Synthesis of molecular tripods based on a rigid 9,9'-spirobifluorene scaffold

Article abstract of DOI:10.1021/jo501029t

The efficient synthesis of a new tripodal platform based on a rigid 9,9'-spirobifluorene with three acetyl protected thiol groups in the positions 2, 3' and 6' for deposition on Au(111) surfaces is reported. The modular 9,9'-spirobifluorene platform provi

Full text of DOI:10.1021/jo501029t

Article
pubs.acs.org/joc
Synthesis of Molecular Tripods Based on a Rigid 9,9′-Spirobifluorene
Scaffold
†
,‡
†
†
†
†
,†,‡,§
Michal Valas
†
́
e
̌
k, Kevin Edelmann, Lukas Gerhard, Olaf Fuhr, Maya Lukas, and Marcel Mayor*
Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), P.O. Box 3640, D-76021 Karlsruhe, Germany
‡
DFG Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology (KIT), Wolfgang-Gaede-Str. 1a, D-76131
Karlsruhe, Germany
§
Department of Chemistry, University of Basel, St. Johannsring 19, CH-4056 Basel, Switzerland
S Supporting Information
*
ABSTRACT: The efficient synthesis of a new tripodal platform based on a rigid 9,9′-spirobifluorene
with three acetyl protected thiol groups in the positions 2, 3′ and 6′ for deposition on Au(111) surfaces is
reported. The modular 9,9′-spirobifluorene platform provides both a vertical arrangement of the
molecular rod in position 7 and its electronic coupling to the gold substrate. To demonstrate the validity
of the molecular design, the model compound 24 exposing a para-cyanophenylethynyl rod is synthesized.
Our synthetic approach is based on a metal−halogen exchange reaction of 2-iodobiphenyl derivative and
his subsequent reaction with 2,7-disubstituted fluoren-9-one to afford the carbinol 16. Further
electrophilic cyclization and separation of regioisomers provided the corresponding 2,7,3′,6′-
tetrasubstituted 9,9′-spirobifluorene 17 as the key intermediate. The molecular structure of 17 was
determined by single-crystal X-ray diffraction crystallography. The self-assembly features of the target
compound 24 were analyzed in preliminary UHV-STM experiments. These results already demonstrated
the promising potential of the concept of the tripodal structure to stabilize the molecule on a Au(111)
surface in order to control the spatial arrangement of the molecular rod.
INTRODUCTION
points for one molecule not only increases the stability of its
binding to the surface but also restricts its tilting with respect to
the surface. In order to orient the structures with respect to the
■
The spatial control of molecular structures on planar substrates
is a remaining challenge. Flat delocalized π-systems have the
tendency to spread with the entire π-surface over the substrate
driven by van der Waals interactions. While delocalized π-
systems are the ideal model compounds of numerous electronic
and optical applications, a more perpendicular arrangement
with the surface would be desired to profit from their
properties. In optical experiments the quenching of molecular
excited states is reduced by a perpendicular arrangement, and in
electronic applications a perpendicular arrangement is required
to separate the π-system from the substrate and to profit from
the entire dimension of the molecule. While for most optical
set-ups the perpendicular arrangement is the only prerequisite,
in electronic applications also the contact point of the molecule
with the substrate, which defines the coupling between
molecule and electrode (substrate), must be controlled.
surface plane, C -symmetric tripods are particularly appealing. A
3
number of tripodal model compounds were synthesized and
chemisorbed on gold substrates. As tripodal branching
2
−6
structures carbon atoms (e.g., tetraphenylmethanes),
atoms (e.g., tetraphenylsilanes),
silicon
7
−10
11−15
or adamantane cages
were used. The three branches of the tripod were functionalized
3
,4,6−15
5
with identical sulfur-
or selenium- containing anchor
groups. While some synthetic papers focused mainly on the
7
−9,11
concept,
initial studies revealed an increased stability of
3,4
the tripodal contact, and surface analysis by scanning probe
6
,12
14
methods
or X-ray absorption techniques displayed an
enlarged separation due to the increased footprint of the tripod.
Further evidence for a perpendicular arrangement of separated
6
,15
molecules were obtained by optical
and electrochemi-
1
0,13,14
cal
analysis of the samples.
Several attempts to increase the spatial control over the
arrangement of rigid-rod type structures on Au(111) as flat
substrate have been reported. A few examples even profit from
the interaction of delocalized π-systems with the flat substrate
to arrange a subunit perpendicular to the surface like, e.g., the
While several of these tripods enable a perpendicular
arrangement of rod-type molecular structures, the electronic
coupling to the rod’s π-system to the metal states is limited due
3
to the tripod architectures comprising sp hybridized atoms.
1
This electronic decoupling of the functional subunit is on the
one hand desired to profit from the subunit’s optical properties,
but on the other hand it represents a considerable handicap for
molecular electronic applications.
triazatriangulenium platforms from Herges and co-workers or
the [4-(4-pyridyl)phenyl]methyl platform from Aso and co-
2
workers. The most commonly used immobilization chemistry
on gold electrodes is the formation of covalent bonds between
thiols and gold substrates. To gain spatial control over the
molecule’s arrangement, structures comprising several thiol
groups as anchor points were suggested. Using several anchor
Received: May 12, 2014
Published: July 15, 2014
©
2014 American Chemical Society
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Here we develop a tripodal platform as modular anchoring
subunit providing both a vertical arrangement of the molecular
rod and its electronic coupling to the gold substrate. In
particular we describe a rigid three-dimensional 9,9′-spirobi-
fluorene with thiol anchoring groups in the positions 2, 3′ and
intrinsic part of the backbone of the immobilized rigid rod, the
task of the electronically decoupled second fluorene subunit
with thiol anchor groups in positions 3′ and 6′ is to fix and
stabilize the upright standing of the rigid rod. The para-position
of the anchor group immobilizing the molecular rod maximizes
16
6
′ and a synthetic variable position 7 allowing to introduce
its electronic coupling to the electrode and thiol function-
rigid-rod type structures experiencing an efficient coupling to
the metal electrode in a modular manner. A first model
compound demonstrating the concept is reported here and
displayed in Chart 1, namely, the platform comprising a para-
cyanophenylethynyl as rigid-rod subunit.
alized fluorene model compounds already displayed favorable
17
electronic transport features in single molecule experiments.
In order to provide modular variability of the anchoring
platform, the extension of the molecular rod para-cyanophe-
nylethynyl is introduced at a late stage of the synthesis.
Furthermore, the cyano group may serve as spectroscopic
18
Chart 1
marker for further surface measurements.
From a synthetic viewpoint the assembly of the target
structure profits from an already developed rich synthetic
chemistry forming differently functionalized 9,9′-spirobifluor-
ene. These π-conjugated spiro compounds have attracted much
attention because of their promising application in the field of
19
enantioselective molecular recognition, molecular tecton-
2
0,21
22
23
ics,
molecular electronics, catalysis, and optoelectronic
materials for the production of organic light-emitting diodes
2
4
and dye-sensitized solar cells owing to their unique
2
5
photophysical properties. The first synthesis of 9,9′-
spirobifluorene was reported by Clarkson and Gomberg,
26
whom started from 2-iodobiphenyl and fluoren-9-one. At
the present time, there are several variations of this procedure
with high yield up to 90%. One of the advantages of 9,9′-
spirobifluorene is its easy functionalization at the four para-
positions 2,2′,7,7′. The same strategy was used for 6-fold
substitution in the 2,2′,4,4′,7,7′ positions. Also 2,2′-substituted
9
,9′-spirobifluorene can be obtained directly by disubstitution
of spirobifluorene if deactivating substituents are used. Selective
,7-substitution and other further advanced substitution
Within this paper the synthesis of the platform is presented
in details and the optical properties of the target structures and
of key intermediates are discussed. Furthermore, preliminary
surface deposition experiments are presented, supporting the
hypothesis of the concept of a rigid tripodal platform as well-
defined anchor group exposing the rigid rod subunit.
2
patterns have to be arranged in the precursors before the
formation of the central spirobifluorene core. Spirobifluorene-
based oligomers and polymers usually consist of para-
interlinked subunits derived from 2- or 2,7-substituted 9,9′-
spirobifluorene building blocks, and only few reports dealing
with alternative substitution patterns have been reported.
Synthesis. Our retrosynthetic approach is using a similar
RESULTS AND DISCUSSION
Molecular Design. This core structure was chosen because
,9′-spirobifluorene and its derivatives form an intriguing class
■
9
26
strategy, which was first described by Clarkson and Gomberg,
based on a metal−halogen exchange reaction of 2-iodobiphenyl
derivative and his subsequent reaction with 2,7-disubstituted
fluoren-9-one to afford the carbinol. Further electrophilic
cyclization provided the corresponding 2,7,3′,6′-tetrasubsti-
tuted 9,9′-spirobifluorene, which is shown in Chart 2. It should
be noted that 2,7,3′,6′-tetrasubstituted 9,9′-spirobifluorene has
of molecules that exhibit a three-dimensional rigid topology and
possess electronic characteristics reflective of two separated
conjugated biphenyl moieties fused at a common spiro center.
The system can be described electronically as π−σ−π, where
conjugation between the orthogonal biphenyl groups is limited.
While the fluorene subunit with a thiol anchor group in
position 2 and ethynyl substituent in position 7 becomes an
27
been reported once so far.
Chart 2. Retrosynthetic Strategy to 2,7,3′,6′-Tetrasubstituted 9,9′-Spirobifluorenes
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a
Scheme 1. Synthesis of 2-Iodobiphenyl Derivative 13 by Different Synthetic Pathways
a
Reagents and conditions: (i) NBS, CH CN; (ii) BBr , CH Cl ; (iii) NaH, R NCSCl, DMF, Δ, (R = Me, Et); (iv) Ph O, Δ; (v) (a) KOH, MeOH,
3
3
2
2
2
2
+
(
b) H ; (vi) vinyltrimethylsilane, AIBN, Δ; (vii) Tf O, CH Cl , Et N; (viii) TMS(CH ) SH, Xantphos, Pd (dba) , iPr EtN, dioxane; (ix)
2
2
2
3
2
2
2
3
2
+
vinyltrimethylsilane, (tert-BuO) , Δ; (x) (a) n-BuLi, THF, (b) (iPrO) B, (c) H , (d) pinacol, Δ; (xi) 9, Pd(PPh ) , Na CO , toluene, H O; (xii) (a)
2
3
3
4
2
3
2
n-BuLi, THF, (b) I , THF.
2
The synthetic strategy to the 2-iodobiphenyl derivative 13,
the first key building block for the preparation of 9,9′-
spirobifluorene, is outlined in Scheme 1. The synthesis started
with regioselective monobromination of commercially available
O,O′-diethyl 3 respectively O,O′-dimethylthiocarbamate 4 was
dissolved in anhydrous diphenyl ether and heated up to 250−
260 °C under an argon atmosphere to afford the S,S′-
dialkylthiocarbamates 5, 6 respectively in almost quantitative
yields. After hydrolysis with KOH in methanol, biphenyl-5,3′-
dithiol 7 was obtained in 97% yield. Subsequently, the dithiol 7
was protected in a form of 2-(trimethylsilyl)ethyl derivative 12,
profiting from the radical reaction of the thiol groups with
vinyltrimethylsilane in the presence of 2,2′-azobis(2-methyl-
3
,3′-dimethoxybiphenyl with equimolar amount of NBS in
acetonitrile at 0 °C to provide 2-bromobiphenyl derivative 1 in
1% yield. Subsequent demethylation with BBr gave almost
9
3
quantitatively biphenyl-5,3′-diol 2. Our following strategy was
to introduce the sufur via a Newman−Kwart rearrangement as
an efficient method to convert phenols to thiophenols by the
thermally activated rearrangement of an O-thiocarbamate to the
2
9,30
propionitrile) (AIBN) as a radical initiator.
To have in
hand more reactive 2-iodobiphenyl 13 for the further halogen-
metal exchange and formation of carbinol 16, 2-bromobiphenyl
12 was treated with n-BuLi and iodinated to provide 2-
iodobiphenyl derivative 13 in 96% yield. We have also tried to
establish alternative synthetic routes to prepare 2-bromobi-
phenyl 12 faster, these attempts are outlined in Scheme 1. The
first alternative approach is based on triflatation of diol 2 with
triflic anhydride to afford triflate 8 in 96% yield. Then the
resulting triflate 8 was converted by the C−S cross-coupling
reaction with 2-(trimethylsilyl)ethanethiol in the presence of 5
mol % of Pd (dba) and 2.5 mol % of Xantphos at 60 °C to the
28
corresponding S-thiocarbamate. The O,O′-dialkylthiocarba-
mates 3, 4 were synthesized by treating diol 2 with
diethylcarbamoyl chloride, dimethylcarbamoyl chloride respec-
tively using sodium hydride (NaH) as base. We expected that
O,O′-dimethylthiocarbamate 4 tends to crystallize and can
therefore by purified more simply. Both O,O′-dimethyl 4 and
O,O′-diethylthiocarbamate 3 were prepared in order to improve
purification of O,O′-thiocarbamates from the reaction mixture;
however, the yield of both derivatives 3, 4 was almost the same.
On the contrary to our expectation, final purification of O,O′-
diethylthiocarbamate 3 was easier, due to the bigger polarity
differences between the desired product and byproducts. Then
2
3
3
1,32
desired product 12.
This strategy suffers from the poor
selectivity of the substitution reaction between both triflates in
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positions 5 and 3′ and the bromine in position 2. The title
product 12 was isolated in a low yield, and still contains other
regioisomers, which cannot be completely separated. In this
case, the chromatography separation does not offer a feasible
means for complete separation of the reaction mixture. Another
synthetic approach to 2-bromobiphenyl 12 started from the
commercial available 3-bromothiophenole, which was protected
in a form of 2-(trimethylsilyl)ethyl derivative 9. Subsequently,
the boronic acid was introduced by treating compound 9 with
n-BuLi solution to perform a bromine−lithium exchange. The
lithiated species is quenched by trisopropyl borate to provide
boronic acid which was further reacted with pinacol to afford
the target pinacol ester 10 in 80% yield. The corresponding
biphenyl 11 was prepared via Suzuki cross-coupling reaction of
bromide 9 with pinacol ester 10 in 80% yield. For the further
monobromination of 2-(trimethylsilyl)ethylsulfanylated bi-
phenyl 11, many mild methods have been employed to prepare
monobrominated biphenyl 12, but all of these attempts
produced mixtures instead of pure single product. We have
used NBS as a bromine source and various solvents like
acetonitrile, THF and dichloromethane at 0 °C and at an
ambient temperature, but the monobromination did not
proceed cleanly, and among the desired product 12 also
other isomers together with disulfides as byproducts have been
observed from the NMR and GC−MS analysis.
bromo-fluoren-9-one, which provided the desired product in
89% yield.
With the both key intermediate 13 and 15 in hand, we have
build up the spirobifluorene core via halogen-metal exchange in
13 and following addition of 2-bromo-7-iodofluoren-9-one 15.
