Synthesis and extension/contraction motion of spiroborate-based double-stranded helicates consisting of substituted oligophenol strands

Article abstract of DOI:10.1016/j.tet.2011.11.079

A new class of ortho- and meta-substituted tetraphenols at the terminal phenyl residues with a biphenylene unit in the middle were synthesized and the effect of the substitution position on the spiroborate-based double-stranded helicate formation with sodium borohydride was investigated. The ortho-substitution considerably hampered the spiroborate formation between the terminal biphenol units and the boron atoms, whereas the meta-substituted oligomers formed a double-stranded helicate bridged by spiroborate groups accommodating a sodium cation in the center, which displayed an extension and contraction motion triggered by the removal and addition of sodium ions in solution.

Full text of DOI:10.1016/j.tet.2011.11.079

Tetrahedron 68 (2012) 4470e4478
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and extension/contraction motion of spiroborate-based double-
stranded helicates consisting of substituted oligophenol strands
*
Kazuhiro Miwa, Kaori Shimizu, Heejun Min, Yoshio Furusho, Eiji Yashima
Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A new class of ortho- and meta-substituted tetraphenols at the terminal phenyl residues with a biphe-
nylene unit in the middle were synthesized and the effect of the substitution position on the spiroborate-
based double-stranded helicate formation with sodium borohydride was investigated. The ortho-sub-
stitution considerably hampered the spiroborate formation between the terminal biphenol units and the
boron atoms, whereas the meta-substituted oligomers formed a double-stranded helicate bridged by
spiroborate groups accommodating a sodium cation in the center, which displayed an extension and
contraction motion triggered by the removal and addition of sodium ions in solution.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 25 October 2011
Accepted 24 November 2011
Available online 1 December 2011
Keywords:
Helicates
Double helix
Oligophenols
Spiroborate
Spring motion
1. Introduction
To this end, we synthesized a series of ortho- (2) and meta-
substituted (3) tetraphenol derivatives with a biphenylene unit in
Helicates are a class of unique metal complexes in which linear
organic ligands, such as pyridine- or phenanthroline-containing
molecular strands, coordinate with two or more transition metal
centers in a helical manner, resulting in the formation of multiple-
stranded helical structures.1,2 In contrast, the helicates that contain
typical metal cations are quite few and only a limited number of
helicates have been prepared using Liþ, Naþ, and Kþ.3,4 Recently, we
found that an ortho-linked hexaphenol (1a)4a and a tetraphenol
with a biphenylene unit in the middle (1b)4b formed unique
double-stranded helicates bridged by two spiroborates. The X-ray
crystallographic analyses of the helicates revealed that a Naþ ion
was accommodated in the center of the helicates coordinated by
oxygen atoms (12ꢀ$BNaB$Naþ) (Scheme 1A).4a,5 Due to the lack of the
central biphenol units in the 1bꢀ2$BNaB$Naþ helicate, the weakly
bound central Naþ ion could be removed by cryptand [2.2.1],
resulting in the formation of an extended helicate. Further, the
addition of a Naþ ion produced the original contracted helicate and
this ion-triggered extension/contraction spring-like motion could
be reversibly controlled by the successive addition and removal of
a Naþ ion in solutions (Scheme 1B).4b In order to apply this unique
twisting motion to the developments of future nanoscale me-
chanical devices6 and catalysis,7 further modification of the helicate
with specific functional groups may be essential.
the middle and investigated their spiroborate-based double-
stranded helicate formations with NaBH4 (Scheme 2).
2. Results and discussion
2.1. Synthesis of substituted hexamers
Four novel ortho-substituted hexamers (2ae2d) and two
meta-substituted hexamers (3a and 3b) strands were synthesized
starting from the tetramethoxy hexamer (6merMe)4b and 3,30-
dibromo-1,10-biphenyl, respectively, according to Schemes 3e6 (see
also Supporting Information).
The regioselective bromination at the ortho-position of the ter-
minal phenyl residues of 6merMe using benzyltrimethyl ammonium
tribromide (BTMA$Br3), followed by Pd-catalyzed Stille cross-
coupling with trimethyl(phenyl)tin gave the dibrominated hexamer
(6merMeeo-Br2), of which the methyl groups were removed by
treatment with BBr3 to afford the tetraphenol 2a (Scheme 3). In the
same way, the Pd-catalyzed Stille cross-coupling of 6merMeeo-Br2
with trimethyl(phenylethynyl)tin gave the desired o-phenylethynyl-
substituted hexamer in 30% isolated yield, but the further treatment
of the hexamer with BBr3 produced complex mixtures including by-
products formed by the reaction with the terminal o-phenylethynyl
residues. Therefore, the methyl groups were removed by treatment
with BBr3, yielding 2d, which was then allowed to react with ben-
zylbromide to give 6merBneo-Br2. The subsequent Pd-catalyzed
Stille cross-coupling with tri-n-butyl(phenylethynyl)tin followed by
* Corresponding author. Fax: þ81 52 789 3185; e-mail address: yashima@
apchem.nagoya-u.ac.jp (E. Yashima).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.11.079

K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
4471
Scheme 1. Synthesis of the boron helicate 12ꢀ$BNaB$Naþ
.
Scheme 2. Synthesis of the boron helicates consisting of ortho-substituted oligophenol strands (2ae2d) (A) and meta-substituted oligophenol strands (3a and 3b) (B).
Scheme 3. Synthesis of ligand 2a.

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K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
Scheme 4. Synthesis of ligands 2b and 2d.
deprotection of themethyl groupswithBBr3, respectively (Scheme 6).
Compound 6merMeem-I2 was synthesized by Suzuki-coupling of
4merMeeBr2 with 2-methoxy-4-trimethylsilylphenyl boronic acid,
each of which was prepared starting from 3,30-dibromo-1,10-biphenyl
and 3-trimethylsilylanisol, respectively, according to Supporting
Information.
