Elaborating boron dipyrromethene dyes with conjugated polyaromatic frameworks

Article abstract of DOI:10.1055/s-0030-1258050

New difluoro-bora-diaza-s-indacenes were synthesized from tetramethyl derivatives following a sequence of reactions including Knoevenagel condensation, selective cross-coupling reactions in order to extend the delocalization pathway. The introduction of flexible chains bearing a terminal ester or based on polyethylene glycol insure a good solubility and import polarity which facilitates the purification procedures. Many polyaromatic subunits (pyrene, perylene, anthracene, naphtalene, ferrocene) were fused to the main central core of the Bodipy. Georg Thieme Verlag Stuttgart - New York.

Full text of DOI:10.1055/s-0030-1258050

2304
LETTER
Elaborating Boron Dipyrromethene Dyes with Conjugated Polyaromatic
Frameworks
Boron
D
ipyrrome
a
thene
D
ye
y
mond Ziessel,* Thomas Bura, Jean-Hubert Olivier
Laboratoire de Chimie Organique et Spectroscopies Avancées (LCOSA, www-lmspc.u-strasbg.fr/lcosa), CNRS, UdS, ECPM,
25 Rue Becquerel, 67087 Strasbourg Cedex 2, France
E-mail: ziessel@unistra.fr
Received 11 May 2010
Various strategies to extend the absorption properties of
Abstract: New difluoro-bora-diaza-s-indacenes were synthesized
Bodipy dyes to the near infrared5 have been devised based
from tetramethyl derivatives following a sequence of reactions in-
on: (i) substitution of the 3,5-positions6 or 1,3,5,7-posi-
cluding Knoevenagel condensation, selective cross-coupling reac-
tions by styryl functions,7 (ii) extension of the electronic
tions in order to extend the delocalization pathway. The
introduction of flexible chains bearing a terminal ester or based on conjugation with unsaturated linkers in the 2,6-positions8
and 3,5-positions,9 (iii) replacement of the meso-8-carbon
polyethylene glycol insure a good solubility and import polarity
by a nitrogen atom leading to an aza-Bodipy,10 (iv) fusion
which facilitates the purification procedures. Many polyaromatic
subunits (pyrene, perylene, anthracene, naphtalene, ferrocene) were
of aromatic rings onto the Bodipy core,11 and finally (v)
fused to the main central core of the Bodipy.
the replacement of pyrrole by isoindole.12 For these dyes,
Key words: Bodipy, pyrene, perylene, anthracene, palladium, vi-
nyl, ferrocene
the electronic absorption and emission profiles are clearly
sensitive to the delocalization over the skeleton although
blue to deep-green colors are provided routinely. The sub-
stitution of the central 8-position with aryl groups has lit-
Contemporary research on synthetic modification of dif-
tle effect on the optical properties except where these
luoro-bora-diaza-s-indacene (F-Bodipy) derivatives has
groups incorporate electron-donating substituents, like
been largely motivated by the need to enhance the (virtu-
linear or cyclic tertiary amines, or electron-withdrawing
substituents, like NO213 or CN.14 Otherwise, the orthogo-
nality of the central fragment with respect to the dipyr-
romethene core prevents orbital contact.
al) Stokes shift, thereby optimizing the performance in
flow cytometry and fluorescence imaging technology, and
to facilitate the harvesting of a larger fraction of solar en-
ergy, thereby helping to engineer improved photon collec-
tors.1,2 A common feature of new derivatives is that the
Bodipy nucleus and the appended light harvester, usually
an aryl polycycle (Figure 1), remain in weak electronic
communication such that each unit retains its own identity
even though intramolecular energy transfer might be ex-
tremely fast.3,4
The availability of more sophisticated Bodipy dyes in
which polyaromatic residues are embedded inside the de-
localization pathway should allow specific problems
linked to the possibility of strong absorption of photons
over much of the visible spectral range and to fluores-
cence in the far-red region to be tackled. To this end, we
have envisaged the synthesis of Bodipy dyes wherein the
ancillary photon collector forms part of the overall conju-
gated network running throughout the dye molecule. Styr-
yl-based connections at the 3,5-positions of the
dipyrromethene core, for example, should ensure excel-
lent conjugation across the molecule.
N
N
Despite the promise of such molecules, synthetic method-
ologies for their construction remain essentially unex-
plored, and the provision of sufficient amounts of these
substances could be a bottleneck for further studies and
development in materials science and optoelectronic de-
vices.