Many metalation agents (n-BuLi, tert-BuLi, Li metal, iPrMgCl·
LiCl, and Mg turnings) have been employed for the halogen-
metal exchange of 2-iodobiphenyl 13, and it was discovered
that both halogen-lithium and halogen-magnesium exchanges
work well. However, in case of lithiated species, subsequent
addition of 2-bromo-7-iodofluoren-9-one 15 did not afford the
desired carbinol 16, but mainly provided the starting 2-
iodobiphenyl derivative 13. We prepared and used several 2-
halogenated biphenyl (2-bromobiphenyl, 2-iodobiphenyl, 2-
bromo-5,3′-dimethoxybiphenyl, 2-iodobiphenyl derivative 13)
for the metalation with n-BuLi respectively tert-BuLi at −78 °C
in both THF and diethyl ether to understand this unexpected
substitution. After lithiation, subsequent addition of 2-bromo-7-
iodofluoren-9-one provided in all cases the reaction mixture
containing mainly 2-iodobiphenyl derivatives, which is shown
in Scheme 3. The results of these experiments provided
evidence, that lithiation proceed almost quantitative with both
n-BuLi and tert-BuLi, but obtained 2-lithiated biphenyl rather
eliminated iodine from the position 7 of 15 than attack the
carbonyl of fluoren-9-one derivative 15 to afford the desired
carbinol 16. The halogen-magnesium exchange of iodobiphenyl
13 was employed to circumvent the problem. The best results
were obtained with iPrMgCl·LiCl complex (“turbo-
We conclude that the most effective and convenient method
for the synthesis of the first key intermediate 13 is via a
Newman−Kwart rearrangement, as discussed in the beginning
of this paragraph.
Two synthetic protocols outlined in Scheme 2 have been
developed to obtain 2-bromo-7-iodofluoren-9-one 15, the
33
Grignard”) as metalation agent at −40 °C, and following
addition of fluoren-9-one 15 afforded the corresponding
carbinol 16 in 59% yield. This “turbo-Grignard” reagent
possesses a high kinetic basicity, favoring halogen/magnesium
exchange on substituted aromatic halides over nucleophilic
attack on sensitive functional groups. Furthermore, the
solubility of the resulting aryl magnesium species is improved,
due to the presence of LiCl. Reaction with “turbo-Grignard”
reagent formed an organometallic species, which reacted with
a
Scheme 2. Synthesis of 2-Bromo-7-iodofluoren-9-one 15
2
-bromo-7-iodofluornen-9-one 15 exclusively via addition to
the carbonyl group and forming the desired carbinol 16, which
is outlined in Scheme 4.
Subsequent electrophilic cyclization of carbinol 16 leads to
the regioisomeric mixture of 9,9′-spirobifluorenes 17 and 18.
However, the separation of the two isomers by column
chromatography turned out to be problematic due to the small
difference in the retention factors between the isomers, which
handicapped the isolation of pure regioisomers. Preliminary
attempts showed that the desired regioisomer 17 can be
separated by fractional crystallization, but only from a 17
enriched solution. Thus, it was important to understand and
control the formation of the desired isomer over the other, in
order to produce the isomerically pure building block 17 for
subsequent functionalization. Screening for acids, solvents and
temperatures allowed us to slightly increase the amount of the
desired isomer 17 over preferred 18. Many of the cyclization
a
+
Reagents and conditions: (i) I , KIO , H ; (ii), CrO , AcOH, Ac O;
2
3
3
2
+
(
iii) I , H IO , H .
2 5 6
second key intermediate for the preparation of 9,9′-
spirobifluorene core structure. The first method is based on
regioselective monobromination and subsequent iodination of
the commercial available 9H-fluorene to provide 2-bromo-7-
iodo-9H-fluorene 14 in 72% yield, which was further oxidized
with chromium oxide to the desired fluoren-9-one 15 in 73%
yield. However, a more convenient and highly efficient method
for the preparation of 2-bromo-7-iodofluoren-9-one 15 is via
the regioselective iodination of commercially available 2-
reactions were attempted with Brønsted acids (HCl, MeSO H,
3
CF COOH), Lewis acid (BF ·Et O), and solvents (acetic acid,
3
3
2
dichloromethane, acetonitrile) at different temperatures −78 to
80 °C and concentrations, and the best ratio (>2/1) of isomers
17/18 was obtained with the mixture of hydrochloric acid and
acetic acid equal to 1:10 (v/v) at 10 °C, where the
concentration of carbinol 16 is 10 mmol/L. This method was
used on a multigram scale and reproducibly provided the
mixture of regioisomers 17/18 with the ratio more than 2/1,
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a
Scheme 3. Synthetic Attempts toward Carbinol
a
Reagents and conditions: (i) (a) iPrMgCl·LiCl, THF, −40 °C, resp. Mg, THF, 50 °C; (b) 15 in THF. (ii) (a) n-BuLi, resp. tert-BuLi, THF, −78
C; (b) 15 in THF.
°
a
Scheme 4. Synthesis of the Spirobifluorene Regioisomers 17 and 18
a
Reagents and conditions: (i) iPrMgCl·LiCl, THF, −40 °C, (ii) AcOH, HCl.
1
which was determined from the H NMR spectrum of the
conditions. For the assembly of the target compound 21, 4-
ethynylbenzonitrile 20 was required. The synthesis of 20
started from the commercial available 4-iodobenzonitrile, which
was coupled with trimethylsilylacetylene via Sonogashira
coupling to afford trimethylsilyl protected acetylene derivative
9 in 90% yield. Subsequent cleavage of trimethylsilyl
protecting group under basic conditions afforded 20 in almost
quantitative yield. For the following Sonogashira coupling of 20
with the 9,9′-spirobifluorne unit, we have used both isomeri-
cally pure derivative 17 and the regioisomeric mixture of 17/18,
and found out, that the presence of the polar nitrile group
permits separation of the target isomeric compounds 21 and 22
by column chromatography on silica gel. Sonogashira coupling
reaction of both, 17 and the isomeric mixture of 17/18 with 4-
ethynylbenzonitrile 20, gave the desired isomer 21 after column
chromatography in yields of 88% and 86% respectively
(Scheme 5).
crude isomeric mixture. To have in hand regioisomeric mixture
enriched with the desired isomer 17 is the crucial step for the
successful separation. If the ratio is lower than 1.5/1, the
separation has not been achieved by fractional crystallization.
Further slow recrystallization of the isomeric mixture from
1
ethanol and toluene (10:1, v/v) provided a first crop of the
symmetric isomer 17, a second crop was obtained by the
column chromatography of the mother liquor on a large excess
of silica gel. The crystals obtained from 17 were of single crystal
quality, enabling solid state structure analysis by X-ray
diffraction further corroborating the identity of the regioisomer
1
7 (Figure 1).
With the isomerically pure spirobifluorene derivative 17 in
hand, the subsequent functionalization via Sonogashira cross-
coupling with acetylenes chemoselectively provided substitu-
tion in position 7, which is based on the differential reactivity of
iodine and bromine toward the Pd catalyzed substitution
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thiols has been successfully performed using AgBF and acetyl
4
chloride (AcCl) in dichloromethane to afford the desired
35
thioacetate 24 in 79% yield. The presence of terminal
thioacetate groups allows the spirobifluorene tripod to be
bound to a gold surface. The acetyl works as a labile thiol
protecting group and can mildly and efficiently be cleaved prior
to the physical investigations or in situ upon binding to the gold
surface.
All new compounds were fully characterized by conventional
1
13
analytical and spectroscopy techniques like H and C NMR
spectroscopy, mass spectrometry, IR, UV−vis and florescence
spectrometry, as well as by elemental analysis.
Single-Crystal X-ray Diffraction. The molecular structure
of regioisomerically pure spirobifluorene 17 obtained by single-
crystal X-ray diffraction is shown in Figure 1. Compound 17
crystallizes in the triclinic space group P1 with two molecules
̅
per unit cell. As expected the molecules are disordered in a way
that the positions of the halogen atoms are occupied in a 0.5:0.5
ratio with iodine or bromine, respectively. Also the methyl
groups of one TMS group (at Si2) are disordered over two
positions. The planes between the two π-systems are nearly
orthogonal (87.3°). The solid state structure of 17 allowed first
estimations of the spatial arrangement of the protruding
molecular rod. On a plane defined by both sulfur atoms (S1,
S2) and Br1/I2 as proxy for the surface the rod direction is the
straight through C1 and I1/Br2. The angle between this
straight and this surface is 52.8° providing a first approximation
of the arrangement of the molecular rod with respect to the
surface plane. Details of the crystallographic data, as well as
bond lengths and angles, can be found in the Supporting
Information.
Figure 1. Molecular structure of spirobifluorene 17 determined by
single-crystal X-ray diffraction (50% probability of thermal ellipsoids).
To introduce the third alkylsulfanyl group, isomerically pure
spirobifluorene derivative 21 was treated with 2-
(
trimethylsilyl)ethanthiol in the presence of Pd (dba) ,
2 3
̈
Xantphos and Hunig’s base to provide the desired tripodal
spirobifluorene 23 in 95% yield which is shown in Scheme 6.
For the transprotection of the 2-(trimethylsilyl)ethylsulfanyl
groups of compound 23 to acetylsulfanyl groups, several
3
0,34
alternative protocols have been reported.
While the 2-
Optical Properties. The π-conjugation in the spirobifluor-
enes was investigated by UV−vis measurements. As reported in
Figure 2 and Table 1, the absorption spectra of spirobifluorenes
(
trimethylsilyl)ethylsulfanyl groups were easily cleaved with
tetrabutylammonium fluoride (TBAF), the subsequent treat-
ment with acetyl chloride resulted in the complex mixture of
acetylated products and side products, considerably reducing
the yield of the desired product 24. Transprotection of the
−5
17−18 and 21−24 in 10 M dichloromethane solutions at
room temperature showed the presence of one sharp band
about 260 nm in addition to a broad one around 310−400 nm,
a
Scheme 5. Coupling of the Rigid Rod Subunit to the Spirobifluorene Subunit 17
a
Reagents and conditions: (i) Trimethylsilylacetylene, PdCl (PPh ) , CuI, Et N, THF; (ii) K CO , MeOH, THF; (iii) 20, PdCl (PPh ) , CuI, Et N.
2
3
2
3
2
3
2
3
2
3
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a
Scheme 6. Introduction of the Third Masked Thiol Group and Subsequent Transprotection
a
Reagents and conditions: (i) TMS(CH ) SH, Pd (dba) , Xantphos, iPr EtN, dioxane, Δ; (ii) AgBF , AcCl, CH Cl .
2
2
2
3
2
4
2
2
clearly signing an extension of the conjugation of the core π-
spirobifluorene system with 4-cyanophenylethynyl group in
position 7. The broadness of the 21−24 spectra is due to a
rotational freedom of the aryl ring around the C−C bond
joining the spirobifluorene unit. The more symmetric
regioisomers 17 and 21 exhibit the first maximum at 312 nm,
3
32 nm respectively bathochromically shifted by 2 nm, 6 nm
respectively compared to the corresponding regioisomers 18
and 22. The UV−vis spectrum also shows the strong
bathochromic shift between thioacetate 24 and 2-
(
trimethylsilyl)ethyl protected spirobifluorene 23.
The fluorescence spectra of regioisomeric spirobifluorenes 17
and 18 in dichloromethane present the emission peaks at λmax
=
3
62 nm, 367 nm respectively (Figure 3). The emission peak of
Figure 2. UV−vis spectra of the spirobifluorenes 17, 18, 21−24 (10−5
M solution in CH Cl ).
2
2
Table 1. UV−Vis Absorption and Emission Spectral Data of
Spirobifluorenes 17, 18, 21−24
Absorption onset λem
/
ε/L mol− cm−1
1
nm (eV)
nm
λabs/nm
[
[
[
[
17] 264, 312, 324,
73 692, 14 615, 19
230, 6604
358 (3.46)
362
367
413
406
342 (sh)
18] 266, 310, 324
52 443, 15 204, 16
355 (3.49)
388 (3.19)
395 (3.13)
0
63
21] 264, 332, 340,
62 687, 45 299, 45
448, 39 254
3
59
22] 263, 326, 342,
60
49 107, 40 682, 43
839, 41 786
3
[
[
23] 264, 358
60 088, 43 109
420 (2.95)
390 (3.17)
453
396
Figure 3. Emission spectra of the spirobifluorenes 17, 18, 21−24 (λ
exc
24] 242, 320, 342,
54 673, 37 664, 47
009, 46 261
−5
=
264 nm, 10 M solution in CH Cl , measured for 17, 18 with both
2 2
359
emission and adsorption slit width = 5 nm, and for 21−24 slit widths
were 2.5 nm).
both laying in the UV region that can be attributed to π−π*
transmissions. The high energy band of spirobifluorenes 17−18
and 21−23 at about 260 nm is almost the same and slightly
dependent on the substitution. This strong band in UV−vis
spectrum of spirobifluorne 18 is about 2 nm bathochromically
shifted as compared to the more symmetric isomer 17. In
contrary, the energy band of thioacetate 24 is strongly
hypsochromically shifted by 22 nm as compared to 2-
spirobifluorene derivatives 21 and 22 (413, 406 nm) is red-
shifted with respect to spirobifluorenes 17 and 18 (362, 367
nm) due to the important contribution of the 4-cyanopheny-
lethynyl substituent leading to a more conjugated excited state.
Introduction of the third 2-(trimethylsilyl)ethylsulfanyl group
in 23 has a remarkable effect not only on the emission
maximum, which is strongly red-shifted by 40 nm, but also on
the fluorescence intensity. In contrary, transprotection of 2-
(trimethylsilyl)ethyl group in 23 to acetyl in 24 leads to the
strong blue shift of 57 nm. Both spirobifluorenes 23 and 24 are
highly fluorescent blue emitting compounds.
(
trimethylsilyl)ethylsulfanyl derivative 23. The broad low
energy absorption band about 310−400 nm, in which one
can distinguish three maxima, has significantly lower absorption
intensity and is further hypsochromically shifted by 20 nm for
17 and 18 compared with the spirobifluorenes 21−24. Which is
7
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The Journal of Organic Chemistry
Article
Figure 4. (a) Highly ordered island of molecular tripods (yellow) and remaining CH Cl (dark purple) on the Au(111) surface. (b) Unit cell of the
2
2
molecular islands as extracted from the directions and distances in (a) with the molecular configuration as extracted from (c). (c) Constant height
mode image with submolecular resolution. (d) STM image of the same molecules as in (c) scanned at lower distance with a model of the molecule
superimposed (model size is to scale). The inset cross sections show the distance between cyano group and the spirobifluorene core.
Surface Deposition of the Tripod 24 and STM
Analysis. Of particular interest was the immobilization and
the spatial arrangement of the target tripod 24 on an Au(111)
surface. The tripod is considered as modular platform enabling
the surface deposition of macromolecular structures with
increased spatial control, and thus, deposition techniques
from dissolved samples are more suitable than sublimation
from the solid phase. Here we applied a technique of depositing
4 dissolved in dichloromethane via a pulse-valve, spraying the
2
dissolved molecules into the vacuum and onto the surface (for
more details see the Experimental Section). The deposition
method allows for higher molecule concentrations in the
solution, i.e., a better molecule/impurity ratio as compared to
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The Journal of Organic Chemistry
Article
3
6
the droplet-deposition used for the tripod structures
CONCLUSION
■
37
comprising metal complexes.
