Iptycene-Containing Azaacenes with Tunable Luminescence

Article abstract of DOI:10.1055/s-0036-1589503

An optimized route toward iptycene-capped, p -dibromo-quinoxalinophenazine was developed, increasing the yield significantly from literature procedures. New iptycene-containing symmetrical aza-acenes were synthesized from this intermediate using Suzuki-Miyaura cross-coupling, and their photophysical properties were evaluated. Tuning the substituents allows modulating emission wavelengths across the visible spectrum. Substitution with 3-methoxy-2-methylthiophene exhibits a quantum yield of 35%. The (triisopropylsilyl)acetylene product has a quantum yield of 38% and serves as a model compound for the synthesis of polymers based on this electrooptically active molecular motif.

Full text of DOI:10.1055/s-0036-1589503

SYNLETT
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
©
Georg Thieme Verlag Stuttgart · New York
2017, 28, A–G
letter
A
en
Synlett
A. L. Schleper et al.
Letter
Iptycene-Containing Azaacenes with Tunable Luminescence
A. Lennart Schleper§
Constantin-Christian A. Voll§
Jens U. Engelhart
Timothy M. Swager*
Department of Chemistry, Massachusetts Institute of
Technology, 77 Massachusetts Avenue, Cambridge MA,
02139, USA
tswager@mit.edu
§
These authors contributed equally
Received: 05.04.2017
Accepted after revision: 15.05.2017
Published online: 19.07.2017
densities.4–6 Emissive stable radicals have also been consid-
ered, but there is currently only a limited number of struc-
tures suitable for this purpose and quantum efficiencies
have thus far been low.7 Recently, high-emission efficien-
cies from thermally activated delayed fluorescence (TADF)
have been reported, and this method is emerging as a
DOI: 10.1055/s-0036-1589503; Art ID: st-2017-r0234-l
,8
Abstract An optimized route toward iptycene-capped, p-dibromo-
quinoxalinophenazine was developed, increasing the yield significantly
from literature procedures. New iptycene-containing symmetrical aza-
acenes were synthesized from this intermediate using Suzuki–Miyaura
cross-coupling, and their photophysical properties were evaluated. Tun-
ing the substituents allows modulating emission wavelengths across
the visible spectrum. Substitution with 3-methoxy-2-methylthiophene
exhibits a quantum yield of 35%. The (triisopropylsilyl)acetylene prod-
uct has a quantum yield of 38% and serves as a model compound for
the synthesis of polymers based on this electrooptically active molecu-
lar motif.
9
promising approach to create efficient OLEDs. Indeed this
method tends to outperform the up-conversion of triplets
10–12
to singlet excitons by triplet–triplet annihilation.
TADF
requires the energetic proximity of the S and T state and
1
1
the first-order mixing coefficients between singlet and
triplet states are inversely proportional to the singlet–trip-
let gap (ΔEST).13 This small ΔEST allows fast intersystem
crossing for the thermal equilibration of triplet and singlet
Key words N-heteroiptycene, Suzuki–Miyaura cross-coupling, Sono-
gashira coupling, pyrazinoquinoxaline, luminescence
excitons. Electroluminescence with η approaching 100%
int
have been realized through TADF.9 There are two classes
,14
of TADF materials that meet the electronic requirements of
In recent years, there has been an immense interest in
organic materials for OLEDs, OFETs, and PVs, encouraged by
the ease of tunability through design and solubility com-
pared to inorganic counterparts, which is conducive to
a low ΔE A torsion angle between donor and acceptor
ST.
