Copper-catalyzed synthesis of pyrido-fused quinazolinones from 2-aminoarylmethanols and isoquinolines or tetrahydroisoquinolines

Article abstract of DOI:10.1039/d1ob00229e

Pyrido-fused quinazolinones were synthesizedviacopper-catalyzed cascade C(sp²)-H amination and annulation of 2-aminoarylmethanols with isoquinolines or pyridines. The transformation proceeded readily in the presence of a commercially available CuCl₂catalyst with molecular oxygen as a green oxidant. Moreover, the dehydrogenative cross-coupling of 2-aminoarylmethanols with tetrahydroisoquinolines was explored, in which CuBr exhibited higher catalytic activity than CuCl₂. Broad substrate scope with good tolerance of functionalities was observed under the optimized reaction conditions. The bioactive naturally occurring alkaloid rutaecarpine could be obtained by this strategy. The remarkable feature of this protocol is that complicated heterocyclic structures are readily achieved in a single synthetic step from easily accessible reactants and catalysts. This pathway to pyrido-fused quinazolinones would be complementary to existing protocols.

Full text of DOI:10.1039/d1ob00229e

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Copper-catalyzed synthesis of pyrido-fused
quinazolinones from 2-aminoarylmethanols and
Cite this: DOI: 10.1039/d1ob00229e
isoquinolines or tetrahydroisoquinolines†
a,b
Thao T. Nguyen,
‡
a,b Khang X. Nguyen,
‡
a,b Phuc H. Pham, a,b Duc Ly,
Duyen K. Nguyen,a,b Khoa D. Nguyen,a,b Tung T. Nguyen
*
a,b and
a,b
Nam T. S. Phan
*
Pyrido-fused quinazolinones were synthesized via copper-catalyzed cascade C(sp2)–H amination and
annulation of 2-aminoarylmethanols with isoquinolines or pyridines. The transformation proceeded
readily in the presence of a commercially available CuCl2 catalyst with molecular oxygen as a green
oxidant. Moreover, the dehydrogenative cross-coupling of 2-aminoarylmethanols with tetrahydroisoqui-
nolines was explored, in which CuBr exhibited higher catalytic activity than CuCl2. Broad substrate scope
with good tolerance of functionalities was observed under the optimized reaction conditions. The bio-
active naturally occurring alkaloid rutaecarpine could be obtained by this strategy. The remarkable feature
of this protocol is that complicated heterocyclic structures are readily achieved in a single synthetic step
from easily accessible reactants and catalysts. This pathway to pyrido-fused quinazolinones would be
complementary to existing protocols.
Received 5th February 2021,
Accepted 23rd April 2021
DOI: 10.1039/d1ob00229e
rsc.li/obc
base-controlled carbonylative coupling followed by nucleophi-
Introduction
lic aromatic substitution,15 C(sp2)–H pyridocarbonylation with
Quinazolinones are a significant class of N-heterocyclic com- carbon monoxide,16 direct carbonylation of C(sp2)–H bonds
pounds, frequently present in a wide range of pharmaceuti- with dimethylformamide,17 and carbonylation/nucleophilic
cally relevant natural products, drug candidates, agricultural aromatic substitution reaction sequences.18 Cheaper copper-
chemicals, and functionalized organic materials.1–3 Among based catalysts have been targeted for reactions, including
numerous quinazolinone derivatives, fused quinazolinones domino transformations between 2′-haloacetophenones and
play essential roles in drug discovery and development due to 2-aminopyridines,19 tandem reactions via oxidation, intra-
their versatile biological and pharmacological activities.4–6 molecular cyclization and decarbonylation20 (Scheme 2a),
Representative fused quinazolinones in natural products and domino transformations from 2-bromopyridines and
drug discovery research are illustrated in Scheme 1.7–10 isatins9 (Scheme 2b), and tandem C(sp2)–H amination fol-
Classical synthetic strategies mainly relied on the reactions of
electron-deficient 2-chloropyridines with substituted anthrani-
lic acids, suffering from several disadvantages.11 Metal-free
protocols have been developed to access these structures.12,13
Alternative pathways utilizing transition metal catalysts have
been explored. Palladium-catalyzed transformations have been
studied, including dearomatizing carbonylation protocols,14
aFaculty of Chemical Engineering, Ho Chi Minh City University of Technology
(HCMUT), 268 Ly Thuong Kiet, District 10, Ho Chi Minh City, Vietnam.
E-mail: tungtn@hcmut.edu.vn, ptsnam@hcmut.edu.vn; Fax: (+84 8)38637504;
Tel: (+84 8) 38647256 ext. 5681
bVietnam National University Ho Chi Minh City, Linh Trung Ward, Thu Duc District,
Ho Chi Minh City, Vietnam
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
d1ob00229e
Scheme 1 Representative fused quinazolinones in natural products and
‡These authors contributed equally to this work.
drug discovery research.
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syntheses which could involve complicated and laborious pro-
tection–deprotection sequences, thus offering the advantages
of atom economy and waste minimization when compared to
