Synthesis of 2-Aryl-10b,10c-dimethyl-10b,10c-dihydropyrenes and a Study of Their Conjugation Behavior: Linear Relationship between the Degree of Conjugation and the Electronic Nature of Substituents

Article abstract of DOI:10.1021/jo962337i

A new Gomberg-Bachmann reaction between 10b,10c-dimethyl-10b,10c-dihydropyrene (3) and an arenediazonium salt under acidic conditions afforded a mixture of mono- and diarylated derivatives of 3. The major product was 2-aryl-10b,10c-dimethyl-10bc,10c-dihydropyrene 6. The desired products were obtained only from diazonium salts prepared from anilines with at least one strongly electron-withdrawing substituent. The combined conjugation and electronic effects of the arene substituent on the diatropicity of the dihydropyrene moiety in the monoarylated product is insignificant. The conjugation effect in 6 is, however, readily observed by the color appearance of 6 in the solid state and the significant red shift in the absorption bands between 300 and 520 nm in its electronic spectrum. A linear relationship was in fact obtained when the degree of conjugation (ρ band λ_max values) is correlated with the electronic nature (σ⁺ values) of the corresponding substituents.

Full text of DOI:10.1021/jo962337i

4412
J . Org. Chem. 1997, 62, 4412-4417
Syn th esis of 2-Ar yl-10b,10c-d im eth yl-10b,10c-d ih yd r op yr en es a n d a
Stu d y of Th eir Con ju ga tion Beh a vior : Lin ea r Rela tion sh ip
betw een th e Degr ee of Con ju ga tion a n d th e Electr on ic Na tu r e of
Su bstitu en ts
Yee-Hing Lai* and J ianping J iang
Department of Chemistry, National University of Singapore, Kent Ridge, Republic of Singapore 119260
Received December 13, 1996X
A new Gomberg-Bachmann reaction between 10b,10c-dimethyl-10b,10c-dihydropyrene (3) and an
arenediazonium salt under acidic conditions afforded a mixture of mono- and diarylated derivatives
of 3. The major product was 2-aryl-10b,10c-dimethyl-10b,10c-dihydropyrene 6. The desired products
were obtained only from diazonium salts prepared from anilines with at least one strongly electron-
withdrawing substituent. The combined conjugation and electronic effects of the arene substituent
on the diatropicity of the dihydropyrene moiety in the monoarylated product is insignificant. The
conjugation effect in 6 is, however, readily observed by the color appearance of 6 in the solid state
and the significant red shift in the absorption bands between 300 and 520 nm in its electronic
spectrum. A linear relationship was in fact obtained when the degree of conjugation (F band λmax
values) is correlated with the electronic nature (σ+ values) of the corresponding substituents.
The stereochemistry and the conjugation effect are
investigation of the effect of conjugation7 on the diatro-
picity of the 14π annulene. Mitchell et al. reported the
isolation4d of 2-phenyl-10b,10c-dimethyl-10b,10c-dihy-
dropyrene (4) in low yield from a very slow coupling
reaction using zero valent nickel complex.8 Reduction in
the ring current of 4 relative to the parent 3 is minimal,
whereas significant conjugation between the two rings
was indicated by electronic spectroscopy. A bridged
derivative of 4, namely, compound 5,9 however shows a
areas of special interests in the chemistry of biaryls. The
dependence of the conjugation effect on coplanarity of the
two aryl rings in a biaryl was evident from the studies
of the electronic spectra of simple biaryls, e.g., 1 and 2.1
Two of the most common classical methods for the
synthesis of unsymmetrical biaryls are the Gomberg-
Bachmann reaction2 between a diazonium salt and an
arene in an alkaline medium and the Ullmann3 reaction
involving a coupling of two aryl halides in the presence
of finely powdered copper. More recently a versatile
synthetic approach to the preparation of biaryls is the
transition metal-catalyzed cross-coupling of electrophilic
and nucleophilic aromatic partners.4 For example, the
palladium-catalyzed couplings of aryl halides or sul-
fonates with arylstannanes (the Stille reaction)5 or aryl-
boronic acids or esters (the Suzuki reaction).6 Most of
these methods are, however, mainly restricted to ben-
zenoid compounds.
further decrease in diatropicity. In order to confirm
whether the conjugation effect in 4 is responsible for the
small decrease in its observed diatropicity, our efforts
were directed toward finding a correlation, if any, of the
conjugation and diatropicity in a series of 2-aryl-10b,10c-
dimethyl-10b,10c-dihydropyrenes 6. We wish to describe
a simple and general synthesis of 6.
10b,10c-Dimethyl-10b,10c-dihydropyrene (3) and its
derivatives have been shown to be good models for the
X Abstract published in Advance ACS Abstracts, April 1, 1997.
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Stoughton, R. W.; Adams, R. J . Am. Chem. Soc. 1932, 54, 4426. (c)
Stanley, W. M.; Adams, R. J . Am. Chem. Soc. 1930, 52, 1200. (d)
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1955, 3776. (f) Murrell, J . N. J . Chem. Soc. 1956, 3779.
Resu lts a n d Discu ssion
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1983, 61, 86. (e) Renger, B. Synthesis 1985, 856.
Syn th esis. The Gomberg-Bachmann reaction was
first investigated based on the fact that various aryldia-
zonium salts are readily accessible and that dihydropy-
(4) (a) Hayashi, T.; Hayashizaki, K.; Kiyo, T.; Ito, Y. J . Am. Chem.
Soc. 1988, 110, 8153. (b) Saa, J . M.; Martorell, G. J . Org. Chem. 1993,
58, 1963. (c) Anderson, J . C.; Namli, H. Synlett 1995, 765. (d) Mitchell,
R. H.; Chaudhary, M.; Dingle, T. W.; Williams, R. V. J . Am. Chem.
Soc. 1984, 106, 7776 and references cited therein.
(5) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
(6) Watanable, T.; Miyaura, N.; Suzuki, A. Synlett 1992, 207.
(7) Lai, Y.-H.; Chen, P.; Peck, T.-G. Pure Appl. Chem. 1993, 65, 81.
(8) Kende, A. S.; Liebeskind, L. S.; Braitsch, D. Tetrahedron Lett.
