Suzuki-Miyaura synthesis of m-terphenyl thioethers and their facilitated oxidation caused by through-space π···S···π interaction

Article abstract of DOI:10.1016/j.tet.2016.03.040

S-tert-Butyl m-terphenyl thioethers have been efficiently synthesized by Suzuki-Miyaura coupling reactions with 2,6-dibromo-S-tert-butylthio benzene. Selective monocoupling could be achieved with o-substituted boronic acids. This facilitated the synthesis of unsymmetrical S-tert-butyl m-terphenyl thioethers and bis(S-tert-butyl m-terphenyl thioether)s. The study of their electrochemistry showed facilitated oxidations resulting from through-space π···S···π interactions.

Full text of DOI:10.1016/j.tet.2016.03.040

Tetrahedron 72 (2016) 2527e2534
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
SuzukieMiyaura synthesis of m-terphenyl thioethers and their
facilitated oxidation caused by through-space
p/S/
p
interaction
,
Takuhei Yamamoto a, Malika Ammam b, Sue A. Roberts a, George S. Wilson b
,
*
,
Richard S. Glass a
*
a Department of Chemistry and Biochemistry, The University of Arizona, Tucson, AZ 85721, USA
b Department of Chemistry, The University of Kansas, Lawrence, KS 66045, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
S-tert-Butyl m-terphenyl thioethers have been efficiently synthesized by SuzukieMiyaura coupling re-
actions with 2,6-dibromo-S-tert-butylthio benzene. Selective monocoupling could be achieved with o-
substituted boronic acids. This facilitated the synthesis of unsymmetrical S-tert-butyl m-terphenyl thi-
oethers and bis(S-tert-butyl m-terphenyl thioether)s. The study of their electrochemistry showed facil-
Received 14 December 2015
Received in revised form 10 March 2016
Accepted 11 March 2016
Available online 29 March 2016
itated oxidations resulting from through-space
p
/S/
p
interactions.
Ó 2016 Elsevier Ltd. All rights reserved.
Keywords:
Regioselectivity
Unsymmetrical substitution
Electrochemistry
1. Introduction
cation as shown by theoretical calculations and the absorption
spectrum of the radical cation prepared under stable ion condi-
Electrochemical oxidation potentials, determined by cyclic
voltammetry, and ionization energies, determined by photo-
electron spectroscopy, for thioethers are lowered when an aro-
matic ring is juxtaposed to the sulfur as in 1.1 This effect was
ascribed to through-space S/
bonding interaction between the p-type sulfur lone pair with the
neighboring aromatic system becomes a new kind of three-
tions.2 To determine whether through-space S/
p
interactions
can be extended to through-space
p/S/p aromatic interactions
m-terphenyl thioethers 2 were prepared.3 The electrochemical
oxidation potentials of 2 and ionization energy of 2b, determined
by photoelectron spectroscopy were indeed lowered, but the
basis for these effects was not clearly determined.4 Of particular
concern was the conformation of the radical cation. Stabilization
of the radical cation of 2 by one or both aromatic rings by
p interaction in which an anti-
electron S/p bond in the radical
* Corresponding authors. E-mail addresses: gwilson@ku.edu (G.S. Wilson),
rglass@email.arizona.edu (R.S. Glass).
http://dx.doi.org/10.1016/j.tet.2016.03.040
0040-4020/Ó 2016 Elsevier Ltd. All rights reserved.

2528
T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
through-space S/p interaction involves conformation 3 in which
the CeSeMe and flanking aromatic rings are perpendicular to the
central phenyl ring. While this conformation is preferred in the
m-terphenyl derivative 2 itself, the barrier for rotation about the
aryl CeS bond is low though the barrier for rotation about the
bond linking the central phenyl ring to m-aryl substituents in 2a
is high (
D
Gs¼66.9 kJ/mol) as determined by variable tempera-
ture 1H NMR spectroscopic studies.3 Since the difference in en-
ergy between the planar conformer (in which the CeSeMe
moiety and central phenyl ring are coplanar) in the radical cation
of thioanisole is calculated to be about 18 kcal/mol, more stable
than the perpendicular conformer (in which the CeSeMe moiety
is perpendicular to the central phenyl ring) owing to resonance
delocalization,5 formation of the resonance stabilized planar
radical cation is a plausible alternative to the perpendicular
radical cation despite steric effects, and initial studies on the
radical cation of 2b, under stable ion conditions, supported this
ambiguity. To prevent planarization in 3, i.e., the CeSeMe moiety
and central phenyl ring are coplanar, the more sterically de-
manding tert-butyl-thioethers 4 were desired.
Previously, SuzukieMiyaura9 coupling of 7 with phenylboronic
acid afforded 2,6-diphenyl-4-methylthioanisole in 27% yield.3
Therefore, dibromide 8a,10 to be used in SuzukieMiyaura cou-
plings, was synthesized. Diazotization11 of aniline 8c followed by
reaction with potassium ethyl xanthate and hydrolysis with KOH12
provided thiol 8b in an overall yield of 72%. Thiol 8b proved sus-
ceptible to oxidative dimerization; therefore, the crude product
was treated with tert-
This paper reports the synthesis, characterization and electro-
chemistry of tert-butyl thioethers 4.
butyl alcohol, glacial AcOH and Ac2O followed by 70% aqueous
13
HClO4 to provide tert-butylsulfide 8a in very high yield. Under
conditions in which
7 was converted to 2,6-diphenyl-4-
methylthioanisole in 27% yield, 8a afforded a mixture of unreacted
8a, mono- and di-substitution products. However, with excess phe-
nylboronic acid the disubstituted product was predominantly
formed. By optimizing conditions, 4a could be formed in 81% yield
without any monosubstituted byproduct. Other examples using
this coupling procedure are listed in Table 1.
Furthermore, the synthetic methodology developed enabled the
facile synthesis of extended systems 5 in which through-space
/S/p/S/p interactions can be assessed.
p
Table 1
SuzukieMiyaura couplinga of 8a with arylboronic acids ArB(OH)2
Ar
Product
Yield (%)
Ph
4a
4b
4c
4d
81
61
72
77
3,5-(MeO)2C6H3
4-ClC6H4
4-O2NC6H4
a
Pd(PPh3)4, LiCl, 2 M aqueous Na2CO3, 1,4-dioxane.
2. Results and discussion
2.1. Synthesis
Selective SuzukieMiyaura couplings with di- and polyhalides
have been reported.14 In this context selective monocoupling of 8a,
under our conditions by varying the equivalents of arylboronic acid
could not be achieved in good yield with the arylboronic acids
shown in Table 1. However, o-MeOC6H4B(OH)2, under the condi-
tions used for the reactions summarized in Table 1, gave only
monocoupled product 9a in 69% yield and none of the di-coupled
product. Nevertheless mono-coupled product 9a underwent cou-
pling with phenylboronic acid to produce unsymmetrically coupled
product 4e in 70% yield. Steric effects15 sometimes play a role in
SuzukieMiyaura couplings especially with di-o-substituted phe-
nylboronic acids16 and a manifestation of steric effects is suggested
to account for mono-coupling with o-MeOC6H4B(OH)2 in our case.
