Copper(I) ion mediated self-assembly of triple-stranded helicates from oligo(2-ethynylpyridines): Synthesis, structure, and properties

Article abstract of DOI:10.1246/bcsj.76.709

The reaction of oligo(2-ethynylpyridines) (L1-L8) with copper(I) ions proceeded smoothly to afford tri-, tetra-, and pentanuclear triple-stranded helicates (CL1-CL8) in good yields. If a chiral ligand was used, the stereoselective self-assembly of chiral helicates with one particular chirality was achieved in the solid state. Racemization of copper(I) helicates was also observed in solution.

Full text of DOI:10.1246/bcsj.76.709

Ó 2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 709–719 (2003)
709
Headline Articles
Copper(a) Ion Mediated Self-Assembly of Triple-Stranded Helicates from
Oligo(2-ethynylpyridines): Synthesis, Structure, and Properties
ꢀ
ꢀ
Tomikazu Kawano, Takahiro Kato, Chong-Xu Du, and Ikuo Ueda
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047
(Received September 11, 2002)
The reaction of oligo(2-ethynylpyridines) (L1–L8) with copper(a) ions proceeded smoothly to afford tri-, tetra-, and
pentanucleartriple-strandedhelicates(CL1–CL8)ingoodyields. Ifachiralligandwasused, thestereoselectiveself-assembly
of chiral helicates with one particular chirality was achieved in the solid state. Racemization of copper(a) helicates was also
observed in solution.
Metal ion assisted self-assembly of functionalized higher order
supramolecular structures is currently of interest in the field of
supramolecular chemistry.1 Over the past decade, various reports
have been published on the self-assembly of supramolecular
helicates, which are discrete helical supramolecular complexes
constituted by one or more covalent organic strands wrapped
about and coordinated to a series of ions defining the helical axis,
from polydentate nitrogen ligands and metal ions.2 Among these
polydentate nitrogen ligands, oligopyridines have been found to
be one of the most versatile building blocks for the constructionof
supramolecular systems.3 Ethynyl-bridged oligopyridines would
especially be expected to provide us a facile entry into molecular
wires based on transition metal complexes with ꢀ-conjugated
ligands. In1993, Pottsand co-workersreported thatunsubstituted
2,6-bis(2-pyridylethynyl)pyridine having three pyridine rings,
which belongs a ꢀ-conjugated oligo(2-ethynylpyridine) system,
could be treated with copper(a) ions to yield a unique trinuclear
triple-stranded helicate.4a However, the stereoselective self-
assembly of the copper(a) helicate and its detailed behavior in
solution remain unsolved. Additionally, no oligo(2-ethynylpyri-
dines) having more than four pyridine rings have been doc-
umented in the literature to date,4b{d although there have been
many reports on the acetylenic-bridged oligo(bi- or terpyridines)5
and the simple 2-ethynylpyridines such as bis(2-pyridyl)acety-
lenes.6 Since supramolecular helicates are intrinsically chiral, the
self-assembly of helicates from achiral ligands and labile metal
centers yields racemic mixtures of right-handed (plus, P) and left-
handed (minus, M) helicates. Various procedures for their
resolution have been successfully applied in order to obtain the
pure enantiomers. The introduction of a chiral substituent into the
backbone of the ligands is one effective method for the
stereoselective synthesis of helicates with one particular chi-
rality.7
complexes8 or molecular rectangular boxes.9 Furthermore, we
have also reported a facile synthesis of a series of oligo(2-
ethynylpyridines) with three, four, five, and six pyridine rings.10
We expected that the stereoselective self-assembly of supramo-
lecular helicates would be achieved by using oligo(2-ethynylpyr-
idines) bearing a chiral substituent, and that the behavior of the
supramolecular helicates in solution would be clarified. In this
paper, we describe the syntheses and copper(a) ion mediated self-
assembly of the chiral oligo(2-ethynylpyridines), L1–L6, along
with the corresponding achiral ones, L7 and L8 (Chart 1). The
solution properties of copper(a) helicates are also reported.
Results and Discussion
Preparation of Oligo(2-ethynylpyridines) L1–L8. Dibro-
mopyridines (1) and 2-ethynylpyridines (2) are key intermediates
for the synthesis of oligo(2-ethynylpyridines). The synthesis of
bis(6-bromo-2-pyridyl)acetylene (1b) is shown in Scheme 1.
Treatment of 2-bromo-6-(hydroxymethyl)pyridine (3),11;12 which
was prepared from commercially available 2,6-dibromopyridine
(1a), with methanesulfonyl chloride (MsCl) in tetrahydrofuran
ꢂ
(THF) at ꢁ40 C, followed by displacement of the resulting
ꢂ
mesylate with iodide ion in acetone at 60 C, gave the cor-
responding primary iodide (4) in 93% yield from 3. Arbuzov re-
ꢂ
action of 4 with triethyl phosphite at 150 C gave the phos-
phonate (5) in quantitative yield. Subjection of 2-bromo-6-
formylpyridine, which was prepared by oxidation of 3 with 1-
iodylbenzoic acid (IBX)13 in dimethyl sulfoxide (DMSO) at room
temperature, to a Horner-Wadsworth-Emmons reaction with the
sodium salt of 5 in THF at room temperature afforded exclusively
trans-disubstituted ethylene derivative (6) in 92% yield. Bromi-
nation of 6 with bromine in chloroform at room temperature gave
the tetrabromide (7) in 92% yield. Dehydrobromination of 7 with
potassium t-butoxide at room temperature yielded the desired
bis(6-bromo-2-pyridyl)acetylene (1b) in 90% yield.
Recently, we reported that the coordination of 1,2-bis(2-
pyridylethynyl)benzenes with metal ions provided planar chelate
The synthesis of other key intermediates (2a–f) is shown in

710 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
HEADLINE ARTICLES
Chart 1.
Scheme 1. Preparation of bis(6-bromo-2-pyridyl)acetylene (1b). Reagents and conditions: (a) (1) n-BuLi, THF, ꢁ78 ꢂC, (2) DMF,
THF, ꢁ78 ꢂC, (3) NaBH4, THF, 0 ꢂC. (b) (1) MsCl, Et3N, DMAP, THF, ꢁ40 ꢂC, (2) NaI, acetone, 60 ꢂC. (c) P(OEt)3, 150 ꢂC. (d) (1)
NaH, THF, rt, (2) 2-bromo-6-formylpyridine, THF, rt. (e) Br2, CHCl3, rt. (f) t-BuOK, THF, rt.
Scheme 2. Preparation of ethynylpyridines (2a–f). Reagents and conditions: (a) (1) TMSA, [PdCl2(PPh3)2], CuI, Et2NH, rt, (2) TBAF,
THF, rt. (b) (1) EtMgBr, THF, rt, (2) TMSCl, rt. (c) see refs. 8, 9, and 13. (d) TMSA or compound 8, [Pd(PPh3)4], Et2NH, 60 ꢂC. (e)
KOH, MeOH, 0 ꢂC.
Scheme 2. 2,6-Bis(ethynyl)pyridine, which was prepared from
1a according to the literature procedure,14 was converted into
mono TMS-ethynyl substituted pyridine (8) by treatment with
ethylmagnesium bromide, followed by mono-silylation with
trimethylsilyl chloride (TMSCl) in THF at room temperature in
64% yield. The cross-coupling reaction of the bromopyridine
derivatives9a,9 9b,9 9e,8;12 and9f12 with(trimethylsilyl)acetylene
(TMSA) or compound 8 in the presence of a catalytic amount of

T. Kawano et al.
Table 1. Synthesis of Oligo(2-ethynylpyridines) (L1–L8)
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
711
Entry
Compounds 1
Compounds 2
R
Products
Yield/%aÞ
1
2
3
4
5
6
7
8
1a
1a
1b
1b
1a
1a
1a
1b
2a
2b
2a
2b
2c
2d
2e
2f
(L)-menthyl
(D)-menthyl
(L)-menthyl
(D)-menthyl
(L)-menthyl
(D)-menthyl
methyl
L1 (x = 1)
L2 (x = 1)
L3 (x = 2)
L4 (x = 2)
L5 (x = 3)
L6 (x = 3)
L7 (x = 1)
L8 (x = 2)
92
90
86
86
75
72
93
96
TBDMSbÞ
a) Isolated yield. b) t-Butyldimethylsilyl.
Scheme 3. Synthesis of copper(a) complexes (L1–L8).
ꢂ
[Pd(PPh3)4] in diethylamine at 60 C gave the corresponding
Self-Assembly of Copper(a) Helicates CL1–CL8. In the
first place, we examined the coordination of the ligand (L3) with
copper(a) ion. The reaction of L3 with 1.4 equiv of [Cu-
(CH3CN)4]BF415 in dichloromethane (CH2Cl2) at room tempera-
ture resulted in the immediate formation of yellow solutions,
indicating a fast complexation with copper(a) ions, from which
the desired copper(a) complex (CL3) was obtained as yellow
blocks in 92% yield (Scheme 3). Elemental analysis of CL3
showedthe complex (CL3) tobe [Cu4(L3)3](BF4)4. Electrospray
ionization (ESI) mass spectrometry of an acetone solution of CL3
did not show the parent peak of CL3; however, it showed average
masspeaks atm=z 2671.0 for[CL3-(BF4)]þ and 1292.1for [CL3-
TMS-protected derivatives (10a–f) in 83–99% yields. Cleavage
ofthe silylgroup with potassium hydroxide(KOH) in methanol at
0 ꢂC afforded the desired products (2a–f) in 88–97% yields.
