Nonplanar Aromatic Compounds. 3. A Proposed New Strategy for the Synthesis of Buckybowls. Synthesis, Structure and Reactions of [7]-, [8]- And [9](2,7)Pyrenophanes

Article abstract of DOI:10.1021/jo0007027

A new strategy for the synthesis of Buckybowls is presented and initial attempts to implement it are reported. This involves annulation of further rings onto polycyclic aromatic systems that prefer to be planar but have been "pre-bent" by the installation of a tether. Pyrenophane 2b reacts with TCNE and PTAD to give 1:1 and 1:2 adducts, respectively. The less strained pyrenophane 2c is unreactive toward TCNE but gives a 1:2 adduct with PTAD. Attempted electrophilic aromatic brominations of pyrenophane 2e under a variety of conditions were unsuccessful, as were attempts to brominate cyclophanediene 1c, the direct synthetic precursor of 2c. Tether cleavage and addition reactions occurred rather than substitution. In an effort to circumvent tether cleavage problems, [7]-, [8]- and [9](2,7)pyrenophanes 22b-d were prepared. However, attempted bromination and Friedel-Crafts acylations failed. Evidence for the fleeting existence of [6](2,7)pyrenophane 22a was also obtained. Comparison of structural data (X-ray and AM1 calculations) for the pyrenophanes 22a-d with their 1,n-dioxa analogues 2a-d indicates that the nature of the tether has a strong effect on the degree of bend in the pyrene moiety and this led to the identification of trioxapyrenophane 28 as the next target in the quest for increasingly bent pyrenes.

Full text of DOI:10.1021/jo0007027

5360
J . Org. Chem. 2000, 65, 5360-5370
Non p la n a r Ar om a tic Com p ou n d s.† 3. A P r op osed New Str a tegy for
th e Syn th esis of Bu ck ybow ls. Syn th esis, Str u ctu r e a n d Rea ction s
of [7]-, [8]- a n d [9](2,7)P yr en op h a n es
Graham J . Bodwell,* J ames J . Fleming, Michael R. Mannion, and David O. Miller
Chemistry Department, Memorial University of Newfoundland, St. J ohn's, NF, Canada A1B 3X7
gbodwell@morgan.ucs.mun.ca
Received May 8, 2000
A new strategy for the synthesis of Buckybowls is presented and initial attempts to implement it
are reported. This involves annulation of further rings onto polycyclic aromatic systems that prefer
to be planar but have been “pre-bent” by the installation of a tether. Pyrenophane 2b reacts with
TCNE and PTAD to give 1:1 and 1:2 adducts, respectively. The less strained pyrenophane 2c is
unreactive toward TCNE but gives a 1:2 adduct with PTAD. Attempted electrophilic aromatic
brominations of pyrenophane 2e under a variety of conditions were unsuccessful, as were attempts
to brominate cyclophanediene 1c, the direct synthetic precursor of 2c. Tether cleavage and addition
reactions occurred rather than substitution. In an effort to circumvent tether cleavage problems,
[7]-, [8]- and [9](2,7)pyrenophanes 22b-d were prepared. However, attempted bromination and
Friedel-Crafts acylations failed. Evidence for the fleeting existence of [6](2,7)pyrenophane 22a
was also obtained. Comparison of structural data (X-ray and AM1 calculations) for the pyrenophanes
22a -d with their 1,n-dioxa analogues 2a -d indicates that the nature of the tether has a strong
effect on the degree of bend in the pyrene moiety and this led to the identification of trioxapy-
renophane 28 as the next target in the quest for increasingly bent pyrenes.
In tr od u ction
to distort them into the conformations that are required
for ring closure to occur. FVT methodology3 has figured
prominently in this regard, although reductive couplings4
now appear to be emerging as viable nonthermolytic
alternatives. However, Buckybowls must still be regarded
as formidable targets.
We propose a conceptually different, three-step ap-
proach to the construction of Buckybowls: (1) bend an
otherwise planar polycyclic aromatic hydrocarbon by
tethering two remote positions; (2) annulate further rings
so as to generate an innately curved polycyclic system;
and (3) remove the tether. The purpose of “pre-bending”
the starting polycyclic aromatic system is to enforce a
geometry in which it is substantially more amenable to
the construction of the “curvature-enforcing” rings than
when it is in a planar, or nearly planar, conformation.
The discovery of the fullerenes1 triggered a surge of
interest in nonplanar polycyclic aromatic compounds,
particularly those that map onto the surface of one or
more of the fullerenes. Fullerene subunits whose lowest
energy conformations are nonplanar have been termed
“Buckybowls”,2 the curvature of which is a consequence
of the presence of one or more five-membered rings. The
pyramidalization of the sp2 hybridized carbon atoms
translates into a high degree of strain in these systems
and this, in turn, renders them synthetically challenging
targets. Most, if not all, reported synthetic approaches
to Buckybowls3 have relied upon some sort of ring closing
reaction to generate the characteristic curvature. Since
the starting materials in these reactions are planar, or
nearly so, a considerable amount of energy is required
† This series of papers was formerly titled “Curved Aromatic
Compounds”.
(1) (a) Kroto, H. W.; Heath, J . R.; O’Brien, S. C.; Curl, R. F.; Smalley,
R. E. Nature 1985, 318, 162-163. (b) Kra¨tschmer, W.; Lamb, L. D.;
Fostiropoulos, K. Huffman, D. R. Nature 1990, 347, 354-358. (c)
Scrivens, W. A.; Bedworth, P. V.; Tour, J . M. J . Am. Chem. Soc. 1992,
114, 7917-7919. (d) Hirsch, A. The Chemistry of the Fullerenes;
Thieme: New York, 1994.
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Z.; Sygula, A.; Sygula, R. J . Am. Chem. Soc. 1994, 116, 7891-7892.
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(b) Mehta, G.; Rao, H. S. P. In Advances in Strain In Organic
Chemistry; Halton, B., Ed.; J AI: London, 1997; Vol. 6, pp 139-187.
(c) Rabideau, P. W.; Sygula, A. Acc. Chem. Res. 1996, 29, 235-242.
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Angew. Chem., Int. Ed. Engl. 1995, 34, 1424-1432. (f) Rabideau, P.
W.; Sygula, A. In Advances in Theoretically Interesting Molecules;
Thummel, R. P., Ed.; J AI: Greenwich, CT, 1995; Vol. 3, pp 1-36. (g)
Scott, L. T.; Bronstein, H. E.; Preda, D. V.; Ansems, R. B. M.; Bratcher,
M. S.; Hagen, S. Atual. Fis.-Quim. Org. 1999, 11, 138-150. (h) Scott,
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10.1021/jo0007027 CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/26/2000

Proposed New Synthesis of Buckybowls
J . Org. Chem., Vol. 65, No. 17, 2000 5361
Sch em e 1
Addition of PTAD to 2b in benzene at room tempera-
ture (Scheme 1) resulted in rapid fading of the red color
of the dienophile until 2 equiv had been added, after
which the color persisted. A significant amount of start-
ing material was still present after the addition of 1 equiv
of PTAD (TLC analysis) and a white precipitate formed
during the addition. The mass of this product cor-
responded to an 88% yield of a 2:1 PTAD-pyrenophane
adduct, but its very low solubility in common organic
solvents and immobility on silica frustrated attempts to
fully purify and characterize it. Nevertheless, quite clean
1H and 13C NMR spectra were obtained, although the
latter was very weak. Assuming that the first equivalent
of PTAD reacted to give an adduct analogous to 4b, then
there is only one possible 2:1 adduct that is consistent
with the NMR spectra, namely 5b. Steric effects likely
preclude addition of the second equivalent of PTAD to
either of the central rings and the retention of an
aromatic sextet in 5b is presumably responsible for the
orientation of addition to the terminal ring. Other
orientations of addition to this ring leave the product with
no aromatic character.
In preparing 1,7-dioxa[7](2,7)pyrenophane 2b5a and
1,8-dioxa[8](2,7)pyrenophane 2c5b from the correspond-
ing cyclophanedienes 1a and 1b, we have demonstrated
that severe nonplanarity can be imparted to the normally
planar pyrene system by the incorporation of a tether
between the 2 and 7 positions. Since pyrene is a repeating
In contrast to TCNE, PTAD did react with pyrenophane
2c. This reaction was clearly slower that that of 2b, as
attested to by the persistence of the red color for over 3
h. As before, a 2:1 adduct was obtained, presumably 5c,
but it was even less soluble than 5b. This compound also
showed signs of instability, a pink color developing when
heated with CHCl3 (presumably retro Diels-Alder reac-
tion) and a brown-yellow color forming upon attempted
dissolution in DMSO. Only a 1H NMR spectrum could
be obtained for 5c and it was very similar to that of 5b.
In line with the trend observed so far, the higher
homologue 2d ,12 having two extra carbon atoms in the
tether, showed only traces of reaction with PTAD after
5 days.
6
subunit around the equators of D5h C70, D6h C84, D5d C80
and in the still hypothetical Buckybowl pinakene 3,7
these results constitute the first successful completion
of step 1 of the strategy outlined above. If pinakene is
the target Buckybowl, then step 2 would be the elabora-
tion of 2, or some other pyrenophane, into a tethered
version of 3. The first task leading toward the ac-
complishment of step 2 is the preparation of functional-
ized pyrenophanes and we now report the results of our
initial attempts to do so.
Resu lts a n d Discu ssion
Rea ction s of 1,n -Dioxa [n ](2,7)p yr en op h a n es 2b
a n d 2c. With gram quantities of pyrenophanes 2b and
2c in hand, a study of their chemistry was undertaken.
In view of the propensity for strained cyclophanes to
undergo cycloaddition reactions,8 the behavior of 2b and
2c toward reactive dienophiles was investigated first. As
we reported earlier, the reaction of 2b with tetracyano-
ethene (TCNE) afforded 1:1 adduct 4b (Scheme 1).5a
Precedent for the observed orientation of addition can be
found in cycloadditions of other small cyclophanes, such
as the reactions between [6]paracyclophane with TCNE9
and [2.2]paracyclophane with 4-phenyl-1,2,4-triazoline-
3,5-dione (PTAD).10 Pyrenophane 2c does not react with
TCNE in benzene at room temperature or at reflux. That
2b and 2c react with TCNE in yields of ca. 100% and
0%, respectively, suggests that there is a significant
difference in their strain energy. AM1 calculations predict
that this difference is of the order of 15 kcal/mol.11
In order for 2b and 2c to serve as precursors to larger,
bowl-shaped polycyclic aromatic structures, methods of
introducing functionality needed to be found. Bromina-
tion was selected for investigation, owing to the potential
offered by an aryl bromide for further elaboration using
palladium-catalyzed cross-coupling methodology.13 Al-
though there is precedent for halogenation of [n]cyclo-
phanes,14 there is also precedent for addition occurring
instead of substitution when the arene is particularly
strained.15 This being the case, the comparatively less
strained pyrenophane 2e was used for preliminary
investigations, but attempted brominations with Br2, Br2‚
dioxane complex,16 pyridinium perbromide,17 and NBS
(11) The heats of formation for (2b + propane) and (2c + ethane)
were calculated using the Chem3D package of software (MOPAC, AM1,
closed shell). The 15.0 kcal/mol difference between the calculated heats
of formation of these two systems was taken to be the difference in
the strain energy between 2b and 2c.
