Effects of aryl and arylethynyl substituents at the 1-position on rotational barrier around C(sp)-C(sp3) bonds and bending deformation of acetylenic carbons in bis(9-triptycyl)ethynes

Article abstract of DOI:10.1016/S0040-4020(01)00232-0

The barriers to rotation around C(sp)-C(sp³) single bonds in (1,4-dimethyl-9-triptycyl)(1-X-9-triptycyl)ethynes [X=phenyl, mesityl, phenylethynyl, or (1-naphthyl)ethynyl] were determined by the dynamic NMR method to examine the effect of nonspherically shaped aromatic substituents on the rotational barriers. The rotational barriers increase in the order of the pheny, arylethynyl and mesityl substituted compounds from 15.8 to 18.8 kcal/mol. This result suggests that not only the bulkiness but also the shape and flexibility of the substituents are important factors in determining the rotational barrier. Significant bending deformations of the acetylenic carbons (～166°) were found in the X-ray structures and the optimized structures by the MM2 calculations.

Full text of DOI:10.1016/S0040-4020(01)00232-0

TETRAHEDRON
Pergamon
Tetrahedron 57 $2001) 3521±3528
Effects of aryl and arylethynyl substituents at the 1-position on
rotational barrier around Cꢀsp)±Cꢀsp3) bonds and bending
deformation of acetylenic carbons in bisꢀ9-triptycyl)ethynesq
Shinji Toyota,p Takao Yamamori and Toshiaki Makino
Department of Chemistry, Faculty of Science, Okayama University of Science, Ridaicho, Okayama 700-0005, Japan
Received 18 August 2000; accepted 22 November 2000
AbstractÐThe barriers to rotation around C$sp)±C$sp3) single bonds in $1,4-dimethyl-9-triptycyl)$1-X-9-triptycyl)ethynes [Xˆphenyl,
mesityl, phenylethynyl, or $1-naphthyl)ethynyl] were determined by the dynamic NMR method to examine the effect of nonspherically
shaped aromatic substituents on the rotational barriers. The rotational barriers increase in the order of the pheny, arylethynyl and mesityl
substituted compounds from 15.8 to 18.8 kcal/mol. This result suggests that not only the bulkiness but also the shape and ¯exibility of the
substituents are important factors in determining the rotational barrier. Signi®cant bending deformations of the acetylenic carbons $,1668)
were found in the X-ray structures and the optimized structures by the MM2 calculations. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
While acetylene units have been frequently utilized as a
rigid and linear fragment in the novel aromatic chemistry,
the rotational isomerism of C$sp)±C bonds in alkynes has
been much less studied than those of C±C bonds involving
tetrahedral and trigonal carbons because of the extremely
low rotational barriers.2,3 The restricted rotation around C$sp)±
C$sp3) bonds was observed in bis$9-triptycyl)ethynes $BTE),
where the two bulky substituents interacted with each other
across the acetylene axis during the bond rotation $Scheme
1).1,4,5 Careful kinetic measurements by the dynamic NMR
technique6 revealed that the rotational barriers were enhanced
almost linearly with the steric size of the 10-substituent $X) in
$1,4-dimethyl-9-triptycyl)$1-X-9-triptycyl)ethynes $1±4) for
spherical or pseudospherical substituents $H, OMe, Me, F,
Cl, Br and I) in the range 10.1±17.3 kcal/mol.1,5
We became interested in the effect of nonspherically shaped
substituents containing aromatic groups on the rotational
barriers in the BTE system. For these groups, various struc-
tural factorsÐshape, conformation and ¯exibilityÐshould
in¯uence the total steric effect in the dynamic process. If the
structures of the substituents are appropriately designed,
further enhancement of the rotational barrier will be
possible. Therefore, we studied compounds 5a±d carrying
phenyl, mesityl $Mes), phenylethynyl, or $1-naphthyl)-
Scheme 1. Rotational isomerization in bis$9-triptycyl)ethynes $only one
enantiomeric form is shown for the sc isomer. The ap and sc forms are
ethynyl group at the 10-position, respectively, by spectro-
scopic methods. Because of the severe steric congestion, the
molecules are subjected to structural deformation as shown
by the X-ray analysis and the MM2 calculation. Especially,
the bending deformation of the acetylenic carbons is
discussed in relation to the rotational isomerism.
q For Parts 2 and 3 of the series see Ref. 1.
Keywords: substituent effect; steric and strain effect; alkynes; stereoisomer-
ism.
Corresponding author. Tel./fax: 181-86-256-9457;
e-mail: stoyo@chem.ous.ac.jp
2. Results
p
The synthetic route to compounds 5 is basically the same as
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020$01)00232-0

3522
S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
Scheme 2. Syntheses of $1,4-dimethyl-9-triptycyl)$1-substituted 9-triptycyl)ethynes $5).
those of 1±4 reported earlier $Scheme 2).1,5 Aryl substituted
compounds, 5a and b, were synthesized from 1-aryl-9-
anthrones, which were converted to 1-aryl-9-ethynyl-
triptycenes $9) in three steps. For 5c and d, an arylethynyl
group at the 1-position was introduced at the stage of the
1-bromo compound $10) by the Sonogashira reaction7 with a
terminal ethyne, and subsequent desilylation gave 9. Thus
the prepared 9-ethynyltriptycenes $9) were transformed to
the desired compounds by the Sonogashira reaction with
9-iodoanthracene followed by the Diels±Alder reaction
with 3,6-dimethylbenzyne.
conformation, is shown in Fig. 2 together with selected
structural parameters. Molecular mechanics calculations
were carried out for both the ap and sc forms of 5a±d
with the MM2 force-®eld parameters. The optimized
Compounds 5a±d exhibited two sets of 1H NMR signals due
to the ap and sc rotamers at room temperature. The assign-
ment of the rotamer was apparent from the equivalency of
the aromatic signals: the sc form gave a signal pattern more
complicated than the ap. The spectra were measured at
higher temperatures in 1,1,2,2-tetrachloroethane-d2 to
show lineshape changes due to the facile exchange between
the two isomers. For example, the temperature dependence
of the 1H NMR signals of 5c is shown in Fig. 1: the signals
due to the 1-Me protons broaden at 708C, and coalesce at
1098C. The total lineshape analysis of these signals afforded
rates of interconversion between the ap and sc isomers via
the bond rotation. The kinetic data are listed in Table 1
together with the free energy difference between the two
rotamers $DG8), which was calculated from the rotamer
population.