The synthesis of oligo(2-ethynylpyridines) (L1–L8) was
achieved by the cross-coupling reaction of 1 with 2.3 equiv of 2
in the presence of a catalytic amount of [Pd(PPh3)4] in dieth-
ylamine at 90 ꢂC (Table 1). No racemization of the chiral centers
took place under the conditions employed. The resulting ligands
(L1–L8) were characterized by IR, UV, 1H NMR, and 13C NMR
spectroscopies and by elemental analysis. All data were con-
sistent with the proposed structures. A slight bathochromic shift
with elongation of the conjugated systems was observed in the
absorption spectra ofthe ligands inthisstudy (ꢁmax 320 nm for L1
(x = 1), 322 nm for L3 (x = 2), 324 nm for L5 (x = 3)).
Furthermore, the ligands (L1–L8) were also found to emit
fluorescence around 341–346 nm. Therefore, the ꢀ-conjugated
framework of L1–L8 should function as a novel fluorescent
probe. Our synthetic methods are also of particular importance in
that most of the compounds in this study were derived from only
one starting material, 2,6-dibromopyridine (1a).
(BF4)2]2þ
. These peaks were not observed by conventional
techniques such as fast-atom bombardment (FAB) mass
spectrometry. The measured isotopic patterns for these ions are
in fair agreement with the calculated isotopic patterns. Examina-
tion of the isotopic abundance of the peak at m=z 1292.1 showed a
peak separation of 0.5 units, which is typical of a doubly charged
species, confirming the presence of the complex [Cu4(L3)3]-
(BF4)4. The electronic spectra of CL3 showed a new weakly
broad absorption in 340–390 nm, which was assigned to a metal-

712 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
HEADLINE ARTICLES
to-ligand charge transfer band. Spectrophotometric titration of a
CH2Cl2 solution of L3 with a CH2Cl2 solution of [Cu(CH3-
CN)4]BF4 gave clear isosbestic points, indicating that a single
species was formed (Fig. 1). The change in absorbance analyzed
by the mole ratio method at 350 nm showed a linear dependence
on the amount of copper(a) salt added up to about 1:1.3 L3:
copper(a) ratio (Fig. 2a). This result indicates that a Cu4(L3)3
composition is generated. The 1H NMR spectra of the free ligand
(L3) and of its copper(a) complex (CL3) are shown in Fig. 3.
Uponmetal complexation, specific signalsof the 1H NMR spectra
undergo significant changes, which also make these signals key
indicators of complexation. The signals of all the aromatic
protons involved in CL3 were shifted relative to those involved in
L3. In particular, the proton signals (Hb and He) of the pyridine
ring (ꢀꢂ ¼ 0:21) are shifted downfield relative to that of the free
ligand (L3). The proton signals (Hc and Hd) of the pyridine ring
(ꢀꢂ ¼ ꢁ0:31) are shifted upfield relative to that of L3. Other
copper(a) complexes also exhibited similar behaviors in their
spectrophotometrictitration experimentsand NMR spectroscopic
studies. The reaction of L4 or L8 with [Cu(CH3CN)4]BF4 in
CH2Cl2 gave the desired copper(a) complexes (CL4: [Cu4(L4)3]-
(BF4)4 or CL8: [Cu4(L8)3](BF4)4, respectively)as yellow blocks.
The complexes (CL3 and CL4) exhibited significant changes in
the specific rotations: copper(a) complexes CL3, ½ꢃꢃD ꢁ418 (c
0.96, CH2Cl2) for L3, ½ꢃꢃD ꢁ60:2 (c 1.08, CH2Cl2); and CL4,
½ꢃꢃD þ422 (c 1.22, CH2Cl2)forL4, ½ꢃꢃD þ60:1 (c 1.15, CH2Cl2).
Such results indicate that the reaction of the present ligands with
Fig. 2. The changes in absorbance analyzed by the mole ratio
methods. a) Cu(a)/L3 at 350 nm. b) Cu(a)/L5 at 330 nm. c)
Cu(a)/L1 at 370 nm.
Fig. 1. Spectrophotometric titration of L3 with [Cu(CH3-
CN)4]BF4 in CH2Cl2.
Fig. 3. 1H NMR spectra (600 MHz, CD2Cl2) of (a) the copper(a) complex (CL3) and (b) the ligand (L3).

T. Kawano et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
713
ꢁ
and Cu2–Cu3 bond distances are approximately 4.71 A and 4.69
copper(a) saltsproceededstereoselectivelytoaffordopticalactive
copper(a) complexes. Similarly, the complex-forming reaction of
16
L1, L2, or L7 with an equimolar amount of [Cu(CH3CN)4]PF6
ꢁ
A, respectively. No intrastrand ꢀ-stacking between pyridine
rings is observed in CL7. Although X-ray quality crystals of
copper(a) complexes other than CL7 were not obtained, we
determined on the basis of the crystal structure of CL7 and the
physicochemical data of the complexes, especially, the specific
rotation (CL1, ½ꢃꢃD ꢁ61:8 (c 0.98, CH2Cl2) for CL1 and ½ꢃꢃD
þ60:7 (c 1.32, CH2Cl2) for CL2), that the complexes (CL1 and
CL2) were chiral trinuclear triple-stranded helicates. Similarly,
we determined that two pairs of complexes (CL3 and CL4, CL5
and CL6) were chiral tetra- and pentanuclear triple-stranded
helicates, respectively, and that complex (CL8) was an achiral
tetranuclear triple-stranded helicate. Figure 5 shows the
schematic representations of the helical structures of tri-, tetra-,
and pentanuclear triple-stranded helicates, respectively. These
structures were also confirmed by elemental analysis and ESI-MS
spectroscopy. The ESI-MS spectrum of trinuclear triple-stranded
helicate (CL1), for example, has an average mass peak at m=z
1093.0 for [CL1-(PF6)2]2þ; the ESI-MS spectrum of tetranuclear
triple-stranded helicate (CL4) has average mass peaks at m=z
2671.0 for [CL4-(BF4)]þ and 1292.0 for [CL4-(BF4)2]2þ, and the
ESI-MS spectrum of pentanuclear triple-stranded helicate (CL5)
in CH2Cl2 at room temperature gave the copper(a) complexes
CL1: [Cu3(L1)3](PF6)3, CL2: [Cu3(L2)3](PF6)3, or CL7: [Cu3-
(L7)3](PF6)3, respectively, as yellow plates, and the reaction of
L5 or L6 with 1.7 equiv of [Cu(CH3CN)4]BF4 in CH2Cl2 at room
temperature gave the copper(a) complexes CL5: [Cu5(L5)3]-
(BF4)5 or CL6: [Cu5(L5)3](BF4)5, respectively, as yellow pow-
ders. However, complexes(CL5 and CL6) were eachobtainedas
a diastereomer mixture, due to the difficulty of purifying the
complex further.
Structure of Copper(a) Helicates.
To investigate the
structure of the copper(a) complexes obtained in this study, we
tried to prepare single crystals of complexes. Recrystallization of
CL7 from CH2Cl2 by the slow diffusion of hexane vapor only
gavesmallsinglecrystals, which appearedtobesuitablefor X-ray
structure analysis. The structural analysis showed CL7 to be
[Cu3(L7)3](PF6)3 (Fig. 4). Complex (CL7) belongs to space
group P21=c, indicative of the racemic mixture of P- and M-
helicates. Complex (CL7) consists of three copper(a) ions, three
ligands, and three counterions. Selected bond distances and
angles of CL7 are shown in Table 2. Each Cu(a) ion has an
approximately trigonal-planar geometry (the average N–Cu–N
bond angles: 119.9ꢂ), which is similar to that reported by Potts et
has an average mass peak at m=z 1519.0 for [CL5-(BF4)2]2þ
.
Therefore, the stereoselective self-assembly of the copper(a)
helicates has been achieved. The final determination as to
whether the directionality within the each chiral copper(a)
helicate is P or M is a next important subject, which will be
al.4a The Cu–N distances (1.980–2.045 A) are unremarkable. No
ꢁ
interaction betweencopper(a) ions is observed, because Cu1–Cu2
ꢂ
ꢁ
Table 2. Selected Bond Distances (A) and Bond Angles ( ) of CL7
Cu1–N1, 2.036(5)
Cu1–N4, 2.045(5)
Cu1–N7, 2.013(5)
Cu2–N2, 2.005(4)
Cu2–N5, 1.993(4)
Cu2–N8, 1.980(5)
Cu3–N3, 2.022(4)
Cu3–N6, 2.017(5)
Cu3–N9, 2.018(4)
N1–Cu1–N4, 113.3(2)
N1–Cu1–N7, 124.6(2)
N4–Cu1–N7, 121.7(2)
N2–Cu2–N5, 112.2(2)
N2–Cu2–N8, 124.7(2)
N5–Cu2–N8, 123.1(2)
N3–Cu3–N6, 120.3(2)
N3–Cu3–N9, 116.9(2)
N6–Cu3–N9, 122.1(2)
Fig. 5. Schematic representations of chiral tri-, tetra-, and
pentanuclear triple-stranded helicates. Copper(a) ion and
ligand molecule are marked with a circle and a thick line,
respectively.
