Regioselective decarboxylative cross-coupling of carboxy isoquinoline N -oxides

Article abstract of DOI:10.1021/acs.joc.5b00475

A straightforward method for direct decarboxylative arylation of 1- and 3-carboxy isoquinaldic acid N-oxides with aryl iodides is reported. The reaction proceeded selectively at the carboxy function site to exclusively give the corresponding C-₁

Full text of DOI:10.1021/acs.joc.5b00475

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Note
Regioselective Decarboxylative Cross-
coupling of Carboxy isoquinoline N-oxides
Jean-Baptiste Emile Yves Rouchet, Cedric Schneider, Corinne Fruit, and Christophe Hoarau
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b00475 • Publication Date (Web): 04 May 2015
Downloaded from http://pubs.acs.org on May 6, 2015
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Regioselective Decarboxylative Cross-Coupling of
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Carboxy isoquinoline N-Oxides
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Jean-Baptiste E. Y. Rouchet, Cédric Schneider, Corinne Fruit, Christophe Hoarau*
Normandie university, COBRA, UMR 6014 et FR 3038, University Rouen; INSA Rouen; CNRS, IRCOF, 1
rue Tesnière, 76821 Mont-Saint-Aignan Cedex, France.
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ABSTRACT: A straightforward method for direct decarboxylative arylation of 1- and 3-carboxy
isoquinaldic acid N-oxides with aryl iodides is reported. The reaction proceeded selectively at the
carboxy function site to exclusively give the corresponding C-1 or C-3 arylated product. This
methodology tolerates various aryl iodides substituted by electronically different groups. Combined
with subsequent Reissert-Henze chlorination and SNAr amination, the decarboxylative arylation
provides an efficient access to 1,3-functionalized isoquinoline-based antitumor agent.
Arylated isoquinoline is a naturally-occurring heterocycle found in several alkaloids and in
pharmaceuticals with a broad array of biological activities, e.g. antitumor, analgesic, antihistaminic,
antimalarial, anti-inflammatory and antifertility activities.1 They are also found in a wide variety of
synthetically and functionally valuable compounds in particular as chiral ligands for transition metal
catalysts,2 phosphorescent materials3 and fluorosensors.4 Due to their widespread applications,
several attractive methodologies have been developed, almost all relying on pre-arylation before the
cyclisation.5-12
Figure 1. Isoquinoline-containing in pharmaceuticals and natural products
In the current context where cross-coupling process remained a synthetic challenge due the
instability of the organometallic species at the C-1 or C-3 positions of the isoquinoline core,13 several
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direct C1H arylation methodologies has been actively developed, mainly from the N-oxide
derivatives through i) the direct CH arylation under palladium catalysis with (pseudo)halides14 or
with carboxyarenes (Scheme 1, eq 1),15 ii) the oxidative CH/CH cross-coupling devoid of
prefunctionalization steps (Scheme 1, eq 2),14e, 16 and iii) the SNH-type reaction by the generation of
17
aryl radicals from arylboronic acids (Scheme 1, eq 3).14e,
In the context where only the
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(hetero)arylation at the C-1 position of the isoquinoline ring has been developed, the substitutive
cross-coupling of pre-functionalized isoquinolines appeared as a reliable and appropriate method to
fully control the selectivity at the C-1 and C-3 positions. Therefore, C-1 and C-3 carboxy isoquinolines
have been selected as suitable substrates for regioselective catalytic cross-coupling reaction via the
selective in situ generation of organometallic species by the transition metal-mediated extrusion of
CO2.18 Since the past decade, the decarboxylative cross-coupling reaction has received remarkable
attention since carboxylic acid derivatives are stable, easy to handle and to store, readily available
and nontoxic. Since the first example reported by Nilsson,19 several groups such as Gooβen,20 Liu,21
Larossa22 and Myers23 have achieved some exciting breakthroughs toward the Pd-catalyzed arylation
with aromatic and electron-rich heteroaromatic carboxylic acids.24-28 However, a very limited number
of examples were reported to use π-deficient heteroaryl carboxylic acids.29
Scheme 1. Various isoquinoline N-oxides coupling
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Recently, our group reported the first decarboxylative cross-coupling of substituted 2-
carboxyazine N-oxides involving a bimetallic Pd(0)/Cu(I) or Pd(0)/Ag(I) catalysis.29c Based on our previous
results, we report here the selective C-3 or C-1 Pd-catalyzed decarboxylative arylation of
carboxyisoquinoline N-oxides respectively leading access indifferently to C-1 or C-3 arylated
isoquinolines (Scheme 1, eq 4). This unprecedented C-3 arylated protocol was also judiciously
combined with a SNAr process at the C-1 position for a rapid elaboration of highly valuable 1,3-
functionalized isoquinoline which has considerable interest as potent anticancer agent.
Table 1. Optimization of the reaction conditionsa
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Entry
1c
2
3
4
[Pd]
PdBr2
PdBr2
PdBr2
PdBr2
PdBr2
PdBr2
PdBr2
PdBr2
Pd(OAc)2
Pd(acac)2
PdBr2
PdBr2
PdBr2
Base
[Ag]
Ligand
Yield [%]b (ratio 3Aa:3Ba)
32 (4/1)
Cs2CO3
Cs2CO3
K2CO3
KOAc
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
AgOAc
Ag2O
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PCy3•HBF4
PPh3
25 (>99/1)
90 (>99/1)d
8 (1:4)
5
6 (1:4)
6
61 (>99:1)
44 (>99:1)
54 (>99:1)
62 (>99:1)
19 (>99:1)
66 (>99:1)
82 (>99:1)
Trace
7e
8f
9
10
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12
13g
CyJohnPhos
PCy3•HBF4
aReaction conditions: 1A (2 equiv), 2a (0.2 mmol), [Pd] (10 mol%), ligand (10 mol%), Ag2CO3 (1 equiv),
b
base (2 equiv), anhydrous DMF, (0.2 M), 150 °C. Yield based on isolated product after flash
chromatography. c1,4-Dioxane instead of DMF as solvent.dWith a ratio PdBr2/PCy3•HBF4 1:2 the yield
was similar. e0.5 equivalent of Ag2CO3 was used.f 1 equivalent of 1A was used. g4-bromotoluene was
used instead of 4-iodotoluene.