(12) Full details of the synthesis and crystal structures of a series
of higher homologues of 2 are contained in a manuscript soon to be
submitted.
(13) (a) Tsuji, J . Palladium Reagents and Catalysts; Wiley: New
York, 1995. (b) Modern Cross-Coupling Reactions; Stang, P. J .,
Diederich, F., Eds.; VCH: Weinheim, 1997.
(14) (a) Keefer, R. M.; Andrews, L. J . J . Am. Chem. Soc. 1957, 79,
4348-4353. (b) Smith, B. H. Ph.D. Thesis, Cornell University, Ithaca,
New York, 1960; cited in Smith, B. H. Bridged Aromatic Compounds;
Academic Press: New York, 1964; p. 211. (c) Parham, W. E.; J ohnson,
D. R.; Hughes, C. T.; Meilahn, M. K.; Rinehart, J . K. J . Org. Chem.
1970, 35, 4048-4552.
(15) (a) Tobe, Y.; Ueda, K.-I.; Kakiuchi, K.; Odaira, Y.; Kai, Y.; Kasai,
N. Tetrahedron 1986, 62, 1851-1858. (b) Liebe, J .; Tochterman, W.
Tetrahedron Lett. 1983, 24, 2549-2552.
(5) (a) Bodwell, G. J .; Bridson, J . N.; Houghton, T. J .; Kennedy, J .
W. J ., Mannion, M. R. Chem. Eur. J . 1999, 5, 1823-1827. (b) Bodwell,
G. J .; Bridson, J . N.; Houghton, T. J .; Kennedy, J . W. J ., Mannion, M.
R. Angew. Chem., Int. Ed. Engl. 1996, 35, 1320-1321.
(6) Wang, C. R.; Sugai, T.; Kai, T.; Tomiyama, T.; Shinohara, H. J .
Chem. Soc., Chem. Commun. 2000, 557-558.
(7) J emmis, E. V.; Sastry, G. N.; Mehta, G. J . Chem. Soc., Perkin
Trans. 2 1994, 437-441.
(8) Misumi, S. Pure Appl. Chem. 1987, 59, 1627-1636.
(9) Hopf, H.; Wituslki, B.; J ones, P. G.; Schomberg, D. Liebigs Ann.
1995, 609-612.
(10) (a) Murad, A. F.; Kleinschroth, J .; Hopf, H. Angew. Chem., Int.
Ed. Engl. 1980, 19, 389-390. (b) Matsumoto, K.; Toda, M.; Kakehi, A.
Hetereocycles 1995, 41, 471-476.

5362 J . Org. Chem., Vol. 65, No. 17, 2000
Bodwell et al.
Sch em e 2
Sch em e 3
bridges. An analogous ring closure is known to occur in
[2.2]metacyclophanes to give tetrahydropyrenes.19 To
determine whether this process could be selectively
suppressed, the reaction was repeated at -78 °C. In this
case, isolation of the least polar spot afforded a brown
solid that blackened upon standing. The 1H NMR and
mass spectra point toward structure 7. The formation of
this product can be accounted for by conversion of 1c to
2c and subsequent formation of the bromonium ion 8,
which undergoes nucleophilic attack by bromide ion to
give ketone 9, a less favorable tautomer of 7.
In light of the disappointing results using mild bromi-
nation reactions, the Friedel-Crafts acylations that had
been initially planned were not carried out. Instead,
attention was turned to the possibility of performing a
directed orthometalation,20 which does not appear to have
any precedent in any [n]cyclophane, but which Hopf has
shown to be compatible with the [2.2]paracyclophane
system.21 Treatment of a -78 °C solution of 2b or 2c with
t-BuLi (Scheme 3) resulted in the formation of a deep
red-orange color. The color was not bleached upon the
addition of excess CH3I but did fade somewhat upon
warming of the reaction mixture to room temperature.
Subsequent addition of water fully bleached the color.
Isolated from these reactions were the pyrene derivatives
10b (51%) and 10c (94%). Higher homologues of 212 were
unreactive under the same conditions, indicating that,
as expected, strain relief is a driving force in these
reactions. These products presumably arise through an
addition-elimination mechanism that goes through the
Meisenheimer-like intermediates 11. That the presumed
lithium alkoxides 12 are not alkylated by CH3I to any
appreciable extent before the aqueous quench is not
surprising.22
all led to the formation of only baseline material (TLC
analysis). No products were isolated from these reactions.
Since tether cleavage was likely occurring in these
reactions, no attempt was made to brominate the more
strained 2b and 2c. The alternative strategy of bromi-
nating the precursor cyclophanedienes was pursued
instead (Scheme 2). Cyclophanediene 1c reacted readily
with 2 equiv of Br2 in CH2Cl2 at room temperature to
give a dark, sparingly soluble (CDCl3) precipitate, from
which no compound could be isolated or identified.
Treatment of 1c with Br2‚dioxane in CH2Cl2 at 0 °C also
led to formation of a poorly soluble precipitate (grey), but
TLC analysis of the supernatant revealed the presence
of a number of mobile spots. The least polar of these was
isolated by column chromatography. Structural assign-
ment of this product was complicated by the absence of
a molecular ion in its mass spectrum and its propensity
to decompose to a brown, tarry substance in the solid
state, thus precluding elemental analysis. The 1H and
13C NMR spectra are consistent with structure 6, which
is tentatively assigned to the product. The carbon signal
at δ 98.9, which is in accord with the bridgehead carbon
(an R-bromo ether),18 rules out a number of other possible
di-, tetra-, and hexabromides with the same number of
proton and carbon signals. This product does not react
with DDQ in toluene at reflux and its reaction with
t-BuOK immediately affords baseline material (TLC
analysis).
The initial decision to include oxygen atoms in the
bridges of pyrenophanes 2b and 2c was made in order
to keep their syntheses as simple as possible, but it was
soon realized that their presence would provide a con-
venient means for the tether removal in step 3 of our
If structure 6 is correct, then it would appear that Br2‚
dioxane brings about intraannular bond formation in 1c
more quickly than addition of Br2 to the unsaturated
(16) (a) Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis; J .
Wiley & Sons: New York, 1967; pp 333-334. (b) Buehler, C. A.;
Pearson, D. E. Survey of Organic Syntheses; Wiley-Interscience: New
York, 1971; p 360.
(17) Husstedt, U.; Schafer, H. J . Tetrahedron Lett. 1981, 22, 623-
624.
(18) (a) Kalinowski, H. O.; Berger, S.; Braun, S. Carbon-13 NMR
Spectroscopy; J . Wiley and Sons: New York, 1988. (b) The calculated
chemical shift of this carbon atom in 6 (Chem NMR in the ChemOffice
Ultra package of software) is δ 101.6. The remaining calculated 13C
NMR resonances for 6 have shifts very similar to those observed.
(19) Umemoto, T.; Satani, S.; Sakata, Y.; Misumi, S. Tetrahedron
Lett. 1975, 3159-3162. Mitchell, R. H., Iyer, V. S.; Khalifa, N.;
Mahadevan, R.; Venugopalan, S.; Weerawarna, S. A.; Zhou, P. J . Am.
Chem. Soc. 1995, 117, 1514-1532.
(20) (a) Snieckus, V. Chem. Rev. 1990, 90, 879-933. (b) Snieckus,
V. Pure Appl. Chem. 1990, 62, 2047-2056.
(21) (a) Pamperin, D.; Schulz, C.; Hopf, H.; Syldatk, C.; Pietzsch,
M. Eur. J . Org. Chem. 1998, 63, 1441-1445. (b) Hopf, H.; Barrett, D.
G. Liebigs Ann. 1995, 449-451.
(22) Pfeffer, P. E.; Silbert, L. S. J . Org. Chem. 1976, 41, 1373-1379.
(b) Guibe, F.; Bram, G. Bull. Soc. Chim. Fr. 1975, 933-948.

Proposed New Synthesis of Buckybowls
J . Org. Chem., Vol. 65, No. 17, 2000 5363
nonadiyne) under Sonogashira conditions13,24 afforded the
diynetetraesters 15a -d . The yields for this reaction were
consistently over 80%, except for the one leading to the
product with the six-carbon tether 15a (21%). The
volatility of the 1,5-hexadiyne may be responsible for this
anomoly. Catalytic hydrogenation of 15a -d afforded
tetraesters 16a -d (81-100%) and these were reacted
with LiAlH4 to give tetraalcohols 17a -d . Unlike their
1,n-dioxa counterparts,5 they could be isolated in reason-
ably pure form by extraction into hot ethyl acetate.
However, they were sparingly soluble at room tempera-
ture and difficult to purify, so they were used without
further purification in the next step.
Sch em e 4a
Initial attempts to brominate tetraalcohols 17a -d with
48% aqueous HBr resulted in very low yields of the
desired tetrabromides 18a -d , presumably due to insolu-
bility of partially brominated products in the aqueous
medium. The use of HBr/HOAc proved to be more
effective, giving acceptable yields (53-88%) of 18a -d .
Treatment of these with Na2S/Al2O325 afforded the dithia-
cyclophanes 19a -d (45-59%) in slightly lower yield than
for their 1,n-dioxa analogues.5,12 Ring contraction was
accomplished by an S-methylation/Stevens rearrange-
ment protocol that gave isomer mixtures 20a -d (73-
98%). The crude products were then S-methylated and
treated with t-BuOK. For 20a and 20b, cyclophanedienes
21a (42% from 19a ) and 21b (72% from 19b), were
obtained. For 20c and 20d , mixtures of products were
obtained, one component of which were the pyrenophanes
1
22c and 22d according to both TLC analysis and the H
NMR spectrum of the crude product. Treatment of these
mixtures with a slight excess of DDQ in reluxing benzene
afforded the pyrenophanes 22c (5% overall from 19c) and
22d (2% overall from 19d ). The majority of the losses
were suffered during the methylation/Hofmann elimina-
tion sequence.26 We continue to find the yields of this
transformation very erratic, but more often than not on
the low side.5,12,25b Reaction of cyclophanediene 21b with
DDQ led to the formation of pyrenophane 22b in 84%
yield.
a
(a) Tf2O, pyridine, 0 °C, CH2Cl2; (b) 1,5-hexadiyne-1,8-
nonadiyne, Pd(PPh3)2Cl2, CuI, DBU, rt, benzene; (c) H2, Pd(OH)/
C, rt, ethyl acetate; (d) LiAlH4, reflux, THF; (e) HBr/acetic acid,
reflux, yields are from 16; (f) Na2S/Al2O3, rt, 10% ethanol (abs)/
CH2Cl2; (g) i. (MeO)2CHBF4, rt, CH2Cl2; ii. t-BuOK, rt, THF; (h) i.