Fig. 4. (a) Ball-and-stick representation and (b) the stereo-
topic view of CL7. Solvate dichloromethane molecule and
hydrogen atoms are omitted for clarity.

714 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
HEADLINE ARTICLES
reported in detail elsewhere.
inversion process could be observed by measurement of the
1H NMR spectra of CL3 at 8-hour intervals (Fig. 7). New signals
were observed after 8 h and 48 h standing. The new signals are
Behavior of Chiral Copper(a) Helicates in Solution.
Complexes (CL1–CL6) are chiral complexes in the solid state.
To observe the behavior of these chiral complexes in solution, we
measured the specific rotation ofchiral copper(a) complex (CL3),
as a typical example, at 10-minute intervals (Fig. 6). The value of
the specificrotationofCL3decreasedexponentially,andthe½ꢃꢃD
value became approximately zero after about 24 hours. The
1
assigned to H signals of a diastereomer of CL3, which has
opposite helicitytoCL3. Theseresultssuggest thataninversion17
of helicity occurs in complex (CL3) by intramolecular
mechanism. To investigate the inversion mechanism in further
1
detail, we measured the H NMR spectra of the 1:1 mixture of
CL3 and CL8 (Fig. 8). As shown in Fig. 8, the 1H NMR spectra
became more complicated along with the appearance of new
signals. This result indicates the generation of new copper(a)
complexes with
a variety of compositions such as a
[Cu4(L3)2(L8)]4þ framework. This framework was confirmed
by ESI-MS spectroscopy, which showed the average mass peak at
m=z 1268.0for{[Cu4(L3)2(L8)](BF4)4-(BF4)2g2þ. Therefore, the
conversion of a complex is also likely to be caused by the
dissociation of the complex. Furthermore, copper(a) helicates in
this study readily reverted to the parent ligands in quantitative
yields by addition of a large excess amount of acetonitrile. This
observation also suggests that the kinetic lability of the metal ions
resultsin the dissociationof the complex incoordinating solvents.
Conclusion
Fig. 6. Change in specific rotation of CL3 in CH2Cl2.
In conclusion, we have demonstrated that the coordination of
chiral oligo(2-ethynylpyridines) with copper(a) ions proceeds
smoothly to yield tri-, tetra-, and pentanuclear triple-stranded
helicates in the solid state stereoselectively, and that the
conversion of helicity of the copper(a) helicates takes place in
solution. The chiral triple-stranded helicates described here
would be applicable as an attractive catalyst for asymmetric
Fig. 8. Change of the 1H NMR spectra of the 1:1 mixture of
CL3 and CL7. a) 0 h; b) 24 h. 1H signals involved in CL3
and CL7, which are assigned to the methylene protons
substituted to the terminal pyridine ring, are marked with a
circle and a triangle, respectively.
Fig. 7. Changes ofthe 1H NMR spectraof CL3. a)0 h; b)8 h;
c) 48 h. New signals are marked with a circle.

T. Kawano et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
715
Hz, 1H), 7.36 (d, J ¼ 7:6 Hz, 1H), 7.35 (d, J ¼ 7:8 Hz, 1H), 4.47 (s,
2H); 13C NMR (100 MHz, CDCl3) ꢂ 159.7, 141.4, 139.2, 127.0,
synthesis because they possess an asymmetric environment.
Furthermore, a new (supra)molecular structure such as macro-
cyclic compounds or catenanes would be generated by using the
copper(a) helicates as a synthetic template.
121.9, 4.4; IR (NaCl) 3050, 1580, 1560, 1410, 1140, 880 cmꢁ1
;
FABMS (NBA) m=z 298 [(M + H)þ]; Found: C, 24.18; H, 1.59; N,
4.53; Br, 26.57; I, 42.79%. Calcd for C6H5BrIN: C, 24.19; H, 1.70; N,
4.70; Br, 26.82; I, 42.06%.
Experimental
Diethyl (6-Bromo-2-pyridyl)methylphosphonate 5. The mix-
ture of 4 (1.78 g, 5.97 mmol) and triethyl phosphite (2.0 mL) was
stirred at 150 ꢂC for 3 h. After being cooled to room temperature, the
reactionmixturewas evaporated todrynessunder reduced pressure to
give 5 (2.07 g, 99%) as an orange oil: 1H NMR (600 MHz, CDCl3) ꢂ
7.52 (t, J ¼ 7:7 Hz, 1H), 7.38 (dd, J ¼ 8:1, 2.6 Hz, 1H), 7.36 (dd,
J ¼ 7:7, 2.6 Hz, 1H), 4.15–4.07 (m, 4H), 3.39 (d, J ¼ 22 Hz, 2H),
1.29 (t, J ¼ 7:0 Hz, 6H); 13C NMR (150 MHz, CDCl3) ꢂ 153.9,
153.9, 141.2, 141.2, 138.7, 138.7, 126.2, 126.1, 123.1, 123.0, 62.3,
62.3, 36.6, 35.3, 16.2, 16.1; FABMS (NBA) m=z 308 [(M + H)þ];
Found: C, 38.76; H, 5.12; Br, 25.88; N, 4.60; P, 10.19%. Calcd for
C10H15BrNO3P: C, 38.98; H, 4.91; Br, 25.93; N, 4.55; P, 10.05%.
1,2-Bis(6-bromo-2-pyridyl)ethene 6. To a suspension of NaH
(60% dispersion in mineral oil, 0.350 g, 14.5 mmol) in dry THF (50
mL) was added a solution of 5 (4.50 g, 14.6 mmol) in dry THF (25
mL) at room temperature. After being heated under reflux for 1 h, the
reaction mixture was cooled to room temperature, and then a solution
of 2-bromo-6-formylpyridine (1.87 g, 10.0 mmol) in dry THF (25
mL) was added at the same temperature. The reaction mixture was
stirredatroomtemperaturefor20h,andthenquenchedwithsaturated
aqueous NH4Cl and extracted with AcOEt. The organic layer was
washed with H2O and brine, and then dried over anhydrous MgSO4.
After removal of the solvent, the oily residue was purified by column
chromatography (silica gel, benzene) to give 6 (3.14 g, 92%) as
colorless needles:mp197.0–198.5ꢂC;1H NMR (400 MHz, CDCl3) ꢂ
7.65 (s, 2H), 7.54 (t, J ¼ 7:6 Hz, 2H), 7.38 (d, J ¼ 7:8 Hz, 2H), 7.35
(d, J ¼ 7:6 Hz, 2H); 13C NMR (100 MHz, CDCl3) ꢂ 155.8, 142.3,
138.9, 131.5, 127.1, 122.4; IR (neat) 3065, 1572, 1543, 1431, 1406,
1327, 1190, 1153, 1111, 974, 880, 791, 729 cmꢁ1; FABMS (NBA)
m=z 341 [(M + H)þ]; Found: C, 42.40; H, 2.45; Br, 47.23; N, 8.19%.
Calcd for C12H8Br2N2: C, 42.39; H, 2.37; Br, 47.00; N, 8.24%.
General.
All reactions were carried out under an argon
atmosphere with dry solvents under anhydrous conditions unless
otherwise noted. Solvents and reagents were purified by literature
methods where necessary.18 All melting points were determined on a
Yanagimoto micro melting point apparatus (Yanaco MP-500D) and
are uncorrected. Infrared (IR) spectra were recorded on a Perkin-
Elmer system 2000 FT-IR spectrometer. UV absorption spectra were
obtainedusingaHitachi260-30spectrophotometer. 1H NMRspectra
were recorded on a JEOL JNM-LA400 (400 MHz) spectrometer;
chemical shifts (ꢂ) are reported in parts per million relative to
tetramethylsilane (TMS). Splitting patterns are designated as s,
singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br, broad; dsp,
double of septets. Mass spectra (MS) were recorded on a JEOL JMS-
600 mass spectrometer. Elemental analyses were performed by the
Material Analysis Center of the Institute of Scientific and Industrial
Research, Osaka University. Optical rotations were measured with a
Perkin-Elmer 241 polarimeter. Circular dichroism spectroscopy was
performed on a JASCO J-725 spectropolarimeter. Column chroma-
tography was performed on Merck silica gel 60. 2-Bromo-6-
(hydroxymethyl)pyridine (3), bromopyridine derivatives (9a, 9b, 9e,
and 9f), and 2,6-bis(ethynyl)pyridine were prepared from commer-
cially available 2,6-dibromopyridine (1a) according to the literature
procedure.
