Vertically-expanded imidazo[1,2-a]pyridines and imidazo[1,5-a]pyridine via dehydrogenative coupling

Article abstract of DOI:10.1039/c4ob02383h

The anion-radical coupling of structurally diverse series of aromatic compounds possessing biaryl linkages led to seven fused, polycyclic heterocycles in reasonable yields. The yield of the key step (K, toluene, O₂) depends on both electronic and steric factors. The whole strategy consists of just two steps starting from an unsubstituted imidazo[1,2-a]pyridine, giving target compounds in an overall yield of 4-34%. The same strategy also works for derivatives of imidazo[1,5-a]pyridine. A new process has been discovered for such vertically-expanded imidazo[1,2-a]pyridines, consisting of a sequential Diels-Alder reaction followed by a retro-Diels-Alder reaction. The optical properties of the library of π-expanded imidazo[1,2-a]pyridines were for the first time fully characterized, showing that fluorescence quantum yields are significantly lower than for the singly-linked compounds.

Full text of DOI:10.1039/c4ob02383h

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Vertically-expanded imidazo[1,2-a]pyridines and
imidazo[1,5-a]pyridine via dehydrogenative
coupling
Cite this: DOI: 10.1039/x0xx00000x
Dikhi Firmansyah,a Marzena Banasiewiczb and Daniel T. Gryko*a,c
Received 00th January 2012,
Accepted 00th January 2012
Anion-radical coupling of structurally diverse series of aromatic compounds possessing biaryl
linkages led to seven fused, polycyclic heterocycles in reasonable yields. The yield of the key step
(K, toluene, O2) depends on both electronic and steric factors. The whole strategy consists of just
two steps starting from unsubstituted imidazo[1,2-a]pyridine, giving target compounds in overall
yield 4-34%. The same strategy also works for derivative of imidazo[1,5-a]pyridine. New process
has been discovered for such vertically-expanded imidazo[1,2-a]pyridines, consisting of sequential
Diels-Alder reaction followed by retro-Diels-Alder reaction. The optical properties of the library of
DOI: 10.1039/x0xx00000x
www.rsc.org/
π
-expanded imidazo[1,2-a]pyridines were for the first time fully characterized, showing that
fluorescence quantum yields of are significantly lower that for the singly-linked compounds.
place, shifting it from C3 to C5, as well as the position of
nitrogen in imidazopyridine.
Introduction
The recent renaissance in the chemistry of polycylic aromatic
hydrocarbons is overwhelmingly visible in the literature.1 New,
previously unthinkable architectures were brought to light such
as corranulene,2 sumanene,3 inherently chiral polycyclic imides,4
dicyclopenta[de,mn]tetracenes5 and cycloparaphenylenes.6
Synthetic methodology leading to these new carbon-rich
compounds is also constantly evolving.7 On the contrary the
chemistry of their heterocyclic counterparts is far less developed.
While heterocyclic analogs acenes are known,8 aza-rylenes are
far less ubiquitous.9
Recently we revealed that 3-(naphthalen-1-yl)-imidazo[1,2-
a]pyridine can be synthesized from singly-linked precursor by
anion-radical coupling10 in 63% yield.11 Since anion-radical
coupling is relatively weakly studied reaction (Scheme 1), we
wondered if this methodology can be expanded to its analogs
possessing other aromatic units instead of naphthalene. This
would allow us to study relationship between structure of
substrates and efficiency of this reaction. The second aim of this
study was to gain further insight into trends in optical properties
of such previously unknown fused heterocyclic compounds.
Scheme 1 The mechanism of anionic cyclodehydrogenation of 1,1'-binaphthyl as
proposed by Scott and co-workers.10d
For the construction of necessary substrates we decided to follow
the same pathway as before i.e. direct arylation of imidazo[1,2-
a]pyridine with bromoarenes. Although many conditions were
recently published, which allow to carry out this transformation
in good yields,12 the best protocol was revealed by Doucet and
co-workers with low loading of simple palladium salts and
Results and discussion
Given the multiple aims of this investigation, we designed small
but diverse library of substrates bearing imidazo[1,2-a]pyridine
as ‘Northern Half’ of the molecule and analogs of naphthalene at
‘Southern Half’. Electronically similar (phenanthrene and
anthracene) as well as structurally similar but electronically
different units (naphthalene-imide and benzo[h]quinoline) have
been chosen as ‘Southern Half’. We also modified the linkage
without any ligand.13 Direct arylation of unsubstituted
14
imidazo[1,2-a]pyridine (
1
)
with bromoarenes 2a-d led to
products 3a-3d in 50-83% (Scheme 2).
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Our attempt to perform direct arylation with 1-iodonaphthalene
led to compound in moderate yield (32%, Scheme 4).
8
Scheme 4 The synthesis of compounds
8 and 9.
The key difference between 3-(naphthalen-1-yl)-imidazo[1,2-
a]pyridine and the corresponding anthracenyl compound 3a is
an additional steric hindrance, which has to be overcome during
fusion. Consequently, it came with no surprise that anion-radical
coupling, performed under previously optimized conditions,11
led to compound 10a in 12% yield only (Scheme 5).