The molecular structures of 5 were obtained by X-ray
analysis or MM2 calculation. Only the mesityl compound
5b gave a single crystal suitable for X-ray analysis. An
ORTEP drawing of 5b, in which molecules take the ap
1
Figure 1. VT H NMR spectra of Me signals in 5c in 1,1,2,2-tetrachloro-
ethane-d2.

S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
3523
Table 1. Thermodynamic and kinetic parameters for rotation around C±C bonds $ap!sc) in compounds 5 in 1,1,2,2-tetrachloroethane-d2
a
r $A)
DH± $kcal/mol)
DS± $cal/$mol K))
DG±273 $kcal/mol)
DG8273 $kcal/mol)
Ê
Compound
5a
5b
5c
5d
14.7^0.4
19.8^0.4
16.4^0.4
18.4^0.6
23.6^1.4
3.4^1.0
23.8^1.0
1.9^1.7
15.7
18.8
17.5
17.8
1.82
2.13
2.00
2.03
0.9
2.4
0.7
0.8
a
Estimated steric size calculated by the linear relationship, rˆ0.102 DG±27310.22.1
highest among the rotational barriers in acyclic acetylene
compounds to the best of our knowledge.
For a quantitative estimation, the kinetic data of 5 are corre-
lated with the linear relationship between the DG± and r
$van der Waals radius)8 established for compounds 1±4,
1
DG±273 $kcal/mol)ˆ9.84r $A)2 2.2 $Fig. 4). The observed
Ê
DG±273 values of 5a±d are input to the equation to afford the
Ê
r values of 1.82, 2.13, 2.00 and 2.03 A, respectively, which
are regarded as `estimated steric size' derived by the rota-
tional barrier in the BTE system. The calculated r values
indicate that arylethynyl groups are little larger than Ph, and
Ê
mesityl group is larger by 0.3 A than Ph. The steric size of
Ph group determined by various methods is 1.62,9 1.778 and
1.77 A,10 and our estimation is consistent with the latter two
Ê
Ê
cases. The value of ca. 1.8 A corresponds to the thickness of
p electron cloud of a benzene plane at each side.8,11
Although examples are limited at present, the BTE system
provides a useful method for the estimation of steric size
of not only spherically but also nonspherically shaped
substituents.
In the X-ray structure of ap-5b, several bending deforma-
tions due to the steric hindrance are notable, while the bond
distances are generally in normal ranges. The mesityl group
conformationally bisects the attaching benzeno plane, and
tilts away from the acetylenic $1,4-Me2-trip) moiety to a
large extent to avoid the steric interactions with the 1,4-
dimethyl-9-triptycyl group: the bond angles of C$26)±
C$9)±C$9a), C$9)±C$9a)±C$1) and C$9a)±C$1)±C$17) are
larger than standard values. Therefore, the distance between
the mesityl group and acetylenic axis becomes large at the
Figure 2. ORTEP drawing of compound 5b with thermal ellipsoids at 50%
probabilities $a solvent molecule is omitted for simplicity). Selected struc-
tural parameters: C$9)±C$26) 1.480$3), C$26)±C$27) 1.201$4), C$27)±
C$36) 1.481$3) A; C$9)±C$26)±C$27) 165.9$2)8, C$26)±C$27)±C$36)
172.1$3)8, C$9a)±C$1)±C$17) 124.8$2)8, C$9)±C$9a)±C$1) 129.1$2)8,
C$26)±C$9)±C$9a) 119.2$2)8, C$9)±C$26)±C$27)±C$36) 133$1)8.
Ê
Ê
tip of the mesityl-phenyl group, C$20)´´´C$36) 4.23 A,
compared with that between the attached peri positions,
Ê
C$1)´´´C$9) 2.68 A.
structures of ap-5a and ap-5c are shown in Fig. 3. The
calculated bond angles of the acetylenic carbons are listed
in Table 2 as a scale of the molecular strain together with the
observed 13C NMR chemical shifts.
Another structural feature is the bending deformation of the
acetylenic moiety, the bond angles being 1668 and 1728 at
C$26) and C$27), respectively. The former is one of the
smallest angles for sp carbons among nonconjugated
acyclic alkynes.12 The bending deformation of acetylenic
carbons usually results in the deshielding of carbon atoms
in 13C NMR spectroscopy due to the rehybridization.13±15
In 5b, only one of the two sp carbon signals is slightly
shifted down®eld relative to an unstrained compound,
2,2,5,5-tetrametheyl-3-hexyne, at d 86.7 $Table 2).16 In
contrast, a notable shift down to d 91±92 was observed
for some signals in 5a, b, and c $Table 2). We cannot ratio-
nalize why the effect of the bond strain on the 13C N MR
chemical shift is so small in 5b from available information.
However, the fact that the signals due to the sterically
congested sc form are always at lower ®eld by 0.4±
1.2 ppm than those due to the ap in 5a, b, and c is attributed
to the effect of hybridization.