2-Bromo-6-(iodomethyl)pyridine 4. To a solution of 2-bromo-
6-(hydroxymethyl)pyridine (3) (3.14 g, 16.7 mmol) in dry THF (70
mL) were added triethylamine (3.4 mL, 24.6 mmol) and 4-
(dimethylamino)pyridine (0.102 g, 0.835 mmol) at room temper-
ature. To the resulting solution was added dropwise methanesulfonyl
chloride (2.0 mL, 25.8 mmol) at ꢁ40 ꢂC. After being stirred at the
same temperature for 2.5 h, the reaction mixture was quenched with
saturated aqueous NH4Cl and extracted with AcOEt. The organic
layer was washed successively with saturated aqueous NaHCO3,
H2O, and brine, and then dried over anhydrous MgSO4. After
removal of the solvent, the oily residue was purified by column
chromatography (silica gel, hexane–AcOEt) to give 2-bromo-6-
(methylsulfonylmethyl)pyridine (4.23 g, 95%) as a colorless oil:
1H NMR (400 MHz, CDCl3) ꢂ 7.62 (t, J ¼ 7:8 Hz, 1H), 7.49 (d,
J ¼ 7:6 Hz, 1H), 7.45 (d, J ¼ 7:6 Hz, 1H), 5.29 (s, 2H), 3.13 (s, 3H);
13C NMR (100 MHz, CDCl3) ꢂ 155.0, 141.6, 139.4, 128.1, 121.0,
70.3, 38.1; IR (NaCl) 3000, 2910, 1570, 1545, 1425, 1395, 1345,
1160, 1110, 955, 820 cmꢁ1; FABMS (NBA) m=z 266 [(M + H)þ];
Found: C, 31.26; H, 2.92; N, 5.14; Br, 30.16; S, 11.91%. Calcd for
C7H8BrNO3S: C, 31.59; H, 3.03; N, 5.26; Br, 30.03; S, 12.05%.
To a solution of 2-bromo-6-(methylsulfonylmethyl)pyridine (3.93
g, 14.8 mmol) in acetone (150 mL) was added NaI (8.87 g, 59.18
mmol)atroomtemperature. Afterbeing heated underreflux for 5.5h,
the reaction mixture was cooled to room temperature, and then
filtered through a pad of Celite. The solvent was evaporated to
dryness under reduced pressure, and then the resulting oily residue
was dissolved with AcOEt. The organic layer was washed
successively with saturated aqueous Na2S2O3, H2O, and brine, and
then dried over anhydrous MgSO4. After removal of the solvent, the
oily residue was purified by column chromatography (silica gel,
hexane–AcOEt) to give 4 (4.31 g, 98%) as pale yellow crystals: mp
56.5–58.5 ꢂC (dec); 1H NMR (400 MHz, CDCl3) ꢂ 7.50 (t, J ¼ 7:8
1,2-Bis(6-bromo-2-pyridyl)-1,2-dibromoethane 7.
To a
solution of 6 (1.84 g, 5.41 mmol) in chloroform (70 mL) was added
dropwise a solution of bromine (0.42 mL, 8.15 mmol) in chloroform
(30 mL) at room temperature. The reaction mixture was stirred at the
same temperature for 2 h; then saturated aqueous Na2S2O3 was
added. The resulting precipitate was collected and washed with H2O
and chloroform to give 7 (2.48 g, 92%) as a white powder: mp 249.0
ꢂC (dec.); 1H NMR (600 MHz, DMSO-d6) ꢂ7.88 (t, J ¼ 7:3 Hz, 2H),
7.85 (d, J ¼ 7:3 Hz, 2H), 7.68 (d, J ¼ 7:3 Hz, 2H), 6.06 (s, 2H);
13C NMR (150 MHz, DMSO-d6) ꢂ 158.7, 141.3, 141.0, 128.7, 123.3,
51.7; IR (neat) 3085, 2999, 1578, 1549, 1427, 1406, 1180, 1153,
1116, 988, 870, 799, 737 cmꢁ1; Found: C, 28.81; H, 1.57; Br, 64.23;
N, 5.59%. Calcd for C12H8Br4N2: C, 28.84; H, 1.61; Br, 63.95; N,
5.60%.
1,2-Bis(6-bromo-2-pyridyl)ethyne 1b. To a solution of potas-
sium t-butoxide (0.140 g, 1.25 mmol) in dry CH2Cl2 (20 mL) was
added 7 (0.300 g, 0.600 mmol) at ꢁ20 ꢂC. After being stirred at room
temperature for 24 h, the reaction mixture was quenched with
saturated aqueous NH4Cl and then extracted with CH2Cl2. The
organic layer was washed with H2O and brine, and then dried over
anhydrous MgSO4. After removal of the solvent, the residue was
recrystallized from CH2Cl2–hexane to give 1b (0.180 g, 90%) as a
white powder: mp 212.0–214.5 ꢂC; 1H NMR (600 MHz, CDCl3) ꢂ
7.58 (d, J ¼ 3:8 Hz, 2H), 7.58 (d, J ¼ 5:4 Hz, 2H), 7.51 (dd, J ¼ 5:2,
3.8 Hz, 2H); 13C NMR (150 MHz, CDCl3) ꢂ 142.6, 142.0, 138.5,

716 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
HEADLINE ARTICLES
128.4, 126.7, 87.8; IR (KBr) 3045, 2356, 1573, 1545, 1442, 1123, 790
cmꢁ1; FABMS (NBA) m=z 339 [(M + H)þ]; Found: C, 42.65; H,
1.82; Br, 47.03; N, 8.09%. Calcd for C12H6Br2N2: C, 42.64; H, 1.79;
Br, 47.28; N, 8.29%.
H)þ];Found:C, 75.76;H, 8.10;N, 6.26%. CalcdforC28H36N2OSi:C,
75.61; H, 8.18; N, 6.30%.
2-[6-(D)-Menthyloxymethyl-2-pyridylethynyl]-6-(trimethyl-
silylethynyl)pyridine 10d. This compound was prepared from 6-
bromo-2-[(D)-menthyloxymethyl]pyridine (9b) and compound (8)
according to the method used for the preparation of 10a. Yellow
powder; yield 85%; ½ꢃꢃD þ50:2 (c 1.20, CHCl3).
2-Ethynyl-6-(trimethylsilylethynyl)pyridine 8. To a solution
of 2,6-bis(ethynyl)pyridine (5.60 g, 44.0 mmol) was added dropwise
ethylmagnesium bromide, which was prepared from ethyl bromide
(3.6 mL, 48.3 mmol), Mg turnings (1.18 g, 48.6 mmol) and dry THF
(100 mL), at room temperature. After being stirred at the same
temperature for 2.5 h, the reaction mixture was quenched with
saturated aqueous NH4Cl, and extracted with AcOEt. The organic
layer was washed with H2O and brine, and then dried over anhydrous
MgSO4. After removal of the solvent, the residue was purified by
columnchromatography (silicagel, hexane–AcOEt) to give8(5.61 g,
2-(Methyloxymethyl)-6-(trimethylsilylethynyl)pyridine 10e.
This compound was prepared from 6-bromo-2-(methoxymethyl)pyr-
idine (9e) and trimethylsilylacetylene according to the method used
for the preparation of 10a. Colorless oil; yield 92%; 1H NMR (400
MHz, CDCl3) ꢂ 7.63 (t, J ¼ 7:8 Hz, 1H), 7.37 (d, J ¼ 8:8 Hz, 1H),
7.35 (d, J ¼ 8:3 Hz, 1H), 4.55 (s, 2H), 3.43 (s, 3H), 0.24 (s, 9H);
13C NMR (100 MHz, CDCl3) ꢂ 159.1, 142.2, 136.6, 126.1, 120.4,
103.6, 94.7, 75.2, 58.7, ꢁ0:3; IR (neat) 2950, 2900, 2850, 2150, 1580,
1440, 1250, 1120, 920, 840, 760 cmꢁ1; FABMS (NBA) m=z 220
[(M + H)þ]; Found: C, 65.53; H, 7.80; N, 6.13%. Calcd for
C12H17NOSi: C, 65.71; H, 7.81; N, 6.39%.
ꢂ
1
64%) as a yellow powder: mp 78.8–79.0 C; H NMR (400 MHz,
CDCl3) ꢂ 7.62 (t, J ¼ 7:8 Hz, 1H), 7.43 (d, J ¼ 7:8 Hz, 1H), 7.41 (d,
J ¼ 7:8 Hz, 1H), 3.14 (s, 1H), 0.26 (s, 9H); 13C NMR (100 MHz,
CDCl3) ꢂ 143.4, 142.5, 136.4, 126.6, 102.9, 95.6, 82.2, 77.6, ꢁ0:4;
FABMS (NBA) m=z 200 [(M + H)þ]; Found: C, 72.39; H, 6.60; N,
6.99%. Calcd for C12H13NSi: C, 72.31; H, 6.57; N, 7.03%.
2-[(t-Butyldimethylsilyloxy)methyl]-6-(trimethylsilylethyn-
yl)pyridine 10f. This compound was prepared from 2-bromo-6-[(t-
butyldimethylsilyloxy)methyl]pyridine (9f) and trimethylsilylace-
tylene according to the method used for the preparation of 10a.
