Thiophene-substituted aza-bodipy as a strategic synthon for the design of near-infrared dyes

Article abstract of DOI:10.1039/c2nj20943h

Original aza-bodipy dyes functionalised by thiophene moieties in 3,5 or 1,7 positions were prepared and characterised by X-ray crystallography. The 3,5 substituted compound 3 exhibits promising photophysical properties red-shifted in the NIR spectral rang

Full text of DOI:10.1039/c2nj20943h

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PAPER
Thiophene-substituted aza-bodipy as a strategic synthon for the design of
near-infrared dyesw
Quentin Bellier,a Fabrice Dalier,a Erwann Jeanneau,b Olivier Maury*a and
Chantal Andraud*a
Received (in Montpellier, France) 7th November 2011, Accepted 13th December 2011
DOI: 10.1039/c2nj20943h
Original aza-bodipy dyes functionalised by thiophene moieties in 3,5 or 1,7 positions were prepared
and characterised by X-ray crystallography. The 3,5 substituted compound 3 exhibits promising
photophysical properties red-shifted in the NIR spectral range. Furthermore, the presence of
bromide atoms has allowed p-conjugated skeleton extension via Sonogashira cross-coupling.
Introduction
The research for chromophores absorbing and/or emitting in
the near-infrared (NIR) spectral range is of growing interest
for various applications ranging from materials science to
biology and medicine.1 Among the various NIR chromophore
families, boron-dipyrromethene and its sub-class aza-boron-
dipyrromethene experienced a tremendous development due
to their exceptional photophysical properties, high photo-
stability and very versatile structure.2 In few years, these
monomethine cyanine analogues were designed for NIR
applications like photovoltaics,3a organic light emitting
diodes, advanced optoelectronics,3b nonlinear optics,3c–e bio-
imaging or sensing3f–g and photodynamic therapy. . .3h–j
The ubiquitous utilisation of these dyes prompted chemists
to find new strategies for shifting their photophysical properties
farther and farther in the red conserving the luminescence
quantum yield efficiency. As example, absorption and emission
red-shift can be achieved by: (i) the replacement of the C-meso
atom by an N atom;4 (ii) the extension of the conjugated
skeleton and/or substitution of the central bodipy core by
Chart 1 Benchmark aza-bodipy (1, 5) and thiophene containing aza-
bodipy dyes (2, 3, 4, 6).
electron-donating moieties resulting in the induction of a
charge transfer contribution in the lowest energy transition;5
(iii) annulation of benzo ring to the pyrrole;6 (iv) rigidification
of the chromophore p-skeleton either by annulation7a,b or by
Table 1 Spectroscopic data in diluted solution
formation of intramolecular B–O six member rings.7c These
Dye
labs/nm
l
em/nm e/L molꢀ1 cmꢀ1
o
1/2/cmꢀ1 t/ns Fa
various strategies have allowed the design of chromophores
absorbing and emitting in the NIR as illustrated by the aza-
bodipy dyes 1 and 5 (Chart 1 and Table 1).3c,5c Thanks to an
1b
3b
4b
5c
6c
658
735
694
740
760
687
751
729
804
818
90 000
111 000
82 000
60 000
57 000
1270
770
1690
2850
3110
1.4
3.1
0.8
0.7
0.7
0.15
0.19
0.04
0.04
0.02
a
´
Laboratoire de Chimie CNRS—Ecole Normale Superieure de
Lyon- Universite de Lyon 1, 46 allee d’Italie, Lyon 69007, France.
a
Aza-bodipy substituted by methoxyphenyl in positions 3/5 as refer-
c
´
´
ence3h,14 (CHCl3, F = 0.36). In dichloromethane solution. In
toluene solution.