Scheme 2 The synthesis of 3-substituted imidazo[1,2-a]pyridines.
Required substrate 2c was prepared by modified Skraup
reaction,15 while compound 2d was obtained via imidation of
anhydride of 4-bromonaphthalene-1,4-dicarboxylic acid with 1-
octylamine.16
Scheme 3 Suzuki reaction leading to 5-aryl-imidazo[1,2-a]pyridines 5a,b
.
Scheme 5 Anion-radical coupling leading to compounds 10a-d
.
Intriguing question was if anion-radical coupling would work if
position C-3 of the heterocyclic core (the most electron-rich one)
is unsubstituted. Consequently, 5-substituted two imidazo[1,2-
a]pyridines were prepared via Suzuki-Miyaura coupling from
boronic acid pinacol esters 4a,b, derived from naphthalene and
Stability of intermediate radical-anions increases when reacting
unit is more electron-deficient.10 As a result, we expected higher
yield of coupling in case of compound 3c vs. substrate 3b. Yet,
structurally analogous derivatives of phenanthrene and
benzo[h]quinoline (3b and 3c) afforded corresponding products
10b and 10c in similar yield (~30%). Yields of fused
heterocycles 10b and 10c were the same regardless if reactions
were performed under air or under oxygen. Unfortunately,
despite thorough optimization, the anion-radical coupling of
derivative 3d led to the formation of compound 10d in a low
yield (Scheme 5). Intriguingly, in this particular case, the yield
of compound 10d was higher if the first step of reaction was
phenathrene (Scheme 3).17 The key substrate i.e. compound 2e
,
was obtained via condensation of 2-amino-6-bromopyridine and
2-chloroacetaldehyde.18 Suzuki coupling was conducted
following known procedure utilizing palladium catalyst.19
In analogy to imidazo[1,2-a]pyridine, C3 at imidazo[1,5-
a]pyridine (6) also possesses the highest reactivity in direct
arylation.20 Murai and co-workers have shown that double direct
arylation can take place in case of this heterocyclic compound.21
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Scheme 7 The synthesis of diester 12 via Diels-Alder reaction.
performed under argon. Groups of Müllen and Swager have
shown that if naphthalene-1,8-carboxyimide is present in the
molecule as one of reacting sites, conditions for dehydrogenative
coupling do not have to be so strong and they can include weaker
bases such as i.e. K2CO3 and DBN/t-BuONa, still leading to
corresponding fused products in good yields.23,24 Attempts to
perform transformation of imide 3d into 10d following these
alternative procedures,23,24 failed.
According to our predictions based on relative stability of
various anion-radicals, coupling of 5-substituted imidazo[1,2-
a]pyridines led to expected products 11a and 11b in lower yields
than in the case of cyclization of their 3-substituted analogs
Careful analysis of the product revealed that instead of expected
Diels-Alder reaction at bay position, process led to π-expanded
indolizine 12 (Scheme 7). The only imaginable rationale behind
this reaction is Diels-Alder reaction at imidazole moiety
followed by retro-Diels-Alder reaction with elimination of HCN.
The overall pathway is quite effective leading to ester 12 in 47%
yield. It is worth to note that vertically-expanded indolizines are
unknown in the literature. Analogous process, albeit in lower
yield, was observed in case of compound 10c (Scheme 8).
Diester 13 was obtained in 22% yield. This reaction resembles
transformation of N-benzoylpyrrole into dimethyl N-benzoyl-
pyrrole-3,4-dicarboxylate upon reaction with DMAD and
elimination of acetylene.26
(Scheme 6). Regioisomeric imidazo[1,5-a]pyridine
8 has been
coupled in the same manner as 3-(naphthalen-1-yl)imidazo[1,2-
a]pyridine under air to give heterocycle
9 in 52% yield (Scheme
4).
Scheme 8 The synthesis of ester 13
.
The successful synthesis of small library of novel aza-
heterocycles and their π-expanded analogs gave us an excellent
opportunity for measuring their photophysical properties for the
first time (Table 1, Fig. 1). While heterocycles 3a-d and 5a,b
absorb mainly UV-radiation and emit violet light, absorption of
fused compounds is bathochromically shifted and they emit
green light. The exception is 3d which has emission maximum
at 513 nm (Table 1). In analogy to what has been noticed
Scheme 6 Anion-radical coupling leading to compounds 11a,b
.