We initiated our investigations with the 3-carboxyisoquinoline N-oxide 1A as substrate model
and p-tolyl iodide 2a as coupling partner. Within initial attempt using our previously designed
procedure for quinaldic- and picolinic N-oxides series,29c the reaction was carried out under bimetallic
PdBr2 (10 mol%)/Ag2CO3 (1 equiv) catalysis in 1,4-dioxane using Cs2CO3 base and PCy3•HBF4 as ligand.
The expected 3-arylisoquinoline N-oxide 3Aa was formed as the major product (Table 1, entry 1) of a
mixture of isomers, 3Aa and the 1-aryl isoquinoline N-oxide 3Ba arising from the
protodecarboxylative30-32 / direct CH arylation side sequence.33 Interestingly, we found that the
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reaction is fully selective at the C-3 position using DMF as solvent (Table 1, entries 2) which was
further selected to optimize the performance of the decarboxylative cross-coupling. The yield of 3Aa
was then immediately improved by switching the Cs2CO3 to K2CO3 as base, whereas KOAc proved to
be ineffective (Table 1, entries 3-4). Under this K2CO3-assistance, the 3-arylated isoquinoline 3Aa was
selectively produced in 90% yield without the formation of the other isomer 3Ba. We next evaluated
other Pd- and Ag-catalyst sources, as well as electronically- and bulky-different phosphines. Selected
results are depicted in Table 1 (entries 5-12). Regarding the source of Pd- and Ag-catalyst, PdBr2 and
Ag2CO3 were the most powerful pair of catalyst/base. On the other hand, reducing the amount of Ag-
catalyst from 1 to 0.5 equivalent, along with amount of acid 1A from 2 to 1.0 equivalents, affect the
efficiency of the Pd(0)/Cu(I)-catalyzed decarboxylative process (Table 1, entries 7-8).
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Scheme 2. Scope of the decarboxylative cross-coupling reaction with various iodoarenes 2b-o and
3-carboxyisoquinoline N-oxide 1A
The scope of the optimized protocol was then examined (Scheme 2). All envisaged
decarboxylative arylations of 1A were successfully performed with both electron-rich and electron-
deficient iodoarenes in high selectivity for the C-3 position, affording the expected 3-arylated
isoquinolines 3Ab-3Ak in fair to excellent yields. Notably, the presence of various substituents such
as ester, nitro, methoxy, trifluoromethyl, and halides at the meta or para positions of the iodoarenes
are tolerated. On the other hands, the decarboxylative cross-coupling of 1A with (hetero)aryl as well
as the ortho-substituted aryl iodides gave no success.
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We next investigated the efficiency of our optimized procedure with the formation of 1-
arylated isoquinoline N-oxides from the 1-carboxyisoquinoline N-oxide (1B) (Scheme 3). As first
assay, the decarboxylative cross-coupling of 1B was carried out with the iodotoluene under the
optimized protocol. We were pleased to obtain the expected 1-arylated isoquinoline N-oxide 3Ba in
64% yield without trace of the 3-arylated isomer 3Aa. Overall, the coupling with various iodo arenes
was also successfully achieved in fair to good yields whatever the electronic effect of substituted
group on aryl iodides. However, only substituents at the meta and para positions are tolerated
revealing that steric hindrance has a strong influence on the efficiency of the reaction. Moreover, the
full selectivity observed at C-1 position allows us to discount the decarboxylative cross-coupling /
direct CH arylation sequence since a mixture of C-1 and C-3 arylated isoquinoline in a 4:1 ratio was
obtained when simple isoquinoline N-oxide as substrate was used under our reaction conditions
with-4-iodotoluene.34
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Scheme 3. Scope of the decarboxylative cross-coupling reaction with various iodoarenes 2b-o and
1-carboxyisoquinoline N-oxide 1B
As application herein, the selective direct C3-CO2H bonds arylation methodology was here
applied to the design of innovative, modular and short synthetic route towards 1,3-functionnalized
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isoquinolines. Notably, the 3-arylisoquinolines have attracted considerable interest as potent
antitumor agent against several types of human tumor cells.35,36. We focused thus on the neat
synthesis of the anticancer chemotherapeutic agent 5 from 3-carboxyisoquinoline N-oxide 1A.36d Its
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preparation was successfully achieved through
a three-step sequential combination of
decarboxylative arylation at the 3-position with iodobenzene followed by Reissert-Henze reaction37
and finally SNAr reaction with N-ethylpiperazine (Scheme 4). This innovative sequence provided the
expected antitumor agent 5 in 28% overall yield.
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Scheme 4. Synthesis of 1,3-functionalized isoquinoline 5, a potent antitumor agent
In summary, we disclosed the first Pd-catalyzed decarboxylative arylations of 1- and 3-
carboxyisoquinoline N-oxides with silver as co-catalyst. This innovative method is functional-group
tolerant, site-selective and proceeds in moderate to good yields. Moreover, the reported
methodology constitutes the first intermolecular approach enable to arylate the C-3 position which
has never been reached selectively by Pd-catalyzed direct CH arylation or by using alternative
methods that require organometallic intermediates. As application, a modular and flexible approach
has been developed for the synthesis of the highly functionalized 1,3-substituted isoquinoline 5, an
antitumor agent, employing Pd-catalyzed decarboxylative cross-coupling and SNAr process.