b
E-mail: chantal.andraud@ens-lyon.fr, olivier.maury@ens-lyon.fr
b
´
Centre de Diffractometrie Henri Longchambon, ICL, Universite
Claude Bernard Lyon1, 69622 Villeurbanne Cedex, France
´
w Electronic supplementary information (ESI) available: Crystallo-
graphic data. CCDC reference number 836074 (3). For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c2nj20943h
important internal charge transfer, chromophore 5 presents
red-shifted linear properties combined with remarkable non-
linear optical properties, e.g. an optical limiter behaviour at
c
768 New J. Chem., 2012, 36, 768–773
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telecommunication wavelengths.3c In addition, it has been
demonstrated that an additional red-shift can be achieved by
substitution of the (aza)-bodipy core by thiophenyl moieties as
illustrated by the recent reports of Goeb and Ziessel8 and
Gresser et al.9 for fused-bodipy or fused-azabodipy (2) reaching
780 nm (f = 0.20) and 840 nm (f not reported) in emission,
respectively. Using a similar approach, we report here the
synthesis, characterisation, X-ray structure and photophysical
properties of original aza-bodipy dyes substituted by thiophene
units either in the 3,5 (3) or 1,7 (4) positions (Chart 1). It is
worth noting that during the redaction of this article, Hartmann
and co-workers published the synthesis, the electrochemical and
photophysical properties of similar thiophene-substituted aza-
bodipy dyes.10 Furthermore, the presence of additional bromide
atoms allows the extension of the p-skeleton using Pd-catalyzed
cross-coupling reaction and induction of additional charge-
transfer character into the dye. As a preliminary example, we
describe the synthesis of chromophore 6 (Chart 1) that merges
the two aforementioned strategies to red-shift the photophysical
properties: substitutions by thiophene in 1,7 positions and by
dialkylaminophenylethynyl moieties in 3,5 positions.
Scheme 2 Synthesis of the target compound 6. (i) 4-Ethynyl-N,N-
i
dihexylaniline, Pd(PPh3)4, Et3N, THF, reflux; (ii) BF3ꢁEt2O, Pr2EtN,
dry CH2Cl2, RT.
On the other hand, 9a could not be isolated and was directly
engaged in the borylation step allowing the isolation of the
desired product 3 in only 2% yield over the two steps after
column chromatography.
The synthesis of chromophore 6, featuring an extended
p-conjugated skeleton, involves a copper-free Sonogashira
cross-coupling using Pd(PPh3)4 as catalyst between 9b and a
4-ethynyl-N,N-dihexylaniline donor, followed by classical
complexation with BF3ꢁEt2O (Scheme 2). It is worth noting
that, contrarily to C-bodipy analogues,11 Pd-catalyzed cross-
coupling reaction results in the loss of a BF2 fragment5c,12 and
therefore aza-dipyrromethene intermediates are used as starting
materials.
Results and discussion
The synthesis of the target compounds 3, 4 (Scheme 1) used
the classical O’Shea’s procedure3h involving the formation of
chalcone 7a,b followed by the addition of nitromethane leading
to the formation of 8a,b in good yield (52 and 72%, respec-
tively). The formation of aza-dipyrromethene 9a,b remains
very problematic and is accompanied by many unidentified
side-products. Only 9b could be isolated after precipitation in
acceptable 21% yield, leading to the formation of 4 (42% yield)
All compounds and intermediates were fully characterized
by NMR spectroscopy and high resolution mass spectrometry
(see ESIw for experimental details). Crystals suitable for X-ray
diffraction analysis were obtained for 3 by diffusion of diethyl-
ether into a dichloromethane solution (Fig. 1 and ESIw). The
asymmetric unit is composed of two independent molecules
(Z0 = 2) which form a three-dimensional framework through
p–p, C–Hꢁ ꢁ ꢁp, C–Brꢁ ꢁ ꢁp and C–Hꢁ ꢁ ꢁF interactions. These two
independent molecules display similar structural parameters
and for clarity only one will be described.
upon reaction with BF ꢁEt O in the presence of Hunig’s base.
¨
3
2
At the molecular level, the structure is similar to other
already described aza-boron-dipyrromethene dyes: the two
central pyrrolic rings fused by a BF2 fragment are completely
planar and the aryl peripheral substituents are slightly twisted.
