Mixed [2.2]cyclophanes of pyrene and benzene

Article abstract of DOI:10.1071/CH10356

An examination of the literature on [2.2]cyclophanes reveals a loose relationship between the relative sizes of the two 'half-cyclophanes' (as measured by the parameter Δd) and the limitations of the dominant general synthetic approaches. Direct coupling methods tend to be successful only for systems with Δd values below 1.0 A, whereas ring-contraction-based approaches are usually viable for systems with Δd values up to 2.0.A For the very few known systems with Δd values greater than 2.0A, aromatization-based approaches are the only ones that have been successful. The syntheses of two [2.2]cyclophanes with very large Δd values, [2]paracyclo[2](2,7)pyrenophane (17) (Δd = 4.25A) and [2]metacyclo[2](2,7)pyrenophane (18) (d≤5.04A) are presented here. The syntheses hinge on a valence isomerization/dehydrogenation reaction. The crystallographically determined bend angle, θ, for 18 is 96.1°. Cyclophane 18 undergoes a degenerate conformational flip, the energy barrier for which was determined to be 18.9 kcal mol^-1 by DNMR. CSIRO 2010.

Full text of DOI:10.1071/CH10356

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2010, 63, 1703–1716
Mixed [2.2]Cyclophanes of Pyrene and Benzene
A
B
B
Rudolf J. Vermeij, David O. Miller, Louise N. Dawe,
C D
,
C E
,
C
Ivan Aprahamian,
Tuvia Sheradsky, Mordecai Rabinovitz,
A F
,
and Graham J. Bodwell
A
Department of Chemistry, Memorial University, St. John’s, NL A1B 3X7, Canada.
CREAIT Network, Memorial University, St. John’s, NL A1B 3S5, Canada.
B
C
Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.
D
Present address: Department of Chemistry, Dartmouth College,
6128 Burke Laboratory, Hanover, NH 03755, USA.
E
Deceased.
F
Corresponding author. Email: gbodwell@mun.ca
An examination of the literature on [2.2]cyclophanes reveals a loose relationship between the relative sizes of the two
‘half-cyclophanes’ (as measured by the parameter Dd) and the limitations of the dominant general synthetic approaches.
˚
Direct coupling methods tend to be successful only for systems with Dd values below 1.0 A, whereas ring-contraction-
˚
based approaches are usually viable for systems with Dd values up to 2.0 A. For the very few known systems with Dd
˚
values greater than 2.0 A, aromatization-based approaches are the only ones that have been successful. The syntheses of
˚
two [2.2]cyclophanes with very large Dd values, [2]paracyclo[2](2,7)pyrenophane (17) (Dd ¼ 4.25 A) and [2]metacyclo
˚
[2](2,7)pyrenophane (18) (Dd ¼ 5.04 A) are presented here. The syntheses hinge on a valence isomerization/
dehydrogenation reaction. The crystallographically determined bend angle, y, for 18 is 96.18. Cyclophane 18 undergoes
a degenerate conformational flip, the energy barrier for which was determined to be 18.9 kcal molꢀ1 by DNMR.
Manuscript received: 28 September 2010.
Manuscript accepted: 22 October 2010.
Introduction
clouds and diminished aromaticity arising from non-planarity of
the aromatic systems.
The [2.2]cyclophanes are comprised of two aromatic units linked
by a pair of two-atom bridges. They form not only one of the
most populous classes of cyclophanes, but also one of the most
thoroughly studied.[1] The majority of work in this area has been
conducted on ‘symmetrical’ cyclophanes, i.e. those consisting of
two identical aromatic units with the same substitution pattern.
[2.2]Paracyclophane (1) and anti-[2.2]metacyclophane (2) are
prime examples. An ‘unsymmetrical’ [2.2]cyclophane, e.g. [2.2]
metaparacyclophane (8), consists of two identical aromatic units
with different substitution patterns. The term ‘mixed’ may then
be applied to the numerous [2.2]cyclophanes that contain two
different aromatic units.
All [2.2]cyclophanes can be viewed as the sum of two
xylylene (or xylylene-like) ‘half-cyclophane’ units (Fig. 1).
In most cases, the lowest energy (usually planar) structures
of the individual half-cyclophanes are not retained in the [2.2]
cyclophane they form. In other words, [2.2]cyclophanes are
usually strained to some extent. This is because the formation of
single bonds between the respective benzylic carbon atoms of
the two half-cyclophanes normally affords a structure in which
ideal structural features are precluded. Ultimately, the lowest
energy structure of the [2.2]cyclophane reflects a happy medium
between a variety of competing energetically unfavourable
situations that come into play, e.g. angle strain, torsional strain,
pyramidalization of quaternary aromatic carbon atoms, repul-
sive non-bonding interactions between proximate aromatic pi
The strained nature of [2.2]cyclophanes makes them inter-
esting from structural, physical, and chemical viewpoints. Of
course, a successful synthesis is required before any of these
properties can be studied. Indeed, synthetic challenge is another
attractive feature of such systems. Two general approaches to
[2.2]cyclophanes have been dominant: the direct coupling
approach (D) and the ring-contraction approach (R). In the
former case, the [2.2]cyclophane is formed through the direct
formation of bonds between the respective benzylic carbon
atoms of the two components. This has most often been
accomplished through the dimerization of a xyxlene species
(typically produced by a Hofmann elimination), cross-coupling
of two xylylenes or Wurtz coupling. In this approach, most,
if not all, of the strain in the [2.2]cyclophane builds up during
the key coupling step. In contrast, the ring-contraction route
involves the synthesis of a less strained [3.3]cyclophane (most
often a dithia[3.3]cyclophane), which is then subjected to a
ring-contraction reaction.[2] In such cases, the strain in the final
product is built up over two stages.[3]
In examining the cyclophane literature, it can be seen that
the ring-contraction approach generally performs better than the
direct coupling approach, not only in terms of yield, but also
with respect to the nature of the [2.2]cyclophanes it can be
used to synthesize. In this regard, it is interesting to note
that limitations of the two major synthetic approaches can be
Ó CSIRO 2010
10.1071/CH10356
0004-9425/10/121703