3. Discussion
The free energies of activation for the C$sp)±C$sp3) bond
rotation increase in the order of 5a,5c<5d,5b from 15.7
to 18.8 kcal/mol. A comparison of these data with those
of compounds 1±4 reveals that the steric effect of the 10-
substituent on the rotational barrier is increased in the order
H,F,OMe,Cl,Me<Ph,Br,I<arylethynyl,Mes.
The effect of Ph is in the middle of Cl and Br, and compar-
able to Me. The arylethynyl groups are comparable to I in
size. The highest barrier was observed for the Mes
compound $5b) in the series of compounds, being the

3524
S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
Figure 3. Optimized structures of ap-5a and ap-5c by MM2 calculations and selected structural parameters $triple bonds are indicated by solid cylinders).
Table 2. Bond angles and 13C NMR data of acetylenic carbons in compounds 5 and the related compounds
Compound 10-X
5a Ph
5b Mes
5c Ph±CuC±
5d Naph±CuC±
1a H
3a Me
Bond angle $8)b
ap 1-C
ap 2-C
sc 1-C
sc 2-C
176.7
172.2
173.3
171.3
177.4 $172.1)
171.3 $165.9)
173.0
177.3
172.4
173.0
172.8
177.2
172.3
172.3
172.9
173.8
177.7
±
175.6 $170.2)
175.6 $171.4)
166.7
c
170.4
166.7
13C NMR $d)d
ap
ap
sc
88.20
91.63
89.34
92.79
87.32
89.42
±
87.34
91.34
87.76
92.10
87.29
91.45
87.75
92.19
87.83
90.34
±
89.40
90.30
e
c
sc
a
Ref. 1.
1-C and 2-C denote the sp carbons attaching to 1,4-Me2-trip and 1-X-trip groups, respectively. Values in parentheses are experimental values determined by
b
X-ray analysis.
Identical with ap.
c
d
Solvent CDCl3. Measured at room temperature except for 2 $2508C), cf. d 86.7 $tBu±CuC±tBu).16
As shown by the structural data of 5b as well as 3 in Table 2,
to enhance the rotational barrier because they were large
enough to reach a notch between two benzeno groups in
the 1,4-Me2-trip moiety in a rigid molecular model. In
the MM2 calculation tends to underestimate the bending
formations of the acetylenic carbons. Nevertheless, the
calculated bond angles are helpful to know the molecular
strain in the initial state of the dynamic process. Although
the barrier in 5b is higher by 3.0 kcal/mol than that in 5a, the
calculated bond angles in the two compounds are not so
different from each other. This suggests that the steric effect
in the transition state rather than the initial state plays a
dominant role in controlling the barrier heights. The high
barrier in 5b is attributed to the direct steric interactions of
three extra Me groups with the 1,4-Me2-trip group that
passes over the 10-substituent at the transition state. Addi-
tionally, the conformational rigidity of the mesityl group
due to the steric effect of the 2,6-Me2 groups makes it
dif®cult to avoid the steric interactions during the rotation
around the acetylenic axis.
Ê
fact, there are some short contacts $3.1±3.3 A for C´´´C
distances)17 between the phenyl group in the 10-substituent
and the nonsubstituted benzeno groups in 1,4-Me2-trip
group in the calculated structure of ap-5c. However, severe
steric congestion is reduced by the bending deformations of
the two C±CuC±C moieties: the interatomic distance of
9-C´´´100-C is much longer than that between the peri posi-
tions $Fig. 3). Although information about the structure in
the transition state is limited, its energy level is not raised so
much because of the ¯exibility of the substituents to reduce
severe steric interactions. As a result, the phenylethynyl
group has a moderate effect on the barrier enhancement.
The substitution of a 1-naphthyl group for the phenyl
group in 5c hardly in¯uences the rotational barrier because
the additionally fused benzene ring is far from the site where
the bond rotation occurs.
We anticipated that arylethynyl groups should be effective

S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
3525
20
15
5b (Mes)
–
–C–
)
(
5d
Naph-C
–
4d (I)
–
–
–
(
5c Ph-C C–)
4c (Br)
5a (Ph)
3 (Me)
4b (Cl)
2 (OMe)
4a (F)
1 (H)
10
1.0
1.5
2.0
van der Waals radius [Å]
Figure 4. Plot of vdW radius of 10-substituents vs DG± for compounds 1±5.
In summary, the barrier to rotation around C$sp)±C$sp3)
bond is enhanced in the order of the phenyl, arylethynyl
and mesityl substituted compounds in the BTE system.
The kinetic and structural data indicate that not only the
steric bulkiness but also the shape and ¯exibility of the
substituents are important factors in determining the barrier
heights. Especially, the springy nature of the C±CuC±C
moieties is ef®cient to relieve the excess steric strain in the
transition state as well as in the initial state in these
sterically crowded compounds. The introduction of a
mesityl group is not suf®cient to interlock the two 9-
triptycyl groups across the acetylenic axis on a laboratory
time scale. It is necessary to introduce bulky and rigid
substituents at more than two peri positions toward success-
ful isolation of this kind of rotational isomer.
was subjected to chromatography on silica gel with hexane
eluent, during which the initially formed 1-phenyl-9-
[$trimethylsilyl)ethynyl]-9-anthrol was dehydrolyzed into
the corresponding anthracene. The desired compound was
obtained as yellow oil, which crystallized upon standing,
with the recovery of 137 mg of the starting anthrone.
1
Yield 307 mg $47%). Mp 98±1018C; H NMR $CDCl3) d
0.09 $s, 9H), 7.34±7.58 $m, 9H), 7.97±8.03 $m, 2H), 8.49 $s,
1H), 8.55 $d, Jˆ8.7 Hz, 1H). Anal. calcd for C25H22Si: C,
85.66; H, 6.33. Found: C, 85.38; H, 6.41.