EXPERIMENTAL SECTION
General comments
Commercially available reagents were used throughout without further purification. Reactions were
routinely carried out under an N2 atmosphere using oven or flame-dried glassware. Melting points
1
were determined on a hot stage melting point apparatus and are uncorrected. H, 19F and 13C NMR
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spectra were recorded using a 300 spectrometer operating at 300 MHz (1H frequency, corresponding
13C and 19F frequencies are 75 and 282 MHz). The chemical shifts are calibrated to residual proton
and carbon resonance of CDCl3 (1H 7.26 and 13C 77.16 ppm) or DMSO (1H 2.52 and 13C 39.5 ppm). In
the 13C NMR spectra, signals corresponding to C, CH, CH2, or CH3 groups are assigned from DEPT. The
obtained signal multiplicities were distinguished with the common abbreviations s (singlet), d
(doublet), t (triplet), q (quartet), bs (broad singlet), hep (heptet), sex (sextet) and the combinations
thereof. IR spectra were recorded on a FT-IR intrument. Low resolution mass spectra analyses were
performed with spectrometer in chemical ionisation. High Resolution Mass spectra (HRMS) were
performed under ESI conditions with a micro Q-TOF detector. All reactions were monitored by thin-
layer chromatography with silica gel 60 F254 pre-coated aluminium plates (0.25 mm). Flash
chromatography was performed with the indicated solvents using silica gel 60 (35-70 µm mesh).
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General procedure A:
Substrate 1A-B were synthesized according to the literature procedure.29c Carboxyisoquinolines (1.0
equiv) and UHP (2.0 equiv) were dissolved in anhydrous CH2Cl2 (0.3 M). The mixture was cooled to 0
°C and trifluoroacetic anhydride (2 equiv) was added dropwise. After 30 min at 0 °C, the mixture was
allowed to warm to room temperature and stirred for 12 hour. A saturated Na2S2O8 aqueous solution
was added. The aqueous layer was extracted with CH2Cl2 (3 times). The combined organic layers
were dried over Na2SO4, and the solvent was removed under reduced pressure. Isoquinoline
carboxylic acid N-oxides were obtained after trituration with Et2O followed by filtration and drying
under high vaccum.
General procedure B:
A flame-dried tube filled with argon was charged with aryl iodides (1 equiv), carboxyisoquinoline N-
oxide (2.0 equiv), PCy3•HBF4 (10 mol%), PdBr2 (10 mol%), Ag2CO3 (1 equiv) and K2CO3 (2 equiv) and
anhydrous DMF (0.2 M). The tube was sealed and heated to 150 °C for 12 hours. The reaction
mixture was filtered through a plug of celite (washed with dichloromethane and MeOH) and the
solvents were removed under reduced pressure. The crude product was then purified by flash
column chromatography.
Synthesis of carboxyisoquinoline N-oxides
3-Carboxyisoquinoline N-oxide 1A
Compound 1A was prepared from isoquinoline-3-carboxylic acid (500 mg, 2.89 mmol) according to
the general procedure A. The desired product was obtained as a colorless solid (455 mg, 2.40 mmol,
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83%) after trituration in Et2O and filtration. Exhibited spectra data identical to previous reports.29c mp
1
= 226 – 228 °C (Et2O). H NMR (300 MHz, CDCl3) δ 8.96 (s, 2H), 8.08-8.05 (m, 1H), 7.98-7.95 (m, 1H),
7.90-7.86 (m, 2H).
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1-Carboxyisoquinoline N-oxide 1B
Compound 1B was prepared from isoquinoline-1-carboxylic acid (1.00 g, 5.77 mmol) according to the
general procedure A. The desired product was obtained as a colorless solid (0.888 g, 4.67 mmol 81%)
after trituration in Et2O and filtration. Exhibited spectra data identical to previous reports.29c mp =
1
150 – 152 °C (Et2O). H NMR (300 MHz, CDCl3) δ 9.78 (d, 1H, J = 8.5 Hz), 8.27 (d, 1H, J = 7.1 Hz), 7.98
(d, 1H, J = 7.1 Hz), 7.90-7.78 (m, 3H).
Decarboxylative cross-coupling at the C-3 position
3-(p-tolyl)isoquinoline N-oxide 3Aa
The compound 3Aa was prepared from [4-iodotoluene (1 equiv, 44 mg, 0.2 mmol), isoquinoline 3-
carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02 mmol), PCy3•HBF4
(10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55 mg, 0.4 mmol),
DMF (1.0 ml)] according to the general procedure B. The crude product was purified by flash column
chromatography (gradient from EtOAc/PE 8:2 to EtOAc) to afford 3-(p-tolyl)isoquinoline N-oxide 3Aa
(42 mg, 0.179 mmol) in 90% yield as a yellow solid. Exhibited spectra data identical to previous
reports.29c mp = 135 °C (Et2O). 1H NMR (300 MHz, Acetone) δ 8.89 (s), 7.98 (s, 1H), 7.94 (d, J = 7.9 Hz,
1H), 7.84 (d, J = 7.9 Hz, 1H), 7.78 (d, J = 8.2 Hz, 2H), 7.66-7.55 (m, 2H), 7.27 (d, J = 7.9 Hz, 2H), 2.38 (s,
3H).