RESEARCH FRONT
1704
R. J. Vermeij et al.
Valence
isomerization/
dehydrogenation
Aromatic
system
Bridge
Bridge
19
20
21
17
Δd ꢀ 4.25 Å
calc ꢀ 100.4ꢁ
18
22
Δd ꢀ 5.04 Å
calc ꢀ 106.6ꢁ
Δd ꢀ 7.05 Å
θcalc ꢀ 130.4ꢁ
θ
θ
Scheme 1. Elaboration of [n](2.7)pyrenophanes into mixed [2.2]cyclophanes of pyrene and benzene.
Symmetrical [2.2]cyclophanes are composed of two identi-
cal halves, so the value of Dd is necessarily zero. Due to the
various factors described above, this does not mean that such
cyclophanes are unstrained. Nevertheless, both general
approaches have been used successfully to synthesize such
systems. Unsymmetrical [2.2]cyclophanes can have larger Dd
values than their symmetrical counterparts and such systems
are typically more strained. This is exemplified by the series
of benzene-based unsymmetrical cyclophanes: [2.2]metapara-
‘Half-cyclophanes’
Mixed
[2.2]cyclophane
Arene 1
d1
Arene 2
Arene 1
Arene 2
cyclophane (8,[11] Dd ¼ 0.79 A), [2.2]orthometacyclophane
˚
[19]
(15,[18] Dd ¼ 2.01 A), and [2.2]orthoparacyclophane (16,
˚
Δd ꢀ d1 – d2
˚
Dd ¼ 3.80 A). The first two members of this series were synthe-
d2
sized using a ring-contraction approach, but an attempted
synthesis of 16 using an analogous approach failed.[19b] This
highly strained system was eventually synthesized, but it
required the use of a new general approach (A ¼ aromatization)
that relies upon more powerful methodology. This involves the
generation of one of the aromatic systems in the final step of the
synthesis. As such, the gain of a substantial amount of aromatic
stabilization energy[21] counteracts the developing strain as the
target cyclophane forms.
Fig. 1. Definition of the parameter Dd.
expressed loosely in terms of the relative sizes of the two half-
cyclophanes that make up a [2.2]cyclophane. A simple measure
of size of a half-cyclophane is the distance between the benzylic
carbon atoms of the corresponding dimethylarene (d1 and d2,
Fig. 1, Table in the Accessory Publication). The absolute value
of the difference between these two values affords the parameter
Dd (Fig. 1).
Whereas the unsymmetrical [2.2]cyclophanes can boast
some significantly strained systems, it is the mixed [2.2]cyclo-
phanes that offer the opportunity for creativity in the design
of new strained systems. This simply requires the union of
half cyclophanes with substantially different sizes (as defined
above). Of course, synthetic methodology that allows this to
happen is a necessity.
Over the past several years, our group has exploited a valence
isomerization/dehydrogenation (VID) reaction to generate a
family of [n](2,7)pyrenophanes 20 from the corresponding
cyclophanedienes 19 (Scheme 1).[20,22] The bridge causes the
pyrene system to adopt a non-planar geometry and the degree of
distortion from planarity can be described by the angle y,[22d]
which is the smallest angle formed between the planes of atoms
defined by C(1)-C(2)-C(3) and C(6)-C(7)-C(8) of the pyrene
system. Semiempirical AM1 calculations typically predict lar-
ger (4–88) bend angles (ycalc) than those obtained from crystal
structures (yX-ray). As such, the AM1-calculated values are quite
reliable indicators. The largest value of y yet observed experi-
mentally is 109.28.[22b]
A selection of [2.2]cyclophanes[4–20] is presented in Table 1
along with their Dd values and their method of formation.
The direct coupling approach has generally been successfully
˚
applied when the Dd value is small (o1.0 A). Synthetic
expedience often comes at the expense of yield. The ring-
contraction approach has the disadvantage of requiring more
steps, but is usually superior when it comes to yield, scope, and
˚
Dd. [2.2]Cyclophanes with Dd values below ,1.5 A are typi-
cally accessible without much difficulty using the ring-
contraction approach and systems with Dd values as high as
[18]
˚
2.0 A, e.g. 15
˚
(Dd ¼ 2.01 A), have been synthesized using
ring-contraction methodology. Of course, Dd values do not tell
the whole story and the limits presented above must be viewed
as very fuzzy, i.e. they should be used predictively only as very
rough guides. This point is illustrated by the pair of [2.2]
˚
˚
cyclophanes 13 (Dd ¼ 1.69 A) and 14 (Dd ¼ 1.70 A). Although
they have essentially the same Dd value, naphthalenophane
13 was synthesized from the corresponding [3.3]dithiacyclo-
phane,[16] but the attempted synthesis of corannulenophane 14
from its dithiacyclophane precursor failed.[17]
Incorporation of an aromatic system into the bridge of 20
affords a class of mixed cyclophane systems 21, which includes

RESEARCH FRONT
Mixed [2.2]Cyclophanes of Pyrene and Benzene
1705
Table 1. Selected [2.2]cyclophanes, their Dd values and their methods of preparation
D, direct coupling approach; R, ring-contraction approach; A, aromatization-based approach
˚
Dd [A]
˚
Dd [A]
Entry
Cyclophane
Method of
preparation
Lit.
Entry
Cyclophane
Method of
preparation
Lit.
1
0.00
D, R
Ref. 4
10
0.95
R
Ref. 13
1
10
2
3
0.00
0.01
D, R
Ref. 5
Ref. 6
11
12
1.45
1.52
R
R
Ref. 14
Ref. 15
N
11
2
3
R
12
13
4
5
6
0.03
0.46
0.58
D
D
R
Ref. 7
Ref. 8
Ref. 9
13
14
15
1.69
1.70
2.01
R
Ref. 16
Ref. 17
Ref. 18
4
R fails
S
5
14
R
6
15
16
7
8
9
0.77
0.79
0.92
R
R
D
Ref. 10
Ref. 11
Ref. 12
16
17
18
3.80
4.25
5.04
A
A
A
Ref. 19
7
8
Ref. 20
17
18
O
This work
9
three mixed [2.2]cyclophanes of pyrene and benzene: 17,[20]
18, and 22 (Scheme 1). To evaluate the viability of these
compounds as synthetic targets, parameters such as y and Dd
can be considered. Both parameters suggest that the synthetic
challenge is likely to increase in going from 17 (Dd ¼ 4.25 A,
˚
˚
ycalc ¼ 100.48, yX-ray ¼ 89.78)[20] to 18 (Dd ¼ 5.04 A, ycalc
¼
˚
106.68) to 22 (Dd ¼ 7.05 A, ycalc ¼ 130.48). Likewise, both
parameters seem to indicate a much larger increase in challenge

RESEARCH FRONT
1706
R. J. Vermeij et al.
Trimethylsilylacetylene
I
I
R
R
Pd(PPh3)2Cl2, CuI
DBU, benzene
rt, 2h, 95%
23
24 R ꢀ SiMe3
25 R ꢀ H
K2CO3, MeOH
rt, 1 h, 77%
27, Pd(PPh3)2Cl2
CuI, DBU, benzene
reflux, 18h, 57%
MeO2C
CO2Me
CO2Me
23, Pd(PPh3)2Cl2
CuI, DBU, benzene
rt, 2.5h, 91%
26
MeO2C
TfO
CO2Me
CO2Me
CO2Me
Trimethylsilylacetylene
R
Pd(PPh3)2Cl2, CuI
DBU, benzene
rt, 2h, 70%
CO2Me
27
28
R ꢀ SiMe3
K2CO3, MeOH
rt, 1.5h, 91%
29 R ꢀ H
Scheme 2. Two synthetic routes to 26.
(or strain) in going from 18 to 22 than in going from 17 to 18.
The Dd values of 17, 18, and 22 are unprecedented for [2.2]
cyclophanes, so there is no basis for comparison with other
systems. Therefore, the ycalc values were used as grounds for
restricting the synthetic work to targets 17 and 18. The ycalc
value for 22 (130.48) is comparable to that of 1,6-dioxa[6](2,7)
pyrenophane (ycalc ¼ 132.18),[22f] which was previously found
to be completely unreactive in the VID reaction.
As a final point, it is worth noting that 17 and 18 are not the
only known mixed [2.2]cyclophanes of pyrene and benzene.
[2]Metacyclo[2](1,3)pyrenophane (3)[6] and several of its
derivatives have been reported.[23] However, with Dd values
approaching zero, these systems are only of peripheral
relevance to the current investigation.
Again, the low solubility of 26 rendered its purification proble-
matic. However, the crude mixture from this Sonogashira
coupling was of higher purity than that obtained from the
previous route. This, in conjunction with the explosive nature
of 25, made the second approach the preferred one for the
production of synthetically useful quantities of 26.
Since diynetetraester 26 already contains all of the carbon
atoms necessary for the synthesis of pyrenophane 17, the
remainder of the synthesis consisted of a series of functional
group interconversions and intramolecular carbon-carbon bond-
forming reactions (Scheme 3). This commenced with catalytic
hydrogenation of the alkyne units in 26 to give tetraester 30
(95%), which revealed the ethano units that would ultimately
become the bridges of pyrenophane 17. The hydrogenation of 26
was somewhat problematic due to its low solubility. Small-scale
hydrogenations could be performed using saturated (dilute)
solutions of 26 in THF or benzene, but when larger amounts
of 30 were required, this method became impractical due to the
large volumes of solvent required. For the catalytic hydrogena-
tion of larger quantities of 26, slow addition of a slurry of 26 in
THF to a suspension of catalyst in THF under an atmosphere
of hydrogen proved to be the most convenient method (both
methods gave 30 in ,95% yield). Tetraester 30 was reacted with
excess LiAlH4 in THF to afford the corresponding tetraalcohol,
which was reacted in crude form with 30% HBr/HOAc to
provide tetrabromide 31 (85%, 2 steps). Attempted conversion
of tetrabromide 31 into dithiacyclophane 32 using Na2S/Al2O3
under standard conditions (10% abs. EtOH/CH2Cl2)[24] afforded
the product in less than 3% yield and in low purity (,75% by
1H NMR analysis). However, when the reaction was performed
at reflux temperature, dithiacyclophane 32 was formed in 28%
yield. Changing the solvent mixture from CH2Cl2/EtOH to
CHCl3/EtOH in order to increase the reflux temperature did
not further increase the yield.
Results and Discussion
For the synthesis of [2]paracyclo[2](2,7)pyrenophane (17), two
complementary routes starting from 1,4-diiodobenzene (23) and
triflate 27[22c] were initially investigated (Scheme 2). In the first
of these, Sonogashira coupling of 1,4-diiodobenzene (23) with
two equivalents of trimethylsilylacetylene gave diyne 24 (95%),
which was protodesilylated to yield 1,4-diethynylbenzene 25
(77%). This compound could be conveniently purified on a
small scale using sublimation at atmospheric pressure, but
explosive decomposition took place when this was attempted
with ,4 g of material. Diyne 25 was subjected to Sonogashira
coupling using two equivalents of triflate 27 to form tetraester
26 (57%). The low solubility of this diyne complicated its pur-
ification and might also have contributed to the relatively low
yield.
An alternative route to 26 was then investigated, in which the
order of the Sonogashira couplings was reversed (Scheme 2).
Starting from triflate 27, Sonogashira coupling with trimethyl-
silylacetylene yielded diester 28 (70%). Protodesilylation gave
the corresponding terminal alkyne 29 (91%), which was coupled
with 1,4-diiodobenzene 23 under Sonogashira conditions to
yield diyne 26 in 91% yield (based on 1,4-diiodobenzene).
The difficulty in synthesizing dithiacyclophane 32 was pre-
sumably due primarily to the strained nature of the product.
An X-ray crystal structure determination (Fig. 2 and Accessory
Publication) revealed several non-ideal structural features.