Yellowoil;yield99%;1H NMR(400 MHz, CDCl3)ꢂ7.66 (t, J ¼ 7:8
Hz, 1H), 7.47 (dd, J ¼ 7:8, 0.7 Hz, 1H), 7.33 (dd, J ¼ 7:6, 0.5 Hz,
1H), 4.83 (s, 2H), 0.95 (s, 9H), 0.26 (s, 9H), 0.12 (s, 6H); 13C NMR
(100 MHz, CDCl3) ꢂ 162.0, 141.8, 136.6, 125.5, 119.3, 103.7, 94.4,
65.9, 25.9, 18.3, ꢁ0:3, ꢁ5:5; IR (neat) 3048, 2958, 2857, 2165, 1558,
1454, 1252, 1121, 843 cmꢁ1 FABMS (NBA) m=z 320 [(M + H)þ];
Found: C, 64.00; H, 8.83; N, 4.23%. Calcd for C17H29NOSi2: C,
63.89; H, 9.15; N, 4.38%.
2-[(L)-Menthyloxymethyl]-6-(trimethylsilylethynyl)pyridine
10a. To a solution of 6-bromo-2-[(L)-menthyloxymethyl]pyridine
(9a) (1.60 g, 4.90 mmol) in dry diethylamine (50 mL) was added
tetrakis(triphenylphosphine)palladium(0) (0.265 g, 0.229 mmol) at
room temperature. To the resulting solution was added dropwise
trimethylsilylacetylene (1.6mL, 11.3mmol) atthe sametemperature.
After being stirred at the same temperature for 18 h, the reaction
mixture was cooled to room temperature and then filtered through a
pad of Celite. The filtrate was evaporated to dryness under reduced
pressure to give an oily residue. The residue was purified by column
chromatography (silica gel, hexane–AcOEt) to give 10a (1.67 g,
99%)asayellowoil:½ꢃꢃD ꢁ63:5 (c 1.2, CHCl3);1H NMR(400MHz,
CDCl3) ꢂ 7.64 (t, J ¼ 7:8 Hz, 1H), 7.46 (d, J ¼ 7:8 Hz, 1H), 7.35 (d,
J ¼ 7:6 Hz, 1H), 4.78(d, J ¼ 13:7 Hz, 1H), 4.54 (d, J ¼ 13:7 Hz,
1H), 3.22 (dt, J ¼ 10:5, 4.1 Hz, 1H), 2.28 (dsp, J ¼ 6:8, 2.7 Hz, 1H),
2.18–2.14 (m, 1H), 1.68–1.61 (m, 2H), 1.43–1.19 (m, 2H), 1.04–0.78
(m, 9H), 0.74 (d, J ¼ 6:8 Hz, 3H); 13C NMR (100 MHz, CDCl3) ꢂ
160.2, 141.7, 136.4, 125.8, 120.6, 103.6, 94.3, 79.5, 71.0, 48.2, 40.2,
34.4, 31.4, 25.6, 23.1, 22.2, 20.9, 16.1, ꢁ0:4; IR (neat): 2954, 2920,
2-Ethynyl-6-[(L)-menthyloxymethyl]pyridine 2a. To a solu-
tion of 10a (2.60 g, 7.57 mmol) in methanol (60 mL) was added
ꢂ
potassium carbonate (0.052 g, 0.376 mmol) at 0 C. After being
stirred at the same temperature for 8 h, the reaction mixture was
quenched with saturated aqueous NH4Cl and extracted with AcOEt.
The organic layer was washed with H2O and brine, and then dried
overanhydrousMgSO4. Afterremovalofthesolvent, theresiduewas
purified by column chromatography (silica gel, hexane–AcOEt) to
give 2a (1.86 g, 90%) as a yellow oil: ½ꢃꢃD ꢁ83:5 (c 2.9, CHCl3);
1H NMR (400 MHz, CDCl3) ꢂ 7.68 (t, J ¼ 7:6 Hz, 1H), 7.51 (d,
J ¼ 7:8 Hz, 1H), 7.37(d, J ¼ 7:6 Hz, 1H),4.78(d, J ¼ 13:7 Hz, 1H),
4.54 (d, J ¼ 13:9 Hz, 1H), 3.23 (dt, J ¼ 10:5, 4.1 Hz, 1H), 3.14 (s,
1H), 2.29 (dsp, J ¼ 6:8, 2.7 Hz, 1H), 2.19–2.15 (m, 1H), 1.69–1.62
(m, 2H), 1.39–1.21 (m, 2H), 1.04–0.78 (m, 9H), 0.73 (d, J ¼ 6:8 Hz,
3H); FABMS (NBA) m=z 272 [(M + H)þ]. This compound and the
other ethynylpyridine derivatives (2b–f) were immediately used for
the next steps withoutfurtherpurification, because compounds (2a–f)
decomposed easily. Compounds (2b–f) were prepared according to
the method used for the preparation of 2a.
2868, 1582, 1568, 1447, 1250, 1113, 932, 843, 797, 760 cmꢁ1
;
FABMS (NBA) m=z 344 [(M + H)þ]; Found: C, 73.69; H, 9.52; N,
4.20%. Calcd for C21H33NOSi: C, 73.41; H, 9.68; N, 4.08%.
2-[(D)-Menthyloxymethyl]-6-(trimethylsilylethynyl)pyridine
10b. This compound was prepared from 6-bromo-2-[(D)-menthy-
loxymethyl]pyridine (9b) and trimethylsilylacetylene according to
the method used for the preparation of 10a. Yellow oil; yield 90%;
½ꢃꢃD þ64:0 (c 1.3, CHCl3).
2-[6-(L)-Menthyloxymethyl-2-pyridylethynyl]-6-(trimethyl-
silylethynyl)pyridine 10c. This compound was prepared from 6-
bromo-2-[(L)-menthyloxymethyl]pyridine (9a) and compound (8)
according to the method used for the preparation of 10a. Yellow
powder; yield 83%; mp 99.8–100.8 ꢂC; ½ꢃꢃD ꢁ54:2 (c 1.07, CHCl3);
1H NMR (400 MHz, CDCl3) ꢂ 7.65 (t, J ¼ 7:8 Hz, 1H), 7.57 (t,
J ¼ 7:8 Hz, 1H), 7.45 (d, J ¼ 6:8 Hz, 1H), 7.44 (d, J ¼ 6:8 Hz, 1H),
7.36 (d, J ¼ 7:8 Hz, 2H), 4.74 (d, J ¼ 13:7 Hz, 1H), 4.50 (d, J ¼
13:7 Hz, 1H), 3.18 (dt, J ¼ 10:7, 4.4 Hz, 1H), 2.23 (dsp, J ¼ 7:0, 2.9
Hz, 1H), 2.22–2.17 (m, 1H), 1.62–1.55 (m, 2H), 1.36–1.23 (m, 2H),
0.98–0.78 (m, 9H), 0.67 (d, J ¼ 6:8 Hz, 3H), 0.21 (s, 9H); 13C NMR
(100 MHz, CDCl3) ꢂ 160.4, 143.4, 142.9, 141.1, 136.7, 136.3, 126.9,
126.8, 126.2, 121.3, 102.9, 95.5, 88.1, 87.1, 79.5, 71.0, 48.2, 40.2,
34.4, 31.4, 25.6, 23.1, 22.2, 20.9, 16.0, ꢁ0:42; IR (KBr) 2940, 2850,
1580, 1450, 1250, 1115, 840 cmꢁ1; FABMS (NBA) m=z 445 [(M +
2-Ethynyl-6-[(D)-menthyloxymethyl]pyridine 2b. Yellow oil;
yield 86%; ½ꢃꢃD þ84:8 (c 2.7, CHCl3).
2-Ethynyl-6-[6-(L)-menthyloxymethyl-2-pyridylethynyl]pyr-
ꢂ
idine 2c. Yellow powder; yield 95%; mp 112.4–113.2 C; ½ꢃꢃD
ꢁ60:7 (c 1.22, CHCl3); 1H NMR (400 MHz, CDCl3) ꢂ 7.68 (t, J ¼
7:8 Hz, 1H), 7.65 (t, J ¼ 7:8 Hz, 1H), 7.56 (d, J ¼ 7:8 Hz, 1H), 7.49
(d, J ¼ 7:8 Hz, 1H), 7.47 (d, J ¼ 7:8 Hz, 1H), 7.42 (d, J ¼ 7:6 Hz,
1H), 4.77 (d, J ¼ 13:7 Hz, 1H), 4.53 (d, J ¼ 13:7 Hz, 1H), 3.21 (dt,
J ¼ 10:7, 4.4 Hz, 1H), 3.15 (s, 1H), 2.26 (dsp, J ¼ 7:0, 2.9 Hz, 1H),
2.16–2.10 (m, 1H), 1.65–1.59 (m, 2H), 1.39–1.26 (m, 2H), 1.01–0.78
(m, 9H), 0.70 (d, J ¼ 6:8 Hz, 3H); FABMS (NBA) m=z 373 [(M +
H)þ].
2-Ethynyl-6-[6-(D)-menthyloxymethyl-2-pyridylethynyl]-

T. Kawano et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
717
pyridine 2d. Yellow powder; yield 93%; ½ꢃꢃD þ60:0 (c 1.50,
CHCl3).
pyridylethynyl)pyridine L5. This compound was prepared from
1a and 2c according to the method used for the preparation of L1.