(MeO)2CHBF4, rt, CH2Cl2; ii. t-BuOK, rt, t-BuOH/THF yield for
21a -b are from 19a -b; (i) DDQ, reflux, benzene; yields for 22c-d
are from 20.
As in the case of its 1,n-dioxa analogue 1a ,5 attempted
conversion of cyclophanediene 21a to pyrenophane 22a
led to the return of the starting material almost quan-
titatively after column chromatography. To more closely
monitor this reaction for the formation of traces of 22a ,
a small scale run was performed in an NMR tube in C6D6.
After heating at 75-80 °C for 20 h, some small new
signals had appeared, clearly not those of pyrenophane
22a . Column chromatography of the reaction mixture
strategy. Thus it was disappointing that the aryl alkyl
ethers cleaved readily during attempted functionalization
of the pyrene moiety. Even if milder aromatic substitu-
tion reactions could be applied successfully, the bridge
would still need to survive subsequent reactions leading
to the formation of a more complex polycyclic aromatic
system. With the prospects for this looking bleak, work
on the substitution of 2b and 2c was abandoned in favor
of preparing and investigating the analogous systems
that lack the oxygen atoms in the bridge. Although the
absence of functionality in the bridges of such systems
was seen as a potential source of problems in step 3 of
the strategy, the inertness of a purely aliphatic tether
was expected to at least permit study of the substitution
chemistry of the pyrene unit.
1
afforded ca. 1 mg of a product, the H NMR spectrum of
which indicated that it was the major product of two
similar, possibly isomeric, new products observed in the
crude reaction mixture. Traces of what may have been
the minor product were obtained, but not enough to allow
measurement of its 1H NMR spectrum. The level of
complexity of the 1H NMR spectrum of the major product
(23) Although this is
a commercially available compound, we
prepared it from the corresponding diacid. See ref 5.
(24) (a) Ritter, K. Synthesis 1993, 735-762. (b) de Meijere, A.;
Meyer, F. E. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379-2411. (c)
Ensley, H. E.; Mahadevan, S.; Mague, J . Tetrahedron Lett. 1996, 37,
6255-6258.
Syn th esis a n d Rea ction s of [n ](2,7)P yr en op h a n es
22. The synthesis of the targeted pyrenophanes 22
(Scheme 4) commenced with the triflation of dimethyl
5-hydroxyisophthalate 1323 to give 14 (99%). Coupling of
14 with a series of diynes (1,5-hexadiyne through 1,8-
(25) (a) Bodwell, G. J .; Houghton, T. J .; Koury, H. E.; Yarlagadda,
B. Synlett 1995, 751-752. See also ref 5 and (b) Bodwell, G. J .;
Houghton, T. J .; Kennedy, J . W. J .; Mannion, M. R. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 2121-2123.
(26) Mitchell, R. H. Heterocycles 1978, 11, 563-568.

5364 J . Org. Chem., Vol. 65, No. 17, 2000
Bodwell et al.
Sch em e 5
Sch em e 6
does occur to a small extent and that 23 can be deydro-
genated by DDQ to give 22a , which then undergoes some
sort of follow-up reaction. However, not enough evidence
is yet available to confidently assign the structure of the
end product and its minor isomer. Obtaining such
evidence is the subject of current investigations.
Having successfully prepared pyrenophanes 22b-d ,
the possibility of functionalizing them was investigated.
Analogous to 2b, 22b reacted with TCNE (Scheme 6) to
give a 1:1 adduct 27 (77%), the structure of which was
confirmed crystallographically. With no ether linkages
in the bridge to pose a threat of cleavage, Friedel-Crafts
acylation (CH3COCl, AlCl3) of 22b was attempted. The
starting material was consumed rapidly, giving rise to a
complex mixture of products. Bearing in mind that even
the minimally strained [10]paracyclophane undergoes
rearrangement under milder conditions,28 it is likely that
migration, rather than cleavage, of the tether is occur-
ring. In fact Lewis acid catalyzed rearrangements of
small cyclophanes to give less strained products are quite
common.29 In the hopes of intentionally generating a less
strained pyrenophane (e.g., a (1,8)pyrenophane) 22b was
treated with AlCl3 alone. Unfortunately, another complex
mixture was produced. However, the mass spectrum of
the crude product mixture contained a cluster of peaks
around m/z ) 596, double that of the molecular ion of
22b (m/z ) 298). This suggests that a telomerization,
akin to that observed for [6](1,4)naphthalenophane30a and
[6](1,4)anthracenophane,30b took place.
was reminiscent of those of the TCNE adducts 4b and
27 (vide infra). This might be indicative of a 1:1 DDQ
adduct, e.g., 24, although the absence of signals above 0
ppm tends not to support this. A 2:1 adduct analogous
to 5 would not be expected to exhibit signals above 0 ppm
but would be expected to exhibit a less complex spectrum
than the one observed.
The mass spectrum contains a small peak at m/z ) 568
(1% relative intensity), double the mass of pyrenophane
22a . The base peak is observed at m/z ) 284, which is
the correct mass for 22a . The peak at m/z ) 568 may be
1
that of a dimer, which, given the complexity of the H
Hopes that bromination would provide the first real
progress toward the accomplishment of step 2 were
dashed when the reaction of 22b with Br2 in CH2Cl2
afforded another complex mixture of products. The 1H
NMR spectrum of the crude product mixture contained
some signals at higher field than δ 0, which suggested
that bridge cleavage was at least partially averted.
However, no inferences regarding the relative amounts
of substitution (if any), addition and bridge migration
products could be drawn. Hopf and Noble’s observation31
that [8]paracyclophane, which is not particularly strained,
does not undergo substitution when reacted with Br2/Fe,
but rather gives bridge cleavage and bridge migration
products serves only to further blacken the outlook for
the efficient aromatic substitution of the pyrenophanes.
The lack of success to date in preparing functionalized
pyrenophanes, while disappointing, does not mean that
NMR spectrum, would have to be a symmetrical dimer
such as 25. However, by analogy to 4b and 27, such a
compound would also be expected to exhibit signals above
1
0 ppm in its H NMR spectrum. Compound 25 could arise
by a [4 + 4] cycloaddition between two molecules of 22a
(Scheme 5). Intramolecular [4 + 4] cycloadditions have
been reported in strained cyclophanes,27 but we are
unaware of any reports of intermolecular reactions. The
strong peak at m/z ) 284 suggests that, whatever the
nature of the isolated compound, it reacts in the mass
spectrometer (e.g., retro Diels-Alder for 24, retro [4 +
4] for 25) to generate 22a . That this peak is actually the
molecular ion of 22a is supported by the presence of a
strong peak at m/z ) 228 (90% relative intensity), which
is the base peak in the mass spectra of each of the
pyrenophanes 22b-d . This corresponds to the quino-
dimethide ion 26. Other strong peaks common to 22b-d
were also present.
The observation of a minor product, presumably an
isomer, is consistent with both 24 and 25. In the case of
24, endo and exo modes of addition are possible, as is
cycloaddition at the chlorine-substituted double bond of
DDQ. Dimer 25, which is a meso compound, has a (()
diastereoisomer.
(28) (a) Smith, B. H. Bridged Aromatic Compounds; Academic
Press: New York, 1964; p 220. (b) Smith, B. H. Ph.D. Thesis, Cornell
University, Ithaca, New York, 1960. (c) Stahl, R. E. Ph.D. Thesis,
Cornell University, Ithaca, New York, 1954. See also (d) Blomquist,
A. T.; Stahl, R. E.; Meinwald, Y. C.; Smith, B. H. J . Org. Chem. 1961,
26, 1687-1691.
(29) Examples can be found in (a) Cyclophanes; Keehn, P. M.,
Rosenfeld, S. M., Eds.; Academic: New York, 1983; Vols. 1-2. (b)
Vo¨gtle, F. Cyclophan-Chemie; Teubner: Stuttgart, 1990. (c) Smith, B.
H. Bridged Aromatic Compounds; Academic Press: New York, 1964.
(30) (a) Tobe, Y.; J imbo, M.; Kobiro, K.; Kakiuchi, K. J . Org. Chem.
1991, 56, 5241-5243. (b) Tobe, Y.; J imbo, M.; Takahashi, T.; Kobiro,
K.; Kakiuchi, K. J . Am. Chem. Soc. 1992, 114, 3479-3491.
(31) Noble, K.-L.; Hopf, H.; Ernst, L. Chem. Ber. 1984, 117, 455-
473.
The results of the reaction of 21a with DDQ suggest
that its valence isomerization to give dihydropyrene 23
(27) (a) Inoue, T.; Kaneda, T.; Misumi, S. Tetrahedron Lett. 1974,
2969-2972. (b) Tsuji, T.; Ohkita, M.; Konno, T.; Nishida, S. J . Am.
Chem. Soc. 1997, 119, 8425-8431.

Proposed New Synthesis of Buckybowls
J . Org. Chem., Vol. 65, No. 17, 2000 5365
Ta ble 1. 1H NMR Ch em ica l Sh ifts (δ) of P yr en op h a n es
22b-d
compound
Ha
Hb
HR
Hâ
Hγ
Hδ
Hꢀ
22b
22c
22d
7.34 7.67 2.30 0.45 -1.38 -1.38
7.59 7.84 2.59 0.88 -0.69 -1.45
7.75 7.91 2.84 1.10
0.05 -0.94 -2.08
2ba
2cb
7.22 7.72
7.44 7.84
3.31 -0.04 -2.10
3.59
0.10 -1.46
F igu r e 1. ORTEP drawing of 22c in the crystal. Carbon
eleven was modeled as two disordered carbons, C(11) and
C(11a), with occupancies of 0.75 and 0.25, respectively. The
angle between the C(1)-C(2)-C(6) plane and its symmetry-
related counterpart in the same molecule is 80.8°.
a
b
Reference 5a. Reference 5b.
proposed strategy for the synthesis of Buckybowls can
be pronounced a failure. It merely suggests that alterna-
tive pathways, such as the introduction of appropriate
substituents at an earlier stage in the synthesis, will have
to be developed. Work aimed at achieving this goal has
been initiated.
pyrene moieties of the pyrenophanes. This made it
difficult to grow crystals for X-ray structure determina-
tion and suitable crystals could ultimately only be
obtained for 22c (Figure 1). Nevertheless, this provided
the first opportunity to examine the effect of changing
atom types in the tether on the degree of bend on the
pyrene moiety. The end-to-end bend5 of 22c is 80.8°, a
full 7.0° smaller than that of its 1,8-dioxa analogue 2c
(87.8°).5a
Since C-C bonds are longer than analogous C-O
bonds,33 the effective length of the tether of 22c would
be expected to be slightly greater than that of 2c.