B
8
7
1
6
2
N
N
Thus, as a response to this challenge, we describe herein
an approach to the fabrication of the next-generation
Bodipy dyes. This required first the development of an ef-
ficient and reliable synthesis of styryl derivatives
(Scheme 1),15 which proved to be possible using Bodipy
derivatives containing acidic methyl substituents in a
Knoevenagel condensation with electron-rich alde-
hydes.16 Thus, reactions of 4-methylbenzaldehyde, 10-
methylanthracene-9-carboxaldehyde, and 4-methyl-1-
5
3
B
4
F
F
A
B
Figure 1
SYNLETT 2010, No. 15, pp 2304–2310
Advanced online publication: 30.08.2010
DOI: 10.1055/s-0030-1258050; Art ID: G15610ST
x
x
.x
x
.2
0
1
0
© Georg Thieme Verlag Stuttgart · New York

LETTER
Boron Dipyrromethene Dyes
2305
naphthaldehyde with dye 1 produced compounds 2–4, re- all styryl-based signals, the observed 16.2 Hz proton–pro-
spectively. The isolated yields depended strongly on the ton coupling constant is in keeping with the E-configura-
experimental conditions (Table 1). The intermediate tion of the double bonds, a situation expected because of
monosubstituted species have similar polarity to the de- the type of condensation employed. A phenyliodo group
sired disubstituted materials and thus contaminate the was introduced in view of the prospect of further function-
products unless conversion is complete. Thus, the forcing alization of the dyes by metal-promoted cross-coupling
methods 6 and 7 of Table 1, involving the use of very high reactions (vide infra).
concentration of reactants (as the solvent evaporated) pro-
vided a reliable procedure for obtaining analytically pure
disubstituted dyes. The less soluble 1-pyrenecarboxalde-
Encouraged by these successes, we attempted to prepare
the pigments 6 and 7 using the forcing conditions of me-
thod 7 (Table 1). After multiple recrystallizations from
hyde always provided a mixture of mono- (5a) and disub-
dichloromethane–ethanol, 6 and 7 were isolated each in
stituted (5b)17 derivatives, although these were readily
about 90% yield. To increase the solubility of the pig-
ments we used two strategies of introduction of flexible
chains either on the boron (position 4), or at the pseudo-
meso-position 8. Use of a Grignard reagent for boron sub-
separated by fractional crystallization or column chroma-
tography in the case of 5a. These new compounds were
characterized unambiguously by NMR spectroscopy. For
I
N
N
B
F
F
I
i)
I
2
ii)
I
N
N
N
N
B
B
F
F
F
F
1
iii)
3
N
N
B
F
F
4
iv)
I
I
N
N
N
N
+
B
B
F
F
F
F
5a
5b
Scheme 1 Formation of styryl-Bodipy species via the Knoevenagel reaction using toluene, piperidine, PTSA, dryness (method 7, Table 1).
Reagents and conditions: (i) 4-methylbenzaldehyde, 95% yield; (ii) 10-methylanthracene-9-carboxaldehyde, 75%; (iii) 4-methyl-1-naphtalde-
hyde, 85%; (iv) 1-pyrenecarboxaldehyde, 25% of 5a and 30% of 5b.
Synlett 2010, No. 15, 2304–2310 © Thieme Stuttgart · New York

2306
R. Ziessel et al.
LETTER
Table 1 Various Experimental Conditions for the Preparation of Blue Dyesa
Method
Exp. Conditions
Temp (°C)
100
Time
Yield (%)
1
2
i-PrOH, piperidine, AcOH
benzene, piperidine, AcOH
toluene, piperidine, AcOH
toluene, piperidine, MW*
24 h
2 (20)
100
24 h
2 (25)
3
140
24 h
2 (20)
4
100
10 min
5 min
trace
5
toluene, piperidine, drynessb
toluene, piperidine, drynessb,c
toluene, piperidine, PTSA, drynessb,c
toluene, piperidine, AcOH
toluene, piperidine, PTSA, drynessb,c
toluene, piperidine, AcOH
toluene, piperidine, PTSA, drynessb,c
140
mixture mono/bis
2 (80)
6
140
2 × 5 min
2 × 5 min
2 × 5 min
2 × 5 min
2 × 5 min
2 × 5 min
7
140
2 (95)
8
140
3 (35)
9
140
3 (80)
10
11
140
4 (29)
140
4 (96)
a Reaction performed at the 200 mg scale, in 5 mL solvent and 1 mL piperidine, 200 mL AcOH or 1 crystal PTSA and using 2 equiv of the
aldehyde (except for method 6 and 7 where 2 × 2 equiv were used). MW* for microwave irradiation, 1000 W 90 °C, 10 min.
