Synthesis of d-glucose and l-phenylalanine substituted phenylene-thiophene oligomers

Article abstract of DOI:10.1016/j.tet.2010.11.004

Phenylene-thiophene oligomers bearing peracetylated β-d-glucose or N-BOC-l-phenylalanine as chiral substituents were synthesized in good yields by a versatile protocol based on the Suzuki-Miyaura cross-coupling reaction. Aryl iodides bearing the chiral bi

Full text of DOI:10.1016/j.tet.2010.11.004

Tetrahedron 67 (2011) 486e494
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of
oligomers
D
-glucose and -phenylalanine substituted phenyleneethiophene
L
,
b
Omar Hassan Omar a, Francesco Babudri b, Gianluca M. Farinola b , Francesco Naso ,
*
Alessandra Operamolla b, Adriana Pedone b
a Istituto di Chimica dei Composti OrganoMetallici CNR ICCOM di Bari, via Orabona 4, I-70126 Bari, Italy
b
ꢀ
Dipartimento di Chimica, Universita degli Studi di Bari ‘Aldo Moro’, via Orabona 4, I-70126 Bari, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 January 2010
Received in revised form 12 October 2010
Accepted 1 November 2010
Available online 5 November 2010
Phenyleneethiophene oligomers bearing peracetylated b-D-glucose or N-BOC-L-phenylalanine as chiral
substituents were synthesized in good yields by a versatile protocol based on the SuzukieMiyaura cross-
coupling reaction. Aryl iodides bearing the chiral biomolecules as substituents efficiently reacted with
pinacol boronates of bi- or terthiophenes leading to the bio-functionalized oligomers in good yields.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Oligothiophenes
Organic semiconductors
p-Conjugated materials
Organoboron compounds
Suzuki cross-coupling
Chiral conjugated oligomers
1. Introduction
The fast and efficient enantioselective detection of chiral
compounds is an issue of primary importance in many research
The wide variety of applications of polymeric1 and oligomeric2
organic semiconductors in organic electronics3 largely benefits
from the possibility to selectively functionalize the conjugated
backbone with several substituents. Side groups not only enable
fine tuning of the properties of conjugated materials, but can also
confer the specific ability to selectively interact with other mole-
cules, thus opening the way to their use as active materials in highly
selective electrical and optical sensors.4 In this context, bio-
molecules used as substituents offer the fascinating possibility to
combine the recognition ability deriving from their biological role
with the semiconducting properties of the conjugated backbone. In
fact, efficient and selective biological sensors employing properly
functionalized organic semiconductors as transducers have been
reported.5 Many classes of biological molecules, including mono-
saccharides and amino acids, can also be considered as easily
available sources of enantiopure multifunctional compounds for
the chiral functionalization of conjugated materials. This would
endow organic semiconductors with enantioselective recognition
ability towards specific chiral analytes6 or larger biological mole-
cules like proteins or DNA.7
and industrial areas, such as synthetic chemistry, pharmacology,
cosmetics, food-monitoring and medical diagnostics. Thus,
a growing interest has been devoted to the synthesis of organic
semiconductors bearing chiral substituents as enantioselective
receptors.8 Most frequently, chirally functionalized conjugated
materials have been used as fluorescence-based enantioselective
markers or sensors.9 Electropolymerized or molecularly imprinted
conducting polymers bearing chiral substituents have also been
reported as active materials in enantioselective electrochemical
sensors.6a,7a,8e,10 Frequently, chiral substituents described in
the literature are biotinylated pendant groups,8e,10a monosac-
charides,9b,c amino acids7a,9a,b or chiral hydrocarbon chains.6a We
reported the synthesis of
D L
-glucose8f and -phenylalanine8g
substituted poly(p-phenyleneethynylene)s and their use as active
layers in quartz crystal microbalance enantioselective gravimetric
sensors for chiral analytes in the vapour phase.6c,d More recently,
in the search for chirally substituted organic semiconductors for
electrical solid state enantioselective sensors, we have synthesized
the
D-glucose and L-phenylalanine substituted oligophenylene-
thiophenes, 1a and 1b, respectively.11 These oligomers have been
used as the sensing layer material in organic thin film transistor
(OTFT)-based enantioselective sensors for chiral analytes in the
vapour phase, exhibiting outstanding performances including
* Corresponding author. Tel.: þ39 080 5442076; fax: þ39 080 5442129; e-mail
address: farinola@chimica.uniba.it (G.M. Farinola).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.11.004

O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
487
a detection threshold three order of magnitude lower than that of
any chiral solid state sensors previously reported.11
paper can be divided into three classes (Fig. 1): the structures of the
first kind (Type 1, compounds 1, 2) are characterized by a dialkoxy-
substituted phenylene ring bonded to two oligothiophene blocks;
the second class (Type 2, compounds 3, 4) consists of oligothieny-
lene segments terminating with two monoalkoxy-substituted
phenyl rings; the third type (Type 3, compounds 5, 6) consists of
linear oligothiophenes terminating on one side with a monoalkoxy-
functionalized phenyl ring. The N-tert-butoxycarbonyl protected
The excellent progress in enantioselective sensing was made
possible by the synthesis of 1a and 1b. However, in the previous
paper we did not systematically investigate the potential of the
protocol affording 1a and 1b described in the Supplementary in-
formation of reference 11. It is important to fully explore the gener-
ality of the synthetic methods as tools for fine tuning properties of
organic semiconductors by small structural modifications. In par-
ticular, changing the sequence of the conjugated backbone and
L-phenylalanine molecule is attached to the phenyl ring through
a six carbon atom alkoxy chain connected to the amino acid car-
boxylic group by an ester linkage. Conversely, the peracetylated
extending the p systemimpactonelectronic andopticalproperties of
the materials while modifying the number and positions of the bio/
chiral substituents can affect polarity and eventually recognition
capability of the receptors.
D-glucose molecules are directly bonded to the phenyl rings through
b-glucosidic linkage.
The synthetic approach for building the conjugated system is
The aim of this synthetic paper is to report a full exploration of
a simple and effective method to obtain several phenylenee
thiophene oligomers functionalized with the required chiral bio-
molecules. The impact of the structural modifications accessible by
our method on the basic spectroscopic properties of this class of
molecular semiconductors is also discussed.
based on the palladium catalyzed SuzukieMiyaura cross-coupling
reaction14 between oligothiophene mono- or bis-pinacol boronic
esters and the mono- or diiodo-benzenes previously functionalized
with the biomolecules. The sequence proposed here offers distinc-
tive advantages compared to a possible alternative protocol in-
volving the synthesis of the conjugated skeleton followed by the
functionalization with the glucose or the amino acid substituents.
Actually, as the presence of the biomolecules on the organic halides
is tolerated in the cross-coupling conditions, our protocol enables
the synthesis of a wide variety of structures by simply using dif-
ferent thiophene boronic derivatives, many of which are commer-
cially available. Moreover, the thiophene pinacol boronates are
among the most stable and readily available boron-derivatives of
thiophene, showing good reactivity in the classical SuzukieMiyaura
cross-coupling conditions and forming low toxicity by-products.14
In this respect, our experiments further extend the usefulness of
thiophene boronic esters as valuable building blocks in the syn-
thesis of functionalized thiophene-based materials, even in the
presence of small biomolecules as substituents on the coupling
partner.
2. Results and discussion
Several phenyleneethienylene oligomers have been described in
the literature,12 showing different connections of phenyl or 1,4-
phenylene units with 2-thienyl or 2,5-thienylene rings. Alkoxy
moieties on the phenyl/phenylene rings are frequently used to
easily introduce several side groups on the main backbone in vari-
ous classes of conjugated oligomers and polymers.13 In the present
study chiral amino acid and glucose molecules were attached to the
benzene rings as alkoxy substituents. The oligomers reported in this
RO
S
S
The cross-coupling reactions were performed in anhydrous di-
oxane in the presence of Na2CO3 as the base and silver oxide15 at
70 ꢀC; these conditions were also compatible with the presence of
both the acetyl and tert-butoxycarbonyl protecting groups.
The synthesis of 2a,b represents an extension of the method
adopted for 1a,b as we have previously reported:11 it consists of
a single step double cross-coupling reaction between the diha-
lides 7a and 7b, which were prepared according to our previous
reports,8f,g and the commercially available boronic esters 8 and 9.