1975, 3375.
(9) (a) Mitchell, R. H.; Mahadevan, R. Tetrahedron Lett. 1981, 22,
5131. (b) Mitchell, R. H.; Iyer, V. S.; Khalifa, N.; Mahadevan, R.;
Venugopalan, S.; Weerawarna, S. A.; Zhou, P. J . Am. Chem. Soc. 1995,
117, 1514.
S0022-3263(96)02337-7 CCC: $14.00 © 1997 American Chemical Society

Dihydropyrenes and Study of Conjugation Behavior
J . Org. Chem., Vol. 62, No. 13, 1997 4413
Ta ble 1. Isola ted Yield s of Mon o- a n d Dia r yla ted
P r od u cts fr om th e Rea ction s of 3 w ith th e Resp ective
Dia zon iu m Sa lts
rene 3 undergoes electrophilic substitution reactions
under mild conditions.10 Our attempts in treating 3 with
the diazonium tetrafluoroborate derived from 4-nitro-
aniline under basic conditions reported for Gomberg-
Bachmann reactions,11 however, failed to afford the
unsymmetrical biaryl 6a . There were several reports on
examples which did not follow the homolytic Gomberg-
Bachmann pathway.12,13 The choice of a solvent suitable
for both the diazonium salt and the substrate seemed to
be an important factor.13
In our work, glacial acetic acid was chosen as an
alternative solvent as it is only weakly nucleophilic and
both the arenediazonium salt and compound 3 are soluble
in it. An aqueous acidic solution of the diazonium salt
formed in situ at 0 °C was then added dropwise to a
solution of 3 in glacial acetic acid at room temperature.
Surprisingly, the reactions studied (Table 1) were com-
pleted in about 20 min to afford a fair to good yield of
the desired biaryls and teraryls.
Results from mass spectral analyses of the product
mixtures always suggested the presence of monoaryl and
diaryl derivatives of 3. The optimum yield of the major
product, namely, 2-aryldihydropyrene 6, was obtained
when the ratio of the diazonium salt to 3 was about 1.5:
1. Increasing the ratio would result in a higher yield of
the 2,7-diaryldihydropyrene 7 (and in some cases its
structural isomer(s), see Table 1) at the expense of
compound 6. The substituent’s position, namely, ortho,
meta, or para, of the monosubstituted examples did not
seem to affect the product yield significantly. The use
of diazonium salts prepared from 2,6-disubstituted
anilines, however, led to low yields of 6m ,n presumably
due to the unfavorable steric interactions in the transi-
tion state. A similar steric factor due the presence of an
ortho substituent should also account for the fact that
1-aryldihydropyrene 8 was only isolated mainly from
reactions involving 4-substituted anilines.
a
b
Mixture of 7 and other bisarylated isomers. Mixture of
monoarylated 8 and 9.
structure of compound 8 was confirmed by a 1H NMR
analysis indicating the AB and AB2 splitting patterns of
the H2,3 and H6,7,8 systems, respectively. All proton
signals in compounds 6-8 were assigned on the basis of
their 2D-1H COSY NMR spectra and the results from a
series of NOE experiments.
Spectroscopic identification of the structures of 6 and
7 was straightforward based on their high symmetry. The
Pure samples of 1-aryldihydropyrenes 8f,8g were
obtained in our work (Table 1). In other examples, a
mixture of 8 and perhaps 4-aryldihydropyrene 9 was
(10) Phillips, J . B.; Molyneux, R. J .; Sturm, E.; Boekelheide, V. J .
Am. Chem. Soc. 1967, 89, 1704.
1
observed by H NMR analyses. It was reported that the
(11) (a) Rosenberg, D. E.; Beadle, J . R. Tetrahedron Lett. 1980, 21,
4141. (b) Beadle, J . R.; Korzeniowski, H.; Rosenberg, D. E.; Garcia-
Slanga, B. J .; Gokel, G. W. J . Org. Chem. 1984, 49, 1594.
(12) (a) Abramovitch, R. A.; Gadallah, F. F. J . Chem. Soc. B 1968,
497. (b) Kobayashi, M.; Minato, H.; Yamada, E.; Kobori, N. Bull. Chem.
Soc. J pn. 1970, 43, 215. (c) Kaul, B. L.; Zollinger, H. Helv. Chim. Acta
1968, 51, 2132.
relative preference for electrophilic substitution in 3 was
C2 > C4 > C1 based on the relative heats of formation
of the intermediate cations.14 The relative strain energies
(14) Mitchell, R. H.; Iyer, V. S.; Mahadevan, R.; Venugopalan, S.;
Zhou, P. J . Org. Chem. 1996, 61, 5116.
(13) Burri, P.; Zollinger, H. Helv. Chim. Acta 1973, 56, 232.

4414 J . Org. Chem., Vol. 62, No. 13, 1997
Lai and J iang
Ta ble 2. P r oton Ch em ica l Sh ift of th e In ter n a l Meth yl
P r oton s a n d P r in cip a l Electr on ic Absor p tion Ma xim a of
6
of the cationic intermediates may, however, follow a
reverse order. Thus a predication on which of 8 and 9 is
preferred would be rather impossible.
2,7-Diaryldihydropyrene 7 was isolated as the only
bisarylated product in several reactions (Table 1). The
other examples, however, were found to be a mixture of
two or more bisarylated products. This is not surprising
as the second arylation on 6 could in principle occur at
C1, C4, C5, or C6.