For 3, the average twist angle of the thienyl substituent in the
3,5 positions j3,5(Th) is about 101. It is worth noting that this
latter value is significantly lower compared to the twist angle
Scheme 1 Synthesis of the target compounds 3 and 4. (i) CH3NO2,
HNEt2 MeOH, reflux; (ii) NH4OAc, dry BuOH, reflux; (iii) BF3ꢁEt2O,
iPr2EtN, dry CH2Cl2, RT.
Fig. 1 X-Ray structure of 3 showing H–F distances.
c
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Fig. 2 JMOD 13C NMR (125.75 MHz, CDCl3) of 3.
of tetraphenyl substituted aza-bodipy dyes reported in the
literature where j3,5(Ph) is generally between 30–401.3h,5c This
flattening of the structure is attributable to the less sterically
demanding five members thienyl ring compared to the six
members phenyl one. The bond lengths are very classical for
this type of structures and the already observed intramolecular
interaction between the two fluorine atoms of the BF2 moiety
and the ortho-protons of the thienyl ring is also present in 3
with distances about 2.4 A slightly shorter but in the same
range than that observed with phenyl (2.5–2.7 A).5c
Fig. 3 Absorption (up) and emission (bottom) spectra of 1 (—),
3 (- -), 4 (– –), 5 (ꢁ ꢁ ꢁ) and 6 (- -) in dichloromethane (black) and
toluene (gray) solution.
Interestingly, this C–Hꢁ ꢁ ꢁF interaction is also observed for 3
by 13C{1H}JMOD NMR where the signal assigned to the
ortho-carbon atom of the thiophene (d: 133.5 ppm) appears as
a well resolved triplet (Fig. 2) due to the through space
a very different behaviour: it conserves a significant fluores-
cence quantum yield of 0.2 and a long lifetime of 3.1 ns
possibly because of the reduced non-radiative losses due
to rigidification of the p-skeleton induced by the C–Hꢁ ꢁ ꢁF
interactions.5c More surprisingly, this compound exhibits an
almost pure ‘‘extended cyanine’’ character15 with a very sharp
absorption transition (o1/2(3) = 770 cmꢀ1) and a rather
small Stokes shift (289 cmꢀ1). These photophysical results
are in agreement with the recent ones reported for a related
compound featuring no bromine substitution.10 In our case,
the presence of bromine results in an almost twice lower
quantum yield efficiency, a phenomenon that could be
ascribed to the heavy atom effect favouring nonradiative
deexcitation pathways. Finally, the functionalisation by an
extended p-conjugated donor group in positions 3,5 provokes
a pronounced red-shift in absorption of 80 and 65 nm for
molecules 5 and 6, respectively, compared to the unsubstituted
compounds 1 and 4. This shift is accompanied by an important
broadening of the lower energy absorption band (o1/2(5) =
2850 cmꢀ1 and o1/2(6) = 3110 cmꢀ1) due to the induction of an
additional strong charge transfer character from the dialkyl-
amino-donor to the accepting aza-bodipy core.16 It is worth
noting that the contribution of a thiophene group in positions
3,5 to the optical properties is conserved for chromophore 6,
which presents a more pronounced red-shift of 20 nm compared
to 5. Whereas no emission is detected in dichloromethane
solution, compounds 5 and 6 show in a less polar solvent, such
as toluene, a weak emission strongly shifted into the NIR
spectral range, with wavelength maxima at 804 and 818 nm,
respectively (Fig. 3).
coupling with the two fluorine atoms with a coupling constant
TS
J
= 7.3 Hz.13 This coupling constant is intermediate
between that observed for 3,5 phenyl substituted aza-bodipy
C–F
TS
described in this article like 4 (J
C–F
TS
= 4.0 Hz) or 6 (J
C–F
=
TS
4.5 Hz) or in the literature (average J
about 4 Hz)5c
C–F
featuring a j3,5(Ph) value of about 30–401 and that of the
rigidified dimethylene annulated bodipy reported by Burgess
TS
C–F
TS
the J
C–F
J
= 12 Hz.13a Therefore, in this class of chromophores,
coupling constant seems to be strongly correlated to
the twist angle between the 3,5 substituted aryl group and the
central bodipy core, both allowing the estimation of the
planarity of the conjugated skeleton.