The reaction yields are summarized in the Scheme 1, showing
that the coupling of 7a,b with 5-(4,4,5,5-tetramethyl-1,3,2-diox-
aborolan-2-yl)-2,20-bithiophene 8 affords products 1a and 1b in
high yields. Similarly, the oligomers 2a and 2b, with a more ex-
tended aromatic system given by the two terthiophene blocks
were obtained by reaction of 7a,b with the 5-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-[2,20:50,200]-terthiophene 9 (see
Scheme 1). Oligomers belonging to the second and third cate-
gories, namely compounds 3, 4, 5, 6, differ from compounds of
n
S
S
n
OR
n = 1 1a-b
n = 2 2a-b
11
Type 1
RO
OR
S
S
S
RO
n
n
n = 2 3a-b
n = 3 4a-b
n = 1 5a-b
n = 2 6a-b
Type 2
Type 3
O
OAc
BOC
HN
O
C6H12
O
R=
AcO
AcO
H
OAc
a
b
Fig. 1. Structures of the phenyleneethiophene oligomers.
OR
OR
Pd(PPh3)4
O
S
S
S
B
n
Na 2CO3
Ag2O
+
I
I
S
O
S
S
dioxane
70 °C
n
RO
8 n = 1
9 n = 2
n
RO
7a-b
yields:
80%
O
OAc
1a n = 1
BOC
HN
1b n = 1 60%
2a n = 2 65%
2b n = 2
O
C6H12 O
R=
AcO
AcO
H
60%
OAc
a
b
Scheme 1. Synthesis of Type 1 compounds.

488
O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
the first type (1, 2) due to the presence of the biomolecules at one
or both ends of the oligoarylene sequence rather than in the
center of the molecule.
Such structural modifications can cause changes in polarity that
may affect solid state organization and processability both via so-
Pd(PPh3)4
Na2CO3
aq2M
O
S
+
I
S
B
toluene/
ethanol
90°C
S
S
S
O
S
14
11
13
60%
O
O
O
lution casting and via layer by layer technique, such as the
B
B
16
€
O
S
LangmuireShafer method. The synthesis of the oligomers 3, 4,
O
O
B
15
B
reported in the Scheme 2, was performed by coupling the diboronic
derivatives 11 and 12 with the halides 10a,b and afforded the
reaction products with good to excellent yields. Accordingly, the
coupling of the halides 10a,b with the monopinacol boronic esters of
di- or terthiophene, 8 or 9, yielded the oligomers 5 and 6 with similar
yields (Scheme 3). While the intermediate bis-boronic ester 11 is
commercially available, the bis-pinacol boronic ester of terthiophene
12 was prepared for the first time starting from the terthiophene 13
in 60% yield by Ir-catalyzed direct activation of the CeH bond in the
S
S
O
O
[IrCl(COD)] 2
dtbpy,n-octane
90°C
12
85%
Scheme 4. Synthesis of 12.
synthesis of molecular structures containing the terthienylene
block.
The halides 10a and 10b were synthesized in high yields starting
from the commercially available 4-iodophenol 16 and the per-
a
position of the thiophene rings17 carried out using the complex
[IrCl(COD)]2 and 4,40di-tert-butyl-2,20-bipyridine (dtbpy) the as
catalyst and a stochiometric amount of bisdioxaborolane 15.
RO
O
O
S
B
S
B
O
S
S
O
OR
3a 91%
11
Pd(PPh3)4
3b 91%
+
RO
I
Na2CO 3
Ag2O
dioxane
70 °C
10a-b
RO
OR
O
O
S
S
S
B
B
S
S
S
O
O
12
4a 80%
4b 85%
O
OAc
BOC
HN
O
C6H12O
R=
AcO
AcO
H
OAc
a
b
Scheme 2. Synthesis of Type 2 compounds.
RO
O
B
S
S
S
O
S
8
5a 84%
5b 74%
Pd(PPh3 4
)
+
RO
I
Na2CO3
Ag2O
RO
10a-b
dioxane
70 °C
O
S
B
S
S
S
S
O
S
6a 85%
6b 79%
9
O
OAc
BOC
HN
O
C6H12O
R=
AcO
AcO
H
OAc
a
b
Scheme 3. Synthesis of Type 3 compounds.
The starting terthiophene 13 was conveniently synthesized by
reacting 2-iodothiophene 14 with the pinacolboronic ester 11. The
reaction sequence leading to 12 is summarized in the Scheme 4.
Product 12 can be considered a useful building block for the
acetylated a-glucopyranose or N-BOC-L-phenylalanine, respectively
(Scheme 5). The two-step synthetic approach here proposed
afforded the compound 10a with improved overall yield compared
with the literature (76% vs 43%).18

O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
489
OAc
O
OAc
AcO
AcO
AcO
AcO
AcO
O
(CH3)3SiCl
OAc
HO
I
(H3C)3SiO
I
O
I
AcO
[(CH3)3Si]2NH
CH3CN
BF3•Et2O, CH2Cl2
17
O
10a
16
94%
81%
OH
NH-BOC
Et3N, DMAP,
1) NaOH
H
O
2) Br(CH2)6OH
DMF, THF, 60 °C
O
I
HO
I
HOC6H12
O
I
O
IPCC, CH2Cl2
H
NH-BOC
10b
18
16
73%
84%
Scheme 5. Synthesis of halides 10a and 10b.
The reaction of p-iodophenol 16 with trimethylchlorosilane in
the presence of bis-trimethylsilylamine in acetonitrile afforded the
corresponding trimethylsilyl ether 17,19 which then reacted
with peracetylated glucose. We used modified conditions (see
Experimental section) for the glycosidation step with respect to
a reference synthetic procedure leading to O-phenylglycosides20
and our procedure resulted in higher reaction yields.
caused by the presence of the central phenylene ring bearing two
bulky substituents that would decrease the effective conjugation
between the two oligothiophene arms. In the other two types of
compounds the steric hindrance of the bio-substituents, and the
consequent reduction of the effective conjugation length is elimi-
nated by bonding them in the external positions of the conjugated
backbone.
The
b configuration of the glycosidic linkage was confirmed by
the coupling constant value (Jz7 Hz) between the protons on C-1
3. Conclusions
and C-2 of the glucose ring. The value is typical of the axial-axial
arrangement in the
b
anomer.21
Summing up, we have reported an effective and versatile syn-
thetic method to phenyleneethienylene oligomeric semiconductors
bearing N-BOC-
L-phenylalanine or D-glucose as chiral substituents.
The reaction of 16 with NaOH, followed by addition of 6-bro-
mohexanol, afforded the derivative 18. The esterification reaction of
the alcohol 18 with the BOC-N-protected L-phenylalanine was
performed using isopropenyl chlorocarbonate (IPCC) as the con-
densing agent, according to our previously reported procedure.8g
The reaction occurs without racemisation of the amino acid unit.22
Table 1 summarizes the main spectroscopic properties of the
oligomers synthesized (maxima of absorption and emission spectra
in solution).
The key step of the synthetic protocol is the palladium catalyzed
SuzukieMiyaura cross-coupling reaction of pinacolboronate de-
rivatives of di- or terthiophenes with iodobenzenes functionalized
with the glucose or the amino acid moieties, which were found to be
tolerated in the cross-coupling reaction conditions.
Our work has also made easily available versatile intermediates
(e.g., compound 12) that in principle can be also used in other
synthetic sequences leading to several thiophene-based oligomers
eventually bearing pendant biological substituents different from
amino acids or monosaccharides.
Table 1
Spectroscopic properties of the synthesized oligomers
lmax abs (nm)
Dlmax abs (nm)
lmax emis. (nm)
(1a) 394
(2a) 427
(1b) 411
(2b) 440
(3a) 377
(4a) 405
(3b) 381
(4b) 410
(5a) 345
(6a) 384
(5b) 348
(6b) 387
33
(1a) 457, 485
(2a) 497, 529
(1b) 467, 495
(2b) 504, 539
(3a) 437, 462
(4a) 474, 505
(3b) 444, 470
(4b) 479, 508
(5a) 405, 423
(6a) 446, 472
(5b) 399, 420
(6b) 452, 476
4. Experimental section
4.1. General
29
28
29
39
39
All reactions were carried out under a nitrogen atmosphere in
oven-dried glassware, with dry solvents unless otherwise noted. All
solvents were distilled immediately prior to use. Tetrahydrofuran,
toluene and dioxane were distilled from benzophenone ketyl.
ꢁ
Acetonitrile, n-octane and dimethylsulfoxide were distilled from 4 A
molecular sieves and dichloromethane from phosphorus pentoxide.