b The solvent was distilled to dryness using a Dean–Stark setup.
c Conditions: 2 equiv of the aldehyde was added after the first evaporation.
stitution provided the soluble compounds 8a and 8b. The which tolerates the subsequent use of a Grignard reagent
second strategy used palladium-promoted cross-coupling for boron substitution with alkyne derivatives, affording
reactions with alkyne-substituted reagents (Scheme 2). In the highly soluble dye 10 bearing potential reactive bromo
both cases the choice of the alkyne derivatives was moti- functions.
vated not only by the solubility increase but also by the
Our next target became the attachment of more elaborate
polarity imported by the diethylene glycol residues or by
polyaromatic scaffolds (Scheme 3). The cross-coupling of
the diethyl ester group. No selectivity of substitution was
highly soluble 9b with 1-ethynylpyrene19 and 3-
found with the triiodo derivative 6, whereas a good selec-
tivity resulted when using the mixed monoiodo/bisbromo
derivative 7. After some experimentation (Table 2), a se-
lectivity of 78% was obtained for compound 9b.18 This se-
lectivity results from the reactivity of the iodo function as
well as the mild conditions used for the cross-coupling re-
actions (Scheme 2). Thus, a library of derivatives bearing
various additional functional groups was ultimately ob-
tained. An interesting case is provided with compound 9e,
ethynylperylene20 under standard conditions proved to be
efficient provided an excess (2.2 equiv) of the alkyne was
used to ensure that double substitution was dominant.
The next challenge was to activate a single position in the
disubstituted derivative 9b and so provide the opportunity
to embed additional ‘intelligent’ modules designed to pro-
mote excitonic energy transfer or electron transfer, inter-
nal spin crossover, and inherent multiple redox activity.21
Given that the bromophenyl residue is less prone to cross-
Table 2 Various Experimental Conditions for the Preparation of Dye 9ba
Entry
Exp. Conditions
Nature of catalystb
Yield (%)c
1
2
3
4
5
6
7
benzene, i-Pr2NH, 80 °C, 15 h
THF, i-Pr2NH, 80 °C, 15 h
THF, i-Pr2NH, 80 °C, 24 h
benzene, i-Pr2NH, 80 °C, 15 h
benzene, i-Pr2NH, 80 °C, 15 h
THF, Et3N, 50 °C, 48 h
Pd2(dba)3, Ph3P (2 equiv)
Pd2(dba)3, Ph3P (20 equiv)
Pd(OAc)2, Ph3P (4 equiv)
Pd(OAc)2, P(C6H11)3 (2 equiv)
[Pd(PPh3)4]
<5
25
25
45
24
35
78
[Pd(PPh3)2Cl2], CuI
benzene, THF, i-Pr2NH, 60 °C, 15 h
[Pd(PPh3)2Cl2], CuI
a Reaction performed at the 50 mg scale, in 1 mL solvent and 1 mL amine, and using 2 equiv of 6-ethylheptynoate.
b The dba accounts for tris(dibenzylideneacetone)diPd(0), P(C6H11)3 for tricyclohexylphosphine.
c Isolated yield obtained after column chromatography.
Synlett 2010, No. 15, 2304–2310 © Thieme Stuttgart · New York

LETTER
Boron Dipyrromethene Dyes
2307
I
I
I
i)
ii)
N
N
N
N
N
N
O
B
B
B
F
F
F
F
1
O
X
X
X
X
6 X = I
7 X = Br
O
O
Me
Me
8a X = I
8b X = Br
X
iii)
9a X = Y =
COOEt
9b X = Br ; Y =
N
N
F
F
Y
B
COOEt
9c X = Br ; Y =
9d X = Br ; Y =
OH
OH
X
9e X = Br ; Y =
N
O
iv)
Br
Me
O
N
N
O
O
B
N
O
O
Me
Br
10
Scheme 2 Further functionalization of styryl-Bodipy derivatives. Reagents and conditions: i) 4-iodobenzaldehyde, 92% or 4-bromobenzal-
dehyde, 90% in toluene, piperidine, PTSA, dryness; (ii) HC≡CCH2OCH2CH2OMe (3 equiv), EtMgBr (2.5 equiv), THF, 60 °C, 94% for 8a and
93% for 8b; (iii) corresponding ethynyl derivative, [Pd(PPh3)2Cl2] (6 mol%), CuI (10 mol%), benzene, i-Pr2NH, 80 °C, 15h, 85% for 9a, 78%
for 9b, 82% for 9c, 79% for 9d, 63% for 9e; (iv) HC≡CCH2OCH2CH2OMe (3 equiv), EtMgBr (2.5 equiv), THF, 60 °C, 94% for 10.