4.1.2. 1-Mesityl-9-[ꢀtrimethylsilyl)ethynyl]anthrancene
ꢀ7b). Yield 53%. Yellow oil; H NMR $CDCl3) d 0.15 $s,
1
9H), 1.89 $s, 6H), 2.40 $s, 3H), 6.90 $s, 2H), 7.19 $dd, Jˆ1.4,
6.8 Hz, 1H), 7.47±7.52 $m, 2H), 7.56 $dt, Jˆ1.5, 6.5 Hz,
1H), 8.00 $d, Jˆ8.6 Hz, 2H), 8.49 $s, 1H), 8.45 $dd, Jˆ1.2,
8.3 Hz, 1H); HRMS $FAB) Found: MH1 393.2016. Calcd
for C28H2828Si: 393.2039.
4. Experimental
4.1. General
4.1.3. 1-Phenyl-9-[ꢀtrimethylsilyl)ethynyl]triptycene ꢀ8a).
This compound was similarly prepared by the Diels±Alder
reaction of 7a with 3 equiv. of benzyne as the method in the
literature.1,5 Yield 57%. Mp 228±2308C $recrystallized from
hexane); 1H NMR $CDCl3) d 0.12 $s, 9H), 5.43 $s, 1H), 6.78
$dd, Jˆ1.4, 7.7 Hz, 1H), 6.97 $t, Jˆ7.5 Hz, 1H), 7.02±7.12
$m, 4H), 7.24 $dd, Jˆ1.4, 7.9 Hz, 2H), 7.30±7.43 $m, 6H),
7.72 $m, 2H). Anal. calcd for C31H26Si: C, 87.27; H, 6.14.
Found: C, 86.96; H, 6.19.
1H and 13C NMR spectra were measured on a Varian
Gemini-300 at 300 and 75 MHz, respectively. The spectra
were collected at room temperature unless otherwise
mentioned. Melting points are uncorrected. Elemental
analyses were performed on a Perkin±Elmer 2400 series
analyzer. High-resolution mass spectra were measured on
a JEOL JMS-700 MStation spectrometer. 1-Mesityl-9-
anthrone was prepared by the Suzuki coupling18 of 1-
iodoanthraquinone19 with mesitylboronic acid, followed
by reduction with Sn/HCl:20 1H NMR $CDCl3) d 1.87 $s,
6H), 2.37 $s, 3H), 4.55 $s, 2H), 6.96 $s, 2H), 7.10 $d,
Jˆ8.6 Hz, 1H), 7.38 $t, Jˆ8.1 Hz, 1H), 7.46 $d, Jˆ7.8 Hz,
1H), 7.51 $dt, Jˆ1.1, 7.7 Hz, 1H), 7.57 $dd, Jˆ1.5, 7.8 Hz,
1H), 7.61 $t, Jˆ7.6 Hz, 1H), 8.15 $dd, Jˆ1.3, 8.0 Hz, 1H).
4.1.4. 1-Mesityl-9-[ꢀtrimethylsilyl)ethynyl]triptycene ꢀ8b).
Yield 63%. Mp 201±2028C; 1H NMR $CDCl3) d 0.14 $s, 9H),
1.72 $s, 6H), 2.38 $s, 3H), 5.42 $s, 1H), 6.57 $dd, Jˆ1.3,
7.7 Hz, 1H), 6.85 $s, 2H), 6.99 $t, Jˆ7.5 Hz, 1H), 7.04±
7.08 $m, 4H), 7.34 $dd, Jˆ1.4, 7.3 Hz, 1H), 7.38±7.42 $m,
2H), 7.64±7.70 $m, 2H). Anal. calcd for C34H32Si: C, 87.13;
H, 6.88. Found: C, 87.12; H, 6.90.
4.1.1. 1-Phenyl-9-[ꢀtrimethylsilyl)ethynyl]anthrancene
ꢀ7a). This compound was similarly prepared from
3.7 mmol of lithium $trimethylsilyl)acetylide and 500 mg
$1.85 mmol) of 1-phenyl-9-anthrone21 in ether by the
method described in the literature.1,5 The crude material
4.1.5. 9-Ethynyl-1-phenyltriptycene ꢀ9a). 8a was desilyl-
ated by treatment with Bu4NF in THF in the usual manner.1,5
Yield 79%. Mp 171±1728C $recrystallized from hexane); 1H
NMR $CDCl3) d 2.50 $s, 1H), 5.45 $s, 1H), 6.84 $dd, Jˆ1.3,

3526
S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
7.7 Hz, 1H), 7.00 $t, Jˆ7.3 Hz, 1H), 7.03±7.10 $m, 2H),
7.23 $dd, Jˆ1.6, 8.3 Hz, 2H), 7.32 $t, Jˆ6.8 Hz, 2H),
7.35±7.44 $m, 6H), 7.71 $m, 2H). Anal. calcd for C28H18:
C, 94.88; H, 5.12. Found: C, 94.86; H, 5.11.
7.0 Hz, 2H), 8.54 $d, Jˆ8.1 Hz, 1H); HRMS $FAB) Found:
MH1 429.1660. Calcd for C34H20: 429.1643.
4.1.9. 9-[ꢀ9-Anthryl)ethynyl]-1-phenyltriptycene ꢀ11a).