All reagents were purchased at the highest commercial quality from
Aldrich Chemicals Co, Acros Organics or Fluka, and used without
further purification, with the exception of triethylamine, which was
As expected, for each type of structures a red shift in absorption
and emission maxima is observed moving from the shorter to the
longer homologous due to the increase of the conjugation length
caused by the addition of one (for Type 2 and Type 3) or two
thiophene rings (for Type 1) to the oligoaromatic chain. Quite
surprisingly, however, the red shifts measured for compounds of
the Type 1 is comparable to and more often slightly smaller than
the red shift obtained for the other two types, in spite of the larger
increase of the conjugation expected in this case (two thiophene
rings are added). This effect may be attributed to a significant
distortion of the conjugated backbone in compounds of the Type 1
ꢁ
distilled from KOH and stored over 4 A molecular sieves. Com-
pounds 7a and 7b were synthesized according to our previous
reports.8f,g Compounds 17, 18 and 13 were synthesised and their
characterisation data were compared with literature reports.23e25
Petroleum ether used refers to fraction boiling in the range
40e60 ꢀC. Column chromatography was performed using silica gel
60, 40e63 mm from Merck. Merck silica gel 60 F254 aluminum sheets
were used for TLC analyses. All new compounds were characterized
by 1H NMR, 13C NMR, IR spectroscopy and elemental analysis. GC
analyses were performed on a Varian 3900 gas chromatograph

490
O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
equipped with an SE-30 (methyl silicone, 30 mꢁ0.25 mm id) cap-
illary column and a FID detector. 1H NMR and 13C NMR spectra were
recorded at 400 MHz and 100 MHz, respectively, on Varian Inova
400, or at 500 MHz (1H NMR) and 125 MHz (13C NMR) on Bruker AM
500, using the residual proton peak of CDCl3 at 7.26 ppm as refer-
ence for 1H spectra and the signals of CDCl3 at 77 ppm for 13C
spectra. Coupling constants values are given in hertz. Melting points
(uncorrected) were obtained on a capillary melting point apparatus.
IR spectra were recorded on a PerkineElmer FTIR BX spectropho-
tometer. Elemental analyses were performed in our laboratories on
a Carlo Erba EA 1108 CHNS Elemental analyzer.
bright yellow solid was recovered (0.900 g, 84%). (Found: C 54.49, H
4.52, S 11.63. C50H50O20S4 requires C 54.63, H 4.58, S 11.67); Rf (pe-
troleum ether/ethyl acetate 1:1) 0.56; mp 218e220 ꢀC (dichloro-
methane/hexane). dH (CDCl3, 500 MHz): 1.82 (6H, s, CH3),1.98 (6H, s,
CH3), 2.02 (6H, s, CH3), 2.06 (6H, s, CH3), 3.97e4.03 (2H, m, CH),
4.21e4.30 (4H, m, 2CH2: two diasterotopic protons signals over-
lapped), 5.18 (2H, t, J 9.5 Hz, CH), 5.19 (2H, d, J 7.7 Hz, anomeric CH)
5.30 (2H, t, J 9.5 Hz, CH), 5.43 (2H, dd, J 9.5, 8.3 Hz, CH), 7.05 (2H, dd, J
5.1, 3.5 Hz, Th), 7.14 (2H, d, J 4.0 Hz, Th), 7.24 (2H, dd, J 5.1, 1.0 Hz, Th),
7.27 (2H, dd, J 3.5,1.0 Hz, Th), 7.32 (2H, d, J 4.0 Hz, Th), 7.43 (2H, s, Ph).
dC (CDCl3, 125 MHz) 20.4 (CH3), 20.6 (2CH3), 20.8 (CH3), 62.3 (CH2),
68.3 (CH, glucose ring), 70.9 (CH, glucose ring), 72.4 (CH, glucose
ring), 73.0 (CH, glucose ring), 99.9 (anomeric CH), 115.5, 124.0, 124.7,
127.5,128.1,136.3,136.4,136.9,138.2,148.8 (C, Ph),169.4 (C]O),169.5
(C]O), 170.2 (C]O), 170.7 (C]O). nmax/cmꢂ1 (KBr): 1036, 1218 (s,
CeOeC), 1367, 1489, 1753 (s, C]O).
4.1.1. (4-Iodo-phenoxy)-trimethylsilane 17. This compound was
prepared following a procedure adopted in similar cases.19 4-
Iodophenol (3.00 g, 13.64 mmol), chlorotrimethylsilane (2.10 mL,
16.37 mmol) and hexamethyldisilazane (3.45 mL, 16.37 mmol)
were dissolved in 40 mL of dry acetonitrile. The reaction mixture
was stirred under nitrogen at room temperature for 12 h and then
the solvent was removed at reduced pressure. The residue was
dissolved in petroleum ether and filtered to remove precipitated
salts. The solution was washed with saturated aqueous bicarbonate
50 mLꢁ3 and brine 50 mLꢁ2, dried over anhydrous Na2SO4 and
evaporated to dryness. The final product was obtained as a pale
yellow oil (3.17 g, 94% yield). (Found: C, 47.02, H, 4.49. C9H13IOSi
requires C, 47.00, H, 4.48); dH (CDCl3, 400 MHz): 0.25 (9H, s, CH3),
6.57e6.67 (2H, app d, J 9 Hz, Ph), 7.48e7.56 (2H, app d, J 9 Hz, Ph).
4.1.4. 1,4-Bis([2,20:50200]terthiophen-5-yl)-2,5-(2,3,4,6-tetra-O-acetyl-
b-D
-glucopyranosyl)benzene 2a. Na2CO3 (0.042 g, 0.39 mmol), Ag2O
(0.091 g, 0.39 mmol) and Pd(PPh3)4 (0.014 g, 0.012 mmol) were
added to a solution of 1,4-bis-(2,3,4,6-tetra-O-acetyl- -gluco-
b-D
pyranosyl)-2,5-diiodobenzene 7a (0.200 g, 0.20 mmol) and 5-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-[2,20:50200]-terthioph
ene 9 (0.161 g, 0.43 mmol) in 8 mL of anhydrous dioxane under
a nitrogen atmosphere. The reaction mixture was heated at 70 ꢀC
overnight and then cooled to room temperature and concentrated
under reduced pressure. The crude material obtained was purified
by preparative chromatography on silica gel, using a mixture of
petroleum ether/ethyl acetate 1:1 as the eluent and then crystal-
lized from dichloromethaneehexane. A orange-yellowish solid was
recovered (0.161 g, 65%). (Found: C 55.37, H 4.43, S 15.34.
C58H54O20S6 requires C 55.14, H 4.31, S 15.23); Rf (petroleum ether/
ethyl acetate 1:1) 0.51; mp 230e231C (dichloromethane/hexane).
dH (CDCl3, 400 MHz): 1.82 (6H, s, CH3), 1.94 (6H, s, CH3), 2.04 (6H, s,
CH3), 2.07 (6H, s, CH3), 3.98e4.04 (2H, m, CH), 4.22e4.31(4H, m,
CH2, two diasterotopic protons signals overlapped), 5.18 (2H, t, J
9.8 Hz, CH), 5.21 (2H, d, J 7.8 Hz, anomeric CH), 5.31 (2H, t, J 9.4 Hz,
CH), 5.45 (2H, t, J 9.0 Hz, CH), 7.03 (2H, dd, J 5.1, 3.9 Hz, Th),
7.10e7.15 (4H, m, Th), 7.17e7.21 (4H, m, Th), 7.23 (2H, d, J 5.1 Hz, Th),
7.33 (2H, d, J 3.9 Hz, Th), 7.43 (2H, s, Ph). dC (CDCl3, 100 MHz) 20.6
(CH3), 20.7 (2CH3), 20.8 (CH3), 62.3 (CH2), 68.2 (CH, glucose ring),
70.9 (CH, glucose ring), 72.4 (CH, glucose ring), 73.0 (CH, glucose
ring), 99.8 (anomeric CH), 115.2, 123.7, 123.8, 124.5, 127.4, 127.8,
135.5, 136.3, 136.4, 136.9, 137.8, 148.7 (C, Ph), 169.2 (C]O), 169.3
(C]O), 170.1 (C]O), 170.5 (C]O). nmax/cmꢂ1 (KBr): 1041, 1225 (s,
CeOeC), 1374, 1418, 1699, 1717, 1742 (s, C]O), 1791.
