Rhodium-Catalyzed Annulation of Primary Benzylamine with α-Diazo Ketone toward Isoquinoline

Article abstract of DOI:10.1021/acs.joc.6b01378

Rhodium-catalyzed annulation of commercially available primary benzylamine with α-diazo ketone was developed, leading to isoquinolines in moderate to good yields. This procedure features the employment of primary benzylamine as starting material as well as high selectivity in the 3- and 4- position of isoquinoline, generating a key compliment to the previously developed annulation with internal alkyne.

Full text of DOI:10.1021/acs.joc.6b01378

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Note
Rhodium-Catalyzed Annulation of Primary Benzylamine
with alpha-Diazo Ketone towards Isoquinoline
Haoke Chu, Peiran Xue, Jin-Tao Yu, and Jiang Cheng
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b01378 • Publication Date (Web): 12 Aug 2016
Downloaded from http://pubs.acs.org on August 18, 2016
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The Journal of Organic Chemistry
Rhodium-Catalyzed Annulation of Primary Benzylamine with α-
Diazo Ketone towards Isoquinoline
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Haoke Chu, Peiran Xue, Jin-Tao Yu and Jiang Cheng*
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School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials & Technology, Jiang-
su Province Key Laboratory of Fine Petrochemical Engineering, Changzhou University, Changzhou 213164, P. R.
China
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jiangcheng@cczu.edu.cn
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the
journal that you are submitting your paper to)
ABSTRACT
A rhodium-catalyzed annulation of commercially available primary benzylamine with α-diazo ketone was de-
veloped, leading to isoquinolines in moderate to good yields. This procedure features with the employment of pri-
mary benzylamine as starting material as well as the high selectivity in the 3- and 4- position of isoquinoline, ren-
dering a key compliment to the previously developed annulation with internal alkyne.
Isoquinolines are ubiquitous in numerous biologically active alkaloids, as well as phosphorescent materials, and
fluorosensors.1 Bischler-Napieralski reaction,2 Pictet-Spengler reaction3 and Pomeranz-Fritsch reaction4 were tradi-
tional methods for the construction of such frameworks. However, in most cases, they suffered from harsh conditions,
such as high temperature and strong acidic reaction media, resulting in low functional groups tolerance.
With the development of organometallic chemistry, recently, much progress has been made to access isoquinoline
via chelation-assisted C-H functionalization. Generally, benzylamine derivatives, including imine,5 amidine,6 oxime7,8
and hydrazone9 served as a four-atom component; while alkynes,5-9 α-diazo ketones10,11 and geminal-substituted vinyl
acetates12 were C2 components. Undoubtedly, the employment of readily available primary benzylamine in such trans-
formation was the most straightforward pathway leading to isoquinoline. However, great challenge remained yet be-
cause not only benzylamine was sensitive to oxidant, but also the primary amino was a poor directing group. Therefore,
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few examples were developed and limited in the annulation of benzylamine with internal alkyne independently devel-
oped by Jun,13 Satoh,14 and Urriolabeitia,15 where the selectivity in 3- and 4- positions of isoquinoline kept inherently
unsolved. Herein, we wish to report the rhodium-catalyzed annulation of primary benzylamine with α-diazo ketone,
allowing the construction of isoquinoline framework with diversity and high selectivity in the 3- and 4- positions.
Initially, the annulation between benzylamine (1a) and ethyl 2-diazoacetoacetate (2a) was selected as model reac-
tion to screen the reaction conditions. To our delight, the target product, ethyl 3-methylisoquinoline-4-carboxylate (3aa)
was obtained in 58% yield in the presence of [Cp*RhCl2]2 (5 mol%) and AgSbF6 (20 mol%) in 1,2-dichloroethane
(DCE) at 100 oC for 12 h (Table 1, entry 1). The blank experiment confirmed both [Cp*RhCl2]2 and AgSbF6 were in-
dispensable (Table 1, entries 2 and 3). The Rh(III) species [Cp*Rh(CH3CN)3](SbF6)2 resulted in a comparable yield
(Table 1, entry 4). After further optimization, we abnegated other Rh catalysts and silver salts (Table 1, entries 5-8).