absorption bands (λmax
)
compd
δ of internal CH3
F
â
â′
6a
6b
6c
6d
6e
6f
6g
6h
6i
-4.01, -4.07
-3.99, -4.02
-3.96, -3.99
-4.02, -4.06
-3.98, -4.00
-3.97, -4.00
-3.98, -4.01
-3.95, -3.99
-4.06, -4.10
-3.99, -4.02
-3.77, -3.81
-3.99, -4.03
-4.00, -4.02,
-4.05, -4.08
-4.03, -4.04,
-4.07, -4.09
484
496
514
490
506
502
498
502
472
496
562
492
476
382
386
396
386
394
390
382
390
378
386
420
384
380
340
342
338
344
350
346
348
344
338
346
336
344
342
In a separate attempt when the ratio of the diazonium
salt of 4-nitroaniline to compound 3 was increased to 2.5:
1, a small quantity of a trisarylated derivative of 3 was
isolated in addition to compounds 6a and 7a . On the
1
6j
6k
6l
basis of a detailed H NMR analysis, the third product
was shown to be 2,4,7-triaryldihydropyrene 10. The
steric factor would again discourage the third aryl
substitution to take place at C1 of 7a . Our result is also
consistent with the report that bromination of dihydro-
pyrene 11a gave the dibromo derivative 11b.15
6m
6n
482
382
344
2:1:1:2 ratio. This is consistent with free rotation about
the aryl-aryl single bonds of aryl rings at C2 and C7
and restricted rotation of the aryl ring at C4 resulting
in two rigid conformational isomers in a 2:1 ratio at room
temperature. A variable-temperature 1H NMR study
indicated no coalescence of the methyl signals up to a
temperature of 90 °C above which a gradual decomposi-
tion of the sample was observed. Using the coalescence
temperature method,17 the conformational energy barrier
Two significant substituent effects were observed in
our work. Firstly, only diazonium salts with electron-
withdrawing substituents led to formation of the desired
biaryls. An example with a weak “electron-withdrawing”
group (i.e., pyridine) gave only a low yield of the product
6j. No biaryl product was formed in separate attempts
by treating 2 with the diazonium salts derived from
4-methoxyaniline, 4-chloroaniline, and 4-toluidine, re-
spectively. A reaction between nitrodihydropyrene 12
with the diazonium salt derived from 4-nitroaniline did
not afford any biaryl product either. Another interesting
observation was that the desired reaction did not occur
when a carbonyl group was ortho to the diazo function
(refer to 13), whereas compounds 6f,g could be isolated
in fair yields. An intramolecular stabilization16 of the
diazonium salt 13 could account for a significant decrease
in its reactivity.
(∆Gq ) for rotation of the aryl ring at C4 in 10 was
c
estimated to be larger than 77 kJ mol-1
.
The 1H NMR spectra of compounds 6m ,n suggest a
restricted rotation of the aryl rings about the aryl-aryl
single bond. Protons of the two “internal” methyl groups
in 6m appear as two pairs of singlets in a 3:2 ratio. In
1
a dynamic H NMR spectroscopic study of a solution of
6m in deuterated chloroform, the coalescence of the two
pairs of singlets was observed at 38 and 40 °C, respec-
tively, corresponding to ∆Gq values of 69.5 and 68.9 kJ
c
mol-1. The energy barrier (about 69 kJ mol-1) for free
rotation of the aryl rings in 6m was thus significantly
lower than that (>77 kJ mol-1) for the rotation of the
aryl ring at C4 in 10, although 6m has bulky groups at
both ortho positions of the benzene ring.
Dia tr op icity a n d Con ju ga tion . The chemical shifts
of the internal methyl protons in the para-substituted
series of 6c,e-h do not change significantly (Table 2). Thus
the conjugation effect of the substituent X in 6 on the
diatropicity of the dihydropyrene moiety, if any, is not
readily observable by employing the proton chemical shift
as a probe. A similar observation was made when
chemical shifts of the internal methyl protons of 6a -c
were compared. Although unrestricted rotation about the
aryl-aryl single bond is expected in the above series of
biaryl systems, a planar conformation for the maximum
conjugation effect would be unfavorable due to steric
interactions among the ortho protons. This is supported
by the fact that the most appreciable shift was observed
for compound 6k . With the two spatially less demanding
heteroatoms at the “ortho” positions of the 5-membered
ring, the biaryl system in 6k could achieve planarity to
result in a stronger conjugation effect leading to a more
appreciable change in the diatropicity of the dihydropy-
rene system. Compounds 6a -c appear in the solid state
Atr op isom er ism . The teraryl system 7a could in
principle exhibit atropisomerism and exist as two con-
formational isomers. The 1H NMR spectrum of 7a at
room temperature shows only a sharp singlet at δ -3.83
for the “internal” methyl protons suggesting a rapid
interconversion between its two conformers. The “inter-
nal” methyl protons in compound 10 appear, however,
as four singlets at δ -3.55, -3.59, -3.63, and -3.67 in a
(15) Mitchell, R. H.; Chen, Y. Tetrahedron Lett. 1996, 37, 5239.
(16) Wallis, J . D.; Easton, R. J . C.; Dunitz, J . D. Helv. Chim. Acta
1993, 76, 1411.
(17) (a) Gutowsky, H. S.; Holm, C. H. J . Chem. Phys. 1956, 25, 1228.
(b) Oki, M. Applications of Dynamic NMR Spectroscopy to Organic
Chemistry; VCH Publishers: Deerfield Beach, FL, 1985.

Dihydropyrenes and Study of Conjugation Behavior
J . Org. Chem., Vol. 62, No. 13, 1997 4415
as yellow-green, yellow-brown, and purple crystals, re-
spectively, seemingly corresponding to an increase in
conjugation. This is clearly reflected by a continuous red
shift (Table 2) in the absorptions between 300 and 520
nm in their electronic spectra. This spectral range
corresponds to Clar’s F, â, and â′ bands4d,18 (the weak R
bands are, however, not detectable) and is chiefly re-
sponsible for the observed chromatic colors of these
compounds. Thus the dependence of the conjugation
effect on the coplanarity of the two aryl rings in 6 could
be monitored satisfactorily. Our semiempirical molecular
orbital PM319 calculations show that in isolation, the
dihedral angle between the two aryl rings in the opti-
mized structure of 6a is about 64° compared to that of
about 37° in 6c. Thus the most significant conjugation
effect is, as expected, observed in the para-substituted
6c. Coplanarity is unfavorable in 6a , and the meta
substituent in 6b does not have a direct resonance
interaction with the dihydroyprene moiety.
Most examples of 6 prepared in our work have bright
colors ranging from green to purple in the solid state.
Their solutions in organic solvents, however, exhibit very
different colors. For example, solutions of 6a ,b in dichlo-
romethane are yellow-green, while that of 6c is red. The
most significant solvent effect on the color appearance
was observed for compound 6k . It forms dark purple
needles in the solid state and has the strongest R band
λmax at 676 nm (ꢀmax 2700) among all examples of 6. A
solution of 6k in dichloromethane is blue, but a red
solution is obtained in hexane.