,15,16
moieties9
or having the donor–acceptor groups in ho-
moconjugation, both provide mechanisms to produce seg-
regated HOMO and LUMO states that lower the exchange
1,2
17
large-scale printing techniques. OLEDs, as an example,
initially struggled with efficiency because upon electro-
chemical excitation, singlet and triplet excitons are formed
energy and give rise the small energy difference. In fact,
another promising approach for OLEDs and other optical
applications involves the spatial segregation of FMOs. In
this context we were interested in investigating cruciforms
comprising two perpendicular π-conjugated linear units
connected by a central aromatic core and thereby can re-
duce HOMO and LUMO orbital overlap.1
3
in a 1:3 statistical ratio. Since only the radiative decay from
singlet excitons is quantum chemically fully allowed and
the long-lived triplet excitons usually relax through nonra-
diative processes, internal electroluminescent quantum ef-
ficiency (ηint) of most organics is limited to 25%. Phospho-
rescent materials and delayed fluorescence have been in-
vestigated as triplet harvesting strategies. Most of these
materials incorporate heavy metals and have been shown
to achieve ηint values that are essentially 100%. However,
their use is constrained by cost, the limited stability of blue
emitters, and triplet–triplet annihilation at high current
8–22
spacious wings to avoid π-stacking
D
N
N
electron-poor core (LUMO) – acceptor
N
N
D
electron-rich substitutents (HOMO) – donor
Figure 1 Generic target structures targeted in this publication
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G

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A. L. Schleper et al.
Letter
O
O
HO
O
O
OH
O
NaOHaq
dioxane
O
TFAA
DMSO
Et3N
1
2
3
O
O
Br
Br
Br
Br
NO2
NO2
H2N
NH2
.
N
N
Zn
AcOH
4
N
N
N
N
S
n AcOH
AcOH
H2N
NH2
Br
Br
5
6
7
Scheme 1 Synthetic procedure for the synthesis of intermediate 7
We postulated the generic structure shown in Figure 1
to display favorable optical properties. The electron-defi-
cient pyrazinoquinoxaline core will have little HOMO–
LUMO orbital overlap with a relatively bulky electron donor
raised the yield to 72% (Table 1, entry 10). Despite the
promising increase in yield, we encountered issues in scal-
ing up the reaction, and diminished yields were observed at
scales more than 60 mg of 4.
23,24
that is forced to adopt a twisted conformation.
The
Having optimized the first reaction cascade, we endeav-
ored to introduce donor groups to 7 through cross-coupling
reactions. We surveyed both Stille and Suzuki–Miyaura
couplings and converged on the latter based upon higher
yields whilst avoiding toxic tin reagents. Reaction optimiza-
tion with (3,5-dimethoxyphenyl)boronic acid revealed that
cross-coupling to 7 could be achieved in 99% yield using
Pd (dba) /P(o-tol) as the catalyst at 60 °C. Other catalysts
three-dimensional structurally rigid iptycene wings mini-
mize the typical tendency of azaacenes for π stacking that
can lead to self-quenching and reduced quantum yields.2
The isolated phenyl groups of the iptycene wings are not ex-
pected to contribute significantly to the HOMO or LUMO.27
We targeted a modular synthetic route for symmetric
azaacenes and envisioned 7 as a valuable key intermediate
because the lateral aryl bromides allow functionalization
through cross-coupling reactions. The diketone intermedi-
ate 4 was synthesized as shown in Scheme 1, through adap-
tation of a literature procedure that involves Diels–Alder re-
action of anthracene with vinylene carbonate, followed by a
5,26
2
3
3
such as Pd(PPh ) , the addition of CuI, Pd-XPhos-G2, or
3
4
Pd(dppf)Cl resulted in low to moderate yields (Table 2).
2
The optimized reaction conditions were applied to a va-
riety of (hetero)aryl boronic acids and the C–C cross-cou-
pling products 9–13 could be obtained in yields ranging
from 65–99% (Figure 2).
28
basic hydrolysis and a Swern oxidation.
The condensation of 4 was complicated by the fact that
,6-dibromobenzene-1,2,4,5-tetraamine (6) is unstable and
3
has to be prepared in situ. Literature procedures for the re-
duction of 4,7-dibromo-5,6-dinitrobenzo[c][1,2,5]thiadi-
azole (5) followed by condensation to a diketone are gener-
ally low yielding (20% and 47% for related structures),29,30
and as a result we decided to optimize the reaction cascade.
Following the established literature procedure provided 7
in 33% yield (Table 1, entry 2). Other reaction conditions
such as varying the temperature, zinc activation by hydro-
chloric acid, increasing the amount of zinc, or the use of hy-
drochloric acid instead of acetic acid, did not increase the
yield of the reaction (Table 1, entries 1, 3–6). Analysis of the
reaction mixture revealed a considerable amount of residu-
al diketone 4, thus encouraging the use of an excess of 5.