The spectroscopic properties, measured in diluted solution,
are reported in Fig. 3 and Table 1 and are discussed versus
the benchmark dyes 1 and 5.3c,5c Substitution by thiophene in
the 3,5 or in 1,7 positions (3 and 4) involves a significant
bathochromic shift compared to 1, both in absorption (735
and 694 nm, respectively) and in emission (751 and 729 nm,
respectively). The thiophene is an electron rich heterocycle and
consequently acts as a donor group inducing a charge transfer
contribution in the lower energy transition. As a result, the
absorption band of 4 is relatively broad for an aza-bodipy dye
(o1/2(4) = 1690 cmꢀ1 compared to o1/2(1) = 1270 cmꢀ1) and
the Stokes shift is larger (about 690 cmꢀ1). However, 4
presents very low quantum yield (0.04) and lifetime (0.8 ns)
compared to 1 and is not competitive for any fluorescence
based applications. On the other hand, compound 3 presents
c
770 New J. Chem., 2012, 36, 768–773
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yellow solid (3.18 g, 90%). 1H-NMR (200.13 MHz, CDCl3): d
7.85 (d, Jtrans = 16 Hz, 1H), 7.66-7.59 (m, 3H), 7.44-7.41
Conclusion
3
(m, 3H), 7.31 (d, Jtrans = 16 Hz, 1H), 7.16 (d, 1H, 3J =
3
The synthesis, X-ray structure and photophysical characteri-
zation of original thiophene-functionalised aza-bodipy dyes
are reported. Compound 4, substituted in the 1,7 position,
exhibits very poor spectroscopic properties. On the other
hand, derivative 3, substituted in the 3,5 position, presents
red-shifted absorption and emission properties with an accep-
table quantum yield efficiency. This thiophene substitution
combines an increased electron-donating effect, a less steric
hindrance with stronger C–Hꢁ ꢁ ꢁF interactions, compared to
the phenyl one which explains its interesting spectroscopic
properties. Finally the incorporation of electron-donating
moieties as aniline in 3,5 positions thanks to the bromine
functionalisation was accomplished successfully. The resulting
4.0 Hz). 13C-NMR (50.33 MHz, CDCl3): d 181.0, 147.2, 144.8,
134.6, 131.9, 131.5, 130.9, 129.1, 128.7, 123.0, 120.6.
HRMS (ES+) calcd. for [M + Na]+: 314.9455. Found:
314.9456.
Anal. calcd. for C13H9BrOSꢁ(H2O)0.5: C, 51.67; H, 3.34%.
Found: C, 51.48; H, 3.01%.
7b. Thiophene-2-carboxaldehyde (3.36 g, 2.8 mL, 30 mmol,
1.2 eq.) and 4-bromoacetophenone (5.0 g, 25.1 mmol, 1 eq.)
were dissolved in methanol (150 mL). An aqueous potassium
hydroxide solution (100 mL, 2.5 M) was added dropwise at
0 1C. Then the solution was stirred at room temperature
overnight. During the course of the reaction, the product
precipitated from the reaction mixture. After cooling down
to 0 1C, the reaction mixture was filtrated off and the resulting
solid was washed with pentane. The crude product was
recrystallized in ethanol to yield product 7b as a yellow solid
(6.20 g, 85%). 1H-NMR (200.13 MHz, CDCl3): d 7.95
compound
6 presents absorption and emission largely
shifted into the near infra-red spectral range. Furthermore,
the presence of thiophene in positions 1,7 as a secondary
donor opens interesting perspective for the optimization of
non-linear optical properties like two-photon absorption at
telecommunication wavelengths.3c
3
(d, Jtrans = 15 Hz, 1H), 7.87 (d, 3J = 8.5 Hz, 2H), 7.64
3
3
3
(d, J = 8.5 Hz, 2H), 7.44 (d, J = 5 Hz, 1H), 7.37 (d, J =
3.5 Hz, 1H), 7.27 (d, 3Jtrans = 15 Hz, 1H), 7.10 (dd, 3J = 5 Hz
and 3J = 3.5 Hz, 1H). 13C-NMR (50.33 MHz, CDCl3): d
188.8, 140.3, 137.9, 137.0, 132.5, 132.1, 130.1, 129.3, 128.6,
128.0, 120.3. HRMS (ES+) calcd. for [M + H]+: 292.9636.