4.1.2. (2,3,4,6-Tetra-O-acetyl-
10a. This compound was prepared following a procedure adopted
in similar cases.20
-Glucose pentaacetate (3.83 g, 9.82 mmol)
b-D-glucopyranosyl)-4-iodobenzene
b-D
and BF3$Et2O (1.24 mL, 9.82 mmol), previously dissolved in 15 mL of
dry dichloromethane, were added under a nitrogen atmosphere to
a
solution of (4-iodo-phenoxy)-trimethylsilane 17 (2.39 g,
8.18 mmol) in 15 mL of CH2Cl2 kept at room temperature. After 12 h
the reaction mixture was washed with saturated aqueous bi-
carbonate 50 mLꢁ3 and brine 50 mLꢁ2 and dried over anhydrous
Na2SO4. Evaporation of the solvent at reduced pressure gave the
crude product that was purified by column chromatography over
silica gel, using a mixture of petroleum ether/ethyl acetate 6:4 as
eluent obtaining 10a as a white solid (3.65 g, 81% yield). (Found: C,
43.61, H, 4.20. C20H23IO10 requires C, 43.65, H, 4.21); Rf (petroleum
ether/ethyl acetate 6:4) 0.49; mp 144e145 ꢀC (methanol). dH
(CDCl3, 400 MHz): 1.99 (3H, s, CH3), 2.00 (3H, s, CH3), 2.01 (3H, s,
CH3), 2.03 (3H, s, CH3), 3.78e3.86 (1H, m, CH), 4.12 (1H, dd, J 12.3,
2.4 Hz, CH2), 4.24 (1H, dd, J 12.3, 5.4 Hz, CH2), 5.00 (1H, d, J 7.6 Hz,
anomeric CH), 5.11 (1H, t, J 9.6 Hz, CH), 5.18e5.29 (2H, m, 2CH),
6.70e6.75 (2H, app d, J 9.0 Hz, Ph), 7.52e7.57 (2H, app d, J 9.0 Hz,
Ph). dC (CDCl3, 100 MHz) 20.5 (CH3), 20.6 (2CH3), 20.8 (CH3), 61.8
(CH2), 68.1 (CH, glucose ring), 71.0 (CH, glucose ring), 72.0 (CH,
glucose ring), 72.5 (CH, glucose ring), 86.2 (CeI, Ph), 98.9 (anomeric
CH), 119.2 (C, Ph), 138.4 (C, Ph), 156.6 (C, Ph), 169.2 (C]O), 169.3
(C]O), 170.2 (C]O), 170.5 (C]O). nmax/cmꢂ1 (KBr): 818, 1041, 1224
(s, CeOeC), 1432, 1485, 1587, 1750 (s, C]O), 2961.
4.1.5. 5,50-Bis-(4-[2,3,4,6-tetra-O-acetyl-
b-D-glucopyranosyl]phe-
nyl)-[2,20]-bithiophene 3a. Na2CO3 (0.038 g, 0.36 mmol), Ag2O
(0.083 g, 0.36) and Pd(PPh3)4 (0.013 g, 0.011 mmol) were added to
a solution of (2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl)-4-iodo-
benzene 10a (0.200 g, 0.36 mmol) and 2,20-bithiophene-5,50-
diboronic acid bis-(pinacol) ester 11 (0.067 g, 0.16 mmol) in 7 mL
of anhydrous dioxane under a nitrogen atmosphere. The reaction
mixture was heated at 70 ꢀC overnight and then cooled to room
temperature and concentrated under reduced pressure. The crude
material obtained was purified by preparative chromatography on
silica gel, using a mixture of dichloromethane/diethyl ether 8.5:1.5
as the eluent and then crystallized from dichloromethane/hexane.
A bright yellow solid was recovered (0.138. g, 91% yield). (Found:
C, 57.04, H, 4.33, S, 6.37. C48H50O20S2 requires C, 57.02, H, 4.98, S,
6.34); Rf (dichloromethane/diethyl ether 8.5:1.5) 0.39; mp
139e140 ꢀC (dichloromethane/hexane). dH (CDCl3, 400 MHz): 2.04
(6H, s, CH3), 2.06 (6H, s, CH3), 2.08 (6H, s, CH3), 2.09 (6H, s, CH3),
3.84e3.91 (2H, m, CH), 4.17 (2H, dd, J 12.3, 2.4 Hz, CH2), 4.30 (2H,
dd, J 12.3, 5.3 Hz, CH2), 5.03 (2H, d, J 7.6 Hz, anomeric CH), 5.19 (2H,
4.1.3. 1,4-Bis([2,20]-bithiophen-5-yl)-2,5-(2,3,4,6-tetra-O-acetyl-
b-D-
glucopyranosyl)benzene 1a. Na2CO3 (0.21 g, 1.98 mmol), Ag2O
(0.45 g,1.94 mmol) andPd(PPh3)4 (0.030g, 0.03mmol) wereaddedto
a solution of1,4-bis-(2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl)-2,5-
diiodobenzene 7a (1.00 g, 0.98 mmol) and 5-(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-2,20-bithiophene 8 (0.630 g, 2.16 mmol) in
30 mL of anhydrous dioxane under a nitrogen atmosphere. The re-
action mixture was heated at 70 ꢀC overnight and then cooled to
room temperature and concentrated under reduced pressure. The
crudematerialobtainedwaspurifiedbypreparativechromatography
on silica gel, using a mixture of petroleum ether/ethyl acetate 1:1 as
the eluent and then crystallized from dichloromethaneehexane. A

O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
491
t, J 9.6 Hz, CH), 5.25e5.35 (4H, m, CH), 6.73e6.77 (4H, app d, J 9 Hz,
Ph), 6.98e7.01 (2H, app d, J 9 Hz, Th), 7.50e7.53 (2H, app d, J 9 Hz,
Th), 7.55e7.59 (4H, app d, J 9 Hz, Ph). dC (CDCl3, 100 MHz) 20.6
(CH3), 20.7 (2CH3), 20.8 (CH3), 61.9 (CH2), 68.2 (CH, glucose ring),
71.1 (CH, glucose ring), 72.1 (CH, glucose ring), 72.6 (CH, glucose
ring), 98.9 (anomeric CH), 117.3, 123.3, 124.3, 126.8, 129.4, 136.2,
142.2, 156.2 (C, Ph), 169.1 (C]O), 169.2 (C]O), 170.0 (C]O), 170.4
(C]O). nmax/cmꢂ1 (KBr): 1177, 1253 (s, CeOeC), 1498, 1506, 1731
(s, C]O), 2940.
169.6 (C]O), 170.5 (C]O), 170.8 (C]O). nmax/cmꢂ1 (KBr): 1045,
1084, 1226 (s), 1235, 1366, 1499, 1747 (s, C]O), 2945.
4.1.8. 5-(4-[2,3,4,6-Tetra-O-acetyl-b-D-glucopyranosyl]phenyl)-
[2,20:50200]terthiophene 6a. Na2CO3 (0.031 g, 0.29 mmol), Ag2O
(0.068 g, 0.29mmol)and Pd(PPh3)4 (0.010g, 0.009mmol)wereadded
to a solution of (2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl)-4-iodo-
benzene 10a (0.165 g, 0.29 mmol) and 5-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-[2,20:50200]-terthiophene 9 (0.124 g, 0.33 mmol) in
5 mL of anhydrous dioxane under a nitrogen atmosphere. The re-
action mixturewasheatedat70 ꢀCovernight and thencooled to room
temperature and concentrated under reduced pressure. The crude
material obtained was purified by preparative chromatography on
silica gel, using a mixture of dichloromethane/ethyl acetate 9:1 as the
eluent and then crystallized from dichloromethane/hexane. A bright
yellow solid was recovered (0.170 g, 85% yield). (Found: C, 57.32, H,
4.51, S, 14.30. C32H30O10S3 requires C, 57.30, H, 4.51, S, 14.34); Rf
(dichloromethane/ethyl acetate 9:1) 0.6; mp 237e238 ꢀC (dichloro-
methane/hexane). dH (CDCl3, 500 MHz): 2.05 (3H, s, CH3), 2.06 (3H, s,
CH3), 2.08 (3H, s, CH3), 2.10 (3H, s, CH3), 3.85e3.91 (1H, m, CH), 4.19
(1H, dd, J 12.4, 2.2 Hz, CH2), 4.30(1H, dd, J 12.4, 5.3 Hz, CH2), 5.11 (1H, d,
J 7.6 Hz, anomeric CH), 5.18 (1H, t, J 9.5, CH), 5.23e5.34 (2H, m, CH),
6.99e7.04 (3H, m, ThePh), 7.09(2H, br s, Th), 7.13 (2H, dd, J 8.9, 3.8 Hz,
Th), 7.18 (1H, dd, J 3.6, 1.1 Hz, Th), 7.22 (1H, dd, J 5.1, 1.1 Hz, Th),
7.51e7.55 (2H, app d, J 9 Hz, Ph). dC (CDCl3, 100 MHz) 20.6 (CH3), 20.7
(2CH3), 20.8 (CH3), 61.9 (CH2), 68.2 (CH, glucose ring), 71.1 (CH, glu-
cose ring), 72.1 (CH, glucose ring), 72.7 (CH, glucose ring), 98.9
(anomeric CH), 117.3, 123.4, 123.6, 124.0, 124.3, 124.4, 126.8, 127.8,
129.3,129.6,136.0,136.1,136.9,142.7,156.2 (C, Ph),169.1 (C]O),169.2
(C]O), 170.1 (C]O), 170.4 (C]O). nmax/cmꢂ1 (KBr): 794, 833, 1043,
1068, 1233 (s), 1368 (w), 1750 (s, C]O).