RESEARCH FRONT
Mixed [2.2]Cyclophanes of Pyrene and Benzene
1707
R
R
MeO2C
CO2Me
CO2Me
H2
Pd(OH)/C
R
R
benzene, rt
2h, 95%
26
MeO2C
30 R ꢀ CO2Me
31 R ꢀ CH2Br
1. LiAlH4, THF
reflux, 16h
2. 30% HBr/HOAc
reflux, 0.5 h
85% (2 steps)
Na2S/Al2O3
10% abs. EtOH/CH2Cl2
reflux, 2.5h, 28%
MeS
SMe
1. (MeO)2CHBF4
CH2Cl2, rt, 3h
S
S
2. t-BuOK, THF
rt, 14h
33
32
1. (MeO)2CHBF4
CH2Cl2, rt, 3h
2. t-BuOK, t-BuOH
THF, rt, 14h
θ
θ
calc ꢀ 100.4°
X-ray ꢀ 89.7°
ꢂ
34
17
DDQ, benzene
rt, 10 min
14% (5 steps)
Scheme 3. Synthesis of [2]paracyclo[2](2,7)pyrenophane 17.
The two trisubstituted benzene rings are boat-shaped, but the
distortion from planarity is slight (a ¼ 2.98 and 2.18 at the bow
and stern, respectively).[25] The b angles[25] for these rings are
also small (1.8–2.58). More striking is that the smallest angle
formed by the average planes of the two trisubstituted rings is
55.88, which is considerably larger than the angle observed
for the parent syn-2,11-dithia[3.3]metacyclophane (20.68).[26]
The disubstituted benzene ring is essentially planar (a ¼ 0.28),
but the benzylic carbon atoms are bent significantly out of the
plane of the benzene ring (b ¼ 8.68). Additionally, significantly
expanded bond angles are observed at all of the benzylic carbon
atoms (116.2(2)8 at C(1), 115.1(2)8 at C(2), 116.4(3)8 at C(9),
113.1(4)8 at C(10)). The size and the rigidity of the p-phenylene
unit is presumably responsible for the splaying of the two
trisubstituted benzene rings and the enlargement of the bond
angles at the benzylic carbon atoms.
rearrangement. This yielded 33 as a mixture of isomers (70%
crude from 32). Methylation of the sulfur atoms in 33 using
Borch reagent, followed by Hofmann elimination of the result-
ing bis(dimethylsulfonium) salts gave a mixture (,1:1 by
1H NMR analysis) of cyclophanediene 34 and the desired [2]
paracyclo[2](2,7)pyrenophane 17. The mixture was converted
cleanly to pyrenophane 17 by treatment of the mixture with
DDQ in benzene to yield 3 in 14% overall yield from dithia-
cyclophane 32.
The formation of 17 during the Hofmann elimination step
was somewhat surprising since the formation of pyrenophanes
with comparable calculated bend angles (y) usually requires
treatment of the corresponding cyclophanediene with DDQ
in hot benzene. The unexpected reactivity of 34 can, as above,
be explained by the presence of the rigid para-phenylene unit,
which forces open the syn-[2.2]metacyclophanediene system
relative to those present in the precursors to the [n](2,7)pyreno-
phanes. The resulting increase in the inter-ring angle moves the
internal C atoms closer to one another and presumably lowers
the activation energy to the formation of a bond between them.
Bridge contraction of dithiacyclophane 32 was accomplished
by methylation of the sulfur atoms using Borch reagent,
followed by treatment of the resulting bis(methylsulfonium)
salt with potassium tert-butoxide to induce thia-Stevens

RESEARCH FRONT
1708
R. J. Vermeij et al.
H(4)
C(5)
C(6)
H(1b)
C(1)
H(2a)
C(2)
C(4)
H(6)
H(1a)
C(3)
C(8)
H(2b)
C(7)
S(1)
H(9a)
C(9)
H(9b)
H(8)
C(10)
C(12)
H(10a)
C(14)
C(13)
H(13)
H(14)
Fig. 2. POV-Ray representation of 32 in the crystal.
At 2%, the overall yield of pyrenophane 17 from triflate 27 is
disappointingly low (longest linear sequence: 3% from 17). This
can be traced back to two particular synthetic transformations:
the cyclization to furnish strained dithiacyclophane 32 and the
often-problematic methylation-Hofmann elimination sequence
to form the mixture of 34 and 17. The crystal structure and
1H NMR spectrum of 17 were discussed in detail in the
communication,[20] so they will not be revisited here.
(Hofmann elimination) to form cyclophanediene 41 in 61%
yield from dithiacyclophane 39. Not only is the yield consider-
ably better than that of 34 (and 17) from 32 (16%), but
cyclophanediene 41 was obtained in pure form, i.e. without
even trace amounts of pyrenophane 18 (1H NMR analysis).
Treatment of a room temperature solution of cyclophanediene
41 in benzene with DDQ resulted in rapid formation of the
desired [2]metacyclo[2](2,7)pyrenophane 18 (97%). Without
any optimization at all, the overall yield of 18 from 1,3-
diiodobenzene 35 is 17% over 10 steps.
The mild conditions for the formation of pyrenophane 18
(and also 17) are interesting because most other VID reactions
leading to pyrenophanes have been conducted using benzene
solutions at reflux. Although it may simply be the case that
pyrenophanes 17 and 18 are well disposed to VID reaction, it
raises the question of whether the VID reactions leading to
previously reported pyrenophanes might also proceed at room
temperature.
Having successfully synthesized 17, attention was turned
to the isomeric [2]metacyclo[2](2,7)pyrenophane 18. This was
expected to be a more challenging target because the calculated
˚
values of y (106.68) and Dd (5.04 A) are both larger than the
corresponding values for 17. As described below, this turned out
not to be the case.
The synthetic plan for pyrenophane 18 mirrored that of 17.
Accordingly, it began with Sonogashira coupling of 1,3-di-
iodobenzene 36 with alkyne 29, which proceeded in 76% yield
to give diyne 36 (Scheme 4). Diyne 36 was found to be more
soluble than its constitutional isomer 26, so it could be purified
easily using column chromatography. Catalytic hydrogenation
of 36 also proceeded more easily, yielding tetraester 37 in
quantitative yield. Reduction of 37 with excess LiAlH4 in
THF, followed by treatment of the crude product with 30%
HBr/HOAc then afforded tetrabromide 38 in 54% yield. In
contrast to the difficulties experienced in the synthesis of
dithiacyclophane 32, reaction of tetrabromide 38 with Na2S/
Al2O3 under standard cyclization conditions[24] delivered
dithiacyclophane 39 smoothly in 68% yield.
Methylation of the sulfur atoms in the bridges of dithia-
cyclophane 39 with Borch reagent, followed by treatment of
the resulting bis(methylsulfonium) salt with potassium tert-
butoxide yielded 40 as a mixture of isomers in 88% crude yield
from 39. After treatment of the isomer mixture 40 with Borch
reagent to methylate the sulfur atoms, the resulting bis(methyl-
sulfonium) salt was treated with potassium tert-butoxide
An X-ray crystal structure determination of 18 (crystals from
toluene) revealed two independent molecules in the unit cell
(Fig. 3, 18a on the bottom, 18b on the top). The bend angles are
yX-ray ¼ 96.58 for 18a and yX-ray ¼ 95.68 for 18b, which are 10.58
(on average) less than the AM1-calculated value (ycalc
¼
106.68). As was observed for 17,[20] this is a little higher than
the previously observed differences between calculated and
experimentally determined values.[22] The b angles (18a: bC(17)
¼
17.78 and bC(26) ¼ 17.68; 18b: bC(43) ¼ 18.48 and bC(52) ¼ 17.48;
average ¼ 17.88) are even larger than in 17 (16.1–16.38) and the
[n](2,7)pyrenophanes (up to 98). The isolated benzene ring in 18
is, similar to that in 17, essentially planar (ao2.58) and the
m-xyxlene unit is bowed slightly towards the concave face of
the pyrene system (b18aC(18) ¼ 3.98, b18aC(25) ¼ 3.38, b18bC(44)
¼
7.08, b18bC(51) ¼ 3.68). However, in contrast to 17, the isolated
benzene ring in 18 does not lie directly underneath the pyrene
system, but rather is slipped to one side. The bridges in 18 exist