In conclusion we profit from the rigid three-dimensional
structure of 9,9′-spirobifluorene as scaffold to control the
arrangement of a rigid-rod subunit on a surface. In particular
the synthesis of a 9,9′-spirobifluorene derivative with sulfur
anchor groups in positions 2, 3′ and 6′ in combination with a
modularly addressable position 7 is developed as tripodal
platform in order to gain control over the spatial arrangement
of the rigid-rod subunit. Interestingly the platform not only
provides an emerging rigid-rod subunit, but also its efficient
electronic coupling to the (electrode) surface. As first model
compound the 4-cyanophenylethynyl derivative 24 is synthe-
sized and fully characterized. Preliminary STM experiments not
only display promising self-assembly features of the model
compound, but corroborate the validity of the molecular design
by a protruding rigid-rod molecular subunit.
Figure 4(a) displays a typical STM image recorded from a
sample prepared as described in the Experimental Section. Two
different island structures can be seen. The dark elongated
islands consist of remaining CH Cl situated in the fcc areas of
the herringbone reconstruction of the Au(111) surface, as
could be confirmed from deposition of pure CH Cl . The
brighter islands consist of ordered arrays of molecule 24. The
striped pattern of the herringbone reconstruction of the gold is
not superimposed to the island structure (in contrast to islands
2
2
2
2
38
of weakly/physisorbed molecules). This is a first indication
that the molecules indeed bind chemically due to the sulfur−
gold bond that lifts the herringbone reconstruction. The
39
molecules arrange in periodic rows (direction d ) that enclose
1
̅
an angle of 11.6° ± 1.5° with the ⟨110⟩ directions of the gold
surface. The direction of periodicity across the rows (direction
The electronic coupling of the rod-type subunit to the
substrate is currently under investigation. Synthetically we are
interested in investigating modular approaches to other
positions of the rigid tripodal platform to increase the spatial
control of attached subunits.
d2) encloses an angle of α = 79° ± 2° with respect to direction
or 28° ± 2° with respect to ⟨11
.36 nm and u = 1.52 nm, respectively. From the length of the
unit vectors and the orientation with respect to the underlying
Au(111) surface we can infer a commensurate √21 × 3√3
structure for the molecules as shown in Figure 4(b). The
commensurability also indicates a strong interaction with the
surface. Therefore, the applied deposition procedure from
1
1
̅
1
0⟩. The unit vectors are u =
2
EXPERIMENTAL SECTION
■
Materials. All starting materials and reagents were obtained from
commercial suppliers and used without further purification. TLC was
performed on silica gel 60 F254 plates, spots were detected by
fluorescence quenching under UV light at 254 nm, and/or staining
with appropriate solutions (anisaldehyde, phosphomolybdic acid,
CH Cl2 and subsequent annealing at 400 K apparently
2
promotes the on-surface deprotection, enabling the S−Au
bond and immobilization by covalent S−Au bonds of the tripod
structures with all three anchoring groups.
By recording images in constant height mode (mapping the
current while keeping the distance to the gold sample
constant), we were able to resolve a submolecular structure
KMnO
). Column chromatography was performed on silica gel 60
4
(
0.040−0.063 mm). All experimental manipulations with anhydrous
solvents were carried out in flame-dried glassware under inert
atmosphere of argon. Degassed solvents were obtained by three
cycles of the freeze−pump−thaw. Tetrahydrofuran, dioxane, toluene
and diethyl ether were dried and distilled from sodium/benzophenone
under argon atmosphere. Acetonitrile, dichlormethane and triethyl-
(
Figure 4(c)). The elongated form of the molecule is clearly
imaged. The middle part of the molecule, where the side legs
couple very well to the surface carries large currents and is
brightly imaged, while the neck obviously shows weaker
coupling, therefore is imaged fainter. The region of the third
leg is so far from the tip, that we do not map a current any
more (note that in cc mode, the tip does not compensate for
height differences and that the tunneling current decreases by
an order of magnitude if the distance increases by 1 Å.). If we
record constant height images at a distance, where the tip
touches the molecule, we will measure a direct and, therefore,
strongly increased current. Narrowing the gap between tip and
sample this will first occur at the most protruding position,
above other parts of the molecules we still obtain a tunneling
current and the image is only slightly altered there. This
situation is shown in Figure 4(d). The contact is made at the
very end of the elongated structure and coincides with the
position of the cyano group. The distances in the constant
height images fit perfectly with the distances of the
corresponding subunits of the molecule. From Figure 4(c)
we can infer the angle between the long axis of the molecule
with respect to the unit vectors of the unit cell. Figure 4(b)
shows the molecules arranged according to these angles. In this
orientation all three of the sulfur legs anchor in equivalent
positions (in the model we chose on-top for clarity).
amine were dried and distilled from CaH under argon atmosphere.
2
Diphenyl ether was dried over 4 Å molecular sieves. 2-Bromo-9H-
40
fluorene was prepared according to published procedure.
Equipment and Measurements. All NMR spectra were recorded
1
at 25 °C in CDCl , CD Cl or acetone-d . H NMR (500.16 MHz)
3
2
2
6
spectra were referenced to TMS as internal standard (δ = 0 ppm) or
H
to the solvent residual proton signal (CDCl , δ = 7.24 ppm; CD Cl
3
H
2
2,
13
δ = 5.32 ppm; acetone-d , δ = 2.05 ppm). C NMR (125.78 MHz)
H
6
H
spectra with total decoupling of protons were referenced to the solvent
CDCl , δ = 77.23 ppm, CD Cl δ = 54.00 ppm, acetone-d , δ =
(
3
C
2
2,
C
6
C
19
1
29.92 ppm). F{ H} NMR (470.57 MHz) spectra were referenced to
CFCl as an external standard in a coaxial capillary (δ = 0.00 ppm).
3
F
11
1
B{ H} NMR (160.47 MHz) spectra were referenced to BF
·Et O as
2
3
an external standard in a coaxial capillary (δ = 0.00 ppm). For correct
B
1
13
1
1
13
assignment of both H and C NMR spectra, the H− H COSY,
C
DEPT-135, HSQC and HMBS experiments were performed; EI MS
spectra were recorded with a GC−MS instrument (samples were
dissolved in diethyl ether, chloroform or introduced directly using
direct injection probes DIP, DEP) and m/z values are given along with
their relative intensities (%) at an ionizing voltage of 70 eV. UV−vis
spectra were recorded with a UV−vis spectrophotometer in a 1 cm
quartz cell at ambient temperature (extinction coefficients are given
−1
−1
below in units of L mol cm ). Fluorescence spectra were measured
at room temperature in a 1 cm quartz cell. HRMS spectra were
obtained with an ESI-TOF mass spectrometer. IR spectra were
measured in KBr pellets. Analytical samples were dried at 40−100 °C
All together the quenching of the gold reconstruction, the
commensurability with the surface structure and the orientation
of the molecule as found by constant height imaging, support
the concept of the tripodal structure to stabilize the molecule
on the Au(111) surface and to control the spatial arrangement
of the molecular rod in an upright orientation.
−
2
under reduced pressure (10 mbar). Melting points were measured
with a melting point apparatus and are not corrected. Elemental
analyses were obtained using an elemental analyzer. Molecules have
been deposited onto an Au(111) surface by spray deposition. The gold
single crystal was cleaned by repeated cycles of argon ion sputtering
and annealing to 720 K. The clean crystal was transferred to a simple
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The Journal of Organic Chemistry
Article
vacuum chamber (ca. 5 mbar). A droplet of 24 dissolved in CH Cl
NaH (3.63 g, 90.6 mmol, 60% in mineral oil) and dry DMF (80 mL)
under argon. After cooling to −5 °C (ice bath, NaCl) a solution of 2
(6 g, 2.65 mmol) in dry DMF (80 mL) was dropwise added over 30
min. [Note: Where the reaction mixture solidifies, more DMF was
added to enable efficient stirring.] After the addition was complete,
stirring was continued for 2 h at room temperature, then the reaction
suspension was cooled down to ∼0 °C, and N,N-diethylthiocarbamoyl
chloride (15.2 g, 100 mmol) was added portionwise as a solid. The
reaction mixture was allowed to warm to room temperature, stirred at
room temperature for 2 h, and then at 80 °C for 12 h. After cooling to
room temperature, the yellow suspension was poured into a mixture of
crushed ice (ca. 500 g) and CH Cl (400 mL), and the two phases
2
2
−5
(conc. approximately 9 × 10 M) was sprayed into the chamber by
opening the pulse valve for 10 ms. This way, a mist including the
dissolved molecules is deposited onto the sample. The sample was
then transferred to UHV and mildly annealed at T = 400 K for 60 min
to remove remaining solvent molecules. The sample was then
transferred to our custom built scanning tunneling microscope
(
STM). STM images were measured in constant current mode at 5 K.
20,41
2
-Bromo-5,3′-dimethoxy-1,1′-biphenyl (1).
To a solution of
3
,3′-dimethoxybiphenyl (12 g, 56 mmol) in dry acetonitrile (130 mL)
stirred under argon at −5 °C was dropwise added a solution of NBS
(
10 g, 56 mmol) in dry acetonitrile (130 mL) over 1 h. The slightly
2
2
yellow solution was stirred at 0 °C for an additional 4 h, after which
the reaction mixture was heated up to room temperature and stirred
overnight. The completion of the reaction was checked by TLC
were separated. The aqueous phase was washed with CH Cl (3 × 150
2 2
mL). The combined organic layer was subsequently washed with
NaOH (150 mL, 2% aqueous solution), brine (100 mL), and dried
over magnesium sulfate. After filtration and evaporation of all solvents,
the crude brown oil was purified by column chromatography on silica
gel (1200 g) in the gradient of hexane:CH Cl equal to 2:1−1:2 to
(
Hex:CH Cl = 2:1). Water (50 mL) was added, and organic solvents
2 2
were evaporated under reduced pressure. The aqueous layer was
extracted with dichloromethane (3 × 100 mL). The combined organic
layer was subsequently washed with Na SO (60 mL, 10%), brine (60
2
2
provide O-thiocarbamate 3 as a pale yellow oil (7.74 g) in 69% yield
2
3
1
mL), and dried over magnesium sulfate. After filtration and
evaporation of the solvent, the crude light yellow oil was purified by
column chromatography on silica gel (2000 g) in the mixture of
hexane:CH Cl equal to 8:1 to afford pure product 1 (14.95 g, 91%) as
(R = 0.28, Hex:EtOAc = 5:1): H NMR (500 MHz, CD Cl ) δ ppm
f
2
2
1.27−1.35 (m, 12H, CH ), 3.65−3.72 (m, 4H, CH ), 3.84−3.91 (m,
3
2
4
4H, CH ), 6.97 (dd, J = 9 Hz, J = 3 Hz, 1H, C H), 7.08−7.10 (m, 1H,
2
4
2
2
2
2
C ′H), 7.10−7.12 (m, 1H, C H), 7.13−7.15 (m, 1H, C ′H), 7.32 (dt, J
6
5
a colorless oil that crystallized on standing (R = 0.28, Hex:CH Cl =
= 8 Hz, J = 1H, C ′H), 7.45 (td, J = 8 Hz, J = 1H, C ′H), 7.67 (d, J = 9
5 13
f
2
2
1
4
:1): mp 64−66 °C; H NMR (500 MHz, CD Cl ) δ ppm 3.80 (s, 3H,
Hz, 1H, C H); C NMR (125.8 MHz, CD Cl ) δ ppm 12.06 (CH ),
2 2 3
2
2
4
CH ), 3.83 (s, 3H, CH ′), 6.80 (dd, J = 9 Hz, J = 3.5 Hz, 1H, C H),
12.12 (CH ), 13.88 (CH ), 13.90 (CH ), 44.95 (CH ), 45.00 (CH ),
3
3
3 3 3 2 2
6
4
6
2
4
6
(
7
.89 (d, J = 3.5 Hz, 1H, C H), 6.85−6.90 (m, 1H, C ′H), 6.91−6.95
48.9 (CH ), 49.0 (CH ), 119.1 (C ), 122.9 (C H), 124.3 (C H), 124.5
2 2
2
6
2
4
6
5
5
m, 1H, C ′H), 6.96−7.00 (dt, J = 8 Hz, J = 1 Hz, 1H, C ′H), 7.31−
(C ′H), 126.3 (C ′H), 127.2 (C ′H), 129.2 (C ′H), 134.1 (C H),
1 1 3 3
5
.37 (td, J = 7.5 Hz, J = 1 Hz, 1H, C ′H), 7.54 (d, J = 8.5 Hz, 1H,
141.8 (C ′), 142.7 (C ), 153.8 (C ), 154.4 (C ′), 186.7 (CS), 187.2
3
13
−1
C H); C NMR (125.8 MHz, CD Cl ) δ ppm 55.8 (CH ), 56.1
(CS); IR (KBr) ν cm 3056 (w, ν(CH)), 2976 (m) and 2934
2
2
3
2
4
4
2
(
(
(
CH ′), 113.2 (C ), 113.7 (C ′H), 115.3 (C H), 115.6 (C ′H), 117.2
(m, ν (CH CH )), 2873 (w, ν (CH CH )), 1584 (w) and 1569 (w,
3
as
2,
3
s
2,
3
6
6
5
3
1
C H), 122.2 (C ′H), 129.6 (C ′H), 134.2 (C H), 143.0 (C ), 143.8
ν(CC), Ph), 1513 (vs), 1458 (s), 1428 (s), 1316 (s), 1286 (s), 1231
(s), 1197 (s), 1174 (s), 1118 (m), 1094 (m), 1022 (m), 965 (w), 944
(w), 909 (w), 875 (w, β (CH CH )), 789 (m), 697 (m) and 667 (w,
1
5
3
C ′), 159.5 (C ), 159.8 (C ′); EI MS m/z (%) 294 (99), 292 (100,
+
−1
M ), 213 (12), 198 (25), 139 (26), 86 (26); IR (KBr) ν cm 3006
w, ν(CH)), 2958 (m) and 2936 (m, ν (CH )), 2857 (m,
as
2,
3
+
(
ν(CH)); EI MS m/z (%) 496 (2), 494 (2, M ), 415 (1), 116 (100),
100 (77), 88 (92), 84 (28), 72 (67), 60 (49). Anal. Calcd for
C H BrN O S (495.49): C, 53.33; H, 5.49; N, 5.65. Found: C,
as
3
ν (CH )), 1591 (s) and 1567(s, ν(CC), Ph), 1491 (m), 1464 (s),
s
3
1438 (s), 1285 (s), 1254 (s), 1231 (vs), 1204 (s), 1174 (m), 1049 (m,
22
27
2
2 2
Ph), 1031 (vs, Ph), 1013 (s), 873 (m, β (CH )), 804 (s), 781 (m),
53.41; H, 5.45; N, 5.71.
as
3
7
00 (m) and 601 (m, ν(CH)). Anal. Calcd for C H BrO (293.16):
O , O ′ - ( 2 - B r o m o - 1 , 1 ′ - b i p h e n y l - 5 , 3 ′ - d i y l ) b i s -
(dimethylthiocarbamate) (4). The desired product was prepared
according to the method described for the preparation of 3, starting
from 2 (34 g, 128 mmol) in dry DMF (300 mL), NaH (14.8 g, 370
mmol, 60% in mineral oil) in dry DMF (300 mL) and N,N-
dimethylthiocarbamoyl chloride (47.5 g, 384 mmol). The reaction
mixture was heated at 80 °C for 26 h under argon atmosphere. The
completion of the reaction was checked by TLC (Hex:EtOAc = 1:1).