4.1.6. 5,500-Bis-(4-[2,3,4,6-tetra-O-acetyl-
b-D-glucopyranosyl]phe-
nyl)-[2,20:50200]terthiophene 4a. Na2CO3 (0.038 g, 0.36 mmol), Ag2O
(0.083 g, 0.36) and Pd(PPh3)4 (0.013 g, 0.011 mmol) were added to
a solution of (2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl)-4-iodo-
benzene 10a (0.200 g, 0.36 mmol) and 5,500-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-[2,20:50200]terthiophene 12 (0.080 g,
0.16 mmol) in 7 mL of anhydrous dioxane under a nitrogen atmo-
sphere. The reaction mixture was heated at 70 ꢀC overnight and
then cooled to room temperature and concentrated under reduced
pressure. The crude material obtained was purified by preparative
chromatography on silica gel, using a mixture of petroleum ether/
diethyl ether 8.5:1.5 as the eluent and then crystallized from
dichloromethane/hexane. A bright yellow solid was recovered
(0.127 g, 80% yield). (Found: C, 57.10, H, 4.81, S, 8.78. C52H52O20S3
requires C, 57.13, H, 4.79, S, 8.80); Rf (petroleum ether/diethyl ether
8.5:1.5) 0.45; mp 247e248 ꢀC (dichloromethane/hexane). dH
(CDCl3, 400 MHz): 2.04 (6H, s, CH3), 2.06 (6H, s, CH3), 2.08 (6H, s,
CH3), 2.10 (6H, s, CH3), 3.85e3.93 (2H, m, CH), 4.19 (2H, dd, J 12.2,
1.9 Hz, CH2), 4.31(2H, dd, J 12.2, 5.2 Hz, CH2), 5.13 (2H, d, J 7.3 Hz,
anomeric CH), 5.20 (2H, t, J 9.5 Hz, CH), 5.26e5.37 (4H, m, CH),
6.97e7.06 (4H, app d, J 9 Hz, Ph), 7.08e7.12 (2H, m, Th), 7.12e7.18
(4H, m, Th), 7.50e7.57 (4H, app d, J 9 Hz, Ph). dC (CDCl3, 100 MHz)
20.7 (3CH3), 20.8 (CH3), 61.9 (CH2), 68.3 (CH, glucose ring), 71.2 (CH,
glucose ring), 72.1 (CH, glucose ring), 72.7 (CH, glucose ring), 99.0
(anomeric CH), 117.4, 123.4, 124.1, 124.5, 126.8, 129.4, 136.0, 136.0,
142.4, 156.3 (C, Ph), 169.1 (C]O), 169.2 (C]O), 170.1 (C]O), 170.4
(C]O). nmax/cmꢂ1 (KBr): 1038, 1234 (s, CeOeC), 1368,1406,1738 (s,
C]O), 2951.
4.1.9. 6-(4-Iodophenoxy)hexan-1-ol 18. 4-Iodophenol (3.0 g, 13.64
mmol) and potassium hydroxide (1.68 g, 30.0 mmol) were dissolved
in 15 mL of DMSO. After stirring for 10 min 6-bromo-1-hexanol
(1.96 ml,15.0 mmol) was added dropwise. After 8 h, the reactionwas
quenched by adding an aqueous solution of 5% HCl. The product was
extracted with dichloromethane (3ꢁ50 mL). The organic phases
were washed thrice with a saturated solution of NaCl and after dried
over anhydrous Na2SO4. The solvent was evaporated at reduced
pressure. The crude product was purified by silica gel column
chromatography (dichloromethane/ethyl acetate 7:3 as eluent)
obtaining 6-(4-iodo-phenoxy)-hexan-1-ol 18 (3.202 g, 73%) as
a colourless oil.24 (Found: C, 45.04, H, 5.33. C12H17IO2 requires C,
45.02, H, 5.35); Rf (dichloromethane/ethyl acetate 7:3) 0.55; dH
(CDCl3, 400 MHz): 1.26 (1H, t, J 7.1 Hz, OH), 1.33e1.54 (4H, m, CH2),
1.60 (2H, quintet, J 7.1 Hz, CH2), 1.78(2H, quintet, J 6.5 Hz, CH2), 3.65
(2H, t, J 6.6 Hz, CH2), 3.91 (2H, t, J 6.5 Hz, CH2), 6.61e6.71 (2H, app d, J
9 Hz, Ph), 7.50e7.58 (2H, app d, J 9 Hz, Ph) ppm.
4.1.7. 5-(4-[2,3,4,6-Tetra-O-acetyl-b-D-glucopyranosyl]phenyl)-
[2,20]-bithiophene 5a. Na2CO3 (0.030 g, 0.28 mmol), Ag2O (0.065 g,
0.28 mmol) and Pd(PPh3)4 (0.09 g, 0.01 mmol) were added to
a solution of (2,3,4,6-tetra-O-acetyl-b-D-glucopyranosyl)-4-iodo-
benzene 10a (0.155 g, 0.28 mmol) and 5-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-2,20-bithiophene 8 (0.091 g, 0.31 mmol) in 5 mL
of anhydrous dioxane under a nitrogen atmosphere. The reaction
mixture was heated at 70 ꢀC overnight and then cooled to room
temperature, filtered through a thin pad of silica gel (eluting with
dichloromethane/ethyl acetate 1:1) and concentrated under re-
duced pressure. The crude material obtained was purified by pre-
parative chromatography on silica gel, using a mixture of petroleum
ether/ethyl acetate 6:4 as the eluent and then crystallized from
dichloromethane/hexane. A bright yellow solid was recovered
(0.140 g, 84% yield). (Found: C, 57.16, H, 4.77, S, 10.86. C28H28O10S2
requires C, 57.13, H, 4.79, S, 10.89); Rf (petroleum ether/ethyl acetate
6:4) 0.43; mp 197e198 ꢀC (dichloromethane/hexane). dH (CDCl3,
400 MHz): 2.04 (3H, s, CH3), 2.06 (3H, s, CH3), 2.08 (3H, s, CH3), 2.09
(3H, s, CH3), 3.84e3.91 (1H, m, CH), 4.17 (1H, dd, J 12.3, 2.4 Hz, CH2),
4.30 (1H, dd, J 12.3, 5.3 Hz, CH2), 5.10 (1H, d, J 7.6 Hz, anomeric CH),
5.19 (1H, app t, J 9.6 Hz, CH), 5.25e5.35 (2H, m, CH), 6.97e7.04 (3H,
m, PheTh), 7.11e7.15 (2H, m, Th), 7.18 (1H, dd, J 3.6, 1.1 Hz, Th), 7.21
(1H, dd, J 5.1, 1.1 Hz, Th), 7.49e7.55 (2H, app d, J 9 Hz, Ph). dC (CDCl3,
100 MHz) 20.8 (2CH3), 20.9 (2CH3), 62.1 (CH2), 68.4 (CH, glucose
ring), 71.3 (CH, glucose ring), 72.3 (CH, glucose ring), 72.9 (CH,
glucose ring), 99.2 (anomeric CH), 117.6, 123.6, 123.8, 124.6, 124.8,
127.1, 128.1, 129.7, 136.6, 137.5, 142.5, 156.5 (C, Ph), 169.5 (C]O),
4.1.10. (S)-4-Iodo-1-(6-(2-tert-butoxycarbonylamino-3-phenyl-
propanoyl)hexyloxy)benzene 10b. Triethylamine (1.70 mL, 12.18
mmol) and DMAP (0.343 g, 2.81 mmol) were added to a solution of
N-BOC-L-phenylalanine (3.23 g, 12.18 mmol) and 6-(4-iodophe-
noxy)-hexan-1-ol 18 (3.0 g, 9.37 mmol) in 30 mL of dichloro-
methane. The mixture was cooled to 0 ꢀC under stirring and
isopropenyl chlorocarbonate (IPCC) was added dropwise (1.33 mL,
12.2 mmol) over 30 min. After 1 h, dichloromethane (20 mL) was
added, and the organic phases were washed with a saturated
aqueous solution of NH4Cl (20 mL) and brine (20 mL). The organic
phases were dried over anhydrous Na2SO4 and the solvent evapo-
rated at reduced pressure. The residue was purified by silica gel