Similarly selective coupling of 8a with o-tolylboronic acid gave 9c in
Previously, we reported3 that the most useful procedure for
synthesizing m-terphenylmethylthioethers 2 was based on the
Saednya and Hart procedure6 in which the presumed intermediary
Grignard reagent 6a is treated with MeSSO2Me. Consequently,
lithio-derivative 6b, prepared from the corresponding iodide 6c,
was treated with t-BuSSO2t-Bu7 or t-BuSSO2p-Tol.8 In neither case
was 4a formed but rather 6d, presumably resulting from t-Bu
elimination rather than nucleophilic substitution on sulfur. Re-
action of aniline 6e with nitrous acid and t-BuSSt-Bu also produced
mainly 6d with a small amount of 4a in contrast to the 42% yield of
2b obtained on performing this reaction with MeSSMe3 instead of
t-BuSSt-Bu.

T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
2529
70% yield; although with higher concentrations of o-tolylboronic
acid some bis-coupled product is also formed. Coupling of 9c with
phenylboronic acid produced 4f in 95% yield.
mixture of 8a and 8d were treated with 1 equiv of o-MeOC6H4
-
B(OH)2 under our coupling conditions. 1H NMR spectroscopic
analysis of the resulting mixture indicated that 8d was approxi-
mately six times more reactive than 8a and produced some bis-
coupled product whereas no bis-coupled product from 8a is
formed. Thus the SuzukieMiyaura coupling reaction senses the
difference in steric size of O versus S and the difference in alkyl
groups (Me vs t-Bu) attached to sulfur.
With this improved SuzukieMiyaura coupling condition in hand
such couplings with the known17 S-methyl dibromide 8d were
explored. Some examples of such couplings are listed in Table 2. In
addition reaction of 8d with o-MeOC6H4B(OH)2 proved to be se-
lective but not as selective as that with 8a. With 8d, 9b was ob-
tained in 79% yield with the balance of the material bis-coupled
product. Notably anisole derivative 8e did not undergo selective
mono-coupling and the bis-coupled product 6f was obtained in 41%
yield.18 This is an expected steric effect since it is known that the
barrier for rotation about the CeC bond connecting the central ring
to the lateral rings in 6f is lower than that in 2a (the van der Waals
radius for sulfur is larger than that for oxygen).19 Calculations on
this barrier for 2a show that the barrier height is determined by
steric interaction between the ortho hydrogen of the rotating lateral
ring and sulfur.3 This raises an interesting question about the steric
effect in the SuzukieMiyaura coupling. That is, would the differ-
ence in steric size between the Me group in 8d and the t-Bu group
in 8a affect their relative rates of reaction. Consequently a 1:1
The selective mono-coupling of 8a with o-MeOC6H4B(OH)2 and
o-MeC6H4B(OH)2 followed by coupling with phenylboronic acid to
obtain unsymmetrical 4e and 4f, respectively, opened up the pos-
sibility of synthesizing more complex systems with multiple al-
ternating thioether and aromatic
space interaction. Morgan and co-workers20 conjectured that al-
ternating S/ -systems may be conduits for electron-transfer
p-systems arranged for through-
p
based on finding this structural motif in redox proteins. To our
knowledge this conjecture has never been tested experimentally.
Consequently, the syntheses shown in Scheme 1 were carried out.
Compounds 5a and b were both obtained in 21% overall yield on
coupling 9a and c, respectively, with 11a and b. Both 11a and b were
obtained as reaction intermediates by coupling 9a and c, re-
spectively, with diboronic acid 10.
An X-ray crystal structure study of 5a showed its molecular
structure as that in Fig. 1. Not only does the structure study un-
equivocally validate the assigned structure but it shows that the
molecule adopts the desired conformation which allows for
Table 2
SuzukieMiyaura couplinga of 8d with arylboronic acids ArB(OH)2
Ar
Product
Yield (%)
through space S/
two thioethers, that is, 2-MeOC6H4/S/C6H4/S/2-MeOC6H4,
S/ alternation and presumably, the geometry in 5b is similar. The
p interaction involving three aromatic rings and
Ph
2b
2c
2d
99
53
53
4-(MeO)C6H4
3,5-(MeO)2C6H3
p
a
Pd(PPh3)4, LiCl, 2 M aqueous Na2CO3, 1,4-dioxane.
Scheme 1. Synthesis of 5a and b.
Fig. 1. The molecular structure of 5a. One-half of the molecule is crystallographically unique and labels are shown for those atoms. A crystallographic inversion center at the center
of the C7eC8eC9 containing aromatic ring generates the remainder of the molecule. Displacement ellipsoids are shown at the 50% probability level.

2530
T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
redox chemistry of these two compounds is reported in the fol-
lowing section.
voltammetry though potentials consistently less anodic are ob-
served. This is likely due to less interference from product accu-
mulation on the electrode. Consequently, through-space
As illustrated above, SuzukieMiyaura couplings proceeded well
in the presence of a thioether moiety. Other examples of such
couplings illustrating the tolerance of thioether groups have been
reported before.9a,21 Thus simple aryl methylthioethers are neither
substrates in the SuzukieMiyaura reaction (although it is known22
that heteroaromatic methylthioethers undergo SuzukieMiyaura
coupling with replacement of the MeS group, as well as other ac-
tivated thioether moieties, in the presence of 1 equiv of copper (I)
2-thiophenecarboxylate and using Pd2dba as catalyst gives the best
results) nor do they act as catalyst poisons.
As pointed out above thioethers do not poison SuzukieMiyaura
catalysts. Indeed ligands used in these reactions are often appended
with thioethers.23 Although thioethers may poison heterogeneous
catalysts they do not poison homogeneous catalysts. Rather, such
groups are often designed into the ligand which coordinates the
metal to act as a semi-labile site, that is, the thioether coordinates
the metal but readily dissociates to generate an open site on the
metal.
p/S/p/S/p does not occur.
Table 4
Oxidation potentialsa for extended S/Ar systems 5a and b and their models 4e and f
Compd
CV
DPV
5a
4e
5b
4f
1.144
1.128
1.180
1.182
1.076
1.052
1.096
1.083
a
Pt electrode, CH3CN, 0.1 M NaClO4, reference electrode: 0.1 M AgNO3 in CH3CN,
scan rate 0.1 V/s.