F igu r e 1. Correlation between F band λmax values of com-
pounds 6c,e-g and σ+ values of p-NO2, p-CN, p-COCH3, and
p-COOCH3.
Con clu sion
The reaction between dihydropyrene 3 (a [14]annulene)
and a diazonium salt under acidic conditions provides a
convenient route to selected 2-aryldihydropyrene 6. This
reaction may be useful for arylation of other annulenes
which undergo electrophilic substitution reactions under
similar conditions. Although the effect of conjugation on
the diatropicity of the dihydropyrene moiety in 6 was not
significant, the electronic influence that substituents
exert on the conjugation effect in the biaryl system could
be readily observed. A linear relationship was in fact
obtained when the degree of conjugation (F band λmax
values) is correlated with the electronic nature (σ+ values)
of the corresponding substituents.
The electronic influence that substituents exert on the
rate and course of a reaction has been described ef-
fectively by the Hammett and related approaches.20,21
A
correlation between the electronic influence that substit-
uents exert on the conjugation effect in a molecule has,
however, not been directly mentioned. In the series of
compounds 6c,e-g, the electron-rich dihydropyrene is in
direct resonance interaction with an electron-deficient
substituent held in a para position. Thus it would be
interesting to observe whether the σ+ values22 of the
substituents could be correlated with the degree of
conjugation in the biaryls. Using σ+ values23 of 0.740,
0.674, 0.567, and 0.472 for p-NO2, p-CN, p-COCH3, and
p-COOCH3, respectively, a linear relationship with a
correlation coefficient of 0.9622 is indeed obtained when
these are plotted against the corresponding F band λmax
values of compounds 6c,e-g (Figure 1). Our results have
thus shown that the electron-withdrawing nature of a
substituent may be directly and quantitatively reflected
in the electronic absorption band of a molecule.
Exp er im en ta l Section
Melting points are uncorrected. 1H NMR spectra were
recorded in CDCl3 on 300 or 500 MHz spectrometer with Me4-
Si as internal standard. All J values are given in hertz (Hz).
Mass spectra were obtained using EI ionization at 70 eV.
Microanalyses were performed by the Microanalytical Labora-
tory of the Department of Chemistry, National University of
Singapore.
Gen er a l P r oced u r e for th e P r ep a r a tion of tr a n s-2-
Ar yl-10b,10c-d im eth yl-10b,10c-d ih yd r op yr en es 6, tr a n s-
2,7-Dia r yl-10b ,10c-d im et h yl-10b,10c-d ih yd r op yr en es 7,
a n d /or tr a n s-1-Ar yl-10b,10c-d im eth yl-10b,10c-d ih yd r o-
p yr en es 8. To a mixture of concd H2SO4 (2 mL) and water (2
mL) in a 25 mL round bottom flask was added the aniline
derivative (0.65 mmol). The solution was cooled to about 0
°C with an ice bath. A solution of NaNO2 (0.78 mmol) in the
minimum amount of water was added dropwise over a period
of 10 min while maintaining the temperature of the reaction
mixture near 0 °C. After the addition of the NaNO2 solution
was completed, the reaction mixture was stirred for an
additional 10 min near 0 °C. Urea (0.25 mmol) was then added
to react with the excess NaNO2, and the solution was stirred
for another 10 min. The resulting solution of the diazonium
salt was then added dropwise to a solution of dimethyldihy-
dropyrene 3 (100 mg, 0.43 mmol) in glacial acetic acid (20 mL)
at room temperature. After 10 min, the solution was poured
into ice water (200 mL). The mixture was extracted succes-
sively with three portions (30 mL each) of dichloromethane.
The organic layers were combined and washed successively
with water, 10% aqueous NaHCO3 solution, and water. The
organic solution was dried and the solvent removed under
(18) Clar, E. Polycyclic Hydrocarbons; Academic Press-Springer Ver-
lag: London, 1964; Vol. 2.
(19) (a) Stewart, J . J . P. J . Comput. Chem. 1989, 10, 209. (b)
Stewart, J . J . P. J . Comput.-Aided Mol. Des. 1980, 4, 1.
(20) (a) Exner, O. Correlation Analysis of Chemical Data; Plenum
Press: New York, 1988. (b) Shorter, J . Correlation Analysis of Organic
Reactivity; Wiley: Chichester, 1982. (c) Shorter, J . In Correlation
Analysis in Chemistry: Recent Advances; Chapman, N. B., Shorter,
J ., Eds.; Plenum Press: New York, 1978. (d) Exner, O. In Advances in
Linear Free Energy Relationships; Chapman, N. B., Shorter, J ., Eds.;
Plenum Press: New York, 1972. (e) Hammett, L. P. Physical Organic
Chemistry; McGraw-Hill: New York, 1970.
(21) (a) Shorter, J . Aust. J . Chem. 1995, 48, 1453. (b) Reis, J . C.;
Segurado, M. A. P.; De Oliveira, J . D. G. J . Phys. Org. Chem. 1995, 8,
5. (c) Shorter, J . Pure Appl. Chem. 1994, 66, 2451. (d) Charton, M.
Prog. Phys. Org. Chem. 1987, 16, 287. (e) Wells, R. P.; Ehrenson, S.;
Taft, R. W. Prog. Phys. Org. Chem. 1968, 6, 147.
(22) Brown, H. C.; Okamoto, Y. J . Am. Chem. Soc. 1958, 80, 4979.
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Press: New York, 1968.