2.2. Spiroborate-based double-stranded helicate formation
The spiroborate helicate formation was then investigated by
mixing the ortho- and meta-substituted hexamers with NaBH4 in
1,2-dichloroethane/ethanol (6:1, v/v) at 80 ꢁC for 20 h. Surpris-
ingly, 2a did not react with NaBH4 at all and the products from
2be2d were quite complicated based on the 1H NMR and elec-
trospray ionization (ESI) mass spectrometry studies, although the
ESI mass spectra in the negative mode indicated the formations of
the target helicate species of 2be2d bridged by two spiroborates
along with those bridged by one spiroborate (Figs. S1eS3). These
results suggest that the ortho-substitution appeared to consider-
ably hamper the spiroborate formation between the terminal
biphenol units and the boron atoms. This speculation was sup-
ported by the fact that the mono-ortho-substituted hexamer (2c)
bearing a phenylethynyl group also produced a complicated spe-
cies with NaBH4.
In sharp contrast, the meta-substituted hexamers (3a and 3b)
formed the corresponding boron helicates with an equimolar
amount of NaBH4 (3aꢀ2$BNaB$Naþ and 3bꢀ2$BNaB$Naþ) in 67 and 40%
yields, respectively, as supported by their ESI mass specꢀtra, show-
ing strong signals due to the monovalent anions (3a2$BNaB and
Scheme 5. Synthesis of ligand 2c.
hydrogenation afforded the tetraphenol derivative bearing phenyl-
ethyl substituents at the terminal ortho-position 2b (Scheme 4). The
mono-substituted hexamer 2c was also prepared in a similar way to
that of 2b. The methoxymethyl (MOM) groups were used as the
protecting groups to avoid the reduction of the ethynyl group
(Scheme 5).
Two meta-substituted hexamers (3a and 3b) strands were pre-
pared from the bis-iodide hexamer (6merMeem-I2) after treatment
with BBr3 or Suzuki-coupling with phenylboronic acid followed by
3bꢀ2$BNaB) at m/z¼1809.58 and 1609.75 along with signals due to the
2ꢀ
divalent anions (3a
and 3b22$ꢀBNaB) at m/z¼893.29 and 793.37,
2$BNaB
respectively (Fig. S4). The 1H NMR spectra of the helicates in CD3CN
also revealed the pseudo-D2-symmetric structures (Figs. 1b and 2b,
respectively); the aromatic protons on the terminal benzene rings
remarkably shifted upfield due to the ring current effect of the
benzene rings of the other strand as observed in 12ꢀ$BNaB$Naþ,4
while the t-Bu signals shifted downfield.

K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
4473
Scheme 6. Synthesis of ligands 3a and 3b.
2ꢀ
2ꢀ
2$BB
2.3. Extension and contraction motion of spiroborate-based
the solutions of 3a
and 3b
quantitatively regenerated the
2$BB
double-stranded helicates
original contracted helicates, 3aꢀ2$BNaB and 3bꢀ2$BNaB, respectively,
as evidenced by their 1H NMR spectral changes (Figs. 1d and 2d,
respectively). In addition, the absorption spectral changes of
3aꢀ2$BNaB$Naþ and 3b2ꢀ$BNaB$Naþ upon the addition of cryptand
[2.2.1], followed by NaPF6 also support the dynamic extension and
contraction motions that take place by the sequential addition of
cryptand [2.2.1] and NaPF6 (Fig. 3A and B, respectively) because
As we previously demonstrated, the weakly bound central Naþ
ion could be removed quantitatively from the 1bꢀ2$BNaB$Naþ heli-
cate assisted by cryptand [2.2.1], resulting in the formation of the
extended helicate (1b22$ꢀBB$(Naþ3221)2) (Scheme 1B).4b We then
added 2 equiv of the cryptand [2.2.1] to CH3CN solutions of
3a2ꢀ$BNaB$Naþ and 3b2ꢀ$BNaB$Naþ. The 1H NMR signals of the aro-
matic and t-Bu protons showed large downfield shifts (Figs. 1c and
2c, respectively) as well as the appearance of the signals assigned
to the cryptand [2.2.1] complexed with Naþ (Naþ3221), which are
in good accordance with those previously observed in the ex-
tended helicate (1b22$ꢀBB$(Naþ3221)2). Further addition of NaPF6 to
2ꢀ
2ꢀ
the absorption spectra of 3a
and 3b
were completely re-
2$BB
2$BB
covered to the initial state after the addition of NaPF6. These
complete recoveries of the absorption spectra unambiguously
indicate that the extension and contraction motions likely proceed
without any breaking and reformation process of the spiroborate
groups.
1
Fig. 1. Partial H NMR spectra (500 MHz, CD3CN, 25 ꢁC) of (a) 3a (black), (b) 3a2ꢀ$BNaB$Naþ (red), (c) (b)þ221 (2.0 equiv) (blue), and (d) (c)þNaPF6 (3.0 equiv).

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K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
1
Fig. 2. Partial H NMR spectra (500 MHz, CD3CN, 25 ꢁC) of (a) 3b (black), (b) 3b2ꢀ$BNaB$Naþ (red), (c) (b)þ221 (2.0 equiv) (blue), and (d) (c)þNaPF6 (2.0 equiv).
Fig. 3. Absorption spectral changes (CH3CN, 25 ꢁC, 0.1 mM, cell length¼0.1 cm) of (A) 3a2ꢀ$BNaB$Naþ and (B) 3b2ꢀ$BNaB$Naþ (a and d, red) before and (b and e, blue) after the addition
of 221 (2.0 equiv), and (c and f, dotted black) further addition of NaPF6 (3.0 equiv).
3. Conclusion
3,30-Dibromo-1,10-biphenyl,11 5-tert-butyl-2-methoxyphenylboronic
acid,12 and 6merMe were prepared according to the literature.
Melting points were measured on a Yanaco MP-500 micro
melting point apparatus and were uncorrected. NMR spectra were
measured on a Varian UNITY INOVA 500AS spectrometer operating
at 500 MHz for 1H and at 125 MHz for 13C. Absorption spectra were
measured using a JASCO V-570 spectrophotometer. Electrospray
ionization (ESI) mass spectra were recorded on a JEOL JMS-T100CS
mass spectrometer.