3. Conclusions
In conclusion, SuzukieMiyaura reactions enabled the efficient
synthesis of m-terphenylmethyl and tert-butyl thioethers. In addi-
tion, highly selective monocouplings of sterically hindered o-
methoxy and o-methylphenylboronic acids with S-t-Bu dibromide
8a were found. This selective monocoupling enabled the syntheses
of unsymmetrical m-terphenyl thioethers as well as extended
systems 5a and b. Electrochemical studies provided evidence for
2.2. Electrochemistry
The redox chemistry of tert-butyl thioethers 4aee was studied in
acetonitrile using cyclic voltammetry. Each compound undergoes
irreversible oxidation with the peak potentials listed in Table 3. The
electrochemical oxidation potential of 4a (1.172 V) is remarkably less
anodic than that reported for t-BuSPh (1.40 V)24 demonstrating
through-space
through-space
p
/S/
p
interaction in 4 and 5 but not extended
p
/S/
p
/S/ interaction in 5. Future studies are
p
through-space p/S/p interaction in 4a. This interaction is further
planned to further explore the possibility of extended through-
space /S/ /S/ interaction by tuning the orbital energies of
the central system (with substituents or fused aromatic rings)
supported by the substituent effects. That is, electron-donating
substituents on the m-phenyl rings lower the oxidation potential;
whereas, electron-withdrawing substituents raise them resulting in
the series of less anodic peak potentials: 4b<4e<4aw4f<4c<4d. It
is also remarkable that the oxidation potential of 4a (1.172 V) is more
anodic than that of 2b (1.12 V)2 by only 50 mV; whereas, those for
PhSMe (1.12,251.2124 V) and t-BuSPh(1.40 V)24 differ byover 200 mV.
This further demonstrates the importance of through-space
p
p
p
p
and alternative geometries decreasing the distance and orientation
between the interacting moieties.
4. Experimental
4.1. General
p
/S/p interaction in 4a. The issues of planar versus perpendicu-
D
D
lar radical cation in 2a and the nature of the bonding in 2ꢀ and 4ꢀ
Proton and carbon-13 nuclear magnetic resonance (NMR)
spectra were recorded on Bruker DRX-500 and Bruker DRX-600
spectrometers. Chemical shifts are reported in parts per million
using residual NMR solvent as reference. All coupling constants (J
values) are reported in Hertz (Hz). Infrared spectra were recorded
on a Nicolet Impact-410 spectrophotometer. All melting points are
uncorrected and were recorded on Thomas Hoover Uni-Melt ap-
paratus. All mass spectra were done at the University of Arizona
Mass Spectrometry Facility using a JEOL HX110A high resolution
mass spectrometer.
Thin layer chromatography (TLC) was carried out on EMD
Chemical, Inc. TLC Plastic Sheets Si 60 F254. Column chromatogra-
phy was performed using Dynamic Adsorbents 32e63 micron flash
silica gel. All reagents were purchased from Aldrich Chemical Co.
and were used without further purification unless otherwise
stated. tert-Butyl alcohol was purchased from J. T. Baker Inc., 200
proof ethanol was purchased from Decon Laboratories, Inc. and all
other solvents were purchased from EMD Chemical, Inc. Tetrahy-
drofuran (THF) was purified and dried by distillation from sodium
and benzophenone. All reactions were carried under argon unless
otherwise indicated.
are addressed in another paper26 in which these species were gen-
erated under stable ion conditions and their structures analyzed
spectroscopically and computationally.
Table 3
Oxidation potentials for tert-butyl thioethers 4aef
a
Compound
Ep
4a
4b
4c
4d
4e
4f
1.172
0.815
1.191
1.30
1.128
1.182
a
CH3CN, 0.1 M NaClO4, reference electrode: 0.1 M AgNO3 in CH3CN, scan rate
0.1 V/s, Pt electrode.
To determine if through-space interaction in 4a can be extended
further to through-space
p/S/p/S/p, the electrochemistry of
5a and b was studied using cyclic voltammetry and differential
pulse voltammetry. Table 4 tabulates the electrochemical results
and the corresponding results for 4e and f. Perusal of this table
reveals that for 5a compared with 4e and 5b compared with 4f are
the same within experimental error. The differential pulse vol-
tammetry shows similar trends in the ease of oxidation as the cyclic
4.2. Syntheses
4.2.1. 2,6-Dibromobenzenethiol (8b). This compound was prepared
by modified literature procedures.11,12 A solution of NaNO2 (0.205 g,
2.97 mmol) in H2O (1.5 mL) was added dropwise to a suspension of

T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
2531
2,6-dibromoaniline, 7c, (678 mg, 2.70 mmol) in concentrated
aqueous HCl (2.6 mL, 12 M) at 0 ꢁC. The mixture was stirred at 0 ꢁC
for 90 min. Additional NaNO2 (55 mg, 0.797 mmol) was added. The
mixture was stirred for an additional 45 min at 0 ꢁC and then the
resulting cold solution was added dropwise to a stirred solution of
potassium ethyl xanthate (525 mg, 3.27 mmol) in H2O (0.65 mL) at
45 ꢁC through a glass pipet with a plug of glass wool. The reaction
mixture was stirred for 30 min at this temperature and then
allowed to cool to room temperature. The reaction mixture was
extracted with diethyl ether (3ꢂ50 mL). The combined organic
extracts were washed with 1 M NaOH solution (100 mL), water
(3ꢂ50 mL), brine (50 mL), dried over anhyd MgSO4, filtered and
evaporated under reduced pressure. The resulting crude product
was dissolved in ethanol (8 mL) and heated to reflux. Potassium
hydroxide pellets (654 mg, 11.6 mmol) were added and refluxing
continued overnight. After cooling to room temperature, the eth-
anol was evaporated under reduced pressure. The residue was
dissolved in water and washed with diethyl ether (100 mL). The
aqueous layer was acidified with 1 M HCl to pH 2 and extracted
with diethyl ether (3ꢂ50 mL). The organic extracts were washed
with water (50 mL), brine (50 mL), dried over anhyd MgSO4, filtered
and evaporated under reduced pressure. The residue was purified
by column chromatography on silica gel using hexanes as eluent to
give 8b as a slightly yellow solid (518 mg, 72%). This compound
always contains trace amounts of oxidized disulfide compound.