An important phenomenon to be investigated was reactivity of
synthesized compounds. It is well-known that perylene
undergoes Diels Alder reaction with maleic anhydride or
dimethyl acetylenedicarboxylate (DMAD) at its bay region.25
The initially attempted reaction of 11a with maleic anhydride
failed, but to our delight compound 11a reacted with DMAD.
before,11 single-linked heterocycles 3a
-d and 5a-d possess
relatively high fluorescence quantum yield (Фfl) and large Stokes
shifts (up to 12300 cm-1 for compound 5a). After intramolecular
dehydrogenative coupling, although dyes become flat (i.e. with
lower probability for free rotation) Фfl dropped significantly to
0.08-0.5% (Table 1). Regioisomeric 10b and 11b differ
significantly in optical properties. Although their absorption and
emission maxima are located at the same regions, the Фfl for
compound 11b is almost ten times higher than for 10b. π-
Expanded indolizine 12 possessed similar properties to that of
dyes 10a-d and 11a,b. The Stokes shifts for fused compounds
9,
10a 11a,b
-
d
,
,
12 and 13 are rather low (400-2400 cm-1). Previous
studied clearly showed that imidazo[1,5-a]pyridines are less
emissive than imidazo[1,2-a]pyridines.27 The same trend is
visible for their π-expanded analogs
9 and 11a. The fluorescence
quantum yield of 11a is 10 times higher than for
9
.
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Materials. All commercially available compounds were used as
Table 1 Spectroscopic properties of compounds 3-12.a
received. All solvents were dried and distilled prior to use.
Transformation and oxygen sensitive compounds were
performed under argon atmosphere. The reaction progress was
monitored by means of thin layer chromatography (TLC) which
was performed on aluminum sheets, coated with silica gel 60 F254
(Merck) with detection by UV-Lamp. Product purification was
performed by column chromatography on silica (flash P 60, 40–
63 mm, SiliCycle), and dry column vacuum chromatography
(DCVC) on silica (MN-Kieselgel P/UV254) or aluminum oxide
(MN-Aluminumoxid G). Identity and purity of prepared
compounds were proved by 1D NMR (1H NMR and 13C NMR)
and 2D NMR (COSY) (on Varian 500 MHz). High-resolution
mass spectra (EI, and ESI) were obtained on MaldiSYNAPT G2-
S HDMS/GCT Premier, Waters. Melting points were measured
with Ez-Melt, SRS and were given without correction.
Compd.
Absmax (nm)
Emissionmax
(exc.)(nm)
(387) 449
(315) 407
(315) 408
(408) 513
(315) 435
(300) 413
(336) 438
(410) 556
(553) 579
(397) 537
(397) 490, 527
(536) 598
(435) 522, 562
Stokes shift
(cm-1)
3500
7700
4100
5100
12300
9100
6900
2000
840
Фflb (%)
3a
3b
3c
3d
5a
5b
8
9
10a
10b
10c
10d
11ac
369, 388
298, 310
318, 333, 349
406
23
45
47
24
22
29
7
0.5
0.08
0.6
8.0
2.5
5
283
300
336
436, 472, 499
552
376, 397, 449, 476
357, 377, 396
536, 574
396, 418, 450, 479,
511
407, 432, 457, 486
428, 454, 483, 516
391, 415, 455, 485
2400
4800
700
400
11b
12
13
(407) 506, 535
(407) 536
(417) 544
800
700
2200
3
2.5
1.3
a measured in DCM. b measured with perylene or quinine sulfate in H2SO4, as a
standard. c published data (in cyclohexane).11
General procedure of direct arylation. Imidazo[1,2-a]pyridine
1
(1.5 mmol), aryl bromide 2a-e (1 mmol) and KOAc (2 mmol)
were reacted in DMAc (4 mL) in the presence of Pd(OAc)2
(0.224 mg, 0.001 mmol, 0.1 mol%) at 150 °C, overnight under
Ar. Upon completion the mixture directly absorbed into celite
and purified as follows:
3-(Anthracen-9-yl)imidazo[1,2-a]pyridine (3a); Compound 1
(0.15 mL, 1.5 mmol), 9-bromoantracene (2a, 257 mg, 1 mmol),
KOAc (200 mg, 2 mmol). The resulting mixture was purified by
DCVC on SiO2 (1% MeOH in CH2Cl2) to affords off-white solid
1
(173 mg, 54%). H NMR (500 MHz, CDCl3): δ = 8.65 (s, 1 H),
8.11 (d, J = 8.5 Hz, 2 H), 7.92 (s, 1 H), 7.84 (dd, J1 = 9.5 Hz, J2
= 1 Hz, 1 H), 7.55 – 7.49 (m, 4 H), 7.41 – 7.38 (m, 2H), 7.34 (dd,
J1 = 7 Hz, J2 = 1 Hz, 1 H), 7.26 (dt, J1 = 6.5 Hz, J2 = 1.5 Hz, 1
H), 6.65 (dt, J1 = 6.5 Hz, J2 = 1.5 Hz, 1 H). Other properties
concur with published data.13
3-(Phenanthren-9-yl)imidazo[1,2-
a]pyridine (3b); Compound
1
(0.15 mL, 1.5 mmol), 9-bromophenanthrene (2b, 257 mg, 1
mmol), KOAc (200 mg, 2 mmol). The resulting mixture was
purified by DCVC on SiO2 (60% EtOAc in hexanes) and
recrystallized (aceton) to affords white crystal (195 mg, 66%),
1
mp. 180-181°C. H NMR (500 MHz, CDCl3): δ = 8.82 (d, J =
Fig. 1 Absorption (solid line) and normalized fluorescence (dotted line) spectra of
8.8 Hz, 1 H), 8.77 (d, J = 8.3 Hz, 1 H), 7.93 (dd, J1 = 7.8 Hz, J2
= 1.5 Hz, 1 H), 7.91 (s, 1 H), 7.87 (s, 1 H), 7.78 – 7.65 (m, 5 H),
7.52 (m, 2 H), 7.24 (ddd, J1 = 9.3 Hz, J2 = 6.8 Hz, J3 = 1.4 Hz, 1
H), 6.72 ppm (td, J1 = 8.3 Hz, J2 = 1.4 Hz, 1 H); 13C NMR (126
MHz, CDCl3): δ = 146.0, 134.1, 131.4686, 130.9, 130.9, 130.8,
130.7, 127.8, 127.4, 127.3, 127.3, 126.2, 125.2, 124.5, 124.4,
123.9, 123.4, 123.4, 122.8, 118.2, 112.5 ppm; HRMS (EI): m/z
(M+) calcd for C21H14N2: 294.1157; found: 294.1157.
