benzoquinone gave the cage compound 2a in relatively low
yields (15Ϫ20%). The major product was the 1:2 adduct 3a
from 1 and two equivalents of p-benzoquinones. (Scheme
1).
for the fullerene C60 (␾ ϭ 31.6°),[4] a sesquinorbornatri-
ex.
ene (␾ ϭ 32.4°)[5] and a secododecahedradiene (␾
ϭ
ex.
ex.
35.3°).[6] The 9,9Ј,10,10Ј-tetradehydrodianthracene (10),
prepared more than twenty years ago, has one of the high-
est ␾ angles for symmetrically out-of-plane bent alkenes
Scheme 1
(␾ ϭ 35.9°).[7] Recent studies have revealed the unusual
ex.
reactivity of this compound.[8] Even higher pyramidaliz-
ation values were determined for bridgehead-substituted
tribenzodihydroacepentalenes (␾ ϭ 45.8 and 47.2°),[9]
ex.
however, these molecules are asymmetrically bent, i.e. the
pyramidalization angles for the second olefinic carbon atom
are much lower (␾ ϭ 27.6 and 30.2°). In the series of
ex.
isolable unsaturated dodecahedrane molecules, for dodeca-
hedradiene a remarkably high pyramidalization angle was
For other monofunctional dienophiles such as maleic an-
calculated (␾
ϭ 42.9°).[10][11] Recently, we discovered a hydride, the equilibrium constant of the double-bond iso-
calc.
simple reaction sequence which results in cage compounds mers I and II could be determined (ca. 5). This was not
with a twofold bridged sesquinorbornene structure.[12] We possible for the benzoquinone adducts Ia and IIa due to the
expected these compounds to exhibit an additional increase rapid consumption of IIa by intramolecular cycloaddition.
in double-bond nonplanarity compared with their un- When the reaction of 1 and benzoquinone was performed
bridged analogues. Herein we describe synthetic improve- with 0.2 equivalents of benzoquinone, the primary Diels-
Eur. J. Org. Chem. 1998, 1759Ϫ1762
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1998
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1759

A. G. Griesbeck, T. Deufel, G. Hohlneicher, R. Rebentisch, J. Steinwascher
1
FULL PAPER
Alder cycloadduct Ia was detected by low-temperature H lations (vide infra). A characteristic property of syn-sesqui-
NMR and the activation barrier for isomerization was de- norbornenes is that they readily add oxygen to give the cor-
termined to be 23 ± 2 kcal/mol (see Scheme 2).
responding epoxides.[16] Actually, the cage compound 2a
was quantitatively epoxidized by a variety of reagents: Di-
methyldioxirane (DMD) gave the epoxides 7 already after
some minutes at Ϫ20°C, singlet oxygen likewise reacted ef-
ficiently, whereas triplet oxygen needed some days for com-
pletion (Scheme 4). Oxirane 7 was crystallized as its meth-
anol adduct and characterized by X-ray analysis.[17] It is
important to mention, that no trace of 1,2-dioxetane or the
corresponding cleavage products were formed in the singlet-
oxygen reaction. Dioxetane formation can be found for
many strained alkenes which have no properly aligned al-
lylic hydrogen atoms.[18] Thus, the pyramidalization of the
central double bond is depicted in a radical-like behaviour
in its reaction with triplet oxygen as well as the unusual
oxygen-atom transfer from singlet oxygen. That this behav-
iour is not a consequence of extreme shielding by the two
flanking methylene bridges became apparent from the reac-
tion of 2a with N-methyl-1,2,4-triazoline-3,5-dione
(MTAD) in aqueous THF which led to the adduct 8. For
TAD [2 ϩ 2] cycloaddition reactions an intermediate aziri-
dinium imide zwitterion has been proven recently.[19] Thus,
adduct 8 probably resulted from the nucleophilic ring open-
ing of such an intermediate with substrate 2a.
Scheme 2
In order to improve the yield of cage compounds we
examined two modifications: (a) Use of more reactive
benzoquinones which should accelerate the intra- versus the
intermolecular cycloaddition, and (b) application of the di-
lution principle in order to suppress the addition of a se-
cond equivalent of benzoquinone to the intermediate I.