column chromatography (petroleum ether/ethyl acetate 8:2 as the
eluent) obtaining (S)-4-iodo-1-(6-(2-tert-butoxycarbonylamino-3-
phenylpropanoyl)hexyloxy)benzene 10b as a pale white solid
(4.48 g, 84% yield). (Found: C, 55.00, H, 6.06, N, 2.49. C26H34INO5

492
O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
requires C, 55.03, H, 6.04, N, 2.47); Rf (petroleum ether/ethyl acetate
8:2) 0.61; mp 45e46 ꢀC (methanol). dH (CDCl3, 400 MHz): 1.31e1.50
(13H, m, CH2eCH3), 1.57e1.68 (2H, m, CH2), 1.71e1.80 (2H, m, CH2),
3.01e3.12 (2H, m, CH2), 3.90 (2H, t, J 6.4 Hz, CH2), 4.04e4.16 (2H, m,
CH2), 4.52e4.61 (1H, br m, CH), 4.98 (1H, br d, J 8.8 Hz, NH),
6.64e6.69 (2H, app d, J 8 Hz, Ph), 7.10e7.15 (2H, app d, J 7 Hz, Ph),
7.20e7.31 (3H, m, Ph), 7.51e7.56 (2H, app d, J 8 Hz, Ph). dC (CDCl3,
100 MHz). 25.6 (2CH2), 28.3 (one CH3 plus one CH2), 28.9 (CH2),
38.4 (CH2), 54.4 (CH2), 65.2 (aliphatic carbon), 67.8 (aliphatic car-
bon), 79.8 (Cquat), 82.4 (CeI, Ph), 116.8 (Ph), 126.9 (Ph), 128.5 (Ph),
129.3 (Ph), 136 (Ph), 138.1 (Ph), 155.0 (Ph), 158.8 (C]O), 172.0 (C]
O). nmax/cmꢂ1 (KBr): 1057, 1168, 1248, 1281, 1487, 1529, 1690 (s, C]
O), 1732 (s, C]O), 2941, 3366 (NeH).
dd, J 5.0, 3.7 Hz, Th), 7.05e7.30 (22H, m, PheTh), 7.43e7.47 (2H, m,
Ph). dC (CDCl3, 100 MHz) 25.8 (CH2), 26.1 (CH2), 28.4 (CH3), 28.6
(CH2), 29.3 (CH2), 38.5 (CH2), 54.5 (CH2), 65.3 (aliphatic carbon), 69.5
(aliphatic carbon), 79.8 (CHquat), 112.0, 122.7, 123.4, 123.6, 123.8,
124.3, 125.9, 126.9, 127.8, 128.4, 129.2, 136.0, 136.4, 136.9, 137.1, 138.0,
149.1, 154.9 (C]O), 171.8 (C]O) ppm. nmax/cmꢂ1 (KBr): 791, 1165,
1261, 1458, 1491, 1521, 1692 (C]O), 1718 (C]O). 2852, 2923, 3368
(m, NeH).
4.1.13. (2S,20S)-5,50-Bis-(4-(6-(2-tert-butoxycarbonylamino-3-phe-
nylpropanoyl)hexyloxy)phenyl)-[2,20]-bithiophene
3b. Anhydrous
Na2CO3 (0.038 g, 0.36 mmol), Ag2O (0.083 g, 0.36) and Pd(PPh3)4
(0.013 g, 0.011 mmol) were added to a stirred solution of 2,20-
bithiophene-5,50-diboronic acid bis-(pinacol) ester 11 (0.067 g,
0.16 mmol) and (S)-4-iodo-1-(6-(2-tert-butoxycarbonylamino-3-
phenylpropanoyl)hexyloxy)benzene 10b (0.204 g, 0.36 mmol) in
5 mL of dry 1,4-dioxane kept under nitrogen atmosphere. The re-
action mixture was heated at 70 ꢀC overnight and then cooled to
room temperature and concentrated under reduced pressure. The
crude material obtained was purified by preparative chromatog-
raphy on silica gel, using a mixture of petroleum ether/dichloro-
methane/ethyl acetate (6:3:1) as eluent and then crystallized from
dichloromethane/hexane. A pale yellow solid was isolated (0.152 g,
91%). (Found: C, 68.92, H, 6.60, N, 2.69, S, 6.11. C60H72N2O10S2 re-
quires C, 68.94, H, 6.94, N, 2.68, S, 6.13); Rf (petroleum ether/
dichloromethane/ethyl acetate (6:3:1)) 0.65; mp 140e141 ꢀC
(dichloromethane/hexane). dH (CDCl3, 400 MHz): 1.29e1.51 (26H,
m, CH2, CH3), 1.52e1.65 (4H, m, CH2), 1.72e1.81 (4H, m, CH2),
2.99e3.12 (4H, m, CH2), 3.95 (4H, t, J 6.4 Hz, CH2), 4.04e4.14 (4H, m,
CH2), 4.50e4.59 (2H, m, CH), 4.96 (2H, br d, J 9 Hz, NH), 6.85e6.91
(4H, app d, J 9 Hz, Ph), 7.06e7.14 (8H, m, PheTh), 7.18e7.30 (6H, m,
Ph), 7.46e7.52 (4H, app d, J 9 Hz, Ph). dC (CDCl3, 100 MHz) 25.6
(CH2), 25.7 (CH2), 28.3 (CH3), 28.4 (CH2), 29.1 (CH2), 38.4 (CH2), 54.4
(CH2), 65.2 (aliphatic carbon), 67.8 (aliphatic carbon), 79.8 (Cquat),
94.3, 114.7, 122.5, 124.0, 126.6, 126.7, 126.8, 128.3, 129.2, 135.6, 135.9,
142.7, 158.5 (C]O), 171.8 (C]O). nmax/cmꢂ1 (KBr): 794, 1025, 1095,
1162, 1258 (S, CeOeC), 1465, 1499, 1517, 1686 (C]O), 1730 (C]O),
2925, 3365 (m, NeH).
4.1.11. (2S,20S)-1,4-Bis-([2,20]-bithiophen-5-yl)-2,5-bis-(6-(2-tert-bu-
toxycarbonylamino-3-phenylpropanoyl)hexyloxy)benzene
1b. Anhydrous Na2CO3 (0.066 g, 0.623 mmol), Ag2O (0.144 g,
0.621 mmol) and Pd(PPh3)4 (0.011 g, 0.009 mmol) were added to
a stirred solution of 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
2,20-bithiophene 8 (0.198 g, 0.678 mmol) and (2S,20S)-1,4-diiodo-2,
5-bis-(6-(2-tert-butoxycarbonylamino-3-phenylpropanoyl)hexyloxy)
benzene 7b (0.326 g, 0.308 mmol) in 5 mL of dry 1,4-dioxane kept
under nitrogen atmosphere. The reaction mixture was heated at
70 ꢀC overnight and then cooled to room temperature and concen-
trated under reduced pressure. The crude material obtained was
purified by preparative chromatography on silica gel, using a mixture
of petroleum ether/dichloromethane/ethyl acetate (8:2:2) as eluent
and then crystallized from dichloromethane/hexane. A yellow solid
was isolated (0.210 g, 60% yield). (Found: C, 65.63; H, 6.36; N, 2.51; S,
11.40. C62H72N2O10S4 requires C, 65.70; H, 6.40; N, 2.47; S, 11.32); Rf
(petroleum ether/dichloromethane/ethyl acetate (8:2:2)) 0.53; mp
121e123 ꢀC (dichloromethane/hexane); dH (CDCl3, 500 MHz):
1.34e1.48 (4H, m, CH2), 1.42 (18H, s, CH3), 1.61 (4H, quintet, J 7.8 Hz,
CH2), 1.63 (4H, quintet, J 7.8 Hz, CH2), 1.93 (4H, quintet J 7.8 Hz, CH2),
3.01e3.14 (4H, m, CH2), 4.07e4.17 (8H, m, CH2), 4.53e4.62 (2H, br m,
CH), 4.99 (2H, br d, J 8 Hz, NH), 7.04 (2H, dd, J 3.9, 5.1 Hz, Th), 7.13 (4H,
dl, J 7.0 Hz, Th), 7.18 (2H, d, J 3.9 Hz, Th), 7.19e7.31 (2H, m, Ph),
7.46 (2H, d, J 3.9 Hz, Ph) ppm. dC (CDCl3, 125 MHz) 25.7 (CH2), 26.0
(CH2), 28.3 (one CH3 plus one CH2), 29.3 (CH2), 38.4 (CH2), 54.4 (CH2),
65.3 (aliphatic carbon), 69.5 (aliphatic carbon), 79.8 (CHquat), 112.1,
122.7, 123.3, 123.5, 124.3, 125.8, 126.9, 127.9, 128.5, 129.3, 136.0,
137.3, 137.6, 138.0, 149.2, 155.0 (C]O), 172.0 (C]O) ppm. nmax/cmꢂ1
(KBr): 1054, 1166, 1214, 1522, 1691 (C]O), 1731 (C]O). 2931, 3365
(m, NeH).