9
(blue) and 10d (red) measured in DCM.
Conclusions
It was proved that intramolecular anion-radical coupling is a
general strategy for the synthesis of heterocyclic analogs of
2a1H-benzo[hi]aceanthrylene possessing imidazo[1,2-a]pyridine
or imidazo[1,5-a]pyridine subunits. The reaction occurs in
presence of oxygen from air and yields the previously unknown
π-expanded systems in moderate efficiency. If electron density
at fusion position is higher the yields of anion-radical coupling
are lower. Fusion of imidazo[1,2-a]pyridine with naphthalene
alters its reactivity against dimethyl acetylenedicarboxylate –
imidazole moiety behaves like azabutadiene. Fusion of
imidazopyridine moiety in vertical manner leads to green-
emitting π-expanded compounds possessing low fluorescence
quantum yield.
6-(Imidazo[1,2-
a
]pyridin-3-yl)-2-methylbenzo[
h]quinoline
(3c); Compound
1
(0.6 mL, mmol), 6-bromo-2-
6
methylbenzo[h]quinoline 2c (1.09 g, 4 mmol), KOAc (800 mg,
8 mmol). The resulting mixture was purified by DCVC on SiO2
(1% MeOH in CH2Cl2) to afford off-white crystals (1.03 g, 83%),
mp. 180-181°C. 1H NMR (500 MHz, CDCl3): δ = 9.48 (dd, J1 =
8.3 Hz, J2 = 1 Hz, 1 H), 8.08 (d, J = 7.8 Hz, 1 H), 7.86 (s, 1 H),
7.81 (s, 1H), 7.77 – 7.71 (m, 3 H), 7.59 (ddd, J1 = 8.3 Hz, J2 =
6.8 Hz, J3 = 1.4 Hz, 1 H), 7.49 (d, J = 7.8 Hz, 1 H), 7.45 (d, J =
8.3 Hz, 1 H), 7.24 (ddd, J1 = 9.3 Hz, J2 = 6.8 Hz, J3 = 1 Hz, 1 H),
6.71 (td, J1 = 6.8 Hz, J2 = 1 Hz, 1 H), 2.88 ppm (s, 3 H); 13C
NMR (126 MHz, CDCl3): δ = 159.0, 146.4, 146.1, 136.3, 134.2,
132.3, 131.9, 129.0, 128.7, 127. 4, 125.4, 125.3, 125.1, 124.5,
124.4, 123.7, 122.8, 118.3, 112.5, 25.7 ppm; HRMS (EI): m/z
(M+) calcd for C21H15N3: 309.1266; found: 309.1261.
Experimental section
General synthetic information.
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MeOH in CH2Cl2) and followed by second DCVC on Al2O3 (5%
6-(Imidazo[1,2-
benzo[de]isoquinoline-1,3(2
mL,
a
]pyridin-3-yl)-2-octyl-1
H-
H
)-dione (3d); Compound
1
(0.3 EtOAc in hexanes) to afford off-white solid (159 mg, 32%), mp.
3
mmol), 6-(imidazo[1,2-a]pyridin-3-yl)-2-octyl-1H- 134°C. 1H NMR (500 MHz, CDCl3): δ = 7.99 (d, J = 8.3 Hz, 1
benzo[de]isoquinoline-1,3(2H)-dione 2d (776 mg, 2 mmol), H), 7.95 (d, J = 8.3 Hz, 1 H), 7.75 – 7.67 (m, 4H), 7.61 (dd, J1 =
KOAc (393 mg, 4 mmol). The resulting mixture was purified by 8.3 Hz, J2 = 6.8 Hz, 1 H), 7.56 – 7.52 (m, 2H), 7.46 (m, 1H), 6.75
DCVC
on
Al2O3
(CH2Cl2)
and
recrystallized (m, 1H), 6.46 ppm (td, J1 = 7.3 Hz, J2 = 1 Hz, 1 H); 13C NMR
(cyclohexane/EtOAc) to affords yellow crystals (424 mg, 50%), (126 MHz, CDCl3): δ = 134.0, 131.9, 131.1, 129.8, 128.5, 127.4,
1
mp. 145-147°C. H NMR (500 MHz, CDCl3): δ = 8.71 (d, J = 126.9, 126.9, 126.3, 125.6, 125.3, 121.8, 120.3, 118.8, 118.6,
7.3 Hz, 1 H), 8.67 (dd, J1 = 7.3 Hz, J2 = 1 Hz, 1 H), 8.10 (dd, J1 112.6 ppm; HRMS (ESI): m/z ([M+H]+) calcd. for C17H13N2:
= 8.6 Hz, J2 = 1 Hz, 1 H), 7.93 (dd, J1 = 7.8 Hz, J2 = 1 Hz, 1 H), 245.1075; found: 245.1069.
