Ir-catalyzed synthesis of substituted tribenzosilepins by dehydrogenative C-H/Si-H coupling

Article abstract of DOI:10.1021/acs.joc.8b00233

The Ir-catalyzed intramolecular reaction of 2′,6′-diaryl-2-(hydrosilyl)biphenyls gave substituted tribenzosilepins by direct dehydrogenative C-H/Si-H coupling. This is the first example of catalytic construction of the tribenzosilepin skeleton. Enantiomer

Full text of DOI:10.1021/acs.joc.8b00233

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Ir-Catalyzed Synthesis of Substituted Tribenzosilepins
by Dehydrogenative C-H/Si-H Coupling
Takanori Shibata, Ninna Uno, Tomoya Sasaki, Hideaki Takano, Tatsuki Sato, and Kyalo Stephen Kanyiva
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b00233 • Publication Date (Web): 19 Mar 2018
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IrꢀCatalyzed Synthesis of Substituted Tribenzosilepins
by Dehydrogenative CꢀH/SiꢀH Coupling
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Takanori Shibata,*†,‡ Ninna Uno,† Tomoya Sasaki,† Hideaki Takano,† Tatsuki Sato,† and Kyalo Stephen
Kanyiva§
†Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda
University, Shinjuku, Tokyo, 169ꢀ8555, Japan
‡JST, ACTꢀC, 4ꢀ1ꢀ8 Honcho, Kawaguchi, Saitama 332ꢀ0012, Japan
§Global Center for Science and Engineering, School of Advanced Science and Engineering, Waseda
University, 3ꢀ4ꢀ1 Okubo, Shinjuku, Tokyo 169ꢀ8555, Japan
tshibata@waseda.jp
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
ABSTRACT. The Irꢀcatalyzed intramolecular reaction of 2’,6’ꢀdiarylꢀ2ꢀ(hydrosilyl)biphenyls gave
substituted tribenzosilepins by direct dehydrogenative CꢀH/SiꢀH coupling. This is the first example of
catalytic construction of the tribenzosilepin skeleton. Enantiomerically pure tribenzosilepin was
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prepared by optical resolution using chiral HPLC, and its inversion barrier was calculated by
measurement of rate of racemization using the Eyring kinetic equation under heating conditions.
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INTRODUCTION
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Heteropin has a sevenꢀmembered 8π conjugated system including a heteroatom (Z) in the ring system. It
is tubꢀshaped and nonꢀaromatic.1 Tribenzoheteropin is a threeꢀbenzeneꢀfused heteropin, the
saddleꢀshaped structure of which is generally more stable than that of heteropin.2 Tribenzoheteropins,
such as tribenzazepin (Z = NR), tribenzoxepin (Z = O), and tribenzosilepin (Z = SiR2), are found in the
substructures of functional materials.3 Among various tribenzoheteropins, a method for the synthesis of
tribenzosilepin remains undeveloped: the reaction of the dilithium salt of a teraryl compound with
dimethylsilyl dichloride has been reported, but the yield is very low (3.5%).4,5 While there are many
reports on the synthesis of other tribenzoheteropins, strategy for the catalytic construction of the
heteropin core have been quite limited: consecutive SuzukiꢀMiyaura coupling was reported for the
synthesis of tribenzoxepins and a tribenzazepin (eq 1 in Scheme 1).6 In contrast, we recently reported
the catalytic and enantioselective [2+2+2] cycloaddition of sulfurꢀcontaining 1,8ꢀdiynes with an alkyne
for the synthesis of chiral tribenzothiepins (eq 2 in Scheme 1).7 In the course of this study, we examined
the reaction of siliconꢀcontaining 1,8ꢀdiynes for the synthesis of tribenzosilepins and realized a Ni
complexꢀmediated cycloaddition (eq 3 in Scheme 1), but we could not achieve a catalytic reaction.
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Scheme 1. Catalytic Construction of Heteropin Core and Cycloaddition for the Synthesis of
Tribenzosilepin
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We here considered the use of dehydrogenative CꢀH/SiꢀH coupling for the construction of a silepin
core. Kuninobu and Takai originally developed the Rhꢀcatalyzed CꢀH/SiꢀH coupling of 2ꢀbiarylsilanes
for the synthesis of dibenzosilole,8 and Takai’s group and another group reported the further use of this
transformation,9 including enantioselective variants.10 To suppress the formation of fiveꢀmembered
silole, we designed a 2’ꢀsubstitutedꢀ6’ꢀarylꢀ2ꢀbiphenyl silane for the selective construction of a
sevenꢀmembered ring (eq 4).
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RESULTS AND DISCUSSION
We chose 2’,6’ꢀdiphenylꢀ2ꢀ(dimethylhydrosilyl)biphenyl (1a) as a model substrate and subjected it
to dehydrogenative CꢀH/SiꢀH coupling using Rh or Ir catalyst having a racꢀBINAP ligand in refluxing
toluene (eq 5). The iridium catalyst gave desired tribenzosilepin 2a in a better yield of 18% along with
desilylated product and silanol, which is probably a hydrolyzed product resulting from the presence of
water.11 When the Irꢀcatalyzed reaction was conducted under dehydrated conditions in the presence of
MS4A, a significant increase in the yield was observed.
To further increase the yield, we screened phosphine ligands for the Irꢀcatalyzed reaction (Table 1).