coupling under mild conditions, we employed a lower tions depends on the solvent, reaction time, temperature,
catalyst concentration, a shorter reaction time, and substo- and concentration of reactants. Trace amounts of PTSA
ichiometric amounts of 3-ethynylperylene. Compound 13 and a high concentration of reactants facilitated the double
was obtained in 42% isolated yield from 9b in a reproduc- substitution. More soluble dyes were obtained by selec-
ible manner. The side product was compound 12 (20% tively grafting a flexible chain onto either the boron or the
yield), and some starting material (15%) could be recov- pseudo-meso-position. Cross-coupling reactions of bromo
ered. With this pivotal compound in hand, the preparation derivatives could be made relatively selective by adjust-
of mixed derivatives such as 14,22 bearing both pyrene and ing the reaction time, catalyst concentration, and temper-
perylene subunits linked to the Bodipy, was straightfor- ature. Unsymmetrically substituted dyes bearing
ward. Similarly, reactions with 9-ethynyl-10-methyl- perylene, pyrene, anthracene, and/or ferrocene groups
anthracene and 1-ethynlferrocene provided dyes 15 and were also prepared in variations on the Knoevenagel reac-
16 in excellent isolated yields (Scheme 4).
tions and metal-catalyzed cross-couplings. An important
factor facilitating the purification of all the present mate-
rials was the introduction of a substituent bearing a polar
terminus, in particular an ester group. There is no reason
why the synthesis cannot be extended to include other
Our design opens up the possibility of engineering sophis-
ticated dyes in which the polyaromatic moieties are cou-
pled electronically with the central dipyrromethene core
via vinyl tethers. The efficiency of the substitution reac-
Synlett 2010, No. 15, 2304–2310 © Thieme Stuttgart · New York

2308
R. Ziessel et al.
LETTER
COOEt
i)
COOEt
N
N
B
F
F
11
COOEt
N
N
F
B
F
Br
Br
9b
N
N
B
F
F
ii)
12
Scheme 3 Synthesis of symmetrically functionalized Bodipy derivatives. Reagents and conditions: i) 1-ethynylpyrene (2.2 equiv), THF, di-
isopropylamine, [Pd(PPh3)4] (6 mol%), 60 °C, 18 h, 89%; ii) 3-ethynylperylene (2.2 equiv) THF, diisopropylamine, [Pd(PPh3)4] (6 mol%),
60 °C, 12 h, 80%.
(2) Earp, A. A.; Smith, G. B.; Swift, P. D.; Franklin, J. Sol.
Energy 2004, 76, 655.
(3) (a) Goze, C.; Ulrich, G.; Mallon, L. J.; Allen, B. D.;
Harriman, A.; Ziessel, R. J. Am. Chem. Soc. 2006, 128,
10231. (b) Harriman, A.; Izzet, G.; Ziessel, R. J. Am. Chem.
Soc. 2006, 128, 10868.
(4) (a) Harriman, A.; Mallon, L. J.; Ziessel, R. Chem. Eur. J.
2008, 14, 11461. (b) Harriman, A.; Mallon, L. J.; Goeb, S.;
Ulrich, G.; Ziessel, R. Chem. Eur. J. 2009, 15, 4553.
(5) Ulrich, G.; Ziessel, R.; Harriman, A. Angew. Chem. Int. Ed.
2008, 47, 1184.
polycyclic frameworks nor why cross-functionalized
dyes, having additional functional groups covalently
linked at the indacene backbone, cannot be prepared. Cur-
rent work is focused on the study of the spectroscopic and
electrochemical properties of the new dyes and results
will be timely disclosed.
References and Notes
(1) Lakowicz, J. R. Principles of Fluorescence Spectroscopy,
3rd ed.; Springer: Heidelberg, 2006.
(6) Saki, N.; Dinc, T.; Akkaya, E. U. Tetrahedron 2006, 62,
2721.