White powder; yield: 75%; mp 230 ꢂC (dec.); ½ꢃꢃD ꢁ54:6 (c 1.12,
CHCl3); 1H NMR (600 MHz, CDCl3) ꢂ7.75(t, J ¼ 7:7 Hz, 1H), 7.74
(t, J ¼ 7:7 Hz, 2H), 7.73 (t, J ¼ 7:7 Hz, 2H), 7.64 (d, J ¼ 7:7 Hz,
2H), 7.63 (dd, J ¼ 7:7, 1.1 Hz, 2H), 7.62 (dd, J ¼ 7:7, 1.1 Hz, 2H),
7.54 (d, J ¼ 7:7 Hz, 4H), 4.82 (d, J ¼ 13:6 Hz, 2H), 4.58 (d, J ¼
13:6 Hz, 2H), 3.25 (dt, J ¼ 10:7, 4.4 Hz, 2H), 2.31 (dsp, J ¼ 7:0, 2.9
Hz, 2H), 2.22–2.17 (m, 2H), 1.68–1.59 (m, 4H), 1.40–1.31 (m, 4H),
1.03–0.84 (m, 18H), 0.75 (d, J ¼ 7:0 Hz, 6H); 13C NMR (150 MHz,
CDCl3) ꢂ 160.6, 143.3, 143.0, 142.9, 141.2, 136.8, 136.8, 136.7,
127.6, 127.5, 127.4, 126.5, 121.5, 88.5, 87.8, 87.7, 87.0, 79.7, 71.1,
48.3, 40.4, 34.5, 31.5, 25.7, 23.2, 22.3, 21.0, 16.2; IR (neat) 2955,
2918, 2866, 1582, 1556, 1454, 1335, 1285, 1161, 1109, 984, 797, 727
cmꢁ1; UV (CH2Cl2) ꢁmax (log ") 324 (4.6), 296 (4.5), 267 (4.4) nm;
FABMS (NBA) m=z 820 [(M + H)þ]; Found: C, 80.34; H, 6.87; N,
8.41%. Calcd for C55H57N5O2: C, 80.55; H, 7.01; N, 8.54%.
2,6-Bis(6-{6-[(D)-menthyloxymethyl]-2-pyridylethynylg-2-
pyridylethynyl)pyridine L6. This compound was prepared from
1a and 2d according to the method used for the preparation of L1.
White powder; yield: 72%; ½ꢃꢃD þ53:6 (c 1.05, CHCl3); Found: C,
80.44; H, 6.98; N, 8.26%. Calcd for C55H57N5O2: C, 80.55; H, 7.01;
N, 8.54%.
2-Ethynyl-6-(methoxymethyl)pyridine 2e. Pale yellow oil;
yield 88%; 1H NMR (400 MHz, CDCl3): ꢂ 7.68 (t, J ¼ 7:8 Hz, 1H),
7.43 (d, J ¼ 7:8 Hz, 1H), 7.38 (d, J ¼ 8:1 Hz, 1H), 4.58 (s, 2H), 3.47
(s, 3H), 3.17 (s, 1H); FABMS (NBA) m=z 148 [(M + H)þ].
2-(t-Butyldimethylsilyloxymethyl)-6-(ethynyl)pyridine 2f.
Orangeoil;yield 97%;1H NMR(400 MHz, CDCl3) ꢂ7.69(t, J ¼ 7:8
Hz, 1H), 7.52 (dd, J ¼ 7:8 Hz, 1H), 7.35 (d, J ¼ 7:8 Hz, 1H), 4.83 (s,
2H), 3.13 (s, 1H), 0.96 (s, 9H), 0.12 (s, 6H); FABMS (NBA) m=z 248
[(M + H)þ].
2,6-Bis{6-[(L)-menthyloxymethyl]-2-pyridylethynylgpyri-
dine L1. To a solution of 2,6-dibromopyridine (1a) (0.240 g, 1.01
mmol) in diethylamine (40 mL) were added a solution of 2a (0.631 g,
2.32 mmol) in triethylamine (20 mL) and tetrakis(triphenylpho-
sphine)palladium(0) (0.060 g, 0.052 mmol) at room temperature.
After being stirred at 90 ꢂC for 18 h, the reaction mixture was cooled
to room temperature, and then filtered through a pad of Celite. The
filtrate was evaporated to dryness under reduced pressure to give an
oily residue. The residue was purified by column chromatography
(silica gel, AcOEt) to give L1 (0.574 g, 92%) as colorless plates: mp
121.5–122.5 ꢂC; ½ꢃꢃD ꢁ74:6 (c 1.08, CHCl3); 1H NMR (400 MHz,
CD2Cl2) ꢂ 7.74 (m, 3H), 7.58 (d, J ¼ 7:8 Hz, 2H), 7.51 (d, J ¼ 7:8
Hz, 4H), 4.78 (d, J ¼ 13:4 Hz, 2H), 4.52 (d, J ¼ 13:7 Hz, 2H), 3.25
(dd, J ¼ 4:2, 6.3 Hz, 2H), 2.30 (m, 2H), 2.19 (m, 2H), 1.69–1.62 (m,
4H), 1.46–1.29 (m, 4H), 1.10–0.83 (m, 18H), 0.77 (d, J ¼ 7:1 Hz,
6H); 13C NMR (100 MHz, CD2Cl2) ꢂ 161.1, 143.5, 141.5, 137.3,
137.1, 127.5, 126.6, 121.8, 88.6, 87.1, 80.0, 71.4, 48.8, 40.7, 35.0,
31.9, 26.2, 23.7, 22.5, 21.2, 16.4; IR (KBr) 2900, 2850, 2210, 1555,
1430, 1090, 770 cmꢁ1; UV (CH2Cl2) ꢁmax (log ") 320 (4.6), 294
(4.5), 265 (4.4) nm; FABMS (NBA) m=z 618 [(M + H)þ]; Found: C,
79.64; H, 8.08; N, 6.93%. Calcd for C41H51N3O2: C, 79.69; H, 8.34;
N, 6.80%.
2,6-Bis{6-[(D)-menthyloxymethyl]-2-pyridylethynylgpyri-
dine L2. This compound was prepared from 1a and 2b according to
the method used for the preparation of L1. Colorless plates; yield
90%; ½ꢃꢃD þ73:5 (c 0.98, CHCl3); Found: C, 79.87; H, 8.13; N,
6.59%. Calcd for C41H51N3O2: C, 79.69; H, 8.34; N, 6.80%.
1,2-Bis(6-{6-[(L)-menthyloxymethyl]-2-pyridylethynylg-2-
pyridyl)acetylene L3. Thiscompoundwaspreparedfrom1band2a
according to the method used for the preparation of L1. White
powder; yield: 86%; mp 201.0–203.0 ꢂC; ½ꢃꢃD ꢁ60:2 (c 1.08,
CHCl3); 1H NMR (600 MHz, CDCl3) ꢂ7.73 (t, J ¼ 7:7 Hz, 2H), 7.72
(t, J ¼ 7:7 Hz, 2H), 7.62 (dd, J ¼ 7:7, 1.1Hz, 2H), 7.62 (dd, J ¼ 7:7,
1.1Hz, 2H),7.54(d, J ¼ 7:7 Hz, 4H), 4.82 (d, J ¼ 13:6 Hz, 2H),4.58
(d, J ¼ 13:6 Hz, 2H), 3.25 (dt, J ¼ 10:6, 4.4 Hz, 2H), 2.30 (dsp,
J ¼ 7:0, 2.6 Hz, 2H), 2.22–2.17 (m, 2H), 1.68–1.59 (m, 4H), 1.39–
1.32 (m, 4H), 1.01–0.86 (m, 18H), 0.75 (d, J ¼ 7:0 Hz, 6H);
13C NMR (150 MHz, CDCl3) ꢂ 160.6, 143.3, 143.0, 141.2, 136.8,
136.7, 127.5, 127.4, 126.4, 121.5, 88.5, 87.8, 87.0, 79.7, 71.1, 48.3,
40.4, 34.5, 31.5, 25.7, 23.3, 22.3, 21.0, 16.2; IR (neat) 2964, 2918,
2847, 1582, 1556, 1454, 1107, 984, 797, 729 cmꢁ1; UV (CH2Cl2)
2,6-Bis[(6-methoxymethyl)-2-pyridylethynyl]pyridine L7.
This compound was preparedfrom1a and 2e according tothe method
used for the preparation of L1. Colorless plates; yield 93%; mp
111.5–113.5 ꢂC; 1H NMR (400 MHz, CDCl3) ꢂ 7.73 (t, J ¼ 7:8 Hz,
2H), 7.71 (dd, J ¼ 8:5, 8.7 Hz, 1H), 7.61 (dd, J ¼ 8:3 Hz, 2H), 7.55
(d, J ¼ 7:8 Hz, 2H), 7.46 (d, J ¼ 7:8 Hz, 2H), 4.62 (s, 4H), 3.49 (s,
6H); 13C NMR (100 MHz, CDCl3) ꢂ 159.4, 143.1, 141.6, 136.8,
136.5, 127.2, 126.2, 121.0, 88.3, 87.2, 75.2, 58.8; IR (KBr) 2960,
2920, 2800, 2200, 1580, 1450, 1100, 980, 910, 800, 790 cmꢁ1; UV
(CH2Cl2) ꢁmax (log ") 319 (4.6), 293 (4.5), 264 (4.4) nm; FABMS
(NBA) m=z 370 [(M + H)þ]; Found: C, 74.64; H, 5.09; N, 11.39%.