In conclusion, we have successfully prepared a series of ortho-
and meta-substituted tetraphenols with a biphenylene unit in the
middle and found an usual substitution effect on the formation of
the spiroborate-based helicates. The present results provide useful
information for further design of the spiroborate-based helicates
with functional units at the ends to develop fluorescent sensors,8
dynamic asymmetric catalysts,9 and molecular nanomachines,6,10
while maintaining their mechanical spring-like motions triggered
by the removal and addition of a sodium ion.
4.1.1. Compound 6merMeeo-Br2. To a solution of 6merMe (1.01 g,
1.25 mmol) in CHCl3 (14.0 mL) and CH3OH (10.0 mL) was added
BTMA$Br3 (2.44 g, 6.25 mmol) at room temperature, and the mix-
ture was stirred at 65 ꢁC for 5 h. After evaporating the solvents, H2O
(34 mL) was added and the residue was extracted with EtOAc
(3ꢂ34 mL). The combined organic layer was washed with brine
(34 mL), dried over anhydrous MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by flash
4. Experimental section
4.1. General
All starting materials were purchased from commercial suppliers
and were used without further purification unless otherwise noted.

K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
4475
chromatography (SiO2 (40 g), n-hexane/EtOAc¼10:0 to 95:5 (v/v))
to give 6merMeeo-Br2 as a white solid in 83% yield. 1H NMR
3.33 mmol) were dissolved in acetone (4.3 mL), and the mixture
was stirred at 60 ꢁC for 3 days. The solution was filtered and the
filtrate was evaporated to dryness. The crude product was purified
by silica gel column chromatography (SiO2 (75 g), n-hexane/
EtOAc¼10:0 to 10:1 (v/v)) to give 6merBneo-Br2 as a white solid in
(500 MHz, CDCl3, 25 ꢁC, 1.0 mM)
d 7.89 (br s, 2H, ArH), 7.59e7.67
(m, 4H, ArH), 7.55 (d, J¼2.4 Hz, 2H, ArH), 7.52 (t, J¼7.7 Hz, 2H, ArH),
7.42 (d, J¼2.6 Hz, 2H, ArH), 7.38 (d, J¼2.6 Hz, 2H, ArH), 7.37 (d,
J¼2.4 Hz, 2H, ArH), 3.58 (s, 6H, OCH3), 3.26 (s, 6H, OCH3), 1.36 (s,
18H, t-Bu), 1.32 (s, 18H, t-Bu).
65% yield. 1H NMR (500 MHz, CDCl3, 25 ꢁC, 0.8 mM)
d 7.81 (br s, 2H,
ArH), 7.61 (d, J¼2.5 Hz, 2H, ArH), 7.57e7.60 (m, 2H, ArH), 7.50e7.54
(m, 2H, ArH), 7.43e7.50 (m, 8H, ArH), 7.16e7.22 (m, 6H, ArH),
7.00e7.09 (m,12H, ArH), 6.63e6.68 (m, 4H, ArH), 4.69 (s, 4H, OCH2),
4.23 (s, 4H, OCH2), 1.34 (s, 18H, t-Bu), 1.29 (s, 18H, t-Bu).
4.1.2. Compound 6merMeeo-Ph2. To a solution of 6merMeeo-Br2
(288 mg, 0.300 mmol), LiCl (76.3 mg, 1.80 mmol), and PdCl2(PPh3)2
(8.42 mg, 0.0120 mmol) in toluene (2 mL) was added trimethyl(-
phenyl)tin (272
m
L, 1.50 mmol). After the mixture was stirred at
4.1.6. Compound 6merBneo-(C2Ph)2. To a solution of 6merBneo-
Br2 (99 mg, 0.078 mmol), LiCl (20 mg, 0.47 mmol), and
PdCl2(PPh3)2 (2.3 mg, 0.0032 mmol) in toluene (1 mL) was added
100 ꢁC for 7 h, saturated aqueous NH4Cl (10 mL) was added and the
mixture was then extracted with EtOAc (3ꢂ10 mL). To the com-
bined organic layer was added saturated aqueous KF (20 mL) and
the mixture was stirred for 14 h to remove tin as the precipitate.
After filtration, the organic layer was dried over anhydrous MgSO4,
filtered, and concentrated under reduced pressure. The crude
product was purified by flash chromatography (SiO2 (50 g), n-
hexane/EtOAc¼20:1 (v/v)) to give 6merMeeo-Ph2 as a white solid
tri-n-butyl(phenylethynyl)tin (139 mL, 0.400 mmol). After the
mixture was stirred at 100 ꢁC for 4 days, saturated aqueous NH4Cl
(2.6 mL) was added and the mixture was extracted with EtOAc
(4ꢂ10 mL). To the combined organic layer was added saturated
aqueous KF (20 mL) and the mixture was stirred for 14 h to remove
the tin as the precipitate. After filtration, the organic layer was then
dried over anhydrous MgSO4, filtered, and concentrated under re-
duced pressure. The crude product was purified by flash chroma-
tography (SiO2 (12 g), n-hexane/EtOAc¼10:0 to 9:1 (v/v)) to give
in 74% yield. 1H NMR (500 MHz, CDCl3, 25 ꢁC, 1.0 mM)
d 7.91 (br s,
2H, ArH), 7.60e7.67 (m, 8H, ArH), 7.52 (t, J¼7.7 Hz, 2H, ArH),
7.40e7.46 (m,10H, ArH), 7.32e7.34 (m, 4H, ArH), 3.34 (s, 6H, OCH3),
3.27 (s, 6H, OCH3), 1.37 (s, 18H, t-Bu), 1.36 (s, 18H, t-Bu).
6merBneo-(C2Ph)2 as
a
white solid in 32% yield. 1H NMR
7.83 (br s, 2H, ArH), 7.58e7.62
(500 MHz, CDCl3, 25 ꢁC, 0.8 mM)
d
4.1.3. Compound 6merHeo-Ph2 (2a). To a solution of 6merMeeo-
Ph2 (143 mg, 0.150 mmol) in CH2Cl2 (5.0 mL) was added a CH2Cl2
solution of BBr3 (1.0 M, 1.5 mL, 1.5 mmol) at ꢀ78 ꢁC under N2. After
being warmed to room temperature, the mixture was stirred for 14 h.