This compound was similarly prepared from 100 mg
$0.282 mmol) of 9a, 120 mg $0.394 mmol) of 9-iodoanthra-
cene,22 28 mg $0.040 mmol) of [PdCl2$PPh3)2] and 3.8 mg
$0.020 mmol) of CuI by the literature method.1,5 The crude
materials were chromatographed on silica gel with hexane±
dichloromethane eluent. The order of elution was 9-iodo-
anthracene, the starting compound, the coupling product
and a by-product $homo coupling product). The third frac-
tion was collected and recrystallized from hexane±dichloro-
methane to give 65 mg $43%) of the desired compound as
yellow crystals containing solvent molecules. Mp 259±
2628C; 1H NMR $CDCl3) d 5.56 $s, 1H), 6.17 $t,
Jˆ7.4 Hz, 1H), 6.63 $t, Jˆ7.5 Hz, 2H), 6.86 $dd, Jˆ1.3,
7.7 Hz, 1H), 7.06 $t, Jˆ7.5 Hz, 1H), 7.10±7.20 $m, 4H),
7.28 $dd, Jˆ1.2, 8.2 Hz, 2H), 7.45±7.58 $m, 8H), 8.02 $d,
Jˆ7.2 Hz, 2H), 8.13 $d, Jˆ6.8 Hz, 2H), 8.42 $s, 1H), 8.46
$d, Jˆ6.8 Hz, 2H). Anal. calcd for C42H26´1/8$CH2Cl2): C,
93.47; H, 4.89. Found: C, 93.14; H, 4.82. MS $FAB) Found:
MH1 531. Calcd for C42H26: 531.
4.1.6. 9-Ethynyl-1-mesityltriptycene ꢀ9b). Yield 73%. Mp
184±1858C $recrystallized from hexane±dichloromethane);
1H NMR $CDCl3) d 1.73 $s, 6H), 2.34 $s, 1H), 2.39 $s, 3H),
5.43 $s, 1H), 6.67 $dd, Jˆ1.6, 7.7 Hz, 1H), 6.86 $s, 2H),
7.00±7.08 $m, 5H), 7.37 $dd, Jˆ1.3, 7.3 Hz, 1H), 7.39±
7.43 $m, 2H), 7.64±7.70 $m, 2H). Anal. calcd for C31H24:
C, 93.90; H, 6.10. Found: C, 93.71; H, 6.07.
4.1.7. 9-Ethynyl-1-ꢀphenylethynyl)triptycene ꢀ9c). To a
solution of 995 mg $2.32 mmol) of 1-bromo-9-[$trimethyl-
silyl)ethynyl]triptycene $10)1 and 1.55 ml $14.1 mmol) of
phenylacetylene in 50 ml of degassed NEt3 were added
98 mg $0.14 mmol) of [PdCl2$PPh3)2] and 14 mg
$0.073 mmol) of CuI under nitrogen atmosphere. The solu-
tion was heated at 608C for 27 h. After the solvent was
evaporated, the residue was subjected to chromatography
on silica gel with hexane±dichloromethane $20:1) eluent
to give a mixture of the cross-coupling product and its
desilylated compound in ca. 1:2 ratio. The analytical sample
of the former was obtained by chromatography on silica gel
as colorless oil. 1-Phenylethenyl-9-[$trimethylsilyl)ethy-
4.1.10. 9-[ꢀ9-Anthryl)ethynyl]-1-mesityltriptycene ꢀ11b).
Yield 65%. Yellow powder; mp 247±2548C $dec); 1H N MR
$CDCl3) d 0.71 $s, 3H), 1.84 $s, 6H), 5.54 $s, 1H), 5.98 $s,
2H), 6.67 $dd, Jˆ1.3, 7.7 Hz, 1H), 7.08 $t, Jˆ7.5 Hz, 1H),
7.11 $dt, Jˆ1.8, 6.7 Hz, 2H), 7.17 $dt, Jˆ1.5, 7.5 Hz, 2H),
7.46 $dd, Jˆ1.3, 8.3 Hz, 1H), 7.49 $dd, Jˆ1.1, 7.2 Hz, 2H),
7.57 $dt, Jˆ1.3, 6.7 Hz, 2H), 7.66 $dt, Jˆ1.4, 7.7 Hz, 2H),
8.06 $d, Jˆ8.1 Hz, 2H), 8.14 $dd, Jˆ1.5, 7.1 Hz, 2H), 8.39
$s, 1H), 8.65 $d, Jˆ8.7 Hz, 2H). Anal. calcd for C45H32: C,
94.37; H, 5.63. Found: C, 94.23; H, 5.80.
1
nyl]triptycene $8c): H NMR $CDCl3) d 0.12 $s, 9H), 5.36
$s, 1H), 6.95 $t, Jˆ7.3 Hz, 1H), 7.05 $dt, Jˆ1.2, 7.3 Hz, 2H),
7.11 $dt, Jˆ1.2, 7.3 Hz, 2H), 7.19 $dd, Jˆ1.2, 7.3 Hz, 2H),
7.32 $dd, Jˆ1.2, 7.3 Hz, 1H), 7.33±7.40 $m, 5H), 7.58 $dd,
Jˆ1.5, 7.9 Hz, 2H), 7.89 $d, Jˆ7.3 Hz, 2H); HRMS $FAB)
Found: MH1 451.1771. Calcd for C33H2628Si: 451.1782.
The above mixture was completely desilylated by treatment
with ¯uoride in a similar manner. Overall yield 67%. Color-
less oil; 1H NMR $CDCl3) d 3.27 $s, 1H), 5.39 $s, 1H), 6.98
$t, Jˆ7.6 Hz, 1H), 7.06 $dt, Jˆ1.5, 7.3 Hz, 2H), 7.11 $dt,
Jˆ1.5, 7.2 Hz, 2H), 7.21 $dd, Jˆ1.5, 7.8 Hz, 1H), 7.34 $dd,
Jˆ1.3, 7.3 Hz, 1H), 7.38±7.43 $m, 5H), 7.59 $dd, Jˆ1.7,
7.3 Hz, 2H), 7.92 $dd, Jˆ1.7, 7.0 Hz, 2H); HRMS $EI)
Found: M1 392.1937. Calcd for C28H2828Si: 392.1960.