Synlett 2010, No. 15, 2304–2310 © Thieme Stuttgart · New York

LETTER
Boron Dipyrromethene Dyes
2309
COOEt
COOEt
COOEt
i)
ii)
N
N
N
N
N
N
B
B
B
F
F
F
F
F
F
Br
Br
Br
9b
14
13
iv)
iii)
N
N
F
F
B
COOEt
15
N
N
F
F
B
COOEt
16
Fe
Scheme 4 Synthesis of unsymmetrically functionalized Bodipy derivatives. Reagents and conditions: (i) 3-ethynylperylene (0.8 equiv), THF,
diisopropylamine, [Pd(PPh3)4] (3 mol%), 50 °C, 6 h, 42%; (ii) 1-ethynylpyrene (1.2 equiv), THF, diisopropylamine, [Pd(PPh3)4] (6 mol%),
60 °C, 12 h 79%; (iii) 9-ethynyl-10-methylanthracene (1.2 equiv), THF, diisopropylamine, [Pd(PPh3)4] (6 mol%), 60 °C, 12 h, 84%; (iv) 1-
ethynylferrocene (1.2 equiv), THF, diisopropylamine, [Pd(PPh3)4] (6 mol%), 60 °C, 12 h, 94%.
(7) Buyukcakir, O.; Bozdemir, O. A.; Kolemen, S.; Erbas, S.;
Akkaya, E. U. Org. Lett. 2009, 11, 4644.
(8) Bonardi, L.; Ulrich, G.; Ziessel, R. Org. Lett. 2008, 10, 2183.
(9) Rihn, S.; Retailleau, P.; Bugsaliewicz, N.; De Nicola, A.;
Ziessel, R. Tetrahedron Lett. 2009, 50, 7008.
(10) (a) Gorma, A.; Killoran, J.; O’Shea, C.; Kenna, T.;
Gallagher, W. M.; O’Shea, D. F. J. Am. Chem. Soc. 2004,
126, 10619. (b) Zhao, W.; Carreira, E. M. Chem. Eur. J.
2006, 12, 7254.
Synlett 2010, No. 15, 2304–2310 © Thieme Stuttgart · New York

2310
R. Ziessel et al.
LETTER
(11) (a) Chen, J.; Burghart, A.; Derecskei-Kowacs, A.; Burgess,
K. J. Org. Chem. 2000, 65, 2900. (b) Umezawa, K.;
Nakamura, Y.; Makino, H.; Citterio, D.; Suzuki, K. J. Am.
Chem. Soc. 2008, 130, 1550.
(12) Ulrich, G.; Goeb, S.; De Nicola, A.; Retailleau, P.; Ziessel,
R. Synlett 2007, 1517.
(13) (a) Ziessel, R.; Bonardi, L.; Retailleau, P.; Ulrich, G. J. Org.
Chem. 2006, 71, 3093. (b) Sathyamoorthi, G.; Boyer, J.-H.;
Allik, T. H.; Chandra, S. Heteroat. Chem. 1994, 5, 403.
(14) Sathyamoorthi, G.; Boyer, J.-H.; Allik, T. H.; Chandra, S.
Heteroat. Chem. 1994, 5, 403.
+ solvent overlap), 7.18 (d, 3J = 16.3 Hz, 2 H), 6.64 (s, 2 H),
4.16 (q, 3J = 7.1 Hz, 2 H), 2.50 (t, 3J = 7.0 Hz, 2 H), 2.39 (t,
3J = 7.3 Hz, 2 H), 1.87–1.82 (m, 2 H), 1.72–1.68 (m, 2 H),
1.49 (s, 6 H), 1.28 (t, 3J = 7.1 Hz, 3 H). 13C{1H} (100 MHz,
CDCl3): d = 173.9, 152.9, 142.8, 139.2, 135.9, 135.4, 134.6,
133.8, 132.7, 132.4, 1296.3, 128.8, 125.3, 123.4, 120.2,
118.4, 91.8 (C≡C), 80.7 (C≡C), 60.8, 34.3, 28.5, 24.7, 19.6,
15.3 (CH3), 14.7 (CH3). MS (EI): m/z (%) = 811.0 (50) [M],
810.0 (100) [M], 808.0 (45) [M]. Anal. Calcd for
C42H37N2BF2Br2O2 (Mr = 810.37): C, 62.25; H, 4.60; N,
3.46. Found: C, 61.89; H, 4.39; N, 3.27.
(15) (a) Haughland, R. P.; Kang, H. C. US 4,774,339, 1988.