H2O (6.5 mL)wasthen added tothemixtureat0 ꢁC, whichwasstirred
at room temperature for 30 min. The mixture was then evaporated to
remove CH2Cl2 and the resultantaqueous solutionwasextractedwith
EtOAc (3ꢂ25 mL). The combined organic layer was washed with 1 M
HCl (25 mL) and brine (25 mL), dried over anhydrous MgSO4, filtered,
and concentrated under reduced pressure. The crude product was
purified by silica gel column chromatography (SiO2 (12 g), n-hexane/
EtOAc¼10:0 to 9:1 (v/v)) to give 2a as a white solid in 73% yield. Mp:
(m, 4H, ArH), 7.51e7.55 (m, 4H, ArH), 7.46e7.50 (m, 8H, ArH), 7.44
(t, J¼7.7 Hz, 2H), 7.31e7.35 (m, 2H, ArH), 7.14e7.18 (m, 6H, ArH),
7.10e7.14 (m, 4H, ArH), 6.99e7.07 (m, 6H, ArH), 6.63e6.68 (m, 4H,
ArH), 4.97 (s, 4H, OCH2), 4.24 (s, 4H, OCH2), 1.36 (s, 18H, t-Bu), 1.32
(s, 18H, t-Bu).
4.1.7. Compound 6merHeo-(PhEt)2 (2b). Compound 6merBneo-
(C2Ph)2 (64 mg, 0.049 mmol) and 30% Pd/C (60 mg) were dispersed
in THF (2 mL) and EtOH (0.2 mL), and the mixture was stirred at
60 ꢁC for 2 days under a H2 atmosphere. After being cooled to room
temperature, the mixture was filtered using Celite and washed with
CHCl3 and the solution was evaporated to dryness. The crude
product was purified by flash chromatography (SiO2 (12 g), n-
hexane/EtOAc¼10:0 to 10:1 (v/v)) to give 2b as a white solid in 81%
157e158 ꢁC.1H NMR (500 MHz, CDCl3, 25 ꢁC,1.1 mM)
d 7.85 (br s, 2H,
ArH), 7.62e7.67 (m, 2H ArH), 7.54e7.60 (m, 8H, ArH), 7.45e7.50 (m,
4H, ArH), 7.42 (d, J¼2.5 Hz, 2H, ArH), 7.35e7.41 (m, 8H, ArH), 3.34 (s,
6H, OCH3), 5.72 (s, 2H, OH), 5.64 (s, 2H, OH),1.36 (s,18H, t-Bu). HRMS
(negative mode ESI, CHCl3/CH3OH (1:1, v/v)): m/z calcd for [MꢀHþ]ꢀ
897.4883; found: 897.4867.
1
yield. Mp: 123e128 ꢁC. H NMR (500 MHz, CDCl3, 25 ꢁC, 1.0 mM)
d
7.83 (br s, 2H, ArH), 7.64e7.69 (m, 2H, ArH), 7.56e7.61 (m, 4H,
ArH), 7.42 (d, J¼2.6 Hz, 2H, ArH), 7.32 (d, J¼2.5 Hz, 2H, ArH),
7.27e7.30 (m, 4H, ArH), 7.21e7.25 (m, 4H, ArH), 7.16e7.20 (m, 4H,
ArH), 7.14 (d, J¼2.4 Hz, 2H, ArH), 5.51 (s, 2H, ArH), 5.47 (s, 2H, ArH),
2.93e3.03 (m, 8H, ArH), 1.37 (s, 18H, t-Bu), 1.29 (s, 18H, t-Bu); 13C
4.1.4. Compound 6merHeo-Br2 (2d). To a solution of 6merMeeo-
Br2 (2.0 g, 2.1 mmol) in CH2Cl2 (68 mL) was added a CH2Cl2 solution
of BBr3 (1.0 M, 28.3 mL, 28 mmol) at ꢀ78 ꢁC under N2. After being
warmed to room temperature, the mixture was stirred for 18 h. H2O
(96 mL) was then added to the mixture at 0 ꢁC, which was stirred at
room temperature for 30 min. The mixture was then evaporated to
remove CH2Cl2 and the resultant aqueous solution was extracted
with EtOAc (3ꢂ100 mL). The combined organic layer was washed
with 1 M HCl (110 mL) and brine (110 mL), dried over anhydrous
MgSO4, filtered, and concentrated under reduced pressure. The
crude product was purified by silica gel column chromatography
(SiO2 (40 g), n-hexane/EtOAc¼10:0 to 4:1 (v/v)) to give 2d as
a white solid in 82% yield. 1H NMR (500 MHz, CDCl3, 25 ꢁC, 1.1 mM)
NMR (125 MHz, CDCl3, 25 ꢁC, 1.0 mM)
d 149.3, 147.5, 144.5, 143.7,
142.5, 141.8, 138.6, 129.5, 129.1, 128.7, 128.6, 128.6, 128.6, 128.4,
128.1, 128.0, 128.0, 126.8, 125.9, 125.7, 124.0, 123.3, 77.4, 77.2, 76.9,
36.5, 34.5, 34.3, 33.4, 31.7, 31.7. HRMS (negative mode ESI, CHCl3/
CH3OH (1:1, v/v)): m/z calcd for [MꢀHþ]ꢀ 953.5468; found:
953.5509.