4.1.11. 9-[ꢀ9-Anthryl)ethynyl]-1-ꢀphenylethynyl)triptycene
ꢀ11c). Yield 62%. Yellow crystals; mp 258±2698C $dec); 1H
NMR $CDCl3) d 5.50 $s, 1H), 6.36 $t, Jˆ7.4 Hz, 2H), 6.45
$dd, Jˆ1.5, 8.3 Hz, 2H), 7.03 $t, Jˆ7.5 Hz, 1H), 7.13 $dt,
Jˆ1.4, 7.3 Hz, 2H), 7.21 $dt, Jˆ1.4, 7.4 Hz, 2H), 7.23 $d,
Jˆ7.3 Hz, 1H), 7.42 $dd, Jˆ1.4, 7.2 Hz, 1H), 7.46±7.49 $m,
5H), 7.57 $ddd, Jˆ1.4, 6.6, 8.8 Hz, 2H), 7.93 $d, Jˆ8.2 Hz,
2H), 8.28 $d, Jˆ6.6 Hz, 2H), 8.31 $s, 1H), 9.03 $d,
Jˆ8.9 Hz, 2H). Anal. calcd for C44H26: C, 95.28; H, 4.72.
Found: C, 95.15; H, 4.59.
4.1.8. 9-Ethynyl-1-[ꢀ1-naphtyl)ethynyl]triptycene ꢀ9d).
This compound was similarly prepared from 10 and 1-ethy-
nylnaphthalene by Sonogashira coupling followed by
desilylation. 1-[$1-Naphthyl)ethynyl]-9-[$trimethylsilyl)-
1
ethynyl]triptycene $8d): colorless oil; H NMR $CDCl3) d
20.16 $s, 9H), 5.42 $s, 1H), 7.01 $t, Jˆ7.6 Hz, 1H), 7.09 $dt,
Jˆ1.3, 7.0 Hz, 2H), 7.15 $dt, Jˆ1.5, 7.5 Hz, 2H), 7.31 $dd,
Jˆ1.5, 8.0 Hz, 1H), 7.37 $dd, Jˆ1.4, 7.3 Hz, 1H), 7.42 $dd,
Jˆ1.5, 7.7 Hz, 2H), 7.50 $t, Jˆ8.2 Hz, 1H), 7.55 $dt, Jˆ1.6,
7.1 Hz, 1H), 7.61 $dt, Jˆ2.1, 8.0 Hz, 1H), 7.82 $dd, Jˆ1.2,
7.2 Hz, 1H), 7.86 $d, Jˆ7.1 Hz, 1H), 7.89 $d, Jˆ7.9 Hz,
1H), 7.93 $d, Jˆ7.4 Hz, 2H), 8.55 $d, Jˆ8.2 Hz, 1H);
HRMS $FAB) Found: MH1 501.2044. Calcd for
C37H2828Si: 501.2039. The terminal acetylene was puri®ed
by chromatography on silica gel. Overall yield 84%. Color-
less oil; 1H NMR $CDCl3) d 3.13 $s, 1H), 5.42 $s, 1H), 7.03
$t, Jˆ7.6 Hz, 1H), 7.08 $dt, Jˆ1.4, 6.7 Hz, 2H), 7.13 $dt,
Jˆ1.5, 7.0 Hz, 2H), 7.34 $dd, Jˆ1.6, 7.8 Hz, 1H), 7.38 $d,
Jˆ8.5 Hz, 1H), 7.41 $dd, Jˆ1.4, 6.7 Hz, 2H), 7.51 $t,
Jˆ7.8 Hz, 1H), 7.55 $dt, Jˆ1.2, 6.7 Hz, 1H), 7.61 $dt,
Jˆ1.4, 6.7 Hz, 1H), 7.82 $dd, Jˆ1.2, 6.0 Hz, 1H), 7.87 $d,
Jˆ6.8 Hz, 1H), 7.89 $d, Jˆ9.4 Hz, 1H), 7.94 $dd, Jˆ1.7,
4.1.12. 9-[ꢀ9-Anthryl)ethynyl]-1-[ꢀ1-naphtyl)ethynyl]-
triptycene ꢀ11d). Yield 74%. Yellow crystals; mp 231±
1
2378C $dec); H NMR $CDCl3) d 5.53 $s, 1H), 6.42 $t,
Jˆ7.8 Hz, 1H), 6.59 $d, Jˆ7.1 Hz, 1H), 6.93 $dd, Jˆ1.3,
7.7 Hz, 1H), 7.04±7.23 $m, 7H), 7.29 $d, Jˆ7.9 Hz, 1H),
7.33±7.42 $m, 5H), 7.46 $dd, Jˆ1.1, 8.2 Hz, 1H), 7.51 $d,
Jˆ6.6 Hz, 2H), 7.71 $d, Jˆ8.3 Hz, 2H), 7.94 $d, Jˆ8.3 Hz,
1H), 7.98 $s, 1H), 8.32 $2H, d, Jˆ7.1 Hz), 8.90 $d,
Jˆ8.8 Hz, 2H); HRMS $FAB) Found: MH1 605.2250.
Calcd for C48H28: 605.2269.
