Extremely long C-C bond in (-)-trans- 1,2-di-tert-butyl- 1,2-diphenyl- and 1,1-di-tert-butyl-2,2-diphenyl-3,8-dichlorocyclobuta[b]naphthalenes

Article abstract of DOI:10.1021/jo982010c

The sterically bulky t-Bu-substituted derivatives of 1,1,2,2- tetraphenyl-3,8-dichlorobuta[b]naphthalene (5), trans-1,2-tert-butyl-1,2- diphenyl- (8) and 1,1-di-tert-butyl-2,2-diphenyl-3,8- dichlorocyclobuta[b]naphthalene (12), were prepared. X-ray analys

Full text of DOI:10.1021/jo982010c

3102
J . Org. Chem. 1999, 64, 3102-3105
Extr em ely Lon g C-C Bon d in
(-)-tr a n s-1,2-Di-ter t-bu tyl-1,2-d ip h en yl- a n d
1,1-Di-ter t-bu tyl-2,2-d ip h en yl-3,8-d ich lor ocyclobu ta [b]n a p h th a len es
Fumio Toda,*,† Koichi Tanaka,† Masaki Watanabe,† Kenichi Tamura,† Ikuko Miyahara,‡
Tadashi Nakai,‡ and Ken Hirotsu*,‡
Department of Applied Chemistry, Faculty of Engineering, Ehime University,
Matsuyama 790-8577, J apan, and Department of Chemistry, Faculty of Science, Osaka City University,
Sugimoto-cho, Sumiyoshi-ku, Osaka 950, J apan
Received October 6, 1998
The sterically bulky t-Bu-substituted derivatives of 1,1,2,2-tetraphenyl-3,8-dichlorobuta[b]naph-
thalene (5), trans-1,2-tert-butyl-1,2-diphenyl- (8) and 1,1-di-tert-butyl-2,2-diphenyl-3,8-dichloro-
cyclobuta[b]naphthalene (12), were prepared. X-ray analysis of 8 and 12 at 150 K showed that
C-C bonds of 8 and 12 are 1.686 and 1.729 Å, respectively. The latter bond length is longer than
that of 1.720 Å in 5 and is the longest one reliably determined to date.
In tr od u ction
naphthalene (8). However, the optical purity of 8 is not
determined. When rac-7 was used instead of (+)-7,
synthesis of 8 failed, although the reason is not clear.
Similar treatment of 1 with a 1:1 mixture of 2 and 1,1-
di(tert-butyl)-2-propyn-1-ol 9 gave a mixture of 3 (51%),
10 (5%), and the unsymmetrically substituted 11 (24%
yield), and these were separated by column chromatog-
raphy on silica gel using toluene as an eluent. Treatment
of 11 with SOCl2 followed by heating gave 1,1-di-tert-
butyl-2,2-diphenyl-3,8-dichlorocyclobuta[b]naphthalene
12. It has been reported that the treatment of 10 with
SOCl2 gives thermally stable diallene corresponding to
4.2 This suggests that the tetra-tert-butyl substituted
cyclobuta[b]naphthalene is too unstable to exist due to a
serious steric repulsion between the tert-butyl groups.
The crystal structures of 8 and 12 were determined
by the X-ray diffraction method at 150 K, with no
detectable crystal damage observed during data collec-
tion, and molecular structures of 8 and 12 are shown in
Figures 1 and 2. The accuracy of the molecular dimension
of 12 is pretty good, with an esd of ∼0.002 Å for bond
lengths, while the crystal 8 contained 1 equiv of disor-
dered n-hexane at 293 K, resulting in relatively low
accuracy of observed geometrical parameters of 8, al-
though n-hexane is ordered at 150 K.
The molecule 8 has a 2-fold symmetry axis that goes
through the midpoints of the C2-C3 and C8-C9 bonds.