7.90 (d, J = 7.3 Hz, 1 H), 7.89 (s, 1 H), 7.80 (dt, J1 = 9.3 Hz, J2
General procedure for anion radical coupling (9, 10a-d,
= 1 Hz, 1 H), 7.74 (dd, J1 = 8.3 Hz, J2 = 7.3 Hz, 1 H), 7.32 (ddd, 11a,b); Imidazopyridine derivative (0.1 mmol) was dissolved in
J1 = 9.3 Hz, J2 = 6.9 Hz, J3 = 1 Hz, 1 H), 6.85 (dd, J1 = 6.8 Hz, dry toluene (1.5 mL) under argon atmosphere in a Schlenck
J2 = 1.4 Hz, 1 H), 4.21 (t, J = 7.8, 2 H), 1.76 (m, 2 H), 1.47 – 1.25 flask. Potassium was then added and the mixture was degassed
(m, 10 H), 0.88 ppm (t, J = 7 Hz, 3 H); 13C NMR (126 MHz, backfill with Ar. The reaction mixture then stirred at 95 °C for
CDCl3): δ = 164.1, 163.9, 146.8, 135.4, 133.0, 131.8, 131.7, 30 minutes under Ar flows with condensator attached.
131.0, 130.4, 129.1, 128.7, 127.8, 123.8, 123.5, 123.2, 121., Subsequently air/oxygen in a balloon introduced and stirred at
118.6, 113.4, 40.8, 32.0, 29.5, 29.4, 28.3, 27.9, 22.8, 14.2 ppm; the same temperature for one day, quenched by EtOH under Ar,
HRMS (ESI): m/z ([M+H]+) calcd for C27H28N3O2: 426.2182; and directly absorbed onto celite. Product was purified as
found: 426.2185.
follows:
Imidazo[2,1,5-de]naphtho[1,8-ab]quinolizine (9); Compound
5-(Naphthalen-1-yl)imidazo[1,2-
a
]pyridine (5a); 4,4,5,5-
8 (49.7 mg, 0.2 mmol), K (39 mg, 1 mmol), and toluene (3 mL)
Tetramethyl-2-(naphthalen-1-yl)-1,3,2-dioxaborolane (4a, 400 were reacted under air. Reaction mixture was pre-purified by
mg, 1.56 mmol) and Pd(PPh3)4 (92 mg, 0.08 mmol) were stirred DCVC on SiO2 (1% MeOH in CH2Cl2) followed by column
in DME (6 mL) at rt under Ar. To this mixture compound 2e (307 chromatography on SiO2 (1% TEA and 15% EtOAc in
mg, 1.56 mmol), EtOH (4 mL), and saturated aqueous Na2CO3 cyclohexane) to afford yellowish-red solid (24.8 mg, 52%), mp.
(4 mL) were added subsequently. The mixture were refluxed at 175-179°C. 1H NMR (500 MHz, CDCl3): δ = 7.93 (d, J = 7.3 Hz,
110 °C for 17 h, cooled and extracted with CH2Cl2/saturated 1 H), 7.73 (d, J = 7.3 Hz, 1 H), 7.58 (d, J = 8.2 Hz, 1 H), 7.45 (d,
NaHCO3. The organic fraction were collected and solvent J = 8.1 Hz, 1 H), 7.40 – 7.32 (m, 3 H), 7.20 (d, J = 9.0 Hz, 1 H),
evaporated. The resulting mixture were purified by DCVC on 7.02 (d, J = 7.0 Hz, 1 H), 6.73 ppm (dd, J1 = 9.0 Hz, J2 = 6.9 Hz,
Al2O3 (15% EtOAc in hexanes) to afford white solid (345 mg, 1 H); 13C NMR (126 MHz, CDCl3): δ = 135.9, 135.2, 133.3,
1
90%), mp. 149-150°C. H NMR (500 MHz, CDCl3): δ = 8.04 131.7, 130,0 128.5, 127.6, 126.4, 126.3, 125.8, 122.2, 119.0,
(dd, J1 = 6.4 Hz, J2 = 3.4 Hz, 1 H), 7.97 (d, J = 8.3 Hz, 1 H), 7.74 117.9, 117.2, 107.3 ppm; HRMS (ESI): m/z ([M+H]+) calcd. for
(d, J = 8.8 Hz, 1 H), 7.64 – 7.60 (m, 2 H), 7.56 – 7.53 (m, 2 H), C17H11N2: 243.0922; found: 243.0919.