Therefore, it came as no surprise that the pyrene unit of
22c was less bent than that of 2c, although the magni-
tude of the difference was perhaps a little greater than
anticipated. The difference in the bond angles about the
benzylic O vs C atoms is also a potential contributor to
the overall bend of the pyrene system. However, the
measured angles at these positions in 2c (C-O-C )
110.6°) and 22c (C-C-C ) 109.2°) are not substantially
different. Thus it would seem that differences in bond
lengths exert a more pronounced effect on the degree of
bend in the pyrene moiety. This being the case, the
judicious incorporation of heteroatoms in the tethers of
[n](2,7)pyrenophanes should provide a means for fine-
tuning the bend of the pyrene unit, much like Bickel-
haupt has done for the fine-tuning of the [5]metacyclo-
phane system.34
NMR P r op er ties of th e P yr en op h a n es. Assignment
of the H NMR spectra of the pyrenophanes 22b-d were
1
made on the basis of NOED and 1H-1H COSY experi-
ments. The results are given in Table 1. Unmistakeable
trends as the tether length shortens and the degree of
bend in the pyrene unit increases are the movements to
higher field of both of the aromatic protons (Ha and Hb),
the benzylic protons (HR), the homobenzylic protons (Hâ)
and the bis(homo)benzylic protons (Hγ). Regarding the
bridge protons HR, Hâ and Hγ, it would appear from
simple inspection of models as though they move out of
the deshielding zone and/or further into the shieding zone
of the pyrene system as the length of the tether decreases.
As for the trend in the aromatic protons, the situation is
less clear. The notion that diminishing ring current in
the increasingly nonplanar aromatic is responsible for
the upfield trend in their chemical shift32 would seem to
be at odds with the presence of tether signals at very high
field for all of the pyrenophanes prepared to date. The
pyrene nucleus clearly still exerts a strong magnetic
anisotropic effect, even when it is in a far from planar
conformation.
Another interesting observation comes from the com-
parison of the H NMR spectra of 22b and 22c with their
1
1,n-dioxa analogues 2b5a and 2c.5b It can be seen that
the chemical shifts of the bridge protons Hâ and Hγ of
any given cyclophane are considerably more different
from those of its counterpart than would be expected from
just a change in the nature of the benzylic atom. This
suggests that a small change in the position of a nucleus
in the region of space underneath a bent pyrene, whether
it be a consequence of changes in the conformation of the
tether or the degree of bend of the pyrene system (vide
infra), results in a substantial change in its chemical
shift. In other words, this appears to be a region of high
magnetic flux.
Structures for 22a -d and their 1,n-dioxa analogues
2a -d were calculated at the AM1 level of theory (MO-
PAC-Chem3D). The calculated and experimentally de-
termined end-to-end bend angles are presented in Table
2. As in the case of semiempirical (MNDO) calculations
on [n]metacyclophanes,35 these AM1 calculations consis-
tently overestimate the degree of bend of the aromatic
system. Nevertheless, the pyrenophanes 22 are consis-
tently calculated to be less bent than the corresponding
dioxa compounds 2. In the case of the [8]pyrenophanes
P yr en op h a n e Str u ctu r es. A noteworthy feature of
22b-d is their high solubility, even in cold pentane,
which contrasts that of many pyrene derivatives. This is
most likely a consequence of the nonplanarity of the
(33) For bond length data, see March, J . Advanced Organic Chem-
istry, 4th ed.; J . Wiley and Sons: New York, 1992; p 21.
(34) (a) Bickelhaupt, F.; de Wolf, W. H. J . Phys. Org. Chem. 1998,
11, 362-376. (b) van Eis, M. J .; de Kanter, F. J . J .; de Wolf, W. H.;
Bickelhaupt, F. J . Am. Chem. Soc. 1998, 120, 3371-3375. (c) Kane,
V. V.; de Wolf, W. H.; Bickelhaupt, F. Tetrahedron 1994, 50, 4575-
4622.
(32) (a) Allinger, N. L.; Freiberg, L. A.; Herman, R. B. Miller, M. A.
J . Am. Chem. Soc. 1963, 85, 1171-1176. See also (b) Allinger, N. L.;
Sprague, J . T.; Liljefors, T. J . Am. Chem. Soc. 1974, 96, 5100-5104.
(35) J enneskens, L. W.; de Kanter, F. J . J .; de Wolf, W. H.;
Bickelhaupt, F. J . Comput. Chem. 1987, 8, 1154-1169.

5366 J . Org. Chem., Vol. 65, No. 17, 2000
Bodwell et al.
Ta ble 2. Ca lcu la ted a n d Exp er im en ta l Ben d An gles
That subtle changes in the tether have a significant
effect on the degree of bend in the pyrene moiety was
ascertained from comparisons of calculated and crystal-
lographically derived structural data for 2a -d and 22a -
d . On the basis of these comparisons, 1,4,7-trioxa[7](2,7)-
pyrenophane 28 was identified as a target that will have
a pyrene moiety more bent than that of the current record
holder, 2b.
(d eg) for P yr en op h a n es 2a -d a n d 22a -d
1,n-dioxa series (2)
parent series (22)
atoms in tether
(series member)
X-ray
calcd
X-ray
calcd
6 (a)
7 (b)
8 (c)
9 (d)
a
132.1
113.3
94.9
a
a
122.9
104.5
87.0
109.2
87.8
72.9b
80.8
a
77.8
70.3
a
b
Crystal structure has not been determined. Reference 12.
Exp er im en ta l Section
Gen er a l. Reactions were performed under air unless oth-
erwise indicated. THF was distilled from sodium/benzophe-
none ketyl under N2 immediately prior to use. Spectroscopic
grade benzene was degassed under reduced pressure prior to
use. All other solvents and chemicals were used as received.
Chromatographic purification was accomplished with 230-
400 mesh silica gel. Tlc plates were visualized using a short
wave (254 nm) UV lamp. Melting points are uncorrected.
Reported multiplicities of 1H NMR signals are apparent.
Combustion analyses were performed by the Microanalytical
Services Laboratory, Department of Chemistry, University of
Alberta, Edmonton, Alberta.
2c and 22c, the only pair for which experimental data
for both pyrenophanes is available, the difference be-
tween the bend angles of the calculated structures (7.9°)
is pleasingly close to that between the observed angles
(7.0°). In examining the calculated bend angles, it is
evident that the bend angle for each member of the
parent series 22 lies approximately halfway between that
of its 1,n-dioxa analogue and the next higher 1,n-dioxa
homolog, e.g., the calculated angle for 22b lies about
halfway between those of 2b and 2c. Thus, according to
calculations, combination of the two pyenophane series
provides a means of increasing the bend of the magnitude
of pyrene skeleton in consistent increments of about
8-9°.
The structural data may help to put some earlier
results in perspective. For a start, the Hâ/Hγ chemical
shift discrepancy between 22b-c and 2b-c would appear
to be a consequence of a significant difference in the
degree of bend in the pyrene unit and not of changes in
the conformation in the tether. Neither the calculated
nor the experimentally determined structure point to
major conformational changes. Second, cyclophanediene
1a showed no signs of conversion to 2a 5 (calculated bend
angle ) 132.1°), even when more forcing conditions were
employed, whereas there is evidence (vide supra) that
21a did react under standard conditions to give traces
of the less distorted 22a (calculated bend angle ) 122.9°).
The next less bent pyrene unit is found in 2b (calculated
bend angle ) 113.3°), which is an isolable compound
(measured bend angle ) 109.2°). Pyrenophane 2b is also
the current record holder for the largest bend angle. If
this record is to be broken, then further fine-tuning of
the tether will have to be carried out. One possibility is
to incorporate another oxygen atom into the tether, giving
1,4,7-trioxa[7](2,7)pyrenophane 28 as a target. The cal-
culated bend angle of this stucture is 117.2°, which is
3.9° greater than that calculated for 2b and 5.7° less than
that calculated for 22a . Work aimed at the synthesis of
28 has been initiated.
Rea ction of P yr en op h a n e 2b w ith P TAD To Give 2:1
Ad d u ct 5b . To a stirred, room-temperature solution of
pyrenophane 2b (0.026 g, 0.085 mmol) in benzene (5 mL) was
added PTAD (0.033 g, 0.19 mmol). After stirring for 1 h, the
mixture was suction filtrered and the precipitate was rinsed
with pentane and dried under high vacuum, leaving 5b as a
fine white powder (0.050 g, 88%): mp >250 °C; 1H NMR (300
MHz, CDCl3) δ 7.56-7.34 (m, 12H), 7.21 (s, 2H), 5.57 (d, J )
2.1 Hz, 2H), 5.08 (d, J ) 2.3 Hz, 2H), 4.00-3.85 (m, 4H), 1.43-
1.27 (m, 2H), 1.20-1.11 (m, 2H), 0.67-0.53 (m, 1H), 0.17-
0.03 (m, 1H); 13C NMR (75 MHz, CDCl3) δ (some quaternary
signals not observed) 171.3, 136.5, 129.1, 128.3, 127.6, 125.6,
121.8, 101.8, 68.6, 59.8, 34.4, 30.0; MS (EI) m/z M+ not
observed, 119 (100).
Rea ction of P yr en op h a n e 2c w ith P TAD To Give 2:1
Ad d u ct 5c. To a stirred, room-temperature solution of
pyrenophane 2c (0.029 g, 0.092 mmol) in benzene (5 mL) was
added PTAD (0.043 g, 0.25 mmol). After stirring for 3 h, the
red color of the dienophile had stopped fading and no mobile
spots were observed by TLC analysis. Stirring was continued
for 21 h, over which no observable change occurred. The
mixture was suction filtered and the precipitate was rinsed
with pentane and dried under high vacuum, leaving 5c as a
fine white powder (0.062 g, 85%): mp >250 °C; 1H NMR (300
MHz, CDCl3) δ 7.50-7.43, (m, 6H), 7.39-7.35, (m, 6H), 7.25
(s, 2H), 5.65 (d, J ) 2.0 Hz, 2H), 5.31 (d, J ) 2.0 Hz, 2H),
3.97-3.88 (m, 2H), 3.83-3.74 (m, 2H), 1.33-1.16 (m, 2H),
0.95-0.76 (m, 6H).