Notably, acetic ion, being an effective additive in numerous rhodium-catalyzed annulations via C-H functionaliza-
tions,10a-c inhibited the reaction (Table 1, entry 9). Among the solvents investigated, acetone gave the highest yield
(Table 1, entry 10, 75%). Using the previously reported procedure,10d 3aa was isolated in 50% yield (Table 1, entry 11).
Table 1. Screening the optimized reaction conditions a
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Catalyst
[Cp*RhCl2]2
[Cp*RhCl2]2
-
Additive Solvent Yield (%)b
Entry
1
AgSbF6
-
AgSbF6
-
AgSbF6
AgSbF6
AgBF4
AgOAc
CsOAc
AgSbF6
AgSbF6
AgSbF6
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
58
<5
0
52
<5
<5
<5
0
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[Cp*Rh(MeCN)3](SbF6)2
[Rh(cod)Cl]2
Rh(PPh3)3Cl
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
[Cp*RhCl2]2
0
acetone 75(43)c(70)d
THF
MeOH
50
<5
52
63
AgSbF6 n-hexane
AgSbF6
C6HF5
a Reaction conditions: 1a (0.2 mmol), 2a (0.3 mmol), Rh catalyst (5 mol%), additive (20 mol%), solvent (2 mL), 100 C, 12 h. Isolated
o
b
yield. c 80 oC. d 120 oC.
The scope and limitation of this reaction were explored under the optimal conditions, as summarized in Fig 1.
Various electron-donating groups (methyl, methoxy and tert-butyl) as well as electron-withdrawing groups (fluoro,
chloro, bromo and trifluoromethyl) were tolerated well, providing the corresponding isoquinoline in moderate to good
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yields. The methyl installed in the frameworks may provide potential handle for further functionalization.16 To our de-
light, the steric hindrance of ortho-substitution had almost no effect on the reaction efficiency, as 2-methylbenzylamine
(1b) gave its corresponding annulation product (3ba) in 72% yield. Importantly, α-substituted substrates, such as α-
methyl and phenyl benzylamines, ran smoothly, allowing to facile access 1,3,4-trisubstituted isoquinolines 3la and 3ma
in moderate yields. Notably, 1-aminomethylnaphthalene (1k) was good reaction partner towards benzo[h]isoquinoline
3ka as fused N-containing hetero aromatic framework in good yield (73%). Moreover, meta-methylbenzylamine pro-
vided 3na as solely product and no regioisomer was observed by GC-MS and 1H NMR spectroscopy. To evaluate the
practicability, the reaction was conducted on a 0.5 mmol scale, and the desired product 3aa was obtained in 64% yield.
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Figure 1. The substrate scope of benzylamines a
a Reaction conditions: 1 (0.2 mmol), 2a (0.3 mmol), [Cp*RhCl2]2 (5 mol%), AgSbF6 (20 mol%), in dry acetone (2 mL) for 12 h, 100 oC. b
0.5 mmol scale.
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Next, the scope of diazo ketones was studied (Fig 2). A variety of diazoacetoacetate esters were tolerated well
with yields ranging from 65 to 80% (3ab-3af). Importantly, the group installed on the 3- position of isoquinoline was
not limited to methyl, as the 3-ethyl, n-propyl and i-propyl analogues were assembled in moderate yields (3ag-3ai).
However, 2-diazobenzoylacetate failed to work under the procedure (3aj, < 5%). In particular, 2-diazoacetoacetone (2k)
took part in the reaction to access 4-acetyl isoquinoline derivatives in moderate yield. Notably, 2-diazodimedone (2l)
generated the fused cyclic products 3al in 40% yield.
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Figure 2. The substrate scope of α-diazo ketones a
a Reaction conditions: 1a (0.2 mmol), 2 (0.3 mmol), [Cp*RhCl2]2 (5 mol%), AgSbF6 (20 mol%), in dry acetone (2 mL) for 12 h, 100 oC.