3-(4-methoxyphenyl)isoquinoline N-oxide 3Ab
The compound 3Ab was prepared from [1-iodo-4-methoxybenzene (1 equiv, 47 mg, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(4-methoxyphenyl)isoquinoline N-
oxide 3Ab (36 mg, 0.143 mmol) in 72% yield as a yellow solid. Exhibited spectra data identical to
previous reports.14b mp = 148 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.90 (s, 1H), 7.78 (m, 4H), 7.73 –
7.68 (m, 1H), 7.60 – 7.51 (m, 2H), 7.02 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H).
3-phenylisoquinoline N-oxide 3Ac
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The compound 3Ac was prepared from [Iodobenzene (1 equiv, 41 mg, 22 µl, 0.2 mmol), isoquinoline
3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02 mmol),
PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55 mg, 0.4
mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by flash
column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-phenylisoquinoline N-oxide 3Ac (39 mg,
0.177 mmol) in 89% yield as a yellow solid. Exhibited spectra data identical to previous reports.14b mp
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1
= 149 – 151 °C (Et2O). H NMR (300 MHz, CDCl3) δ 8.93 (s, 1H), 7.83 – 7.79 (m, 4H), 7.75 – 7.72 (m,
1H), 7.61 – 7.58 (m, 2H), 7.52-7.47 (m, 3H).
3-(4-chlorophenyl)isoquinoline N -oxide 3Ad
The compound 3Ad was prepared from [1-chloro-4-iodobenzene (1 equiv, 48 mg, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(4-chlorophenyl)isoquinoline N-oxide
3Ad (31 mg, 0.121 mmol) in 61% yield as a yellow solid. Exhibited spectra data identical to previous
reports.38 mp = 193 – 195 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.91 (s, 1H), 7.82 – 7.70 (m, 5H), 7.67
– 7.54 (m, 2H), 7.47 (d, J = 8.2 Hz, 2H).
3-(4-fluorophenyl)isoquinoline N-oxide 3Ae
The compound 3Ae was prepared from [1-fluoro-4-iodobenzene (1 equiv, 44 mg, 23 µl, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the genral procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(4-fluorophenyl)isoquinoline N-oxide
3Ae (38 mg, 0.158 mmol) in 79% yield as a yellow solid. Exhibited spectra data identical to previous
reports.39 mp = 190 – 192 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.90 (s, 1H), 7.86 – 7.75 (m, 4H), 7.73
– 7.71 (m, 1H), 7.63 – 7.55 (m, 2H), 7.18 (t, J = 8.7 Hz, 2H). 19F NMR (282 MHz, CDCl3) δ -111.30 (tt, J =
8.6, 5.3 Hz).
3-(4-(trifluoromethyl)phenyl)isoquinoline N -oxide 3Af
The compound 3Af was prepared from [1-iodo-4-(trifluoromethyl)benzene (1 equiv, 54 mg, 29 µl, 0.2
mmol), isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg,
0.02 mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2
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equiv, 55 mg, 0.4 mmol), DMF (1 ml)] according to the procedure B. The crude product was purified
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column
chromatography
(CH2Cl2/Acetone:
7:3)
to
afford
3-(4-
trifluoromethylphenyl)isoquinoline N-oxide 3Af (37 mg, 0.128 mmol) in 64% yield as a yellow solid.
mp = 207 – 209 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.92 (s, 1H), 7.95 (d, J = 8.1 Hz, 2H), 7.83 – 7.81
(m, 2H), 7.77 – 7.74 (m, 3H), 7.63 – 7.58 (m, 2H). 19F NMR (282 MHz, CDCl3) δ -62.82 (s). 13C NMR
(75.5 MHz, CDCl3) δ 145.8 (C), 137.3 (CH), 136.5 (C), 131.4 (C, J = 33 Hz), 130.3 (2xCH), 129.7 (CH),
129.4 (C), 129.3 (C), 129.1 (C), 126.9 (CH), 125.4 (CH), 125.3 (CH) 125.2 (CH), 124.7 (CH), 124.1 (C, J =
270 Hz). IR (neat) νmax: 3048, 2962, 1718, 1633, 1599, 1488, 1439, 1407, 1313, 1261, 1237, 1201,
1178, 1162, 1108, 1064, 1017, 959, 919, 897, 875 cm-1. HMRS (ESI-TOF): calc. for C16H11F3NO:
290.0793; found 290.0790.
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3-(4-nitrophenyl)isoquinoline N-oxide 3Ag
The compound 3Ag was prepared from [1-iodo-4-nitrobenzene (1 equiv, 50 mg, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(4-nitrophenyl)isoquinoline N-oxide
3Ag (44 mg, 0.165 mmol) in 83% yield as a yellow solid. mp = 238 – 240 °C (Et2O). 1H NMR (300 MHz,
CDCl3) δ 8.92 (s, 1H), 8.34 (d, J = 8.9 Hz, 2H), 8.03 (d, J = 8.9 Hz, 2H), 7.85 – 7.82 (m, 2H), 7.78 – 7.75
(m, 1H), 7.69 – 7.60 (m, 2H). 13C NMR (75.5 MHz, CDCl3) δ 148.3 (C), 144.8 (C), 139.2 (C), 137.4 (CH),
130.9 (2xCH), 130.1 (CH), 129.6 (C), 129.5 (CH), 129.0 (C), 127.0 (CH), 125.5 (CH), 124.7 (CH), 123.5
(2xCH). IR (neat) νmax: 3018, 1599, 1510, 1438, 1344, 1309, 1260, 1238, 1204, 1173, 1124, 1017, 957,
934, 918, 853 cm-1. HMRS (ESI-TOF): calc. for C15H11N2O3: 267.0770; found 267.0768.