4.1.14. (2S,20S)-5,500-Bis-(4-(6-(2-tert-butoxycarbonylamino-3-phenyl-
propanoyl)hexyloxy)phenyl)-[2,20:50200]-terthiophene 4b. Anhydrous
Na2CO3 (0.038 g, 0.36 mmol), Ag2O (0.083 g, 0.36) and Pd(PPh3)4
(0.013 g, 0.011 mmol) were added to a stirred solution of 5,500-bis
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-[2,20:50200]terthiophene
12 (0.080 g, 0.16 mmol) and (S)-4-iodo-1-(6-(2-tert-butoxy-
carbonylamino-3-phenylpropanoyl)hexyloxy)benzene 10b (0.204 g,
0.36 mmol) in 5 mL of dry 1,4-dioxane kept under nitrogen atmo-
sphere. The reaction mixture was heated at 70 ꢀC overnight and then
cooled to room temperature and concentrated under reduced pres-
sure. The crude material obtained was purified by preparative chro-
matography on silica gel, using a mixture of petroleum ether/
dichloromethane/ethyl acetate (6:3:1) as eluent and then crystallized
from dichloromethane/hexane. A pale yellow solid was isolated
(0.153 g, 85%). (Found: C, 68.16, H, 6.60, N, 2.50, S, 8.53. C64H74N2O10S3
requires C, 68.18, H, 6.62, N, 2.48, S, 8.53); Rf (petroleum ether/
dichloromethane/ethyl acetate (6:3:1)) 0.39; mp 178e179 ꢀC
(dichloromethane/hexane). dH (CDCl3, 400 MHz): 1.31e1.52 (26H, m,
CH2, CH3), 1.57e1.66 (4H, m, CH2), 1.74e1.83 (4H, m, CH2), 3.01e3.13
(4H, m, CH2), 3.96 (4H, t, J 6.4 Hz, CH2), 4.05e4.14 (4H, m, CH2),
4.53e4.62 (2H, m, CH), 4.96 (2H, br d, J 8.5 Hz, NH), 6.67e6.93 (4H, app
d, J 9 Hz, Ph), 7.05e7.07 (2H, m, Th), 7.09e7.11 (4H, m, Ph), 7.11e7.17
(4H, app d, J 7 Hz, Th), 7.20e7.31 (6H, m, Ph), 7.47e7.54 (4H, app d, J
9 Hz, Ph). dC (CDCl3, 100 MHz) 25.7 (2CH2), 28.3 (CH3), 28.4 (CH2), 29.1
(CH2), 38.5 (CH2), 54.5 (CH2), 65.3 (aliphatic carbon), 67.8 (aliphatic
carbon), 79.8 (Cquat),114.8,122.6,123.8,124.3,126.5,126.7,126.9,128.5,
129.2, 135.2, 135.9, 143.1, 154.9, 158.6 (C]O), 171.8 (C]O). nmax/cmꢂ1
4.1.12. (2S,20S)-1,4-Bis-([2,20:50200]terthiophen-5-yl)-2,5-bis-(6-(2-
tert-butoxycarbonylamino-3-phenylpropanoyl)hexyloxy)benzene
2b. Anhydrous Na2CO3 (0.042 g, 0.392 mmol), Ag2O (0.091 g,
0.392 mmol) and Pd(PPh3)4 (0.014 g, 0.0118 mmol) were added to
a stirred solution of 4,4,5,5-tetramethyl-2-[2,20:50200]terthiophen-5-
yl-[1,3,2]dioxaborolane 9 (0.161 g, 0.431 mmol) and (2S,20S)-1,4-
diiodo-2,5-bis-(6-(2-tert-butoxycarbonylamino-3-phenylpropanoyl)
hexyloxy)benzene 7b (0.207 g, 0.196 mmol) in 5 mL of dry 1,4-di-
oxane kept under nitrogen atmosphere. The reaction mixture was
heated at 70 ꢀC overnight and then cooled to room temperature and
concentrated under reduced pressure. The crude material obtained
was purified by preparative chromatography on silica gel, using
a mixture of petroleum ether/dichloromethane/ethyl acetate (8:1:2)
as eluent and then crystallized from dichloromethane/hexane. A
brown-yellow solid was isolated (0.153 g, 60% yield). (Found: C,
46.75, H, 5.93, N, 2.17, S, 15.87. C70H76N2O10S6 requires C, 64.78; H,
5.90; N, 2.16; S, 14.83); Rf (petroleum ether/dichloromethane/ethyl
acetate (7:1:2)) 0.35; mp 121e123 ꢀC (dichloromethane/hexane). dH
(CDCl3, 400 MHz): 1.38 (18H, s, CH3), 1.49e1.68 (12H, m, CH2), 1.92
(4H, quintet, J 7.4 Hz, CH2), 2.97e3.10 (4H, m, CH2), 4.05e4.15 (8H, m,
CH2), 4.48e4.59 (2H, m, CH), 4.90 (2H, br d, J 8.0 Hz, NH), 7.00 (2H,

O. Hassan Omar et al. / Tetrahedron 67 (2011) 486e494
493
(KBr): 791, 1055, 1176, 1250, 1464, 1496, 1694 (C]O), 1730 (C]O),
2930, 3380 (m, NeH).
3.11 mmol) and 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
2,20-bithiophene 8 (1.00 g, 3.42 mmol). Then 12.5 mL of ethanol,
previously degassed by flushing nitrogen for 30 min, the catalyst
Pd(PPh3)4 (0.107 g, 0.093 mmol), toluene (50 mL) and finally 20 mL
of a 2 M aqueous solution of Na2CO3 (40.4 mmol), previously
degassed for 30 min were added. The reaction mixture was heated
at 95 ꢀC with vigorous stirring until the aryl halide had been
completely consumed (GC). The reaction mixture was then cooled
to room temperature and concentrated under reduced pressure.
The base excess was neutralized with an aqueous solution of HCl
5%, and the mixture extracted with dichloromethane (3ꢁ30 mL).
The organic phase was collected, washed three times with satu-
rated aqueous NaCl (3ꢁ50 mL), dried over anhydrous Na2SO4, fil-
tered and concentrated under reduced pressure. The crude
product was purified by preparative column chromatography over
silica gel, using a mixture of petroleum ether/dichloromethane
95:5 as the eluent. A white solid was recovered (0.594 g, 60% yield).
(Found: C, 58.01, H, 3.25, S, 38.71. C12H8S3 requires C, 58.03, H 3.25,
S, 38.73); Rf (petroleum ether/dichloromethane 95:5) 0.5; mp
90e91 ꢀC (lit.25 93e95 ꢀC). dH (CDCl3, 400 MHz): 7.01 (2H, dd, J 4.8,
3.8 Hz), 7.07 (2H, m), 7.16 (2H, J 3.8 Hz), 7.20 (2H, d, J 4.8 Hz). dC
(CDCl3, 100 MHz) 123.7, 124.3, 124.4, 127.8, 136.2, 137.1. nmax/cmꢂ1
(KBr): 674, 680, 796, 832, 1055, 1421, 2923, 3063.