7.41 (m, 1 H), 7.35 – 7.32 (m, 2 H), 6.98, (s, 1 H) 6.89 ppm (d, J
Anthra[1,9-ab]imidazo[5,1,2-de]quinolizine
(10a);
= 6.8 Hz, 1 H); 13C NMR (126 MHz, CDCl3): δ = 146.1, 137.1, Compound 3a (59 mg, 0.2 mmol), K (78 mg, 2 mmol) were
133.8, 133.5, 131.8, 130.9, 130.5, 128.8, 128.0, 127.3, 126.7, reacted in toluene (3 mL) under air. Purification using DCVC on
125.7, 125.0, 124.5, 117. 1, 114.0, 112.0 ppm; HRMS (EI): m/z SiO2 (1% TEA in CH2Cl2, Et2O) followed by crystallization
(M+) calcd. for C17H12N2: 244.1000; found: 244.0995.
5-(Phenanthren-9-yl)imidazo[1,2-
procedure of 5a, 4,4,5,5-tetramethyl-2-(phenanthren-9-yl)-1,3,2- 1 H), 8.26 (s, 1 H), 7.80 (s, 1 H), 7.78 (d, J = 8.5 Hz, 1 H), 7.59
dioxaborolane 4b (600 mg 1.95 mmol), Pd(PPh3)4 (115 mg, 0.1 – 7.58 (m, 2 H), 7.47 (t, J = 8.1 Hz, 1 H), 7.42 (t, J = 7.6 Hz, 1
(CH2Cl2/cyclohexane) afforded red crystal (6.8 mg, 12%), mp.
a
]pyridine (5b); following 178-180°C. 1H NMR (500 MHz, CDCl3): δ = 8.32 (d, J = 8.1 Hz,
,
mmol), DME (7.5 mL), compound 2e (385 mg, 1.95 mmol), H), 7.35 (t, J = 5.3 Hz, 1 H), 7.22 – 7.18 ppm (m, 3 H); 13C NMR
EtOH (5 mL), and saturated Na2CO3 (5 mL) were reacted. The (126 MHz, CDCl3): δ = 145.9, 136.2, 133.5, 132.7, 132.5, 129.1,
resulting mixture was purified by column chromatography on 129.0, 128.0, 127.4, 126.6, 126.6, 126.0, 125.3, 124.9, 124.7,
SiO2 (2% MeOH in CH2Cl2) and recrystallized (EtOAc) to afford 124.1, 123.2, 121.9, 117.7, 116.2, 106.7 ppm; HRMS (EI): m/z
white crystals (419 mg, 73%), mp. 178.6-179.6°C. 1H NMR (500 (M+) calcd. for C21H12N2: 292.1000; found: 292.1003.
MHz, CDCl3): δ = 8.82 (d, J = 8.3 Hz, 1 H), 8.79 (d, J = 8.3 Hz,
1 H), 7.94 (d, J = 7.8 Hz, 1 H), 7.91 (s, 1 H), 7.80 – 7.67 (m, 4
Imidazo[5,1,2-de]phenanthro[1,10-ab]quinolizine
(10b);
H), 7.54 (d, J = 1.5 Hz, 1 H), 7.48 (ddd, J1 = 8.3 Hz, J2 = 6.8 Hz, Compound 3b (58.9 mg, 0.2 mmol) and K (78 mg, 2 mmol) were
J3 = 1 Hz, 1 H), 7.39 – 7.33 (m, 2 H), 7.01 (s, 1 H), 6.98 ppm reacted in toluene (3 mL) under air. Purification using DCVC on
(dd, J1 = 6.8 Hz, J2 = 1 Hz, 1 H); 13C NMR (126 MHz, CDCl3): SiO2 (2% MeOH in CH2Cl2) followed by crystallization
δ = 146.0, 137.2, 133.6, 131.2, 131.1, 130.8, 130.6, 129.5, 129.3, (CH2Cl2/EtOAc) afforded red crystals (22.6 mg, 38%), mp. 257-
1
129.3, 128.2, 127.5, 127.5, 127.4, 125.9, 124.5, 123., 122.9, 259°C. H NMR (500 MHz, CDCl3): δ = 8.34 (d, J = 8.2 Hz, 1
117.2, 114.0, 112.1 ppm; HRMS (EI): m/z (M+) calcd. for H), 8.32 (d, J = 8.4 Hz, 1 H), 7.91 (s, 1 H), 7.80 (d, J = 7.6 Hz, 1
C21H14N2: 294.1157; found: 294.1147.