While a monoꢀphosphine ligand was ineffective, a diphosphine ligand possessing a longer alkylene
tether gave a better yield of 2a, and DPPB achieved a moderate yield of 58% (entries 1ꢀ4).
orthoꢀphenyleneꢀtethered diphosphine resulted in the best yield of ca. 70% (entry 5). A comparable yield
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was achieved in the absence of 4Å molecular sieves through the use of freshly distilled toluene as a
solvent (entry 6). Since the addition of a bulky alkene as a hydrogen acceptor8b further increased the
yield, we determined that this represented the optimal reaction conditions (entry 7). Moreover,
recrystallization of 2a gave a single crystal, which was submitted to Xꢀray analysis and its
saddleꢀshaped structure was ascertained (Figure 1).
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Table 1. Screening of Phosphine Ligand for Ir-Catalyzed C-H/Si-H Coupling of 1a
entry ligand
additive
yield (%)
a
1
PPh3
4Å MS (600 wt%)
4Å MS (600 wt%)
4Å MS (600 wt%)
4Å MS (600 wt%)
trace
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2
DPPE
DPPP
DPPB
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68
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6b
DPPBen 4Å MS (600 wt%)
DPPBen none
3,3ꢀdimethylbutꢀ1ꢀene
7b
DPPBen
(1 equiv)
77
a Triphenylphosphine (40 mol %) was used. b Freshly distilled toluene was used as a solvent.
Ligand:
DPPE:
1,2ꢀbis(diphenylphosphino)ethane;
DPPP:
1,3ꢀbis(diphenylphosphino)propane;
DPPB:
1,4ꢀbis(diphenylphosphino)butane; DPPBen: 1,2ꢀbis(diphenylphosphino)benzene
Figure 1. ORTEP Diagram of Compound 2a (thermal ellipsoids shown at 50% probability)
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The substrate scope of the present Irꢀcatalyzed CꢀH/SiꢀH coupling was examined under the optimal
conditions (Table 2). When both electronꢀdonating and ꢀwithdrawing groups were installed at the
paraꢀposition of the two aryl groups, the corresponding tribenzosilepins 2bꢀ2d were obtained in
acceptable yields (entries 1ꢀ3). However, trifluoromethyl as a stronger electronꢀwithdrawing group
suppressed the reaction, 2e was obtained in a moderate yield as a mixture with the desilylated product
(entry 4). The methylꢀsubstituted tetraarylsilane 1f was transformed into tribenzosilepin 2f in high yield
(entry 5).
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Table 2. Substrate Scope of Ir-Catalyzed C-H/Si-H Coupling
entry
R1
R2
H
yield (%)
2b, 67
2c, 84
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5
MeO
Me
Cl
1b
1c
1d
1e
1f
H
H
2d, 67
2e, 45a
2f, 90
CF3
H
H
Me
a NMR yield.
In the reaction of metaꢀsubstituted substrate 1g, while there are two CꢀH bonds that may be cleaved,
the less hindered CꢀH bond was selectively cleaved, and tribenzosilepin 2g was obtained as a sole
product in the best yield of 92% among all entries (eq 6).
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Naphthaleneꢀcontaining substrate 1h was also used in this reaction, and selective formation of a
sevenꢀmembered ring was achieved, while the formation of a sixꢀmembered ring by CꢀH bond
activation of the peri position of the naphthalene ring was not be observed at all (eq 7).12
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In the reaction of methylꢀ and phenylꢀsubstituted biphenylsilane 1i, sp3 CꢀH bond cleavage at the
benzylic position also proceeded13 in addition to sp2 CꢀH bond cleavage, and the yield of tribenzosilepin
2i was low (eq 8).
All of substituted tribenzoheteropins potentially have chirality, but their stability strongly depends
on the heteroatom and the substituent(s).6a We examined the optical resolution of tribenzosilepin 2b by
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chiral HPLC, but could not completely resolve the racemic mixture because of its low polarity.
However, when we transformed it to polar diol 3b by using an excess amount of BBr3 (eq 9),14 we
achieved complete separation by chiral HPLC. We measured the circular dichroism (CD) spectra of the
two isolated fractions (faster and slower): they displayed perfect mirror symmetry, which indicated that
they are enantiomers (Figure 2). The simulated CD spectrum of (S,R)ꢀ3b was in good agreement with the
experimental results, and revealed that it corresponded to the slower peak.
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Me
Me
OH
Si
R
S
HO
Figure 2. (a) CD spectra of both enantiomers of 3b (faster: green curve, slower: blue curve). CD spectra
of 3b in CH3CN solution (green:1.27×10ꢀ3 M, blue:1.01×10ꢀ3 M). Maximum values were 205, 219, 238,
260, 286, 304 nm. (b) TDꢀDFT calculations of (S,R)ꢀisomer (red bar). Simulated CD spectrum was
calculated by timeꢀdependent DFT method at the CAMꢀB3LYP level of theory with 6ꢀ31G(d,p) basis
set using Gaussian 09 program.
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Tribenzosilepin 3b was stable at 60 °C for 1 h, but racemization was observed at 90 °C. The rate
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constant of racemization for 3b at 90 °C (363 K) was determined to be 1.03×10ꢀ5 sꢀ1, and the barrier to
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saddle inversion (∆G‡) was calculated to be 29.7 kcal per mole, according to the Eyring equation
(Figure 3),15 which means that the halfꢀlife of 3b at 20 °C (293 K) is 24 years,16 and that it hardly
racemizes at room temperature.
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Figure 3. Rate of racemization. Plot of ln[a/(aꢀ2x)] versus t (s), a is the concentration of an enantiomer
of 3b (a = 1.00) and x is the concentration of newly generated opposite enantiomer at time t. A linear
curve fitting equation
CONCLUSIONS
In summary, we achieved the first catalytic construction of a tribenzosilepin skeleton by Irꢀcatalyzed
CꢀH/SiꢀH coupling. The intramolecular reaction of 2’,6’ꢀdiarylꢀ2ꢀ(dimethylhydrosilyl)biphenyls gave
substituted tribenzosilepin derivatives along with the formation of a sevenꢀmembered ring. An
enantiomerically pure tribenzosilepin was prepared by optical resolution, and the inversion barrier of the
chiral saddleꢀshaped molecule was elucidated.