Both sides of the cyclobutene ring are very crowded with
the ring almost completely covered by 1,2-diphenyl-1,2-
di-tert-butyl groups from above and below. The naphtha-
lene ring of 8 is planar within 0.056(4) Å, and C2 and
C3 deviate by 0.22 and -0.24 Å from this plane, respec-
tively, indicating that the cyclobutene ring is not planar
but twisted. The bond lengths of the cyclobutene ring in
8 are C2-C3 ) 1.686(5) Å, C1-C2 ) 1.542(5) Å, C3-C4
) 1.536(5) Å, and C1-C4 ) 1.419(5) Å.
An extremely long C-C bond length 1.720 Å1 has been
reported for the Csp3-Csp3 linkage in 1,1,2,2-tetraphen-
yl-3,8-dichlorobuta[b]naphthalene (5) prepared according
to a new cyclobutaarene synthetic method (Scheme 1).2
This was the longest C-C single bond,3 although a
comparable value 1.713 Å was recently reported for a
similar compound (6) by Herges and his co-workers.4
These extremely lengthened bonds were proven to be
reasonable by theoretical calculations by Herges et al.,4
Kertesz et al.,5 Schleyer et al.,6 and Siegel et al.7 for 5
and by Herges et al. for 6.4 However, for the origin of
the long bond in 5, Herges4 and Siegel7 estimated a steric
repulsion among phenyl groups on the cyclobutene ring,
and Schleyer6 estimated a through-bond interaction
between the two phenyl groups located at the transposi-
tions. In order to clarify the inconsistency, we prepared
two di-tert-butyl-substituted derivatives 8 and 12, and
their molecular structures were studied by X-ray analy-
sis.
Resu lts a n d Discu ssion
Treatment of 1 with optically pure (-)-1-tert-butyl-1-
phenyl-2-propyn-1-ol (7)8 in the presence of Pd catalyst9
gave the diacetylene diol corresponding to 3, which upon
treatment with SOCl2 followed by heating gave (-)-trans-
1,2-di-tert-butyl-1,2-diphenyl-3,8-dichlorocyclobuta[b]-
† Ehime University.
‡ Osaka City University.
(1) Toda, F.; Tanaka, K.; Stein, Z.; Goldberg, I. Acta Crystallogr.,
Sect. C 1996, 52, 177.
(2) Toda, F.; Tanaka, K.; Sano, I.; Isozaki, T. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1757.
(3) Kaupp, G.; Boy, J . Angew. Chem., Int. Ed. Engl. 1997, 36, 48.
(4) Kammermeier, S.; J ones, P. G.; Herges, R. Angew. Chem., Int.
Ed. Engl. 1997, 36, 1757.
The naphthalene ring of 12 is planar within 0.046(1)
Å, and C2 and C3 deviate from this plane by 0.24 and
-0.13 Å, respectively, showing that the similar twist of
the cyclobutene ring is observed compared with that of
8. The cyclobutene ring is completely shielded from the
surroundings by 1,1-diphenyl-2,2-di-tert-butyl groups.
The bond lengths of the cyclobutene ring in 12 are C2-
(5) Choi, C.-H.; Kertesz, M. J . Chem. Soc., Chem. Commun. 1997,
2199.
(6) Bettinger, H. F.; Schleyer, P. v. R.; Schaefer, H. F., III. J . Chem.
Soc., Chem. Commun. 1998, 769.
(7) Baldrige, K. K.; Kasahara Y.; Ogawa, K.; Siegel, J . S.; Tanaka,
K.; Toda, F. J . Am. Chem. Soc. 1998, 120, 6167.
(8) Toda, F.; Tanaka, K.; Ueda, H. Tetrahedron Lett. 1981, 22, 4669.
(9) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
4467.
10.1021/jo982010c CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/02/1999

Extremely Extended C-C Bonds
J . Org. Chem., Vol. 64, No. 9, 1999 3103
Sch em e 1
F igu r e 1. Compound 8 with atomic labeling. Selected dis-
tances (Å) and angles (deg) determined at 150 K (standard
deviations 0.005 Å and 0.3°) and 293 K (0.008 Å and 0.6°) are
as follows: C2-C3 ) 1.686 (1.696 at 293 K), C1-C2 ) 1.542
(1.540), C3-C4 ) 1.536 (1.538), C1-C4 ) 1.419 (1.416), C4-
C5 ) 1.365 (1.367), C1-C12 ) 1.351 (1.340); C1-C2-C3 )
85.1 (84.5), C2-C3-C4 ) 83.7(84.0), C2-C1-C4 ) 93.1(94.1),
C1-C4-C3 ) 95.3(94.9). Selected nonbonded contacts (Å) are
as follows: C13-C30 ) 3.489, C13-C32 ) 3.134, C14-C32
) 3.154, C20-C23 ) 3.287, C20-C24 ) 3.228, C22-C28 )
3.430.
