Full Papers
doi.org/10.1002/ejoc.202100199
was added portionwise. The reaction was vigorously stirred at 0°C
CHCl (3x50 mL). The organic phases were reunited and dried over
3
for 3 h, then it was allowed to reach room temperature and stirred
for an additional 6 h. The mixture was cooled down in the freezer
anhydrous Na SO , filtered and the solvent evaporated under
2
4
reduced pressure. The crude was purified by flash chromatography
(gradient: from petroleum ether 90% - DCM 10%, to petroleum
(
-20°C) to allow the formation of a precipitate, that was filtered
through a fritted funnel. The solid residue was washed with cold
acetonitrile (100 mL) and cold diethyl ether (100 mL), obtaining
compound 5 as a pale grey solid (4.4 g). Note: while the
ether 85% – DCM 15%) to give compound 9 as a bright yellow
1
solid (1.8 g, 85% yield). H NMR (400 MHz, THF-d ): δ= 7.34 (s, 1H),
8
7.15 (t, J=7.7 Hz, 2H), 7.12-6.96 (m, 17H), 6.83 (d, J=8.6 Hz, 2H),
[22]
13
corresponding free amine of derivative 5 is prone to oxidation,
6.79 (d, J=8.8 Hz, 2H), 6.76 (t, J=7.5 Hz, 1H). C NMR (100 MHz,
the diammonium salt 5 is stable and could be stored in the freezer
THF-d ): δ= 145.2, 145.0, 144.9, 144.1, 143.3, 141.8, 140.2, 135.7,
8
1
for months. H NMR (400 MHz, DMSO-d ): δ= 7.09 (s, 2H), 5.19 (bs,
132.9, 132.1, 132.04, 132.01, 129.5, 128.2, 128.11, 128.11, 126.8,
6
+
+
6
H). MS (ESI) m/z: 114.96 [M+H] . Spectroscopic data are in
126.7, 126.65, 120.7, 118.2, 116.2. MS (ESI) m/z: 424.18 [M+H] .
[
14]
agreement with those reported in the literature.
4
-Bromo-N-phenyl-N-(4-(1,2,2-triphenylvinyl)phenyl)aniline
(2):
[
14]
2
,3-Diphenylthieno[3,4-b]pyrazine (1a): In a round bottom flask,
Pd(OAc) (48 mg, 0.21 mmol) and Xantphos (184 mg, 0.318 mmol)
2
diammonium salt 5 (500 mg, 2.67 mmol) and benzil (diphenyletha-
nedione) 6a (590 mg, 2.80 mmol) were suspended in an EtOH:DCM,
were added to a Schlenk tube and put under inert atmosphere by
performing three vacuum-nitrogen cycles. The solids were then
dissolved in dry toluene (85 mL) and the solution was stirred for 5
minutes. Then 1-bromo-4-iodobenzene 10 (720 mg, 2.54 mmol), N-
phenyl-4-(1,2,2-triphenylvinyl)aniline 9 (900 mg, 2.12 mmol) and
caesium carbonate (4.82 g, 14.8 mmol) were added in the order
and the reaction was stirred at 80°C for 20 h. The reaction was
1
:1 mixture (27 mL), then triethylamine (1.50 mL, 10.7 mmol) was
added and the reaction stirred at 50°C for 5 h. Complete conversion
was assessed by TLC monitoring (petroleum ether:EtOAc, 1:1).
Water (40 mL) was added to the reaction and the mixture extracted
with EtOAc (3x30 mL). The reunited organic phases were dried over
anhydrous Na SO , the solution was filtered, and the solvent was
allowed to cool down to room temperature, water (300 mL) was
2
4
evaporated under reduced pressure. The crude was purified by
flash chromatography (gradient: from petroleum ether:EtOAc, 20:1
added, and the mixture extracted with CHCl (3x150 mL). The
3
organic phases were reunited and dried over anhydrous Na SO ,
2
4
to 10:1) to give pure 1a as a yellow solid (464 mg, 60% yield over
filtered and the solvent evaporated under reduced pressure. The
crude was purified by flash chromatography (gradient: from
petroleum ether 98% – DCM 2%, to petroleum ether 90% - DCM
1
2
steps). H NMR (400 MHz, CDCl ): δ= 8.07 (s, 2H), 7.46–7.42 (m,
3
4
H), 7.38–7.28 (m, 6H); Spectroscopic data are in agreement with
[
14]
those reported in the literature.
10%) to give compound 2 as a bright yellow solid (1.17 g, 96%
1
yield). H NMR (400 MHz, THF-d ): δ=7.33 (d, J=8.9 Hz, 2H), 7.23 (t,
[
14]
8
Thieno[3,4-b]pyrazine (1b): In a round bottom flask, diammo-
nium salt 5 (381 mg, 3.33 mmol) was dissolved in a Na CO aqueous
J=7.8 Hz, 2H), 7.16–6.97 (m, 18H), 6.89 (dd, J=8.8, 2.1 Hz, 4H), 6.76
2
3
13
(
d, J=8.6 Hz, 2H). C NMR (100 MHz, THF-d ): δ= 148.0, 147.8,
8
solution (5% w/w, 18 mL), followed by the addition of glyoxal 6b
358 mg, 6.17 mmol) as a 0.65 M aqueous solution, prepared by
1
1
1
46.4, 144.8, 144.5, 144.2, 141.7, 141.4, 139.5, 133.0, 132.7, 131.99,
31.95, 131.93, 130.0, 128.3, 128.20, 128.19, 127.1, 127.02, 126.95,
25.9, 125.2, 124.0, 123.7, 115.3. MS (ESI) m/z: 577.17 [M] .