EXPERIMENTAL SECTION
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1
General: HꢀNMR spectra were recorded on JEOL ALꢀ500 (500 MHz) spectrometers. The chemical
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3
shifts were reported in parts per million (δ) relative to internal TMS (0 ppm) for CDCl3. The coupling
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13
constants, J, are reported in Hertz (Hz). C NMR spectra were obtained by JEOL ALꢀ500 (125 MHz)
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spectrometer and referenced to the internal solvent signal (central peak is 77.0 ppm) in CDCl3). 19F
NMR spectra were obtained by JEOL ALꢀ500 (470 MHz) spectrometer and trifluoroacetic acid was
used as an external standard. CDCl3 was used as a NMR solvent. Highꢀresolution mass spectra (HRMS)
were measured on a TOFMS using JMSꢀT100CS with ESI (Electro Spray Ionization) method and
DART (Direct Analysis in Real Time) method.16 Preparative thinꢀlayer chromatography (PTLC) was
performed with silica gelꢀprecoated glass plates (Wakogel Bꢀ5F) prepared in our laboratory. Flash
column chromatography was performed over silica gel 200ꢀ300. All reagents were weighed and handled
in air and backfilled with argon at room temperature. Unless otherwise noted, all reactions were
conducted under an argon atmosphere. Toluene was distilled from CaH2 under an argon atmosphere and
was used immediately as a solvent. All reagents were purchased from Wako, Kanto, Aldrich, TCI, and
Strem and used without further purification.
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Synthetic scheme for the preparation of substrates 1
An experimental procedure for the synthesis of 2,6-diphenyliodobenzene: A solution of
phenylmagnesium bromide was prepared from Mg (390 mg, 16 mmol) in dry THF (15 ml) and
bromobenzene (1.7 ml, 16 mmol). To this solution, a solution of 1,3ꢀdibromoꢀ2ꢀiodobenzene (1.45 g,
4.0 mmol) in dry THF (12 ml) was added dropwise, and the resulting mixture was stirred at room
temperature for 3 hours. After cooling to 0 °C, a solution of I2 (3.25 g, 12.8 mmol) in dry THF (12 ml)
was added dropwise to the above mixture. The solution was stirred overnight at 0 °C. After the
quenched with a saturated aqueous Na2S2O3, the mixture was extracted with Et2O. the organic layer was
dried over Na2SO4, filtered and concentrated under reduced pressure.18 The crude products were
purified by column chromatography on silica gel (hexane only) to give 2,6ꢀdiphenyliodobenzene (981
mg, 2.75 mmol, 69%), whose physical properties were accorded with those in the literature.19 In the
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case of substituted 2,6ꢀdiphenyliodobenzenes, the crude products were passed through a short plug of
silica gel and subject them to next reaction without further purification.
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An experimental procedure for the synthesis of 2-bromo-6’-phenyl-1,1’:2’,1”-terphenyl: To a
solution of 2,6ꢀdiphenyliodobenzene (425 mg, 1.2 mmol) in dry toluene (18 ml) at ꢀ20 °C was added
nꢀBuLi (1.6 ml, 1.55 M in hexane) dropwise over 5 min under an atmosphere of argon. After stirring for
5 min, 1,2ꢀdibromobenzene (0.22 ml, 1.8 mmol) was added dropwise over 5 min, and the resulting
mixture was allowed to warm to room temperature, and stirred for 2 h. After the reaction was quenched
with MeOH (9 ml) at ꢀ78 °C, the mixture was allowed to warm to room temperature for 1 h. After the
solvent was evaporated, the residue was purified by column chromatography on silica gel (hexane/DCM
= 20/1) and recrystallization with hexane to afford 2ꢀbromoꢀ6’ꢀphenylꢀ1,1’:2’,1”ꢀterphenyl (288 mg,
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1
0.75 mmol, 63%).20 Mp 180ꢀ182 °C; H NMR δ 7.55ꢀ7.51 (m, 1H), 7.44ꢀ7.42 (m, 2H),7.26ꢀ7.25 (m,
13
3H), 7.15ꢀ7.14 (m, 8H), 7.00ꢀ6.99 (m, 2H), 6.91ꢀ6.87(m, 1H); C NMR δ 142.0, 141.3, 140.7, 138.0,
133.4, 132.0, 129.6, 129.3, 128.2, 128.0, 127.4, 126.4, 126.2, 125.1; HRMS(DART, positive) calcd for
C24H2179BrN [M
+
NH4]+: 402.0852; found: 402.0844. In the case of substituted
2ꢀbromoꢀ6’ꢀphenylꢀ1,1’:2’,1”ꢀterphenyls, the crude products were isolated by column chromatography
on silica gel and subject them to next reaction without further purification.