4.1.8. Compound 6merMeeo-Br. To a solution of 6merMe (1.57 g,
1.95 mmol) in CHCl3 (22 mL) and CH3OH (15.7 mL) was added
BTMA$Br3 (1.90 g, 4.87 mmol) at room temperature and the mix-
ture was stirred at 30 ꢁC for 17 h. After evaporating the solvents,
H2O (53 mL) was added, and the residue was extracted with EtOAc
(3ꢂ53 mL). The combined organic layer was washed with brine
(53 mL), dried over anhydrous MgSO4, filtered, and concentrated
under reduced pressure. The crude product was purified by flash
chromatography (SiO2 (100 g), n-hexane/EtOAc¼10:1 to 50:1 (v/v))
to give 6merMeeo-Br as a white solid in 35% yield. 1H NMR
d
7.83 (br s, 2H, ArH), 7.64e7.69 (m, 2H, ArH), 7.56e7.59 (m, 4H,
ArH), 7.55 (d, J¼2.4 Hz, 2H, ArH), 7.41 (d, J¼2.5 Hz, 2H, ArH), 7.31 (d,
J¼2.4 Hz, 2H, ArH), 7.29 (d, J¼2.5 Hz, 2H, ArH), 5.96 (s, 2H, OH), 5.59
(s, 2H, OH), 1.36 (s, 18H, t-Bu), 1.32 (s, 18H, t-Bu). HRMS (negative
mode ESI, CHCl3/CH3OH (1:1, v/v)): m/z calcd for [MꢀHþ]ꢀ
903.2454; found: 903.2440.
(500 MHz, CDCl3, 25 ꢁC, 4.5 mM)
d 7.89 (br s,1H, ArH), 7.87 (br s,1H,
ArH), 7.57e7.66 (m, 4H, ArH), 7.55 (d, J¼2.5 Hz, 1H, ArH), 7.48e7.54
(m, 2H, ArH), 7.87 (br s, 1H, ArH), 7.41 (d, J¼2.5 Hz, 1H, ArH),
7.37e7.40 (m, 4H, ArH), 7.36 (d, J¼2.7 Hz, 1H, ArH), 7.34 (t, J¼2.3 Hz,
4.1.5. Compound 6merBneo-Br2. Compound 2d (1.0 g, 1.1 mmol),
benzylbromide (0.66 mL, 5.6 mmol), and K2CO3 (460 mg,

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K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
1H, ArH), 6.94 (d, J¼8.7 Hz, 1H, ArH), 3.80 (s, 3H, OCH3), 3.58 (s, 3H,
OCH3), 3.26 (s, 3H, OCH3), 3.25 (s, 3H, OCH3), 1.36 (s, 9H, t-Bu), 1.36
(s, 9H, t-Bu), 1.33 (s, 9H, t-Bu), 1.32 (s, 9H, t-Bu).
The mixture was warmed to room temperature and stirred for 17 h.
After saturated NaHCO3 aqueous (5 mL) was added, the mixture
was extracted with EtOAc (3ꢂ10 mL). The combined organic layer
was washed with brine (10 mL), dried over anhydrous MgSO4, fil-
tered, and concentrated under reduced pressure. The crude product
was purified by recycling SEC using CHCl3 as the eluent to afford 2c
as a white solid in 87% yield. Mp: 132e133 ꢁC. 1H NMR (500 MHz,
4.1.9. Compound 6merHeo-Br. To a solution of 6merMeeo-Br
(486 mg, 0.551 mmol) in CH2Cl2 (16.4 mL) was added a CH2Cl2 so-
lution of BBr3 (1.0 M, 7.5 mL, 7.5 mmol) at ꢀ78 ꢁC under N2. After
being warmed to room temperature, the mixture was stirred for
20 h. H2O (23 mL) was then added to the mixture at 0 ꢁC, which was
stirred at room temperature for 30 min. The mixture was then
evaporated to remove CH2Cl2 and the resultant aqueous solution was
extracted with EtOAc (3ꢂ28 mL). The combined organic layer was
washed with 1 M HCl (28 mL) and brine (28 mL), dried over anhy-
drous MgSO4, filtered, and concentrated under reduced pressure.
The crude product was purified by silica gel column chromatography
(SiO2 (50 g), n-hexane/EtOAc¼10:0 to 25:1 (v/v)) to give 6merHeo-
CDCl3, 25 ꢁC, 4.5 mM)
d 7.88 (br s, 1H, ArH), 7.67e7.70 (m, 1H, ArH),
7.51e7.66 (m, 1H, ArH), 7.43 (d, J¼5.9 Hz, 1H, ArH), 7.41 (d, J¼5.9 Hz,
1H, ArH), 7.39 (d, J¼6.3 Hz,1H, ArH), 7.30e7.38 (m, 7H, ArH), 7.04 (s,
1H, ArH), 7.00 (d, J¼8.3 Hz, 1H, ArH), 6.19 (br s, 1H, OH), 5.75 (br s,
1H, OH), 5.66 (br s, 1H, OH), 5.60 (br s, 1H, OH), 1.38 (s, 9H, t-Bu),
1.36 (s, 9H, t-Bu), 1.35 (s, 9H, t-Bu), 1.33 (s, 9H, t-Bu); 13C NMR
(125 MHz, CDCl3, 25 ꢁC, 1.1 mM)
d 151.23, 151.05, 147.97, 147.24,
144.53, 144.27, 144.24, 143.90, 142.15, 141.19, 139.34, 138.33, 131.83,
130.16, 129.53, 129.15, 129.11, 128.93, 128.87, 128.79, 128.63, 128.62,
128.59, 128.36, 128.25, 128.16, 127.98, 127.94, 127.90, 126.94, 126.92,
126.91, 126.35, 124.98, 124.26, 124.18, 124.09, 122.60, 116.74, 110.27,
95.88, 83.95, 34.53, 34.49, 34.48, 34.38, 31.75, 31.71, 31.58. HRMS
(negative mode ESI, CHCl3/CH3OH (1:1, v/v)): m/z calcd for
[MꢀHþ]ꢀ 845.4570; found: 845.4597.
1
Br as a white solid in 78% yield. H NMR (500 MHz, CDCl3, 25 ꢁC,
0.8 mM) d 7.83e7.87 (m, 2H, ArH), 7.64e7.70 (m, 2H, ArH), 7.53e7.61
(m, 5H, ArH), 7.41 (t, J¼2.6 Hz, 2H, ArH), 7.36 (dd, J¼8.6, 2.5 Hz, 1H,
ArH), 7.33 (t, J¼2.2 Hz, 2H, ArH), 7.31 (d, J¼2.3 Hz, 1H, ArH), 7.29 (d,
J¼2.5 Hz, 1H, ArH), 7.02 (d, J¼8.5 Hz, 1H, ArH), 6.06 (s, 1H, OH), 5.72
(s, 1H, OH), 5.63 (s, 1H, OH), 5.61 (s, 1H, OH), 1.37 (s, 9H, t-Bu), 1.36 (s,
9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.33 (s, 9H, t-Bu).