To explore the reaction mechanism, imine 4 was prepared and subjected to the procedure in THF, which gave a
higher yield (56%) than benzylamine (Table 1, entry 11, 50%). Based on the previously reported examples on the rho-
dium-catalyzed annulation with diazo compounds,10d-f a proposed mechanism was outlined in Scheme 1. Firstly, in the
case of ketone as solvent, imine 4 was formed by the reaction between benzylamine and acetone, by which, the coordi-
nation with catalyst is enhanced. Then, the reaction between [Cp*RhCl2]2 and AgSbF6 generates [Cp*Rh(III)]2+ as an
active cation Rh(III) species. Secondly, coordination of cationic rhodium species with imine 4 facilitates the ortho ar-
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omatic C-H bond cleavage to produce intermediate 5. Then, the insertion of diazo 2 to C-Rh bond of 5 takes place
leading to rhodium carbene intermediate 6, along with the the loss of N2. Afterwards, the migratory insertion of rhodi-
um carbene 7 provides intermediate 7. Thirdly, the protonation of 7 produces intermediate 8, where the cation Rh(III)
species is regenerated. Then, the intermediate 8 takes part in the proton-catalyzed equilibrium reactions with interme-
diate 9 and acetone, followed by the intra- molecular annulation of amino and carbonyl in 9 furnishes the ring closure
leading to 1,2-dihydroisoquinoline. Finally, the aromatization of 1,2-dihydroisoquinoline provides the final product
isoquinoline by the extrusion of H2, as confirmed by PdCl2 testing paper (For detail, please see Supporting Infor-
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i
mation). No PrOH was determined by GC-MS. This step is believed to be the driving force in the equilibrium reac-
tions between 8 and 9.
Scheme 1. Mechanism Study
In conclusion, we have developed a rhodium-catalyzed annulation of benzylamine with diazo compounds, such as
diazoacetoacetate esters and 2-diazoacetoacetone leading to a diverse of 3,4-disubstituted isoquinoline in moderate to
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good yields with high regioselectivities. As such, it represents a key compliment to the previously developed annula-
tion with internal alkyne.
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EXPERIMENTAL SECTION
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General Information: Unless otherwise noted, all chemicals were purchased from commercial suppliers and used
without further purification. 1H NMR and 13C NMR spectra were recorded at ambient temperature on a 400 MHz (100
MHz for 13C) NMR spectrometer. NMR experiments are reported in δ units, parts per million (ppm), and were refer-
enced to CDCl3 ( 7.26 or 77.0 ppm) as the internal standard. The coupling constants J are given in Hz. Column chro-
matography was performed using EM Silica gel 60 (300-400 mesh). High-resolution mass spectra (HRMS) were ob-
tained using a Bruker micro TOF II focus spectrometer (ESI).
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Experimental Procedure:
General Procedure for the Rhodium-Catalyzed Annulations.
Under air, a 20 mL Schlenk tube equipped with a stir bar was charged with 1 (0.2 mmol), diazo compound 2 (0.3
mmol, 1.5 eq.), [Cp*RhCl2]2 (6.2 mg, 5 mol%), AgSbF6 (13.8 mg, 20 mol%), acetone (2 mL). The tube was sealed
with a Teflon lined cap. The reaction mixture was stirred at 100 °C for 12 h in oil bath. After the completion of the
reaction, the solvent was concentrated in vacuum and the residue was purified by flash column chromatography on
silica gel with petroleum ether-EtOAc as the eluent to give the desired product.
Ethyl 3-methylisoquinoline-4-carboxylate (3aa)17:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3aa (32.3 mg, 75% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.20 (s, 1H), 7.94 (d, J = 8.1 Hz, 1H), 7.87 (d, J = 8.5 Hz, 1H), 7.70 (t, J =
7.6 Hz, 1H), 7.56 (t, J = 7.5 Hz, 1H), 4.54 (q, J = 7.1 Hz, 2H), 2.74 (s, 3H), 1.46 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3,
100 MHz) δ 168.5, 153.3, 149.4, 133.1, 131.3, 127.8, 126.7, 126.4, 123.6, 123.2, 61.6, 22.9, 14.3.
Ethyl 3,8-dimethylisoquinoline-4-carboxylate (3ba):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ba (32.8 mg, 72% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.39 (s, 1H), 7.67 (d, J = 8.5 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H), 7.32 (t, J =
7.0 Hz, 1H), 4.52 (q, J = 7.2 Hz, 2H), 2.75 (s, 3H), 2.72 (s, 3H), 1.45 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz)
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δ 168.8, 150.0, 148.7, 135.6, 133.4, 131.1, 127.6, 125.4, 123.6, 121.7, 61.6, 22.7, 18.5, 14.3; HRMS (ESI) m/z calcd
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for C14H16NO2 (M + H)+ 230.1175, found 230.1176.