Yields improved up to 65% when 1.38 equivalents of 5 were
utilized (Table 1, entry 8).
Table 1 Reaction Optimization for the Synthesis of 7
Entry
Temp
(°C)a
Activated Acid
zincb
Zinc
(equiv)
5
Yield
(%)
(equiv)
1
2
50
60
70
60
60
60
60
60
60
60
No
No
No
Yes
No
No
No
No
No
No
AcOH
20
20
20
20
20
200
20
20
20
20
0.50
0.50
0.50
0.50
0.50
0.50
1.25
1.38
1.50
1.38
trace
AcOH
AcOH
AcOH
HCl
33c
3
trace
trace
trace
trace
61c
4
5
6
AcOH
AcOH
AcOH
AcOH
AcOH
7
8
65c
9
57c
10
72c
Having the tetraamine 6 in excess, however, increases
the likelihood of monocondensation, hence the order of ad-
dition was reversed. Slowly adding the amine to a solution
of the diketone in acetic acid over one hour furthermore
a
b
c
Temperature used for reduction of 5 to 6.
Zinc activation by HCl.
Isolated yield.
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A. L. Schleper et al.
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Table 2 Optimization of Suzuki–Miyaura Cross-Coupling
MeO
MeO
OMe
B(OH)2
MeO
N
Br
N
N
N
N
N
N
H2O/dioxane/toluene (0.1 M)
0 °C
N
Br
6
OMe
7
8
MeO
Entry
Catalyst
CuI (equiv)
Yield (%)
1
2
3
4
5
Pd(PPh
Pd(PPh
3
3
)
)
4
4
–
trace
trace
47a
0.2
–
Pd-XPhos-G2
Pd(dppf)Cl
Pd (dba) /P(o-tol)
54a
2
–
–
99a
2
3
3
aIsolated yield.
We furthermore attempted to extend the scope to in-
clude palladium-catalyzed N-arylation with carbazole in or-
der to introduce stronger donors. Unfortunately, initial at-
tempts using a variety of ligands (XPhos, t-BuBrettPhos, Ru-
Phos, or t-BuXPhos) only produced unreacted and reduced
forms of 7. However, the N-arylation with iminodibenzyl,
which is known to be a better nucleophile than carbazole,31
proceeded smoothly to give 14 in 56% yield using the
Buchwald precatalyst Pd-RuPhos-G4 (Scheme 2).
These promising coupling results with aryl bromides
also encouraged us to synthesize a (triisopropylsilyl)acety-
lene product 15 via a Sonogashira reaction catalyzed by
Pd(PPh ) and CuI in 57% yield (Scheme 3). This compound
3
4
serves as a model compound for a hypothetical acetylene-
linked polymer of 7. The yield of the Sonogashira reaction
O
O
N
N
N
N
N
N
N
N
N
N
N
O
N
O
9
(99%)
10 (66%)
11 (99%)
O
S
S
N
N
N
N
N
N
N
N
S
S
O
12 (69%)
13 (65%)
Figure 2 Substrate scope of aryl boronic acid coupling with 7
N
Pd-RuPhos-G4
LiHMDS
Br
N
N
N
N
N
N
N
+
N
N
1,4-dioxane
60 °C, 16 h
N
Br
H
7
14 (56%)
Scheme 2 N-Arylation reaction of iminodibenzyl with 7
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TIPS
TIPS
Br
N
N
N
N
CuI (0.2 equiv)
Pd(PPh3)4 (0.2 equiv)
N
N
N
N
Br
THF/Et3N (0.1 M)
7
15
TIPS
Scheme 3 Sonogashira coupling of 7 with (triisopropylsilyl)acetylene to form 15
in this case is too low to be of utility for the synthesis of
polymers, which require near quantitative yields. We note
that 15 has very recently been synthesized by Bunz and co-
To determine if this class of compounds displays TADF
behavior, we measured the quantum yields in both deoxy-
genated and oxygen-containing solvents. In TADF systems,
triplet states contribute to a delayed component, which
32
workers through a different synthetic route.