RESEARCH FRONT
Mixed [2.2]Cyclophanes of Pyrene and Benzene
1709
CO2Me
CO2Me
29
Pd(PPh3)2Cl2
CuI, DBU
I
I
MeO2C
CO2Me
benzene
rt, 3h, 76%
35
36
H2, Pd/C, benzene, HOAc
rt, 16h, 100%
R
R
37–R ꢀ CO2Me
38–R ꢀ CH2Br
1. LiAlH4, THF
rt, 22h
2. 30% HBr/HOAc
reflux, 10 min
54% (2 steps)
R
R
Na2S/Al2O3
10% abs. EtOH/CH2Cl2
rt, 1.5h, 68%
MeS
SMe
1. (MeO)2CHBF4
CH2Cl2, rt, 10 h
S
S
2. t-BuOK, THF
rt, 3.5 h
40
39
1. (MeO)2CHBF4
CH2Cl2, rt, 2h
2. t-BuOK, t-BuOH, THF
rt, 3.5h, 61% (4 steps)
DDQ, benzene
rt, 10 min, 97%
θ
θ
calc ꢀ 106.6°
X-ray ꢀ 96.1°
41
18
Scheme 4. Synthesis of [2]metacyclo[2](2,7)pyrenophane 18.
in nearly staggered conformations, with a torsional angle around
the ethano unit of 518. This aspect of the structure stands in stark
contrast to the nearly eclipsed bridges in 17 and the torsional
strain associated with eclipsing may well be a major reason why
18 and its cyclophane precursors (39–41) were considerably
easier to synthesize than their para-substituted counterparts
(32–34 and 17).
non-planar aromatic systems. A previously reported compound
that also contains two chemically equivalent moieties in the
asymmetric unit was also observed to exhibit C-H ꢁ ꢁ ꢁ p inter-
[22l]
˚
actions in the range of 2.59–2.85 A.
The 500 MHz 1H NMR spectrum of pyrenophane 18 showed
four signals for the pyrene system instead of the usual two,[22]
and four signals were observed for the protons on the ethano
bridges. This is consistent with a slow conformational flip of the
isolated benzene ring on the NMR time scale that interconverts
two degenerate conformers (Fig. 4).
A final noteworthy feature of the crystal structure of 18 is the
presence of several short intermolecular C–H ꢁ ꢁ ꢁ p contacts,
˚
which are indicated in Fig. 3. H(48) in molecule 18b is 2.96 A
from the centroid of the C(4)-C(5)-C(10)-C(11)-C(12)-C(13)
1
All signals in the H NMR spectrum were assigned unam-
˚
ring in molecule 18a and 3.65 A from the centroid of the
C(3)-C(4)-C(7)-C(8)-C(9)-C(10) ring, also in molecule 18a.
Additionally, H(40) and H(52A) in molecule 18b are 3.41 and
biguously using a variety of standard NMR experiments, includ-
ing HMQC, HMBC, and NOESY (Fig. 4). The internal proton
of the isolated benzene ring in 5 is located in the heart of the
shielding cone of the pyrene system, so it appears at very high
field (d 4.18). Coincidentally, this is almost identical to that of
the internal proton of anti-[2.2]metacyclophane 8.[28] A smaller
shielding effect was observed for the external protons, which
˚
3.23 A, respectively, from the centroid of the C(9)-C(10)-C(11)-
C(14)-C(15)-C(16) ring in molecule 18a. It would now appear
that ‘edge-to-face’ C-H?p interactions, which are well docu-
mented for planar p systems,[27] can also be observed in

RESEARCH FRONT
1710
R. J. Vermeij et al.
C(39)
C(31)
C(32)
C(27)
C(38)
C(37)
C(30)
C(28) C(29)
C(36)
C(43)
C(33)
C(35)
C(42)
C(44)
C(45)
C(34)
C(40)
C(41)
C(46)
H(40)
C(50)
C(49)
C(47)
C(52)
C(51)
C(48)
H(48)
H(52A)
C(8)
C(9)
C(14)
C(7)
C(10)
C(15)
C(26)
C(4)
C(11)
C(16)
C(3)
C(2)
C(5)
C(12)
C(13)
C(25)
C(21)
C(6)
C(1)
C(20)
C(19)
C(22)
C(23)
C(17)
C(18)
C(24)
Fig. 3. POV-Ray representation of 18 in the crystal. Short intermolecular C–H?p distances are indicated by dashed lines.
appeared as a triplet at d 6.56 and a doublet at d 6.31. Being
situated underneath one side of the pyrene system, the isolated
benzene ring shields the two types of aryl protons that lie above
it. Thus Hh (d 7.15) and Hj (d 7.32) resonate at higher field than
their counterparts Hi (d 7.47) and Hk (d 7.68) on the other side of
the pyrene system. All four bridge protons are mutually coupled,
giving rise to a set of four ddd, one of which (Hd) appears at
unusually high field (d 1.21). Upon examination of a three-
dimensional structure of 18 (crystal structure or even simple
molecular models), it can be seen that Hd is situated in the
shielding zone of the pyrene system.
benzene ring results in an exchange in the environments of
Hd and He, Hf and Hg, Hi and Hh, and Hj and Hk. Although any
of these pairs of signals could be used to determine the energy
barrier, it proved to be most straightforward to use the signals
for Hf and Hg. A DNMR experiment were performed
using a solution of [2]metacyclo[2](2,7)pyrenophane 18 in
nitrobenzene-d5. A coalescence temperature of 396.8 K and
d0 ¼ 134.0 Hz were used to calculate an activation barrier of
carbon atoms bonded to Hh and Hi are presumably the most
reactive sites) would afford diastereomeric products, but an
energy barrier of this size would make any room temperature
separation problematic and temporary.
18.9 kcal molꢀ1 [29]
Substitution of the pyrene system (the
.
The energy barrier for the interconversion of 18 and 180 was
determined from a DNMR study. The flipping of the isolated