(
diluting 895 mg of a 40% wt glyoxal solution in water to 9.5 mL.
The reaction was stirred at room temperature overnight, then
poured in an extraction funnel and extracted with diethyl ether
+
General Procedure for the synthesis of TPa-c dyes: The pyrazine
derivative 1 (0.05 mmol), 4-bromo-N-phenyl-N-(4-(1,2,2-triphenyl-
(7x30 mL). The reunited organic phases were dried over anhydrous
Na SO , the solution was filtered, and the solvent was evaporated
vinyl)phenyl)aniline
2 (86.8 mg, 0.150 mmol), and potassium
2
4
under reduced pressure to give crude 1b as a brownish solid
357 mg), which was judged pure enough to be used in the next
carbonate (20.8 mg, 0.150 mmol) were added to a Schlenk tube
and put under inert atmosphere by performing three vacuum-
nitrogen cycles. The solids were dissolved in dry DMF (620 μL) and
(
1
synthetic step without further purification. H NMR (200 MHz,
CDCl ): δ= 8.52 (s, 2H), 8.05 (s, 2H). Spectroscopic data are in
agreement with those reported in the literature.
a solution of Pd(OAc) (0.56 mg, 2.50 μmol), tricyclohexylphospho-
nium tetrafluoroborate (1.84 mg, 5.00 μmol) and pivalic acid
3
2
[
14]
(
1.54 mg, 15.0 μmol) in DMF (100 μL) was added. Unless otherwise
[
14]
2
,3-Dimethylthieno[3,4-b]pyrazine (1c): In a round bottom flask,
stated, the reaction was stirred at 100°C for 20 h, then was allowed
diammonium salt 5 (500 mg, 2.67 mmol) and 2,3-butanedione 6c
253 mg, 2.94 mmol) were suspended in a EtOH:DCM, 2:1 mixture
40 mL), then triethylamine (1.5 mL, 10.68 mmol) was added and
the reaction stirred at 50°C for 16 h. Water (50 mL) was added to
the reaction and the mixture extracted with EtOAc (3x30 mL). The
reunited organic phases were dried over anhydrous Na SO , the
to cool down to room temperature, water (30 mL) was added, and
(
(
the mixture extracted with CHCl (3x10 mL). Reunited organic
3
phases were dried over anhydrous Na SO , the solution filtered, and
2
4
the solvent evaporated under reduced pressure. The crude was
purified by flash chromatography to give the corresponding TP
compound.
2
4
solution was filtered, and the solvent was evaporated under
reduced pressure to give crude 1c as a tan solid (354 mg), which
4,4’-(2,3-Diphenylthieno[3,4-b]pyrazine-5,7-diyl)bis(N-phenyl-N-
(4-(1,2,2-triphenylvinyl)phenyl)aniline) (TPa): Prepared following
the general procedure using 2,3-diphenylthieno[3,4-b]pyrazine 1a
(14.4 mg, 50.0 μmol). The reaction was stirred at 100°C for 30
was judged pure enough to be used in the next synthetic step
1
without further purification. H NMR (200 MHz, CDCl ): δ= 7.79 (s,
3
2
H), 2.62 (s, 6H). Spectroscopic data are in agreement with those
[14]
reported in the literature.
minutes, then was allowed to cool down to room temperature and
directly purified by flash chromatography (gradient: from petro-
leum ether 90% - DCM 10%, to petroleum ether 70%–DCM 30%)
[15]
N-Phenyl-4-(1,2,2-triphenylvinyl)aniline (9):
To a Schlenk tube
under nitrogen atmosphere, Pd (dba)3 (64 mg, 0.070 mmol) was
1
2
to give compound TPa as a dark blue solid (65.0 mg, quant.). H
added and dissolved in dry toluene (30 mL), followed by the
addition of tri-tert-butylphosphine (20 μL, 0.080 mmol) and (2-(4-
bromophenyl)ethene-1,1,2-triyl)tribenzene 7 (2.1 g, 5.0 mmol). The
mixture was stirred for 10 minutes, then aniline 8 (59 μL, 6.5 mmol)
and sodium tert-butoxide (625 mg, 6.50 mmol) were added and the
reaction stirred at 120°C for 20 h. Then the reaction was cooled
NMR (400 MHz, THF-d ): δ= 8.25 (d, J=8.6 Hz, 4H), 7.52 (d, J=
8
7
8
.1 Hz, 4H), 7.35–7.22 (m, 10H), 7.18–6.98 (m, 40H), 6.92 (d, J=
13
.4 Hz, 4H), 6.85 (d, J=8.5 Hz, 4H). C NMR (100 MHz, THF-d ; two
8
signals are overlapped): δ= 153.0, 148.0, 147.9, 146.4, 144.8, 144.5,
1
1
1
44.3, 141.7, 141.5, 140.5, 139.5, 139.2, 133.0, 132.02, 131.97, 130.6,
30.5, 130.0, 129.2, 128.9, 128.6, 128.4, 128.3, 128.22, 128.21, 127.1,
27.0, 125.5, 124.1, 124.0, 123.7. HRMS (ESI): m/z calcd for
down to room temperature, concentrated under reduced pressure,
water (100 mL) was added and the mixture was extracted with
+
+
C H N S : 1282.50027 [M] ; found: 1282.49963.
9
4
66
4
Eur. J. Org. Chem. 2021, 2655–2664
2662
© 2021 Wiley-VCH GmbH