4.1.13. Compound 6merMeem-TMS2. A mixture of 4merMeeBr2
(522 mg, 1.00 mmol), 1merMeeB-TMS (560 mg, 2.50 mmol), and
Pd(PPh3)4 (116 mg, 0.100 mmol) in toluene (10 mL) and 2 M aque-
ous K2CO3 (10 mL) was stirred at 100 ꢁC for 20 h under N2. After
extraction with EtOAc (100 mL), the organic layer was washed with
H2O (100 mL) and brine (100 mL), dried over anhydrous MgSO4,
filtered, and concentrated under reduced pressure. The crude
product was purified by flash chromatography (SiO2 (12 g), n-
hexane/EtOAc¼10:0 to 4:1 (v/v)) to give 6merMeem-TMS2 as
a white solid in 64% yield. 1H NMR (500 MHz, CDCl3, 25 ꢁC, 1.2 mM)
4.1.10. Compound 6merMOMeo-Br. To
a suspension of NaH
(29.4 mg, 1.22 mmol) in THF (1 mL) was added 6merHeo-Br
(100 mg, 0.121 mmol) at 0 ꢁC. The mixture was stirred at that
temperature for 20 min, and then MOMCl (44.0 mL, 0.580 mmol)
was added. The mixture was warmed to room temperature and
stirred for 6 h. After H2O (1 mL) was added to the mixture at 0 ꢁC,
the mixture was extracted with EtOAc (3ꢂ5 mL). The organic layer
was washed with brine (5 mL), dried over anhydrous MgSO4, fil-
tered, and concentrated under reduced pressure to give
6merMOMeo-Br as a white solid in 74% yield. 1H NMR (500 MHz,
d
7.91 (br s, 2H, ArH), 7.58e7.64 (m, 4H, ArH), 7.49 (t, J¼7.7, 7.7 Hz,
2H), 7.39 (d, J¼2.6 Hz, 2H, ArH), 7.35 (d, J¼7.3 Hz, 2H, ArH), 7.30 (d,
J¼2.6 Hz, 2H, ArH), 7.18 (dd, J¼7.3, 0.9 Hz, 2H, ArH), 7.12 (s, 2H, ArH),
3.83 (s, 6H, OCH3), 3.24 (s, 6H, OCH3),1.35 (s, 18H, t-Bu), 0.32 (s,18H,
TMS).
CDCl3, 25 ꢁC, 0.8 mM)
d 7.86 (br s, 1H, ArH), 7.82 (br s, 1H, ArH),
7.58e7.67 (m, 4H, ArH), 7.56 (d, J¼2.4 Hz, 1H, ArH), 7.46e7.54 (m,
2H, ArH), 7.43 (t, J¼2.7 Hz, 2H, ArH), 7.39e7.42 (m, 3H, ArH), 7.36 (d,
J¼2.6 Hz, 1H, ArH), 7.32 (dd, J¼8.6, 2.6 Hz, 1H, ArH), 7.14 (d,
J¼8.7 Hz, 1H, ArH), 5.12 (s, 2H, OCH2), 4.87 (s, 2H, OCH2), 4.42 (br s,
2H, OCH2), 4.37 (s, 2H, OCH2), 3.38 (s, 3H, OCH3), 3.06 (s, 3H, OCH3),
2.62 (s, 3H, OCH3), 2.59 (s, 3H, OCH3), 1.37 (s, 18H, t-Bu), 1.33 (s, 9H,
t-Bu), 1.33 (s, 9H, t-Bu).
4.1.14. Compound 6merMeem-I2. To a solution of 6merMeem-
TMS2 (451 mg, 0.539 mmol) in CH2Cl2 (250 mL) was added
a CH2Cl2 solution of ICl (1.0 M, 1.27 mL, 1.3 mmol) at ꢀ78 ꢁC
under N2. After being warmed to room temperature, the mixture
was stirred for 26 h. Na2S2O3 (1.0 M aqueous, 40 mL) was then
added under stirring over 1 h. The mixture was evaporated to
remove CH2Cl2 and the resultant aqueous solution was extracted
with EtOAc (2ꢂ100 mL). The combined organic layer was washed
with H2O (100 mL) and brine (100 mL), dried over anhydrous
MgSO4, filtered, and concentrated under reduced pressure. The
crude product was purified by flash chromatography (SiO2 (40 g),
n-hexane/EtOAc¼10:0 to 9:1 (v/v)) to give 6merMeem-I2 as
4.1.11. Compound
6merMOMeo-Br (65.8 mg, 65.6
and PdCl2(PPh3)2 (1.94 mg, 2.76
tri-n-butyl(phenylethynyl)tin (230
6merMOMeo-C2Ph. To
a
solution
of
mol),
mmol), LiCl (16.3 mg, 384
m
mmol) in toluene (1 mL) was added
m
L, 65.6 mol). After the mix-
m
ture was stirred at 100 ꢁC for 37 h, saturated aqueous NH4Cl
(2.5 mL) was added, and the mixture was extracted with EtOAc
(3ꢂ5 mL). To the combined organic layer was added saturated
aqueous KF (15 mL) and the mixture was stirred for 3 h to remove
the tin as the precipitate. After filtration, the organic layer was then
dried over anhydrous MgSO4, filtered, and concentrated under re-
duced pressure. The crude product was purified by flash chroma-
tography (SiO2 (12 g), n-hexane/EtOAc¼10:0 to 95:5 (v/v)) to give
6merMOMeo-C2Ph as a white solid in 66% yield. 1H NMR
1
a white solid in 93% yield. H NMR (500 MHz, CDCl3, 25 ꢁC,
1.1 mM)
d 7.88 (br s, 2H, ArH), 7.55e7.64 (m, 4H, ArH), 7.50 (t,
J¼7.7 Hz, 2H), 7.39 (d, J¼2.6 Hz, 2H, ArH), 7.37 (dd, J¼7.9, 1.6 Hz,
2H, ArH), 7.30 (s, J¼1.6 Hz, 2H, ArH), 7.24 (d, J¼2.6 Hz, 2H, ArH),
7.08 (d, J¼7.9 Hz, 2H, ArH), 3.80 (s, 6H, OCH3), 3.21 (s, 6H, OCH3),
1.35 (s, 18H, t-Bu).