Therefore, compound 8b was used in next step without further
4H); 13C NMR (150 MHz, CD2Cl2)
130.1, 130.6, 131.8, 143.7, 151.2; IR (KBr) 1448, 1560, 2965,
3054 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for C22H22S, 318.1442;
found: 318.1432.
d
31.5, 49.6, 127.2, 127.8, 129.3,
4.2.4. . tert-Butyl(3,300,5,500-tetramethoxy-[1,10:30,100-terphenyl]-20-yl)
sulfane (4b). Compound 4b was synthesized by coupling com-
pound 8a (200 mg) with 3,5-dimethoxyphenylboronic acid using
the procedure for the synthesis of 4a. The crude product was pu-
rified by column chromatography on silica gel with dichlor-
omethane:hexanes (4:1) as eluent to give 4b as a white solid
(166 mg, 61%). The product was further purified by recrystallization
twice from diethyl ether:hexanes (1:1): mp 147e152 ꢁC; 1H NMR
(600 MHz, CD2Cl2)
6.66 (d, J¼2.4 Hz, 4H), 7.38 (dd, J¼9.0, 6.0 Hz, 2H), 7.42 (dd, J¼9.0,
5.4 Hz,1H); 13C NMR (150 MHz, CD2Cl2)
31.8, 49.4, 56.0, 99.3,110.1,
d
0.79 (s, 9H), 3.82 (s, 12H), 6.45 (t, J¼2.4 Hz, 2H),
d
129.0, 130.2, 130.4, 145.5, 150.9, 160.4; IR (KBr) 1062, 1162, 1326,
1457, 1590, 2834, 2974 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for
C26H30O4S 438.1865; found: 438.1849.
4.2.5. .tert-Butyl(4,400-dichloro-[1,10:30,100-terphenyl]-20-yl)sulfane
(4c). Compound 4c was synthesized by coupling compound 8a
(300 mg) with 4-chlorophenylboronic acid using the procedure for
the synthesis of 4a. The crude product was purified by column
chromatography on silica gel using chloroform/hexanes. Com-
pound 4c was obtained as a white solid (260 mg, 72% yield). The
product was further purified by recrystallization twice from diethyl
ether:hexanes (1:1): mp 168e170 ꢁC; 1H NMR (600 MHz, CD2Cl2)
purification. 1H NMR (500 MHz, CD2Cl2)
J¼7.0 Hz, 1H), 7.52 (d, J¼7.0 Hz, 2H); IR (KBr) 1400, 1421, 1543, 2553
(SH), 3064, 3458 cmꢃ1
d 5.04 (s, 1H), 6.87 (t,
.
d
0.69 (s, 9H), 7.38 (m, 6H), 7.46 (m, 5H); 13C NMR (150 MHz,
CD2Cl2)
d 30.8, 49.7, 127.3, 128.9, 129.3, 130.1, 132.6, 132.7, 141.4,
4.2.2. tert-Butyl(2,6-dibromophenyl)sulfane (8a). This compound
149.4; IR (KBr) 1086, 1448, 1487, 1592, 2952, 3043 cmꢃ1; HRMS (EI)
ꢀ
was prepared using modified procedure reported by Dieguez
m/z: [M]þ calcd for C22H20Cl2S 386.0663; found: 386.0660.
et al.13 A solution of compound 8b (180 mg, 0.671 mmol), tert-
butyl alcohol (0.332 mL, 3.49 mmol), AcOH (2.7 mL), and acetic
anhydride (0.39 mL) was stirred at 0 ꢁC for 20 min under argon,
and then 70% aqueous HClO4 (0.11 mL) was added. The solution
was allowed to warm to room temperature and stirred overnight.
After tert-butyl alcohol was removed under reduced pressure,
water (50 mL) was added to the solution. The solution was
extracted with CH2Cl2 (3ꢂ50 mL). The combined organic layer was
washed with 1 M NaOH (50 mL), brine (50 mL), dried with anhyd
MgSO4, filtered and evaporated under reduced pressure. The
resulting crude product was purified by column chromatography
on silica gel using hexanes as eluent to give 8a as a slightly yellow
4.2.6. .tert-Butyl(3,300-dinitro-[1,10:30,100-terphenyl]-20-yl)sulfane
(4d). Compound 4d was synthesized by coupling compound 8a
(250 mg) with 2.2 equiv of 3-nitrophenyl-boronic acid but other-
wise the same procedure as that for the synthesis of 4a. The crude
product was purified by column chromatography on silica gel using
chloroform/hexanes. Compound 4d was obtained as a white solid
(250 mg, 77% yield). The product was further purified by re-
crystallization twice from diethyl ether:hexanes (1:1): mp
225.5e227 ꢁC; 1H NMR (600 MHz, CDCl3)
d 0.64 (s, 9H), 7.48 (d,
J¼7.8 Hz, 2H), 7.55 (dd, J¼7.8, 6.6 Hz, 1H), 7.57 (t, J¼8.4 Hz, 2H), 7.86
(d, J¼7.8 Hz, 2H), 8.20 (dd, J¼7.8, 1.8 Hz, 2H), 8.38 (t, J¼1.8 Hz, 2H);
oil (219 mg, quantitative yield): 1H NMR (600 MHz, CD2Cl2)
d
1.41
13C NMR (150 MHz, CDCl3)
d 31.2, 50.9, 122.3, 126.3, 128.5, 129.8,
(s, 9H), 7.02 (t, J¼9.0 Hz, 1H), 7.68 (d, J¼9.0 Hz, 2H); 13C NMR
129.8, 131.1, 137.7, 144.1, 147.8, 148.6; IR (KBr) 1347, 1529,
2972 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for C22H20N2O4S 408.1144;
found:408.1125.
(150 MHz, CD2Cl2)
d 32.2, 52.7, 131.63, 133.4, 135.5, 136.4; IR (neat)
1413, 1542, 2959 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for C10H12Br2S,
321.9026; found: 321.9013.
4.2.7. (3-Bromo-20-methoxy-[1,10-biphenyl]-2-yl)(tert-butyl)sulfane
(9a). Compound 9a was synthesized by coupling compound 8a
(80 mg) with 2-methoxyphenylboronic using the procedure for the
synthesis of 4a. The crude product was purified by column chro-
matography on silica gel with chloroform:hexanes (1:9 ramped up
to 1:1) as eluent to give 9a as a slightly yellow oil (65 mg, 69%
4.2.3. [1,10:30,100-Terphenyl]-20-yl(tert-butyl)sulfane (4a). To a solu-
tion of 8a (400 mg, 1.23 mmol) in distilled 1,4-dioxane (2.0 mL)
under argon, were added a 2 M aqueous solution of Na2CO3 (2.5 mL,
2.46 mmol), LiCl (167 mg, 3.93 mmol), phenylboronic acid (630 mg,
4.92 mmol), and Pd(PPh3)4 (142 mg, 0.123 mmol). The mixture was
stirred for 24 h at reflux. H2O (50 mL) was added to the resulting
suspension and extracted with EtOAc (50 mL). The organic layer
was washed successively with 1 M NaOH (50 mL), brine (50 mL),
and H2O (50 mL), dried with MgSO4, filtered and evaporated under
reduced pressure. The crude product was purified by column
chromatography on silica gel using 1:9 chloroform/hexanes as el-
uent to give 4a as a white solid (315 mg, 81% yield). The product was
further purified by recrystallization twice using diethyl ether:-
yield): 1H NMR (600 MHz, CD2Cl2)
d 1.05 (s, 9H), 3.75 (s, 3H), 6.94
(d, J¼8.4 Hz, 1H), 6.98 (dt, J¼7.2, 0.6 Hz, 1H), 7.18 (dd, J¼7.2, 1.8 Hz,
1H), 7.22 (t, J¼7.8 Hz, 1H), 7.29 (dd, J¼7.8, 1.2 Hz, 1H), 7.33 (dt, J¼7.8,
1.8 Hz, 1H), 7.70 (dd, J¼7.8, 1.2 Hz, 1H); 13C NMR (150 MHz, CD2Cl2)
d
31.9, 50.3, 55.8, 111.1, 120.2, 129.5, 130.2, 131.1, 132.1, 132.9, 135.7,
148.9, 157.2; IR (neat) 751, 1436, 1456, 1576, 1599, 2917, 3048 cmꢃ1
;
HRMS (EI) m/z: [M]þ calcd for C17H19BrOS 350.0340; found:
350.0342.