4416 J . Org. Chem., Vol. 62, No. 13, 1997
Lai and J iang
reduced pressure. The residue was chromatographed on silica
gel using CH2Cl2-hexane (1:1) as an eluant. Eluted first was
compound 6 followed by 8 or a mixture of 8 and 9. The last
component eluted was compound 7 or a mixture of 7 and its
structural isomers.
tr a n s-2-(2-Nit r op h en yl)-10b ,10c-d im et h yl-10b ,10c-d i-
h yd r op yr en e (6a ). Recrystallization (n-hexane) gave 6a
(48%) as yellow-green needles: mp 180-182 °C; 1H NMR (500
MHz) 8.65, 8.64 (AB q, J ) 7.9, 4H), 8.60 (d, J ) 7.7, 2H),
8.56 (s, 2H), 8.12 (t, J ) 7.7, 1H), 8.04 (dd, J ) 7.7, 1.3, 1H),
7.88 (dd, J ) 7.7, 1.3, 1H), 7.76 (dt, J ) 7.7, 1.3, 1H), 7.59 (dt,
J ) 7.7, 1.3, 1H), -4.01, -4.07 (s, ratio 1:1, total 6H); UV (n-
hexane) λmax 484 (ꢀ 13 300), 382 (31 300), 340 (100 000); MS
m/ z 353 (M+, 23), 338 (32), 323 (20), 305 (72), 291 (100), 276
(28), 145 (37), 138 (22). Anal. Calcd for C24H19NO2: C, 81.57;
H, 5.42; N, 3.96. Found: C, 81.18; H, 5.53; N, 3.95.
(M+, 25), 318 (100), 303 (75), 276 (13), 158 (35), 137 (35). Anal.
Calcd for C25H19N: C, 90.06; H, 5.74; N, 4.20. Found: C, 89.54;
H, 5.76; N, 4.43.
tr a n s-2,7-Bis(2-cyan oph en yl)-10b,10c-dim eth yl-10b,10c-
d ih yd r op yr en e (7d ). Chromatography (n-hexane-CH2Cl2
(1:1)) on silica gel gave 7d (15%) as a red solid: mp 258-260
°C; 1H NMR δ (300 MHz) 8.82 (s, 4H), 8.76 (s, 4H), 7.96 (br d,
J ) 7.7, 2H), 7.93 (dd, J ) 7.7, 1.1, 2H), 7.81 (dt, J ) 7.7, 1.1,
2H), 7.55 (dt, J ) 7.7, 1.1, 2H), -3.83 (s, 6H); UV (hexane)
λmax 490 (ꢀ 20 600), 390 (30 400), 350 (79 500); MS m/ z 434
(M+, 8), 419 (100), 404 (25), 209 (15); Mr calcd for C32H22N2
434.1783, found (MS) 434.1783.
tr a n s-2-(4-Cya n op h en yl)-10b,10c-d im eth yl-10b,10c-d i-
h yd r op yr en e (6e). Recrystallization (n-hexane) gave 6e
(35%) as brown needles: mp 202-204 °C; 1H NMR δ (500
MHz) 8.88 (s, 2H), 8.71, 8.63 (AB q, J ) 7.7, 4H), 8.57 (d, J )
7.7, 2H), 8.22, 7.87 (AB q, J ) 8.5, 4H), 8.11 (t, J ) 7.7, 1H),
-3.98, -4.00 (s, ratio 1:1, total 6H); UV (hexane) λmax 506 (ꢀ
18 800), 394 (29 000), 350 (73 400); MS m/ z 333 (M+, 15), 318
(100), 303 (90). Anal. Calcd for C25H19N: C, 90.06; H, 5.74;
N, 4.20. Found: C, 89.60; H, 5.62; N, 3.90.
tr a n s-2,7-Bis(2-n itr op h en yl)-10b,10c-d im eth yl-10b,10c-
d ih yd r op yr en e (7a ). Recrystallization (n-hexane-CH2Cl2)
1
gave 7a (20%) as brown crystals: mp 226-228 °C; H NMR
(300 MHz) 8.64 (s, 4H), 8.54 (s, 4H), 8.05 (dd, J ) 7.7, 1.1,
2H), 7.88 (dd, J ) 7.7, 1.1, 2H), 7.79 (dt, J ) 7.7, 1.1, 2H),
7.60 (dt, J ) 7.7, 1.1, 2H), -3.83 (s, 6H); UV (n-hexane) λmax
484 (ꢀ 11 600), 376 (29 000), 342 (93 300); MS m/ z 474 (M+,
40), 459 (100), 444 (33), 425 (67), 379 (50), 350 (49), 175 (39).
Anal. Calcd for C30H22N2O4: C, 75.94; H, 4.67; N, 5.90.
Found: C, 75.76; H, 4.74; N, 5.80.
tr a n s-2-(4-Acetylp h en yl)-10b,10c-d im eth yl-10b,10c-d i-
h yd r op yr en e (6f). Recrystallization (n-hexane) gave 6f (41%)
1
as red needles: mp 156-158 °C; H NMR δ (500 MHz) 8.94
(s, 2H), 8.71, 8.63 (AB q, J ) 7.7, 4H), 8.57 (d, J ) 7.7, 2H),
8.23, 8.19 (AB q, J ) 8.6, 4H), 8.10 (t, J ) 7.7, 1H), 2.72 (s,
3H), -3.97, -4.00 (s, ratio 1:1, total 6H); UV (hexane) λmax
502 (ꢀ 21 100), 390 (30 500), 346 (69 100); MS m/ z 350 (M+,
20), 335 (100), 320 (50), 276 (47), 138 (62). Anal. Calcd for
C26H22O: C, 89.11; H, 6.33. Found: C, 88.83; H, 6.34.
tr a n s-1-(4-Acetylp h en yl)-10b,10c-d im eth yl-10b,10c-d i-
h yd r op yr en e (8f). Chromatography (n-hexane-CH2Cl2 (1:
1)) on silica gel gave 8f (7%) as a green solid: mp 121-123
t r a n s-2,4,7-T r is (2-n it r o p h e n y l)-10b ,10c -d im e t h y l-
10b,10c-d ih yd r op yr en e (10). When the ratio of the diazo-
nium salt derived from 2-nitroaniline to compound 3 was
increased to 2.5:1, a mixture of conformational isomers of
compound 10 (7%) was isolated (in addition to 6a and 7a ) as
1
a red solid: mp 180-200 °C; H NMR (500 MHz) 8.63-8.66
(m), 8.58, 8.50 (AB q, J ) 10.3), 8.53 (s), 8.06-8.18 (m), 7.96
(d, J ) 8.1), 7.53-7.88 (m), -3.55, -3.59, -3.63, -3.67 (s, ratio
2:1:1:2); UV (n-hexane) λmax 498 (ꢀ 12 800), 394 (28 300), 348
(70 900); MS m/ z 595 (M+, 12), 580 (55), 565 (18), 546 (20),
366 (42), 276 (30), 57 (100). Anal. Calcd for C36H25N3O6: C,
72.60; H, 4.27; N, 7.06. Found: C, 72.23; H, 4.71; N, 6.65.