3-(4-(ethoxycarbonyl)phenyl)isoquinoline N-oxide 3Ah
The compound 3Ah was prepared from [Ethyl 4-iodobenzoate (1 equiv, 55 mg, 34 µl, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash
column
chromatography
(CH2Cl2/Acetone:
7:3)
to
afford
3-(4-
(ethoxycarbonyl)phenyl))isoquinoline N-oxide 3Ah (41 mg, 0.140 mmol) in 70% yield as a yellow
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solid. Exhibited spectra data identical to previous reports.14b mp = 205 – 207 °C (Et2O). H NMR (300
MHz, CDCl3) δ 8.91 (s, 1H), 8.16 (d, J = 8.3 Hz, 2H), 7.90 (d, J = 8.3 Hz, 2H), 7.81 – 7.79 (m, 2H), 7.75 –
7.72 (m, 1H), 7.64 – 7.56 (m, 2H), 4.41 (q, J = 7.1 Hz, 2H), 1.41 (t, J = 7.1 Hz, 3H).
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3-(naphthalen-2-yl)isoquinoline N-oxide 3Ai
The compound 3Ai was prepared from [2-iodonaphthalene (1 equiv, 41 mg, 0.16 mmol), isoquinoline
3-carboxylic acid N-oxide 1A (2 equiv, 61 mg, 0.32 mmol), PdBr2 (10 mol%, 4 mg, 0.016 mmol),
PCy3•HBF4 (10 mol%, 6 mg, 0.016 mmol), Ag2CO3 (1 equiv, 44 mg, 0.16 mmol), K2CO3 (2 equiv, 44 mg,
0.32 mmol), DMF (0.8 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(naphthalen-2-yl)isoquinoline N-
oxide 3Ai (38 mg, 0.140 mmol) in 88% yield as a yellow solid. mp = 111 – 113 °C (Et2O). 1H NMR (300
MHz, CDCl3) δ 8.91 (s, 1H), 8.21 (s, 1H), 7.97 – 7.85 (m, 5H), 7.79 – 7.68 (m, 2H), 7.59 – 7.48 (m, 4H).
13C NMR (75 MHz, CDCl3) δ 147.1 (C), 137.0 (CH), 133.6 (C), 133.1 (C), 130.6 (C), 129.4 (CH), 129.3 (C),
129.1 (CH), 129.0 (C), 128.9 (CH), 128.5 (CH), 127.7 (CH), 127.5 (CH), 126.9 (CH), 126.9 (CH), 126.7
(CH), 126.3 (CH), 125.1 (CH), 124.4 (CH). IR (neat) νmax: 3673, 2986, 2904, 1394, 1249, 1066, 892, 743
cm-1. HMRS (ESI-TOF): calc. for C19H14NO: 272.1075; found 272.1072.
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3-(3-methoxyphenyl)isoquinoline N-oxide 3Aj
The compound 3Aj was prepared from [1-iodo-3-methoxybenzene (1 equiv, 47 mg, 24 µl, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(3-methoxyphenyl)isoquinoline N-
oxide 3Aj (38 mg, 0.151 mmol) in 77% yield as a yellow solid. mp = 122 – 124 °C (Et2O). 1H NMR (300
MHz, CDCl3) δ 8.91 (s, 1H), 7.80 – 7.77 (m, 2H), 7.74 – 7.70 (m, 1H), 7.61 –7.56 (m, 2H), 7.43 – 7.32
(m, 3H), 7.03 – 6.99 (m, 1H), 3.86 (s, 3H). 13C NMR (75 MHz, CDCl3) δ 13C NMR (75 MHz, CDCl3) δ
159.4 (C), 146.9 (C), 137.4 (CH), 134.1 (C), 129.5 (C), 129.4 (CH), 129.3 (CH), 129.2 (CH), 129.0 (C),
126.8 (CH), 125.1 (CH), 124.7 (CH), 122.2 (CH), 115.6 (CH), 115.1 (CH), 55.5 (CH3). IR (neat) νmax: 3351,
2929, 1597, 1578, 1489, 1468, 1423, 1313, 1281, 1247, 1212, 1144, 1123, 1087, 1046. 922, 876 cm-1.
HMRS (ESI-TOF): calc. for C16H14NO2: 252.1025; found 252.1023.
3-(3-nitrophenyl)isoquinoline N-oxide 3Ak
The compound 3Ak was prepared from [1-iodo-3-nitrobenzene (1 equiv, 50 mg, 0.2 mmol),
isoquinoline 3-carboxylic acid N-oxide 1A (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 3-(3-nitrophenyl)isoquinoline N-oxide
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3Ak (46 mg, 0.173 mmol) in 86% yield as a yellow solid. mp = 232 – 234 °C (Et2O). 1H NMR (300 MHz,
CDCl3) δ 8.93 (s, 1H), 8.67 (t, J = 1.8 Hz, 1H), 8.34 (dd, J = 8.2 and 1.3 Hz, 1H), 8.26 (d, J = 7.9 Hz, 1H),
7.88 – 7.83 (m, 2H), 7.79 – 7.76 (m, 1H), 7.71 – 7.61 (m, 3H). 13C NMR (75 MHz, CDCl3) δ 148.2 (C),
144.6 (C), 137.3 (C), 136.1 (CH), 134.4 (C), 130.0 (CH), 129.6 (CH), 129.5 (CH), 129.3 (CH), 129.2 (C),
127.0 (CH), 125.4 (CH), 125.0 (CH), 124.8 (CH), 124.4 (CH). IR (neat) νmax: 3100, 3066, 3020, 2924,
1600, 1521, 1463, 1443, 1342, 1317, 1265, 1238, 1169, 1126, 1025, 989, 960, 923, 871, 837, 805 cm-