Treatment of the 1,5-dihydropentalene 1 with 2-(4-nitro-
phenyl)benzoquinone as bifunctional nonsymmetric dieno-
phile resulted in two regioisomeric products 2b and 2c in a
ratio of 57:43 (Scheme 1). The constitution of the cage
products could be easily derived from the H-H coupling
patterns. Surprisingly, no 1:2 cycloaddition products were
isolated. As can be seen from the product substituent pat-
tern, the primary cycloaddition exclusively involves the un-
substituted benzoquinone double bond (which can be easily
derived from the H-H coupling pattern in the products).
Thus, the secondary intramolecular cycloaddition must
have been accelerated by the p-nitrophenyl group and the
intermolecular reaction is widely suppressed. The second
alternative was the use of dilution conditions. By slow ad-
dition of p-benzoquinone to a solution of 1 in dichloro-
methane the yield of 2a could be raised to 52%. More im-
portant was the fact that this procedure allowed the prep-
aration of the unsubstituted cage compound 6 from 1,5-
dihydropentalene 5 (Scheme 3). The starting material 5 is
easily available by thermolysis of the pentafulvene 4.[14][15]
After treatment with 1.1 equivalents of p-benzoquinone un-
der dilution conditions, a 65:35 mixture of cage product 6
and a 1:2 cycloaddition product were isolated. After flash
chromatography, 6 could be isolated as a colorless oil in
29% yield.
In order to gain more detailed information on the degree
of double-bond deformation, we performed a series of semi-
empirical and DFT calculations for the unsubstituted cage
compound 6, its deoxygenated (hypothetical) analogue 9 (in
order to exclude through-space carbonyl-carbonyl interac-
tions) and the tetradehydrodianthracene 10 (Figure 2).
Force field calculations (MM2[20]) resulted in too high val-
ues for the pyramidalization angle ␾: e.g. for GreeneЈs com-
pound 10 a ␾ value of 43.3° resulted (␾ ϭ 35.9°). Semi-
ex.
empirical methods resulted in more realistic values: AM1[21]
calculation gave 35.4° for 10 [for C60
␾
is 31.9° (␾
ϭ
calc.
ex.
31.6°)]. For compound 6 the force field predicts a pyrami-
dalization of 52.8°, the AM1 calculation gave 48.6°. To
further optimize these results we performed density func-
tional theory calculations (DFT-B3LYP[22]) with the 6-
31G* basis set.[23] The GAUSSIAN94 program package
was used for these calculations.[24] The results for 6 and 9
were nearly identical: for 6 a ␾ value of 46.5° (9: 47.1°)
resulted (Table 1). Another useful parameter for the de-
scription of large symmetrical out-of-plane bending is the
αav value.[25][26][28] For GreeneЈs compound 10 αav is 114.8°,
Scheme 3
for C60 aav ϭ 116° (from X-ray data). The DFT calculations
for 6 and 9 resulted in αav values of 114.4° and 114.2°,
respectively. These calculations lead to the suggestion that
the (at room temperature stable) cage compounds 2, 6 have
remarkably high double-bond pyramidalizations. This pyr-
amidalization results mainly from the fact that the strong
compression of the α and β angles, which is typical for ses-
Unfortunately, no X-ray analysis could be performed so quinorbornenes, cannot be counterbalanced by expansion
far, neither from the parent compound 6 nor from its de- of the γ angle. In typical syn-sesquinorbornenes the γ angle
rivatives 2 due to low crystal quality. Nevertheless, we tried can reach values up to 144°.[3a]
to gain more information on the double-bond deformation
by studying the chemical behaviour and performing calcu-
This work was supported by the Deutsche Forschungsgemein-
schaft (SFB 347, University of Würzburg) and the Fonds der Chem-
ischen Industrie.