Rea ction of Cyclop h a n ed ien e 1c w ith Br 2‚Dioxa n e a t
0 °C To Give 6. To a stirred 0 °C solution of cyclophanediene
1c (0.150 g, 0.47 mmol) in CH2Cl2 (20 mL) was added Br2‚
dioxane (0.250 g, 1.03 mmol). A gray precipitate formed
immediately and this was removed by suction filtration.
Concentration of the filtrate afforded a sticky brown solid.
Column chromatography of this mixture (hexanes) afforded a
colorless solid (0.060 g), tentatively assigned as 6 (20%), that
became brown upon standing: mp 190 °C (dec); 1H NMR (300
MHz, CDCl3) δ 7.63 (s, 4H), 5.48 (s, 4H), 3.39-3.37 (m, 4H),
1.10-1.06 (m, 4H), -0.02 to -0.06 (m, 4H); 13C NMR (75 MHz,
CDCl3) δ 134.3, 128.5, 125.9, 98.9, 65.6, 51.0, 29.2, 24.4; MS
(EI) m/z M+ not observed, 80 (100).
Con clu sion
A new three step strategy for the synthesis of Bucky-
bowls has been proposed. Step 1 has been successfully
completed, but efforts toward accomplishing step 2 have
so far been thwarted by tether cleaveage, bridge migra-
tion and addition reactions. Effective methods for func-
tionalizing the pyrenophanes or their synthetic precur-
sors will need to be found if step 2 is to be accomplished.
Work aimed at achieving these goals is underway.
Rea ction of Cyclop h a n ed ien e 1c w ith Br 2‚Dioxa n e a t
-78 °C To Give 7. To a stirred -78 °C solution of cyclophane-
diene 1c (0.059 g, 0.19 mmol) in CH2Cl2 (10 mL) was added
dropwise a solution of Br2‚dioxane (0.046 g, 0.19 mmol) in CH2-
Cl2 (10 mL). After the starting material had been consumed
(TLC analysis), aqueous 5% Na2S2O3 solution (10 mL) was
added and the mixture was allowed to warm to room temper-
ature. The organic layer was separarted and washed with

Proposed New Synthesis of Buckybowls
J . Org. Chem., Vol. 65, No. 17, 2000 5367
1
saturated NaCl solution (20 mL), dried (MgSO4) and solvents
were removed under reduced pressure. Column chromatogra-
phy of the residue (40% CH2Cl2/hexanes) afforded a brown
solid (20 mg), tentatively assigned as 7 (22%), that darkened
°C (cyclohexane); H NMR (300 MHz, CDCl3) δ 8.58 (s, 2H),
8.25 (s, 4H), 3.94 (s, 12H), 2.77 (s, 4H); 13C NMR (75 MHz,
CDCl3) δ 165.6, 136.9, 130.8, 129.7, 124.5, 90.2, 80.0, 52.4, 19.5;
MS (EI) m/z 462 (6, M+), 231 (100). Anal. Calcd for C26H22O8:
C, 67.53; H, 4.79. Found: C, 67.49; H, 4.80.
1
upon standing: mp 92-94 °C; H NMR (300 MHz, CDCl3) δ
8.28 (d, J ) 9.2 Hz, 1H), 8.08 (d, J ) 9.2 Hz, 1H), 7.96 (d, J )
9.0 Hz, 1H), 7.90 (d, J ) 9.0 Hz, 1H), 7.80 (s, 1H), 7.72 (s,
2H), 6.05 (s, 1H), 4.25 (t, J ) 6.4 Hz, 2H), 3.46 (t, J ) 6.8 Hz,
2H), 1.99-1.91 (m, 4H), 1.62-1.56 (m, 4H); MS (EI) m/z 478
(43), 476 (84, M+ 81Br79Br), 474 (40), 314 (98), 312 (100).
1,7-Bis(3,5-b is(m et h oxyca r b on yl)p h en yl)-1,6-h ep t a -
d iyn e (15b). Triflate 14 (31.29 g, 91.42 mmol), 1,6-heptadiyne
(4.01 g, 43.4 mmol), DBU (17.5 g, 115 mmol), Pd(PPh3)2Cl2
(0.86 g, 1.20 mmol) and CuI (0.86 g, 4.52 mmol) in benzene
(400 mL) afforded 15b (19.00 g, 87%) as a colorless solid: mp
105-107 °C (ethyl acetate/hexanes); 1H NMR (300 MHz,
CDCl3) δ 8.57 (s, 2H), 8.24 (s, 4H), 3.95 (s, 12H), 2.64 (t, J )
7.0 Hz, 4H), 1.94 (quintet, J ) 7.0 Hz, 2H); 13C NMR (75 MHz,
CDCl3) δ 165.7, 136.6, 130.7, 129.6, 124.8, 91.2, 79.6, 52.5, 27.4,
18.6; MS (EI) m/z 476 (68, M+), 411 (100). Anal. Calcd for
7-ter t-Bu tyl-2-(5-h yd r oxyp en toxy)p yr en e (10b). To a
-78 °C solution of pyrenophane 2b (0.025 g, 0.083 mmol) in
THF (20 mL) under N2 was added t-BuLi (1.0 M in pentane,
0.2 mL, 0.2 mmol) and the reaction was stirred at -78 °C for
1 h. Dry CH3I (1 mL) was added and the mixture was allowed
to warm to room temperature. The reaction was quenched with
water (ca.1 mL) and then poured into a separatory funnel
containing water (25 mL) and CH2Cl2 (25 mL). The layers were
separated and the aqueous layer was extracted with CH2Cl2
(25 mL). The combined organic layers were washed with
saturated NaCl solution (25 mL), dried (MgSO4) and the
solvents were removed under reduced pressure. Column
chromatography (CH2Cl2) afforded 10b (0.015 g, 51%) as an
C
27H24O8: C, 68.06; H, 5.08. Found: C, 67.61; H, 4.81.
1,8-Bis(3,5-b is(m e t h oxyca r b on yl)p h e n yl)-1,7-oct a -
d iyn e (15c). Triflate 14 (33.19 g, 96.98 mmol), 1,7-octadiyne
(5.15 g, 48.5 mmol), DBU (18.3 g, 120 mmol), Pd(PPh3)2Cl2
(0.90 g, 1.28 mmol) and CuI (0.90 g, 4.73 mmol) in benzene
(400 mL) afforded 15c (20.48 g, 91%) as a colorless solid: mp
105-107 °C (2:3 toluene/cyclohexane); 1H NMR (300 MHz,
CDCl3) δ 8.56 (s, 2H), 8.23 (s, 4H), 3.94 (s, 12H), 2.53-2.50
(m, 4H), 1.84-1.79 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 165.7,
136.5, 130.7, 129.5, 124.9, 91.9, 79.2, 52.5, 27.6, 19.0; MS (EI)
m/z 490 (100, M+). Anal. Calcd for C28H26O8: C, 68.56; H, 5.34.
Found: C, 69.03; H, 5.22.
off-white solid: mp 108-112 °C; IR (CHCl3) 3620 cm-1 1H
;
NMR (300 MHz, CDCl3) δ 8.18 (s, 2H), 8.02 (d, J ) 9.0 Hz,
2H), 7.94 (d, J ) 9.0 Hz, 2H), 7.67 (s, 2H), 4.25 (t, J ) 6.2 Hz,
2H), 3.73-3.69 (m, 2H), 1.98-1.93 (m, 2H), 1.73-1.65 (m, 4H),
1.57 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 157.0, 147.9, 132.4,
130.0, 128.2, 126.7, 122.9, 122.4, 120.0, 110.7, 68.2, 62.9, 35.1,
32.5, 31.9, 29.2, 22.5; MS (EI) m/z 360 (93, M+), 259 (100).
1,9-Bis(3,5-b is(m e t h oxyca r b on yl)p h e n yl)-1,8-n on a -
d iyn e (15d ). Triflate 14 (7.49 g, 21.9 mmol), 1,8-nonadiyne
(1.31 g, 10.9 mmol), DBU (4.12 g, 27.1 mmol), Pd(PPh3)2Cl2
(0.30 g, 0.43 mmol) and CuI (0.40 g, 2.1 mmol) in benzene (100
mL) afforded 15d (4.45 g, 81%) as a waxy, pale yellow solid:
7-ter t-Bu tyl-2-(6-h yd r oxyh exoxy)p yr en e (10c). Using
the procedure described for 10b above, pyrenophane 2c (0.040
g, 0.17 mmol) and t-BuLi (1.0 M, 0.2 mL, 0.2 mmol) afforded
10c (0.055 mg, 94%) as a pale brown solid: mp 95-97 °C; 1H
NMR (300 MHz, CDCl3) δ 8.18 (s, 2H), 8.02 (d, J ) 9.0 Hz,
2H), 7.95 (d, J ) 9.0 Hz, 2H), 7.67 (s, 2H), 4.25 (t, J ) 6.5 Hz,
2H), 3.71-3.67 (m, 2H), 1.95-1.91 (m, 2H), 1.67-1.50 (m, 6H),
1.57 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 157.1, 147.9, 132.4,
130.0, 128.1, 126.7, 122.9, 122.4, 120.0, 110.7, 68.3, 63.0, 35.1,
32.7, 32.0, 29.7, 26.0, 25.6; MS (EI) m/z 374 (100, M+). Anal.
Calcd for C26H30O2: C, 83.38; H, 8.07. Found: C, 83.07; H,
8.08.
3,5-Bis(m eth oxyca r bon yl)p h en yl Tr ifla te (14). To a 0
°C solution of dimethyl 5-hydroxyisophthalate 13 (21.39 g,
101.8 mmol) and pyridine (12.0 mL, 148 mmol) in CH2Cl2 (450
mL) under N2 was added by syringe trifluoromethanesulfonic
anhydride (18.0 mL, 105 mmol). The mixture was stirred for
20 min and then quenched with 5% HCl solution (100 mL).
The layers were separated and the organic layer was washed
with 1 M HCl solution (200 mL), saturated NaHCO3 solution
(200 mL), saturated NaCl solution (200 mL), dried (MgSO4)
and the solvents were removed under reduced pressure. The
residue was taken up in CH2Cl2 and passed through a ca. 10
cm plug of silica. Removal of the solvent under reduced
pressure afforded 14 (34.45 g, 99%) as a white solid: mp 68.5-
69 °C; 1H NMR (300 MHz, CDCl3) δ 8.71 (s, 1H), 8.13 (s, 2H),
4.00 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 164.3, 149.2, 133.0,
130.3, 126.5, 118.6 (q, J C-F ) 320 Hz), 52.8; MS (EI) m/z 342
(52, M+), 311 (100). Anal. Calcd for C11H9F3O7S: C, 38.60; H,
2.65. Found: C, 38.55; H, 2.49.
Gen er a l P r oced u r e for th e P r ep a r a tion of Diyn etetr a -
ester s 15a -d . To a degassed solution of triflate 14, the
appropriate diyne and DBU in benzene under N2 was added
Pd(PPh3)Cl2 and CuI and the reaction was stirred at room
temperature for 24 h. The mixture was washed with 1 M HCl
solution (2 × ca. 100 mL), brine (ca.100 mL), dried (MgSO4)
and the solvents were removed under reduced pressure. The
residue was then chromatographed (CH2Cl2). Samples for
analysis were obtained by recrystallization.