4.1.13. ꢀ1,4-Dimethyl-9-triptycyl)ꢀ1-phenyl-9-triptycyl)-
ethyne ꢀ5a). A solution of 65 mg $0.12 mmol) of 11a in
10 ml of 1,2-dimethoxyethane $DME) was re¯uxed in a
¯ask. From respective dropping funnels, a solution of
99 mg $0.60 mmol) of 3,6-dimethylanthranilic acid23 in
5 ml of DME and a solution of 120 ml $0.90 mmol) of

S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
3527
isopentyl nitrite in 5 ml of DME were added to the boiling
4.2. X-Ray analysis
solution over 1 h. After the reaction mixture was re¯uxed
for 2 h, the volatile materials were evaporated. The residue
was passed through a plug silica gel column to remove polar
materials, and the crude mixture was further chromato-
graphed on silica gel with hexane±dichloromethane $1:1)
eluent. Recrystallization from dichloromethane gave
42 mg $55%) of the product as colorless crystals. Mp
A crystal of 5b used for the measurement was grown from a
hexane±chloroform solution. The crystal size was
0.20£0.20£0.10 mm3. The diffraction data were collected
on a Rigaku RAXIS-IV imaging plate diffractometer with
MoKa radiation $lˆ0.71070 A) to a maximum 2u value of
Ê
55.18 at 2808C. A total of 12£6.008 oscillation images were
collected, each being exposed for 90.0 min. The re¯ection
data were corrected for the Lorentz-polarization effects and
secondary extinction $coef®cientˆ3.65472£1026). The
crystal-to-detector distance was 100.0 mm with the detector
at the zero swing position. The readout was performed in the
0.100 mm pixel mode. The structure was solved by the
direct method and re®ned by the full-matrix least-squares
method by using a teXsan program on a Comtec O2 work-
station. The non-hydrogen atoms were re®ned anisotropi-
cally. Some hydrogen atoms were re®ned isotropically, and
the rest were included in ®xed positions. Among 8439
observed re¯ections, 6362 re¯ections $I.3.0s$I)) were
1
300±3078C $dec); H NMR $CDCl3) d 2.33 $s, 3Hap),
2.45 $s, 3Hap), 2.50 $s, 3Hsc), 2.65 $s, 3Hsc), 5.55 $s,
1H), 5.60 $s, 1Hap), 5.60 $s, 1Hsc), 6.13 $t, Jˆ7.4 Hz,
1Hap), 6.43±7.88 $brm, 23Hap126Hsc), 8.20 $d,
Jˆ6.7 Hz, 2Hap), rotamer ratio $ap/sc) 62:38; 13C N MR
$CDCl3) d 18.87, 21.63, 21.84, 49.87, 53.84, 54.59, 54.58,
88.20, 89.34, 91.63, 92.79, and 58 aromatic carbon signals
at 122.7±146.3. Anal. calcd for C50H34: C, 94.60; H, 5.40.
Found: C, 94.69; H, 5.57.
4.1.14. ꢀ1,4-Dimethyl-9-triptycyl)ꢀ1-mesityl-9-triptycyl)-
ethyne ꢀ5b). Yield 80%. Colorless crystals; mp 265±
1
2748C $dec); H NMR $CDCl3) ap form d 0.91 $s, 3H),
used for the re®nement of 671 variables. The function
2
P
1.92 $s, 6H), 2.24 $s, 3H), 2.44 $s, 3H), 5.54 $s, 1H), 5.61
$s, 1H), 6.14 $s, 2H), 6.41 and 6.61 $ABq, Jˆ7.8 Hz, 2H),
6.63 $dd, Jˆ1.4, 7.7 Hz, 1H), 7.03±7.24 $m, 9H), 7.39 $d,
Jˆ7.0 Hz, 2H), 7.43 $d, Jˆ7.2 Hz, 1H), 7.52 $dd, Jˆ1.6,
6.8 Hz, 2H), 7.81 $d, Jˆ7.2 Hz, 2H), 8.16 $d, Jˆ7.1 Hz,
2H); sc form $readable signals only) d 1.78 $s, 3H), 1.90
$s, 3H), 1.98 $s, 3H), 2.84 $s, 3H), 2.50 $s, 3H), rotamer
minimized was ‰wꢀuFou 2 uFcu† Š; where w ˆ ‰s2cuFou 1
2
21
ꢀp2=4†uFou Š
$pˆ0.1610). Formula C53H40´CHCl3, FW
796.28, monoclinic, space group P21/n, aˆ22.0004$2),
Ê
bˆ8.299$2),
cˆ24.133$3) A,
bˆ111.849$7)8,
Vˆ
Ê 3
4090.4$9) A ,
Zˆ4,
Dcˆ1.293 g/cm3,
m$MoKa)ˆ
2.62 cm21, Rˆ0.080, Rwˆ0.148, goodness of ®t 1.82.
Additional information will be given from CCDC.
ratio $ap/sc) 97:3; 13C N MR $CDCl) d 18.88, 19.24,
3
21.42, 21.80, 49.88, 53.54, 54.07, 54.50, 87.32, 89.42,
and 28 aromatic carbon signals 122.50±146.17; HRMS
$FAB) Found: MH1 677.3236. Calcd for C53H40:
677.3208.
4.3. MM calculation
The calculations were carried out by the Chem3D Pro ver.
5.0 program.24 The MM2 force-®eld parameters were
employed without modi®cation.
4.1.15. ꢀ1,4-Dimethyl-9-triptycyl)[1-ꢀphenylethynyl)-9-
triptycyl]ethyne ꢀ5c). Yield 24%. Colorless crystals; mp
4.4. Dynamic NMR measurement
1
323±3518C $dec); H NMR $CDCl3) d 2.48 $s, 3Hap),
Variable temperature 1H NMR spectra were measured on a
Bruker AMX-400 at 400 MHz. About 5 mg of sample was
dissolved in ca. 0.6 ml of 1,1,2,2-tetrachloroethane-d2.