H), 7.63 (d, J = 7.6 Hz, 1 H), 7.52 – 7.44 (m, 4 H), 7.36 (d, J =
3-(Naphthalen-1-yl)imidazo[1,5-a]pyridine (8); In a pressure 8.7 Hz, 1 H), 7.17 (d, J = 6.9 Hz, 1 H), 7.11 ppm (dd, J1 = 8.6
reaction tube, Cs2CO3 (0.7 g, 2.2 mmol) was heated at 150 °C Hz, J2 = 7.2 Hz, 1 H); 13C NMR (126 MHz, CDCl3): δ = 145.7,
under Ar flow. Subsequently Pd(OAc)2 (22.4 mg, 5 mol%), PPh3 134.3, 132.3, 132.0, 129.5, 128.1, 127.8, 127. 6, 127.4, 127.0,
(26.4 mg, 5 mol%), imidazo[1,5-a]pyridine (6, 240 mg, 2 mmol), 126.3, 126.1, 125.8, 124.0, 123.1, 122.6, 122.6, 120.4, 116.8,
1-iodonaphthalene (0.32 mL, 2.2 mmol), and DMAc (4 mL) 115.6, 106.8 ppm; HRMS (EI): m/z (M+) calcd. for C21H12N2:
were added under Ar. The vessel was closed and the reaction was 292.1000; found: 292.0993.
stirred at the same temperature for 21 h. The resulting mixture
was absorbed into celite, pre-purified by DCVC on SiO2 (1%
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H), 7.67 (d, J = 7.5 Hz, 1 H), 7.51 (d, J = 8.1 Hz, 1 H), 7.67 (d,
10-Methylimidazo[5,1,2-de]pyrido[2',3':5,6]naphtho[1,8-
ab]quinolizine (10c); Compound 3c (1.03 g, 3.3 mmol) and K J = 7.8 Hz, 1 H), 7.29 – 7.21 (m, 4 H), 7.05 ppm (dd, J1 = 8.8
(1.3 g, 33 mmol) were reacted in toluene (50 mL) under O2. Hz, J2 = 7.5 Hz, 1 H); 13C NMR (126 MHz, CDCl3): δ = 168.1,
Purification using DCVC on SiO2 (3% MeOH in CH2Cl2) 163.8, 136.0, 135.0, 134.7, 128.7, 128.5, 127.4, 126.4, 126.1,
followed by crystallization (CH2Cl2/EtOAc) afforded orange 125.9, 125.5, 125.1, 120.5, 119.4, 119.2, 118.9, 116.9, 108.5,
solid (314 mg, 31%), mp. 282°C. 1H NMR (500 MHz, CDCl3): 104.0, 53.1, 51.4 ppm; HRMS (EI): m/z (M+) calcd. for
δ = 9.10 (d, J = 8.2 Hz, 1 H), 7.94 (d, J = 7.7 Hz, 1 H), 7.92 (s, 1 C22H15NO4: 357.1001; found: 357.1010..
H), 7.81 (d, J = 8.2 Hz, 1 H), 7.58 (t, J = 7.7 Hz, 1 H), 7.48 (s, 1
Dimethyl 5-methylindolizino[5',4',3':1,2,3]isoquinolino[4,5-
H), 7.40 (d, J = 8.7 Hz, 1 H), 7.28 – 7.26 (m, 2 H), 7.17 (t, J = gh]quinoline-9,10-dicarboxylate (13); Following procedure for
7.5 Hz, 1 H), 2.75 ppm (s, 3 H); 13C NMR (126 MHz, CDCl3): δ 12, compound 10c (30.5 mg, 0.1 mmol), mesitylene (2 mL), and
= 156.9, 145.6, 143.9, 135.0, 134.3, 132.9, 129.2, 128.9, 127.3, DMAD (122 µL, 2 mmol). The mixture was stirred at 150 °C for
126.8, 126.1, 125.5, 124.8, 123.2, 122.9, 122.4, 121.7, 116.6, 2h. The resulting mixture was then directly loaded into DCVC
113.8, 107.1, 25.3 ppm; HRMS (EI): m/z (M+) calcd. for on SiO2 (1% MeOH in CH2Cl2) and recrystallized
C21H13N3: 307.1109; found: 307.1109.
2-Octyl-1 -imidazo[5,1,2-
de]pyrido[3',4',5':4,5]naphtho[1,8-ab]quinolizine-1,3(2
(Et2O/cyclohexane) to afford red crystals (9.5 mg, 22%), mp.
255-257°C. 1H NMR (500 MHz, CDCl3): δ = 9.04 (d, J = 8.1 Hz,
1 H), 7.86 (d, J = 7.6 Hz, 1 H), 7.83 (d, J = 8.8 Hz, 1 H), 7.77 (d,
H
H)-
dione (10d); Compound 3d (86 mg, 0.2 mmol) and K (39 mg, 1 J = 8.2 Hz, 1 H), 7.48 (d, J = 8.1, Hz, 1 H), 7.30 (s, 1 H), 7.24
mmol) were reacted in toluene (3 mL) under Ar atmosphere. (d, J = 7.32 Hz, 1 H), 7.21 (d, J = 8.1, Hz, 1 H), 7.06 (dd, J1 =
DCVC on SiO2 (1% MeOH in CH2Cl2), followed by column 8.7 Hz, J2 = 7.3 Hz, 1 H) 4.14 (s, 3 H), 3.92 (s, 3 H), 2.72 ppm
chromatography on SiO2 (50% Et2OAc in CH2Cl2) afforded red (s, 3H); 13C NMR (126 MHz, CDCl3): δ = 168.0, 163.8, 157.0,
solid (7 mg, 8%), mp. 178-180°C. 1H NMR (500 MHz, CDCl3): 136.0, 136.0, 135.9, 135.5, 133.8, 128.3, 127.1, 126.2, 125.9,
δ = 8.47 (d, J = 7.9 Hz, 1 H), 8.41 (d, J = 7.9 Hz, 1 H), 8.30 (s, 1 124.9, 124.8, 123.1, 123.0, 121.9, 119.6, 119.4, 119.2, 114.9,
H), 7.96 (d, J = 7.9 Hz, 1 H), 7.76 (d, J = 8.7 Hz, 1 H), 7.71 (d, 108.7, 104.3, 53.1, 51.5, 25.0 ppm; HRMS (ESI): m/z ([M+H]+)
J = 7.3 Hz, 1 H), 7.65 (d, J = 7.8 Hz, 1 H), 7.65 (t, J = 8.2 Hz, 1 calcd. for C26H19N2O4: 423.1345; found: 423.1343.