1,6-Bis(3,5-b is(m e t h oxyca r b on yl)p h e n yl)-1,5-h e xa -
d iyn e (15a ). Triflate 14 (6.85 g, 20.0 mmol), 1,5-hexadiyne
(0.80 g, 10 mmol), DBU (3.60 g, 23.6 mmol), Pd(PPh3)2Cl2 (0.30
g, 0.43 mmol) and CuI (0.50 g, 2.63 mmol) in benzene (60 mL)
afforded 15a (0.99 g, 21%) as a colorless solid: mp 133-135
1
mp 80-85 °C (1:1 toluene/cyclohexane); H NMR (300 MHz,
CDCl3) δ 8.54 (s, 2H), 8.20 (s, 4H), 3.94 (s, 12H), 2.48-2.44
(m, 4H), 1.69-1.66 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 165.6,
136.5, 130.6, 129.3, 124.6, 92.3, 79.0, 52.4, 28.0, 27.9, 19.2; MS
(EI) m/z 504 (100, M+). Anal. Calcd for C29H28O8: C, 69.04;
H, 5.59. Found: C, 69.04; H, 5.64.
Gen er a l P r oced u r e for th e P r ep a r a tion of Tetr a ester s
16a -d . Pd(OH)/C (Pearlman’s catalyst) was added to a solu-
tion of diynetetraester 15 in ethyl acetate and the mixture was
stirred under an atmosphere of hydrogen for 20 min. The flask
was subjected to reduced pressure and let down to nitrogen
several times before being filtered through a plug of Celite.
Removal of the solvent afford tetraesters 16a -d , which were
sufficiently pure for use in the following step. Samples for
analysis were obtained by recrystallization.
1,6-Bis(3,5-bis(m eth oxyca r bon yl)p h en yl)h exa n e (16a ).
Diynetetraester 15a (0.90 g, 1.9 mmol) and Pearlman’s catalyst
(0.50 g) in ethyl acetate (200 mL) afforded tetraester 16a (0.90
g, 98%) as a colorless solid: mp 119-121.5 °C (1:1 ether/
1
hexanes); H NMR (300 MHz, CDCl3) δ 8.50 (s, 2H), 8.04 (s,
4H), 3.94 (s, 12H), 2.67 (t, J ) 7.5 Hz, 4H), 1.65-1.61 (m, 4H),
1.39-1.35 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 166.2, 143.4,
133.6, 130.3, 128.0, 52.1, 35.3, 31.0, 29.3; MS (EI) m/z 470 (6,
M+), 438 (100). Anal. Calcd for C26H30O8: C, 66.37; H, 6.43.
Found: C, 65.95; H, 6.44.
1,7-Bis(3,5-bis(m eth oxycar bon yl)ph en yl)h eptan e (16b).
Diynetetraester 15b (9.55 g, 20.0 mmol) and Pearlman’s
catalyst (1.40 g) in ethyl acetate (250 mL) afforded tetraester
16b (9.67 g, 100%) as a colorless solid: mp 89-91 °C (ethyl
1
acetate/hexanes); H NMR (300 MHz, CDCl3) δ 8.50 (s, 2H),
8.04 (s, 4H), 3.94 (s, 12H), 2.70 (t, J ) 7.6 Hz, 4H), 1.67-1.63
(m, 6H), 1.35 (br s, 4H); 13C NMR (75 MHz, CDCl3) δ 166.3,
143.5, 133.7, 130.4, 128.1, 52.2, 35.4, 31.1, 29.1, 28.9; MS (EI)
m/z 484 (7, M+), 189 (100). Anal. Calcd for C27H32O8: C, 66.93;
H, 6.66. Found: C, 66.76; H, 6.74.
1,8-Bis(3,5-bis(m eth oxyca r bon yl)p h en yl)octa n e (16c).
Diynetetraester 15c (9.00 g, 18.3 mmol) and Pearlman’s
catalyst (1.20 g) in ethyl acetate (250 mL) afforded tetraester
16c (9.14 g, 100%) as a colorless solid: mp 80.5-83 °C (1:1
1
toluene/hexanes); H NMR (300 MHz, CDCl3) δ 8.50 (s, 2H),
8.05 (s, 4H), 3.94 (s, 12H), 2.70 (t, J ) 8.0 Hz, 4H), 1.64-1.60
(m, 4H), 1.31 (br s, 8H); 13C NMR (75 MHz, CDCl3) δ 165.9,

5368 J . Org. Chem., Vol. 65, No. 17, 2000
Bodwell et al.
143.6, 133.3, 130.1, 127.8, 51.8, 35.1, 30.8, 28.9, 28.8; MS (EI)
m/z 498 (2, M+), 189 (100). Anal. Calcd for C28H34O8: C, 67.45;
H, 6.87. Found: C, 67.58; H, 7.01.
mL, 35.0 mmol) afforded tetrabromide 18d (2.14 g, 88% from
16d ) as a colorless solid: mp 69-71.5 °C (toluene/heptane);
1H NMR (300 MHz, CDCl3) δ 7.20 (s, 2H), 7.12 (s, 4H), 4.41
(s, 8H), 2.56 (t, J ) 8.0 Hz, 4H), 1.63-1.57 (m, 4H), 1.32 (br s,
10H); 13C NMR (75 MHz, CDCl3) δ 144.0, 138.0, 129.0, 126.8,
35.5, 33.1, 31.1, 31.0, 29.2, 29.1; MS (EI) m/z M+ not observed,
197 (100). Anal. Calcd for C25H32Br4: C, 46.04; H, 4.95.
Found: C, 46.05; H, 4.82.
1,9-Bis(3,5-bis(m eth oxyca r bon yl)p h en yl)n on a n e (16d ).
Diynetetraester 15d (4.35 g, 8.62 mmol) and Pearlman’s
catalyst (0.50 g) in ethyl acetate (300 mL) afforded tetraester
16d (3.60 g, 81%) as a colorless solid: mp 62.5-64 °C
(cyclohexane); 1H NMR (300 MHz, CDCl3) δ 8.50 (s, 2H), 8.05
(s, 4H), 3.94 (s, 12H), 2.70 (t, J ) 7.1 Hz, 4H), 1.67-1.61 (m,
4H), 1.30 (br s, 10H); 13C NMR (75 MHz, CDCl3) δ 166.5, 143.7,
133.8, 130.5, 128.2, 52.3, 35.5, 31.2, 29.7, 29.3, 29.1; MS (EI)
m/z 512 (2, M+), 448 (100). Anal. Calcd for C29H36O8: C, 67.95;
H, 7.08. Found: C, 67.95; H, 7.30.
Gen er a l P r oced u r e for th e P r ep a r a tion of Tetr a br o-
m id es 18a -d . To a stirred 0 °C suspension of LiAlH4 in THF
(100 mL) was added dropwise a solution of the tetraester 16
in THF (100 mL) under nitrogen. The reaction was held at
reflux for 15 h and then cooled to 0 °C. The reaction was
quenched by the slow addition of ethyl acetate (300 mL) and
then 1 M HCl solution (100 mL). After stirring for 1 h, the
layers were separated and the aqueous layer was extracted
with ethyl acetate (2 × 50 mL). The combined organic layers
were washed with saturated NaCl solution (100 mL), dried
(MgSO4) and concentrated to afford the tetraalcohol 17, which
was used immediately in the following step.
The tetraalcohol 17 thus obtained was suspended in glacial
acetic acid (50 mL). To this was added 30% HBr in acetic acid
and the mixture was heated at reflux for 12-16 h. After cooling
to room temperature, water (50 mL) was added and the
resulting mixture was extracted with CH2Cl2 (3 × 50 mL). The
combined organic layers were washed with water (50 mL),
saturated NaHCO3 solution (50 mL), saturated NaCl solution
(50 mL), dried (MgSO4) and the solvents were removed under
reduced pressure. Chromatographic separation (40% CH2Cl2/
hexanes) of the resulting brown oil afforded the tetrabromide
18.
1,6-Bis(3,5-bis(br om om eth yl)p h en yl)h exa n e (18a ). Li-
AlH4 (1.87 g, 49.3 mmol) and tetraester 16a (1.90 g, 4.04 mmol)
gave tetraalcohol 17a (1.20 g, 83%) as a light gray solid.
Reaction of 17a (1.14 g, 3.18 mmol) with 30% HBr/HOAc (5.0
mL, 25 mmol) afforded tetrabromide 18a (1.24 g, 53% from
16a ) as a colorless solid: mp 73-74 °C (ether/hexanes); 1H
NMR (300 MHz, CDCl3) δ 7.23 (s, 2H), 7.13 (s, 4H), 4.44 (s,
8H), 2.58 (t, J ) 7.4 Hz, 4H), 1.61-1.57 (m, 4H), 1.38-1.34
(m, 4H); 13C NMR (75 MHz, CDCl3) δ 144.0, 138.2, 129.1, 126.9,
35.5, 33.1, 31.0, 29.0; MS (EI) m/z M+ not observed, 197 (100).
Anal. Calcd for C22H26Br4: C, 43.31; H, 4.30. Found: C, 43.49;
H, 4.31.
Gen er a l P r oced u r e for th e P r ep a r a tion of th e Dith ia -
cyclop h a n es 19a -d . To a solution of the tetrabromide 18 in
25a
10% ethanol (abs)/CH2Cl2 was added Na2S/Al2O3
in four
roughly equal portions over 1 h. After stirring at room
teperature overnight, the reaction mixture was suction filtered
and the solvents were removed under reduced pressure.
Column chromatography (1:1 CH2Cl2/hexanes) of the residue
afforded the thiacyclophane 19, a small portion of which was
recrystallized for analysis.
syn -14,23-Dith ia [6.3.3](1,3,5)ben zen op h a n e (19a ). Tet-
rabromide 18a (1.12 g, 1.84 mmol) and Na2S/Al2O3 (2.50 g,
6.60 mmol) in 10% ethanol (abs)/CH2Cl2 (250 mL) afforded
dithiacyclophane 19a (0.35 g, 53%) as a colorless solid: mp
147-149 °C (1:1 ether/hexane); 1H NMR (300 MHz, CDCl3) δ
7.04 (s, 2H), 6.59 (s, 4H), 3.77 (d, J ) 15.1 Hz, 4H), 3.70 (d, J
) 15.0 Hz, 4H), 2.39-2.35 (m, 4H), 1.55-1.51 (m, 4H), 0.99-
0.96 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 142.3, 136.8, 128.4,
127.1, 38.8, 35.5, 28.7, 28.0; MS (EI) m/z 354 (100, M+). Anal.