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Ethyl 3,6-dimethylisoquinoline-4-carboxylate (3ca):
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ca (28.2 mg, 62% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.12 (s, 1H), 7.83 (d, J = 8.4 Hz, 1H), 7.60 (s, 1H), 7.38 (d, J = 7.9 Hz, 1H),
4.54 (q, J = 7.2 Hz, 2H), 2.71 (s, 3H), 2.52 (s, 3H), 1.46 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.7,
152.8, 149.3, 142.0, 133.4, 129.0, 127.6, 124.9, 122.7, 122.4, 61.6, 22.9, 22.4, 14.3; HRMS (ESI) m/z calcd for
C14H16NO2 (M + H)+ 230.1175, found 230.1178.
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Ethyl 6-methoxy-3-methylisoquinoline-4-carboxylate (3da):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3da (33.8 mg, 69% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.02 (s, 1H), 7.81 (d, J = 8.7 Hz, 1H), 7.18-7.15 (m, 2H), 4.53 (q, J = 7.2 Hz,
2H), 3.90 (s, 3H), 2.70 (s, 3H), 1.46 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.7, 161.8, 152.3, 150.4,
135.3, 129.6, 122.3, 122.1, 119.7, 101.6, 61.4, 55.4, 23.2, 14.3; HRMS (ESI) m/z calcd for C14H16NO3 (M + H)+
246.1124, found 246.1129.
Ethyl 6-(tert-butyl)-3-methylisoquinoline-4-carboxylate (3ea):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ea (34.7 mg, 64% yield) as
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yellow oil: H NMR (CDCl3, 400 MHz) δ 9.13 (s, 1H), 7.88 (d, J = 8.7 Hz, 1H), 7.78 (s, 1H), 7.65 (dd, J = 8.7 Hz,
1H), 4.55 (q, J = 7.1 Hz, 2H), 2.72 (s, 3H), 1.48 (t, J = 7.1 Hz, 3H), 1.39 (s, 9H); 13C NMR (CDCl3, 100 MHz) δ 168.8,
154.6, 152.6, 149.4, 133.3, 127.4, 125.8, 124.8, 123.2, 118.5, 61.5, 35.5, 30.9, 22.9, 14.4; HRMS (ESI) m/z calcd for
C17H22NO2 (M + H)+ 272.1645, found 272.1651.
Ethyl 3-methyl-6-phenylisoquinoline-4-carboxylate (3fa):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3fa (33.2 mg, 57% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.22 (s, 1H), 8.05-8.00 (m, 2H), 7.81 (d, J = 8.5 Hz, 1H), 7.69-7.67 (m, 2H),
7.52-7.40 (m, 3H), 4.56 (q, J = 7.1 Hz, 2H), 2.76 (s, 3H), 1.48 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ
168.5, 153.0, 149.9, 144.1, 140.2, 133.5, 129.0, 128.4, 128.3, 127.6, 126.7, 125.5, 123.2, 121.5, 61.7, 23.0, 14.3;
HRMS (ESI) m/z calcd for C19H18NO2 (M + H)+ 292.1332, found 292.1335.
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Ethyl 6-bromo-3-methylisoquinoline-4-carboxylate (3ga):
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ga (45.3 mg, 77% yield) as
yellow solid: mp 51-52 oC; 1H NMR (CDCl3, 400 MHz) δ 9.14 (s, 1H), 8.06 (s, 1H), 7.79 (d, J = 8.6 Hz, 1H), 7.63 (d,
J = 8.6 Hz, 1H), 4.54 (q, J = 7.1 Hz, 2H), 2.73 (s, 3H), 1.46 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 167.8,
153.1, 150.9, 134.2, 130.4, 129.3, 126.6, 126.2, 124.7, 122.0, 61.8, 23.2, 14.2; HRMS (ESI) m/z calcd for
C13H13BrNO2 (M + H)+ 294.0124, found 294.0126.
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Ethyl 6-chloro-3-methylisoquinoline-4-carboxylate (3ha)17:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ha (38.8 mg, 78% yield) as
yellow solid: mp 64-66 oC; 1H NMR (CDCl3, 400 MHz) δ 9.15 (s, 1H), 7.88-7.86 (m, 2H), 7.49 (dd, J = 8.7 Hz, 1H),
4.54 (q, J = 7.1 Hz, 2H), 2.73 (s, 3H), 1.46 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 167.9, 153.0, 151.0,
137.9, 133.9, 129.4, 127.9, 124.6, 122.9, 122.1, 61.8, 23.2, 14.2.