Found: 292.9625. Anal. calcd. for C13H9BrOS: C, 53.26; H,
3.09%. Found: C, 52.81; H, 3.08%.
Experimental
Methods
NMR spectra (1H, 13C) were recorded at room temperature on
a BRUKER AC 200 operating at 200.13 MHz and 50.33 MHz
1
for H and 13C, respectively, and on a VARIAN Unity Plus
8a. 7a (2.96 g, 10.1 mmol, 1 eq.), nitromethane (3.08 g, 2.8 mL,
50 mmol, 5 eq.) and diethylamine (3.69 g, 5.2 mL, 50 mmol,
5 eq.) were dissolved in methanol (60 mL) and heated under
reflux overnight. After cooling down to 0 1C, the solution was
quenched with an aqueous solution of hydrochloric acid (75 mL,
2.5 M) until pH = 2/3. During the course of the quenching, the
product precipitated. The reaction mixture was filtrated off and
the resulting solid was washed with pentane. The crude product
was recrystallized in methanol to yield product 8a as a white solid
(2.04 g, 58%). 1H-NMR (200.13 MHz, CDCl3): d 7.42 (d, 3J =
operating at 500.10 MHZ and 125.75 MHz for H and 13C,
1
respectively. Data are listed in parts per million (ppm) and
are reported relative to tetramethylsilane (1H, 13C), residual
solvent peaks being used as internal standard (CHCl3 1H:
7.26 ppm, 13C: 77.16 ppm). UV-visible spectra were recorded
on a Jasco V-550 spectrophotometer in diluted dichloro-
methane solution (ca. 10ꢀ6 mol Lꢀ1). The luminescence spectra
were measured using
a
Horiba-JobinYvon Fluorolog-3s
spectrofluorimeter, equipped with a three slit double grating
excitation and emission monochromator with dispersions of
2.1 nm mmꢀ1 (1200 grooves mmꢀ1). The steady-state lumines-
cence was excited by unpolarized light from a 450 W xenon CW
lamp and detected at an angle of 901 for diluted solution
measurements by a Peltier-cooled red-sensitive Hamamatsu
R2658P photomultiplier tube (300–1010 nm). High resolution
mass spectrometry measurements and elemental analysis
were performed at the Service Central d’Analayse du CNRS
(Vernaison, France). Column chromatography was performed
on a Merck Gerduran 60 (40–63 mm) silica.
3
4 Hz, 1H), 7.35-7.29 (m, 5H), 7.09 (d, J = 4 Hz, 1H), 4.80
3
(dd, Jgem = 12.5 Hz and J = 7 Hz, 1H), 4.70 (dd, Jgem
=
12.5 Hz and J = 7 Hz, 1H), 4.16 (q, J = 7 Hz, 1H), 3.30
3
3
3
(d, J = 7 Hz, 2H).
13C-NMR (50.33 MHz, CDCl3): d 188.8, 145.1, 138.7,
132.5, 131.5, 129.3, 128.2, 127.5, 123.7, 79.5, 41.6, 39.6.
HRMS (ES+) calcd. for [M + Na]+: 375.9619. Found:
375.9632. Anal. calcd. for C14H12BrNO3S: C, 47.47; H, 3.41;
N, 3.95%. Found: C, 46.99; H, 3.39; N, 3.83%.
8b. 7b (6 g, 20.5 mmol, 1 eq.), nitromethane (6.25 g, 5.6 mL,
0.102 mol, 5 eq.) and diethylamine (7.48 g, 10.5 mL, 0.102 mol,
5 eq.) were dissolved in methanol (120 mL) and heated under
reflux overnight. After cooling down to 0 1C, the solution
was quenched with an aqueous solution of hydrochloric acid
(200 mL, 2.5 M) until pH = 2/3. Methanol was evaporated
and then by dissolving the crude product with dichloro-
methane, the solution was washed with water and brine.