We were interested to determine if these materials dis-
played desirable optical properties, including TADF. Repre-
sentative absorption spectra of the compounds 9–13 are
shown in Figure 3. All of the compounds display vibronic
fine structure with peaks that are summarized in Table 3.
The broad tails at longer wavelength are suggestive of
charge-transfer character.
renders the compounds susceptible to quenching by oxy-
gen.3
3,34
An increase in quantum yield in an oxygen-free sol-
vent is therefore an indication of TADF. As shown in Figure
4, compounds 9–13 were emissive, however, saturating the
solutions with oxygen did not significantly affect the quan-
Figure 4 Emission spectra of compounds 9–13 in hexane
Figure 3 Absorption spectra with molar absorptivity for 9–13 in hex-
ane
Table 3 Optical Properties of Compounds 9–15, Measured in Hexane
Compd
λ
max(emis)
QY (%)
λ
max(abs)
9
470
478
510
586
608
–
2.2·10–3
0.06
268, 300, 367, 385
1
1
1
1
1
0
1
2
3
4
5
268, 397, 368, 387
0.07
274, 303, 368, 386
0.35
248, 274, 309, 373, 397
266, 301, 374, 393
0.11
–
265, 360, 378, 400, 522
275, 307, 378, 400, 427, 454
1
466, 495
0.29 (0.38)a
a
Degassed by bubbling argon through solution.
Figure 5 Photophysical characterization of 15, measured in hexane
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A. L. Schleper et al.
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tum yield, thereby suggesting that these compounds are not
TADF active or have a sufficient lifetime because of rapid
nonradiative processes. Compound 14, which has a stronger
donor in the iminodibenzyl group, was only weakly emis-
sive as a result of a weak charge-transfer band (Figure S10).
Nevertheless, the absorption and emission compounds pro-
duced impressively cover essentially the whole visible spec-
trum.
The (triisopropylsilyl)acetylene product 15 shows sev-
eral well-defined absorption maxima as shown in Figure 5.
The compound is emissive with a maximum at 466 nm
with a pronounced shoulder peak at 495 nm, to give a visi-
bly green emission. The quantum yield was 38% in degassed
hexane, but decreased to 29% after oxygen exposure. This
suggests the presence of long-lived excited states, most
likely triplet states, that are quenched by O2.
Figure 6 DFT calculations of HOMO and LUMO for compounds 8–15. The calculations were performed using the B3LYP functional and 6-31+G* basis
set.
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We performed DFT calculations using the B3LYP func-
tional and 6-31+G* basis set to evaluate the HOMO–LUMO
separation of all of the products (Figure 6). They show, as
anticipated, the iptycene wings do not contribute to either
HOMO or LUMO states. The HOMO and LUMO frontier or-
bitals, however, have sizable overlap in products 9–11. The
exchange energy that stabilizes the triplet is therefore sig-
nificant and produces a larger ΔEST that decreases the cou-
pling between the singlet and triplet states and reduces the
reverse intersystem crossing (RISC). This is consistent with
the experimental data that the aryl-substituted products
are TADF inactive. Our DFT calculations suggest that prod-
ucts 8, 12, and 13 seem to have favorable spatial HOMO–
LUMO separation that provides only minor orbital overlay
and at the onset we expected these compounds to be TADF
active. However, these are gas phase, ground state, calcula-
tions with equilibrium conformations. It is possible that in
the excited-state conformations and dynamics are present
that promote larger ΔEST and competitive nonradiative re-
laxations. With regard to the latter, the quantum yields of
these materials are modest to low. The TIPS acetylene prod-
uct 15 shows high overlap between the HOMO and LUMO
states. This is inconsistent with TADF behavior. This effect
may be the result of the silicon groups, however, conforma-
tion of the origin of the intersystem crossing will require
additional investigations that are beyond our initial syn-
thetic studies that are the focus of this publication.
References and Notes
(1) Krebs, F. C. Sol. Energy Mater. Sol. Cells 2009, 93, 394.