RESEARCH FRONT
Mixed [2.2]Cyclophanes of Pyrene and Benzene
1711
Hk Hj
Hi Hh
Hb
Hc
Hf
Ha
Hg
He
Hd
10
8
6
4
2
ppm
Nucleus
δ [ppm]
Ha
Hb
Hc
Hd
He
Hf
Hg
Hh
Hi
4.18
6.31
6.56
1.21
2.31
2.69
3.09
7.15
7.47
7.32
7.68
18
ΔG‡ ꢀ 18.9 kcal molꢄ1
Hk
Hi
Benzene deck
shields Hh and
Hj relative to
Hi and Hk,
Hg
Hf
Hj
Hh
Ha
Hd
respectively
He
Hb
Hj
Hk
Hc
18ꢃ
Fig. 4. 1H NMR spectrum of 18, assignments and the ring flipping conformational process.
Conclusions
Experimental
Methods and Materials
The VID methodology was found to be very effective in gen-
erating two strained mixed [2.2]cyclophanes of pyrene and
benzene, pyrenophanes 17 and 18, under very mild conditions
(room temperature). Whereas the synthesis of 17 was proble-
matic at several points, the synthesis of 18 was essentially
problem-free. This is contrary to what might have been expected
form the predicted values of y and Dd, which are both sig-
nificantly larger for 18 than they are for 17. This serves to
illustrate an important point: parameters such as y and Dd are
limited in their predictive value. For a start, they apply to the
final targets and not to any of the synthetic precursors. More to
the point, they describe a single structural feature, which may
not necessarily be an adequate reflection of the strain in a given
molecule. This is because the structure of any strained system
derives from a compromise between various forms of strain and
there is no reason to suggest that the exact position of the middle
ground is anything other than case-dependent. In the case at
hand, it seems likely that the difference in torsional strain (which
is not accounted for in y and Dd) between the bridges of 17 and
18 plays an important role.
All chemicals were reagent grade and were used as received.
Chromatographic separations were performed on Merck silica
gel 60 (particle size 40–63 mm, 230–400 mesh). Melting points
were determined on a Fisher–Johns apparatus and are uncor-
rected. Elemental analyses were performed at the Micro-
Analytical Service Laboratory, Department of Chemistry,
University of Alberta. Mass spectroscopic (MS) data were
1
obtained on a V. G. Micromass 7070HS instrument. H NMR
(500 MHz) and 13C NMR (126 MHz) spectra were obtained
on a Bruker AVANCE spectrometer. 1H NMR (300 MHz) and
13C NMR (75.5 MHz) spectra were obtained on a General
Electric GE 300-NB spectrometer. 1H shifts are relative to
internal tetramethylsilane; 13C shifts are relative to the solvent
resonance (CDCl3: d ¼ 77.0). DNMR experiments were recor-
ded on a Bruker DRX-400 pulsed FT spectrometer operating
1
at 400.1 MHz for H. Chemical shifts were measured relative
to the most downfield nitrobenzene-d5 peak. All experiments
with moisture- or air-sensitive compounds were performed in
anhydrous solvents under nitrogen unless otherwise stated.

RESEARCH FRONT
1712
R. J. Vermeij et al.
Solvents were dried and distilled according to standard
procedures.
concentrated under reduced pressure and the residue was taken
up in a mixture of CHCl3 (1000 mL) and saturated aqueous
NH4Cl solution (500 mL). The layers were separated and the
aqueous layer was extracted with CHCl3 (500 mL). The com-
bined organic layers were washed with water (2 ꢂ 500 mL),
washed with saturated aqueous NaCl solution (500 mL), dried
(MgSO4), and concentrated under reduced pressure. The residue
was purified by column chromatography (silica gel, chloroform)
to give 26 (8.51 g, 16.7 mmol, 91%) as an off-white solid.
1,4-Bis(trimethylsilylethynyl)benzene 24
To a solution of 1,4-diiodobenzene 23 (10.25 g, 31.07 mmol)
in degassed benzene (225 mL) under a nitrogen atmosphere,
were added (Ph3P)2PdCl2 (1.05 g, 1.50 mmol) and CuI (1.00 g,
5.25 mmol), followed after 5 min by trimethylsilylacetylene
(7.65 g, 77.9 mmol) and DBU (14.19 g, 93.21 mmol). The
reaction mixture was stirred at room temperature for 2 h, washed
with saturated aqueous NH4Cl solution (100 mL), washed with
water (2 ꢂ 100 mL), washed with saturated aqueous NaCl
solution (100 mL), dried (MgSO4), and concentrated under
reduced pressure. The residue was purified by column chro-
matography (silica gel, hexanes) to give 24 (7.99 g, 29.5 mmol,
95%) as colourless crystals, mp 118–1198C (hexanes) (lit.[30]
1228C). nmax (nujol)/cmꢀ1 2155 (s), 1492 (m), 1246 (s). dH
(500 MHz, CDCl3) 7.40 (s, 4H), 0.25 (s, 18H). dC (126 MHz,
CDCl3) 131.7, 123.1, 104.6, 96.3, ꢀ0.1. EI-MS (70 eV) m/z [%]
270 (27, Mþ), 255 (100).
Dimethyl 5-(Trimethylsilylethynyl)benzene-
1,3-dicarboxylate 28
To a solution of (Ph3P)2PdCl2 (2.57 g, 3.66 mmol) and CuI
(1.39 g, 7.30 mmol) in degassed benzene (400 mL) was added
triflate 27 (25.07 g, 73.25 mmol), followed after 10 min by a
solution of trimethylsilylacetylene (10.07 g, 102.5 mmol) in
degassed benzene (200 mL) and DBU (16.70 g, 109.7 mmol).
The mixture was stirred under a nitrogen atmosphere for 2 h,
concentrated under reduced pressure and the residue was taken
up in a mixture of chloroform (250 mL) and saturated NH4Cl
solution (200 mL). The aqueous layer was extracted with
chloroform (150 mL). The combined organic layers were
washed with water (200 mL), washed with saturated aqueous
NaCl solution (200 mL), dried (MgSO4), and concentrated
under reduced pressure. The residue was purified by column
chromatography (silica gel, 10% ethyl acetate/hexanes) to yield
28 (14.92 g, 51.38 mmol, 70%) as a colourless solid, mp 100–
101.58C. nmax (nujol)/cmꢀ1 2159 (w), 1734 (s), 1593 (w),
1332 (m), 1242 (s). dH (500 MHz, CDCl3) 8.61 (s, 1H), 8.30 (s,
2H), 3.96 (s, 6H), 0.27 (s, 9H). dC (126 MHz, CDCl3) 165.5,
136.8, 130.8, 130.3, 124.2, 102.7, 96.7, 52.5, ꢀ0.22. m/z (EI,
70 eV) 290 (Mþ, 10%), 275 (100), 259 (9), 201 (10). Anal. Calc.
for C15H18O4Si: C 62.04, H 6.25. Found: C 62.23, H 6.36%.
1,4-Diethynylbenzene 25
K2CO3 (3.54 g, 25.6 mmol) and 1,4-bis(trimethylsilylethynyl)
benzene 24 (2.77 g, 13.3 mmol) were added to methanol (50 mL)
and the reaction mixture was stirred for 1 h. The mixture was
poured into ice water (100 mL) and filtered under suction. The
residue was sublimed at atmospheric pressure (,958C oil bath;
CAUTION: in one instance this procedure led to explosive
decomposition of the material) to give 25 (0.99 g, 77%) as
colourless plates, mp 94–958C (sublimes slowly above 768C)
(lit.[30] 95–968C). dH (300 MHz, CDCl3) 7.45 (s, 4H), 3.18 (s,
2H). dC (75 MHz, CDCl3) 132.0, 122.5, 82.9, 79.2.
1,4-Bis(3,5-bis(methoxycarbonyl)phenylethynyl)
benzene 26
Dimethyl 5-Ethynylisophthalate 29
A
mixture of dimethyl 5-(trimethylsilylethynyl)benzene-
Method A. To a solution of triflate 27 (3.22 g, 9.41 mmol)
in degassed benzene (80 mL) under a nitrogen atmosphere
were added (Ph3P)2PdCl2 (0.08 g, 0.1 mmol) and CuI (0.08 g,
0.4 mmol), followed after 5 min by 1,4-diethynylbenzene 25
(0.54 g, 4.3 mmol) and DBU (1.95 g, 12.8 mmol). The reaction
mixture was refluxed for 18 h, concentrated under reduced
pressure and the residue was taken up in a mixture of CHCl3
(250 mL) and saturated aqueous NH4Cl solution (100 mL). The
layers were separated and aqueous layer was extracted with
CHCl3 (100 mL). The combined organic layers were washed
with water (2 ꢂ 100 mL), washed with saturated aqueous NaCl
solution (100 mL), dried (MgSO4), and concentrated under
reduced pressure. The residue was purified by column chro-
matography (silica gel, chloroform) to give 26 (1.25 g, 57%)
as an off-white solid; mp 42908C dec. (chloroform). nmax
(nujol)/cmꢀ1 1732 (s), 1247 (m). dH (500 MHz, CDCl3) 8.66
(s, 2H), 8.39 (s, 4H), 7.56 (s, 4H), 3.99 (s, 12H). dC (126 MHz,
CDCl3) 165.6, 136.5, 131.7, 131.1, 130.1, 124.1, 122.9, 90.7,
89.4, 52.5. m/z (EI, 70 eV) 510 (Mþ, 100%), 479 (10), 224 (10).
m/z (HRMS-EI, 70 eV). Anal. Calc. for C30H22O8: 510.1313.
Found: 510.1334.
1,3-dicarboxylate 28 (14.92 g, 51.38 mmol), K2CO3 (9.23 g,
66.8 mmol), and methanol (650 mL) was stirred under a nitrogen
atmosphere for 1.5 h and then poured into water (1000 mL). The
resulting mixture was subjected to suction filtration and the
solids were washed with water (2 ꢂ 100 mL) and dried under
vacuum to afford dimethyl 5-ethynylisophthalate 29 (10.19 g,
46.70 mmol, 91%) as a colourless powder, mp 127–1288C. dH
(500 MHz, CDCl3) 8.53 (s, 2H), 8.07 (s, 4H), 7.11 (s, 4H), 3.95
(s, 12H), 3.04–2.97 (m, 4H), 2.96–2.89 (s, 4H). dC (126 MHz,
CDCl3) 166.4, 142.9, 138.9, 133.9, 130.6, 128.6 (2C), 52.3,
37.6, 37.2. m/z (EI, 70 eV) 218 (Mþ, 50%), 187 (100), 159 (28),
144 (22).
1,4-Bis(2-(3,5-bis(methoxycarbonyl)phenyl)ethyl)
benzene 30
To a solution of diyne 26 (0.64 g, 1.3 mmol) in degassed benzene
(300 mL) was added Pd(OH)/C (Pearlman’s catalyst, 0.40 g)
and the mixture was stirred vigorously under an atmosphere of
hydrogen for 2 h. The flask was purged with nitrogen several
times before the contents were filtered through a plug of Celite.
The filtrate was concentrated under reduced pressure to afford
tetraester 30 (0.62 g, 95%) as a colourless solid, mp 146–
147.58C (chloroform/hexanes). dH (500 MHz, CDCl3) 8.56 (s,
2H), 8.10 (s, 4H), 7.14 (s, 4H), 3.98 (s, 8H), 3.04 (m, 4H), 2.96
(m, 4H). dC (126 MHz, CDCl3) 166.4, 142.7, 138.8, 133.9,
130.6, 128.5 (2C), 52.3, 37.6, 37.2. m/z (EI, 70 eV) 518 (Mþ,
Method B. To a solution of 1,4-diiodobenzene 23 (6.03 g,
18.3 mmol) in degassed benzene (400 mL) under a nitrogen
atmosphere was added (Ph3P)2PdCl2 (0.64 g, 0.91 mmol) and
CuI (0.35 g, 1.8 mmol), followed after 5 min by dimethyl
5-ethynylisophtalate 29 (9.98 g, 45.7 mmol) and DBU (8.35 g,
54.8 mmol). The reaction mixture was stirred for 2.5 h,

