J. Am. Chem. Soc. 1997, 119, 619-620
619
and use of iodanes with chiral ligands are still rare.5,6 Reported
studies include asymmetric oxidation of sulfides to sulfoxides
with chiral organoiodanes5 and the synthesis of organoiodanes
bearing chiral binaphthyl ligands.6
A New Route to Chiral Diaryldiacetylenic Liquid
Crystals. Preparation of Iodonium Salts Bearing
Chiral Alkynyl Ligands and Utility for Chiral
Alkynyl Transfer Agents
Among hypervalent iodine compounds, the alkynylphenyl-
iodonium salts 2 are especially valuable in organic reactions
because they contain a synthetically significant carbon-carbon
triple bond and can serve as synthons of alkynyl cations.4,7 We
have found that reactions of alkynyliodonium salts with orga-
nocopper reagents are useful for introduction of alkynyl
components into various organosubstrates.8,9 Selective synthesis
of unsymmetrical diaryldiacetylenes is particularly important
from the standpoint of synthesis of functionalized materials.
Tsugio Kitamura,* Chi Han Lee, Yuki Taniguchi, and
Yuzo Fujiwara
Department of Chemical Science and Technology
Faculty of Engineering, Kyushu UniVersity 36
Hakozaki, Fukuoka 812-81, Japan
Masaru Matsumoto and Youichi Sano
Chiral alkynylphenyliodonium salts 1 were prepared by the
following two methods (Scheme 1). Method A was conducted
according to the procedures of Koser10 and Stang.11 ((S)-(2-
Methylbutoxy)phenyl)acetylene ([R]D27 +12.3° (c 1.0, CH2Cl2))
was treated with [hydroxy(tosyloxy)iodo]benzene in CH2Cl2 in
the presence of a drying agent at room temperature. Evaporation
of the solvent followed by trituration with hexane-ether
afforded ((((S)-2-methylbutoxy)phenyl)ethynyl)phenyliodonium
tosylate (1a) ([R]27D +5.5° (c 0.40, CH2Cl2)) as crystals in 30%
yield. Method B is a modification of the procedure of Bachi
and Stang.12 1-[4-[((S)-(2-Methylbutoxy)carbonyl]phenyl]-2-
(trimethylsilyl)acetylene was treated with µ-oxobis[((trifluo-
romethylsulfonyl)oxy)phenyliodine], prepared in situ from PhIO
and triflic anhydride in CH2Cl2. However, the desired [[4-[((S)-
2-methylbutoxy)carbonyl]phenyl]ethynyl]phenyliodonium tri-
flate could not be obtained as crystals and was unstable. The
CH2Cl2 solution of the crude iodonium triflate was then treated
with aqueous NaOTs and stirred vigorously. Extraction with
CH2Cl2 gave [[4-[((S)-2-methylbutoxy)carbonyl]phenyl]ethynyl]-
phenyliodonium tosylate (1b) as crystals in 38% yield. The
chiral alkynylphenyliodonium tosylates 1 were stable to air and
moisture and used without any special precautions.
Reactions of the chiral alkynyliodonium salts 1 with the
alkynylcopper reagents 3 were conducted under argon (Scheme
2). Addition of the chiral alkynyliodonium tosylate 1a to
solutions of the lithium alkynylcuprates 3, prepared from lithium
arylacetylides and CuCN, in THF at -70 °C and workup of
the reaction mixture gave chiral diaryldiacetylenes (4) in good
isolated yields (54-58%) after separation by column chroma-
tography on silica gel or by recrystallization from ethanol. The
lithium alkynylcuprates 3 bearing electron-withdrawing groups
provide the unsymmetrical diaryldiacetylenes 4 selectively. For
Department of Industrial Chemistry
Faculty of Engineering, Kyushu Sangyo UniVersity
Matsukadai, Fukuoka 813, Japan
ReceiVed September 12, 1996
1,4-Disubstituted diacetylenes display liquid-crystalline and
nonlinear optical properties.1 The extensive conjugation and
polarity of these diacetylenes are associated with high nonlinear
optical coefficients.2 Long-chain alkyl groups play an important
role in the generation of such properties and are essential for
the molecular assembly that is useful for crystal engineering
and molecular devices.3 Moreover, introduction of chiral units
into liquid-crystalline materials creates new functionality; the
generation of ferroelectricity is especially important for high-
speed display devices. In view of the increasing importance
of chiral materials, we thought that chiral alkynylphenyliodo-
nium salts might be suitable transfer agents of chiral alkynyl
components and applicable to the synthesis of novel chiral
diaryldiacetylenes which are potent ferroelectric liquid crystals.
We report here the novel chiral alkynylphenyliodonium tosylates
1 and their application as chiral alkynyl transfer agents for the
synthesis of chiral diaryldiacetylenic liquid crystals.
Hypervalent iodine reagents are versatile reagents in oxidation
and functionalization of organic compounds.4 However, despite
their potential utility for asymmetric synthesis, the preparation
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