An
experimental
procedure
for
the
synthesis
of
Dimethyl(6’-phenyl-[1,1’:2’,1”-terphenyl]-2-yl)silane
(1a):
A
solution
of
2ꢀbromoꢀ6’ꢀphenylꢀ1,1’:2’,1”ꢀterphenyl (78 mg, 0.2 mmol) in THF (1 ml) was cooled to ꢀ78 °C, and
nꢀBuLi (0.4 ml, 1.55 M in hexane) was added dropwise under an atmosphere of argon. After 15 min,
chlorodimethylsilane (88 ꢁl, 0.8 mmol) was added dropwise at ꢀ78 °C and the mixture was allowed to
warm to room temperature slowly. After 12 h, the reaction was quenched with saturated aqueous NH4Cl,
and the mixture was extracted with DCM. The combined organic layer was dried over Na2SO4, filtered,
and concentrated under reduced pressure. The residue was isolated by column chromatography on silica
gel (hexane only) and thinꢀlayer chromatography (hexane/DCM
=
20/1) to give
dimethyl(6’ꢀphenylꢀ[1,1’:2’,1”ꢀterphenyl]ꢀ2ꢀyl)silane (1a) (45.5mg, 0.12 mmol, 62%).10b Mp 67ꢀ70 °C;
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1H NMR δ 7.51ꢀ7.48 (m, 1H), 7.42ꢀ7.41 (m, 2H), 7.20ꢀ7.18 (m, 1H), 7.14ꢀ7.04 (m, 12H), 6.98ꢀ7.97 (m,
1H), 3.89ꢀ3.3.86 (m, 1H), ꢀ0.18 (d, J = 3.7 Hz, 6H); 13C NMR δ 145.3, 141.8, 141.7, 140.1, 137.8, 133.8,
132.2, 130.2, 129.3, 127.7, 127.5, 127.4, 126.1, 125.8, ꢀ3.4; HRMS(ESI, positive) calcd for C26H24NaSi
[M + Na]+: 387.1539; found: 387.1540.
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Typical experimental procedure for intramolecular silylation of 1: [Ir(cod)2Cl]2 (3.4 mg, 0.005
mmol), DPPBen (4.5 mg, 0.01 mmol), silane (18.2 mg, 0.05 mmol) and 3,3ꢀdimethylꢀ1ꢀbutene (6.5 ꢁl,
0.05 mmol) were dissolved in distilled toluene (1 ml). The resulting mixture was stirred at 120 °C. After
stirring for 24 h, the solution was filtered through a short plug of silica gel with ethyl acetate and the
filtrate was evaporated under reduced pressure. The crude products were purified by thinꢀlayer
chromatography (hexane/dichloromethane = 20/1) to give compound 2.
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Dimethyl(6’-phenyl-[1,1’:2’,1”-terphenyl]-2-yl)silane (1a). Isolated by thinꢀlayer chromatography
(hexane/dichloromethane = 20/1, Rf = 0.3). The title compound was obtained as a white solid (41.5 mg,
1
0.12 mmol, 62%). Mp 67ꢀ70 °C; H NMR δ 7.51ꢀ7.48 (m, 1H), 7.42ꢀ7.41 (m, 2H), 7.20ꢀ7.18 (m, 1H),
7.14ꢀ7.04 (m, 12H), 6.98ꢀ6.97 (m, 1H), 3.89ꢀ3.86 (m, 1H), ꢀ0.18 (d, J = 3.7 Hz, 6H); 13C NMR δ 145.3,
141.8, 141.7, 140.1, 137.8, 133.8, 132.2, 130.2, 129.3, 127.7, 127.5, 127.4, 126.1, 125.8, ꢀ3.4;
HRMS(ESI, positive) calcd for C26H24NaSi [M+Na]+: 387.1539; found: 387.1540.
Dimethyl(4”-methoxy-6’-(4-methoxyphenyl)-[1,1’:2’,1”-terphenyl]-2-yl) silane (1b). Isolated by
silica gel column chromatography (hexane/ethyl acetate = 8/1) + thinꢀlayer chromatography
(hexane/dichloromethane = 20/1, 4 times, Rf = 0.6). The title compound was obtained as a white solid
1
(93.2 mg, 20% in three steps). Mp 108ꢀ110 °C; H NMR δ 7.46ꢀ7.42 (m, 1H), 7.36ꢀ7.35 (m, 2H),
7.23ꢀ7.22 (m, 1H), 7.08ꢀ7.06 (m, 2H), 6.99ꢀ6.96 (m, 5H), 6.66 (d, J = 8.9 Hz, 4H), 3.89ꢀ3.84 (m, 1H),
3.72 (s, 6H), ꢀ0.16 (d, J = 3.8 Hz, 6H); 13C NMR δ 158.0, 145.8, 141.4, 140.0, 137.8, 134.3, 133.9,
132.2, 131.2, 128.9, 127.8, 127.4, 125.7, 112.9, 55.1, ꢀ3.4; HRMS(ESI, positive) calcd for
C28H28NaO2Si [M+Na]+: 447.1751; found: 447.1753.
Dimethyl(4”-methyl-6’-(p-tolyl)-[1,1’:2’,1”-terphenyl]-2-yl)silane (1c). Isolated by thinꢀlayer
chromatography (hexane/dichloromethane = 20/1, 4 times, Rf = 0.5). The title compound was obtained
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1
as a colorless solid (238.5 mg, 38%, in three steps). Mp 112ꢀ113 °C; H NMR δ 7.47ꢀ7.44 (m, 1H),
7.38ꢀ7.36 (m, 2H), 7.22ꢀ7.20 (m, 1H), 7.08ꢀ7.06 (m, 2H), 6.99ꢀ6.91 (m, 9H), 3.88ꢀ3.85 (m, 1H), 2.24 (s,
6H), ꢀ0.18 (d, J = 3.8 Hz, 6H); 13C NMR δ 145.7,141.8, 140.0, 138.8, 137.8, 135.6, 133.8, 132.2, 130.1,
129.1, 128.1, 127.7, 127.4, 125.6, 21.0, ꢀ3.4; HRMS(ESI, positive) calcd for C28H28NaSi [M+Na]+:
415.1852; found: 415.1852.
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(4”-Chloro-6’-(4-chlorophenyl)-[1,1’:2’,1”-terphenyl]-2-yl)dimethylsilane
(1d).