H), 4.16 (t, J = 7.6 Hz, 2 H), 1.74 (t, J = 7.6 Hz, 2 H), 1.47 – 1.25
(m, 12 H), 0.88 ppm (t, J = 7.0 Hz, 3 H); 13C NMR (126 MHz,
Optical properties
CDCl3): δ = 163.3, 163.3, 134.8, 134.8, 132.7, 132.6, 131.4, Absorption and fluorescence spectra of all compounds in liquid
131.1, 130.6, 130.2, 128.0, 126.6, 122.0, 121.3, 119.1, 118.0, solutions of CH2Cl2 (spectroscopic grade) at room temperature
117.6, 115.7, 111.2, 40.6, 31.8, 29. 4, 29.2, 28.0, 27.2, 22.6, 14.1 were measured with the aid of a PerkinElmer UV/VIS
ppm; HRMS (ESI): m/z ([M+H]+) calcd. for C27H26N3O2: Spectrometer Lambda 35, and a Perkin-Elmer 512 Fluorescence
424.2025; found: 424.2025.
Spectrometer, respectively. Fluorescence quantum yield (Φfl)
was determined using perylene in cyclohexane as a standard
(Φfl=0.96). We estimate that the error inherent with the Φfl
Imidazo[5,1,2-de]naphtho[1,8-ab]quinolizine
(11a).
Compound 5a (49.8 mg, 0.2 mmol) and K (39 mg, 1 mmol) were estimation does not exceeds 10%.
reacted in toluene (3 mL) under air. Purification by DCVC on
Al2O3 (1% MeOH in CH2Cl2) afforded yellow solid (19.2 mg,
Acknowledgements
38%). 1H NMR (500 MHz, CDCl3): δ 7.89 (s, 1H), 7.72 (d, J =
7 Hz, 1H), 7.57 (d, J = 8.3 Hz, 1H), 7.46 (dd, J1 = 7.2 Hz, J2 =
0.8 Hz, 1H), 7.40 – 7.30 (m, 4H), 7.23 (d, J = 7 Hz, 1H), 7.16
(dd, J1 = 8.8 Hz, J2 = 7.3 Hz, 1H). Other properties concur with
published data.11
Authors would like to kindly acknowledge financial support
from Foundation for Polish Science (MISTRZ).
Notes and references
a Warsaw University of Technology, Faculty of Chemistry, Noakowskiego
3, 00-664 Warsaw, Poland.
Imidazo[5,1,2-de]phenanthro[10,1-ab]quinolizine
(11b);
Compound 5b (404 mg, 1.37 mmol) and K (0.53 g, 13.7 mmol)
were reacted in toluene (20 mL) under O2. Purification by DCVC
on SiO2 (3% MeOH in CH2Cl2) followed by recrystallization
(CH2Cl2/EtOAc) afforded orange solid (67.2 mg, 16%), mp. 267-
b
Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46,
02-668 Warsaw, Poland
c Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka
1
268°C. H NMR (500 MHz, CDCl3): δ = 8.37 (d, J = 7.8 Hz, 1
H), 8.16 (d, J = 8.2 Hz, 1 H), 7.87 (s, 1 H), 7.82 (s, 1 H), 7.70 (d,
J = 7.6 Hz, 1 H), 7.57 – 7.51 (m, 3 H), 7.43 (t, J = 7.8 Hz, 1 H),
7.39 (d, J = 8.7 Hz, 1 H), 7.25 ppm (d, 1 H), (t, J = 7.9 Hz, 1 H);
13C NMR (126 MHz, CDCl3): δ = 134.7, 131.8, 131.5, 129.9,
129.2, 128.9, 127.7, 127.5, 127.4, 126.9, 125.7, 125.5, 124.4,
122.6, 122.5, 120.3, 119.4, 118.3, 116.4, 106.8 ppm; HRMS
(EI): m/z (M+) calcd. for C21H12N2: 292.1000; found: 292.0993..
44/52, 01-224 Warsaw, Poland.
1
Electronic Supplementary Information (ESI) available: [copies of H and
13C NMR spectra for all new compounds]. See DOI: 10.1039/b000000x/
1
2
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6 | J. Name., 2012, 00, 1-3
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