(b) Rurack, K.; Kollmansberger, M.; Daub, J. New J. Chem.
2001, 25, 289. (c) Dost, Z.; Atilgan, S.; Akkaya, E. U.
Tetrahedron 2006, 62, 8484. (d) Atilgan, S.; Ekmekci, Z.;
Dogan, A. L.; Guc, D.; Akkaya, E. U. Chem. Commun. 2006,
4398.
(19) Hissler, M.; Harriman, A.; Khatyr, A.; Ziessel, R. Chem.
Eur. J. 1999, 11, 3366.
(20) Inouye, M.; Hyodo, Y.; Nakazumi, H. J. Org. Chem. 1999,
64, 2704.
(21) Ziessel, R.; Retailleau, P.; Elliott, K. J.; Harriman, A. Chem.
Eur. J. 2009, 15, 10369.
(16) Knoevenagel, E. Ber. Dtsch. Chem. Ges. 1898, 31, 2596.
(17) Compound 5b: 1H (400.13 MHz, CDCl3): d = 8.61 (d,
3J = 8.2 Hz, 2 H), 8.53 (d, 3J = 9.3 Hz, 2 H), 8.46 (d,
3J = 16.6 Hz, 2 H), 8.27–8.16 (m, 6 H), 8.12 (d, 3J = 9.3 Hz,
2 H), 8.09–7.96 (M, 6 H), 7.93 (d, 3J = 8.2 Hz, 2 H), 7.89 (d,
3J = 8.2 Hz, 2 H), 7.37 (d, 3J = 8.2 Hz, 2 H), 7.00 (s, 2 H),
1.26 (s, 6 H). 13C{H} (100.61 MHz, CDCl3): d = 158.2,
156.6, 156.2, 154.3, 155.5, 148.2, 136.8, 139.5, 132.8,
135.7, 133.6, 135.5, 134.9, 133.6, 130.7, 129.7, 124.9,
128.9, 127.5, 128.9, 127.0, 128.6, 127.0, 125.8, 124.7,
120.4, 96.9, 15.4. MS (EI): m/z (%) = 874.1 (100) [M]. Anal.
Calcd for C53H34N2BF2I (Mr = 874.56): C, 72.79; H, 3.92;
N, 3.20. Found: C, 72.44; H, 3.67; N, 3.02.
(22) Compound 14: 1H (400 MHz, CDCl3): d = 8.72 (d, 3J = 7.8
Hz, 1 H), 8.35 (d, 3J = 7.6 Hz, 1 H), 8.38–8.03 (m, 14 H),
7.83–7.52 (m 12 H), 7.58–7.62 (m, 4 H), 7.35–7.26 (m, 4 H),
6.74 (s, 1 H), 6.72 (s, 1 H), 4.16 (q, 3J = 7.2 Hz, 2 H), 2.52
(t, 3J = 7.0 Hz, 2 H), 2.39 (t, 3J = 7.2 Hz, 2 H), 1.92–1.80 (m,
2 H), 1.73–1.67 (m, 2 H), 1.48 (s, 6 H), 1.29 (t, 3J = 7.1 Hz,
3 H). 13C{1H} (100 MHz, CDCl3): d = 173.8, 153.3, 152.5,
142.9, 142.4, 139.0, 136.9, 132.7, 132.5, 132.4, 131.6,
130.1, 128.9, 128.0, 127.8, 127.7, 126.7, 126.1, 125.0,
121.4, 121.2, 121.0, 118.6, 96.5 (C≡C), 91.9 (C≡C), 91.4
(C≡C) 90.6 (C≡C), 90.2 (C≡C), 80.8 (C≡C), 60.8, 34.3, 28.5,
27.3, 24.7, 19.6, 15.30 (CH3), 14.7 (CH3). MS (EI): m/z (%)
= 1151.2 (90) [M], 1150.2 (100) [M]. Anal. Calcd for
C82H57N2BF2O2 (Mr = 1151.15): C, 85.56; H, 4.99; N, 2.43.
Found: C, 85.33; H, 4.62; N, 2.15.
(18) Compound 9b: 1H (400 MHz, CDCl3): d = 7.70 (d, 3J = 16.3
Hz, 2 H), 7.56–7.48 (m, 10 H), 7.27 (d, 3J = 8.2 Hz, ca. 2 H
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