Isolated
by
thinꢀlayer chromatography (hexane/dichloromethane = 20/1, twice, Rf = 0.5) + GPC (chloroform). The
title compound was obtained as a colorless solid (69.2 mg, 8% in three steps). Mp 141ꢀ142 °C; 1H NMR
δ 7.50ꢀ7.46 (m, 1H), 7.38ꢀ7.37 (m, 2H), 7.24ꢀ7.22 (m, 1H), 7.11ꢀ7.07 (m, 6H), 6.99 (d, J = 8.6 Hz, 4H),
6.95ꢀ6.93 (m, 1H), 3.85ꢀ3.82 (m, 1H), ꢀ0.15 (d, J = 3.8 Hz, 6H); 13C NMR δ 144.8, 140.8, 140.0, 140.0,
137.6, 134.2, 132.4, 132.0, 131.4, 129.4, 128.1, 127.7, 127.6, 126.2, ꢀ3.4; HRMS(DART, positive) calcd
for C26H2635Cl2NSi [M+NH4]+: 450.1206; found: 450.1203.
Dimethyl(4”-(trifluoromethyl)-6’-(4-(trifluoromethyl)phenyl)-[1,1’:2’,1”-terphenyl]-2-yl)silane
(1e). Isolated by thinꢀlayer chromatography (hexane, twice, Rf = 0.5) + GPC (chloroform). The title
1
compound was obtained as colorless solid (92.2 mg, 4% in three steps). Mp 126ꢀ129 °C; H NMR δ
7.56ꢀ7.53 (m, 1H), 7.45ꢀ7.43 (m, 2H), 7.39 (d, J = 8.1 Hz, 4H), 7.24ꢀ7.22 (m, 1H), 7.18 (d, J = 8.0 Hz,
13
4H), 7.13ꢀ7.07 (m, 2H), 6.95ꢀ6.93 (m, 1H), 3.87ꢀ3.84 (m, 1H), ꢀ0.16 (d, J = 3.8 Hz, 6H); C NMR δ
145.1 (q, J = 1.5 Hz), 144.3, 140.7, 140.1, 137.7, 134.3, 132.0, 130.4, 129.9, 128.5 (q, J = 32.2 Hz),
128.2, 127.9, 126.5, 124.4 (q, J = 3.9 Hz), 124.2 (q, J = 272.1 Hz), ꢀ3.5; 19F NMR δ ꢀ63.5;
HRMS(DART, positive) calcd for C28H26F6NSi [M+NH4]+: 518.1733; found: 518.1732.
Dimethyl(4’-methyl-6’-phenyl-[1,1’:2’,1”-terphenyl]-2-yl)silane (1f). Isolated by thinꢀlayer
chromatography (hexane/dichloromethane = 20/1, 4 times, Rf = 0.7). The title compound was obtained
1
as a white solid (81.1 mg, 6% in three steps). Mp 83ꢀ85 °C; H NMR δ 7.24 (d, J = 0.6 Hz, 2H),
7.19ꢀ7.17 (m, 1H), 7.13ꢀ7.03 (m, 12H), 6.96ꢀ6.95 (m, 1H), 3.91ꢀ3.88 (m, 1H), 2.48 (s, 3H), ꢀ0.18 (d, J =
3.7 Hz, 6H); 13C NMR δ 145.4, 141.9, 141.7, 138.0, 137.3, 136.9, 133.7, 132.4, 130.2, 130.0, 127.7,
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127.3, 126.0, 125.6, 21.2, ꢀ3.3; HRMS(ESI, positive) calcd for C27H26NaSi [M+Na]+: 401.1696; found:
401.1697.
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Dimethyl(3”-methyl-6’-(m-tolyl)-[1,1’:2’,1”-terphenyl]-2-yl)silane (1g). Isolated by thinꢀlayer
chromatography (hexane/dichloromethane = 20/1, Rf = 0.5). The title compound was obtained as
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1
colorless oil (255.0 mg, 24% in three steps).; H NMR δ 7.48ꢀ7.45 (m, 1H), 7.40ꢀ7.38 (m, 2H),
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7.19ꢀ7.17 (m, 1H), 7.05ꢀ7.03 (m, 2H), 7.01ꢀ6.96 (m, 3H), 6.91ꢀ6.90 (m, 4H), 6.86 (d, J = 7.6 Hz, 2H),
3.88ꢀ3.85 (m, 1H), 2.2 (s, 6H), ꢀ0.17 (d, J = 3.7 Hz, 6H); 13C NMR δ 145.5, 141.9, 141.6, 140.2, 137.9,
136.8, 133.6, 132.1, 131.1, 129.0, 127.5, 127.3, 127.3, 127.2, 126.8, 125.7, 21.2, ꢀ3.4; HRMS(ESI,
positive) calcd for C28H28NaSi [M+Na]+: 415.1852; found: 415.1852.
Dimethyl(2-(2-phenylnaphthalen-1-yl)phenyl)silane (1h). Prepared from 1ꢀiodoꢀ2ꢀphenylnaphthalene,
whose physical properties were reported in the literature.21 Isolated by thinꢀlayer chromatography
(hexane/ethyl acetate = 20/1, twice, Rf = 0.5). The title compound was obtained as a white solid (89.7
1
mg, 20% in two steps). Mp 100ꢀ103 °C; H NMR δ 7.94 (d, J = 8.5 Hz, 1H), 7.90 (d, J = 8.1 Hz, 1H),
7.58 (d, J = 8.5 Hz, 1H), 7.51ꢀ7.44 (m, 2H), 7.39ꢀ7.29 (m, 4H), 7.25ꢀ7.23 (m, 1H, overlapped with
CHCl3), 7.21ꢀ7.10 (m, 5H), 3.73ꢀ3.69 (m, 1H), ꢀ0.16 (d, J = 3.8 Hz, 3H), ꢀ0.31 (d, J = 3.8 Hz, 3H); 13C
NMR δ 145.0, 141.7, 138.3, 138.1, 137.9, 134.5, 133.4, 132.4, 131.6, 130.3, 128.4, 128.2, 127.7, 127.7,
127.4, 127.3, 126.4, 126.2, 126.0, 125.6, ꢀ3.1, ꢀ3.7; HRMS(ESI, positive) calcd for C24H22NaSi
[M+Na]+: 361.1383; found: 361.1383.