RESEARCH FRONT
Mixed [2.2]Cyclophanes of Pyrene and Benzene
1713
6%), 486 (55), 426 (5), 311 (33), 281 (100), 207 (79), 104 (45).
Anal. Calc. for C30H30O8: C 69.49, H 5.83. Found: C 69.24,
H 5.94%.
stirred overnight and saturated aqueous NH4Cl solution (50 mL)
was added. The resulting mixture was concentrated under
reduced pressure and the residue was taken up in degassed
CH2Cl2 (100 mL). The organic solution was washed with satu-
rated aqueous NH4Cl solution (50 mL), washed with water
(50 mL), washed with saturated aqueous NaCl solution (50 mL),
dried (MgSO4), and concentrated under reduced pressure. The
residue was passed through a plug of silica gel (CHCl3) and
concentration of the filtrate afforded a mixture of bis(methyl-
thio)cyclophane isomers 33 (0.45 g, 70% from 32) as a foamy,
light yellow solid. To a solution of this solid in degassed CH2Cl2
(100 mL) was added slowly (MeO)2CHBF4 (0.85 g, 5.3 mmol)
and the mixture was stirred for 3 h under an atmosphere of
nitrogen. The mixture was concentrated under reduced pressure
and ethyl acetate (15 mL) and methanol (5 mL) were added to
the residue. The resulting mixture was stirred for 5 min and then
concentrated under reduced pressure to give a brown oil. This
oil was stirred in degassed 1:1 t-BuOH/THF (100 mL) under
nitrogen and t-BuOK (0.35 g, 3.1 mmol) was added. After stir-
ring for 16 h, saturated aqueous NH4Cl solution (20 mL) was
added and the mixture was concentrated under reduced pressure.
The residue was taken up in degassed CH2Cl2 (100 mL) and
saturated aqueous NH4Cl solution (75 mL). The layers were
separated and the aqueous layer was extracted with degassed
CH2Cl2 (50 mL). The combined organic layers were washed
with water (100 mL) and saturated aqueous NaCl solution
(100 mL), dried (MgSO4), and concentrated under reduced
pressure. The residue was concentrated under reduced pressure
to afford a mixture of cyclophanediene 34 and [2]paracyclo[2]
(2,7)pyrenophane 17 (0.08 g, 16% from 32) as a colourless solid.
The mixture was dissolved in degassed benzene (25 mL) under
nitrogen and DDQ (0.04 g, 0.2 mmol) was added. The mixture
was stirred for 10 min at room temperature and then con-
centrated under reduced pressure. The residue was purified by
preparative TLC (silica gel, 60% CHCl3/hexanes) to yield [2]
paracyclo[2](2,7)pyrenophane 17 (0.07 g, 14% from 32) as a
colourless solid, which was crystallized from heptane, mp 216–
2198C. dH (500 MHz, CDCl3) 7.67 (s, 4H), 7.40 (s, 4H), 5.54 (s,
4H), 2.99 (t, J 7.3, 4H), 2.32 (t, J 7.2, 4H). dC (126 MHz, CDCl3)
135.7, 134.2, 131.3, 129.3, 128.6, 128.0, 126.1, 36.5, 33.8. m/z
(EI, 70 eV) 332 (Mþ, 11%), 228 (100). m/z (HRMS-EI, 70 eV).
Anal. Calc. for C26H20: 332.1564. Found: 332.1562.
1,4-Bis(2-(3,5-bis(bromomethyl)phenyl)ethyl)benzene 31
A solution of tetraester 30 (2.16 g, 4.17 mmol) in THF (100 mL)
was added dropwise to a well stirred suspension of LiAlH4
(1.90 g, 50.1 mmol) in THF at 08C under nitrogen. The resulting
mixture was stirred at reflux for 16 h, cooled in an ice-bath, and
quenched with ethyl acetate (10 mL). The mixture was con-
centrated under reduced pressure and the residue was suspended
in glacial acetic acid (100 mL). 30% HBr/HOAc (10 mL,
50 mmol) was then added and the resulting mixture was heated
at reflux for 30 min. After cooling to room temperature, the
mixture was poured into water (200 mL) and extracted with
CH2Cl2 (2 ꢂ 200 mL). The combined organic layers were
washed with water (2 ꢂ 150 mL), washed with saturated aqu-
eous NaHCO3 solution (2 ꢂ 150 mL), washed with water
(100 mL), washed with saturated aqueous NaCl solution
(100 mL), dried (MgSO4), and concentrated under reduced
pressure. The residue was purified by column chromatography
(silica gel, 50% CHCl3/hexanes) to afford tetrabromide 31
(2.33 g, 85%) as a white solid, mp 142.5–143.58C (hexanes). dH
(500 MHz, CDCl3) 7.26 (overlapped with solvent, s, 2H), 7.13
(s, 4H), 7.09 (s, 4H), 4.45 (s, 8H), 2.89 (s, 8H). dC (126 MHz,
CDCl3) 143.1, 138.9, 138.3, 129.3, 128.5, 127.2. m/z (EI, 70 eV)
658 (Mþ (81Br)2(79Br)2, 5%), 497 (17), 417 (27), 381 (100).
m/z (HRMS-EI, 70 eV). Anal. Calc. for C30H22(79Br)4:
653.8765. Found: 653.8772.
Belta-2,11-dithia[3.3](1,3)(1,3)[2](5)(1)[2](4)(5)
benzeno/3Sphane[31] 32
To a well stirred, refluxing solution of tetrabromide 31 (2.48 g,
3.77 mmol) in degassed 10% ethanol (abs)/CH2Cl2 (825 mL)
was added Na2S/Al2O3[24] (7.83 g, 19.4 mmol) in three roughly
equal portions over 1 h. After stirring for 1.5 h at reflux tem-
perature, the reaction mixture was cooled to room temperature
and suction filtered through a plug of Celite. The filtrate was
concentrated under reduced pressure and the residue was sub-
jected to column chromatography (silica gel, 25% CHCl3/
hexanes) to afford dithiacyclophane 32 (0.43 g, 28%) as a
colourless, foamy solid, mp 42808C. dH (500 MHz, CDCl3)
6.96 (br s, 2H), 6.87 (s, 4H), 6.52 (s, 4H), 3.71 (nearly degenerate
AB system, 8H), 2.99 (t, J 7.0, 4H), 2.86 (t, J 6.9, 4H). dC
(126 MHz, CDCl3) 140.4, 137.2, 137.0, 129.1, 128.7, 128.0,
40.5, 34.9, 32.8. m/z (EI, 70 eV) 402 (Mþ, 100%), 369 (27),
338 (36). m/z(HRMS-EI, 70 eV). Anal. Calc. for C26H26S2:
402.1475. Found: 402.1493.
1,3-Bis(3,5-bis(methoxycarbonyl)phenylethynyl)
benzene 36
To a solution of (Ph3P)2PdCl2 (0.39 g, 0.56 mmol) and CuI
(0.39 g, 2.0 mmol) in degassed benzene (250 mL) under nitrogen
was added 1,3-diiodobenzene 35 (3.66 g, 11.1 mmol), followed
after 5 min by a solution of triflate 29 (5.33 g, 24.4 mmol) in
degassed benzene (150 mL) and DBU (4.23 g, 27.8 mmol).
The reaction mixture was stirred at room temperature under
an atmosphere of nitrogen for 3 h, concentrated under reduced
pressure and taken up in a mixture of CHCl3 (200 mL) and
saturated aqueous NH4Cl solution (100 mL). The layers were
separated and the aqueous layer was extracted with CHCl3
(150 mL). The combined organic layers were washed with
saturated aqueous NH4Cl solution (100 mL), washed with
water (100 mL), washed with saturated aqueous NaCl solution
(100 mL), dried (MgSO4), and concentrated under reduced
pressure. The residue was subjected to column chromatography
(silica gel, 2% EtOAc/CHCl3) to yield 36 (4.31 g, 8.44 mmol,
76%) as a beige solid that was crystallized from EtOH/CHCl3,
Belta[2.2](1,3)(1,3)[2](5)(1)[2](4)(5)benzeno/3Sphane-
1,9-diene[31] 34 and [2]Paracyclo[2](2,7)pyrenophane 17
To a stirred solution of dithiacyclophane 32 (0.60 g, 1.5 mmol)
in degassed CH2Cl2 (120 mL) under an atmosphere of nitrogen,
was added (MeO)2CHBF4 (1.21 g, 7.47 mmol) and after 3 h the
mixture was concentrated under reduced pressure. Ethyl acetate
(50 mL) was added to the residue and the mixture was stirred
for 5 min before being suction filtered. The beige solid that was
collected was washed with ethyl acetate (2 ꢂ 3 mL) and dried
under vacuum to yield a bis(sulfonium tetrafluoroborate) salt.
This was slurried in degassed THF (120 mL) under nitrogen and
t-BuOK (0.50 g, 4.5 mmol) was added. The reaction mixture was