1. HMRS (ESI-TOF): calc. for C15H11N2O3: 267.0770; found 267.0767.
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Decarboxylative cross-coupling at the C-1 position
1-(p-tolyl)isoquinoline N-oxide 3Ba
The compound 3Ba was prepared from [4-iodotoluene (1 equiv, 44 mg, 0.2 mmol), isoquinoline 1-
carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02 mmol), PCy3•HBF4
(10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55 mg, 0.4 mmol),
DMF (1 ml)] according to the general procedure B. The crude product was purified by flash column
chromatography (gradient from EtOAc/PE 8:2 to EtOAc) to afford 1-(p-tolyl)isoquinoline N-oxide 3Ba
(30 mg, 0.128 mmol) in 64% yield as a yellow solid. Exhibited spectra data identical to previous
1
reports.14b mp = 129 – 131 °C (Et2O). H NMR (300 MHz, CDCl3) δ 8.29 (d, J = 7.2 Hz, 1H), 7.80 (d, J =
8.0 Hz, 1H), 7.66 (d, J = 7.2 Hz, 1H), 7.59 – 7.46 (m, 3H), 7.45 – 7.35 (m, 4H), 2.47 (s, 3H).
1-(4-methoxyphenyl)isoquinoline N-oxide 3Bb
The compound 3Bb was prepared from [1-iodo-4-methoxybenzene (1 equiv, 47 mg, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(4-methoxyphenyl)isoquinoline N-
oxide 3Bb (41 mg, 0.163 mmol) in 82% yield as a yellow solid. Exhibited spectra data identical to
previous reports.13b mp = 178 – 180 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.28 (d, J = 7.2 Hz, 1H), 7.80
– 7.77 (m, 1H), 7.62 (d, J = 7.2 Hz, 1H), 7.65 –7.63 (m, 5H), 7.11 (d, J = 8.7 Hz, 2H), 3.90 (s, 3H).
1-phenylisoquinoline N-oxide 3Bc
The compound 3Bc was prepared from [iodobenzene (1 equiv, 41 mg, 22 µl, 0.2 mmol), isoquinoline
1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02 mmol),
PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55 mg, 0.4
mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by flash
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column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-phenylisoquinoline N-oxide 3Bc (38 mg,
0.172 mmol) in 86% yield as a yellow solid. Exhibited spectra data identical to previous reports.16a,40
mp = 141 – 143 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.29 (d, J = 7.2 Hz, 1H), 7.81 (d, J = 7.8 Hz, 1H),
7.68 (d, J = 7.2 Hz, 1H), 7.59 – 7.45 (m, 8H).
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1-(4-chlorophenyl)isoquinoline N-oxide 3Bd
The compound 3Bd was prepared from [1-chloro-4-iodobenzene (1 equiv, 48 mg, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(4-chlorophenyl)isoquinoline N-oxide
3Bd (34 mg, 0.133 mmol) in 66% yield as a yellow solid. Exhibited spectra data identical to previous
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reports.14b mp = 191 – 193 °C (Et2O). H NMR (300 MHz, CDCl3) δ 8.27 (d, J = 7.2 Hz, 1H), 7.81 (d, J =
7.5 Hz, 1H), 7.68 (d, J = 7.1 Hz, 1H), 7.58– 7.55 (m, 3H), 7.50 – 7.43 (m, 4H).
1-(4-fluorophenyl)isoquinoline N-oxide 3Be
The compound 3Be was prepared from [1-fluoro-4-iodobenzene (1 equiv, 44 mg, 23 µl, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(4-fluorophenyl)isoquinoline N-oxide
3Be (23 mg, 0.096 mmol) in 48% yield as a yellow solid. mp = 201 – 203 °C (Et2O). 1H NMR (300 MHz,
CDCl3) δ 8.28 (d, J = 7.2 Hz, 1H), 7.82 (d, J = 7.4 Hz, 1H), 7.68 (d, J = 7.2 Hz, 1H), 7.59 – 7.45 (m, 5H),
7.31 – 7.25 (m, 3H). 19F NMR (282 MHz, CDCl3) δ -111.1 (tt, J = 8.6 and 5.3 Hz). 13C NMR (75.5 MHz,
CDCl3) δ 163.9 (C, J = 255 Hz), 145.3(C), 137.5 (CH), 132.5 (2xCH, J = 8 Hz), 129.7 (C), 129.4 (CH), 129.3
(C), 128.5 (CH), 127.1 (CH), 126.8 (C, J = 8 Hz), 125.6 (CH), 123.6 (CH), 116.1 (2xCH, J = 23 Hz). IR
(neat) νmax: 2986, 1599, 1514, 1493, 1425, 1394, 1318, 1220, 1154, 1140, 1091, 960, 824 cm-1. HMRS
(ESI-TOF): calc. for C15H11FNO: 240.0825; found 240.0823.
1-(4-(trifluoromethyl)phenyl)isoquinoline N-oxide 3Bf
The compound 3Bf was prepared from [1-iodo-4-(trifluoromethyl)benzene (1 equiv, 54 mg, 29 µl, 0.2
mmol), isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg,
0.02 mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2
equiv, 55 mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was
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trifluoromethylphenyl)isoquinoline N-oxide 3Bf (26 mg, 0.090 mmol) in 64% yield as a yellow solid.