Dimethyl(6’-methyl-[1,1’:2’,1”-terphenyl]-2-yl)silane
(1i).
Prepared
from
2ꢀbromoꢀ6’ꢀmethylꢀ1,1’:2’,1”ꢀterphenyl, whose physical properties were reported in the literature.22
Isolated by thinꢀlayer chromatography (hexane/ethyl acetate = 20/1, Rf = 0.5). The title compound was
1
obtained as colorless oil (165 mg, 0.55 mmol, 70%). H NMR δ 7.40ꢀ7.38 (m, 1H), 7.35ꢀ7.28 (m, 2H),
7.25ꢀ7.19 (m, 3H), 7.17ꢀ7.15 (m, 1H), 7.11ꢀ7.06 (m, 5H), 3.87ꢀ3.84 (m, 1H) , 2.04 (s, 3H), ꢀ0.07 (d, J =
3.8 Hz, 3H), ꢀ0.09 (d, J = 3.8 Hz, 3H); 13C NMR δ 146.4, 141.7, 141.2, 141.2, 136.7, 136.5, 134.5,
130.6, 130.1, 128.8, 128.4, 127.6, 127.4, 127.2, 126.0, 126.0, 21.3, ꢀ3.2, ꢀ3.8; HRMS(ESI, positive)
calcd for C21H22NaSi [M+Na]+: 325.1383; found: 325.1383.
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9,9-Dimethyl-1-phenyl-9H-tribenzo[b,d,f]silepin (2a). Isolated by thinꢀlayer chromatography
1
2
3
(hexane/dichloromethane = 20/1, 7 times, Rf = 0.5). The title compound was obtained as a white solid
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5
1
(14.5 mg, 83%). Mp 183ꢀ185 °C; H NMR δ 7.50ꢀ7.40 (m, 6H), 7.37 (ddd, J = 7.5, 7.5, 1.4 Hz, 1H),
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7
8
7.27ꢀ7.23 (m, 1H, overlapped with CHCl3), 7.15ꢀ7.10 (m, 3H), 7.04ꢀ7.00 (m, 3H), 6.80 (ddd, J = 7.6,
9
13
7.6, 1.4 Hz, 1H), 6.69 (d, J = 7.7 Hz, 1H), 0.78 (s, 3H), ꢀ0.01 (s, 3H); C NMR δ 146.4, 143.2, 143.0,
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142.7, 142.6, 142.2, 141.9, 139.3, 132.6, 131.2, 130.7, 130.3, 129.9, 129.8, 129.8, 129.3, 127.8, 127.6,
127.2, 126.1, 125.9, 125.6, ꢀ4.3, ꢀ5.5; HRMS(ESI, positive) calcd for C26H22NaSi [M+Na]+: 385.1383;
found: 385.1384. The crystal data of compound 2a: C26H22Si, M = 362.55, orthorhombic, space group
Pbca (#61), a = 15.2591(3) Å, b = 6.82403(12) Å, c = 37.8298(7) Å, V = 3939.17(12) Å3, Z = 8,
ꢀ(CuꢀKα) = 10.811 cmꢀ1; number of reflections measured: total 41798 and unique 3610, R1 = 0.0372,
wR2 = 0.1035. CCDC 1824338. The CIF file is available in Supporting Information.
7-Methoxy-1-(4-methoxyphenyl)-9,9-dimethyl-9H-tribenzo[b,d,f]silepin (2b). Isolated by thinꢀlayer
chromatography (hexane/dichloromethane = 40/1, 4 times, Rf = 0.5). The title compound was obtained
as a white solid (13.8 mg, 67%). Mp 138ꢀ141 °C; 1H NMR δ 7.44ꢀ7.35 (m, 5H), 7.02 (ddd, J = 7.4, 7.4,
1.3 Hz, 1H), 6.99 (d, J = 2.3 Hz, 1H), 6.91ꢀ6.87 (m, 3H), 6.83 (ddd, J = 7.6, 7.6, 1.4 Hz, 1H), 6.70 (d, J
= 7.7 Hz, 1H), 6.67 (d, J = 8.9 Hz, 2H), 3.79 (s, 3H), 3.74 (s, 3H), 0.76 (s, 3H), ꢀ0.02 (s, 3H); 13C NMR
δ 157.9, 157.8, 143.7, 143.7, 142.3, 142.2, 141.5, 139.3, 139.1, 135.6, 132.6, 131.1, 130.8, 130.7, 130.3,
129.5, 128.0, 127.2, 125.6, 116.6, 113.9, 113.1, 55.1, 55.1, ꢀ4.4, ꢀ5.5; HRMS(ESI, positive) calcd for
C28H26NaO2Si [M+Na]+: 445.1594; found: 445.1594.