RESEARCH FRONT
1714
R. J. Vermeij et al.
mp 176–177.58C (ethanol/chloroform). nmax (nujol)/cmꢀ1
2216 (w), 1734 (s), 1290 (w), 1249 (m), 1008 (w), 751 (w). dH
(500.1 MHz, CDCl3) 8.65 (s, 2H), 8.38 (s, 4H), 7.76 (s, 1H), 7.56
(d, J 7.9, 2H), 7.04 (t, J 7.7, 1H), 3.98 (s, 12H). dC (126 MHz,
CDCl3) 165.6, 136.5, 134.9, 131.9, 131.0, 130.3, 128.7, 124.1,
123.0, 90.2, 88.1, 52.6. m/z (EI, 70 eV) 510 (Mþ, 100%), 479
(25), 224 (25). Anal. Calc. for C30H22O8: C 70.58, H 4.34.
Found: C 70.10, H 4.19%.
(500.1 MHz, CDCl3) 7.25 (t, J 7.6, 1H), 7.10 (s, 2H), 7.06 (d,
J 7.8, 2H), 6.56 (s, 4H), 6.31 (s, 1H), 3.74 (m, 8H), 2.96 (m, 4H),
2.80 (m, 4H). dC (126 MHz, CDCl3) 140.5, 140.3, 136.9, 129.3,
129.0, 128.0, 127.0, 125.9, 39.3, 35.1, 34.2. m/z (EI, 70 eV) 402
(Mþ, 100%), 369 (23), 338 (25), 217 (14), 119 (29). Anal. Calc.
for C26H26S2: C 77.56, H 6.51. Found: C 76.44, H 6.51%.
Belta[2.2](1,3)(1,3)[2](5)(1)[2](3)(5)benzeno/3S
phane-1,9-diene[31] 40
1,3-Bis(2-(3,5-bis(methoxycarbonyl)phenyl)ethyl)
benzene 37
To a well stirred solution of 39 (0.98 g, 2.4 mmol) in CH2Cl2
(200 mL) was added Borch reagent (1.18 g, 7.3 mmol) and the
mixture was stirred at room temperature for 10 h. The reaction
mixture was concentrated under reduced pressure, quenched
with ethyl acetate (5 mL) and suction filtered, to yield (after
drying under vacuum) a white solid (1.41 g) that was suspended
in dry THF (200 mL). KO-t-Bu (1.37 g, 12.2 mmol) was added
and the mixture was stirred vigorously at room temperature for
3.5 h. The reaction was quenched by the addition of saturated
aqueous NH4Cl solution (5 mL) and the mixture was con-
centrated under reduced pressure. The residue was taken up in a
mixture of CH2Cl2 (75 mL) and H2O (25 mL) and the layers
were separated. The aqueous layer was extracted with CH2Cl2
(30 mL) and the combined organic extracts were washed with
H2O (50 mL), washed with saturated aqueous NaCl solution
(50 mL), dried (MgSO4), and concentrated under reduced
pressure. The residue was dissolved in CHCl3 and passed
through a plug of silica gel to yield isomer mixture 40 (0.92 g,
2.1 mmol, 88% crude from 39) as a light yellow solid.
A mixture of 36 (4.31 g, 8.44 mmol), 20% Pd/C (0.35 g),
degassed benzene (700 mL), and acetic acid (0.1 mL) was stirred
under a hydrogen atmosphere for 16 h. The reaction mixture was
purged with nitrogen for 20 min and then filtered through a plug
of MgSO4. The filtrate was concentrated under reduced pressure
to yield 37 (4.37 g, 8.44 mmol, 100%) as a colourless oil, which
solidified upon standing, mp 150–151.58C (benzene). dH
(500.1 MHz, CDCl3) 8.53 (s, 2H), 8.05 (s, 4H), 7.22 (t, J 7.4,
1H), 7.04 (d, J 7.6, 2H), 6.98 (s, 1H), 3.94 (s, 9H), 2.99 (m, 4H),
2.92 (m, 4H). dC (126 MHz, CDCl3) 166.4, 142.6, 141.1, 133.9,
130.6, 128.7, 128.6, 128.5, 126.3, 52.3, 37.6. m/z (EI, 70 eV) 518
(Mþ, 6%), 486 (83), 311 (22), 281 (100), 207 (50), 177 (10),
104 (17). Anal. Calc. for C30H30O8: C 69.49, H 5.83. Found:
C 69.28, H 5.89%.
1,3-Bis(2-(3,5-bis(bromomethyl)phenyl)ethyl)benzene 38
A solution of 37 (4.33 g, 8.35 mmol) in dry THF (150 mL) was
added over 45 min to a well stirred, 08C suspension of LiAlH4
(3.80 g, 10.0 mmol) in dry THF (200 mL) under a nitrogen
atmosphere. The resulting mixture was stirred at room tem-
perature for 22 h, cooled in an ice-bath, quenched with ethyl
acetate (20 mL) and concentrated under reduced pressure. 30%
HBr/HOAc (125 mL) was carefully added to the residue and the
mixture was heated to reflux, cooled and poured into ice water
(300 mL). The resulting mixture was extracted with CH2Cl2
(3 ꢂ 100 mL). The combined organic extracts were washed with
saturated aqueous NaHCO3 solution (3 ꢂ 100 mL), washed with
water (100 mL), washed with saturated aqueous NaCl solution
(100 mL), dried (MgSO4), and concentrated under reduced
pressure. The residue was subjected to column chromatography
(silica gel, 50% CHCl3/hexanes) to yield 38 (2.95 g, 4.48 mmol,
54%) as a white solid, mp 109–111.58C (CHCl3/hexanes).
dH (500.1 MHz, CDCl3) 7.27 (s, 2H), 7.22 (t, J 7.5, 1H), 7.14
(s, 4H), 7.02 (d, J 7.5, 2H), 6.94 (s, 1H), 4.45 (s, 8H), 2.89
(s, 8H). dC (126 MHz, CDCl3) 143.1, 141.3, 138.4, 129.3, 128.7,
128.5, 127.2, 126.2, 37.6, 37.5, 33.0. m/z (EI, 70 eV) 658 (Mþ
(81Br)2(79Br)2, 5%), 577 (3), 497 (59), 417 (87), 381 (100),
335 (29), 219 (43). Anal. Calc. for C26H26Br4: C 47.45, H 3.98.
Found: C 47.37, H 3.72%.
To a vigorously-stirred solution of isomer mixture 40 in
CH2Cl2 (200 mL) was added Borch reagent (1.04 g, 6.4 mmol)
dropwise over 5 min. The resulting mixture was stirred at
room temperature for 2 h and then concentrated under reduced
pressure. Ethyl acetate (5 mL) and methanol (1 mL) were added
to the residue and the mixture was again concentrated under
reduced pressure. The residue was slurried with THF (200 mL)
and HO-t-Bu (2 mL) and KO-t-Bu (1.20 g, 10.7 mmol) were
added. The mixture was stirred vigorously for 3.5 h and the
reaction was quenched by the addition of saturated aqueous
NH4Cl solution (5 mL). The reaction mixture was concentrated
under reduced pressure and the residue was taken up in CH2Cl2
(50 mL) and H2O (25 mL). The layers were separated and the
aqueous layer was extracted with CH2Cl2 (40 mL). The com-
bined organic extracts were washed with H2O (25 mL) washed
with saturated aqueous NaCl solution (20 mL), dried (MgSO4),
and concentrated under reduced pressure. The residue was
subjected to column chromatography (silica gel, 25% CHCl3/
hexanes) to yield 41 (0.50 g, 1.4 mmol, 61%) from 39 as a
colourless crystalline solid, mp 204–2058C (chloroform/
hexanes). dH (500.1 MHz, CDCl3) 7.67 (s, 2H), 7.16 (t, J 7.5,
1H), 7.11 (s, 4H), 6.96 (d, J 7.5, 2H), 6.27 (s, 4H), 5.95 (s, 1H),
2.81 (m, 4H), 2.71 (m, 4H). dC (126 MHz, CDCl3) 140.3, 137.1,
135.6, 135.5, 132.6, 131.4, 128.0, 125.6, 125.5, 36.3, 35.5. m/z
(EI, 70 eV) 334 (Mþ, 36%), 229 (100), 215 (67). m/z (HR) Anal.
Calc. for C26H22: 334.1720. Found: 334.1726.
Belta-2,11-dithia[3.3](1,3)(1,3)[2](5)(1)[2](3)(5)
benzeno/3Sphane[31] 39
To a vigorously stirred solution of 38 (2.35 g, 3.57 mmol) in
ethanol (abs, 200 mL) and CH2Cl2 (1800 mL) was added Na2S/
Al2O3 (12.0 g, 4.0 mmol; 3.0 mmol gꢀ1) in three approximately
equal portions over 30 min. The reaction mixture was stirred
for 1.5 h and filtered through a plug of Celite. The filtrate was
concentrated under reduced pressure and the residue was
subjected to column chromatography (silica gel, 50% CHCl3/
hexanes) to yield 39 (0.98 g, 2.4 mmol, 68%) as a colourless,
crystalline solid, mp 42188C dec. (CHCl3/hexanes). dH
[2]Metacyclo[2](2,7)pyrenophane 18
To a solution of 41 (0.26 g, 0.78 mmol) in degassed benzene
(20 mL) was added a solution of DDQ (0.19 g, 0.86 mmol) in
degassed benzene (5 mL) over 10 min. The reaction mixture was
stirred at room temperature for an additional 5 min and con-
centrated under reduced pressure. The residue was dissolved in
CHCl3 and filtered through a plug of silica to yield 18 (0.25 g,

