which hampers isolation, (ii) steric requirement for coordination
to the transition metal centers, which would raise the transition
state energy of the ring formation, or (iii) consumption of the
product due to secondary reactions. Although in some cases
the reason for the elusive macrocycle was ascribed to its low
solubility,4e the second and third instances have not been proven
experimentally. During the course of preparation of diethynyl-
benzene macrocycles (DBMs)3,5 having extraannular alkoxym-
ethyl substituents, we encountered a case for the third instance,
which is the topic of this Note, though the reason for the unusual
behavior is not understood. Namely, the dehydrohexameric
macrocycle 2a underwent spontaneous polymerization, while
the corresponding tetramer 1a and octamer 3a were robust
enough to show their melting points at ca. 140-150 °C. This
Note also reports an alternative route to unsymmetrically
substituted dehydrodimer unit 8 through the use of (trimethyl-
silyl)butadiyne (TMSB).
A Clue to Elusive Macrocycles: Unusually Facile,
Spontaneous Polymerization of a Hexagonal
Diethynylbenzene Macrocycle
Akihiro Nomoto, Motohiro Sonoda, Yui Yamaguchi,
Tomoyuki Ichikawa, Keiji Hirose, and Yoshito Tobe*
DiVision of Frontier Materials Science,
Graduate School of Engineering Science, Osaka UniVersity, and
CREST, Japan Science and Technology Agency (JST),
1-3 Machikaneyama, Toyonaka 560-8531, Japan
ReceiVed September 20, 2005
A hexagonal diethynylbenzene macrocycle having exterior
octyloxymethyl groups undergoes spontaneous polymeriza-
tion at room temperature to form hardly soluble materials,
in contrast to the corresponding dehydrotetramer and dehy-
drooctamer, which are stable enough to show their melting
points at higher than 140 °C.
Macrocyclic phenylene ethynylene and phenylene butadiy-
nylene dehydrooligomers constitute a central class of shape-
persistent macrocycles and dehydrobenzoannulenes that have
been attracting much interest principally because of their self-
organizing properties1 and optoelectronic applications,2 respec-
tively. These compounds are typically prepared by Cu(II)-
mediated oxidative coupling reactions between terminal alkynes
or by Pd(0)-catalyzed cross-coupling between sp and sp2
carbons. However, it has been sometimes observed that mac-
rocycles of certain ring size were elusive, especially in the case
of phenylene butadiynylene macrocycles,3,4 even though they
did not seem to be particularly disfavored in terms of enthalpy
(i.e., ring strain) and entropy of the ring formation. This unusual
behavior can be attributed to (i) low solubility of the macrocycle,
As a part of our study on the one- and two-dimensional self-
assembly of DBMs such as 1b-3b,3a,5a,c we planned to prepare
octyloxymethyl-substituted DBMs 1a-3a.6 To this end, we first
improved the synthetic method for the key intermediate,
dehydrodimer unit 8, by the use of (trimethylsilyl)butadiyne
(3) For m-diethynylbenzene macrocycles, see: (a) Tobe, Y.; Utsumi, N.;
Kawabata, K.; Naemura, K. Tetrahedron Lett. 1996, 37, 9325-9328. (b)
Tobe, Y.; Utsumi, N.; Nagano, A.; Sonoda, M.; Naemura, K. Tetrahedron
2001, 57, 8075-8083.
(4) For dehydrobenzo[18]annulene, see: (a) Eglinton, G.; Galbraith, A.
R. Proc. Chem. Soc., London 1957, 350-351. (b) Behr, O. M.; Eglinton,
G.; Raphael, A. R. Chem. Ind. 1959, 699-700. (c) Eglinton, G.; Galbraith,
A. R. J. Chem. Soc. 1960, 3614-3625. (d) Zhou, Q.; Carroll, P. J.; Swager,
T. M. J. Org. Chem. 1994, 59, 1294-1301. (e) Wan, W. B.; Brand, S. C.;
Pak, J. J.; Haley, M. M. Chem.-Eur. J. 2000, 6, 2044-2052.
(5) (a) Tobe, Y.; Utsumi, N.; Nagano, A.; Naemura, K. Angew. Chem.
Int. Ed. 1998, 37, 1285-1287. (b) Tobe, Y.; Nagano, A.; Kawabata, K.;
Sonoda, M.; Naemura, K. Org. Lett. 2000, 2, 3265-3268. (c) Tobe, Y.;
Utsumi, N.; Kawabata, K.; Nagano, A.; Adachi, K.; Araki, S.; Sonoda, M.;
Hirose, K.; Naemura, K. J. Am. Chem. Soc. 2002, 124, 5350-5364.
(1) For recent reviews, see: (a) Grave, C.; Schlu¨ter, A. D. Eur. J. Org.
Chem. 2002, 3075-3098. (b) Zhao, D.; Moore, J. S. Chem. Commun. 2003,
807-818. (c) Ho¨ger, S. Chem.-Eur. J. 2004, 10, 1320-1329. (d) Ho¨ger,
S. In Acetylene Chemistry, Chemistry, Biology and Material Science;
Diederich F., Stang, P. J., Tykwinski, R. R., Eds.; Wiley-VCH: Weinheim,
Germany, 2005; pp 427-452.
(2) For recent reviews, see: (a) Haley, M. M.; Pak, J. J.; Brand, S. C.
Top. Curr. Chem. 1999, 201, 81-130. (b) Marsden, J. A.; Palmer, G. I.;
Haley, M. M. Eur. J. Org. Chem. 2003, 2355-2369. (c) Bunz, U. H. F.
Top. Curr. Chem. 1999, 201, 131-161. (d) Bunz, U. H. F.; Rubin, Y.;
Tobe, Y. Chem. Soc. ReV. 1999, 28, 107-119. (e) Youngs, W. J.; Tessier,
C. A.; Bradshaw, J. D. Chem. ReV. 1999, 99, 3153-3180.
10.1021/jo051969e CCC: $33.50 © 2006 American Chemical Society
Published on Web 12/01/2005
J. Org. Chem. 2006, 71, 401-404
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