tr a n s-2-(3-Nit r op h en yl)-10b ,10c-d im et h yl-10b ,10c-d i-
h yd r op yr en e (6b). Recrystallization (n-hexane) gave 6b
(47%) as yellow-brown needles: mp 140-142 °C; 1H NMR (500
MHz) 8.98 (t, J ) 1.9, 1H), 8.92 (s, 2H), 8.74, 8.65 (AB q, J )
7.7, 4H), 8.59 (d, J ) 7.7, 2H), 8.45 (br d, J ) 7.8, 1H), 8.28
(br d, J ) 7.8, 1H), 8.12 (t, J ) 7.7, 1H), 7.76 (t, J ) 7.8, 1H),
-3.99, -4.02 (s, ratio 1:1, total 6H); UV (n-hexane) λmax 496
(ꢀ 18 000), 386 (36 100), 342 (92 800); MS m/ z 353 (M+, 24),
338 (100), 323 (73), 276 (62), 216 (22),138 (60). Anal. Calcd
for C24H19NO2: C, 81.57; H, 5.42; N, 3.96. Found: C, 81.50;
H, 5.37; N, 3.80.
1
°C; H NMR δ (500 MHz) 8.68 (s, 2H), 8.66 (d, J ) 7.8, 1H),
8.64 (d, J ) 8.4, 1H), 8.62 (d, J ) 8.4, 1H), 8.59 (d, J ) 7.7,
2H), 8.20, 7.90 (AB q, J ) 8.5, 4H), 8.13 (t, J ) 7.7, 1H), 8.11
(d, J ) 7.8, 1H), 2.76 (s, 3H), -4.08 (s, 6H); UV (hexane) λmax
468 (ꢀ 21 100), 382 (30 500), 344 (152 200); MS m/ z 350 (M+,
24), 335 (100), 320 (60), 292 (27), 276 (66), 138 (58); Mr calcd
for C26H22O 350.1671, found (MS) 350.1665.
tr a n s-Meth yl 2-(10b,10c-Dim eth yl-10b,10c-d ih yd r op y-
r en yl)ben zen e-4-ca r boxyla te (6g). Recrystallization (n-
hexane) gave 6g (43%) as brown crystals: mp 152-154 °C;
1H NMR δ (500 MHz) 8.94 (s, 2H), 8.71, 8.63 (AB q, J ) 7.7,
4H), 8.57 (d, J ) 7.7, 2H), 8.26, 8.21 (AB q, J ) 8.6, 4H), 8.10
(t, J ) 7.7, 1H), 4.00 (s, 3H), -3.98, -4.01 (s, ratio 1:1, total
6H); UV (hexane) λmax 498 (ꢀ 15 100), 382 (50 600), 348
(112 900); MS m/ z 366 (M+, 15), 351 (100), 336 (70), 276 (47),
138 (62). Anal. Calcd for C26H22O2: C, 85.22; H, 6.05.
Found: C, 85.26; H, 6.16.
tr a n s-Meth yl 1-(10b,10c-Dim eth yl-10b,10c-d ih yd r op y-
r en yl)ben zen e-4-ca r boxyla te (8g). Chromatography (n-
hexane-CH2Cl2 (1:1)) on silica gel gave 8g (9%) as a green
solid: mp 120-122 °C; 1H NMR δ (500 MHz) 8.68 (s, 2H),
8.61-8.67 (m, 3H), 8.59 (d, J ) 7.7, 2H), 8.27, 7.87 (AB q, J )
8.5, 4H), 8.13 (t, J ) 7.7, 1H), 8.11 (d, J ) 7.8, 1H), 4.02 (s,
3H), -4.08 (s, 6H); UV (hexane) λmax 468 (ꢀ 20 700), 382
(123 700), 346 (155 800); MS m/ z 366 (M+, 18), 351 (100), 336
(70), 292 (27), 276 (35), 138 (52); Mr calcd for C26H22O2
366.1620, found (MS) 366.1618.
tr a n s-4-[2-(10b,10c-Dim eth yl-10b,10c-dih ydr opyr en yl)]-
ben zop h en on e (6h ). Recrystallization (n-hexane) gave 6h
(50%) as brown needles: mp195-196 °C; 1H NMR δ (500 MHz)
8.96 (s, 2H), 8.72, 8.63 (AB q, J ) 7.7, 4H), 8.57 (d, J ) 7.7,
2H), 8.25, 8.06 (AB q, J ) 8.4, 4H), 8.10 (t, J ) 7.7, 1H), 7.91
(br d, J ) 7.5, 2H), 7.64 (br t, J ) 7.5, 1H), 7.55 (br t, J ) 7.5,
2H), -3.95, -3.99 (s, ratio 1:1, total 6H); UV (hexane) λmax
502 (ꢀ 17 400), 390 (27 200), 370 (30 100), 346 (60 300); MS
m/ z 412 (M+, 13), 397 (100), 382 (47), 276 (33), 105 (75), 77
(32). Anal. Calcd for C31H24O: C, 90.26; H, 5.86. Found: C,
89.82; H, 5.86.
tr a n s-2,7-Bis(3-n itr op h en yl)-10b,10c-d im eth yl-10b,10c-
d ih yd r op yr en e (7b). Chromatography (n-hexane-CH2Cl2
(1:1)) on silica gel gave 7b (23%) as a red solid: mp 246-248
°C; 1H NMR (300 MHz) 8.98 (t, J ) 1.9, 2H), 8.91 (s, 4H), 8.74
(s, 4H), 8.45 (br d, J ) 8.3, 2H), 8.29 (dd, J ) 8.3, 1.9, 2H),
7.78 (t, J ) 8.3, 2H), -3.76 (s, 6H); UV (n-hexane) λmax 492 (ꢀ
16 800), 390 (47 500), 350 (96 900); MS m/ z 474 (M+, 30), 459
(100), 444 (85), 349 (45), 337 (31), 276 (26), 175 (64); Mr calcd
for C30H22N2O4 474.1580, found (MS) 474.1588.