(500 MHz, CDCl3, 25 ꢁC, 0.8 mM)
d 7.87 (br s,1H, ArH), 7.83 (br s,1H,
ArH), 7.58e7.67 (m, 4H, ArH), 7.46e7.57 (m, 6H, ArH), 7.39e7.45 (m,
4H, ArH), 7.29e7.38 (m, 5H, ArH), 7.14 (d, J¼8.8 Hz,1H, ArH), 5.10 (br
s, 4H, OCH2), 4.44 (br s, 2H, OCH2), 4.37 (s, 2H, OCH2), 3.38 (s, 3H,
OCH3), 3.04 (s, 3H, OCH3), 2.63 (s, 3H, OCH3), 2.59 (s, 3H, OCH3),1.38
(s, 9H, t-Bu), 1.36 (s, 9H, t-Bu), 1.36 (s, 9H, t-Bu), 1.33 (s, 9H, t-Bu).
4.1.15. Compound 6merHem-I2 (3a). To a solution of 6merMeem-
I2 (394 mg, 0.419 mmol) in CH2Cl2 (12.8 mL) was added a CH2Cl2
solution of BBr3 (1.0 M, 5.7 mL, 5.7 mmol) at ꢀ78 ꢁC under N2. After
being warmed to room temperature, the mixture was stirred for 7 h.
H2O (18 mL) was then added to the mixture at 0 ꢁC, which was
stirred at room temperature for 30 min. The mixture was then
evaporated to remove CH2Cl2 and the resultant aqueous solution
was extracted with EtOAc (3ꢂ25 mL). The combined organic layer
was washed with 1 M HCl (25 mL) and brine (25 mL), dried over
4.1.12. Compound 6merHeo-C2Ph (2c). To
6merMOMeo-C2Ph (40.0 mg, 39.1 mol) in CHCl3 (1 mL) and
CH3OH (1 mL) was added concd HCl aqueous (0.081 mL) at 0 ꢁC.
a
solution of
m

K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
4477
anhydrous MgSO4, filtered, and concentrated under reduced pres-
sure. The crude product was purified by silica gel column chroma-
tography (SiO2 (100 g), n-hexane/EtOAc¼10:0 to 2:1 (v/v)) to give 3a
as a white solid in 84% yield. Mp: 176e183 ꢁC. 1H NMR (500 MHz,
124.2, 123.8, 120.4, 115.9. HRMS (negative mode ESI, CHCl3/CH3OH
(1:1, v/v)): m/z calcd for [MꢀHþ]ꢀ, 785.3631; found: 785.3628.
4.1.19. Compound 3b2ꢀ$BNaB$Naþ. To a solution of 3b (17.6 mg,
CDCl3, 25 ꢁC, 1.1 mM)
d
7.77 (br s, 2H, ArH), 7.68e7.72 (m, 2H, ArH),
22.4
mmol) in 1,2-dichloroethane (3.0 mL) was added a solution of
7.61 (t, J¼7.7 Hz, 2H, ArH), 7.51e7.55 (m, 2H, ArH), 7.44 (d, J¼1.7 Hz,
2H, ArH), 7.40 (dd, J¼8.1,1.7 Hz, 2H, ArH), 7.38 (d, J¼2.5 Hz, 2H, ArH),
7.28 (d, J¼2.5 Hz, 2H, ArH), 7.06 (d, J¼8.0 Hz, ArH), 6.09 (s, 2H, OH),
5.60 (s, 2H, OH),1.35 (s,18H, t-Bu); 13C NMR (125 MHz, CDCl3, 25 ꢁC,
NaBH4 in ethanol (44.6 mM, 0.50 mL, 22 mmol) under N2. After
being stirred at 80 ꢁC for 20 h, the solvents were removed by
evaporation. The residue was then washed with n-hexane to give
3b2ꢀ$BNaB$Naþ as a white solid in 40% yield. Mp: >300 ꢁC. 1H NMR
1.1 mM)
d
155.6, 149.2, 144.5, 141.9, 140.4, 134.5, 130.7, 130.2, 129.8,
(500 MHz, CD3CN, 25 ꢁC, 0.9 mM)
d 7.27e7.38 (m, 16H, ArH),
129.7, 129.2, 128.6, 128.6, 126.8, 126.8, 126.1, 125.9, 93.9, 34.8, 31.7.
HRMS (negative mode ESI, CHCl3/CH3OH (1:1, v/v)): m/z calcd for
[MꢀHþ]ꢀ 885.0938; found: 885.0920.
7.14e7.24 (m, 12H, ArH), 7.05 (br s, 4H, ArH), 6.86 (br s, 4H, ArH),
6.74 (br s, 4H, ArH), 6.47e6.58 (m, 8H, ArH), 6.07 (br s, 4H, ArH),1.40
13
(s, 18H, t-Bu); C NMR (125 MHz, CD3CN, 25 ꢁC, 2.8 mM)
d 156.4,
151.3, 144.1, 142.4, 141.2, 140.9, 140.7, 133.6, 133.5, 133.1, 130.3, 129.1,
129.0, 128.7, 128.6, 128.4, 128.1, 127.5, 126.9, 125.8, 120.2, 119.1, 34.8,
31.9. HRMS (negative mode ESI, CHCl3/CH3OH (1:1, v/v)): m/z calcd
for [MꢀNaþ]ꢀ, 1609.6906; found: 1609.6834.