Ethyl 6-fluoro-3-methylisoquinoline-4-carboxylate (3ia):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ia (31.7 mg, 68% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.15 (s, 1H), 7.97-7.94 (m, 1H), 7.54 (dd, J = 10.5 Hz, 1H), 7.32 (td, J = 8.6
Hz, 1H), 4.53 (q, J = 7.1 Hz, 2H), 2.74 (s, 3H), 1.46 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.0, 164.0
(d, JC-F = 252 Hz), 152.8, 151.0, 134.9 (d, JC-F = 11 Hz), 130.9 (d, JC-F = 10 Hz), 123.7, 122.6, 117.4 (d, JC-F = 7 Hz),
107.9 (d, JC-F = 23 Hz), 61.8, 23.2, 14.2; HRMS (ESI) m/z calcd for C13H13FNO2 (M + H)+ 234.0924, found 234.0922.
Ethyl 3-methyl-6-(trifluoromethyl)isoquinoline-4-carboxylate (3ja):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ja (36.2 mg, 64% yield) as
1
yellow oil: H NMR (CDCl3, 400 MHz) δ 9.29 (s, 1H), 8.23 (s, 1H), 8.08 (d, J = 8.5 Hz, 1H), 7.74 (dd, J = 8.5 Hz,
1H), 4.57 (q, J = 7.2 Hz, 2H), 2.78 (s, 3H), 1.48 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 167.6, 153.3,
151.5, 132.8 (d, JC-F = 33 Hz), 132.5, 129.1, 127.0, 125.0, 123.5, 122.6 (q, JC-F = 3.0 Hz), 121.7 (q, JC-F = 4.0 Hz), 62.0,
23.2, 14.2; HRMS (ESI) m/z calcd for C14H13F3NO2 (M + H)+ 284.0892, found 284.0893.
Ethyl 3-methylbenzo[h]isoquinoline-4-carboxylate (3ka):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ka (39.3 mg, 73% yield) as
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yellow solid: mp 54-55 C; H NMR (CDCl3, 400 MHz) δ 9.95 (s, 1H), 8.72 (d, J = 8.2 Hz, 1H), 7.93-7.87 (m, 2H),
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7.73-7.69 (m, 2H), 7.63 (d, J = 7.4 Hz, 1H), 4.57 (q, J = 7.1 Hz, 2H), 2.77 (s, 3H), 1.48 (t, J = 7.1 Hz, 3H); 13C NMR
(CDCl3, 100 MHz) δ 168.7, 150.9, 147.1, 133.2, 132.7, 131.4, 129.0, 128.8, 128.1, 127.4, 124.5, 122.6, 121.7, 121.5,
61.7, 22.9, 14.3; HRMS (ESI) m/z calcd for C17H16NO2 (M + H)+ 266.1175, found 266.1179.
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Ethyl 1,3-dimethylisoquinoline-4-carboxylate (3la)18:
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3la (27.9 mg, 61% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 8.09 (d, J = 8.4 Hz, 1H), 7.86 (d, J = 8.5 Hz, 1H), 7.67 (t, J = 7.7 Hz, 1H),
7.54 (t, J = 7.6 Hz, 1H), 4.52 (q, J = 7.2 Hz, 2H), 2.94 (s, 3H), 2.68 (s, 3H), 1.45 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3,
100 MHz) δ 168.9, 159.8, 148.0, 133.2, 130.8, 126.4, 125.7, 125.1, 124.1, 121.9, 61.5, 22.9, 22.6, 14.3.
Ethyl 3-methyl-1-phenylisoquinoline-4-carboxylate (3ma)10f:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ma (37.3 mg, 64% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 8.04 (d, J = 8.5 Hz, 1H), 7.93 (d, J = 8.5 Hz, 1H), 7.72-7.65 (m, 3H), 7.56-
7.46 (m, 4H), 4.58 (q, J = 7.1 Hz, 2H), 2.80 (s, 3H), 1.49 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.8,
161.7, 148.4, 139.1, 134.1, 130.9, 129.8, 128.8, 128.4, 127.8, 126.5, 124.5, 123.8, 122.5, 61.6, 23.1, 14.3.