Calcd for C23H19N3O2: C, 74.78; H, 5.18; N, 11.37%.
1,2-Bis(6-{6-[t-butyldimethylsilyloxymethyl]-2-pyridyleth-
ynylg-2-pyridyl)acetylene L8. This compound was prepared from
1b and 2f according to the method used for the preparation of L1.
White powder; yield: 96%; mp 216 ꢂC (dec.); 1H NMR (600 MHz,
CDCl3) ꢂ 7.74 (t, J ¼ 7:7 Hz, 2H), 7.73 (t, J ¼ 7:3 Hz, 2H), 7.62 (d,
J ¼ 7:7 Hz, 4H), 7.55 (d, J ¼ 8:0 Hz, 2H), 7.52 (d, J ¼ 7:7 Hz, 2H),
4.87 (s, 4H), 0.97 (s, 18H), 0.13 (s, 12H); 13C NMR (150 MHz,
CDCl3) ꢂ 162.2, 143.2, 142.9, 141.1, 136.9, 136.6, 127.4, 127.4,
126.1, 120.0, 88.5, 87.7, 86.9, 65.8, 25.9, 18.3, ꢁ5:4; IR (KBr) 3054,
2930, 2857, 2327, 1577, 1461, 1254, 1112, 852 cmꢁ1; UV (CH2Cl2)
ꢁ
max (log ") 323 (4.65), 302 (4.49), 294 (4.53), 275 (4.47), 262 (4.53)
nm; FABMS (NBA) m=z 671 [(M + H)þ]; Found: C, 71.46; H, 6.72;
N, 8.15%. Calcd for C40H46N4O2Si2: C, 71.60; H, 6.91; N, 8.35%.
Chiral Trinuclear Copper(a) Helicate CL1: [Cu3(L1)3]-
(PF6)3. To a solution of tetrakis(acetonitrile)copper(a) hexafluor-
ophosphate (1.14 g, 2.98 mmol) in dichloromethane (30 mL) was
added dropwise a solution of L1 (1.84 g, 2.98 mmol) in dichlor-
omethane (70 mL) at room temperature. After being stirred at the
same temperature for 12 h, the reaction solution was evaporated to
dryness under reduced pressure to give the crude yellow crystals.
Recrystallization of the crude crystals from dichloromethane–hexane
gave the pure complex (CL1) (2.38 g, 97%) as yellow crystals: mp
ꢁ
max (log ") 322 (4.5), 296 (4.4), 266 (4.3) nm; FABMS (NBA) m=z
719 [(M + H)þ]; Found: C, 79.95; H, 7.24; N, 7.55%. Calcd for
C48H54N4O2: C, 80.19; H, 7.57; N, 7.79%.
1,2-Bis(6-{6-[(D)-menthyloxymethyl]-2-pyridylethynylg-2-
pyridyl)acetylene L4. This compound was prepared from 1b and
2b according to the method used for the preparation of L1. White
powder; yield: 86%; ½ꢃꢃD þ60:1 (c 1.15, CHCl3); Found: C, 79.90;
H, 7.40; N, 7.63%. Calcd for C48H54N4O2: C, 80.19; H, 7.57; N,
7.79%.
ꢂ
1
238–239 C; ½ꢃꢃD ꢁ61:8 (c 0.92, CH2Cl2); H NMR (400 MHz,
CD2Cl2) ꢂ 7.93 (t, J ¼ 7:8, 8.1 Hz, 2H), 7.87–7.79 (m, 3H), 7.28–
7.17 (m, 4H), 4.82 (d, J ¼ 13:4 Hz, 1H), 4.62 (d, J ¼ 13:2 Hz, 1H),
4.52 (d, J ¼ 13:2 Hz, 1H), 4.33 (d, J ¼ 13:7 Hz, 1H), 3.20–3.08 (m,
2H), 2.14 (t, J ¼ 7:1, 6.8 Hz, 2H), 1.62 (ddd, J ¼ 11:7, 10.2 Hz, 6H),
2,6-Bis(6-{6-[(L)-menthyloxymethyl]-2-pyridylethynylg-2-

718 Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
HEADLINE ARTICLES
1.28–1.16 (m, 4H), 0.99–0.70 (m, 18H), 0.66 (d, J ¼ 7:1 Hz, 3H),
0.52 (q, J ¼ 11:5, 11.7 Hz, 1H); 13C NMR (100 MHz, CD2Cl2) ꢂ
159.6, 159.2, 140.1, 139.6, 139.1, 128.6, 128.1, 124.9, 88.8, 80.7,
70.2, 69.8, 47.7, 47.5, 39.9, 39.5, 33.8, 31.1, 25.7, 25.4, 22.9, 22.7,
21.8, 21.6, 20.4, 15.9, 15.4; IR (KBr) 2875, 2820, 1570, 1540, 1440,
1095, 1065, 820, 783 cmꢁ1; UV (CH2Cl2) ꢁmax (log ") 297 (4.49),
227 (4.56) nm; Found: C, 59.33; H, 6.08; N, 5.06; P, 3.90; F, 13.89%.
Calcd for C41H51CuF6N3O2P: C, 59.58; H, 6.23; N, 5.09; P, 3.75; F,
13.79%.
Chiral Trinuclear Copper(a) Helicate CL2: [Cu3(L2)3]-
(PF6)3. This compound was prepared from L2 and [Cu(CH3-
CN)4]PF6 in 1:1 ratio according to the methods used for the
preparation of CL1. Yellow crystals; yield 95%; ½ꢃꢃD þ60:7 (c 1.32,
CH2Cl2);Found:C, 59.36;H, 6.08;N, 5.36;P, 3.48;F, 13.84%.Calcd
forC41H51CuF6N3O2P:C,59.58;H,6.23;N,5.09;P,3.75;F,13.79%.
Chiral Tetranuclear Copper(a) Helicate CL3: [Cu4(L3)3]-
(BF4)4. This compound was prepared from L3 and [Cu(CH3-
CN)4]BF4 in 1:1.4 ratio according to the methods used for the
preparation of CL1. Yellow blocks; yield 92%; mp 264 ꢂC (dec.);
½ꢃꢃD ꢁ418 (c 0.96, CH2Cl2); 1H NMR (600 MHz, CD2Cl2) ꢂ 7.94 (t,
J ¼ 7:7 Hz, 6H), 7.90 (t, J ¼ 7:7 Hz, 6H), 7.83 (d, J ¼ 7:3 Hz, 6H),
7.47 (dd, J ¼ 7:7, 1.1 Hz, 6H), 7.28 (dd, J ¼ 7:7, 0.7 Hz, 6H), 7.21
(dd, J ¼ 8:1, 1.1 Hz, 6H), 4.81 (d, J ¼ 13:6 Hz, 6H), 4.33 (d, J ¼
13:6 Hz, 6H), 3.10 (dt, J ¼ 10:6, 4.4 Hz, 6H), 2.12 (dsp, J ¼ 7:3, 2.9
Hz,6H),1.72–1.69(m, 6H),1.66–1.61(m, 12H),1.26–1.21(m, 12H),
0.94–0.75 (m, 54H), 0.65 (d, J ¼ 7:0 Hz, 18H); IR (neat) 3084, 2950,
2920, 2868, 2361, 1587, 1555, 1466, 1049, 804 cmꢁ1; Found: C,
62.49; H, 5.71; F, 11.15; N, 6.14%. Calcd for C144H162B4Cu4-
F16N12O6: C, 62.70; H, 5.92; F, 11.02; N, 6.09%.
7.14 (d, J ¼ 8:1 Hz, 6H), 4.58 (d, J ¼ 13:4 Hz, 6H), 4.38 (d, J ¼
13:4 Hz, 6H), 3.30 (s, 18H); 13C NMR (100 MHz, CD2Cl2): ꢂ 158.9,
140.8, 140.4, 139.9, 139.8, 129.0, 128.8, 125.6, 89.7, 89.2, 74.7, 59.2;
IR (KBr) 3030, 2890, 2780, 1570, 1540, 1440, 1100, 820, 785 cmꢁ1
;
UV (CH2Cl2) ꢁmax (log ") 295 (4.42), 232 (4.42) nm; Found: C,
47.52; H, 3.11; N, 7.25; P, 5.20; F, 19.55%. Calcd for C69H57-
Cu3F18N9O6P3: C, 47.80; H, 3.31; N, 7.27; P, 5.36; F, 19.72%.