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mp = 204 – 206 °C (Et2O). H NMR (300 MHz, CDCl3) δ 8.29 (d, J = 7.2 Hz, 1H), 7.85 (m, 3H), 7.74 –
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7.67 (m, 3H), 7.56 (dtd, J = 16.6, 7.0 and 1.2 Hz, 2H), 7.40 (d, J = 8.2 Hz, 1H). 19F NMR (282 MHz,
CDCl3) δ -62.83 (s). 13C NMR (75 MHz, CDCl3) δ 144.6 (C), 137.5 (CH), 134.8 (C), 131.5 (C, J = 32 Hz),
130.9 (2xCH), 129.6 (CH), 129.3 (C), 129.2 (C) 128.6 (CH), 127.2 (CH), 125.9 (CH), 125.9 (CH), 125.1
(CH), 124.0 (C, J = 270 Hz), 124.0 (CH). IR (neat) νmax: 3422, 2922, 2854, 1620, 1562, 1495, 1456, 1398,
1321, 1222, 1161, 1107, 1065, 1019 962, 825 cm-1. HMRS (ESI-TOF): calc. for C16H11F3NO: 290.0793;
found 290.0790.
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1-(4-nitrophenyl)isoquinoline N-oxide 3Bg
The compound 3Bg was prepared from [1-iodo-4-nitrobenzene (1 equiv, 50 mg, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv,
55 mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified
by flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(4-nitrophenyl)isoquinoline N-
oxide 3Bg (46 mg, 0.173 mmol) in 87% yield as a yellow solid. mp = 212 – 214 °C (Et2O). 1H NMR (300
MHz, CDCl3) δ 8.45 (d, J = 8.7 Hz, 2H), 8.29 (d, J = 7.2 Hz, 1H), 7.86 (d, J = 7.8 Hz, 1H), 7.77 – 7.74 (m,
3H), 7.64 – 7.52 (m, 2H), 7.37 (d, J = 8.3 Hz, 1H). 13C NMR (75 MHz, CDCl3) δ 148.5 (C), 143.8 (C), 137.7
(C), 137.5 (CH), 131.9 (2xCH), 129.9 (CH), 129.2 (C), 129.1 (C), 128.8 (CH), 127.4 (CH), 124.7 (CH),
124.4 (CH), 124.1 (2xCH). IR (neat) νmax: 1508, 1440, 1397, 1344, 1280, 1222, 1149, 1104, 1059, 987,
958, 853 cm-1.HMRS (ESI-TOF): calc. for C15H10N2O3: 266.0691; found 266.0690.
1-(4-(ethoxycarbonyl)phenyl)isoquinoline N-oxide 3Bh
The compound 3Bh was prepared from [Ethyl 4-iodobenzoate (1 equiv, 55 mg, 34 µl, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash
column
chromatography
(CH2Cl2/Acetone:
7:3)
to
afford
1-(4-
(ethoxycarbonyl)phenyl))isoquinoline N-oxide 3Bh (30 mg, 0.102 mmol) in 51% yield as a yellow
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solid. Exhibited spectra data identical to previous reports.14b mp = 198 – 200 °C (Et2O). H NMR (300
MHz, CDCl3) δ 8.30 – 8.26 (m, 3H), 7.83 (d, J = 7.6 Hz, 1H), 7.71 (d, J = 7.1 Hz, 1H), 7.64 – 7.62 (m, 2H),
7.58-7.48 (m, 2H), 7.40 (d, J = 8.1 Hz, 1H), 4.44 (q, J = 7.1 Hz, 2H), 1.43 (t, J = 7.1 Hz, 3H).
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The compound 3Bi was prepared from [2-iodonaphthalene (1 equiv, 51 mg, 0.2 mmol), isoquinoline
1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02 mmol),
PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55 mg, 0.4
mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by flash
column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(naphthalen-2-yl)isoquinoline N-oxide 3Bi
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(19 mg, 0.070 mmol) in 35% yield as a yellow solid. mp = 135 – 137 °C (Et2O). H NMR (300 MHz,
CDCl3) δ 8.31 (d, J = 7.2 Hz, 1H), 8.04 (d, J = 8.5 Hz, 1H), 7.99 (s, 1H), 7.94 – 7.88 (m, 2H), 7.82 (d, J =
8.0 Hz, 1H), 7.70 – 7.64 (m, 2H), 7.60 – 7.44 (m, 5H). 13C NMR (75 MHz, CDCl3) δ 146.1 (C), 137.4 (CH),
133.6 (C), 133.2 (C), 130.1 (CH), 129.7 (C), 129.2 (C), 129.2 (CH), 128.5 (CH), 128.4 (CH), 128.4 (C),
128.3 (CH), 127.9 (CH), 127.2 (CH), 127.1 (CH), 126.9 (CH), 126.4 (CH), 125.8 (CH), 123.5 (CH). IR
(neat) νmax: 2980, 1750, 1605, 1517, 1495, 1450, 1354, 1303, 1245, 1204, 1131, 1072, 1017, 963, 927
cm-1. HMRS (ESI-TOF): calc. for C19H14NO: 272.1075; found 272.1071.
1-(3-methoxyphenyl)isoquinoline N-oxide 3Bj
The compound 3Bj was prepared from [1-iodo-3-methoxybenzene (1 equiv, 47 mg, 24 µl, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(3-methoxyphenyl)isoquinoline N-
oxide 3Bj (45 mg, 0.179 mmol) in 90% yield as a yellow solid. Exhibited spectra data identical to
previous reports.40 mp = 103 – 105 °C (Et2O). 1H NMR (300 MHz, CDCl3) δ 8.29 (d, J = 7.3 Hz, 1H), 7.81
(d, J = 8.0 Hz, 1H), 7.68 (d, J = 7.2 Hz, 1H), 7.58 – 7.48 (m, 4H), 7.09 – 7.06 (m, 3H), 3.85 (s, 3H).