Ethyl 3,7-dimethylisoquinoline-4-carboxylate (3na):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3na (32.8 mg, 65% yield) as
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yellow oil: H NMR (CDCl3, 300 MHz) δ 9.10 (s, 1H), 7.77 (d, J = 8.6 Hz, 1H), 7.69 (s, 1H), 7.52 (dd, J = 8.6 Hz,
1H), 4.52 (q, J = 7.1 Hz, 2H), 2.71 (s, 3H), 2.50 (s, 3H), 1.45 (t, J = 7.1 Hz, 3H); 13C NMR (CDCl3, 75 MHz) δ 168.6,
152.6, 148.5, 136.7, 133.7, 131.4, 126.6, 126.6, 123.4, 123.0, 61.6, 22.8, 21.5, 14.3; HRMS (ESI) m/z calcd for
C14H16NO2 (M + H)+ 230.1175, found 230.1179.
Methyl 3-methylisoquinoline-4-carboxylate (3ab)19:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ab (32.2 mg, 80% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.19 (s, 1H), 7.93 (d, J = 8.2 Hz, 1H), 7.84 (d, J = 8.5 Hz, 1H), 7.69 (t, J =
7.7 Hz, 1H), 7.54 (t, J = 7.5 Hz, 1H), 4.04 (s, 3H), 2.72 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 169.0, 153.4, 149.6,
133.1, 131.4, 127.8, 126.8, 126.3, 123.6, 122.8, 52.4, 23.0.
n-Propyl 3-methylisoquinoline-4-carboxylate (3ac):
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ac (32.1 mg, 70% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.19 (s, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.86 (d, J = 8.5 Hz, 1H), 7.70 (t, J =
7.7 Hz, 1H), 7.55 (t, J = 7.5 Hz, 1H), 4.43 (t, J = 6.7 Hz, 2H), 2.74 (s, 3H), 1.84 (m, J = 6.7 Hz, 2H), 1.04 (t, J = 7.4
Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.6, 153.2, 149.4, 133.2, 131.3, 127.8, 126.7, 126.4, 123.6, 123.2, 67.3,
22.9, 22.0, 10.5; HRMS (ESI) m/z calcd for C14H16NO2 (M + H)+ 230.1176, found 230.1175.
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i-Propyl 3-methylisoquinoline-4-carboxylate (3ad):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ad (31.2 mg, 68% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.19 (s, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.86 (d, J = 8.5 Hz, 1H), 7.70 (m, 1H),
7.55 (t, J = 7.4 Hz, 1H), 5.46 (m, J = 6.3 Hz, 1H), 2.73 (s, 3H), 1.46-1.44 (m, 6H); 13C NMR (CDCl3, 100 MHz) δ
168.0, 153.1, 149.0, 133.1, 131.3, 127.8, 126.7, 126.4, 123.5, 123.4, 69.4, 22.8, 21.9; HRMS (ESI) m/z calcd for
C14H16NO2 (M + H)+ 230.1176, found 230.1175.
tert-Butyl 3-methylisoquinoline-4-carboxylate (3ae)19:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ae (31.5 mg, 65% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.17 (s, 1H), 7.93 (d, J = 8.2 Hz, 1H), 7.86 (d, J = 8.5 Hz, 1H), 7.70 (m, 1H),
7.54 (t, J = 7.5 Hz, 1H), 2.74 (s, 3H), 1.68 (s, 9H); 13C NMR (CDCl3, 100 MHz) δ 167.8, 152.7, 148.4, 133.0, 131.2,
127.8, 126.6, 126.4, 124.5, 123.4, 82.8, 28.2, 22.6.
Benzyl 3-methylisoquinoline-4-carboxylate (3af)19:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3af (45.2 mg, 82% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.20 (s, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.82 (d, J = 8.5 Hz, 1H), 7.69-7.65 (m,
1H), 7.57-7.48 (m, 3H), 7.43-7.34 (m, 3H), 5.51 (s, 2H), 2.70 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.3, 153.4,
149.6, 135.2, 133.2, 131.4, 128.7, 128.6, 128.6, 127.8, 126.8, 126.3, 123.5, 122.8 , 67.4, 23.0.