hexanes (1:1): mp 99e100 ꢁC; 1H NMR (600 MHz, CD2Cl2)
d 0.66 (s,
9H), 7.32 (tt, J¼7.8, 1.4 Hz, 2H), 7.38 (t, J¼7.8 Hz, 4H), 7.39 (d,
4.2.8. (2-Methoxy-[1,10:30,100-terphenyl]-20-yl)(tert-butyl)sulfane
(4e). Compound 4e was synthesized by coupling compound 9a
J¼7.8 Hz, 2H), 7.45 (dd, J¼7.8, 6.6 Hz, 1H), 7.50 (dd, J¼7.8, 1.6 Hz,

2532
T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
(159 mg) with phenylboronic acid using the procedure for the
synthesis of 4a. The crude product was purified by column chro-
matography on silica gel using chloroform/hexanes (1:9 ramped
up to 1:1) as eluent to give 4e as a white solid (110 mg, 70% yield).
The product was further purified by recrystallization twice from
diethyl ether:hexanes (1:1): mp 145e146 ꢁC; 1H NMR (500 MHz,
2d as a white solid (148 mg, 53% yield). The product was further
purified by recrystallization twice from diethyl ether:hexanes
(1:1): mp 119e120 ꢁC; 1H NMR (600 MHz, CD2Cl2)
d 1.79 (s, 3H),
3.83, (s, 12H), 6.49 (t, J¼2.4 Hz, 2H), 6.64 (d, J¼2.4 Hz, 4H), 7.29 (dd,
J¼7.8, 6.6 Hz, 2H), 7.34 (dd, J¼8.4, 6.6 Hz, 1H); 13C NMR (150 MHz,
CD2Cl2)
d 19.7, 55.9, 99.6, 108.3, 127.7, 130.3, 134.3, 144.6, 146.8,
CD2Cl2)
d
0.67 (s, 9H), 3.80 (s, 3H), 6.95 (d, J¼8.0 Hz, 1H), 6.99 (dt,
160.9; IR (KBr) 1157, 1208, 1336, 1456, 1591, 2832, 2921, 3051 cmꢃ1
;
J¼7.5, 1.0 Hz, 1H), 7.25 (dd, J¼7.5, 1.0 Hz, 1H), 7.29e7.40 (m, 6H),
HRMS (EI) m/z: [M]þ calcd for C23H24O4S 396.1395; found:
7.44 (t, J¼7.5 Hz, 1H), 7.53 (d, J¼7.0 Hz, 2H); 13C NMR (150 MHz,
396.1384.
CD2Cl2)
d 31.6, 48.9, 55.8, 111.0, 120.2, 127.2, 127.8, 129.1, 130.5,
131.8, 143.7, 157.4; IR (KBr) 1231, 1460, 1596, 2833, 2956,
3056 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for C23H24OS 348.1548;
found: 348.1541.
4.2.14. (3-Bromo-20-methoxy-[1,10-biphenyl]-2-yl)(methyl)sulfane
(9b). Compound 9b was synthesized by coupling compound 8d
(100 mg) with 2-methoxyphenylboronic using the procedure for
the synthesis of 4a. The crude product was purified by column
chromatography on silica gel with chloroform:hexanes as eluent to
give 9b as a clear oil (87 mg, 79% yield): 1H NMR (500 MHz, CDCl3)
4.2.9. (3-Bromo-20-methyl-[1,10-biphenyl]-2-yl)(tert-butyl)sulfane
(9c). Compound 9c was synthesized by coupling compound 7a
(100 mg) with o-tolylboronic acid using the procedure for synthesis
of 4a. The crude product was purified by column chromatography
on silica gel with chloroform:hexanes as eluent to give 9c as a clear
d
2.18 (s, 3H), 3.76 (s, 3H), 6.95 (d, J¼8.0 Hz, 1H), 7.00 (dt, J¼1.0,
7.0 Hz, 1H), 7.12 (dd, J¼2.0, 7.5 Hz, 1H), 7.15e7.22 (m, 2H), 7.36 (dt,
J¼1.5, 6.5 Hz, 1H), 7.63 (dd, J¼2.0, 7.5 Hz, 1H); 13C NMR (125 MHz,
oil (73 mg, 70% yield): 1H NMR (500 MHz, CDCl3)
d
1.09 (s, 9H), 2.10
CDCl3) d 19.3, 55.7, 110.7, 120.4, 129.4, 129.5, 130.2, 130.6, 131.3,
(s, 3H), 7.14e7.27 (m, 6H), 7.71 (dd, J¼7.0, 2.5 Hz, 1H); 13C NMR
131.4, 132.9, 137.3, 146.0, 156.80; IR (neat) 763, 796, 1023, 1054,
1123, 1233, 1271, 1397, 1433, 1457, 1494, 2834, 2918, 2958, 3010,
3056 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for C14H13BrOS 307.9870;
found: 307.9862.
(125 MHz, CDCl3)
d 20.5, 31.9, 50.1, 124.6, 127.4, 129.5, 129.8, 129.9,
130.7,132.5,133.8,135.6,136.2,142.1, 150.9; IR (neat) 758, 788,1047,
1161, 1363, 1457, 1542, 2960, 3055 cmꢃ1; HRMS (EI) m/z: [M]þ calcd
for C17H19BrS 334.0391; found: 334.0377.
4.2.15. (2,20000-Dimethoxy-[1,10:30,100:400,1000:3000,10000-quinquephenyl]-
20,2000-diyl)bis(tert-butylsulfane) (5a). First, compound 9a (250 mg,
0.714 mmol) was coupled with benzene-1,4-diboronic acid, 10
(472 mg, 2.85 mmol) using the procedure for the synthesis of 4a.