tr a n s-2-(4-Nit r op h en yl)-10b ,10c-d im et h yl-10b ,10c-d i-
h yd r op yr en e (6c). Recrystallization (n-hexane) gave 6c
(49%) as purple needles: mp 175-177 °C; 1H NMR (500 MHz)
8.93 (s, 2H), 8.74, 8.64 (AB q, J ) 7.8, 4H), 8.59 (d, J ) 7.7,
2H), 8.45, 8.28 (AB q, J ) 7.1, 4H), 8.13 (t, J ) 7.7, 1H), -3.96,
-3.99 (s, ratio 1:1, total 6H); UV (n-hexane) λmax 514 (ꢀ 22 400),
396 (27 500), 338 (66 000); MS m/ z 353 (M+, 21), 338 (100),
323 (51), 292 (12), 276 (48), 138 (43). Anal. Calcd for C24H19
-
NO2: C, 81.57; H, 5.42; N, 3.96. Found: C, 81.04; H, 5.09; N,
3.68.
tr a n s-2-(2-Cya n op h en yl)-10b,10c-d im eth yl-10b,10c-d i-
h yd r op yr en e (6d ). Recrystallization (n-hexane) gave 6d
(65%) as brown needles: mp 168-170 °C; 1H NMR (500 MHz)
8.82 (s, 2H), 8.74, 8.67 (AB q, J ) 7.7, 4H), 8.62 (d, J ) 7.7,
2H), 8.14 (t, J ) 7.7, 1H), 7.97 (br d, J ) 7.8, 2H), 7.92 (dd, J
) 7.8, 1.1, 1H), 7.79 (dt, J ) 7.8, 1.1, 1H), 7.54 (dt, J ) 7.8,
1.1, 1H), -4.02, -4.06 (s, ratio 1:1, total 6H); UV (n-hexane)
λmax 490 (ꢀ 12 600), 386 (33 900), 344 (76 400); MS m/ z 333
tr a n s-4,4′-[2,7-(10b ,10c-Dim et h yl-10b ,10c-d ih yd r op y-
r en o)]d iben zop h en on e (7h ). Chromatography (n-hexane-
CH2Cl2 (1:1)) on silica gel gave 7h (27%) as a red solid: mp
1
250-252 °C; H NMR δ (500 MHz) 8.93 (s, 4H), 8.71 (s, 4H),
8.25, 8.06 (AB q, J ) 8.4, 8H), 7.91 (br d, J ) 7.5, 4H), 7.64

Dihydropyrenes and Study of Conjugation Behavior
J . Org. Chem., Vol. 62, No. 13, 1997 4417
(br t, J ) 7.5, 2H), 7.55 (br t, J ) 7.5, 4H), -3.71 (s, 6H); UV
(hexane) λmax 504 (ꢀ 19 000), 406 (27 000), 386 (35 400), 358
(81 100); MS m/ z 592 (M+, 7), 577 (80), 562 (35), 350 (7), 276
(6), 105 (100), 77 (45). Anal. Calcd for C44H32O2: C, 89.16;
H, 5.44. Found: C, 89.56; H, 5.68.
-4.03 (s, ratio 1:1, total 6H); UV (hexane) λ max 492 (ꢀ 17 000),
384 (30 400), 344 (76 600); MS m/ z 424 (M+, 23), 409 (100),
394 (75), 350 (29), 276 (31), 189 (37); Mr calcd for C28H24O4:
424.4936, found (MS) 424.4932.
tr a n s-2-(2-Met h yl-6-n it r op h en yl)-10b ,10c-d im et h yl-
10b,10c-d ih yd r op yr en e (6m ). Recrystallization (n-hexane)
gave a mixture of conformational isomers of 6m (27%) as green
needles: mp 135-150 °C; 1H NMR δ (300 MHz) 8.66-8.59 (m,
6H), 8.41 (s, 2H), 8.11 (t, J ) 7.7, 1H), 7.88, 7.85 (d, J ) 7.9,
total 1H), 7.63 (br d, J ) 7.9, 1H), 7.52 (t, J ) 7.9, 1H), 2.33,
2.14 (s, total 3H), -4.00, -4.02, -4.05, -4.08 (s, ratio 2:1:1:2,
total 6H); UV (hexane) λmax 476 (ꢀ 8400), 380 (25 000), 342
(67 600); MS m/ z 367 (M+, 40), 352 (78), 337 (62), 320 (100),
289 (75), 145 (70). Anal. Calcd for C25H21NO2: C, 81.72; H,
5.76; N, 3.81. Found: C, 81.85; H, 5.65; N, 3.64.
tr a n s-2-[2-(Tr iflu or om eth yl)p h en yl]-10b,10c-d im eth yl-
10b,10c-d ih yd r op yr en e (6i). Recrystallization (n-hexane)
1
gave 6i (32%) as green needles: mp 104-106 °C; H NMR δ
(300 MHz) 8.65 (br s, 4H), 8.60 (d, J ) 7.6, 2H), 8.59 (s, 2H),
8.11 (t, J ) 7.6, 1H), 7.88 (br d, J ) 7.8, 1H), 7.68-7.71 (m,
2H), 7.58 (br t, J ) 7.8, 1H), -4.06, -4.10 (s, ratio 1:1, total
6H); UV (hexane) λmax 472 (ꢀ 9 100), 378 (29 600), 338 (75 400);
MS m/ z 376 (M+, 30), 361 (100), 346 (88), 326 (41), 276 (18).
