Synthesis of the parent resorcin[4]arene
Hisatoshi Konishi,* Hijiri Sakakibara, Kazuhiro Kobayashi and Osamu Morikawa
Department of Materials Science, Tottori University, Koyama-minami, Tottori 680-8552,
Japan. E-mail: konis@chem.tottori-u.ac.jp
Received (in Cambridge, UK) 12th July 1999, Accepted 12th August 1999
The treatment of 2,4-bis(allyloxy)benzyl alcohols with
Sc(OTf)3 in acetonitrile produced a cyclic tetramer as the
major product, which was deallylated by ammonium
formate and PdCl2(PPh3)2 to produce the parent resorcin-
[4]arene.
Resorcinarenes are [1.n]metacyclophane compounds in which
resorcinol units are linked via methylene bridges at their 4,6-
positions.1 Numerous potential applications of these resorcin-
arene derivatives as building blocks for supramolecular
chemistry have been reported.1–4 A variety of resorcin[4]arenes
carrying alkyl or aryl substituents at the bridge positions are
readily prepared by the acid-catalyzed condensation of resorci-
nols with aliphatic or aromatic aldehydes.5,6 Analogously, the
resorcin[n]arenes having no substituents at their methylene
bridges were synthesized from 2-alkylresorcinols and formalde-
hyde.7 Another procedure for preparing the unsubstituted-
methylene bridged resorcin[4]arene involves the treatment of
2,4-dimethoxybenzyl alcohol 1a with trifluoroacetic acid.8 The
resulting octamethyl ether 2a was treated with BBr3 to give a
brick-red solid, which was presumed to be the parent resorcin-
[4]arene 3. However, no spectroscopic characterization has been
described in the literature. We would now like to describe a
new synthetic method for resorcinarene octaethers, including
the preparation of 3. Its spectral properties have also been
measured.
Due to the versatility of the allyl ether group as a phenolic
hydroxy-protecting group in resorcinarene chemistry,9 the octal-
lyl ether 2b was expected to be a promising starting material for
the preparation of 3. Thus, we attempted the condensation of
2,4-bis(allyloxy)benzyl alcohol 1b.† However, the trifluoro-
acetic acid catalyzed reaction of 1b did not produce any cyclic
oligomers. Recently, it has been demonstrated that scandium
trifluoromethanesulfonate, Sc(OTf)3, promotes the Friedel–
Crafts alkylation with benzyl alcohols as alkylating agents.10
Furthermore, the Sc(OTf)3 catalyst is not deactivated by
water.11 Therefore, we directed our efforts toward using this
catalyst for the cyclocondensation of 1b.
Scheme 1
plets were found. Furthermore, the 13C NMR (CDCl3, 30 ЊC) of
2b showed eight signals as expected for the cyclic molecule.
The parent resorcin[4]arene 3 was prepared from 2b by deal-
lylation.12 A mixture of 2b (1.21 g, 1.5 mmol), PdCl2(PPh3)2
(0.17 g, 0.24 mmol), and ammonium formate (3.02 g, 0.48
mmol) in dioxane (90 ml) was refluxed for 6.5 h under an
atmosphere of argon. The white solid that precipitated during
the reaction was collected and dissolved in methanol. After
removal of the methanol and insoluble material, the solvent
was evaporated to leave almost pure 3‡ in 52% yield. A sample
for analysis was obtained by recrystallization from methanol
as needles, mp 235 ЊC (decomp.). Its 1H NMR spectrum in
methanol-d4 at 30 ЊC showed that 3 possesses a highly sym-
metrical structure. One singlet for the methylene protons (3.63
ppm), two singlets for the aromatic protons (6.25 and 6.87
ppm), and a singlet for the OH protons (8.53 ppm) are compat-
ible with a time-averaged D4h conformation. When a few drops
of trifluoroacetic acid-d1 were added to this methanol sample,
the signal at 6.25 ppm gradually decreased, which is ascribed to
the aromatic electrophilic deuteration at the ortho position to
the OH groups at the extraannular positions (Hex). Therefore,
the singlet at 6.87 ppm was assigned to the Hin. This assignment
was also supported by NOE experiments.
To a stirred solution of Sc(OTf)3 (0.075 g, 0.15 mmol) in
acetonitrile (100 ml) was added a solution of 1b (3.3 g, 15
mmol) in acetonitrile (50 ml) over a period of 2 h at 30 ЊC. The
reaction mixture immediately turned purple. After a further 3 h
of stirring, most of the solvent was removed under reduced
pressure. The residue was then dissolved in chloroform and
washed with water. The organic layer was dried over Na2SO4
and evaporated in vacuo to give the crude product from which
the cyclic tetramer 2b‡ was readily isolated by recrystallization
from chloroform–hexane to give colorless crystals (mp 158–
160 ЊC, 1.64 g, 54% yield). Analogously, the resorcinarene
octamethyl ether 2a was prepared from 1a in 34% yield.§
The formation of metacyclophane structures was confirmed
by their positive-ion FAB-mass spectra (m-nitrobenzyl alcohol
matrix). In the 270 MHz 1H NMR spectra at ambient temper-
ature in CDCl3, the resorcinarenes 2b showed three singlets
for the bridge methylene protons (3.79 ppm), extraannular
aromatic protons (Hex, 6.40 ppm) and intraannular aromatic
protons (Hin, 6.30 ppm). The assignment of the aromatic pro-
tons was confirmed by an NOE observed between the Hin and
the methylene protons. In addition, well-defined allylic multi-
To gain insight into the conformational behavior of the
resorcinarenes 2b and 3, we performed dynamic 1H NMR
experiments.¶ In CDCl3, the 1H NMR spectra of 2b showed the
bridging methylene signal as a sharp singlet and the Hin as a
singlet (6.30 ppm) in the range Ϫ50 to 50 ЊC, indicating that
2b exists in a 1,3-alternate conformation or is at a fast equilib-
rium among the conformational flexible species on the NMR
J. Chem. Soc., Perkin Trans. 1, 1999, 2583–2584
This journal is © The Royal Society of Chemistry 1999
2583
Konishi, Hisatoshi