The crude reaction mixture was purified by column chromatography
on silica gel (4000 g) in the gradient of hexane:CH Cl equal to 2:1−
14
13
2
C, 57.36; H, 4.47. Found: C, 57.08; H, 4.61.
2
7
2
-Bromo-1,1′-biphenyl-5,3′-diol (2). To a solution of 1 (15 g, 51
mmol) in dry dichloromethane (350 mL) stirred under argon at −78
C was dropwise added BBr (150 mL, 150 mmol, 1 M in CH Cl )
°
3
2
2
over 30 min. The dark red reaction mixture was stirred at −78 °C for
an additional 1 h, and then allowed to warm to room temperature and
stirred at room temperature for 26 h. The completion of the reaction
was checked by TLC (Hex:CH Cl = 2:1, Hex:EtOAc = 1:1). The
2
2
flask was placed in an ice bath and water (250 mL) was slowly added.
2
2
The aqueous layer was extracted with CH Cl (3 × 150 mL). The
1:2. The O-thiocarbamate 4 was isolated as a white foamy solid (42.1
2
2
1
combined organic layer was subsequently washed with Na SO (100
g) in 75% yield (R = 0.38, CH Cl ): mp 67−68 °C; H NMR (500
2
3
f
2
2
mL, 10%), brine (100 mL), and dried over magnesium sulfate. After
filtration and evaporation of the solvent, the crude light brown oil was
purified by column chromatography on silica gel (1500 g) in the
gradient of hexane:EtOAc equal to 8:1−2:1. The product 2 was
MHz, CDCl ) δ ppm 3.32 (m, 6H, CH ), 3.43 (m, 6H, CH ), 6.93
3
3
3
4
4
(dd, J = 8.5 Hz, J = 3 Hz, 1H, C H), 7.04−7.08 (m, 1H, C ′H), 7.08−
2
2
7.10 (m, 1H, C H), 7.11−7.14 (m, 1H, C ′H), 7.32 (dt, J = 8.5 Hz, J =
6
5
1H, C ′H), 7.42 (td, J = 8 Hz, J = 1H, C ′H), 7.63 (d, J = 8.5 Hz, 1H,
5
13
isolated as a light brown solid (12.15 g) in 90% yield (R = 0.58,
C H); C NMR (125.8 MHz, CDCl ) δ ppm 38.98 (CH ), 39.00
3 3
f
1
6
2
Hex:EtOAc = 1:1): mp 142−144 °C; H NMR (500 MHz, acetone-
(CH ), 43.48 (CH ), 43.54 (CH ), 119.2 (C ), 122.5 (C H), 123.8
3 3 3
4
4
2
4
6
5
d ) δ ppm 6.75−6.81 (td, J = 8.5 Hz, J = 3 Hz, 1H, C H), 6.82−6.88
(C H), 124.1 (C ′H), 125.9 (C ′H), 127.2 (C ′H), 128.9 (C ′H),
5 1 1 3 3
6
2,2 ,4 ,6
5
(
m, 4H, C ′ ′ ′H), 7.25 (m, 1H, C ′H), 7.48 (d, J = 8.5 Hz, 1H,
133.8 (C H), 141.4 (C ′), 142.4 (C ), 153.2 (C ), 153.8 (C ′), 187.4
5
13
−1
C H), 8.61 (bs, 2H, OH); C NMR (125.8 MHz, acetone-d ) δ ppm
(CS), 187.8 (CS); IR (KBr) ν cm 3054 (vw, ν(CH)), 2932
6
6
4
2
4
2
1
1
1
11.8 (C ), 115.5 (C ′H), 117.1 (C ′H), 117.2 (C H), 119.0 (C H),
(m, ν (CH )), 2870 (w, ν (CH )), 1573 (m, ν(CC), Ph), 1538 (vs),
as
3
s
3
6
5
5
1
1
21.3 (C ′H), 130.0 (C ′H), 134.7 (C H), 143.5 (C ′), 144.4 (C ),
1459 (s), 1393 (vs), 1285 (s), 1254 (m), 1203 (vs), 1181 (s), 1126
3
5
−1
57.8 (C ′), 157.9 (C ); IR (KBr) ν cm 3234 (bs, ν(OH)), 1582 (s,
(vs), 1062 (m), 1021 (m), 974 (w), 909 (vw), 875 (w, β (CH )), 838
as
3
ν(CC), Ph), 1458 (s), 1453 (s), 1429 (s), 1308 (s), 1255 (m), 1236
(m), 818 (w), 793 (m), 698 (m, ν(CH)); EI MS m/z (%) 440 (2),
+
(
(
(
vs), 1218 (vs), 1178 (vs), 1021 (w), 941 (w), 858 (m), 832 (m), 808
438 (2, M ), 88 (100), 86 (72), 84 (93), 72 (92), 51 (31), 49 (82), 47
m), 780 (m), 696 (m, ν(CH)); ESI(−) HRMS Calcd for C H BrO
(14), 44 (11). Anal. Calcd for C H BrN O S (439.39): C, 49.20; H,
12
8
2
18 19
2
2 2
−
[M − H] , 262.9713), found m/z 262.9710. Anal. Calcd for
4.36; N, 6.38. Found: C, 49.51; H, 4.48; N, 6.25.
C H BrO (265.11): C, 54.37; H, 3.42. Found: C, 55.09; H, 3.80.
S,S′-(2-Bromo-1,1′-biphenyl-5,3′-diyl) bis(diethylthiocarbamate)
(5). A 250 mL Schlenk flask fitted with a reflux condenser, an argon
inlet and a boiling chips was charged with O-thiocarbamate 3 (7.1 g,
14.3 mmol) and dry diphenyl ether (80 mL) under argon. The flask
12
9
2
O,O′-(2-Bromo-1,1′-biphenyl-5,3′-diyl) bis(diethylthiocarbamate)
3). A 500 mL three-necked flask fitted with a dropping funnel, a reflux
condenser, an argon inlet and a magnetic stirring bar was charged with
(
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The Journal of Organic Chemistry
Article
was heated at 250−260 °C for 10 h under argon in a mineral oil bath.
After cooling to room temperature, diphenyl ether was distilled off
found m/z 294.9239. Anal. Calcd for C H BrS (297.23): C, 48.49;
H, 3.05. Found: C, 48.70; H, 3.18.
2-Bromo-1,1′-biphenyl-5,3′-diyl bis(trifluoromethansulfonate)
(8). Triflic anhydride (11.7 g, 7 mL, 41.6 mmol) was added dropwise
to a solution of 2 (5 g, 18.9 mmol) in dry triethylamine (8.1 g, 11 mL,
12
9
2
−2
under the reduced pressure (10 mbar) at 130 °C, and the crude
brown oil was purified by column chromatography on silica gel (2300
g) in the gradient of hexane:CH Cl = 1:6−pure CH Cl to provide S-
2
2
2
2
8
0 mmol) and dichloromethane (120 mL) at −78 °C under argon.
thiocarbamate 5 as a pale yellow oil (6.8 g) in 95% yield (R = 0.21,
f
1
The solution was stirred for 4 h, and then allowed to warm to room
temperature and stirred for an additional 6 h. The resulting solution
was passed through a pad of silica gel (60 g), and washed with CH Cl
2
CH Cl :MeOH = 100:1): H NMR (500 MHz, CDCl ) δ ppm 1.15
2
2
3
and 1.25 (bs, 12H, CH ), 3.37−3.45 (m, 8H, CH ), 7.32 (dd, J = 8 Hz,
3
2
4
6
5
J = 2 Hz, 1H, C H), 7.39−7.45 (m, 2H, C ′H, C ′H), 7.45−7.47 (m,
2
2
4
2
(100 mL). After extraction with NH Cl (100 mL, 10%) and drying
1
H, C H), 7.50−7.55 (m, 2H, C ′H, C ′H), 7.64 (d, J = 8 Hz, 1H,
4
5
13
with magnesium sulfate, the solvents were evaporated under reduced
pressure. The crude product was purified by column chromatography
C H); C NMR (125.8 MHz, CDCl ) δ ppm 13.4 (CH ), 14.1
3
3
6
6
3
3
(
(
1
CH ), 42.7 (CH ), 124.0 (C ), 128.6 (C ′H, C ), 128.9 (C ′), 130.4
3
2
5
5
4
4
2
on silica gel (800 g) in hexane:EtOAc (30:1) to give triflate 8 (9.6 g)
C ′H), 133.7 (C H), 135.3 (C ′H), 136.2 (C H), 136.4 (C ′H),
1
2
1
1
as a clear, colorless oil in 96% yield (R = 0.38, Hex:EtOAc = 20:1): H
38.2 (C H), 141.0 (C ′), 142.3 (C ), 165.00 (CO), 165.6 (C
f
−1
NMR (500 MHz, CDCl ) δ ppm 7.19 (dd, J = 8.5 Hz, J = 3 Hz, 1H,
O); IR (KBr) ν cm 3058 (w, ν(CH)), 2974 (m) and 2934 (w,
3
4
2
2
4
C H), 7.23 (d, J = 4 Hz, 1H, C H), 7.33−7.37 (m, 2H, C ′H, C ′H),
ν (CH CH )), 2873 (w, ν (CH CH )), 1664 (vs, ν(CO)), 1593
as
2,
3
s
2,
3
6
7
.40 (dt, J = 7.5 Hz, J = 1 Hz, 1H, C ′H), 7.55 (td, J = 8 Hz, J = 0.5
(
(
vw) and 1576 (vw, ν(CC), Ph), 1453 (m), 1405 (s), 1380 (m), 1362
5 5 13
Hz, 1H, C ′H), 7.76 (d, J = 8.5 Hz, 1H, C H); C NMR (125.8 MHz,
m), 1307 (m), 1248 (s), 1217 (s), 1117 (s), 1098 (s), 1071 (m),
1
1
CDCl ) δ ppm 118.9 (d, J = 320.7 Hz, CF ), 119.0 (d, J = 320.7
1
019 (m), 941 (w), 887 (w, β (CH CH )), 853 (s), 790 (m), 697
3
CF
3
CF
as
2,
3
4
6
2
4
+
Hz, CF ), 121.7 (C ′H), 122.3 (C ), 122.61 (C ′H), 122.64 (C H),
3
(
(
w) and 659 (m, ν(CH)); EI MS m/z (%) 496 (6), 494 (6, M ), 100
100), 86 (73), 84 (85), 72 (71), 51 (42), 49 (77), 44 (19). Anal.
2
6
5
5
1
1
1
24.1 (C H), 129.4 (C ′H), 130.6 (C ′H), 135.3 (C H), 141.6 (C ′),
1 3 3 19 1
42.7 (C ), 148.7 (C ), 149.4 (C ′); F{ H} NMR (470.6 MHz,
−1
Calcd for C H BrN O S (495.49): C, 53.33; H, 5.49; N, 5.65.
22
27
2
2
2
CDCl ) δ ppm −72.61 (s, CF ), −72.71 (s, CF ); IR (KBr) ν cm
3
3
3
Found: C, 53.50; H, 5.37; N, 5.52.
3
1
9
086 (bw, ν(CH)), 1598 (w), 1579 (w) and 1567 (w, ν(CC), Ph),
S , S ′ - ( 2 - B r o m o - 1 , 1 ′ - b i p h e n y l - 5 , 3 ′ - d i y l ) b i s -
460 (s), 1429 (vs), 1242 (vs), 1212 (vs, ν(CF )), 1027 (m, ν (SO )),
(
dimethylthiocarbamate) (6). The product was prepared according
3
s
3
45 (s), 888 (vs), 829 (s), 797 (w), 694 (w), 626 (m), 609 (s,
to the method described for the preparation of S-thiocarbamate 5,
starting from 4 (13 g, 29.6 mmol) in dry diphenyl ether (120 mL).
The reaction mixture was heated at 250−260 °C for 16 h under argon
atmosphere. The crude reaction mixture was purified by column
chromatography on silica gel (3000 g) in the gradient of
hexane:EtOAc equal to 3:1−2:1. The pure product 6 was isolated as
δ (CF )), and 515 (m, δ (CF )); EI MS m/z (%) 530 (83), 528 (81,
s
3
as
3
+
M ), 397 (81), 395 (82), 369 (89), 367 (89), 305 (54), 303 (55), 155
(
1
100), 84 (64). Anal. Calcd for C H BrF O S (529.22): C, 31.77; H,
14 7 6 6 2
.33. Found: C, 31.82; H, 1.35.
-Bromo-3-[2-(trimethylsilyl)ethylsulfanyl]benzene (9). A 25 mL
1
pressure tube was charged with 3-bromothiophenol (14.3 g, 75.5
mmol), vinyltrimethylsilane (8.9 g, 13 mL, 88.8 mmol) and di-tert-
butyl peroxide (2 mL, 10.6 mmol) under argon. The tube was sealed,
and stirred at 100 °C for 20 h. After cooling to room temperature, the
solution was diluted with hexane (400 mL), washed with NaOH (100
mL, 2 M), water (100 mL), and brine (100 mL). The combined
organic layer was dried with magnesium sulfate, and solvents were
evaporated under reduced pressure. The residue was purified by
column chromatography on silica gel (800 g) in hexane to provide
a clear sticky solid (12.1 g) in 93% yield (R = 0.31, Hex:EtOAc = 1:1):
f
1
H NMR (500 MHz, CDCl ) δ ppm 3.01 (bs, 6H, CH ), 3.05 (bs, 6H,
3
3
4
CH ), 7.30 (dd, J = 8 Hz, J = 2 Hz, 1H, C H), 7.34−7.44 (m, 2H,
3
6
5
2
4
C ′H, C ′H), 7.44−7.46 (m, 1H, C H), 7.46−7.54 (m, 2H, C ′H,
2
5
13
C ′H), 7.64 (d, J = 8 Hz, 1H, C H); C NMR (125.8 MHz, CDCl ) δ
3
6
3
6
3
ppm 37.1 (CH ), 124.1 (C ), 128.5 (C ), 128.6 (C ′H), 128.8 (C ′),
3
5
5
4
4
1
30.4 (C ′H), 133.7 (C H), 135.2 (C ′H), 136.1 (C H), 136.4
2 2 1 1
(
(
2
C ′H), 138.1 (C H), 141.0 (C ′), 142.2 (C ), 166.2 (CO), 166.8
−
1
CO); IR (KBr) ν cm 3054 (w, ν(CH)), 2931 (m, ν (CH )),
as
3
product 9 (18.4 g) as a pale yellow oil in 84% yield (R = 0.44,
f
865 (w, ν (CH )), 1669 (vs, ν(CO)), 1592 (w) and 1534 (m,
1
s
3
Hexane): H NMR (500 MHz, CDCl ) δ ppm 0.04 (s, 9H, CH ), 0.91
3
3
ν(CC), Ph), 1455 (m), 1396 (s), 1363 (s), 1286 (m), 1256 (s), 1203
5
(
7
1
(
(
m, 2H, CH Si), 2.94 (m, 2H, SCH ), 7.09−7.13 (m, 1H, C H),
2
2
(
(
(
(
4
s), 1120 (bs), 1094 (s), 1062 (m), 1018 (m), 904 (m, β (CH )), 815
6
4
as
3
.16−7.20 (m, 1H, C H), 7.24−7.28 (m, 1H, C H), 7.38−7.41 (m,
w), 792 (m), 687 (m) and 652 (m, ν(CH)); EI MS m/z (%) 440
2 13
H, C H); C NMR (125.8 MHz, CDCl ) δ ppm −1.6 (CH ), 16.8
+
3
3
11), 438 (10, M ), 88 (18), 86 (87), 84 (95), 72 (100), 51 (42), 49
1
6
4
CH Si), 29.5 (SCH ), 123.0 (C ), 127.1 (C H), 128.7 (C H), 130.3
2 2
92), 47 (16), 44 (13). Anal. Calcd for C H BrN O S (439.39): C,
5
2
3
−1
18
19
2
2 2
C H), 130.9 (C H), 140.1 (C ); IR (KBr) ν cm 3060 (w, ν(
9.20; H, 4.36; N, 6.38. Found: C, 49.01; H, 4.53; N, 6.26.