F igu r e 2. Compound 12 with atomic labeling. Selected
distances (Å) and angles (deg) determined at 150 K (standard
deviations 0.002 Å and 0.1°) and 293 K (0.002 Å and 0.1°) are
as follows: C2-C3 ) 1.729 (1.734 at 293 K), C1-C2 ) 1.529
(1.530), C3-C4 ) 1.539 (1.535), C1-C4 ) 1.409 (1.409), C4-
C5 ) 1.365 (1.370), C1-C12 ) 1.367 (1.365); C1-C2-C3 )
83.8 (83.6), C2-C3-C4 ) 83.2(83.3), C2-C1-C4 ) 95.4(95.5),
C1-C4-C3 ) 95.3(95.5). Selected nonbonded contacts (Å) are
as follows: C13-C26 ) 3.354, C13-C28 ) 3.156, C14-C28
) 3.261, C18-C26 ) 3.388, C19-C30 ) 2.964, C20-C30 )
3.314, C24-C31 ) 3.296.
C3 ) 1.729(2) Å, C1-C2 ) 1.529(1) Å, C3-C4 )
1.539(2) Å, and C1-C4 ) 1.409(2) Å.
Both structures of 8 and 12 have been solved also at
293 K. The bond distances and angles determined at 150
and 293 K are consistent within experimental errors. The
Csp3-Csp3 single bonds of the cyclobutene ring in 8 and
12 are unusually long when compared with the typical
Csp3-Csp3 bond, 1.51-1.59 Å.4 The Csp3-Csp3 bond in
12 is even longer than the corresponding distance of

3104 J . Org. Chem., Vol. 64, No. 9, 1999
Toda et al.
PdCl2] (0.31 g), PPh3 (0.24 g), and NEt3 (100 mL) was heated
under reflux for 24 h. After filtration, the organic layer was
evaporated and the residue chromatographed on silica gel
using toluene as an eluent to give 3 (2.23 g, 51% yield), 10
(0.18 g, 5% yield), and 11 (0.97 g, 24% yield). 3. Colorless
prisms. Mp: 162-164 °C. IR (Nujol): 3280, 2227 cm-1 1H
.
NMR: δ 2.9 (OH, 2H), 7.3-7.5 (Ar, 24H). Anal. Calcd for
36H26O2: C, 88.14; H, 5.34. Found: C, 88.30; H, 5.20. 10.
Colorless prisms. Mp: 160-163 °C. IR (Nujol): 3588, 2229
cm-1 1H NMR: δ 1.24 (Me, 36H), 2.35 (OH, 2H), 7.22-7.26
C
.
(Ar, 2H), 7.40-7.43 (Ar, 2H). Anal. Calcd for C28H42O2: C,
81.90; H, 10.31. Found: C, 81.81; H, 10.36. 11. Colorless
prisms. Mp: 97-99 °C. IR (Nujol): 3494, 2216 cm-1 1H
.
NMR: δ 1.15 (Me, 18H), 2.35 (OH, 2H), 7.16-7.70 (Ar, 14H).
Anal. Calcd for C32H34O2: C, 85.29; H, 7.60. Found: C, 85.22;
H, 7.23. A solution of 11 (0.92 g), pyridine (1.32 mL), and SOCl2
(1.16 mL) in THF (50 mL) was stirred at 0 °C for 4 h. The
reaction mixture was worked up by the usual method to give
12 as colorless prisms (0.22 g, 22% yield, mp 197-199 °C). 1H
NMR: δ 1.14 (Me, 18H), 7.19-7.26 (Ph, 10H), 7.72 (Ar, 2H),
8.49 (Ar, 2H). UV (CHCl3): λmax (ꢀ) ) 243 (26 000), 275 (4100),
286 (4800), 297 (5400), 309 nm (4200). Anal. Calcd for C32H32
Cl2: C, 78.84; H, 6.62. Found: C, 78.94; H, 6.60.