Calcd for C22H26S2: C, 74.53; H, 7.39. Found: C, 74.06; H, 7.52.
syn -15,24-Dith ia [7.3.3](1,3,5)ben zen op h a n e (19b). Tet-
rabromide 18b (4.31 g, 6.91 mmol) and Na2S/Al2O3 (11.0 g,
24.2 mmol) in 10% ethanol (abs)/CH2Cl2 (1500 mL) afforded
dithiacyclophane 19b (1.60 g, 63%) as a colorless solid: mp
145.5-146.5 °C (1:1 ether/hexane); 1H NMR (300 MHz, CDCl3)
δ 7.10 (s, 2H), 6.65 (s, 4H), 3.83 (d, J ) 15.3 Hz, 4H), 3.77 (d,
J ) 15.3 Hz, 4H), 2.37-2.33 (m, 4H), 1.56-1.52 (m, 4H), 1.16-
1.08 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 142.9, 137.0, 128.7,
127.1, 39.2, 34.1, 28.8, 26.5, 26.3; MS (EI) m/z 368 (100, M+).
Anal. Calcd for C23H28S2: C, 74.95; H, 7.66. Found: C, 75.07;
H, 7.86.
syn -16,25-Dith ia [8.3.3](1,3,5)ben zen op h a n e (19c). Tet-
rabromide 18c (5.00 g, 7.84 mmol) and Na2S/Al2O3 (9.87 g, 27.4
mmol) in 10% ethanol (abs)/CH2Cl2 (2000 mL) afforded dithia-
cyclophane 19c (1.67 g, 56%) as a colorless solid: mp 119-
1
121 °C (heptane); H NMR (300 MHz, CDCl3) δ 7.20 (s, 2H),
6.66 (s, 4H), 3.84 (s, 8H), 2.42-2.38 (m, 4H), 1.44-1.28 (m,
8H), 1.03-0.98 (m, 4H); 13C NMR (75 MHz, CDCl3) δ 137.2,
138.6, 127.4, 120.3, 39.7, 35.5, 29.4, 26.0, 24.5; MS (EI) m/z
382 (100, M+). Anal. Calcd for C24H30S2: C, 75.34; H, 7.90.
Found: C, 75.04; H, 8.08.
1,7-Bis(3,5-bis(br om om eth yl)p h en yl)h ep ta n e (18b). Li-
AlH4 (8.40 g, 221 mmol) and tetraester 16b (9.07 g, 18.7 mmol)
gave tetraalcohol 17b (8.62 g, >100%) as a light gray solid.
Reaction of 17b (6.97 g) with 30% HBr/HOAc (25 mL, 125
mmol) afforded tetrabromide 18b (9.90 g, 85% from 16b) as a
syn -17,26-Dith ia [9.3.3](1,3,5)ben zen op h a n e (19d ). Tet-
rabromide 18d (1.76 g, 2.70 mmol) and Na2S/Al2O3 (3.14 g,
7.85 mmol) in 10% ethanol (abs)/CH2Cl2 (500 mL) afforded
dithiacyclophane 19d (0.48 g, 45%) as a colorless solid: mp
158-159 °C (1:1 toluene/hexane); 1H NMR (300 MHz, CDCl3)
δ 7.12 (s, 2H), 6.64 (s, 4H), 3.83 (d, J ) 14.9 Hz, 4H), 3.77 (d,
J ) 15.0 Hz, 4H), 2.39-2.35 (m, 4H), 1.58-1.49 (m, 4H), 1.31
(br s, 10H); 13C NMR (75 MHz, CDCl3) δ 142.5, 137.1, 128.7,
126.4, 39.1, 33.9, 27.4, 26.4, 25.4, 24.8; MS (EI) m/z 396 (80,
M+), 158 (100). Anal. Calcd for C25H32S2: C, 75.70; H, 8.13.
Found: C, 75.76; H, 8.37.
[6.2.2](1,3,5)Ben zen oph an e-13,21-dien e (21a). To a stirred
solution of dithiacyclophane 19a (0.32 g, 0.90 mmol) in CH2-
Cl2 (50 mL) under N2 was added (MeO)2CHBF4 (0.3 mL, 0.3
mmol) and the mixture was stirred for 1 h. The solvent was
removed under reduced pressure, ethyl acetate (10 mL) was
added. The mixture was then stirred for a further 20 min and
suction filtered. The solid was washed with cold ethyl acetate
(5 mL) and dried under vacuum to yield a bis(sulfonium
tetrafluoroborate) salt (0.51 g). This was slurried in THF (50
mL) under N2 and t-BuOK (0.43 g, 3.8 mmol) was added. The
mixture was stirred overnight and the solvent was removed
under reduced pressure. The residue was taken up in CH2Cl2
(50 mL).and washed with 1 M HCl solution (50 mL), water
(50 mL) and saturated NaCl solution (50 mL). The resulting
solution was dried (MgSO4) and the solvent was removed
under reduced pressure. The residue was passed through a
1
colorless solid: mp 59-64 °C (heptane); H NMR (300 MHz,
CDCl3) δ 7.22 (s, 2H), 7.12 (s, 4H), 4.42 (s, 8H), 2.57 (t, J )
7.5 Hz, 4H), 1.61-1.57 (m, 4H), 1.32 (br s, 6H); 13C NMR (75
MHz, CDCl3) δ 144.0, 138.1, 129.1, 126.8, 35.4, 33.1, 31.0, 29.1,
29.0; MS (EI) m/z 660 (3), 658 (11), 656 (16, M+ 81Br81Br79Br-
79Br), 654 (11), 652 (3). Anal. Calcd for C23H28Br4: C, 44.26;
H, 4.52. Found: C, 44.33; H, 4.51.
1,8-Bis(3,5-bis(br om om eth yl)p h en yl)octa n e (18c). Li-
AlH4 (8.42 g, 222 mmol) and tetraester 16c (8.70 g, 17.4 mmol)
gave tetraalcohol 17c (6.69 g, 99%) as a light gray solid.
Reaction of 17c (3.44 g) with 30% HBr/HOAc (6.0 mL, 30
mmol) afforded tetrabromide 18c (2.78 g, 49% from 16c) as a
1
colorless solid: mp 85-86 °C (heptane); H NMR (300 MHz,
CDCl3) δ 7.23 (s, 2H), 7.14 (s, 4H), 4.46 (s, 8H), 2.59 (t, J )
7.5 Hz, 4H), 1.63-1.57 (m, 4H), 1.32 (br s, 8H); 13C NMR (75
MHz, CDCl3) δ 144.2, 138.2, 129.2, 126.9, 35.6, 33.1, 31.1, 29.3,
29.2; MS (EI) m/z M+ not observed, 199 (100). Anal. Calcd for
C
24H30Br4: C, 45.17; H, 4.74. Found: C, 45.43; H, 4.69.
1,9-Bis(3,5-bis(br om om eth yl)p h en yl)n on a n e (18d ). Li-
AlH4 (1.94 g, 51.1 mmol) and tetraester 16d (2.32 g, 4.53 mmol)
gave tetraalcohol 17d (1.53 g, 85%) as a light gray solid.
Reaction of 17d (1.50 g, 3.74 mmol) with 30% HBr/HOAc (7.0

Proposed New Synthesis of Buckybowls
J . Org. Chem., Vol. 65, No. 17, 2000 5369
short plug of silica (CH2Cl2) and concentration of the eluate
afforded a mixture of bis(methylthio)cyclophane isomers 20a
(0.31 g, 90% from 19a ) as a foamy, colorless solid. This was
dissolved in CH2Cl2 (20 mL) and (MeO)2CHBF4 (0.25 mL, 0.25
mmol) was added. The mixture was stirred under N2 for 6 h
and the solvent was under reduced pressure. The resulting
oily brown residue was slurried in 1:1 t-BuOH/THF (50 mL)
and to this mixture was added t-BuOK (0.40 g, 3.6 mmol). After
stirring under N2 overnight, the solvents were removed under
reduced pressure and to the residue was added water (20 mL)
and CH2Cl2 (50 mL). The organic layer was extracted with 1
M HCl solution (2 × 50 mL), water (50 mL), saturated NaCl
solution (50 mL), dried (MgSO4) and concentrated under
reduced pressure to afford a yellow-brown oil. Column chro-
matography (35% CH2Cl2/hexanes) afforded cyclophanediene
21a (0.11 g, 47% from isomer mixture 20a ) as a colorless
solid: mp 60.5-65.5 °C (sublimed); 1H NMR (300 MHz, CDCl3)
δ 7.44 (s, 2H), 7.12 (s, 4H), 6.36 (s, 4H), 2.37-2.33 (m, 4H),
1.48-1.42 (m, 4H), 0.72-0.69 (m, 4H); 13C NMR (75 MHz,
CDCl3) δ 138.7, 136.8, 136.1, 133.8, 126.3, 35.5, 30.1, 28.7; MS
(EI) m/z 286 (82, M+), 215 (100). Anal. Calcd for C22H22: C,
92.26; H, 7.74. Found: C, 91.98; H, 7.74.
m/z 312 (41, M+), 229 (25), 228 (100), 215 (32). Anal. Calcd
for C24H24: C, 92.26; H, 7.74. Found: C, 92.01; H, 7.80.
[9](2,7)P yr en op h a n e (22d ). Using the procedure described
above for 21a , dithiacyclophane 19d (0.43 g, 1.1 mmol) and
(MeO)2CHBF4 (0.35 mL, 0.36 mmol) gave a bis(sulfonium
tetrafluoroborate) salt (0.60 g) and treatment of this with
t-BuOK (0.35 g, 3.1 mmol) afforded isomer mixture 20d (0.40
g, 87% from 19d ) as a foamy, colorless solid. Reaction of this
mixture with (MeO)2CHBF4 (0.3 mL, 0.3 mmol) and then
t-BuOK (0.60 g, 5.4 mmol) afforded, after column chromatog-
raphy (hexanes), a mixture of products. Reaction of this
mixture with DDQ (0.60 g, 2.6 mmol) in benzene (20 mL) at
reflux for 3 h followed by gravity filtration, concentration under
reduced pressure and column chromatography (hexanes) of the
residue afforded pyrenophane 22d (0.020 g, 6% from isomer
mixture 20d ) as a colorless solid: mp 213-215.5 °C (hexanes);
1H NMR (300 MHz, CDCl3) δ 7.91 (s, 4H), 7.75 (s, 4H), 2.86-
2.82 (m, 4H), 1.14-1.06 (m, 4H), 0.29-0.20 (m, 4H), -0.90 to
-0.97 (m, 2H), -2.03 to -2.14 (m, 4H); 13C NMR (75 MHz,
CDCl3) δ 136.9, 131.3, 127.6, 126.7, 126.2, 36.3, 30.8, 29.7, 29.3,
25.2; MS (EI) m/z 327 (26), 326 (97, M+), 240 (23), 229 (31),
228 (100), 215 (45). Anal. Calcd for C25H26: C, 91.96; H, 8.04.