1-(p-Tolyl)-7,9,9-Trimethyl-9H-tribenzo[b,d,f]silepin (2c). Isolated by thinꢀlayer chromatography
(hexane/dichloromethane = 20/1, twice, Rf = 0.5). The title compound was obtained as a white solid
(16.2 mg, 84%). Mp 164ꢀ166 °C; 1H NMR δ 7.45ꢀ7.34 (m, 5H), 7.24 (s, 1H), 7.17 (dd, J = 7.9, 1.2 Hz,
1H), 7.02 (ddd, J = 7.4, 7.4, 1.1 Hz, 1H), 6.95ꢀ6.87 (m, 4H), 6.81 (ddd, J = 7.5, 7.5, 1.4 Hz, 1H), 6.70 (d,
13
J = 7.7 Hz, 1H), 2.33 (s, 3H), 2.26 (s, 3H), 0.76 (s, 3H), ꢀ0.03 (s, 3H); C NMR δ 143.7, 143.5, 142.7,
142.6, 142.0, 141.8, 140.2, 139.3, 135.5, 135.4, 132.6, 131.5, 130.9, 130.2, 130.0, 129.8, 129.8, 129.7,
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128.3, 127.8, 127.2, 125.5, 21.1, 21.1, ꢀ4.3, ꢀ5.5; HRMS(ESI, positive) calcd for C28H27Si [M+H]+:
391.1877; found: 391.1877.
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7-Chloro-1-(4-chlorophenyl)-9,9-dimethyl-9H-tribenzo[b,d,f]silepin (2d). Isolated by thinꢀlayer
chromatography (hexane/dichloromethane = 20/1, twice and hexane, Rf =0.7). The title compound was
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9
1
obtained as white solid (14.6 mg, 67%). Mp 180ꢀ182 °C; H NMR δ 7.48ꢀ7.45 (m, 1H), 7.42ꢀ7.36 (m,
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5H), 7.32ꢀ7.30 (m, 1H), 7.11ꢀ7.05 (m, 3H), 6.90ꢀ6.85 (m, 3H), 6.66 (d, J = 7.8 Hz, 1H), 0.78 (s, 3H),
13
ꢀ0.04 (s, 3H); C NMR δ 144.5, 144.4, 142.8, 141.9, 141.6, 141.3, 140.9, 139.2, 133.0, 132.5, 132.1,
131.3, 131.2, 131.0, 130.6, 130.5, 130.0, 129.2, 128.4, 127.9, 127.5, 126.1, ꢀ4.5, ꢀ5.6; HRMS(DART,
positive) calcd for C26H2435Cl2NSi [M+NH4]+: 448.1050; found: 448.1035.
9,9-Dimethyl-7-(trifluoromethyl)-1-(4-(trifluoromethyl)phenyl)-9H-tribenzo[b,d,f]silepin
(2e).
Isolated by thinꢀlayer chromatography (hexane only, 4 times, Rf = 0.5). The title compound was
1
obtained as a white solid (45%, NMR yield). Mp 148ꢀ150 °C; H NMR δ 7.66 (s, 1H), 7.63ꢀ7.61 (m,
1H), 7.56ꢀ7.51 (m, 2H), 7.46ꢀ7.42 (m, 3H, contained desilylated starting material), 7.40 (d, J = 8.4 Hz,
2H), 7.10ꢀ7.06 (m, 3H), 6.84 (ddd, J = 7.7, 7.7, 1.3 Hz, 1H), 6.64 (d, J = 7.7 Hz, 1H), 0.83 (s, 3H), ꢀ0.00
(s, 3H); 13C NMR δ 149.5 (q, J = 1.5 Hz), 146.4 (q, J = 1.5 Hz), 143.3, 142.4, 141.9, 141.5, 140.9, 139.3,
132.6, 131.6, 131.4, 130.8, 130.4, 130.1 (q, J = 1.8 Hz), 130.0, 130.0, 128.5, 128.3 (q, J = 31.9 Hz),
128.3 (q, J = 32.5 Hz), 127.7, 127.6 (q, J = 3.6 Hz), 126.4, 126.1 (q, J = 3.6 Hz), 124.6 (q, J = 3.9 Hz),
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124.5 (q, J = 272.4 Hz), 124.2 (q, J = 271.8 Hz), ꢀ4.5, ꢀ5.6; F NMR δ ꢀ63.4, ꢀ63.3; HRMS(DART,
positive) calcd for C28H24F6NSi [M+NH4]+: 516.1577; found: 516.1569.
1-Phenyl-3,9,9-trimethyl-9H-tribenzo[b,d,f]silepin (2f). Isolated by thinꢀlayer chromatography
(hexane/dichloromethane = 20/1, 4 times, Rf = 0.6). The title compound was obtained as colorless oil
(16.9 mg, 90%). 1H NMR δ 7.46ꢀ7.44 (m, 2H), 7.40ꢀ7.34 (m, 2H), 7.24ꢀ7.22 (m, 3H), 7.12ꢀ7.08 (m, 3H),
7.01ꢀ6.98 (m, 3H), 6.80ꢀ6.77 (m, 1H), 6.67 (d, J = 7.8 Hz, 1H), 2.47 (s, 3H), 0.76 (s, 3H), 0.01 (s, 3H);
13C NMR δ 146.6, 143.3, 143.2, 142.7, 142.6, 142.1, 141.8, 136.7, 136.6, 132.7, 131.8, 130.8, 130.7,
130.3, 129.8, 129.8, 129.2, 127.8, 127.5, 126.1, 125.8, 125.5, 21.1, ꢀ4.2, ꢀ5.5; HRMS(ESI, positive)
calcd for C27H24NaSi [M + Na]+: 399.1539; found: 399.1540.