The organic layer was dried over sodium sulfate and the
solvents were evaporated. The crude residue was purified by
flash chromatography on silica gel (1 : 5 ether : petroleum
ether) to afford a yellow oil 8b (5.23 g, 72%). 1H-NMR
Syntheses
7a. 2-Acetyl-5-bromothiophene (2.50 g, 12.2 mmol, 1 eq.) and
benzaldehyde (1.54 g, 14.6 mmol, 1.5 mL, 1.2 eq.) were
dissolved in methanol (150 mL). An aqueous potassium
hydroxide solution (100 mL, 2.5 M) was added dropwise at
0 1C. Then the solution was stirred at room temperature
overnight. During the course of the reaction, the product
precipitated from the reaction mixture. After cooling down
to 0 1C, the reaction mixture was filtered off and the resulting
solid was washed with pentane to yield product 7a as a light
c
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New J. Chem., 2012, 36, 768–773 771

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(500.10 MHz, CDCl3): d 7.92 (d, 3J = 4 Hz, 2H), 7.86
(d, J = 8 Hz, 4H), 7.61-7.58 (m, 6H), 7.20 (t, J = 4 Hz,
2H), 6.87 (s, 2H). 13C NMR (125.75 MHz, CDCl3): d 158.4,
145.3, 138.8, 134.7, 132.1, 131.0 (t, JTCS–F = 4 Hz), 130.9, 130.4,
128.6, 126.0, 116.6. HRMS (APCI) calcd. for [M]+: 664.9209.
Found: 664.9220.
(200.13 MHz, CDCl3): d 7.80 (d, 3J = 8.5 Hz, 2H), 7.61
(d, 3J = 8.5 Hz, 2H), 7.21 (dd, 3J = 4 Hz, 4J = 1.5 Hz, 1H),
3
3
3
6.96-6.92 (m, 2H), 4.82 (dd, Jgem = 12.5 Hz and J = 7 Hz,
1H), 4.72 (dd, Jgem = 12.5 Hz and 3J = 7 Hz, 1H), 4.53
(q, 3J = 7 Hz, 1H), 3.47 (d, 3J = 7 Hz, 2H). 13C-NMR
(50.33 MHz, CDCl3): d 195.4, 141.7, 134.8, 131.9, 129.4, 128.7,
127.1, 125.6, 124.7, 79.7, 42.1, 34.5. HRMS (ES+) calcd. for
[M + Na]+: 375.9619. Found: 375.9612. Anal. calcd. for
C14H12BrNO3S: C, 47.47; H, 3.41; N, 3.95%. Found: C,
47.57; H, 3.34; N, 4.01%.
10b. Aza-dipyrromethene 9b (100 mg, 0.16 mmol, 1 eq.)
and 4-ethynyl-N,N-dihexylaniline (138 mg, 0.48 mmol, 3 eq.)
were dissolved in a THF/triethylamine mixture (V/V =
2.5/2.5 mL). The solution was degassed three times by a
freeze–pump method. Then Pd(PPh3)4 (20 mg, 0.016 mmol,
0.1 eq.) was added. The dark blue solution was stirred over-
night at reflux under argon. After cooling down to room
temperature, the reaction mixture was diluted in dichloro-
methane, washed with saturated aqueous ammonium chloride
solution, brine and water, then dried over sodium sulfate and
concentrated under vacuum. The crude residue was purified
twice by flash chromatography on silica gel (1 : 4 dichloro-
methane : pentane and 1 : 8 diethyl ether : petroleum ether) to
afford 10b as a blue solid (23 mg, 14%). 1H-NMR (200.13 MHz,
CDCl3): d 7.84-7.80 (m, 6H), 7.59 (d, 3J = 8 Hz, 4H), 7.43-7.39
9b. In a Schlenk vessel, ammonium acetate was sublimated
under vacuum (7.6 g, 98 mmol, 35 eq.), 8b (1 g, 2.82 mmol,
1 eq.) and anhydrous butanol (20 mL) were added under
argon. The solution was heated under reflux for 24 h. The
reaction mixture was cooled down to room temperature. The
solvent was concentrated to half and filtered. The isolated
solid was washed with pentane to yield product 9b as a
1
blue solid (0.196 g, 21%). H-NMR (200.13 MHz, CD2Cl2):
3
3
d 7.85 (d, J = 3 Hz, 2H), 7.78 (d, J = 8.5 Hz, 4H), 7.66
(d, 3J = 8.5 Hz, 4H), 7.48 (d, 3J = 5 Hz, 2H), 7.18 (dd, 3J =
5 Hz and 3J = 3 Hz, 2H), 7.09 (s, 2H). 13C NMR
(125.75 MHz, CD2Cl2): d 155.3, 150.1, 138.0, 136.4, 133.2,
131.6, 128.9, 128.74, 128.66, 128.6, 125.4, 114.0. HRMS
(ES+) calcd. for [M + H]+: 619.9465. Found: 619.9458.