CH)), 2951 (m, ν (CH CH )), 2895 (w, ν (CH CH )), 1577 (s)
as
2,
3
s
2,
3
2
-Bromo-1,1′-biphenyl-5,3′-dithiol (7). Solid KOH was added
and 1556 (m, ν(CC), Ph), 1460 (s), 1400 (w), 1250 (s), 1165 (w),
portionwise to a degassed solution of S-thiocarbamate 5 (2.1 g, 4.24
mmol) in the mixture of methanol (100 mL) and water (6 mL). The
reaction mixture was heated to reflux (ca. 100 °C) and stirred for 5 h
under argon. The solution was cooled to 0 °C and acidified with HCl
1
7
083 (w), 1068 (w), 1011 (w), 991 (w), 856 (s), 841 (s), 769 (m),
55 (m), 693 (w) and 677 (w, ν(CH)); EI MS m/z (%) 290 (3), 288
+
(3, M ), 262 (5), 260 (5), 247 (4), 245 (4), 88 (10), 86 (64), 84
100), 73 (52), 51 (29), 49 (90), 44 (49), 28 (24). Anal. Calcd for
(
(
1 M) to pH ≈ 1. After removal of methanol under reduced pressure,
C H BrSSi (289.31): C, 45.67; H, 5.92. Found: C, 45.78; H, 6.05.
11
17
the aqueous residue was washed with CH Cl (3 × 120 mL). The
2
2
3-[2-(Trimethylsilyl)ethylsulfanyl]phenylboronic acid pinacol
combined organic layer was washed with water (100 mL), brine (100
mL), and dried over magnesium sulfate. After filtration and
ester (10). In a 500 mL Schlenk flask, bromide 9 (8 g, 27.5 mmol)
was dissolved in THF (150 mL) under argon and cooled to −78 °C.
The solution was treated with n-BuLi (14.1 g, 21 mL, 33 mmol, 15% in
hexane) and the reaction mixture was stirred for 30 min at −78 °C.
Triisopropyl borate (7.3 g, 39 mmol) was added dropwise, and the
reaction mixture was stirred for 1 h at −78 °C, and then allowed to
warm to room temperature and stirred overnight. The milky solution
was quenched with water (50 mL), and HCl solution (50 mL, 1 M)
was added. After evaporation of the organic solvents, an additional
HCl solution (100 mL, 1 M) was added and white suspension was
quickly stirred for 1 h. White solid was filtered off, washed with water
(3 × 60 mL), pentane (2 × 50 mL) and vacuum-dried (10− mbar, 40
°C). The boronic acid was isolated as a white solid (5.85 g) in 84%
yield. The product was further converted to the pinacol ester, which
was prepared from the boronic acid (5.8 g, 22.8 mmol), pinacol (4.6 g,
evaporation of the solvent, the product was isolated as a pale brown
1
oil (1.22 g) in 97% yield: H NMR (500 MHz, CDCl ) δ ppm 3.45 (s,
3
1
H, SH′), 3.49 (s, 1H, SH), 7.09 (dd, J = 8.5 Hz, J = 2.5 Hz, 1H,
4
4
2
C H), 7.13−7.17 (m, 1H, C ′H), 7.18−7.20 (m, 1H, C H), 7.25−7.30
6
5
2
5
13
(
(
(
1
m, 3H, C ′H, C ′H, C ′H), 7.49 (d, J = 8.5 Hz, 1H, C H); C NMR
6
4
125.8 MHz, CDCl ) δ ppm 119.7 (C ), 126.9 (C ′H), 128.95
3
6
2
4
5
3
C ′H), 128.98 (C ′H), 130.0 (C H), 130.2 (C ′H), 130.8 (C ′),
3
2
5
1
1
31.0 (C H), 131.8 (C H), 133.8 (C H), 141.4 (C ′), 142.6 (C ); IR
−1
(
1
1
KBr) ν cm 3050 (w, ν(CH)), 2566 (m, ν(S−H)), 1592 (m) and
2
575 (m, ν(CC), Ph), 1452 (vs), 1405 (m), 1375 (m), 1292 (vw),
268 (vw), 1245 (vw), 1140 (m), 1108 (s), 1018 (s), 920 (w), 878
(
m), 843 (w), 811 (s), 787 (vs), 729 (w), 708 (w), and 696 (s,
−
ν(CH)); ESI(−) HRMS Calcd for C H BrS ([M − H] , 294.9245),
12
8
2
7
352
dx.doi.org/10.1021/jo501029t | J. Org. Chem. 2014, 79, 7342−7357

The Journal of Organic Chemistry
Article
3
9 mmol) and toluene (100 mL) by azeotropic distillation. After 12 h
acetate equal to 50:1) to provide the title compound 12 (432 mg) as a
of reflux, toluene was distilled off, and the light yellow residue was
purified by sublimation on a Kugelrohr apparatus at 180 °C and 3 ×
pale yellow oil (which contains about 10% of other isomers) in 46%
1
yield: H NMR (500 MHz, CDCl ) δ ppm 0.02 (s, 18H, CH ), 0.93
3
3
−
1
1
8
0
mbar to provide 7.4 g of pure pinacol ester 10 as a white solid in
(m, 4H, CH Si), 2.96 (m, 4H, SCH ), 7.10 (dd, J = 7.5 Hz, J = 2 Hz,
2
2
1
4
6
0% yield (after two steps): mp 53−54 °C; H NMR (500 MHz,
1H, C H), 7.16 (dt, J = 7 Hz, J = 2 Hz, 1H, C ′H), 7.21 (d, J = 2.5 Hz,
2 4 5
CD Cl ) δ ppm 0.05 (s, 9H, CH , TMS), 0.93 (m, 2H, CH Si), 1.33
1H, C H), 7.28−7.35 (m, 2H, C ′H, C ′H), 7.30 (d, J = 2 Hz, 1H,
2
2
3
2
5
2
5
13
(
s, 12H, CH , Bpin), 2.99 (m, 2H, SCH ), 7.26−7.32 (m, 1H, C H),
C ′H), 7.53 (d, J = 8.5 Hz, 1H, C H); C NMR (125.8 MHz, CDCl )
3
2
3
6
4
7
1
1
.36−7.42 (m, 1H, C H), 7.52−7.57 (m, 1H, C H), 7.68−7.72 (m,
δ ppm −1.52 and −1.50 (CH ), 17.0 and 17.1 (CH Si), 29.69 and
3
2
2
13
6
6
5
4
H, C H); C NMR (125.8 MHz, CD Cl ) δ ppm −1.6 (CH , TMS),
7.5 (CH Si), 25.2 (CH , Bpin), 29.8 (SCH ), 84.5 (C, Bpin), 128.8
29.71 (SCH ), 119.6 (C ), 126.8 (C ′H), 128.3 (C ′H), 128.7 (C ′H),
2
2
3
2
4 2 2 5 3
129.1 (C H), 129.7 (C ′H), 131.2 (C H), 133.5 (C H), 137.3 (C ),
2
3
2
5
6
4
2
3
11
1
3 1 1 −1
(
C H), 132.0 (C H), 132.3 (C H), 135.4 (C H), 137.4 (C ); B{ H}
137.4 (C ′), 141.5 (C ′), 142.6 (C ); IR (KBr) ν cm 3053 (vw, ν(
CH)), 2952 (s, ν (CH CH )), 2914 (w, ν (CH CH )), 1591 (w),
−1
NMR (160.5 MHz, CD Cl ) δ ppm 30.8; IR (KBr) ν cm 3054 (w,
2
2
as
2,
3
s
2,
3
ν(CH)), 2954 and 2975 (s, ν (CH CH )), 2893 (m, ν (CH
as
2,
3
s
2,
CH )), 1593 (s) and 1561 (m, ν(CC), Ph), 1478 (s, δ (CH ), Bpin),
s
3
3
as
3
1
1
1
400 (bs, δ (CH ), Bpin), 1353 (vs) and 1322 (vs, ν(CC), Bpin),
3
s
3
+
273 (vs), 1250 (vs, δ (CH ), TMS), 1213 (m), 1162 (s), 1143 (s),
3
s
3
112 (s), 1087 (m), 965 (s, Bpin), 885 (s), 865 (vs, β (CH ), Bpin,
as
3
δ (CH ), TMS), 793 (s), 724 (s), 705 (s, v (SiC ), TMS), 667 (m,
as
3
as
3
+
ν(CH), Bpin); EI MS m/z (%) 336 (8, M ), 308 (26), 208 (15), 166
36), 151 (20), 86 (60), 84 (86), 73 (100), 49 (80). Anal. Calcd for
(
C H BO SSi (336.37): C, 60.70; H, 8.69. Found: C, 60.98; H, 8.51.
17
29
2
3
,3′-Bis[2-(trimethylsilyl)ethylsulfanyl]-1,1′-biphenyl (11). A 500
mL Schlenk flask was charged with aryl bromide 9 (2.9 g, 10 mmol),
pinacol ester 10 (3.5 g, 10.4 mmol), sodium carbonate (4.2 g, 40
mmol) and put under argon. Toluene (100 mL) and water (10 mL)
were added, and the resulting solution was degassed before Pd(PPh3)4
(693 mg, 0.6 mmol) was added. The reaction mixture was again
degassed (3×), and then heated at 95 °C for 18 h. The completion of
the reaction was checked by TLC (Hex:CH Cl = 50:1). After cooling
2
2
to room temperature, the dark reaction mixture was passed through a
short pad of silica gel (40 g) and washed with CH Cl (300 mL).
Solvents were evaporated under reduced pressure, and the crude
product was purified by column chromatography on silica gel (800 g,
extracted with diethyl ether (3 × 80 mL). The combined organic layer
was subsequently washed with brine (100 mL), and dried over
magnesium sulfate. After filtration over a short pad of silica gel (80 g,
diethyl ether), evaporation, and drying under a vacuum (10− mbar),
2
2
2
Hex:CH Cl2 = 80:1) to provide biphenyl 11 (3.4 g) as a clear,
2
1
colorless oil in 80% yield (R = 0.24, Hex:CH Cl = 50:1): H NMR
the pure product was isolated as a light yellow oil (2.1 g) in 96% yield
f
2
2
1
(
3
500 MHz, CD Cl ) δ ppm 0.06 (s, 18H, CH ), 0.97 (m, 4H, CH Si),
(R
0.02 (s, 18H, CH
(m, 2H, SCH ), 2.98 (m, 2H, SCH
f
= 0.40, Hex:CH
2
Cl
2
= 50:1): H NMR (500 MHz, CDCl
3
) δ ppm
Si′), 2.94
′), 6.93 (dd, J = 8 Hz, J = 2 Hz,
2
2
3
2
6
,6
.03 (m, 4H, SCH ), 7.27−7.32 (m, 2H, C ′H), 7.34−7.40 (m, 4H,
), 0.92 (m, 2H, CH Si), 0.96 (m, 2H, CH
3 2 2
2
4,4
5,5
2,2
13
C ′H, C ′H), 7.49−7.52 (m, 2H, C ′H); C NMR (125.8 MHz,
2
2
4
6
2
CD Cl ) δ ppm −1.5 (CH ), 17.4 (CH Si), 29.9 (SCH ), 125.0
1H, C H), 7.16 (m, 1H, C ′H), 7.18 (d, J = 2.5 Hz, 1H, C H), 7.23
2
2
3
2
2
4
,4
2,2
6,6
5,5
3,3
2
4
5
(
1
C ′H), 127.8 (C ′H), 128.1 (C ′H), 129.8 (C ′H), 138.8 (C ′),
(m, 1H, C ′H), 7.29−7.35 (m, 2H, C ′H, C ′H), 7.79 (d, J = 8 Hz,
1,1
−1
5 13
41.9 (C ′); IR (KBr) ν cm 3057 (w, ν(CH)), 2952 (bs,
1H, C H); C NMR (125.8 MHz, CDCl
(CH ), 16.9 and 17.1 (CH Si), 29.4 and 29.7 (SCH
126.7 (C ′H), 128.3 (C ′H), 128.7 (C ′H), 128.9 (C H), 129.6
3
) δ ppm −1.52 and −1.46
6
ν (CH CH )), 2918 (m, ν (CH CH )), 1586 (s) and 1561 (m,
3
2
), 94.4 (C ),
2
as
2,
3
s
2,
3
6
4
5
4
ν(CC), Ph), 1465 (m), 1422 (w), 1384 (w), 1260 (s), 1251 (s,
2
2
3
3
5
δ (CH ), TMS), 1162 (s), 1106 (w), 1088 (w), 1009 (m), 852 (bs,
(C ′H), 129.8 (C H), 137.4 (C ′), 138.4 (C ′), 139.8 (C H), 144.5
s
3
1
1
−1
δ (CH ), TMS), 773 (m), 701 (m, v (SiC ), TMS); EI MS m/z (%)
(C ′), 146.7 (C ); IR (KBr) ν cm 3054 (vw, ν(CH)), 2951 (s,
)), 2916 (w, ν (CH2, CH )), 1590 (w), 1567 (m) and
1539 (w, ν(CC), Ph), 1476 (w), 1448 (m), 1421 (w), 1365 (w), 1260
(m), 1249 (s, δ (CH ), TMS), 1164 (w), 1101 (m), 1008 (m), 858
(vs) and 841 (vs, δas(CH ), TMS), 786 (w), 753 (w), 731 (w), 697
(m, vas(SiC ), TMS); EI MS m/z (%) 544 (5, M ), 488 (13), 101
as
3
as
3
+
4
18 (12, M ), 362 (24), 347 (8), 101 (11), 73 (100), 51 (31). Anal.
ν
as(CH2, CH
3
s
3
Calcd for C H S Si (418.80): C, 63.09; H, 8.18. Found: C, 63.17;
22
34
2
2
H, 8.23.