4.1.15. (S)-5-(4-(6-(2-tert-Butoxycarbonylamino-3-phenylpropanoyl)
hexyloxy)phenyl)-[2,20]-bithiophene 5b. Anhydrous Na2CO3 (0.056 g,
0.53 mmol), Ag2O (0.123 g, 0.53 mmol) and Pd(PPh3)4 (0.018 g,
0.016 mmol) were added to a stirred solution of 5-(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-2,20-bithiophene 8 (0.170 g, 0.58
mmol) and (S)-4-iodo-1-(6-(2-tert-butoxycarbonylamino-3-phenyl-
propanoyl)hexyloxy)benzene 10b (0.300 g, 0.53 mmol) in 8 mL of dry
1,4-dioxane kept under nitrogen atmosphere. The reaction mixture
was heated at 70 ꢀC overnight and then cooled to room temperature
and concentrated under reduced pressure. The crude material
obtained was purified by preparative chromatography on silica gel,
using a mixture of petroleum ether/ethyl acetate 8:2 as the eluent and
then crystallized from dichloromethane/hexane. A yellow solid was
isolated (0.237 g, 74% yield). (Found: C, 67.42, H, 6.46, N, 2.30, S, 10.57.
C34H39NO5S2 requires C, 67.41, H, 6.49, N, 2.31, S, 10.59); Rf (petroleum
ether/ethyl acetate 8:2) 0.43; mp 102e103 ꢀC (dichloromethane/
hexane). dH (CDCl3, 400 MHz): 1.33e1.53 (13H, m, CH2, CH3),1.57e1.67
(2H, m, CH2),1.75e1.83 (2H, m, CH2), 3.04e3.13 (2H, m, CH2), 3.98 (2H,
t, J 6.4 Hz, CH2), 4.08e4.16 (2H, m, CH2), 4.54e4.61 (1H, br m, CH), 4.98
(1H, br d, J 8 Hz, NH), 6.88e6.92 (2H, app d, J 9 Hz, Ph), 7.02 (1H, dd, J
5.1, 3.6 Hz, Th), 7.09e7.15 (4H, m, PheTh), 7.17 (1H, dd, J 3.6, 1.1 Hz, Th),
7.20 (1H, dd, J 5.1, 1.2 Hz, Th), 7.23e7.32 (3H, m, Ph), 7.34e7.49 (2H, app
d, J 9 Hz, Ph). dC (CDCl3, 125 MHz) 25.6 (CH2), 25.7 (CH2), 28.3 (CH3),
28.4 (CH2), 29.1 (CH2), 38.4 (CH2), 54.4 (CH2), 65.3 (CH2 or CH), 67.8
(aliphatic carbon), 79.8 (Cquat), 114.8, 122.5, 123.3, 124.1, 124.5, 126.7,
126.8, 126.9, 127.8, 128.5, 129.3, 135.6, 136.0, 137.6, 143.2, 155.0, 158.7
(C]O), 172.0 (C]O). nmax/cmꢂ1 (KBr): 699, 797, 1167, 1180, 1251 (s),
1279, 1499, 1516, 1692 (C]O), 1728 (s, C]O), 2934, 3399 (m, NH).
4.1.18. 5,500-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
[2,20:50200]terthiophene 12. An oven-dried Schlenk tube containing
a magnetic stirrer was evacuated and backfilled with nitrogen three
times. Then it was charged with [IrCl(COD)]2 (0.020 g, 0.0303mmol),
4,40di-tert-butyl-2,20-bipyridine (dtbpy) (0.016 g, 0.0606 mmol) and
pin2B2 (0.307 g, 1.21 mmol). Dry n-octane (20 mL) was added to the
mixture, that was stirred for few minutes at room temperature. Then,
[2,20:50200]terthiophene 13 (0.250 g, 1.01 mmol) was added and the
mixture was heated at 90 ꢀC for 12 h. The reaction was monitored by
TLC that showed the disappearance of 13. The reaction mixture was
then allowed to reach room temperature and concentrated under
reduced pressure. The crude material obtained was purified by pre-
parative chromatographyonsilica gelelutingwith dichloromethane/
methanol in volumetric ratio 9.5:0.5. A green solid was recovered
(0.422 g, 84% yield). (Found: C, 57.60, H, 6.05, S, 19.25. C24H30B2O4S3
requires C, 57.62, H, 6.04, S, 19.23); Rf (dichloromethane/methanol
9.5:0.5) 0.46; mp; 103e104 ꢀC (dichloromethane/hexane). dH (CDCl3,
500 MHz): 7.52 (2H, d, J 3.8 Hz), 7.23 (2H, J 3.8 Hz), 7.14 (2H, s), 1.35
(24H, 8CH3). dC (CDCl3, 125 MHz) 24.8 (8CH3), 84.2 (4Cquat), 123.7,
124.9, 125.0, 127.8, 136.5, 137.8. nmax/cmꢂ1 (KBr): 850, 1125, 1285,
1350, 1450, 1512, 2925, 2979.
4.1.16. (S)-5-(4-(6-(2-tert-Butoxycarbonylamino-3-phenylpropanoyl)
hexyloxy)phenyl)-[2,20:50200]-terthiophene 6b. Anhydrous Na2CO3
(0.032 g, 0.30 mmol), Ag2O (0.070 g, 0.32 mmol) and Pd(PPh3)4
(0.010 g, 0.008 mmol) were added to a stirred solution of 5-(4,4,
5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-2,20:50200-terthiophene 9
(0.124 g, 0.33 mmol) and (S)-4-iodo-1-(6-(2-tert-butoxycar-
bonylamino-3-phenylpropanoyl)hexyloxy)benzene 10b (0.170 g,
0.30 mmol) in 5 mL of dry 1,4-dioxane kept under nitrogen atmo-
sphere. The reaction mixture was heated at 70 ꢀC overnight and
then cooled to room temperature and concentrated under reduced
pressure. The crude material obtained was purified by preparative
chromatography on silica gel, using a mixture of petroleum ether/
dichloromethane/ethyl acetate (8:2:1) as eluent and then crystal-
lized from dichloromethane/hexane. A yellow solid was isolated
(0.163 g, 79%). (Found: C, 66.32, H, 6.00, N, 2.02, S, 14.01.
C38H41NO5S3 requires C, 66.34, H, 6.01, N, 2.04, S, 13.98); Rf (pe-
troleum ether/dichloromethane/ethyl acetate (8:2:1)) 0.45; mp
163e164 ꢀC (dichloromethane/hexane). dH (CDCl3, 400 MHz):
1.31e1.55 (13H, m, CH2, CH3), 1.57e1.71 (2H, m, CH2), 1.74e1.85 (2H,
m, CH2), 3.00e3.14 (2H, m, CH2), 3.98 (2H, t, J 6.3 Hz, CH2),
4.05e4.18 (2H, m, CH2), 4.54e4.63 (1H, br m, CH), 4.99 (1H, br d, J
7.7 Hz, NH), 6.87e6.96 (2H, app d, J 9 Hz, Ph), 7.03 (1H, dd, J 5.1,
3.6 Hz, Th), 7.09e7.19 (7H, m, PheTh), 7.21e7.33 (4H, m, PheTh),
7.48e7.55 (2H, app d, J 9 Hz, Ph). dC (CDCl3, 100 MHz) 25.6 (CH2),
25.7 (CH2), 28.3 (CH3), 28.4 (CH2), 29.1 (CH2), 38.4 (CH2), 54.4 (CH2),
65.3 (aliphatic carbon), 67.8 (aliphatic carbon), 79.9 (Cquat), 114.9,
122.6, 123.6, 123.9, 124.3, 124.4, 124.5, 126.7, 1 26.9, 127.0, 127.9,
128.5, 129.3, 135.2, 135.8, 136.0, 136.4, 137.1, 143.3, 155.0, 158.8 (C]
O), 172.0 (C]O). nmax/cmꢂ1 (KBr): 790, 1169, 1251, 1496, 1691 (C]
O), 1731 (C]O), 2934, 3350 (m, NeH).
Acknowledgements
This work was financially supported by Ministero dell’Is-
ꢀ
truzione, dell’Universita e della Ricerca (MIUR), ‘Progetto PRIN
ꢀ
2007 PBWN44’ and by Universita degli Studi di Bari.
Supplementary data
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.11.004.
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