-
Cr ysta llogr a p h ic Stu d ies. The X-ray data were collected
on a Rigaku AFC7R four-circle diffractometer using ω/2θ scan
mode. All calculations were performed with the crystal-
lographic software package teXsan (Molecular Structure Corp.,
1985, 1992).
F igu r e 3. X-X deformation electron densities of 12 in the
plane of the C1, C4, C5, C6, C11, and C12 rings. Contour
interval 0.04 e/Å3, negative electron densities dashed.
1.720(4) Å in 51 and is the longest one reliably determined
to date.
Cr ysta l d a ta for 8 (from n-hexane):
orthorhombic, space group P212121, Cu KR radiation, 2θmax
C
32H32Cl2‚C6H14
,
)
The X-X deformation electron density of 12 clearly
shows bonding electrons of the cyclobutarene ring (Figure
3).10 The bonding electron densities of cyclobutene are
placed outside the ring to reduce the ring strain, which
is essentially the same as that found in cyclobutarene
compounds.11 The unusual elongation of the Csp3-Csp3
bond in the cyclobutene ring may be mainly attributed
to the steric repulsion among bulky substituents at C2
and C3. The larger steric congestion of 12 than that of 8
is consistent with the longer Csp3-Csp3 distance of 12
than that of 8. On the contrary, through-bond interaction
between two phenyls is not expected in 12, although the
interaction is expected in 8.
120°. The structure was solved by direct methods (SIR92)12
and subsequent Fourier recycling (DIRDIF94)13 and refined
by full-matrix least-squares refinement against |F|, with all
hydrogen atoms fixed at the calculated positions. Empirical
absorption corrections were applied. (a) T ) 293 K, a ) 18.114-
(1) Å, b ) 20.916(2) Å, c ) 8.585(1) Å, U ) 3252.5(4) Å3. Dc )
1.171 g cm-3, µ ) 19.59 cm-1, 2794 independent intensities,
2515 observed (I > 2.00σ(I)). Weighting scheme ) 1/[σ2(Fo)2 +
2
(0.025)2Fo
]
-1, R ) 0.072, Rw ) 0.111, GOF ) 3.46, maximum
residual electron density 0.44 e Å-3. (b) T ) 150 K, a ) 18.059-
(8) Å, b ) 20.540(9) Å, c ) 8.479(5) Å, U ) 3145(2) Å3, Dc )
1.211 g cm-3, µ ) 20.26 cm-1, 2711 independent intensities,
2646 observed (I > 2.00σ(I), weighting scheme ) 1/[σ2(Fo)2 +
(0.035)2Fo -1, R ) 0.055, Rw ) 0.084, GOF ) 2.37, maximum
]
2
residual electron density 0.37 e Å-3
.
Cr ysta l d a ta for 12 (from toluene): C32H32Cl2, triclinic,
space group P-1, Mo KR radiation. The structure was solved
by direct methods (SHELX86)14 and subsequent Fourier
recycling (DIRDIF94) and refined by full-matrix least-squares
refinement against |F| with isotropic hydrogens. Empirical
absorption corrections were applied. (a) T ) 293 K: a )
9.935(1) Å, b ) 15.092(4) Å, c ) 9.293(1) Å, R ) 105.10(1)°, â
) 109.15(1)° γ ) 89.40(1)°, U ) 1266.6(4) Å3, Dc ) 1.278 g
cm-3, µ ) 2.75 cm-1, 2θmax ) 50°, 4443 independent intensities,
Exp er im en ta l Section
P r ep a r a tion of 8. A mixture of 1 (2 g, 8.5 mmol), 78 (8 g,
16.3 mmol), CuI (0.1 g), [(Ph3P)2PdCl2] (0.3 g), PPh3 (0.4 g),
and NEt3 (100 mL) was heated under reflux for 12 h. After
filtration, the organic layer was evaporated and the residue
chromatographed on silicagel to give (+)-1,2-bis(3-hydroxy-3-
tert-butyl-3-phenyl-1-propynyl)benzene as colorless prisms (1.4
g, 37% yield, mp 95-97 °C, [R]D +42° (c 0.2, THF)). IR
3955 observed (I > 2.00σ(I)), weighting scheme ) 1/[σ2(Fo)2 +
(Nujol): 3536, 3503 cm-1 1H NMR: δ 0.95 (Me, 18H), 2.24
.