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1-(m-Tolyl)-6,9,9-trimethyl-9H-tribenzo[b,d,f]silepin (2g). Isolated by thinꢀlayer chromatography
1
2
3
(hexane/dichloromethane = 20/1, 3 times, Rf = 0.5). The title compound was obtained as white solid
4
5
1
(18.3 mg, 92%). Mp 131ꢀ133 °C; H NMR δ 7.46ꢀ7.38 (m, 4H), 7.34 (d, J = 7.4 Hz, 1H), 7.28 (s, 1H),
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8
9
7.06 (d, J = 7.4 Hz, 1H), 7.02ꢀ6.96 (m, 2H), 6.91 (d, J = 7.6 Hz, 1H), 6.85 (s, 1H), 6.80 (ddd, J = 7.4,
7.4, 1.4 Hz, 1H), 6.73 (d, J = 7.2 Hz, 1H), 6.68 (d, J = 7.8 Hz, 1H), 2.33 (s, 3H), 2.21 (s, 3H), 0.75 (s,
3H), ꢀ0.03 (s, 3H); 13C NMR δ 146.6, 143.4, 143.0, 142.9, 142.8, 141.9, 139.4, 139.0, 138.8, 137.1,
132.5, 131.0, 130.9, 130.8, 130.7, 130.2, 129.8, 127.7, 127.3, 127.1, 127.0, 126.9, 126.6, 125.6, 21.4,
21.4, ꢀ4.1, ꢀ5.5; HRMS(ESI, positive) calcd for C28H27Si [M+H]+: 391.1877; found: 391.1877.
9,9-Dimethyl-9H-dibenzo[b,f]naphtho[1,2-d]silepine (2h). Isolated by thinꢀlayer chromatography
(hexane/dichloromethane = 20/1, 5 times, Rf = 0.5). The title compound was obtained as a white solid
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48
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56
57
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59
60
1
(9.5 mg, 57%). Mp 56ꢀ60 °C; H NMR δ 7.89 (d, J = 8.5 Hz, 2H), 7.68 (d, J = 8.5 Hz, 1H), 7.58ꢀ7.55
(m, 3H), 7.50ꢀ7.45 (m, 2H), 7.42ꢀ7.37 (m, 2H), 7.35ꢀ7.7.29 (m, 3H), 7.28ꢀ7.24 (m, 1H, overlapped with
CHCl3), 0.73 (s, 3H), ꢀ0.41 (s, 3H); 13C NMR δ 146.5, 1443.5, 142.9, 142.0, 138.3, 137.4, 133.1, 132.8,
132.3, 131.2, 130.9, 129.8, 129.7, 129.2, 127.8, 127.8, 127.7, 127.6, 126.5, 126.1, 126.1, 125.7, ꢀ4.6,
ꢀ5.5; HRMS(ESI, positive) calcd for C24H21Si [M+H]+: 337.1407; found: 337.1407.
1,9,9-Trimethyl-9H-tribenzo[b,d,f]silepin
(2i).
Isolated
by
thinꢀlayer
chromatography
(hexane/dichloromethane = 20/1, twice, Rf = 0.5). The title compound was obtained as pale yellow oil
1
(4.0 mg, 24%). H NMR δ 7.48ꢀ7.47 (m, 1H), 7.43 (d, J = 7.4 Hz, 1H), 7.40 (dd, J = 7.3, 1.2 Hz, 1H),
7.34 (dd, J = 7.5, 1.4 Hz, 1H), 7.30ꢀ7.25 (m, 3H, overlapped with CHCl3), 7.23ꢀ7.18 (m, 4H), 2.17 (s,
3H), 0.70 (s, 3H), ꢀ0.29 (s, 3H); 13C NMR δ 146.7, 143.4, 142.3, 142.2, 141.6, 140.1, 136.9, 130.9,
130.9, 130.7, 129.5, 129.4, 129.2, 129.2, 128.0, 126.9, 126.0, 125.8, 22.3, ꢀ4.5, ꢀ5.5; HRMS(ESI,
positive) calcd for C21H21Si [M+H]+: 301.1407; found: 301.1408.
9,9-Dimethyl-1-(4-hydroxyphenyl)-9H-tribenzo[b,d,f]silepin-7-ol (3b). Isolated by thinꢀlayer
chromatography (hexane/ethyl acetate = 1/1, Rf = 0.5). The title compound was obtained as a white
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solid (7.7 mg, 68%). Mp 200ꢀ203 °C; H NMR δ 7.44ꢀ7.39 (m, 2H), 7.37ꢀ7.32 (m, 3H), 7.03 (ddd, J =
7.4, 7.4, 1.1 Hz, 1H), 6.91 (d, J =2.1 Hz, 1H), 6.86ꢀ6.83 (m, 3H), 6.81 (dd, J = 8.3, 2.8 Hz, 1H), 6.70 (d,
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J = 7.4 Hz, 1H), 6.60ꢀ6.59 (m, 2H), 4.74 (br s, 2H), 0.74 (s, 3H), ꢀ0.03 (s, 3H); 13C NMR δ 153.9, 153.7,
144.0, 143.6, 142.2, 141.4, 139.3, 139.2, 1358, 132.6, 131.4, 131.4, 131.1, 130.7, 130.3, 129.5, 128.0,
127.2, 125.6, 117.5, 116.0, 114.6, ꢀ4.4, ꢀ5.5; HRMS(ESI, positive) calcd for C26H22NaO2Si [M+Na]+:
417.1281; found: 417.1280. Enantiomers of 3b were resolved using a Daicel Chiralpak ADꢀH (10 x 250
mm, 254 nm UV detector, rt, eluent: 10% 2ꢀpropanol in hexane, flow rate: 2.0 ml/min, retention time:
28.3 min and 36.4 min).
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ACKNOWLEDGEMENT
This work was supported by ACTꢀC from JST (Japan).
Supporting Information Available
NMR spectra of products This material is available free of charge via the internet at http://pubs.acs.org.
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