SCHEME 1
F a cile In tr a m olecu la r Cycliza tion in
Oxid a tive Cou p lin g of Acetylen es Lin k ed to
1,3-P osition s of Ben zen e: Str a in ed
[12]Meta cyclop h a n ed ien etetr a yn e System
Yoshito Tobe,* J un-ya Kishi, Ichiro Ohki, and
Motohiro Sonoda
Department of Chemistry, Faculty of Engineering Science,
Osaka University, Toyonaka, Osaka 560-8531, J apan, and
CREST, J apan Science and Technology Corporation (J ST),
Toyonaka, Osaka 560-8531, J apan
by this method.6 We extended this method to the forma-
tion of [12.12]paracyclophanedodecayne from the corre-
sponding propellane precursor and the stepwise de-
tobe@chem.es.osaka-u.ac.jp
Received December 10, 2002
chlorination to form of C36 in the LDMS.7,8 We also
-
designed a C48 precursor 2 which would be prepared by
dimerization of 3b by oxidative intermolecular coupling
of each alkyne terminals anchored by a 1,3,5-substituted
benzene (Scheme 1). This paper reports the formation of
unexpected dimer 4, having a strained [12]metacyclo-
phanedienetetrayne ring system, derived by intramo-
lecular coupling followed by dimerization. To confirm the
generality of the mode of cyclization, we also investigated
the oxidative coupling of simple benzo-fused diyne 5b
which furnished [12]metacyclophanedienetetrayne 6 in
a high yield. The spectroscopic and structural features
of 6 and the relationship between the mode of cyclization
and the structure of the precursory alkynes are discussed.
The Sonogashira coupling of trichlorotriiodobenzene 74b
with the monoprotected propellatriene 84b gave the triad
3a in 59% yield (Scheme 2).9 After deprotection of the
TIPS group, the terminal acetylene 3b was subjected to
oxidative coupling with Cu(OAc)2 under high dilution
conditions just like the preparation of 1a and 1b, forming
a dimeric product in 85% yield. However, the 13C NMR
of the product exhibited 7 and 12 groups of peaks due to
sp and sp2 carbons, respectively, which were far more
than those expected for the cage dimer 2. Moreover, the
presence of an sp2 signal at 152 ppm suggested the
presence of a distorted benzene ring.10 Such a low field
resonance was not observed in the cage compounds 1a
and 1b. These results indicated that the product was not
2 but 4 which was formed by intramolecular oxidative
Abstr a ct: Oxidative coupling of ethynylpropellane linked
to 1,3,5-position of a benzene core 3b did not give the cage
dimer 2 but the dimer 4 having a strained [12]metacyclo-
phanedienetetrayne system. The spectral and structural
features of the novel ring system were revealed for the
simple dibenzo derivative 6, which was also prepared
efficiently by the intramolecular cyclization of the open-chain
precursor.
Three-dimensional, cagelike cyclophanes have been
attracting a great deal of interest as receptors of organic
molecules1 and as precursors of carbon cage fullerenes.2
Rubin3 and we4 reported the individual endeavor to
produce C60 from [16.16.16](1,3,5)cyclophanetetracosayne
and its chloro derivative, which were formed from their
appropriate precursors having cyclobutenedione or [4.3.2]-
propelladiene units (compounds 1a , 1b) as masking
groups of a triple bond, by the cyclization of the polyyne
chains.5 Although C60+ and C60- ions were formed in the
(6) Recently, preparative scale synthesis of C60 was accomplished
by flash vacuum pyrolysis of a polycyclic chlorinated hydrocarbon:
Scott, L. T.; Boorum, M. M.; McMahon, B. J .; Hagen, S.; Mack, J .;
Blank, J .; Wagner, H.; de Meijere, A. Science 2002, 295, 1500.
(7) Tobe, Y.; Furukawa, R.; Sonoda, M.; Wakabayashi, T. Angew.
Chem., Int. Ed. 2001, 40, 4072.
(8) For representative examples for the formation of small carbon
clusters from organic precursors: (a) Prinzbach, H.; Weiler, A.;
Landenberger, P.; Wahl, F.; Wo¨rth, J .; Scott, L. T.; Gelmont, M.;
Olevano, D.; Issendorff, B. v. Nature 2000, 407, 60. (b) Manini, P.;
Amrein, W.; Gramlich, V.; Diederich, F. Angew. Chem., Int. Ed. 2002,
41, 4339.
laser-desorption mass spectra (LDMS) of the precursors,
preparative-scale synthesis of C60 has not been achieved
(1) For a review: Diederich, F. Cyclophanes; The Royal Society of
Chemistry: Cambridge, 1991.
(2) For reviews: (a) Rubin, Y. Chem. Eur. J . 1997, 3, 1009. (b) Bunz,
U. H. F.; Rubin, Y.; Tobe, Y. Chem. Soc. Rev. 1999, 28, 107. (c) Tobe,
Y. In Advances in Strained and Interesting Organic Molecules; Halton,
B., Ed.; J AI Press: Greenwich, 1999; Vol. 7, p 153.
(3) (a) Rubin, Y.; Parker, T. C.; Khan, S. I.; Holliman, C. L.;
McElvany, S. W. J . Am. Chem. Soc. 1996, 118, 5308. (b) Rubin, Y.;
Parker, T. C.; Pastor, S.; J alisatgi, S.; Boulle, C.; Wilkins, C. L. Angew.
Chem., Int. Ed. 1998, 37, 1226.
(4) (a) Tobe, Y.; Nakagawa, N.; Naemura, K.; Wakabayashi, T.;
Shida, T.; Achiba, Y. J . Am. Chem. Soc. 1998, 120, 4544. (b) Tobe, Y.;
Nakagawa, N.; Kishi, J .; Sonoda, M.; Naemura, K.; Wakabayashi, T.;
Shida, T.; Achiba, Y. Tetrahedron 2001, 57, 3629.
(9) Compounds 3a , 3b, and 4 were unseparable mixtures of dia-
stereomers, of which one isomer is drawn for clarity.
(10) (a) Both sp and sp2 carbon signals of highly strained, acetylene-
bridged metacyclophanes exhibit downfield shifts: (a) Kawase, T.;
Ueda, N.; Darabi, H. R.; Oda, M. Angew. Chem., Int. Ed. Engl. 1996,
35, 1556. (b) Kawase, T.; Ueda, N.; Oda, M. Tetrahedron Lett. 1997,
38, 6681. (c) Kawase, T.; Hosokawa, Y.; Kurata, H.; Oda, M. Chem.
Lett. 1999, 745. (d) Hosokawa, Y.; Kawase, T.; Oda, M. Chem. Commun.
2001, 1948.
(5) A similar mechanism was proposed: Fallis, A. G. Can. J . Chem.
1999, 77, 159.
10.1021/jo0268299 CCC: $25.00 © 2003 American Chemical Society
Published on Web 03/19/2003
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J . Org. Chem. 2003, 68, 3330-3332