-Bromo-5,3′-bis[2-(trimethylsilyl)ethylsulfanyl]-1,1′-biphenyl
12). Method A: A 25 mL pressure tube was charged with thiol 7 (2.9
s
3
2
3
+
(
3
g, 9.8 mmol), vinyltrimethylsilane (7.8 g, 11.5 mL, 78.1 mmol) and
AIBN (82 mg, 0.5 mmol) under argon. The tube was sealed and
stirred at 100 °C for 30 h. After cooling to room temperature, the
solution was diluted with CH Cl (150 mL), passed through a short
(14), 73 (100). Anal. Calcd for C22
6.11. Found: C, 48.78; H, 6.23.
2-Bromo-7-iodo-9H-fluorene (14)..
H
33IS
2
Si
2
(544.70): C, 48.51; H,
42,43
A 500 mL Schlenk flask
was charged with 2-bromo-9H-fluorene (15 g, 61 mmol), iodine (6.6
g, 26 mmol), and potassium iodate (3.2 g, 15 mmol), flushed with
argon, and then water (12 mL), acetic acid (260 mL) and
concentrated sulfuric acid (6 mL) were added. The reaction mixture
was heated at 90 °C for 2 h under argon. After cooling to room
temperature, the purple suspension was filtered off, washed with acetic
2
2
pad of silica gel (20 g, CH Cl ), and evaporated. The residue was
2
2
purified by column chromatography on silica gel (900 g) in
Hexane:CH Cl (10:1) to provide product 12 (4.5 g) as a colorless
2
2
oil in 91% yield (R = 0.37, Hex:CH Cl = 5:1). Method B: A dry 25
f
2
2
mL flask was charged with triflate 8 (1 g, 1.9 mmol), Xantphos (58 mg,
1
00 μmol), Pd (dba) (52 mg, 50 μmol), and dry dioxane (15 mL).
acid (150 mL), Na
dried. A light yellow solid was recrystallized from toluene (120 mL) to
provide 16.3 g of a white solid in 72% yield (R = 0.33, Hex:CH Cl
) δ ppm 3.81 (s,
), 7.45 (d, J = 8 Hz, 1H, C H), 7.47 (dd, J = 8 Hz, J =1 Hz,
2 3
SO (150 mL, 10%), water (300 mL), and air-
2
3
The tube was evacuated under a vacuum and refilled with argon three
times. Then N,N-diisopropylethylamine (776 mg, 1 mL, 6 mmol), and
=
2
f
2
1
2-(trimethylsilyl)ethanethiol (537 mg, 4 mmol) were added under
20:1): mp 180−181 °C; H NMR (500 MHz, CDCl
3
9
5
argon and the tube was quickly capped with a rubber septum. The
reaction mixture was stirred at 60 °C for 14 h, and at 90 °C for 6 h.
The completion of the reaction was checked by TLC (Hex:EtOAc =
2H, C H
2
3
4
1
1H, C H), 7.57 (d, J = 8 Hz, 1H, C H), 7.63 (d, J = 2 Hz, 1H, C H),
7.67 (dd, J = 8 Hz, J =1 Hz, 1H, C H), 7.84 (d, J = 1 Hz, 1H, C H);
), 92.5 (C ), 121.3
(C ), 121.5 (C H), 121.7 (C H), 128.5 (C H), 130.3 (C H), 134.4
6
8
13
9
7
20:1). After cooling, the reaction mixture was diluted with diethyl
C NMR (125.8 MHz, CDCl
3
5
) δ ppm 36.6 (C H
2
2
4
1
3
ether (60 mL), filtered through a pad of silica gel (30 g, diethyl ether),
and the filtrate was concentrated in vacuo. The crude product was
purified by column chromatography on silica gel (800 g, hexane:ethyl
8
6
11
12
10
(C H), 136.2 (C H), 140.0 (C ), 140.5 (C ), 144.8 (C ), 145.2
13
−1
(C ); IR (KBr) ν cm 3056 (vw, ν(CH)), 2890 (w, ν (CH )),
s
2
7
353
dx.doi.org/10.1021/jo501029t | J. Org. Chem. 2014, 79, 7342−7357

The Journal of Organic Chemistry
Article
6
1
1
596 (w) and 1567 (w, ν(CC), Ph), 1419 (m), 1396 (s), 1273 (m),
5.88, 5.89 (2 × m, 2 × 1H, 2 × C ″H), 5.90, 5.93 (2 × m, 2 × 1H, 2 ×
2 5
161 (m), 1128 (w), 1050 (m), 951 (w), 930 (w), 832 (m) and 804
C ″H), 6.59, 6.61 (2 × m, 2 × 1H, 2 × C ″H), 6.78 (m, 2H, 2 ×
4 2 5
+
(
(
vs, ν(CH)); EI MS m/z (%) 372 (91), 370 (93, M ), 291 (52), 245
51), 243 (52), 164 (89), 163 (100), 146 (35), 82 (30), 81 (86). Anal.
C ″H), 6.83 (d, J = 2.1 Hz, 2H, 2 × C ′H), 6.90 (m, 1H, C H), 6.96
5 4
(d, J = 7.9 Hz, 1H, C H), 7.02 (m, 1H, C H), 7.09 (d, J = 8.1 Hz, 1H,
4
1
3
Calcd for C H BrI (371.02): C, 42.09; H, 2.17. Found: C, 42.14; H,
C H), 7.29−7.33 (m, 3H, 2 × C H, C H), 7.37 (dd, J = 8.1 Hz, J = 1.9
3 4
13
8
2
.16.
-Bromo-7-iodofluoren-9-one (15). Method A: To a suspension of
H-fluorene 14 (6 g, 16 mmol) in the mixture of acetic acid (100 mL)
Hz, 1H, C H), 7.42 (dd, J = 8.4 Hz, J = 2.1 Hz, 2H, 2 × C ′H), 7.50−
8 6
2
7.53 (m, 3H, 2 × C H, C H), 7.57 (dd, J = 7.9 Hz, J = 1.6 Hz, 1H,
6 5 13
9
C H), 8.30 (d, J = 8.4 Hz, 2H, 2 × C ′H); C NMR (125.7 MHz,
(
→3 )
(→3
)
and acetic anhydride (100 mL) was portionwise added CrO (8 g, 80
mmol) over 3 h. The reaction mixture was vigorously stirred at room
temperature for 16 h, and then poured into crushed ice (ca. 2 kg), and
carefully neutralized with saturated NaHCO solution. The yellow
precipitate was filtered off, washed with water (2 L), and air-dried. The
crude product was treated with chloroform (600 mL), and passed
through a short silica gel column (500 g, CHCl ). After evaporation in
vacuo, the residue was recrystallized from ethanol to provide product
1
CDCl ) δ ppm −1.73 (CH
′ ), −1.67, −1.59 (CH
″ ), 16.46,
3
3
3
3
(→3
)
(→3 )
(→3
)
16.52 (CH Si ″ ), 16.63 (CH Si ′ ), 28.3, 28.5 (SCH
″ ), 28.7
2
2
2
→3 )
9
7
4
(
SCH2( ′ ), 81.8 (C ), 93.1, 93.2 (C ), 121.5, 121.6 (C H), 121.7,
5 2 4
3
121.8 (C H), 122.0, 122.1 (C ), 125.5, 125.6 (C ″H), 126.16, 126.22
6
4
5
5
(
C ″H), 126.5 (C ′H), 126.76, 126.78, 126.80 (C ′H, C ″H), 127.6
1 1 2 2 2
(
C H), 127.75, 127.76 (C H, C ″H), 128.1 (C ″H), 130.2 (C ′H),
3
8
6
3
131.9, 132.4 (C H), 133.4, 133.6 (C H), 135.28, 135.29 (C ′), 136.1
3 3 11 6 11
(
C ″), 137.2 (C ′), 137.88 (C ), 137.90 (C H), 138.2 (C ), 138.41
5 (4.5 g) as a yellow solid in 73% yield (R = 0.42, Hex:CH Cl =
6 12 1 1
f
2
2
(C H), 138.43, 138.8 (C ), 140.127, 140.134 (C ″), 140.6 (C ′),
2
:1). Method B: A 500 mL two-necked flask fitted with a reflux
10 13 −1
1
51.4, 151.7 (C ), 151.7, 152.0 (C ); IR (KBr) ν cm 3400 (bm,
condenser, and a magnetic stirring bar was charged with 2-
bromofluoren-9-one (10 g, 38.6 mmol), water (20 mL), acetic acid
ν(OH)), 3050 (vw, ν(CH)), 2950 (m, ν (CH CH )), 2893 (w,
as
2,
3
ν (CH CH )), 1582 (m), 1565 (w) and 1540 (w, ν(CC), Ph), 1460
s
2,
3
(
120 mL), and concentrated sulfuric acid (4 mL), and heated at 60 °C
(
m), 1446 (m), 1410 (m), 1396 (m), 1371 (w), 1248 (vs, δ (CH ),
TMS), 1164 (m), 1090 (m), 1054 (m), 1006 (bm), 925 (w), 879 (m),
58 (vs) and 839 (vs, δ (CH ), TMS), 809 (s), 786 (m), 751 (m),
27 (m), 704 (m, v (SiC ), TMS), 670 (m), 640 (w); ESI(+) HRMS
s 3
for 1 h. Then iodine (9.9 g, 39 mmol), and periodic acid (4.3 g, 19
mmol) were added, and the reaction mixture was stirred at 85 °C for
1
poured into Na SO (200 mL, 10%) solution, and a yellow solid was
filtered off, washed with water (600 mL), and air-dried. A bright yellow
solid was recrystallized from ethyl acetate to give 13.2 g of yellow
needles in 89% yield: mp 197−198 °C; H NMR (500 MHz, CDCl )
δ ppm 7.22 (d, J = 8 Hz, 1H, C H), 7.34 (d, J = 8 Hz, 1H, C H), 7.59
8
7
as 3
8 h. After cooling to room temperature, the reaction mixture was
as
3
2
3
+
Calcd for C H BrIONaS Si ([M + Na] , 825.0185), found m/z
35
40
2
2
8
5
25.0186. Anal. Calcd for C H BrIOS Si (803.80): C, 52.30; H,
35 40 2 2
.02. Found: C, 52.19; H, 4.92.
-Bromo-7-iodo-3′,6′-bis[2-(trimethylsilyl)ethylsulfanyl]-9,9′-spi-
robifluorene (17) and (R,S)-2-Bromo-7-iodo-1′,6′-bis[2-
trimethylsilyl)ethylsulfanyl]-9,9′-spirobifluorene (18). An argon-
flushed 100 mL Schlenk flask was charged with carbinol 16 (0.5 g,
0.62 mmol), and glacial acetic acid (50 mL) was added. The solution
was cooled to 10 °C, and concentrated HCl (1 mL, 37%) was added.
The reaction mixture was keep stirring at 10 °C for 6 h under argon,
and then allowed to warm to room temperature and stirred for an
additional 12 h. The reaction mixture was diluted with water (30 mL),
and after 20 min of stirring, the white precipitate was filtered off,
washed with water (ca. 400 mL), air and vacuum-dried to provide 476
mg (98% yield) of a white solid as a mixture of two regioisomers 17
and 18 in a ratio of 2:1 (R = 0.35, Hex:CH Cl = 5:1). The ratio of
regioisomers was determined by H NMR of the crude reaction
mixture. The regioisomeric mixture was further purified by the slow
crystallization from the mixture of ethanol and toluene (10:1) to give a
first crop of the pure symmetric isomer 17 (160 mg) as a white
crystalline material. The mother liquor was evaporated, and the residue
was purified by column chromatography on a large excess of silica gel
1
3
2
5
4
3
1
(
dd, J = 8 Hz, J =2 Hz, 1H, C H), 7.71 (d, J = 2 Hz, 1H, C H), 7.80
(
6
8
13
(
dd, J = 8 Hz, J =1.5 Hz, 1H, C H), 7.91 (d, J = 1.5 Hz, 1H, C H);
C
7
4
NMR (125.8 MHz, CDCl ) δ ppm 94.6 (C ), 122.1 (C H), 122.3
3
5
2
1
8
13
(
(
(
C H), 123.7 (C ), 127.9 (C H), 133.8 (C H), 135.1 (C ), 135.4
C ), 137.6 (C H), 142.5 (C ), 143.0 (C ), 143.6 (C H), 191.1
C O); IR (KBr) ν cm 3054 (vw, ν(CH)), 1723 (vs) and 1709 (s,
10
3
11
12
6
9
−1
ν(CO), CpCO), 1603 (w) and 1589 (m, ν(CC), Ph), 1445 (m),
415 (s), 1274 (w), 1242 (m), 1221 (w), 1203 (w), 1184 (s), 1153
m), 1052 (m), 1028 (m), 905 (m), 841 (w), 822 (s) and 780 (vs,
1
(
+
ν(CH)), 675 (bm); EI MS m/z (%) 386 (77), 384 (77, M ), 231 (20),
29 (20), 150 (73), 86 (74), 84 (100), 75 (32), 51 (32), 49 (87). Anal.
Calcd for C H BrIO (385.00): C, 40.56; H, 1.57. Found: C, 40.49; H,
2
f
2
2
13
6
1
1
.53.