(
2) Burgues-Ceballos, I.; Stella, M.; Lacharmoise, P.; Martinez-
Ferrero, E. J. Mater. Chem. A 2014, 2, 17711.
3) Segal, M.; Baldo, M.; Holmes, R.; Forrest, S.; Soos, Z. Phys. Rev. B
2003, 68, 1.
(
(4) Adachi, C.; Baldo, M. A.; Thompson, M. E.; Forrest, S. R. J. Appl.
Phys. 2001, 90, 5048.
(
(
(
5) Hashimoto, M.; Igawa, S.; Yashima, M.; Kawata, I.; Hoshino, M.;
Osawa, M. J. Am. Chem. Soc. 2011, 133, 10348.
6) Baldo, M. A.; Adachi, C.; Forrest, S. R. Phys. Rev. B: Condens.
Matter Mater. Phys. 2000, 62, 10967.
7) Peng, Q.; Obolda, A.; Zhang, M.; Li, F. Angew. Chem. Int. Ed. 2015,
54, 7091.
(8) Obolda, A.; Ai, X.; Zhang, M.; Li, F. ACS Appl. Mater. Interfaces
016, 8, 35472.
9) Uoyama, H.; Goushi, K.; Shizu, K.; Nomura, H.; Adachi, C. Nature
London, U.K.) 2012, 492, 234.
2
(
(
(
(
10) Luo, Y.; Aziz, H. Adv. Funct. Mater. 2010, 20, 1285.
11) Kondakov, D. Y.; Pawlik, T. D.; Hatwar, T. K.; Spindler, J. P. J. Appl.
Phys. 2009, 106, 124510.
(12) Li, W.; Pan, Y.; Xiao, R.; Peng, Q.; Zhang, S.; Ma, D.; Li, F.; Shen,
F.; Wang, Y.; Yang, B.; Ma, Y. Adv. Funct. Mater. 2014, 24, 1609.
(
(
(
13) Cui, L.-S.; Nomura, H.; Geng, Y.; Kim, J. U.; Nakanotani, H.;
Adachi, C. Angew. Chem. Int. Ed. 2017, 56, 1571.
14) Turro, N. J. Modern Molecular Photophysics; Benjamin Cum-
mings: San Francisco CA, 1978.
15) Nakanotani, H.; Higuchi, T.; Furukawa, T.; Masui, K.; Morimoto,
K.; Numata, M.; Tanaka, H.; Sagara, Y.; Yasuda, T.; Adachi, C. Nat.
Commun. 2014, 5, 4016.
(
(
(
16) Goushi, K.; Yoshida, K.; Sato, K.; Adachi, C. Nat. Photonics 2012,
In conclusion, we report the synthesis of 7 through an
35–39
6, 253.
optimized synthetic route.
The in situ reduction of 4,7-
17) Kawasumi, K.; Wu, T.; Zhu, T.; Chae, H. S.; Van Voorhis, T.; Baldo,
M. A.; Swager, T. M. J. Am. Chem. Soc. 2015, 137, 11908.
18) Chavez, R. III; Cai, M.; Tlach, B.; Wheeler, D. L.; Kaudal, R.;
Tsyrenova, A.; Tomlinson, A. L.; Shinar, R.; Shinar, J.; Jeffries-EL,
M. J. Mater. Chem. 2016, 4, 3765.
dibromo-5,6-dinitrobenzo[c][1,2,5]thiadiazole was opti-
mized to boost the yield to 72%. The versatility of the dibro-
moaryl intermediate 7 was exemplified in a variety of Suzuki–
Miyaura cross-coupling reactions that proceed in moderate
to excellent yields (65–99%), a palladium-catalyzed N-aryl-
ation with iminodibenzyl, and a Sonogashira reaction with
(19) Lim, J.; Albright, T. A.; Martin, B. R.; Miljanić, O. S. J. Org. Chem.
011, 76, 10207.
2
(20) Marsden, J. A.; Miller, J. J.; Shirtcliff, L. D.; Haley, M. M. J. Am.
Chem. Soc. 2005, 127, 2464.
(triisopropylsilyl)acetylene. Most of the products are lumi-
nescent with emission colors ranging from blue to orange.