4.1.16. Compound 3a2ꢀ$BNaB$Naþ. To a solution of 3a (25.0 mg,
28.2
mmol) in 1,2-dichloroethane (3.8 mL) was added a solution of
NaBH4 in ethanol (44.6 mM, 0.63 mL, 28
m
mol) under N2. After
being stirred at 80 ꢁC for 20 h, the mixture was cooled to ambient
temperature to form a white precipitate, which was collected by
filtration, and dried in vacuo to afford 3aꢀ2$BNaB$Naþ as a white solid
Acknowledgements
1
in 67% yield. Mp: >300 ꢁC. H NMR (500 MHz, CD3CN, 25 ꢁC,
This work was supported in part by Grant-in-Aids for Scientific
Research (S) from the Japan Society for the Promotion of Science
(JSPS) and for Scientific Research on Innovative Areas, ‘Emergence
in Chemistry’ (21111508) from the MEXT, and the Knowledge
Cluster Initiative ‘Nagoya Nano-Technology Manufacturing Cluster’
of the MEXT, Japan. The authors are grateful to Assistant Professor
Dr. Daisuke Taura (Nagoya University) for helpful supports.
3.0 mM)
d 7.77 (br s, 2H, ArH), 7.68e7.72 (m, 2H, ArH), 7.61 (t,
J¼7.7 Hz, 2H, ArH), 7.51e7.55 (m, 2H, ArH), 7.44 (d, J¼1.7 Hz, 2H,
ArH), 7.40 (dd, J¼8.1, 1.7 Hz, 2H, ArH), 7.38 (d, J¼2.5 Hz, 2H, ArH),
7.28 (d, J¼2.5 Hz, 2H, ArH), 7.06 (d, J¼8.0 Hz, ArH), 6.62 (d, J¼8.2 Hz,
4H, ArH), 6.22 (br s, 4H, ArH), 1.40 (s, 36H, t-Bu); 13C NMR
(125 MHz, CD3CN, 25 ꢁC, 2.8 mM)
d 157.0, 151.1, 144.4, 141.2, 140.7,
133.1, 132.1, 131.8, 130.6, 130.2, 129.8, 129.4, 128.7, 128.5, 128.3,
126.7, 126.4, 93.3, 34.8, 31.9. HRMS (negative mode ESI, CHCl3/
CH3OH (1:1, v/v)): m/z calcd for [MꢀNaþ]ꢀ, 1809.1515; found
1809.1458.
Supplementary data
The experimental details for the synthesis of 4merMe, 4mer-
MeeBr, and 1merMeeB-TMS; ESI mass spectroscopic data for the
reaction products of 2b, 2c, and 2d with NaBH4, and those for
3aꢀ2$BNaB$Naþ and 3b2ꢀ$BNaB$Naþ. Supplementary data associate with
this article can be found at doi:10.1016/j.tet.2011.11.079.
4.1.17. Compound 6merMeem-Ph2. A mixture of 6merMeem-I2
(500 mg, 0.550 mmol), phenylboronic acid (184 mg, 1.51 mmol),
and Pd(PPh3)4 (70 mg, 0.061 mmol) in toluene (10 mL) and 2 M
aqueous K2CO3 (10 mL) was stirred at 100 ꢁC for 20 h under N2.
The mixture was then extracted with EtOAc (50 mL) and the or-
ganic layer was washed with H2O (50 mL) and brine (50 mL), dried
over anhydrous MgSO4, filtered, and concentrated under reduced
pressure. The crude product was purified by flash chromatography
(SiO2 (12 g), n-hexane/EtOAc¼10:0 to 4:1 (v/v)) to give
6merMeem-Ph2 as a white solid in 58% yield. 1H NMR (500 MHz,
References and notes
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CDCl3, 25 ꢁC, 0.9 mM)
d
7.93 (t, J¼1.7 Hz, 2H, ArH), 7.58e7.70 (m,
8H, ArH), 7.33e7.54 (m, 14H, ArH), 7.27 (d, J¼1.8 Hz, 1H, ArH),
7.25e7.27 (m, 4H, ArH), 3.89 (s, 6H, OCH3), 3.27 (s, 6H, OCH3), 1.38
(s, 18H, ArH).
4.1.18. Compound 6merHem-Ph2 (3b). To
a
solution of
6merMeem-Ph2 (235 mg, 0.337 mmol) in CH2Cl2 (6 mL) was added
a CH2Cl2 solution of BBr3 (1.0 M 3.2 mL, 3.2 mmol) at ꢀ78 ꢁC under
N2. After being warmed to room temperature, the mixture was
stirred for 24 h. H2O (10 mL) was then added to the mixture at 0 ꢁC,
which was stirred at room temperature for 30 min. The mixture
was then evaporated to remove CH2Cl2 and the resultant aqueous
solution was extracted with EtOAc (50 mL). The combined organic
layer was washed with H2O (50 mL), and brine (50 mL), dried over
anhydrous MgSO4, filtered, and concentrated under reduced pres-
sure. The crude product was purified by silica gel column chro-
matography (SiO2 (50 g), n-hexane/EtOAc¼5:1 (v/v)) to give 3b as
a white solid in 77% yield. Mp: 145e146 ꢁC. 1H NMR (500 MHz,
CDCl3, 25 ꢁC, 0.9 mM)
d 7.84 (br s, 2H ArH), 7.69e7.73 (m, 2H, ArH),
7.59e7.67 (m, 6H, ArH), 7.55e7.59 (m, 2H, ArH), 7.40e7.48 (m, 8H,
ArH), 7.35e7.39 (m, 4H, ArH), 7.30e7.34 (m, 4H, ArH), 6.05 (s, 2H,
ArH), 5.67 (s, 2H, OH), 1.37 (s, 18H, t-Bu); 13C NMR (125 MHz, CDCl3,
25 ꢁC, 2.8 mM)
d
153.8, 147.0, 144.8, 143.1, 141.8, 140.5, 138.3, 131.9,
129.9, 129.0, 128.6, 128.6, 128.5, 128.5, 127.9, 127.7, 127.2, 127.0,

4478
K. Miwa et al. / Tetrahedron 68 (2012) 4470e4478
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9601e9605.
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