Anal. Calcd for C25H19F3: C, 79.77; H, 5.09; F, 15.14. Found:
C, 79.72; H, 5.04; F, 15.32.
tr a n s-2,7-Bis[2-(t r iflu or om et h yl)p h en yl]-10b ,10c-d i-
m eth yl-10b,10c-d ih yd r op yr en e (7i). Recrystallization (n-
hexane) gave 7i (34%) as green needles: mp 218-219 °C; H
NMR δ (500 MHz) 8.66 (s, 4H), 8.58 (s, 4H), 7.89 (br d, J )
7.9, 2H), 7.68-7.72 (m, 4H), 7.59 (br t, J ) 7.9, 2H), -3.92 (s,
6H); UV (hexane) λmax 482 (ꢀ 16 500), 384 (35 200), 346
(105 800); MS m/ z 520 (M+, 13), 505 (100), 490 (71), 400 (20),
215 (32), 149 (68). Anal. Calcd for C32H22F6: C, 73.84; H, 4.26;
F, 21.90. Found: C, 73.26; H, 4.22; F, 22.53.
tr a n s-2,7-Bis(2-m eth yl-6-n itr oph en yl)-10b,10c-dim eth yl-
10b,10c-d ih yd r op yr en e (7m ). Chromatography (n-hexane-
CH2Cl2 (1:1)) on silica gel gave a mixture of isomers of 7m
(17%) as a green solid: mp 226-240 °C; 1H NMR δ (300 MHz)
8.61 (s, 4H), 8.40 (s, 4H), 7.85-7.92 (m, 2H), 7.64 (d, J ) 7.7,
2H), 7.52 (t, J ) 7.7, 2H), 2.34, 2.16 (s, total 6H), -3.81, -3.84,
-3.85, -3.87 (s, total 6H); UV (hexane) λmax 486 (ꢀ 13 500),
382 (27 800), 346 (77 900); MS m/ z 502 (M+, 20), 487 (100),
472 (30), 455 (70), 408 (40), 182 (73); Mr calcd for C32H26N2O4
502.1893, found (MS) 502.1888.
t r a n s-2-(4-Br om o-2-m e t h yl-6-n it r op h e n yl)-10b ,10c-
d im eth yl-10b,10c-d ih yd r op yr en e (6n ). Recrystallization
(n-hexane) gave a mixture of isomers of 6n (16%) as brown
needles: mp 160-182 °C; 1H NMR δ (300 MHz) 8.59-8.67 (m,
6H), 8.37 (s, 2H), 8.13 (t, J ) 7.7, 1H), 8.03, 7.99 (br s, total
1H), 7.78 (br s, 1H), 2.32, 2.13 (s, total 3H), -4.03, -4.04,
-4.07, -4.09 (s, ratio 2:1:1:2, total 6H); UV (hexane) λmax 482
(ꢀ 9200), 382 (25 600), 344 (72 400); MS m/ z 445 (M+, 22), 430
1
tr a n s-2-(4-P yr id yl)-10b,10c-d im eth yl-10b,10c-d ih yd r o-
p yr en e (6j). Chromatography (n-hexane-CH2Cl2 (1:1)) on
1
silica gel gave 6j (34%) as a green solid: mp 166-167 °C; H
NMR δ (500 MHz) 8.94 (s, 2H), 8.80 (dd, J ) 6.2, 1.6, 2H),
8.74, 8.64 (AB q, J ) 7.7, 4H), 8.59 (d, J ) 7.7, 2H), 8.13 (t, J
) 7.7, 1H), 8.04 (dd, J ) 6.2, 1.6, 2H), -3.99, -4.02 (s, ratio
1:1, total 6H); UV (hexane) λmax 496 (ꢀ 12 400), 386 (25 000),
344 (68 800); MS m/ z 309 (M+, 15), 294 (93), 279 (100). Anal.
Calcd for C23H19N: C, 89.28; H, 6.19; N, 4.53. Found: C, 89.08;
H, 5.98; N, 4.02.
(50), 398 (100), 289 (69), 145 (86). Anal. Calcd for C25H20
-
tr a n s-2-(5-Nitr oth iazole-2-yl)-10b,10c-dim eth yl-10b,10c-
d ih yd r op yr en e (6k ). Recrystallization (n-hexane) gave 6k
(45%) as purple needles: mp 254-256 °C; 1H NMR δ (300
MHz) 9.20 (s, 2H), 8.78, 8.60 (AB q, J ) 7.9, 4H), 8.73 (s, 1H),
8.55 (d, J ) 7.7, 2H), 8.17 (t, J ) 7.7, 1H), -3.77, -3.81 (s,
ratio 1:1, total 6H); UV (hexane) λmax 676 (ꢀ 2700), 562 (27 000),
420 (53 600), 336 (86 800); MS m/ z 360 (M+, 25), 345 (100),
242 (53), 227 (67). Anal. Calcd for C21H16N2O2S: C, 69.98;
H, 4.47; N, 7.77; S, 8.90. Found: C, 69.64; H, 4.55; N, 7.93; S,
8.59.
tr a n s-Dim eth yl 5-[2-(10b,10c-Dim eth yl-10b,10c-d ih y-
d r op yr en yl)]ben zen e-1,3-d ica r boxyla te (6l). Recrystalli-
zation (n-hexane) gave 6l (34%) as yellow-green crystals: mp
177-178 °C; 1H NMR δ (500 MHz) 8.99 (d, J ) 1.6, 2H), 8.96
(s, 2H), 8.73, 8.65 (AB q, J ) 7.7, 4H), 8.72 (t, J ) 1.6, 1H),
8.59 (d, J ) 7.7, 2H), 8.11 (t, J ) 7.7, 1H), 4.06 (s, 6H), -3.99,
BrNO2: C, 67.27; H, 4.52; N, 3.14; Br, 17.90. Found: C, 67.29;
H, 4.41; N, 2.90; Br, 17.67.
Com p u ta tion a l Deta ils. The initial geometries were
generated using the MMX24 force field with PCMODEL v4.0.25
The semiempirical PM326 calculations were carried out with
the MOPAC system (v6.0)27 on a personal IRIS computer.
J O962337I
(24) Based on the MM2(87) force field with expanded parameter sets;
See: Bays, J . P. J . Chem. Educ. 1992, 62, 209.
(25) Serena Software, P.O. Box 3076, Bloomington, IN 47402-3076.
(26) (a) Fukazawa, Y.; Ogata, K.; Usui, S. J . Am. Chem. Soc. 1988,
110, 8692. (b) Longuet-Higgins, H. C.; Salem, L. Proc. R. Soc. (London)
1960, A257, 445. (c) Mallion, R. B. Mol. Phys. 1973, 25, 1415.
(27) Stewart, J . J . P. MOPAC v6.0, Program 455, QCPE; University
of Indiana: Bloomington, IN.