1760
Eur. J. Org. Chem. 1998, 1759Ϫ1762

Synthesis, Structure, and Properties of Twofold Bridged Sesquinorbornenes
Scheme 4
FULL PAPER
nitrogen at room temp. to a solution of 2.20 g (11.3 mmol) of 1 in
600 ml of CH2Cl2 by means of a motor-driven syringe during 24
h. After evaporation of the solvent, column chromatography re-
sulted in 1.90 g (40%) of a mixture of 2b and 2c as a brown solid
which was recrystallized several times from cyclohexane to give
1.20 g (25%) of a 1.3:1 mixture of 2b and 2c as a colorless powder.
Ϫ IR (CCl4, mixture): ν˜ ϭ 3010 cmϪ1, 2940, 1695, 1590, 1510,
Table 1. Results of calculations for 6 (9)
MM2
AM1
B3LYP/6-31G*
α
107.25
107.25
121.23
335.73
52.8
106.77
106.77
128.18
341.72
48.6
107.62 (107.55)
107.62 (107.55)
127.87 (127.53)
343.11 (342.63)
46.5 (47.1)
β
γ
α ϩ β ϩ γ
␾
1
1340, 1250, 1130. Ϫ 2b: H NMR (CDCl3): δ ϭ 1.55 (s, 3H), 1.73
(d, J ϭ 10.1 Hz, 1 H, 11-Hanti), 1.93 (d, J ϭ 10.3 Hz, 1 H, 14-
Hanti), 2.19 (m, 2 H, 11-Hsyn, 14-Hsyn), 2.96 (dd, J ϭ 2.9, 8.0 Hz, 1
H, 2-H), 3.08 (dd, J ϭ 2.9, 3.5 Hz, 1 H, 4-H), 3.52 (d, J ϭ 8.0 Hz,
1 H, 7-H), 3.65 (m, 1 H, 12-H), 4.03 (s, 1 H, 10-H), 7.20Ϫ7.51 (m,
7 H, Ar.-H), 8.10Ϫ8.20 (m, 2 H, Ar.-H). Ϫ 13C NMR (CDCl3):
δ ϭ 15.1 (q), 41.8 (t), 51.5 (d), 55.0 (d), 56.2 (t), 60.2 (s), 62.4 (d),
65.4 (d), 65.6 (d), 68.8 (s), 70.0 (s), 123.3 (d), 127.3 (d), 127.6 (d),
128.8 (d), 129.7 (d), 136.4 (s), 137.2 (s), 146.7 (s), 157.7 (s), 160.3
αav.
111.91
113.91
114.37 (114.21)
Figure 2. Pyramidalized alkenes 6, 9, 10
1
(s), 208.5 (s), 209.4 (s). Ϫ 2c: H NMR (CDCl3): δ ϭ 1.54 (s, 3H),
1.75 (d, J ϭ 10.6 Hz, 1 H, 11-H), 1.94 (d, J ϭ 10.3 Hz, 1 H, 14-
H), 2.19 (m, 2 H, 11Ј-H, 14Ј-H), 3.01 (d, J ϭ 8.0 Hz, 1 H, 2-H),
3.02 (dd, J ϭ 2.8, 3.6 Hz, 1 H, 5-H), 3.46 (dd, J ϭ 2.8, 8.0 Hz, 1
H, 7-H), 3.65 (m, 1 H, 10-H), 4.03 (s, 1 H, 12-H), 7.20Ϫ7.51 (m,
7 H, Ar.-H), 8.10Ϫ8.20 (m, 2 H, Ar.-H). Ϫ 13C NMR (CDCl3):
δ ϭ 15.1 (q), 41.8 (t), 52.2 (d), 54.0 (d), 55.9 (t), 60.7 (s), 63.2 (d),
65.1 (d), 65.2 (d), 68.3 (s), 69.6 (s), 123.4 (d), 127.3 (d), 127.6 (d),
128.8 (d), 129.7 (d), 136.4 (s), 137.2 (s), 147.0 (s), 154.8 (s), 157.4
(s), 208.5 (s), 209.4 (s).