After 24 h, H2O (50 mL) was added to the resulting suspension
and extracted with EtOAc (50 mL). The organic layer was washed
successively with brine (50 mL), and H2O (50 mL), dried with
anhyd MgSO4, filtered and evaporated under reduced pressure.
The crude product was purified by column chromatography on
silica gel using ethyl acetate/chloroform (1:1) to remove less
polar impurities and then 5% MeOH in chloroform to obtain
crude (20-(tert-butylthio)-200-methoxy-[1,10:30,100-terphenyl]-4-yl)
boronic acid 11a as a slightly yellow solid (184 mg). This crude
product was used without further purification in next Suzuki
coupling reaction with compound 9a (41 mg, 0.117 mmol). The
crude product was purified by preparative plate chromatography
on silica gel using dichloromethane/hexanes (1:1) as eluent to
give 5a as a white solid (15.4 mg, 21% yield): mp 215e216 ꢁC; 1H
4.2.10. (2-Methyl-[1,10:30,100-terphenyl]-20-yl)(tert-butyl)sulfane
(4f). Compound 4f was synthesized by coupling compound 9c
(100 mg) with phenylboronic acid using the procedure for the
synthesis of 4a. The crude product was purified by column chro-
matography on silica gel using chloroform/hexanes as eluent to
give 4f as a white solid (94 mg, 95% yield). The product was further
purified by recrystallization twice from diethyl ether:hexanes
(1:1): mp 78e79 ꢁC; 1H NMR (500 MHz, CD2Cl2)
d 0.71 (s, 9H), 2.17
(s, 3H), 7.18e7.27 (m, 5H), 7.32 (tt, J¼1.5, 7.5 Hz) 7.37e7.42 (m, 3H)
7.45 (t, J¼7.5 Hz) 7.50e7.53 (m, 2H); 13C NMR (125 MHz, CD2Cl2)
d
31.6, 48.8,124.6, 126.7, 127.0, 127.3, 128.6,129.4,129.7, 130.0,130.6,
130.9, 131.2, 136.5, 142.8, 142.9, 149.8, 150.1; IR (KBr) 810, 1032,
1169, 1363, 1440, 1560, 2856, 2893, 2918, 2935, 2958, 3012, 3024,
3056 cmꢃ1; HRMS (EI) m/z: [M]þ calcd for C23H24S 332.1599; found:
332.1585.
4.2.11. [1,10:30,100-Terphenyl]-20-yl(methyl)sulfane (2b). Compound
2b was synthesized by coupling (2,6-dibromophenyl)(methyl)sul-
fane, 8d (100 mg), prepared using a method reported by Bryant
et al.27 with phenylboronic acid using the procedure for the syn-
thesis of 4a. The crude product was purified by column chroma-
tography on silica gel using hexanes to remove a less polar impurity
and then 1:4 chloroform/hexanes to isolate the compound 2b as
a white solid (99% yield): the NMR and IR spectra, and melting point
of the compound were consistent with previously reported data.3
NMR (500 MHz, CD2Cl2)
d 0.74 (s, 18H), 3.82 (s, 6H), 6.96 (d,
J¼8.5 Hz, 2H), 7.00 (dt, J¼7.5, 1.0 Hz, 2H), 7.28 (d, J¼6.5 Hz, 2H),
7.34 (m, 4H), 7.45 (m, 4H), 7.56 (s, 4H); 13C NMR (125 MHz,
CD2Cl2)
d 31.7, 49.2, 55.9, 111.0, 120.2, 129.0, 130.6, 130.8, 132.7,
142.1, 148.0, 150.2, 157.4; IR (KBr) 1217, 1365, 1738, 2957 cmꢃ1
;
þ
HRMS (MALDI) m/z: [MꢃC8H15
]
calcd for C32H26O2S2,
506.13687; found: 506.13733.
4.2.16. (2,20000-Dimethyl-[1,10:30,100:400,1000:3000,10000-quinquephenyl]-
20,2000-diyl)bis(tert-butylsulfane) (5b). Compound 9c (610 mg,
1.81 mmol) was coupled with benzene-1,4-diboronic acid, 10
(301 mg, 1.81 mmol) using the procedure for the synthesis of 4a at
90 ꢁC. After 24 h, H2O (50 mL) was added to the resulting sus-
pension and extracted with EtOAc (50 mL). The organic layer was
washed successively with brine (50 mL), and H2O (50 mL), dried
with anhyd MgSO4, filtered and evaporated under reduced pres-
sure. The crude product was purified by column chromatography
on silica gel using chloroform/hexanes to give 5b as a white solid
(113 mg, 21% yield): mp 224.5e225.5 ꢁC; 1H NMR (500 MHz,
4.2.12. (4,400-Dimethoxy-[1,10:30,100-terphenyl]-20-yl)(methyl)sulfane
(2c). Compound 2c was synthesized by coupling 8d with 4-
methoxyphenylboronic acid using the procedure for the synthesis
of 4a. The crude product was purified by column chromatography
on silica gel using chloroform/hexanes (1:1) as eluent to give 2c as
a white solid (53% yield). The NMR and IR spectra, and melting
point of the compound were consistent with previously reported
data.3
4.2.13. (3,300,5,500-Tetramethoxy-[1,10:30,100-terphenyl]-20-yl)(methyl)
sulfane (2d). Compound 2d was synthesized by coupling 8d with
3,5-dimethoxyphenylboronic acid using the procedure for the
synthesis of 4a. The crude product was purified by column chro-
matography on silica gel using dichloromethane as eluent to give
CD2Cl2)
7.23e7.28 (m, 8H), 7.44e7.50 (m, 4H), 7.55 (s, 2H), 7.56 (s, 2H); 13
NMR (125 MHz, CD2Cl2) 20.8, 31.8, 49.5, 125.0, 127.3, 129.1, 129.7,
130.2, 130.5, 130.52, 130.6, 130.7, 130.7, 136.8, 141.9, 143.2, 150.2,
d 0.78 (s, 9H), 0.78 (s, 9H), 2.20 (s, 6H), 7.19e7.23 (m, 2H),
C
d

T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
2533
150.3, 150.5; IR (KBr) 757, 798, 1165, 1363, 1457, 2856, 2895, 2918,
4.5. Electrochemistry
2962, 3012, 3044 cmꢃ1; HRMS (ICR-ESI) m/z: [MꢃC8H15
]
þ calcd for
C
32H27S2, 475.1548; found: 475.1541.