3. In a Schlenk vessel, ammonium acetate was sublimated
under vacuum (7.6 g, 98 mmol, 35 eq.), 8a (1 g, 2.82 mmol,
1 eq.) and anhydrous butanol (20 mL) were added under
argon. The solution was heated under reflux for 24 h. The
reaction mixture was cooled down to room temperature. The
solvent was concentrated to half and filtered. The isolated
solid was washed with pentane to yield the not purified
intermediate as a blue solid. The crude (124 mg, 0.20 mmol,
1 eq.) was dissolved in distilled dichloromethane (15 mL) and
distilled diisopropylethylamine (259 mg, 0.33 mL, 2.0 mmol,
10 eq.) was added dropwise. The solution was stirred at room
temperature for 1 h and then BF3ꢁEt2O (426 mg, 0.38 mL,
3.0 mmol, 15 eq.) was added. The solution was stirred at room
temperature for 48 h under argon and the solution was
washed with brine and water. The organic layer was dried
over sodium sulfate and the solvent was evaporated. The crude
product was purified by chromatography on silica gel (1 : 4
dichloromethane : petroleum ether) to afford a brown solid 3
(20 mg, 2% over the two steps). 1H-NMR (500.10 MHz,
CDCl3): d 8.04-8.01 (m, 6H), 7.47-7.42 (m, 6H), 7.22
3
3
(m, 6H), 7.13 (t, J = 4.5 Hz, 2H), 7.05 (s, 2H), 6.60 (d, J =
8.5 Hz, 4H), 3.29 (t, 3J = 7 Hz, 8H), 1.67-1.51 (m, 8H), 1.40-1.30
(m, 24H), 0.93-0.86 (m, 12H). 13C-NMR (50.33 MHz, CDCl3): d
154.6, 149.7, 148.3, 137.0, 136.2, 133.3, 131.9, 130.5, 128.0,
127.9, 127.3, 126.5, 126.4, 113.4, 111.4, 108.6, 94.5, 87.8, 51.1,
31.9, 27.4, 27.0, 22.8, 14.2. HRMS (ES+) calcd. for [M + H]+:
1028.5699. Found: 1028.5720.
6. 10b (23 mg, 0.022 mmol, 1 eq.) was dissolved in distilled
dichloromethane (5 mL) and distilled diisopropylethylamine
(28 mg, 36 mL, 0.22 mmol, 10 eq.) was added dropwise.
The solution was stirred at room temperature for 1 h and
then BF3ꢁEt2O (48 mg, 42 mL, 0.34 mmol, 15 eq.) was added.