RESEARCH FRONT
Mixed [2.2]Cyclophanes of Pyrene and Benzene
1715
0.75 mmol, 97%) as a crystalline, slightly yellow solid, which
was recrystallized from heptane, mp 184–1868C (heptane). dH
(500.1 MHz, CDCl3) 7.68 (s, 2H), 7.47 (s, 2H), 7.32 (s, 2H), 7.15
(s, 2H), 6.56 (t, J 7.5, 1H), 6.31 (d, J 7.5, 2H), 4.18 (s, 1H), 3.09
(ddd, J 13.0, 5.8, 1.9, 2H), 2.69 (ddd, J 13.3, 13.0, 5.3, 2H), 2.31
(ddd, J unresolved, 2H), 1.21 (ddd, J 13.9, 13.3, 5.8, 2H). dC
(126 MHz, CDCl3) 137.4, 134.0, 133.0, 131.3, 130.3, 129.8,
129.4, 127.9, 126.2, 126.0, 125.1, 125.1, 38.0, 35.3. m/z (EI,
70 eV) 332 (Mþ, 100%), 317 (10), 228 (97), 213 (8), 202 (7), 166
(17). m/z (HRMS) Anal. Calc. for C26H20: 332.1564. Found:
332.1562.
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Accessory Publication
1H and 13C NMR spectra for compounds 17, 18, 24, 25, 26, 28,
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of d for a selection of dimethylarenes are available on the
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Acknowledgements
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Financial support of this work from the Natural Sciences and Engineering
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