Found: C, 91.81; H, 8.11.
[7.2.2](1,3,5)Ben zen op h a n e-14,22-d ien e (21b). Using the
procedure described above for 21a , dithiacyclophane 19b (4.40
g, 11.9 mmol) and (MeO)2CHBF4 (3.0 mL, 30 mmol) gave a
bis(sulfonium tetrafluoroborate) salt (6.70 g) and treatment
of this with t-BuOK (4.06 g, 36.2 mmol) afforded isomer
mixture 20b (4.53 g, 98% from 19b) as a foamy, colorless solid.
Reaction of this mixture with (MeO)2CHBF4 (3.1 mL, 29 mmol)
and then t-BuOK (6.41 g, 57.1 mmol) afforded, after column
chromatography (20% CH2Cl2/hexanes), cyclophanediene 21b
(2.46 g, 72% from isomer mixture 20b) as a colorless solid:
mp 82-84 °C (hexanes); 1H NMR (300 MHz, CDCl3) δ 7.39 (s,
2H), 7.19 (s, 4H), 6.40 (s, 4H), 2.30-2.26 (m, 4H), 1.46-1.43
(m, 4H), 0.86-0.83 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 138.4,
136.9, 135.8, 132.8, 125.7, 34.7, 30.7, 27.8, 26.9; MS (EI) m/z
300 (47, M+), 215 (100). Anal. Calcd for C23H24: C, 91.95; H,
8.05. Found: C, 91.97; H, 8.08.
Rea ction of Cyclop h a n ed ien e 21a w ith DDQ. A solution
of 21a (0.025 g, 0.087 mmol) and DDQ (0.020 g, 0.088 mmol)
in C6D6 (1 mL) was heated at 70-80 °C under nitrogen in an
NMR tube for 20 h. The solvent was removed under reduced
pressure and the residue was chromatographed (hexanes) to
afford 21a (0.023 g, 92% recovery) and then an off-white solid
(ca. 1 mg): 1H NMR (300 MHz, CDCl3) δ 7.37 (s, 1H), 7.22-
7.10 (m, 6H), 6.75 (s, 1H), 6.29-6.25 (m, 3H), 5.14-5.10 (m,
1H), 2.56-2.49 (m, 1H), 2.16-1.97 (m, 2H), 1.80-1.69 (m, 1H),
1.60-1.50 (m, 1H), 1.27-1.15 (m, 1H), 1.05-0.97 (m, 1H),
0.87-0.78 (m, 1H), 0.30-0.15 (m, 2H); MS (EI) m/z 568 (1),
478 (7), 285 (29), 284 (100), 269 (20), 256 (19), 255 (68), 253
(20), 252 (19), 241 (54), 240 (39), 239 (61), 230 (26), 229 (38),
228 (90), 227 (24), 226 (34), 216 (55), 215 (86), 203 (21), 202
(36).
Rea ction of [7](2,7)P yr en op h a n e 22b w ith TCNE To
Give Ad d u ct 27. A solution of pyrenophane 22b (0.130 g,
0.436 mmol) and TCNE (0.056 g, 0.43 mmol) in benzene (20
mL) was stirred for 1 h. Cooling the mixture on a water bath
resulted in the formation of colorless crystals, which were
isolated by gravity filtration (0.041 g, 22%). Concentration of
the filtrate afforded a second crop of crystals (0.10 g, 55%; total
yield ) 77%) of 27: mp 110 °C (dec); 1H NMR (300 MHz,
CDCl3) δ 7.69 (d, J ) 8.5 Hz, 1H), 7.59 (s, 1H), 7.49 (d, J ) 8.4
Hz, 1H), 7.28 (d, J ) 9.9 Hz, 1H), 7.15 (s, 1H), 6.70 (d, J ) 9.9
Hz, 1H), 5.99 (s, 1H), 4.43 (s, 1H), 3.11-3.04 (m, 1H), 2.39-
2.33 (m, 2H), 1.94-1.72 (m, 2H), 1.09-0.80 (m, 3H), 0.42-
0.28 (m, 1H), 0.20-0.00 (m, 1H), -0.29 to -0.36 (m, 1H), -0.48
to -0.62 (m, 1H), -0.86 to -0.96 (m, 1H), -1.37 to -1.43 (m,
1H); 13C NMR (75 MHz, CDCl3) (prominent peaks, some
decomposition apparent) δ 153.3, 141.5, 135.1, 133.9, 130.3,
130.1, 128.0, 124.6, 122.8, 120.3, 111.8, 54.6, 53.7, 35.3, 34.8,
31.6, 30.6, 26.3, 24.5.
[7](2,7)P yr en op h a n e (22b). To a stirred, degassed solution
of cyclophanediene 21b (1.66 g, 5.52 mmol) in benzene (100
mL) under N2 was added DDQ (1.61 g, 7.09 mmol) and the
mixture was heated at reflux for 3 h. After cooling, the mixture
was suction filtered, the solvent was removed under reduced
pressure and the residue taken up in a mixture of CH2Cl2 (50
mL) and water (20 mL). The organic layer was washed with 1
M HCl solution (2 × 50 mL), 1 M NaOH solution (50 mL),
saturated NaCl solution (50 mL), dried (MgSO4) and concen-
trated under reduced pressure. The residue was subjected to
column chromatography (5% CH2Cl2/hexanes) to provide
pyrenophane 22b (1.18 g, 71%) as a colorless solid: mp 151.5-
1
153 °C (hexanes); H NMR (300 MHz, CDCl3) δ 7.67 (s, 4H),
7.34 (s, 4H), 2.32-2.28 (m, 4H), 0.47-0.43 (m, 4H), -1.35 to
-1.41 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 136.3, 131.7, 130.3,
129.9, 126.4, 35.7, 33.2, 31.4, 23.5; MS (EI) m/z 298 (36, M+),
241 (27), 229 (24), 228 (100), 215 (34). Anal. Calcd for C23H22
C, 92.57; H, 7.43. Found: C, 92.29; H, 7.59.
:
Cr ysta l Da ta for 22c. Colorless irregular crystal (ap-
proximately 0.30 × 0.10 × 0.35 mm) from heptane, C24H24, M
) 320.47, monoclinic, C2/c (#15), Z ) 4, a ) 19.540 (2), b )
7.454 (1), c ) 14.023 (2) Å, â ) 120.372 (7)°, V ) 1762.2 (4) Å3,
Dc ) 1.178 g cm-3, F(000) ) 672, µ (Cu KR) ) 4.94 cm-1. Data
collection at 26 ( 1 °C with a Rigaku AFC6S diffractometer
with graphite monochromated Mo KR radiation (λ ) 1.54178
Å), ω-2θ scan type with ω scan width ) 1.57 + 0.14 tan θ, ω
scan speed 4.0° min-1 (up to 10 rescans for weak reflections),
1484 reflections measured, 1434 unique (Rint ) 0.009), empiri-
cal absorption correction (max., min. corrections ) 1.00, 0.88)
and secondary extinction correction (coefficient, 1.80917 ×
10-6), giving 994 with I > 2σ(I). Solution and refinement by
direct methods using the teXsan package of the Molecular
Structure Corporation; all non-hydrogen atoms were refined
anisotropically; full matrix least squares refinement with 119
variable parameters led to R ) 0.066 and Rw ) 0.056, GOF )
4.05. Carbon eleven, was modeled as two disordered carbons,
C(11) and C(11a), with occupancies of 0.75 and 0.25, respec-
[8](2,7)P yr en op h a n e (22c). Using the procedure described
above for 21a , dithiacyclophane 19c (11.75 g, 30.75 mmol) and
(MeO)2CHBF4 (8.0 mL, 74 mmol) gave a bis(sulfonium tet-
rafluoroborate) salt (20.37 g) and treatment of this with
t-BuOK (10.40 g, 92.7 mmol) afforded isomer mixture 20c (9.24
g, 73% from 19c) as a foamy, colorless solid. Reaction of this
mixture with (MeO)2CHBF4 (6.1 mL, 56 mmol) and then
t-BuOK (13.0 g, 116 mmol) afforded, after column chromatog-
raphy (hexanes), a mixture of products (1.50 g). Reaction of
this mixture with DDQ (1.30 g, 5.72 mmol) in benzene (100
mL) at reflux for 3 h followed by gravity filtration, concentra-
tion under reduced pressure and column chromatography
(hexanes) of the residue afforded pyrenophane 22c (0.78 g, 11%
from isomer mixture 20c) as a colorless solid: mp 175.5-176.5
1
°C (hexanes); H NMR (300 MHz, CDCl3) δ 7.84 (s, 4H), 7.59
(s, 4H), 2.61-2.57 (m, 4H), 0.92-0.84 (m, 4H), -0.67 to -0.70
(m, 4H), -1.43 to -1.48 (m, 4H); 13C NMR (75 MHz, CDCl3) δ
137.8, 131.3, 128.9, 127.8, 126.6, 35.9, 31.7, 31.1, 23.5; MS (EI)

5370 J . Org. Chem., Vol. 65, No. 17, 2000
Bodwell et al.
1
tively. Only C(11) was included in ORTEP drawing. Further
details of the crystal structure may be obtained from the
Cambridge Crystallographic Data Centre, 12 Union Road, GB-
Cambridge CB2 1EZ (U.K.), on quoting the full journal
citation.
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra of compounds 5b, 5c, 6, 7, 10b, 10c, 14, 15a -d , 16a -
d , 18a -d , 19a -d , 21a -b, 22b-d , 27 and the product of the
reaction of 21a with DDQ. Copies of 13C NMR spectra of
compounds 5b, 6, 10b, 10c, 14, 15a -d , 16a -d , 18a -d , 19a -
d , 21a -b, 22b--d and 27. X-ray crystallographic data for 22c
and 27. This material is available free of charge via the
Internet at http://pubs.acs.org.
Ack n ow led gm en t. Financial support of this work
from the Natural Sciences and Engineering Research
Council of Canada (NSERC) and Xerox Research Centre
of Canada (XRCC) is gratefully acknowledged.
J O0007027