The solution was stirred at room temperature for one night
under argon and the solution was washed with brine and
water. The organic layer was dried over sodium sulfate and the
solvent was evaporated. The crude product was purified by
chromatography on silica gel (1 : 3 dichloromethane : petro-
1
leum ether) to afford a blue solid 6 (18 mg, 75%). H-NMR
(200.13 MHz, CDCl3): d 8.04 (d, 3J = 8.5 Hz, 4H), 7.93
(d, 3J = 3.5 Hz, 2H), 7.59-7.55 (m, 6H), 7.39 (d, 3J = 8.5 Hz,
3
4H), 7.20 (t, J = 4.5 Hz, 2H), 6.97 (s, 2H), 6.59 (d, 3J =
8.5 Hz, 4H), 3.29 (t, 3J = 7.5 Hz, 8H), 1.70-1.49 (m, 8H),
1.40-1.24 (m, 24H), 0.96-0.85 (m, 12H). 13C-NMR (125.75 MHz,
(d, 3J = 4 Hz, 2H), 7.08 (s, 2H). 13C NMR (125.75 MHz,
CDCl3): d 158.3, 148.4, 145.4, 137.9, 134.9, 133.3, 131.4, 130.2,
TS
TS
130.0, 129.71, 129.67 (t, J
C–F
CDCl3): d 148.6, 145.9, 143.2, 135.6, 133.5 (t, J
= 7.5 Hz),
= 4.5 Hz), 128.4, 127.4, 117.0,
C–F
132.9, 132.1, 129.8, 129.4, 128.8, 120.5, 118.4. HRMS (APCI)
calcd. for [M]+: 664.9209. Found: 664.9218.
111.3, 108.5, 95.1, 88.0, 51.1, 31.9, 27.3, 27.0, 22.8, 14.2. HRMS
(ES+) calcd. for [M]+: 664.9209. Found: 664.9220.
4. 9b (50 mg, 0.075 mmol, 1 eq.) was dissolved in distilled
dichloromethane (5 mL) and distilled diisopropylethylamine
(97 mg, 0.12 mL, 0.75 mmol, 10 eq.) was added dropwise.
The solution was stirred at room temperature for 1 h and then
BF3ꢁEt2O (160 mg, 0.14 mL, 1.13 mmol, 15 eq.) was added.
The solution was stirred at room temperature for 48 h under
argon and the solution was washed with brine and water.
The organic layer was dried over sodium sulfate and the
solvent was evaporated. The crude product was purified by
chromatography on silica gel (1 : 4 dichloromethane : petro-
Crystallography
X-Ray crystallographic data were collected on a Gemini
kappa-geometry diffractometer (Agilent Technologies UK
Ltd.) equipped with an Atlas CCD detector and using Cu
radiation (l = 1.5418 A). Intensities were collected at 100 K
by means of CrysalisPro software.17 Reflection indexing, unit-
cell parameters refinement, Lorentz-polarization correction,
peak integration and background determination were carried
out with the CrysalisPro software. An analytical absorption
1
leum ether) to afford a blue solid 4 (28 mg, 42%). H-NMR
c
772 New J. Chem., 2012, 36, 768–773
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2012

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correction was applied using the modeled faces of the crystal.18
The structure was solved by direct methods with SIR9719 and
the least-square refinement on F2 was achieved with the
CRYSTALS software.20 All non-hydrogen atoms were refined
anisotropically. The hydrogen atoms were all located in a
difference map and initially refined with soft restraints on the
bond lengths and angles to regularize their geometry (C–H in
the range 0.93–0.98 A) and Uiso(H) (in the range 1.2–1.5 times
Ueq of the parent atom), after which the positions were refined
with riding constraints. Crystal data of 3: C28H16BBr2F2N3S2,
M = 667.19 g molꢀ1, crystal size: 0.08 ꢂ 0.17 ꢂ 0.36 mm,
monoclinic P21/c (No. 14), a = 14.606(1) A, b = 14.212(1) A,
c = 25.060(2) A, b = 106.091(7)1, V = 4998.2(7) A3, Z = 8,
Dc = 1.773 g cmꢀ3, F000 = 2640, l(CuKa) = 1.5418 A, m =
6.02 mmꢀ1, T = 110(1) K, 54 285 refl. collected, 8863 unique
(Rint = 0.073), 8407 gt. with I 4 2s(I), R1 = 0.040, wR2 =
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Acknowledgements
We thank F. Albrieux, C. Duchamp, and N. Henriques from
the Universite de Lyon for assistance and access to the mass
spectrometry facility. The authors thank the Direction Generale
´
´
´
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