R,S)-9-{5,3′-Bis[2-(trimethylsilyl)ethylsulfanyl]-1,1′-biphen-2-yl}-
-bromo-7-iodofluoren-9-ol (16). A dry and argon-flushed 100 mL
(
2
Schlenk flask was charged with 2-iodobiphenyl 13 (1.4 g, 2.57 mmol),
and anhydrous THF (30 mL) was added. The solution was cooled to
−
40 °C (acetonitrile/CO (s)), and iPrMgCl·LiCl complex solution
2
(
1400 g) in the mixture of hexane:EtOAc (50:1) to give a second crop
of the symmetric isomer 17 (120 mg) and the isomer 18 (135 mg) as
a light yellow foamy solid. For the isomer 17: mp 165−166 °C; H
NMR (500 MHz, CDCl ) δ ppm 0.06 (s, 18H, CH ), 0.99 (m, 4H,
CH Si), 3.03 (m, 4H, SCH ), 6.60 (d, J = 8 Hz, 2H, C ′H, C ′H), 6.81
d, J = 1.5 Hz, 1H, C H), 7.01 (d, J = 1.5 Hz, 1H, C H), 7.06 (dd, J =
(
“turbo-Grignard”, 2.4 mL, 3.1 mmol, 1.3 M in THF) was added
dropwise over 10 min. The reaction mixture was stirred at −40 °C for
h under argon. The reaction mixture was stirred at the same
1
4
temperature until completion of the I/Mg exchange was detected by
3
3
1
8
GC−MS analysis. In a second 100 mL Schlenk flask, fluoren-9-one 15
2
2
1
8
(
8
(
1.2 g, 3.1 mmol) was dissolved in dry THF (40 mL), cooled to −40
2
7
Hz, J = 1.5 Hz, 2H, C ′H, C ′H), 7.46 (dd, J = 8.5 Hz, J = 2 Hz, 1H,
°C, and degassed. This solution was slowly added via a cannula into
3
5
4
C H), 7.51 (d, J = 8 Hz, 1H, C H), 7.63 (d, J = 8.5 Hz, 1H, C H), 7.67
the flask containing the Grignard reagent, and the mixture was stirred
at −40 °C for 2 h, then allowed to warm to room temperature and
stirred for an additional 16 h. The reaction mixture was quenched with
6
4
(
dd, J = 8 Hz, J = 1.5 Hz, 1H, C H), 7.71 (d, J = 1.5 Hz, 2H, C ′H,
5 13
C ′H); C NMR (125.8 MHz, CDCl ) δ ppm −1.5 (CH ), 17.1
3
3
9
7
4
5
(
CH Si), 29.9 (SCH ), 65.1 (C ), 93.6 (C ), 120.5 (C ′H, C ′H),
saturated aq. NH Cl solution (80 mL). The aqueous layer was washed
2
2
4
4 5 2 1 8
1
(
21.7 (C H), 122.0 (C H), 122.3 (C ), 124.6 (C ′H, C ′H), 127.5
with diethyl ether (3 × 80 mL). The combined organic layer was
subsequently washed with brine (100 mL), dried over magnesium
sulfate, and filtered. Volatiles were removed under reduced pressure,
and the residue was purified by column chromatography on silica gel
1 2 7 3 8 6
C H), 128.8 (C ′H, C ′H), 131.4 (C H), 133.4 (C H), 137.3 (C H),
3 6 11 12 11 12
138.1 (C ′, C ′), 139.8 (C ), 140.4 (C ), 142.1 (C ′, C ′), 145.1
10
13
10
13
−1
(C ′, C ′), 150.2 (C ), 150.5 (C ); IR (KBr) ν cm 3044 (w, ν(
(
1
800 g) in hexane:EtOAc (50:1) to afford 1.23 g of the title product
6 (R = 0.21, Hex:EtOAc = 20:1) as a light yellow foamy solid in 59%
CH)), 2946 (s, νas(CH2, CH )), 2891 (m, ν (CH2, CH )), 1595 (s),
3
s
3
1568 (m) and 1546 (w, ν(CC), Ph), 1469 (m), 1454 (s), 1440 (m),
1415 (m), 1405 (m), 1397 (m), 1282 (m), 1277 (m), 1258 (s), 1248
f
yield. The title carbinol 16 is a mixture of two diastereomers in a ratio
∼
1:1, which was determined by NMR analysis at different temper-
(vs, δ
(m), 1063 (m), 1054 (m), 1006 (s), 955 (w), 949 (w), 932 (m), 886
(m), 850 (vs) and 833 (bs, δas(CH ), TMS), 811 (s), 807 (s), 804 (s),
766 (w), 751 (m), 736 (w), 704 (m) and 690 (m, v (SiC ), TMS),
s 3
(CH ), TMS), 1161 (m), 1108 (w), 1099 (w), 1090 (w), 1083
1
atures: mp 65−67 °C; H NMR (500.0 MHz, CDCl ) δ ppm 0.02,
3
(
→3
(→3 )
0
.03 (2 × s, 2 × 9H, 2 × CH
″), 0.04 (s, 18H, 2 × CH
′ ), 0.83
3
3
3
(→3
)
(→3 )
(
m, 4H, 2 × CH Si ″ ), 0.97 (m, 4H, 2 × CH Si ′ ), 2.25 (s, 2H, 2
2
2
as
3
(
→3
)
(→3 )
+
×
OH), 2.68 (m, 4H, 2 × SCH2 ″ ), 2.99 (m, 4H, 2 × SCH2 ′ ),
665 (m), 635 (m); EI MS m/z (%) 786 (3), 784 (3, M ), 730 (6), 728
7
354
dx.doi.org/10.1021/jo501029t | J. Org. Chem. 2014, 79, 7342−7357

The Journal of Organic Chemistry
Article
(
6), 626 (7), 73 (100). Anal. Calcd for C H BrIS Si (785.79): C,
Calcd for C H N (127.15): C, 85.02; H, 3.96; N, 11.02. Found: C,
35
38
2
2
9
5
5
3.50; H, 4.87. Found: C, 53.56; H, 4.89.
85.20; H, 3.85; N, 10.93.
1
For the isomer 18: mp 153−154 °C; H NMR (500 MHz, CDCl )
4-({2-Bromo-3′,6′-bis[2-(trimethylsilyl)ethylsulfanyl]-9,9′-spirobi-
3
(
→1 )
(→6 )
δ ppm −0.12 (s, 9H, CH
′ ), 0.06 (s, 9H, CH
′ ), 0.40 (m, 2H,
fluoren-7-yl}ethynyl)benzonitrile (21) and 4-({2-Bromo-1′,6′-bis[2-
3
3
(→1 )
(→6 )
(→1 )
(
trimethylsilyl)ethylsulfanyl]-9,9′-spirobifluoren-7-yl}ethynyl)-
CH Si ′ ), 0.98 (m, 2H, CH Si ′ ), 2.47 (m, 2H, SCH
′ ), 3.01
2
2
2
(→6 )
8
benzonitrile (22). An argon-flushed 50 mL Schlenk flask was charged
with a regioisomeric mixture of spirobifluorenes 17 and 18 in a ratio of
2:1 (160 mg, 204 μmol), PdCl (PPh ) (8 mg, 11 μmol), and CuI (4
(
1
m, 2H, SCH2 ′ ), 6.47 (d, J = 8 Hz, 1H, C ′H), 6.81 (d, J = 1.5 Hz,
1
8
H, C H), 7.01 (d, J = 1.5 Hz, 1H, C H), 7.02 (dd, J = 8 Hz, J = 1.5
7
4
Hz, 1H, C ′H), 7.14 (d, J = 7.5 Hz, 1H, C ′H), 7.40 (td, J = 7.5 Hz, J =
1
2
3 2
3
3
mg, 22 μmol), and dry triethylamine (12 mL) was added. Then
acetylene derivative 20 (28 g, 220 μmol) was added under argon, and
the mixture was stirred at room temperature for 16 h. The completion
of the reaction was checked by TLC (Hex:EtOAc = 10:1). The
reaction mixture was treated with diethyl ether (60 mL) and the
precipitate was filtered through a pad of silica gel (10 g, diethyl ether),
and the filtrate was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (200 g, Hex:EtOAc equal to
Hz, 1H, C ′H), 7.47 (dd, J = 8 Hz, J = 2 Hz, 1H, C H), 7.53 (d, J = 8
5 4 2 6
Hz, 1H, C H), 7.63−7.69 (m, 3H, C H, C ′H, C H), 7.71 (d, J = 1
5
13
Hz, 1H, C ′H); C NMR (125.8 MHz, CDCl ) δ ppm −1.6
3
(
→1 )
(→6 )
(→1 )
(→6 )
(
CH
′ ), −1.5 (CH
′ ), 17.0 (CH Si ′ ), 17.2 (CH Si ′ ),
3
3
2
2
(
→1 )
(→6 ) 9 7
2
9.8 (SCH2 ′ ), 29.9, 30.00 (SCH
′ ), 65.8 (C ), 93.3 (C ), 117.7
2
2
5
4
5 2
(
(
1
1
1
C ′H), 120.7 (C ′H), 121.6 (C H), 121.9 (C H), 122.0 (C ), 124.1
8 1 7 4 3
C ′H), 127.0 (C H), 128.9 (C ′H), 129.2 (C ′H), 129.4 (C ′H),
3 8 1 6 6
31.1 (C H), 132.8 (C H), 135.2 (C ′), 137.0 (C H), 137.6 (C ′),
11 12 12 11 13
2
0:1) to provide the symmetric isomer 21 (92 mg) as a white foamy
41.0 (C ), 141.5 (C ), 141.7 (C ′), 142.7 (C ′), 145.5 (C ′),
10
10
13
−1
solid and the isomer 22 (45 mg) as a white foamy solid in 86% yield
(Rf = 0.29 for the isomer 21; R = 0.36 for the isomer 22, Hex:EtOAc =
46.0 (C ′), 149.0 (C ), 149.3 (C ); IR (KBr) ν cm 3054 (vw,
ν(CH)), 2952 (s) and 2920 (s, ν (CH CH )), 2851 (m, ν (CH
f
as
2,
3
s
2,
1
1
0:1). For the isomer 21: mp 99−100 °C; H NMR (500 MHz,
CH )), 1730 (bm), 1594 (w), 1567 (w) and 1517 (w, ν(CC), Ph),
3
CDCl ) δ ppm 0.06 (s, 18H, CH ), 0.99 (m, 4H, CH Si), 3.03 (m, 4H,
1
448 (m), 1422 (w), 1406 (w), 1389 (w), 1260 (m), 1249 (s,
3
3
2
1
8
SCH ), 6.62 (d, J = 8 Hz, 2H, C ′H, C ′H), 6.87 (d, J = 2 Hz, 1H,
δ (CH ), TMS), 1162 (m), 1104 (w), 1079 (m), 1054 (w), 1006 (m),
2
s
3
1
8
946 (vw), 934 (w), 856 (bs) and 840 (bs, δ (CH ), TMS), 807 (s),
C H), 6.89 (d, J = 1 Hz, 1H, C H), 7.06 (dd, J = 8 Hz, J = 1.5 Hz, 2H,
as
3
2
7
3
5
7
68 (m), 746 (m), 722 (w), 703 (w, v (SiC ), TMS), 664 (m), 635
C ′H, C ′H), 7.46 (dd, J = 7 Hz, J = 1.5 Hz, 2H, C ″H, C ″H), 7.49
as
3
3
(
m).
-[(Trimethylsilyl)ethynyl]benzonitrile (19).
(dd, J = 8 Hz, J = 1.5 Hz, 1H, C H), 7.53 (dd, J = 8 Hz, J = 1.5 Hz, 1H,
4
4,45
6
2
6
4
A 500 mL Schlenk
C H), 7.55 (dd, J = 7 Hz, J = 1.5 Hz, 2H, C ″H, C ″H), 7.67 (d, J = 8
4
4
5
flask was charged with 4-iodobenzonitrile (7.5 g, 32.7 mmol),
PdCl (PPh ) (1.2 g, 1.7 mmol), CuI (630 mg, 3.3 mmol) under
Hz, 1H, C H), 7.73 (d, J = 1.5 Hz, 2H, C ′H, C ′H), 7.78 (d, J = 8 Hz,
5 13
1H, C H); C NMR (125.8 MHz, CDCl
) δ ppm −1.5 (CH ), 17.1
3
2
3 2
3
9
7
8
1
argon, and dry THF (60 mL), and dry triethylamine (100 mL) were
added. Then trimethylsilylacetylene (4.9 g, 7.1 mL, 50 mmol) was
added, and the mixture was stirred at room temperature for 10 h. The
reaction mixture was treated with diethyl ether (300 mL), and the
precipitate was filtered through a pad of silica gel (30 g, diethyl ether),
and the filtrate was concentrated in vacuo. The residue was purified by
column chromatography on silica gel (600 g, hexane:CH Cl equal to
(CH
Si), 29.9 (SCH ), 65.2 (C ), 88.7 (C ″), 94.1 (C ″), 111.7 (C ″),
2 2
4 5 5 7 2
118.7 (CN), 120.4 (C ′H, C ′H, C H), 121.97 (C ), 122.00 (C ),
4
1
8
1
8
4
122.6 (C H), 124.6 (C ′H, C ′H), 127.7 (C H, C H), 128.2 (C ″),
2
7
3
6
3
128.7 (C ′H, C ′H), 131.5 (C H), 132.07 (C H), 132.10 (C ″H,
5
2
6
3
6
11
C ″H), 132.2 (C ″H, C ″H), 138.1 (C ′, C ′), 139.9 (C ), 141.7
12
11
12
10
13
13
10
(C ), 142.1 (C ′, C ′), 145.1 (C ′, C ′), 148.7 (C ), 151.0 (C );
−1
IR (KBr) ν cm 3050 (w, ν(CH)), 2950 (m, νas(CH2, CH
(w, ν (CH2, CH
)), 2227 (m, ν(CN)), 2213 (m, ν(CC)), 1601
(s) and 1564 (w, ν(CC), Ph), 1509 (w), 1503 (m), 1467 (m), 1453
(s), 1416 (m), 1405 (m), 1259 (s), 1249 (vs, δ (CH ), TMS), 1161
(m), 1124 (w), 1104 (w), 1083 (w), 1063 (m), 1006 (m), 956 (w),
858 (vs) and 838 (vs, δas(CH ), TMS), 814 (vs), 749 (m), 724 (w),
694 (m, vas(SiC ), TMS), 637 (m), 553 (m); EI MS m/z (%) 785 (2),
783 (2, M ), 729 (5), 727 (5), 86 (90), 84 (100), 51 (60), 49 (96), 47
(27). Anal. Calcd for C44 42BrNS Si (785.02): C, 67.32; H, 5.39; N,
)), 2894
2
2
3
2:1) to afford the title compound 19 (5.9 g) as a white solid in 90%
s
3
1
yield (R = 0.35, Hex:CH Cl = 2:1): mp 102−103 °C; H NMR (500
MHz, CDCl ) δ ppm 0.24 (s, 9H, CH ), 7.51 (dd, J = 7.5 Hz, J = 2
f
2
2
3
3
s
3
3
5
2
6
Hz, 2H, C H, C H), 7.57 (dd, J = 6.5 Hz, J = 2 Hz, 2H, C H, C H);
1
3
C NMR (125.8 MHz, CDCl ) δ ppm −0.1 (CH ), 99.8 (CSi),
3
3
3
1
4
2
1
03.2 (ArC), 112.0 (C ), 118.7 (CN), 128.2 (C ), 132.1 (C H,
3
6
3
5
−1
+
C H), 132.7 (C H, C H); IR (KBr) ν cm 3064 (w) and 3048 (vw,
ν(CH)), 2964 (m) and 2956 (m, ν (CH )), 2898 (w, ν (CH )),
H
as
3
s
3
2
2
2
235 (m, ν(CN)), 2158 (m, ν(CC)), 1603 (w, ν(CC), Ph), 1499
1.78. Found: C, 67.48; H, 5.46; N, 1.71.
For the isomer 22: mp 97−98 °C; H NMR (500 MHz, CDCl
1
(
(
(
(
m), 1407 (w), 1272 (w), 1251 (m), 1246 (m, δ (CH ), TMS), 1217
w), 1177 (w), 862 (vs) and 842 (vs, δ (CH ), TMS), 758 (s), 724
m), 699 (w, v (SiC ), TMS), 630 (w), 557 (m); EI MS m/z (%) 197
4, M ), 183 (8), 165 (8), 139 (10), 101 (22), 73 (100). Anal. Calcd
3
) δ
s
3
(
→1 )
(→6 )
ppm −0.15 (s, 9H, CH
′ ), 0.04 (s, 9H, CH
′ ), 0.37 (m, 2H,
as
3
3
3
(→1 )
(→6 )
(→1 )
CH
Si ′ ), 0.97 (m, 2H, CH
Si ′ ), 2.45 (m, 2H, SCH
′ ), 3.00
as
3
2
2
2
+
(→6 )
8
(m, 2H, SCH
′ ), 6.48 (d, J = 8 Hz, 1H, C ′H), 6.84 (d, J = 1.5 Hz,
2
1
8
for C H NSi (199.33): C, 72.31; H, 6.57; N, 7.03. Found: C, 72.42;
1H, C H), 6.88 (d, J = 1 Hz, 1H, C H), 7.01 (dd, J = 8 Hz, J = 2 Hz,
12
13
7
4
H, 6.51; N, 7.09.