1-(3-nitrophenyl)isoquinoline N-oxide 3Bk
The compound 3Bk was prepared from [1-iodo-3-nitrobenzene (1 equiv, 50 mg, 0.2 mmol),
isoquinoline 1-carboxylic acid N-oxide 1B (2 equiv, 76 mg, 0.4 mmol), PdBr2 (10 mol%, 5 mg, 0.02
mmol), PCy3•HBF4 (10 mol%, 7 mg, 0.02 mmol), Ag2CO3 (1 equiv, 55 mg, 0.2 mmol), K2CO3 (2 equiv, 55
mg, 0.4 mmol), DMF (1 ml)] according to the general procedure B. The crude product was purified by
flash column chromatography (CH2Cl2/Acetone: 7:3) to afford 1-(3-nitrophenyl)isoquinoline N-oxide
3Bk (31 mg, 0.116 mmol) in 58% yield as a yellow solid. mp = 243 – 245 °C (Et2O). 1H NMR (300 MHz,
CDCl3) δ 8.45 – 8.41 (m, 2H), 8.30 (d, J = 7.2 Hz, 1H), 7.93 (d, J = 7.7 Hz, 1H), 7.86 (d, J = 7.6 Hz, 1H),
7.82 – 7.75 (m, 2H), 7.64 – 7.53 (m, 2H), 7.40 (d, J = 8.4 Hz, 1H). 13C NMR (75 MHz, CDCl3) δ 148.6 (C),
143.5 (C), 137.3 (CH), 136.89 (CH), 132.6 (C), 130.0 (CH), 129.9 (CH), 129.2 (C), 129.2 (C), 128.9 (CH),
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127.4 (CH), 125.9 (CH), 124.7 (CH), 124.5 (CH), 124.4 (CH). IR (neat) νmax: 3039, 2920, 2853, 1623,
1526, 1502, 1393, 1349, 1321, 1292, 1224, 1141, 1132, 1082, 976, 894 cm-1. HMRS (ESI-TOF): calc. for
C15H11N2O3: 267.0770; found 267.0768.
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Synthesis of 1-(4-ethylpiperazin-1-yl)-3-phenylisoquinoline
1-chloro-3-phenylisoquinoline 4
Phosphoryl chloride (4.6 ml, 0.2M) was added dropwise to 3-phenylisoquinoline N-oxyde 3Ac (200
mg, 0.92 mmol, 1.0 equiv) under N2 atmosphere. The mixture was refluxed for 6 h, then cooled to
room temperature and poured onto ice. A saturated solution of Na2CO3 was added dropwise until
the solution was basic. The layers were separated and the aqueous phase was extracted with CH2Cl2
(2×20 mL). Combined organic extracts were dried over Na2SO4 and concentrated under reduced
pressure. The crude product was purified by flash chromatography (PE/AcOEt, 80:20) to afford 1-
chloro-3-phenylisoquinoline 4 (117 mg, 0.488 mmol, 53%) as a yellow oil. Exhibited spectra data
match to previous reports.41 1H NMR (300 MHz, CDCl3) δ 8.33 (d, J = 8.3 Hz, 1H), 8.14 – 8.11 (m, 2H),
8.00 (s, 1H), 7.88 (d, J = 8.1 Hz, 1H), 7.73 (t, J = 7.1 Hz, 1H), 7.65 (t, J = 7.5 Hz, 1H), 7.53 – 7.48 (m, 2H),
7.45 – 7.40 (m, 1H).
1-(4-ethylpiperazin-1-yl)-3-phenylisoquinoline 5
The compound 5 was prepared following the reported procedure.42 1-Chloro-3-phenylisoquinoline 4
(60 mg, 0.25 mmol) and N-ethyl piperazine (2.5 ml, 0.1 M) were added to a microwave tube and
heated at 160 °C for 1 hour. The resulting mixture was diluted with water and extracted with EtOAc.
Drying over Na2SO4 and concentrated under reduced pressure. The crude product was purified by
flash column chromatography (EtOAc) to afford 1-(4-ethylpiperazin-1-yl)-3-phenylisoquinoline 5 (48
mg, 0.15 mmol, 60%) as a pale yellow oil. 1H NMR (300 MHz, CDCl3) δ 8.18 (d, J = 7.4 Hz, 2H), 8.08 (d,
J = 8.3 Hz, 1H), 7.79 (d, J = 8.1 Hz, 1H), 7.71 (s, 1H), 7.59 (t, J = 7.3 Hz, 1H), 7.51 – 7.44 (m, 3H), 7.40 –
7.36 (m, 1H), 3.65 – 3.62 (m, 4H), 2.82 – 2.79 (m, 4H), 2.60 (q, J = 7.2 Hz, 1H), 1.20 (t, J = 7.2 Hz, 2H).
13C NMR (75 MHz, CDCl3) δ 160.6 (C), 148.3 (C), 139.8 (C), 139.2 (C), 129.8 (CH), 128.7 (2xCH), 128.4
(CH), 127.8 (CH), 126.7 (2xCH), 125.9 (CH), 125.6 (CH), 120.7 (C), 111.3 (CH), 52.9 (2x CH2), 52.6 (CH2),
51.0 (2xCH2), 11.98 (CH3) IR (neat) νmax: 3056, 2966, 2924, 2808, 1618, 1560, 1498, 1410.3, 1395,
1368, 1264, 1168, 1015, 950, 874 cm-1. HMRS (ESI-TOF): calc. for C21H24N3: 318.1970; found:
318.1967.
ASSOCIATED CONTENT
Supporting Information
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1H and 13C NMR. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
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Corresponding Author
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*Email: christophe.hoarau@insa-rouen.fr.
ACKNOWLEDGMENT
This work has been partially supported by INSA Rouen, Rouen University, CNRS, EFRD, European
INTERREG IV A France (Channel) and Labex SynOrg (ANR-11-LABX-0029). We also thanks the CRIHAN
for software optimization and kind technical support.
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