Ethyl 3-ethylisoquinoline-4-carboxylate (3ag):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ag (30.1 mg, 66% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.23 (s, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.83 (d, J = 8.5 Hz, 1H), 7.72-7.68 (m,
1H), 7.56 (t, J = 7.5 Hz, 1H), 4.53 (q, J = 7.1 Hz, 2H), 2.97 (q, J = 7.5 Hz, 2H), 1.45 (t, J = 7.1 Hz, 3H), 1.38 (t, J =
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7.5 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.6, 154.2, 153.5, 133.1, 131.2, 127.8, 126.8, 126.4, 123.6, 122.8, 61.6,
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Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ah (32.4 mg, 67% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.22 (s, 1H), 7.93 (d, J = 8.2 Hz, 1H), 7.82 (d, J = 8.5 Hz, 1H), 7.71-7.67 (m,
1H), 7.55 (t, J = 7.5 Hz, 1H), 4.53 (q, J = 7.2 Hz, 2H), 2.92 (t, J = 7.7 Hz, 2H), 1.84 (m, J = 7.7 Hz, 2H), 1.45 (t, J =
7.1 Hz, 3H), 0.99 (t, J = 7.4 Hz, 3H); 13C NMR (CDCl3, 100 MHz) δ 168.6, 153.4, 153.0, 133.1, 131.2, 127.8, 126.8,
126.4, 123.6, 123.2, 61.6, 38.4, 23.3, 14.3, 14.0.
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Ethyl 3-isopropylisoquinoline-4-carboxylate (3ai):
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ai (26.8 mg, 55% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.27 (s, 1H), 7.94 (d, J = 8.2 Hz, 1H), 7.77 (d, J = 8.4 Hz, 1H), 7.71-7.67 (m,
1H), 7.57-7.54 (m, 1H), 4.53 (q, J = 7.1 Hz, 2H), 3.25 (hept, J = 6.7 Hz, 1H), 1.45 (t, J = 7.1 Hz, 3H), 1.39-1.38 (m,
6H); 13C NMR (CDCl3, 100 MHz) δ 168.8, 157.0, 153.5, 132.9, 131.2, 127.8, 126.8, 126.5, 123.6, 122.3, 61.6, 33.6,
22.4, 14.3; HRMS (ESI) m/z calcd for C15H18NO2 (M + H)+ 244.1332, found 244.1333.
1-(3-Methylisoquinolin-4-yl)ethan-1-one (3ak)17:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3ak (21.5 mg, 58% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.19 (s, 1H), 7.97 (d, J = 8.2 Hz, 1H), 7.72-7.68 (m, 1H), 7.62-7.55 (m, 2H),
2.66 (s, 3H), 2.65 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 206.0, 152.7, 145.8, 132.0, 131.3, 131.3, 128.1, 126.8, 126.5,
122.9, 32.7, 22.3.
3,3-Dimethyl-3,4-dihydrophenanthridin-1(2H)-one (3al)17:
Flash column chromatography on a silica gel (ethyl acetate: petroleum ether, 1: 3) give 3al (18.0 mg, 40% yield) as
yellow oil: 1H NMR (CDCl3, 400 MHz) δ 9.39 (d, J = 8.7 Hz, 1H), 9.28 (s, 1H), 7.96 (d, J = 8.1 Hz, 1H), 7.83 (t, J =
7.8 Hz, 1H), 7.61 (t, J = 7.5 Hz, 1H), 3.23 (s, 2H), 2.66 (s, 2H), 1.16 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 201.1,
159.6, 157.3, 133.5, 133.2, 128.2, 127.7, 127.1, 125.7, 119.7, 54.1, 47.7, 32.8, 28.1.
ASSOCIATED CONTENT
Supporting Information:
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The Supporting Information is available free of charge via the Internet at http://pubs.acs.org.
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Experimental details on the mechanism study, along with copies of H and 13C NMR spectra of compounds 3aa-3ma
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and 3ab-3al.
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ACKNOWLEDGMENT
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We thank the National Natural Science Foundation of China (nos. 21272028 and 21572025), “Innovation & En-
trepreneurship Talents” Introduction Plan of Jiangsu Province, the Key University Science Research Project of Jiangsu
Province (15KJA150001), Qing Lan Project of Jiangsu Province, Jiangsu Key Laboratory of Advanced Catalytic Ma-
terials &Technology (BM2012110) and Advanced Catalysis and Green Manufacturing Collaborative Innovation Cen-
ter for financial supports. Chu thanks the Research Innovation Program for College Graduates of Jiangsu Province
(Grant No. KYZZ15-0304) for financial supports.
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