All electrochemical experiments were performed using a CH
Instruments Model 620C potentiostat (Austin, TX). Acetonitrile
(CH3CN), extra dry (water<10 ppm) (Acros) was used without
further purification. The supporting electrolyte was NaClO4 anhy-
drous (Alfa Aesar) which was vacuum dried prior to use. A three
compartment electrochemical cell was employed with one com-
partment containing the working electrode Pt (2 mm od) or glassy
carbon (3 mm od) obtained from CH Instruments. The counter
electrode was glassy carbon and the reference electrode was 0.1 M
Agþ in CH3CN. Ferrocene (SigmaeAldrich) was used for monitoring
the stability of the reference electrode which had a potential of
0.028 V versus a ferrocene peak obtained by differential pulse
voltammetry (DPV) (amplitude 10 mV), Cyclic voltammetry (CV)
experiments were all carried out at a scan rate of 0.1 V/s. Before
4.3. Competition experiment
4.3.1. Competition between 8d and 8a in the SuzukieMiyaura cou-
pling reaction. To a solution of 8d (50 mg, 0.177 mmol) and 8a
(57 mg, 0.177 mmol) in distilled 1,4-dioxane (0.2 mL) under argon,
were added
a 2 M aqueous solution of Na2CO3 (0.35 mL,
0.70 mmol), 2-methoxyphenylboronic acid (26.9 mg, 0.177 mmol),
and Pd(PPh3)4 (40.9 mg, 0.0354 mmol). The mixture was stirred
overnight at reflux. H2O (30 mL) was added to the resulting sus-
pension and extracted with EtOAc (30 mL). The organic layer was
washed successively with 1 M aqueous NaOH (30 mL), brine
(30 mL), and H2O (30 mL), dried with anhyd MgSO4, filtered and
evaporated under reduced pressure. The crude mixture was column
chromatographed on silica gel using 1:1 chloroform/hexanes to
obtain a mixture of 8a, 8d, 9a and 9d whose relative abundance was
determined by 1H NMR spectroscopic analysis.
each experiment the working electrode was polished with 0.3 mm
alumina powder, washed with the solvent and dried. All experi-
ments were carried out in a glove box.
Acknowledgements
4.4. X-ray diffraction
The authors gratefully acknowledge financial support of this
work by the National Science Foundation (Grant No. 0956581).
A clear, colorless crystal of 5a 0.1ꢂ0.15ꢂ0.2 mm was used for
data collection. Data was collected using Mo K
a radiation on
Supplementary data
a Bruker Kappa Apex II Duo diffractometer. The crystal was non-
merohedrally twinned with the two domains related by a rota-
tion of 180ꢁ around the c* axis. The data was detwinned using
CELLNOW,28 integrated using SAINT,29 and scaled using TWI-
NABS.30 After detwinning, structure solution and refinement using
SHELXL97 was routine.31 The molecule lies on an inversion center,
with half of a molecule in the asymmetric unit. Table 5 lists crys-
tallographic data and structural refinement.
Supplementary data (Tables of crystallographic data for 5a.
Copies of NMR spectra) related to this article can be found, in the
online version at http://dx.doi.org/10.1016/j.tet.2016.03.040.
References and notes
1. Chung, W. J.; Ammam, M.; Gruhn, N. E.; Nichol, G. S.; Singh, W. P.; Wilson, G. S.;
Glass, R. S. Org. Lett. 2009, 11, 397e400.
2. Monney, N. P.-A.; Bally, T.; Bhagavathy, G. S.; Glass, R. S. Org. Lett. 2013, 15,
4932e4935.
3. Zakai, U. I.; Bloch-Mechkour, A.; Jacobsen, N. E.; Abrell, L.; Lin, G.; Nichol, G. S.;
Table 5
Crystal data and structure refinement of 5a
Bally, T.; Glass, R. S. J. Org. Chem. 2010, 75, 8363e8371.
4. Ammam, M.; Zakai, U. I.; Wilson, G. S.; Glass, R. S. Pure Appl. Chem. 2010, 82,
555e563.
5. (a) Baciocchi, E.; Gerini, M. F. J. Phys. Chem. A 2004, 108, 2332e2338; (b) Kor-
zeniowska-Sobczak, A.; Hug, G. L.; Carmichael, I.; Bobrowski, K. J. Phys. Chem. A
2002, 106, 9251e9266.
Crystal system
Space group
Unit cell dimensions
Monoclinic
P 1 21/c 1
¼90ꢁ
ꢁ
a¼14.2500(3) A
a
b¼14.2983(3) A
b
¼101.1930(10)ꢁ
ꢁ
¼90ꢁ
ꢁ
c¼8.5433(2) A
g
6. Saednya, A.; Hart, H. Synthesis 1996, 1455e1458.
3
ꢁ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
1707.59(6) A
2
7. (a) Derbesy, G.; Harpp, D. N. J. Org. Chem. 1995, 60, 1044e1052; (b) Luu, T. X. T.;
Nguyen, T.-T. T.; Le, T. N.; Spanget-Larsen, J.; Duus, F. J. Sulfur Chem. 2015, 36,
340e350.
8. (a) Parsons, T. F.; Buckman, J. D.; Pearson, D. E.; Field, L. J. Org. Chem. 1965, 30,
1923e1926; (b) Girijavallabhan, V.; Alvarez, C.; Njoroge, F. G. J. Org. Chem. 2011,
76, 6442e6446.
1.204 g/cm3
0.189 mmꢃ1
660
Theta range for
data collection
1.46e25.40ꢁ
9. (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457e2483; (b) Suzuki, A. J.
Organomet. Chem. 1999, 576, 147e168; (c) Suzuki, A. In Metal-catalyzed Cross-
coupling Reactions; Diederich, F., Stang, P. J., Eds.; VCH: Weinheim, 1998;
pp 49e97; (d) Miyaura, N. Top. Curr. Chem. 2002, 219, 11e59; (e) Hassan, J.;
Reflections collected
Coverage of independent
reflections
Absorption correction
Max. and min. transmission
Data/restraints/parameters
Goodness-of-fit on F2
3137
99.7%
ꢀ
Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem. Rev. 2002, 102,
Multi-scan
0.9813 and 0.9631
3137/0/203
1.065
1359e1470; (f) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58,
9633e9695; (g) Alonso, F.; Beletskaya, I. P.; Yus, M. Tetrahedron 2008, 64,
3047e3101.
10. Stoyanovich, F. M.; Marakatkin, M. A.; Gol’dfarb, Y. L. Izv. Akad. Nauk SSSR. Ser.
Khim. 1976, 11, 2537e2543.
D
/
smax
0.001
11. Kilyanek, S. M.; Fang, X.; Jordan, R. F. Organometallics 2009, 28, 300e305.
Final R indices
2618 data; I>2
s
(I)
R1¼0.0476,
wR2¼0.0977
R1¼0.0615,
wR2¼0.0976
12. McGinley, P. L.; Koh, J. T. J. Am. Chem. Soc. 2007, 129, 3822e3823.
ꢀ
13. Dieguez, M.; Ruiz, A.; Claver, C.; Doro, F.; Sanna, M. G.; Gladiali, S. Inorg. Chim.
All data
Acta 2004, 357, 2957e2964.