We anticipate this molecular scaffold could potentially be
used to create new materials with useful electrooptical
properties.
(21) Zucchero, A. J.; McGrier, P. L.; Bunz, U. H. F. Acc. Chem. Res. 2010,
43, 397.
(22) Kivala, M.; Diederich, F. Acc. Chem. Res. 2009, 42, 235.
(23) Endo, A.; Sato, K.; Yoshimura, K.; Kai, T.; Kawada, A.; Miyazaki,
H.; Adachi, C. Appl. Phys. Lett. 2011, 98, 10.
(
24) Hirata, S.; Sakai, Y.; Masui, K.; Tanaka, H.; Lee, S. Y.; Nomura, H.;
Nakamura, N.; Yasumatsu, M.; Nakanotani, H.; Zhang, Q.; Shizu,
K.; Miyazaki, H.; Adachi, C. Nat. Mater. 2015, 14, 330.
Funding Information
Financial support was provided through the Airforce Office of Scien-
tific Research, a Cusanuswerk scholarship of ALS, a MITei fellowship
of CCAV sponsored by Eni S.p.A., and the German Research Foundation
(
(
(
(
(
25) Anthony, J. E. Chem. Rev. 2006, 106, 5028.
26) Li, J.; Zhang, Q. ACS Appl. Mater. Interfaces 2015, 7, 28049.
27) Swager, T. M. Acc. Chem. Res. 2008, 41, 1181.
28) Wright, M. W.; Welker, M. E. J. Org. Chem. 1996, 61, 133.
29) Zhang, L.; Jiang, K.; Li, G.; Zhang, Q.; Yang, L. J. Mater. Chem. A
(DFG) of JUEAorfirce
Oceif
of
Secnifit
Reseacrh
F(A
9
5
5
0-14-1-0
2
2
6)
2
014, 2, 14852.
Supporting Information
(
30) Wang, E.; Hou, L.; Wang, Z.; Hellström, S.; Mammo, W.; Zhang,
F.; Inganäs, O.; Andersson, M. R. Org. Lett. 2010, 12, 4470.
31) Huang, W.; Buchwald, S. L. Chem. Eur. J. 2016, 22, 14186.
32) Ganschow, M.; Koser, S.; Hahn, S.; Rominger, F.; Freudenberg, J.;
Bunz, U. H. F. Chem. Eur. J. 2017, 23, 4415.
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1588872.
(
(
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
(33) Tao, Y.; Yuan, K.; Chen, T.; Xu, P.; Li, H.; Chen, R.; Zheng, C.;
Zhang, L.; Huang, W. Adv. Mater. 2014, 26, 7931.
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(
(
(
34) Zhang, Q.; Li, J.; Shizu, K.; Huang, S.; Hirata, S.; Miyazaki, H.;
Adachi, C. J. Am. Chem. Soc. 2012, 134, 14706.
35) Preparation of Compounds 2 and 3
Following a literature procedure, see ref. 21.
36) Preparation of Compound 7
(38) Preparation of Compound 14
In a heat-gun-dried Schlenk tube under an atmosphere of
argon, a mixture of 7 (15 mg, 21.7 μmol), iminodibenzyl (9 mg,
47.7 μmol), and Pd-RuPhos-G4 (1.8 mg, 2.17 μmol) was dis-
solved in dry 1,4-dioxane (0.5 mL). The resulting mixture was
degassed in a stream of argon for 10 min. At this point LiHMDS
(0.1 M in THF, 54 μL, 54.2 μmol) was added. After heating to 60
°C for 16 h the reaction mixture was dissolved with CH Cl and
subsequently washed with water and brine. After drying over
MgSO4 and evaporating under reduced pressure, flash column
chromatography (SiO2, hexane–CH Cl = 1:1) afforded the
The optimized reaction was carried out in a 20 mL vial, contain-
ing zinc powder (470 mg, 7.19 mmol) suspended in AcOH (3.5
mL). Under stirring compound 5 (138 mg, 358 μmol) was added,
and the reaction mixture was heated to 60 °C for 1 h. The
reduced colorless intermediate 6 was separated from the zinc
powder by filtration through a pad of Celite and added drop-
wise to a solution of 4 (61 mg, 260 μmol) in AcOH (1.5 mL) over
2
2
2
2
1
product as a yellow solid in 56% yield. H NMR (500 MHz,
1
h. A yellow precipitate immediately formed. The solution was
CD Cl ): δ = 7.51 (dd, J = 5.4, 3.2 Hz, 8 H), 7.14 (ddd, J = 8.6, 6.5,
2
2
stirred for another 1 h and extracted several times with CH Cl
2.4 Hz, 12 H), 6.72 (td, J = 7.3, 1.2 Hz, 4 H), 6.54 (ddd, J = 8.7, 7.2,
1.7 Hz, 4 H), 6.37 (dd, J = 8.4, 1.2 Hz, 4 H), 5.61 (s, 4 H), 3.67 (s, 8
H) ppm. ESI-HRMS: m/z [M + H] = 921.3700; found: 921.3703.