-Ethynylbenzonitrile (20).
acetylene 19 (3.6 g, 18.1 mmol) was dissolved in the mixture of THF
60 mL) and methanol (60 mL). Potassium carbonate (25 g, 181
1H, C ′H), 7.14 (dd, J = 7.5 Hz, J = 0.5 Hz, 1H, C ′H), 7.41 (td, J = 8
6
,46
3
3
4
In a 250 mL flask, the silylated
Hz, J = 0.5 Hz, 1H, C ′H), 7.45 (dd, J = 7 Hz, J = 1.5 Hz, 2H, C ″H,
5 3
C ″H), 7.49 (dd, J = 8 Hz, J = 2 Hz, 1H, C H), 7.54 (dd, J = 8 Hz, J =
6
2
6
(
1.5 Hz, 1H, C H), 7.55 (dd, J = 7 Hz, J = 2 Hz, 2H, C ″H, C ″H),
2 4
mmol) was added, and suspension was vigorously stirred at room
temperature for 14 h. The reaction mixture was filtered through a pad
of Celite (diethyl ether), and the remaining solution concentrated
under reduced pressure. The crude product was treated with diethyl
ether (200 mL), and passed through a short pad of silica gel (100 g,
diethyl ether). After evaporation, and drying under vacuo at room
temperature, the title compound 20 (2.24 g) was isolated as a white
solid in 97% yield (R = 0.28, Hex:CH Cl = 2:1): mp 158−159 °C;
7.67 (dd, J = 8 Hz, J = 0.5 Hz, 1H, C ′H), 7.69 (d, J = 8 Hz, 1H, C H),
5 5 13
7.71 (d, J = 1.5 Hz, 1H, C ′H), 7.79 (d, J = 8 Hz, 1H, C H); C NMR
(→1 )
(→6 )
(125.8 MHz, CDCl ) δ ppm −1.7 (CH
′ ), −1.5 (CH
′ ), 17.0
3
3
3
(→1 )
(→6 )
(→1 )
(→6 )
(CH Si ′ ), 17.2 (CH Si ′ ), 29.9 (SCH
′ ), 30.0 (SCH
′ ),
2
2
2
2
9
7
8
1
2
65.9 (C ), 88.5 (C ″), 94.5 (C ″), 111.5 (C ″), 117.8 (C ′H), 118.7
5
5
7
4
(CN), 120.4 (C H), 120.7 (C ′H), 121.6 (C ), 122.0 (C H), 122.3
2
8
8
1
4
(C ), 124.1 (C ′H), 127.16 (C H), 127.19 (C H), 128.4 (C ″), 128.8
7
4
3
3
6
f
2
2
(C ′H), 129.3 (C ′H), 129.5 (C ′H), 131.2 (C H), 131.9 (C H),
1
3
5
2
6
1
6
H NMR (500 MHz, CDCl ) δ ppm 3.28 (s, 1H, CH), 7.55 (dd, J = 7
132.1 (C ″H, C ″H), 132.2 (C ″H, C ″H), 135.2 (C ′), 137.6 (C ′),
11 12 12 11 13
3
3
5
Hz, J = 1.5 Hz, 2H, C H, C H), 7.60 (dd, J = 7 Hz, J = 1.5 Hz, 2H,
141.1 (C ), 141.7 (C ′), 142.8 (C ), 142.9 (C ′), 145.6 (C ′),
10 13 10 −1
2
6
13
C H, C H); C NMR (125.8 MHz, CDCl ) δ ppm 81.8 (CH),
146.1 (C ′), 147.5 (C ), 149.8 (C ); IR (KBr) ν cm 3059 (w,
ν(CH)), 2950 (m, ν (CH CH )), 2894 (w, ν (CH CH )), 2228
3
1
4
2
8
2.1 (ArC), 112.5 (C ), 118.5 (CN), 127.2 (C ), 132.2 (C H,
as
2,
3
s
2,
3
5
3
5
−1
C H), 132.9 (C H, C H); IR (KBr) ν cm 3052 (vw, ν(CH)),
228 (m, ν(CN)), 2103 (m, ν(CC)), 1602 (w, ν(CC), Ph), 1408
w), 1272 (w), 841 (s), 731 (m), 688 (w), 556 (m); EI MS m/z (%)
(m, ν(CN)), 2213 (m, ν(CC)), 1726 (w), 1601 (s) and 1567 (w,
ν(CC), Ph), 1503 (m), 1450 (s), 1419 (m), 1405 (m), 1389 (m),
1259 (m), 1249 (s, δ (CH ), TMS), 1156 (m), 1126 (vw), 1104 (vw),
2
(
s
3
+
127 (100, M ), 100 (18), 86 (11), 84 (16), 49 (15), 44 (21). Anal.
1080 (m), 1059 (w), 1006 (m), 954 (w), 858 (vs) and 839 (vs,
7
355
dx.doi.org/10.1021/jo501029t | J. Org. Chem. 2014, 79, 7342−7357

The Journal of Organic Chemistry
Article
5
8
4
2
3
6
δ (CH ), TMS), 814 (s), 771 (m), 746 (m), 724 (w), 693 (w,
C ′H), 127.9 (C H), 128.4 (C ″), 129.11 (C ), 129.13 (C ′, C ′),
1 3 5 2 6 6
as
3
v (SiC ), TMS), 638 (m), 554 (m).
130.3 (C H), 132.5 (C ″H, C ″H), 132.6 (C ″H, C ″H, C H), 135.0
2 7 3 12 11 12
as
3
4
-({2,3′,6′-Tris[2-(trimethylsilyl)ethylsulfanyl]-9,9′-spirobifluoren-
(C ′H, C ′H), 135.5 (C H), 142.2 (C ), 142.5 (C ′, C ′), 142.7
11 13 10 10 13 −1
7
-yl}ethynyl)benzonitrile (23). A dry 15 mL pressure tube was
(C ), 148.8 (C ), 149.1 (C ), 149.3 (C ′, C ′); IR (KBr) ν cm
charged with spirobifluorene 21 (280 mg, 357 μmol), Xantphos (21
mg, 36 μmol), Pd (dba) (19 mg, 18 μmol), and dry dioxane (8 mL).
3055 (w, ν(CH)), 2228 (m, ν(CN)), 2215 (m, ν(CC)), 1707
(vs, ν(CO)), 1601 (m, ν(CC), Ph), 1503 (m), 1470 (w), 1459 (m),
1416 (m), 1404 (m), 1392 (m), 1351 (m), 1123 (bs), 1024 (w), 1004
(w), 950 (bm), 878 (w), 838 (m), 817 (s), 638 (m), 620 (s), 610 (s),
2
3
The tube was evacuated under a vacuum and refilled with argon three
times. Then N,N-diisopropylethylamine (129 mg, 170 μL, 1 mmol),
and 2-(trimethylsilyl)ethanethiol (73 mg, 540 μmol) were added
under argon and the tube was quickly capped with a rubber septum.
The reaction mixture was heated at 100 °C for 10 h. The completion
of the reaction was checked by TLC (Hex:EtOAc = 10:1). After
cooling, the reaction mixture was diluted with diethyl ether (60 mL),
filtered through a pad of silica gel (10 g, diethyl ether), and the filtrate
was concentrated in vacuo. The crude product was purified by column
chromatography on silica gel (300 g, hexane:ethyl acetate equal to
+
555 (w); EI MS m/z (%) 663 (6, M ), 621 (27), 579 (16), 537 (20),
504 (16), 103 (57), 76 (43), 57 (46), 43 (100). Anal. Calcd for
C H NO S (663.82): C, 72.37; H, 3.80; N, 2.11. Found: C, 72.53;
40
25
3 3
H, 3.89; N, 2.02.
ASSOCIATED CONTENT
■
*
S
Supporting Information
1
13
1
5:1) to provide the title compound 23 (285 mg) as a light yellow
H and C NMR spectra of compounds 1−24 containing
foamy solid in 95% yield (R = 0.35, Hex:EtOAc = 10:1): mp 72−73
chemical structures and numbering used for the complete peak
assignment. Crystallographic data (CIF) for 17. This material is
available free of charge via the Internet at http://pubs.acs.org.
f
1
(→2)
°
C; H NMR (500 MHz, CDCl ) δ ppm −0.10 (s, 9H, CH
), 0.06
3
3
(
→3 )
(→6 )
(→2)
(→2)
(
s, 18H, CH
′ , CH
′ ), 0.75 (m, 2H, CH Si ), 0.99 (m, 4H,
3
3
2
(
→3 )
(→6 )
CH Si ′ , CH Si ′ ), 2.79 (m, 2H, SCH
SCH2 ′ , SCH
), 3.02 (m, 4H,
′ ), 6.61 (d, J = 1 Hz, 1H, C H), 6.63 (d, J = 8 Hz,
2
2
2
(→3 )
(→6 )
1
2
1
8
8
AUTHOR INFORMATION
2
1
7
=
7
7
H, C ′H, C ′H), 6.87 (d, J = 1 Hz, 1H, C H), 7.05 (dd, J = 8 Hz, J =
■
2
7
3
.5 Hz, 2H, C ′H, C ′H), 7.28 (dd, J = 8 Hz, J = 1.5 Hz, 1H, C H),
Corresponding Author
E-mail: marcel.mayor@unibas.ch.
3
5
.45 (dd, J = 8 Hz, J = 1.5 Hz, 2H, C ″H, C ″H), 7.51 (dd, J = 8 Hz, J
*
6
2
6
1 Hz, 1H, C H), 7.54 (dd, J = 8 Hz, J = 1.5 Hz, 2H, C ″H, C ″H),
4
4
5
Notes
.71 (d, J = 8 Hz, 1H, C H), 7.72 (d, J = 1.5 Hz, 2H, C ′H, C ′H),
5 13
.75 (d, J = 8 Hz, 1H, C H); C NMR (125.8 MHz, CDCl ) δ ppm
The authors declare no competing financial interest.
3
(
→2)
(→3 )
(→6 )
(→2)
−
1.7 (CH
), −1.5 (CH3 ′ , CH3 ′ ), 16.9 (CH Si ), 17.1
3
2
(
→3 )
(→6 ) (→2) (→3 )
(
CH Si ′ , CH Si ′ ), 29.3 (SCH
), 30.0 (SCH
′ ,
2
2
2
2
ACKNOWLEDGMENTS
(→6 )
9
7
8
1
■
SCH2 ′ ), 65.2 (C ), 88.4 (C ″), 94.4 (C ″), 111.5 (C ″), 118.7
5
4
5
4
7
The authors acknowledge the support by the Research
Network “Functional Nanostructures” of the Baden-Wu
(
1
CN), 120.1 (C H), 120.4 (C ′H, C ′H), 121.0 (C H), 121.2 (C ),
1 1 8 8 4
̈
rttem-
24.1 (C H), 124.6 (C ′H, C ′H), 127.6 (C H), 128.3 (C ″), 128.5
3 2 7 6 3 5
(
(
C H), 128.8 (C ′H, C ′H), 132.0 (C H), 132.1 (C ″H, C ″H), 132.2
berg Stiftung. The authors also thank the Institute of
Nanotechnology (INT), Karlsruhe Institute of Technology
(KIT) for ongoing support.
2
6
3
6
2
11
11
C ″H, C ″H), 137.8 (C ′, C ′), 138.2 (C ), 138.6 (C ), 142.1 (C ′,
12
12
10
13
13
10
C ′), 142.5 (C ), 145.9 (C ′, C ′), 148.7 (C ), 149.7 (C ); IR
−1
(
(
(
(
(
(
(
KBr) ν cm 3054 (w, ν(CH)), 2950 (m, ν (CH CH )), 2890
as
2,
3
w, ν (CH CH )), 2227 (w, ν(CN)), 2212 (w, ν(CC)), 1601
s 2, 3
REFERENCES
■
m) and 1564 (w, ν(CC), Ph), 1502 (w), 1456 (w), 1414 (m), 1249
s, δ (CH ), TMS), 1162 (m), 1123 (w), 1104 (w), 1083 (w), 1073
(
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3
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%) 837 (3, M ), 753 (2), 648 (2), 73 (55), 44 (100). Anal. Calcd for
as
3
(
2) Ie, Y.; Hirose, T.; Nakamura, H.; Kiguchi, M.; Takagi, N.; Kawai,
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+
(
C H NS Si (838.42): C, 70.20; H, 6.61; N, 1.67. Found: C, 70.02;
49
55
3
3
H, 6.55; N, 1.60.
(
S,S′,S″-[7-(4-Cyanophenylethynyl)-9,9′-spirobifluorene-2,3′,6′-
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3 (110 mg, 131 μmol) was dissolved in the mixture of dry
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4
in hexane) and a light brown suspension was stirred at room
temperature for 3 h. The completion of the reaction was checked by
TLC (Hex:EtOAc = 3:1). The reaction mixture was diluted with
dichloromethane (50 mL) and slowly poured into a saturated solution
of NaHCO (50 mL). The precipitate was filtered through a pad of
3
Celite (CH Cl ), and the filtrate was concentrated in vacuo. The crude
2
2
product was purified by column chromatography on silica gel (200 g,
Hex:EtOAc equal to 4:1) to provide thioacetate 24 (69 mg) as a light
yellow foamy solid in 79% yield (R = 0.19, Hexane:EtOAc = 3:1): mp
f
1
>
CH
400 °C (dec.); H NMR (500 MHz, CD Cl ) δ ppm 2.31 (s, 3H,
2
2
(
→2)
(→3 )
(→6 )
), 2.45 (s, 6H, CH3 ′ , CH3 ′ ), 6.81 (d, J = 8 Hz, 2H,
3
1
8
1
C ′H, C ′H), 6.82 (d, J = 0.5 Hz, 1H, C H), 6.97 (d, J = 1 Hz, 1H,
8
2
7
C H), 7.23 (dd, J = 8 Hz, J = 2 Hz, 2H, C ′H, C ′H), 7.49 (dd, J = 8
3
3
Hz, J = 2 Hz, 1H, C H), 7.51 (dd, J = 7 Hz, J = 1.5 Hz, 2H, C ″H,
5
2
6
C ″H), 7.59 (dd, J = 7 Hz, J = 1.5 Hz, 2H, C ″H, C ″H), 7.63 (dd, J =
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5
8
Hz, J = 1.5 Hz, 1H, C H), 7.92 (d, J = 8 Hz, 1H, C H), 7.94 (d, J = 2
4
5
4
13
Hz, 2H, C ′H, C ′H), 7.95 (d, J = 8 Hz, 1H, C H); C NMR (125.8
(
→2)
(→3 )
(→6 )
MHz, CD Cl ) δ ppm 30.5 (CH
), 30.7 (CH
′ , CH3 ′ ),
2
2
3
3
9
7
8
1
6
(
5.9 (C ), 89.3 (C ″), 93.9 (C ″), 112.1 (C ″), 119.0 (CN), 121.5
C H), 121.8 (C H), 122.9 (C ), 125.2 (C ′H, C ′H), 127.2 (C ′H,
5
4
7
1
8
4
7
356
dx.doi.org/10.1021/jo501029t | J. Org. Chem. 2014, 79, 7342−7357

The Journal of Organic Chemistry
Article
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