Experimental Section
General: The dihydropentalenes 1 and 5 were synthesized accord-
ing to literature procedures.[13][14] Ϫ IR: Perkin-Elmer 1420. Ϫ H
1
NMR: AC 200 (200 MHz), Bruker AC 250 (250 MHz), Bruker AC
300 (300 MHz) Bruker AC 500 (500 MHz). Ϫ 13C NMR: Bruker
AC 200 (50.3 MHz), Bruker AC 250 (63.4 MHz), carbon multi-
plicities were determined by DEPT. Ϫ For 1H NMR, CDCl3 as
Hexacyclo[6.5.1.02,7.04,12.05,10.09,13]tetradec-9(13)-ene-3,6-dione
(6): A solution of 1.36 g (12.65 mmol) of p-benzoquinone in 100 ml
of CH2Cl2 was added under nitrogen at room temp. to a solution of
1.20 g (11.5 mmol) of 5 in 1000 ml of CH2Cl2 by means of a motor-
driven syringe during 24 h. After evaporation of the solvent, flash
chromatography resulted in 0.71 g (29%) of 6 as a colorless oil. Ϫ
solvent, TMS as internal standard; for 13C NMR, CDCl3 (δC
ϭ
77.0). Ϫ Column chromatography: Silica gel (Merck) 60Ϫ230
mesh; petroleum ether (PE, 40Ϫ60°C), ethyl acetate (EA). Ϫ Com-
bustion analyses: Institut für Anorganische Chemie der Univer-
sität Würzburg.
1-Methyl-8-phenyl-hexacyclo[6.5.1.02,7.04,12.05,10.09,13]tetradec-
9(13)-ene-3,6-dione (2a): A solution of 1.95 g (18.0 mmol) of p-
benzoquinone in 100 ml of CH2Cl2 was added under nitrogen at
room temp. to a solution of 3.50 g (18.0 mmol) of 1 in 1000 ml of
CH2Cl2 by means of a motor-driven syringe during 24 h. After
evaporation of the solvent, column chromatography (CH2Cl2/EA,
5:1, Rf ϭ 0.45) resulted in 2.83 g (52%) of 2a as a colorless powder,
m.p. 108Ϫ109°C (ref.[12] 106Ϫ108°C).
IR (CCl4): ν ϭ 2975 cmϪ1, 1725, 1685, 1265, 1090. Ϫ 1H NMR
˜
(CDCl3): δ ϭ 1.35 (d, J ϭ 10.2 Hz, 2 H, 11-Hanti, 14-Hanti), 1.84
(d, J ϭ 10.2 Hz, 2 H, 11-Hsyn, 14-Hsyn), 2.64 (s, 4H), 3.35 (s, 4H).
Ϫ
13C NMR (CDCl3): δ ϭ 42.3 (t, C-11, C-14), 52.3 (d, 4C), 56.6
(d, 4C), 154.9 (s, C-9, C-13), 211.7 (s, 2 CϭO). Ϫ C14H12O2 (212.2):
calcd. C 79.21, H 5.70; found C 79.40, H 5.64.
1-Methyl-8-phenyl-9,13-epoxyhexacyclo[6.5.1.02,7.04,12
.
05,10.09,13]tetradeca-3,6-dione (7): A solution of 80 mg (0.27 mmol)
of compound 2a in 2 ml of CH2Cl2 and 1 mg of tetraphenylpor-
phine (TPP) was irradiated with a 150-W sodium lamp at Ϫ10°C
under constant purging with dry oxygen (syringe needle). After
1-Methyl-5-(4-nitrophenyl)-8-phenylhexacyclo[6.5.1.02,7.04,12
.