During VT measurements, the temperatures of the sample
were read from a thermocouple equipped with the instru-
ment after calibration with the chemical shift differences of
the methanol or 1,2-ethanediol signals. The total lineshape
analysis was performed by the DNMR3K program, which is
a modi®ed version of the DNMR3 program.25 Lineshapes of
the 1-Me signals were analyzed as exchange between two
unpopulated sites. Chemical shift differences and rotamer
populations were measured at several temperatures where
the rotation takes place very slowly on the NMR time scale.
The chemical shift differences $Dn) were assumed to be
correlated linearly with the temperature $t, 8C). The rotamer
population was analyzed by the van't Hoff equation. Spin±
spin relaxation times $T2) were estimated from the line-
shapes at slow exchange limit. Selected input parameters
2.54 $s, 3Hsc), 2.65 $s, 3Hap), 3.22 $s, 3Hsc), 5.51 $s,
1H), 5.60 $s, 1Hap), 5.69 $s, 1Hsc), 5.93 $d, Jˆ7.7 Hz,
2Hap), 6.46±7.52 $m, 22Hap124Hsc), 7.80±7.88 $m,
2Hsc), 8.30±8.39 $m, 2Hap11Hsc), 8.43 $d, Jˆ7.1 Hz,
2Hap), 8.54 $d, Jˆ7.2 Hz, 1Hsc), rotamer ratio $ap/sc)
44:56; 13C NMR $CDCl3) d 18.88, 22.03, 22.10, 49.88,
49.99, 53.62, 53.86, 54.07, 87.34, 87.76, 88.09, 89.00,
91.34, 92.11, 96.56, 96.56, and 50 aromatic carbon
signals
at
119.7±146.1.
Anal.
calcd
for
C52H34´1/4$CH2Cl2): to C, 92.28; H, 5.11. Found: C,
92.24; H, 5.12. HRMS $FAB) Found: MH1 659.2728.
Calcd for C52H34: 659.2739.
4.1.16. ꢀ1,4-Dimethyl-9-triptycyl){1-[ꢀ1-naphthyl)ethynyl]-
9-triptycyl}ethyne ꢀ5d). Yield 54%. Colorless crystals; mp
304±3228C $dec); 1H NMR $CDCl3) d 2.45 $s, 3Hap), 2.53
$s, 3Hsc), 2.64 $s, 3Hap), 3.15 $s, 3Hsc), 5.15 $d, Jˆ7.1 Hz,
1Hap), 5.54 $s, 1H), 5.56 $s, 1Hap), 5.67 $s, 1Hsc), 6.09±
7.68 $m, 22Hap124Hsc), 7.79±7.88 $m, 2Hsc), 8.08
$d, Jˆ6.8 Hz, 1Hap), 8.29±8.40 $m, 4Hap11Hsc), 8.47
$d, Jˆ7.1 Hz, 1Hsc), rotamer ratio $ap/sc) 49:51; 13C
NMR $CDCl3) d 18.86, 22.10, 49.83, 49.96, 53.61,
53.92, 54.08, 87.29, 87.75, 91.45, 92.19, 93.18, 93.98,
94.75, and 55 aromatic carbon signals at 119.8±146.2.
Anal. calcd for C56H36: C, 94.88; H, 5.12. Found: C,
94.59; H, 5.33.
and rate constants $kap!sc
)
are as follows. 5a:
Dnˆ0.738t145.1 Hz, T2ˆ0.07±0.09 s; k, s21 [t, 8C]ˆ16.0
[24.8], 28.0 [31.0], 46 [37.1], 74 [43.3], 120 [49.4], 180
[55.6]. 5b: Dnˆ0.145t1150.5 Hz, T2ˆ0.12±0.15 s; k, s21
[t, 8C]ˆ7.0 [65.9], 11.0 [71.0], 17.0 [76.1], 26.0 [81.2], 40
[86.2], 62 [91.4], 89 [96.5], 125 [101.4], 180 [106.8]. 5c:
Dnˆ0.072t1215.0 Hz, T2ˆ0.09±0.10 s; k, s21 [t, 8C]ˆ36.0
[70.1], 55 [75.0], 73 [79.9], 100 [84.8], 140 [89.7], 190

3528
S. Toyota et al. / Tetrahedron 57 &2001) 3521±3528
12. The Cambridge Crystallographic Database analysis was
performed for nonconjugated acyclic alkynes with the
substructure of C$sp3)±C$sp)uC$sp)±C$sp3) to give 14 struc-
tures in which at least one bond angle was smaller than 1748.
Twenty of these structures carry functional groups such as
±OH, ±NR31 at the a-position $169.9±173.28). As for alkynes
without a-functional groups, the values of 172.28 and 172.68
were found in a sterically crowded tricyclic compound and a
simple alkynoic acid, respectively. The bond angle observed
in ap-3 $170.28),5 which has not registered in the database yet,
is smaller than these angles.
[94.6], 270 [99.5], 360 [104.4], 480 [109.3], 650 [114.2].
5d: Dnˆ0.031t1189.0 Hz, T2ˆ0.10±0.11 s; k, s21 [t,
8C]ˆ16.5 [60.8], 26.0 [65.7], 40 [71.0], 62 [75.9], 95
[81.1], 143 [86.2], 205 [91.4], 270 [96.2], 380 [101.6],
530 [106.5].
Acknowledgements
The present work was partly supported by a special fund
from the Japan Private School Promotion Foundation. The
Å
helpful discussion of Prof. M. Oki is greatly appreciated.
The authors also thank Dr H. Akashi for his assistance with
X-ray data analysis.
13. Breitmaier, E.; Voelter, W. Carbon-13 NMR Spectroscopy;
VCH: New York, 1990 $Chapter 4.3).
14. Meier, H.; Petersen, H.; Kolshorn, H. Chem. Ber. 1980, 113,
2398±2409.
15. For recent examples of strained cyclic acetylenes and their 13
C
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