Achiral Tetranuclear Copper(a) Helicate CL8: [Cu4(L8)3]-
(BF4)4. This compound was prepared from L7 and [Cu(CH3-
CN)4]BF4 in 1:1.4 ratio according to the methods used for the
preparation of CL1. Yellow blocks; yield 96%; mp 256 ꢂC (dec.);
1H NMR (400 MHz, CD2Cl2) ꢂ 7.96 (t, J ¼ 7:8 Hz, 6H), 7.85 (t,
J ¼ 7:8 Hz, 12H),7.45 (d, J ¼ 7:8 Hz, 6H), 7.28(d, J ¼ 7:6 Hz, 6H),
7.19 (d, J ¼ 7:8 Hz, 6H), 4.82 (d, J ¼ 14:8 Hz, 6H), 4.55 (d, J ¼
14:6 Hz, 6H), 0.86 (s, 54H), ꢁ0:04 (d, J ¼ 5:4 Hz, 36H); IR (KBr)
3086, 2932, 2858, 2360, 1557, 1468, 1049, 805 cmꢁ1; UV (CH2Cl2)
ꢁmax (log ") 301 (4.98), 273 (4.88) nm; Found: C, 55.24; H, 5.29; F,
11.90; N, 6.55%. Calcd for C120H138B4Cu4F16N12O6Si6: C, 55.13; H,
5.32; F, 11.63; N, 6.43%.
Crystal Structure Determination. Single crystals of CL7 were
grown from dichloromethane by the slow diffusion of hexane vapor.
Each single crystal was sealed into a glass capillary and mounted on a
crystal goniometer. The X-ray diffraction data were collected on a
Rigaku RAXIS-d imaging area detector with graphite monochro-
ꢁ
mated Mo-Kꢃ radiation (ꢁ ¼ 0:71070 A). Indexing was performed
from 3 oscillations that were exposed for 8.0 minutes. The camera
radius was 105.00 mm with the detector at the zero swing position,
and readout was performed inthe 0.100mmpixelmode. A total of40
data images (2.0 oscillation range) were collected, each being
exposed for 15.0 minutes. The data were corrected for Lorentz and
polarization effects. Calculations were carried out on an SGI Indy
usingtheteXsan19 crystallographicsoftwarepackagefromMolecular
Science Corporation. The structure was solved by direct methods of
SIR9220 and expanded using Fourier techniques. The non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were fixed in
Chiral Tetranuclear Copper(a) Helicate CL4: [Cu4(L4)3]-
(BF4)4. This compound was prepared from L4 and [Cu(CH3-
CN)4]BF4 in 1:1.4 ratio according to the methods used for the
preparation of CL1. Yellow blocks; yield: 95%; ½ꢃꢃD þ422 (c 1.12,
CH2Cl2).
Chiral Pentanuclear Copper(a) Helicate CL5: [Cu5(L5)3]-
(BF4)5. This compound was prepared as a diastereomer mixture
from L5 and [Cu(CH3CN)4]BF4 in 1:1.7 ratio according to the
methodsusedforthepreparationofCL1. Yellow powder; yield 89%;
1H NMR (600 MHz, CD2Cl2) ꢂ 7.96–7.87 (m, 6H), 7.83 (d, J ¼ 7:7
Hz, 2H), 7.81 (d, J ¼ 8:1 Hz, 1/3H), 7.49 (dd, J ¼ 8:1, 1.1 Hz, 1/3H),
7.47 (dd, J ¼ 8:1, 1.1 Hz, 2H), 7.46 (d, J ¼ 8:1 Hz, 2H), 7.44 (d,
J ¼ 8:4 Hz, 1/3H), 7.27 (d, J ¼ 7:7 Hz, 2H), 7.26 (d, J ¼ 8:4 Hz, 1/
3H), 7.23 (dd, J ¼ 7:7, 1.1 Hz, 6H), 7.18 (dd, J ¼ 8:1, 0.7 Hz, 1/3H),
4.81 (d, J ¼ 13:9 Hz, 2H), 4.63 (d, J ¼ 12:8 Hz, 1/3H), 4.51 (d,
J ¼ 12:8 Hz, 1/3H), 4.33 (d, J ¼ 13:6 Hz, 2H), 3.17 (dt, J ¼ 10:6,
4.4 Hz, 1/3H), 3.10 (dt, J ¼ 10:6, 4.1 Hz, 2H), 2.15–2.09 (m, 7/3H),
1.72–1.70 (m, 7/3H), 1.66–1.61 (m, 7/3H), 1.26–1.21 (m, 5H), 0.95–
0.77 (m, 22H), 0.65 (d, J ¼ 7:0 Hz, 6H); Found: C, 61.68; H, 5.31; F,
11.96; N, 6.66%. Calcd for C165H171B5Cu5F20N15O6: C, 61.70; H,
5.37; F, 11.83; N, 6.54%.
Chiral Pentanuclear Copper(a) Helicate CL6: [Cu5(L6)3]-
(BF4)5. This compound was prepared as a diastereomer mixture
from L6 and [Cu(CH3CN)4]BF4 in 1:1.7 ratio according to the
methodsusedforthepreparationofCL1. Yellow powder; yield 91%;
Found: C, 61.77; H, 5.36; F, 11.90; N, 6.72%. Calcd for C165H171B5-
Cu5F20N15O6: C, 61.70; H, 5.37; F, 11.83; N, 6.54%.
Achiral Trinuclear Copper(a) Helicate CL7: [Cu3(L7)3]-
(PF6)3. This compound was prepared from L7 and [Cu(CH3-
CN)4]PF6 in 1:1 ratio according to the methods used for the
preparation of CL1. Yellow prisms; yield 96%; mp >300 ꢂC;
1H NMR (400 MHz, CD2Cl2): ꢂ 7.86 (t, J ¼ 7:8 Hz, 6H), 7.79 (t,
J ¼ 7:8 Hz, 3H), 7.68 (d, J ¼ 7:8 Hz, 6H), 7.15 (d, J ¼ 8:1 Hz, 6H),
Table 3. Crystallographic Data of CL7 CH2Cl2
ꢄ
Formula
Fw
C70H59Cl2Cu3F18N9O6P3
1818.73
0:30 ꢅ 0:25 ꢅ 0:05
monoclinic
P21=c (No. 14)
13.797(2)
21.054(4)
27.27(2)
101.693(3)
7756(2)
4
Crystal size/mm
Crystal system
Space group
ꢁ
a/A
ꢁ
b/A
ꢁ
c/A
ꢄ/deg
ꢁ 3
V/A
Z
Dcalc/g cmꢁ3
T/K
ꢅ/cmꢁ1
1.557
288
10.45
3672
55.1
14846
Fð000Þ
2ꢆmax/deg
No. of reflections measured
No. of observed data (I > 3:0ꢇðIÞ)
10378
1000
0.01
0.069
0.071
No. of variables
Shift/Error
R
Rw
2
2
1=2
R¼ꢂkF0j ꢁ jFck=ꢂjF0j;Rw ¼½ꢂwðjF0j ꢁ jFcjÞ =ꢂwjF0j ꢃ
w ¼ 1=ꢇ2ðjF0jÞ
;

T. Kawano et al.
Bull. Chem. Soc. Jpn., 76, No. 4 (2003)
719
calculated positions. The refinement of the structure was performed
by full-matrix least-squares methods. Neutral atom scattering factors
were taken from the literature.21 The crystallographic data and
structure refinement parameters are summarized in Table 3. Crystal-
lographic data (excluding structure factors) for CL7 have been
deposited at the Cambridge Crystallographic Data Centre as
supplementary publication number CCDC 199007. Copies of the
data can be obtained free of charge from the CCDC (12 Union Road,
Cambridge CB2 1EZ, UK (http://www.ccdc.cam.ac.uk).
Angew. Chem., Int. Ed., 37, 290 (1998). c) C. Provent, S. Hewage, G.
Brand, G. Bernardinelli, L. Charbonniere, and A. F. Williams,
Angew. Chem., Int. Ed. Engl., 36, 1287 (1997). d) E. C. Constable, T.
Kulke, M. Neuburger, and M. Zehnder, Chem. Commun., 1997, 489.
e) C. R. Woods, M. Benaglia, F. Cozzi, and J. S. Siegel, Angew.
Chem., Int. Ed. Engl., 35, 1830 (1996). f) W. Zarges, J. Hall, J.-M.
Lehn, and C. Bolm, Helv. Chim. Acta, 74, 1843 (1991).
8 a) T. Kawano, T. Shinomaru, and I. Ueda, Org. Lett., 4, 2545
(2002). b) T. Kawano, J. Kuwana, T. Shinomaru, C.-X. Du, and I.
Ueda, Chem. Lett., 2001, 1230.
T. Kawano, J. Kuwana, C.-X. Du, and I. Ueda, Inorg. Chem.,
9
41, 4078 (2002).
We thank the Material Analysis Center of ISIR-Sanken, Osaka
University for assisting us with elemental analysis.
10 T. Kawano, T. Kato, C.-X. Du, and I. Ueda, Tetrahedron
Lett., 43, 6697 (2002).
11 D. Cai, D. L. Hughes, and T. R. Verhoeven, Tetrahedron
Lett., 37, 2537 (1996).
12 H. Tsukube, J. Uenishi, H. Higaki, K. Kikkawa, T. Tanaka,
S. Wakabayashi, and S. Oae, J. Org. Chem., 58, 4389 (1993).
13 M. Frigerio and M. Santagostino, Tetrahedron Lett., 35,
8019 (1994).
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7
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