05,10.09,13]tetradec-9(13)-ene-3,6-dione (2b) and 1-Methyl-4-(4- evaporation of the solvent, the residue was chromatographed which
nitrophenyl)-8-phenylhexacyclo[6.5.1.02,7.04,12.05,10.09,13]tetradec- resulted in 60 mg (71%) of colorless needles, m. p. 115Ϫ117°C. Ϫ
9(13)-ene-3,6-dione (2c): A solution of 2.60 g (11.3 mmol) of 2-(4-
nitro-phenyl)benzoquinone in 150 ml of CH2Cl2 was added under NMR (CDCl3): δ ϭ 1.33 (dd, J ϭ 1.3, 10.7 Hz, 1 H, 11-Hanti), 1.39
IR (CCl4): ν˜ ϭ 3020 cmϪ1, 2920, 1700, 1680, 1425, 1255. Ϫ 1H
Eur. J. Org. Chem. 1998, 1759Ϫ1762
1761

A. G. Griesbeck, T. Deufel, G. Hohlneicher, R. Rebentisch, J. Steinwascher
FULL PAPER
[8c]
1283Ϫ1289. Ϫ
R. Herges, S. Kammermaier, H. Neumann,
(s, 3H), 1.55 (d, J ϭ 10.7 Hz, 1 H, 14-Hanti), 2.19 (dd, J ϭ 1.6, 10.7
Hz, 1 H, 11-Hsyn), 2.36 (d, J ϭ 10.7 Hz, 1 H, 14-Hsyn), 2.93 (dd, 1
H, J ϭ 2.8, 9.7 Hz, 1 H, 2-H), 3.02 (m, 2 H, 4-H, 5-H), 3.21 (m,
2 H, 10-H, 12-H), 3.43 (dd, J ϭ 2.8, 9.7 Hz, 1 H, 7-H), 7.28Ϫ7.42
(m, 5 H, Ph.-H). Ϫ 13C NMR (CDCl3): δ ϭ 14.6 (q), 37.4 (t), 45.6
(d), 45.9 (d), 51.3 (t), 53.9 (s), 57.2 (d), 57.6 (d), 60.8 (s), 62.1 (s),
62.2 (d), 62.9 (s), 64.7 (d), 126.6 (d), 127.6 (d), 128.8 (d), 137.0 (s),
208.3 (s), 208.4 (s). Ϫ C21H18O3 (318.4): calcd. C 79.20, H 5.70;
found C 78.67, H 5.60. Ϫ Crystallization of the crude material from
methanol resulted in a methanol addition product in 96% yield.[17]
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ഠ 85°:
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13-Hydroxy-1-methyl-9-(4-methyl-3,5-dioxo-1,2,4-triazolin-1-yl)-
8-phenylhexacyclo[6.5.1.02,7.04,12.05,10.09,13]tetradec-9(13)-ene-3,6-
dione (8): A solution of 1.00 g (3.3 mmol) of 2a in 100 ml of aqeous
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g (35%) of 8 crystallized as colorless needles m.p. 279Ϫ280°C. Ϫ
IR (CCl4): ν˜ ϭ 3280 cmϪ1, 2920, 1735, 1670, 1090, 1070. Ϫ 1H
NMR (CDCl3): δ ϭ 0.72 (s, 3H), 1.39 (d, J ϭ 11.0 Hz, 1 H, 11-
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anti), 1.49 (d, J ϭ 11.3 Hz, 1 H, 14-Hanti), 2.31 (d, J ϭ 12.2 Hz,
[16]
[17]
[18]
1 H, 2-H), 2.46 (d, J ϭ 12.2 Hz, 1 H, 7-H), 2.50 (mc, 1 H, 11-
Hsyn), 2.56 (s, 2 H, 4-H, 5-H), 2.63 (s, 3 H), 2.70 (s, 1 H, 12-H),
3.18 (d, J ϭ 11.3 Hz, 1 H, 14-Hsyn), 4.69 (s, 1 H, 10-H), 5.72 (s, 1
H, OH), 6.72Ϫ6.96 (m, 5 H, Ph.-H), 8.44 (s, 1 H, NH). Ϫ 13C
NMR (CDCl3): δ ϭ 15.9 (q), 24.7 (q), 43.3 (t), 50.3 (d), 52.3 (d),
52.7 (d), 53.5 (d), 54.2 (t), 57.4 (s), 57.8 (d), 60.0 (d), 63.9 (s), 80.1
(s), 91.3 (s), 126.9 (d), 127.6 (d), 128.0 (d), 138.3 (s), 153.3 (s), 153.4
(s), 208.5 (s), 210.7 (s). Ϫ C24H23N3O4 (417.5): calcd. C 69.05, N
10.07, H 5.55; found C 68.93, N 9.93, H 5.70.
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