€
14. (a) Ronan, D.; Baudry, Y.; Jeannerat, D. Org. Lett. 2004, 6, 885e887; (b) Schoter,
ꢁꢃ3
0.301 and ꢃ0.318 eA
Largest diff. peak and hole
€
S.; Stock, C.; Bach, T. Tetrahedron 2005, 61, 2245e2267; (c) Schnurch, M.; Flasik,
R.; Khan, A. F.; Spina, M.; Mihovilovic, M. D.; Stanetty, P. Eur. J. Org. Chem. 2006,
3283e3307; (d) Handy, S. T.; Sabatini, J. J. Org. Lett. 2006, 8, 1537e1539; (e)
Conreaux, D.; Bossharth, E.; Monteiro, N.; Desbordes, P.; Vors, J.-P.; Balme, G.
Org. Lett. 2007, 9, 271e274; (f) Kawaguchi, K.; Nakano, K.; Nozaki, K. J. Org.
Chem. 2007, 72, 5119e5128; (g) Miguez, J. M. A.; Adrio, L. A.; Sousa-Pedrares, A.;
Vila, J. M.; Hii, K. K. J. Org. Chem. 2007, 72, 7771e7774; (h) Handy, S. T.; Wilson,
T.; Muth, A. J. Org. Chem. 2007, 72, 8496e8500; (i) Dang, T. T.; Ahmad, R.; Dang,
T. T.; Reinke, H.; Langer, P. Tetrahedron Lett. 2008, 49, 1698e1700; (j) Varello, S.;
Handy, S. T. Synthesis 2009, 138e142; (k) Beaumard, F.; Dauban, P.; Dodd, R. H.
Crystallographic data have been deposited with the Cambridge
Crystallographic Data Centre CCDC 1049877. Copies of the data can
be obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, or email: deposit@ccdc.cam.ac.uk.

2534
T. Yamamoto et al. / Tetrahedron 72 (2016) 2527e2534
Org. Lett. 2009, 11, 1801e1804; (l) Hung, N. T.; Hussain, M.; Malik, I.; Villinger,
22. Liebeskind, L. S.; Srogl, J. Org. Lett. 2002, 4, 979e981.
23. (a) Broutin, P.-E.; Colobert, F. Org. Lett. 2005, 7, 3737e3740; (b) Punji, B.; Mague,
J. T.; Balakrishna, M. S. Inorg. Chem. 2007, 46, 10268e10275; (c) Kuriyama, M.;
Shinazawa, R.; Shirai, R. Tetrahedron 2007, 63, 9393e9400; (d) Fliedel, C.;
Braunstein, P. Organometallics 2010, 29, 5614e5626; (e) Li, H.-L.; Wu, Z.-S.;
Yang, M.; Qi, Y.-X. Catal. Lett. 2010, 137, 69e73; (f) Qazi, A.; Sullivan, A. Dalton
Trans. 2011, 40, 10637e10642; (g) Dorta, R. Chimia 2011, 65, 806e812.
24. Matsumura, Y.; Yamada, M.; Kise, N.; Fujiwara, M. Tetrahedron 1995, 51,
6411e6418.
A.; Langer, P. Tetrahedron Lett. 2010, 51, 2420e2422; (m) Rossi, R.; Bellina, F.;
Lessi, M. Tetrahedron Lett. 2011, 67, 6969e7025; (n) Rossi, R.; Bellina, F.; Lessi, M.
Adv. Synth. Catal. 2012, 354, 1181e1255.
15. Skaff, D.; Jolliffe, K. A.; Hutton, C. A. J. Org. Chem. 2005, 70, 7353e7363.
16. (a) Altenhoff, G.; Goddard, R.; Lehmann, C. W.; Glorius, F. J. Am. Chem. Soc. 2004,
126, 15195e15201; (b) Barder, T. E.; Walker, S. D.; Martinelli, J. R.; Buchwald, S.
L. J. Am. Chem. Soc. 2005, 127, 4685e4696; (c) Tang, W.; Capacci, A. G.; Wei, X.;
Li, W.; White, A.; Patel, N. D.; Savoie, J.; Gao, J. J.; Rodriguez, S.; Qu, B.; Haddad,
N.; Lu, B. Z.; Krishnamurthy, D.; Yee, N. K.; Senanayake, C. H. Angew. Chem., Int.
Ed. 2010, 48, 5879e5883.
25. Elinson, M. N.; Simonet, J. J. Electroanal. Chem. 1992, 336, 363e367.
26. Monney, N. P.-A.; Bally, T.; Yamamoto, T.; Glass, R. S. J. Phys. Chem. A 2015, 119,
12990e12998.
17. Barbero, M.; Degani, I.; Diulgheroff, N.; Dughera, S.; Fochi, R.; Migliaccio, M. J.
Org. Chem. 2000, 65, 5600e5608.
27. Bryant, J. A.; Helgeson, R. C.; Knobler, C. B.; DeGrandpre, M. P.; Cram, D. J. J. Org.
18. Yamamoto, T.; Chen, P.-Y.; Lin, G.; Bloch-Mechkour, A.; Jacobsen, N. E.; Bally, T.;
Glass, R. S. J. Phys. Org. Chem. 2012, 25, 878e882.
19. (a) Pauling, L. The Nature of the Chemical Bond; Cornell University: Ithaca, NY,
1960; p 260; (b) Bondi, A. J. Phys. Chem. 1964, 68, 441e451.
Chem. 1990, 55, 4622e4634.
28. Sheldrick, G. M. CELL_NOW (Absorption Correction); CELL_NOW. Bruker AXS:
Madison, Wisconsin, USA, 2003.
29. Bruker. SAINT (Integration); SAINT Bruker AXS: Madison, Wisconsin, USA, 2007.
30. Sheldrick. TWINABS (Integration and Reduction); TWINABS. Bruker AXS: Madi-
son, Wisconsin, USA, 2002.
20. Morgan, R. S.; Tatsch, D. E.; Gushard, R. H.; McAdon, J. M.; Warme, P. K. Int. J.
Pept. Protein Res. 1978, 11, 209e217.
21. (a) Hua, D. H.; McGill, J. W.; Ueda, M.; Stephany, H. A. J. Organomet. Chem. 2001,
637, 832e836; (b) Dobler, M. Tetrahedron Lett. 2003, 44, 7115e7117.
31. SHELXTL (structure solution and refinement) Sheldrick, G. M. Acta Crystallogr.
2008, A64, 112e122.