2
2
(20 mL) until the organic phase was colorless. The combined
+
organic layers were washed with an aq NaHCO3 solution (100
mL) and water (100 mL). After evaporation of the solvent, the
crude product was purified via column chromatography (SiO2,
hexane–CH Cl = 3:1 → 0:1). The product (7, 65 mg, 93.8 μmol,
(39) Preparation of Compound 15
Compound 7 (20 mg, 28.9 μmol), Pd(PPh ) (6.4 mg, 5.54 μmol),
3
4
and CuI (1.0 mg, 5.25 μmol) were suspended in THF–Et N (1:1,
2
2
3
1
7
2%) was obtained as a yellow powder. H NMR (400 MHz,
1.5 mL). After degassing with argon for 15 min, TIPS acetylene
(150 μL, 578 μmol) was added, and the resulting reaction
mixture was stirred at 50 °C for 60 h. The green luminescent
reaction mixture was quenched by addition of water (5 mL) and
extracted three times with CH Cl (10 mL). The combined
CDCl ): δ = 7.59 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 4 H, CH), 7.17 (dd, J3
3
=
5.4 Hz, J4 = 3.2 Hz, 4 H, CH), 5.84 (s, 4 H, CH) ppm.
(
37) Preparation of Compounds 8–13 (GP1)
A Schlenk flask was filled with 7 (10 mg, 14.4 μmol), arylbo-
ronic acid (2.2 equiv, 31.7 μmol), and K PO (12.3 mg, 57.8
2
2
organic layers were dried over MgSO , and the solvent was
3
4
4
μmol), evacuated, and purged with argon. A mixture of water–
toluene–1,4-dioxane (1:1.8:5.5, 0.5 mL) was added, and the
resulting suspension degassed with argon for 15 min. Subse-
quently, Pd (dba) (0.4 mg, 0.437 μmol) and P(o-tol)3 (1.1 mg,
evaporated under reduced pressure. The crude was purified by
column chromatography (SiO , hexane–CH Cl = 4:1 to 1:2).
2
2
2
Compound 15 (15 mg, 57%) was obtained as a yellow solid. 1
H
NMR (400 MHz, CDCl ): δ = 7.54 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 8H,
2
3
3
3
.61 μmol) were added, and the reaction was heated to 60 °C for
CH), 7.14 (dd, J3 = 5.4 Hz, J4 = 3.2 Hz, 8 H, CH), 5.60 (s, 4 H, CH),
13
14 h. Upon full conversion of the starting material, the reaction
1.34 (s, 36 H, CH ), 1.26 (s, 6 H, CH) ppm. C NMR (100 MHz,
3
was diluted with CH Cl (10 mL) and washed with water (15
CDCl ): δ = 157.7, 141.7, 140.2, 127.0, 125.4, 121.3, 107.6, 55.4,
19.1, 11.9 ppm. ESI-HRMS: m/z [M + H] : 895.4586; found:
2
2
3
+
mL) three times. The organic phase was dried over MgSO , the
4
solvent evaporated under reduced pressure, and the crude puri-
895.4566.
fied by column chromatography (SiO , gradient of hexane–
2
CH Cl ).
2
2
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–G