(0.035)2Fo
]
-1, R ) 0.037, Rw ) 0.058, GOF ) 1.65, maximum
2
(OH, 2H), 7.27-7.57 (Ar, 14H). Anal. Calcd for C32H34O2: C,
85.29; H, 7.60. Found: C, 85.02; H, 7.90. A solution of (+)-
1,2-bis(3-hydroxy-3-tert-butyl-3-phenyl-1-propynyl)benzene (1.2
g), pyridine (3.5 mL), and SOCl2 (3 mL) in THF (50 mL) was
stirred at room temperature for 4 h. The reaction mixture was
worked up by the usual method to give 8 as colorless prisms
(0.31 g, 10% yield) Mp: 173-176 °C. [R]D: -12° (c 0.05,
CHCl3)). 1H NMR: δ 0.69 (Me, 18H), 7.29-8.52 (Ar, 14H). UV
(CHCl3): λmax (ꢀ) ) 247 (11 100), 263 (2900), 274 (3600), 285
(5000), 296 (5900), 307 nm (4300). Anal. Calcd for C32H32Cl2:
C, 78.84; H, 6.62. Found: C, 78.59; H, 6.53.
residual electron density 0.39 e Å-3. (b) T ) 150 K: a )
9.861(5) Å, b ) 1 4.983(8) Å, c ) 9.253(5) Å, R ) 105.37(7)°, â
) 109.22(4)°, γ ) 89.50(6)°, U ) 1239(1) Å3, Dc ) 1.306 g cm-3
,
µ ) 2.81 cm-1, 2θmax ) 60°, 6530 independent intensities, 5837
observed (I > 2.00σ (I)), weighting scheme ) 1/[σ2(Fo)2
+
(0.035)2Fo
]
-1, R ) 0.037, Rw ) 0.066, GOF ) 1.68, maximum
2
residual electron density 0.48 e Å-3
.
(12) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Polidori, G. J . Appl. Crystallogr. 1994,
27, 435.
(13) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
de Gelder, R.; Israel, R.; Smits, J . M. M. The DIRDIF-94 program
system; Technical Report of the Crystallography Laboratory; University
of Nijmegen: The Netherlands, 1944.
(14) Sheldrick, G. M. Crystallographic Computing 3; Sheldrick, G.
M., Kruger, C., Goddard, R., Eds.; Oxford University Press: Oxford,
1985; pp 175-189.
P r ep a r a tion of 12. A mixture of 1 (2.1 g, 8.9 mmol), 2 (3.41
g, 16.4 mmol), 9 (2.76 g, 16.4 mmol), CuI (0.04 g), [(Ph3P)2-
(10) Dunitz, J . D. X-Ray Analysis and The Structure of Organic
Molecules; Verlag: New York, 1995; pp 391-417.
(11) Boese, R.; Blaeser, D. Angew. Chem., Int. Ed. Engl. 1988, 27,
304.

Extremely Extended C-C Bonds
J . Org. Chem., Vol. 64, No. 9, 1999 3105
as supplementary publication nos. CCDC 114661-114664.
Copies of the data can be obtained, free of charge, on applica-
tion to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.
(fax: +44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk). (50
pages). This material is available free of charge via the
Internet at http://pubs.acs.org.
Ack n ow led gm en t. This work was partly supported
by the Grant-in-Aid for scientific research from the
Ministry of Education, Science, Sports and Culture,
J apan.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic details for 8 and 12. Crystallographic data (excluding
structure factors) for the structures in this paper have been
deposited with the Cambridge Crystallographic Data Centre
J O982010C