traditional synthetic approaches.26–28 Cascade reactions have
emerged as key steps in the efficient synthesis of complex
structures, minimizing the amounts of waste generated by
several chemical processes.29,30 Therefore, cascade reactions
via direct C–H bond amination would be desirable for the syn-
thesis of nitrogen-containing heterocycles.31 Over the last
decade, numerous structures have been achieved through the
C–H bond amination pathway, using different transition metal
catalysts, including nickel,32 rhodium,33 iron,34 manganese,35
copper,36 cobalt,37 and palladium.36 In this work, we would
like to present the synthesis of pyrido-fused quinazolinones
via copper-catalyzed cascade C(sp2)–H amination and annula-
tion of 2-aminoarylmethanols with isoquinolines or pyridines
(Scheme 2d). A variety of pyrido-fused quinazolinone deriva-
tives were obtained in the presence of a readily available
copper(II) chloride catalyst, utilizing molecular oxygen as a
green oxidant. This synthetic strategy would be complementary
to previous approaches in the synthesis of these valuable
heterocyclic structures.
Scheme 2 Copper-catalyzed synthesis of pyrido-fused quinazolinones.
lowed by annulation21 (Scheme 2c). Additionally, a cobalt
nano-catalyst has been employed for the synthesis of ring-
fused quinazolinones from aminoarylmethanols and cyclic
amines.22
Direct C–H bond functionalization has been considered as
an environmentally benign and robust method in organic syn-
thesis, averting the necessity of pre-installation of a reactive
functional group in coupling precursors.23–25 This strategy
typically reduces the number of transformations in multi-step
Results and discussion
The research was commenced with the reaction of 2-amino-
benzyl alcohol (1a) and isoquinoline (2a) to form 8H-isoquino-
lino[1,2-b]quinazolin-8-one (3aa) (Table 1). Initial studies indi-
cated that the transformation required the presence of a
Table 1 Screening of conditions for the annulation of 2-aminobenzyl alcohol with isoquinolinea
Entry
Temperature (°C)
Catalyst (mol%)
1a : 2a (mol : mol)
Additive (equiv.)
Solvent (mL)
Yieldb (%)
1
2
3
4
5
6
7
8
80
Cu(OAc)2 (20%)
Cu(OAc)2 (20%)
Cu(OAc)2 (20%)
—
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 2.5
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
1 : 3
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
TsOH·H2O (1.5)
—
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMF (0.5 mL)
DMAc (0.5 mL)
NMP (0.5 mL)
DMSO (0.5 mL)
DMF (1.5 mL)
27
52
51
0
64
62
61
63
58
6
37
46
65
68
67
64
58
81
100
120
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
CuCl2 (20%)
CuBr2 (20%)
CuBr (20%)
CuCl (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
CuCl2 (20%)
9
10
11
12
13
14
15
16
17
18
HCOOH (1.5)
AcOH (1.5)
CH3SO3H (1.5)
TsOH·H2O (0.2)
TsOH·H2O (0.2)
TsOH·H2O (0.2)
TsOH·H2O (0.2)
TsOH·H2O (0.2)
a Reaction conditions: 2-aminobenzyl alcohol (0.1 mmol; 12 h; reactor flushed with oxygen). TsOH: p-toluenesulfonic acid; DMF: N,N-dimethyl-
formamide; DMSO: dimethyl sulfoxide; DMAc: N,N-dimethylacetamide; and NMP: N-methyl-2-pyrrolidone. b GC yield.
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copper catalyst, an acidic additive, and molecular oxygen as an lower activity than CuCl2. Furthermore, the reactant molar
oxidant. Primarily, the reaction conditions were screened to ratio significantly influenced the transformation, and using 3
improve the yield of 3aa, regarding temperature, catalyst, addi- equivalents of 2a offered the best result. Only 6% yield was
tive, reactant molar ratio, and solvent (see Table S1† for obtained in the absence of any acidic additive (entry 10).
detailed data). Conducting the reaction at various tempera- Several organic acids were tested, and utilizing 20 mol%
tures revealed that the best yield was obtained at 100 °C (entry p-toluenesulfonic acid led to 68% yield (entry 14). Both
2). No trace amounts of the pyrido-fused quinazolinone increasing and decreasing the amount of the additive dis-
product were detected in the absence of any catalyst (entry 4). played a negative impact on the transformation. Moreover, by
A series of copper salts were employed for the reaction, and changing the solvent and solvent volume, the yield of 3aa
20 mol% CuCl2 exhibited the best performance with 64% yield could be enhanced to 81% (entry 18). It should be noted that
of 3aa being achieved (entry 5). Increasing or decreasing the the reaction conducted under air afforded 37% yield while no
amount of CuCl2 resulted in lower yields of the desired product was detected for the experiment carried out under
product. Additionally, several iron salts were tested, offering argon.
Scheme 3 Annulation of 2-aminoarylmethanols with isoquinolines and pyridines. Reaction conditions: 2-aminoarylmethanols 1 (0.1 mmol, 1.0
equiv.); isoquinolines 2 (0.3 mmol, 3.0 equiv.); CuCl2 (20 mol%), TsOH·H2O (20 mol%); DMF (1.5 mL), 100 °C; 12 h. a Reaction was performed at
120 °C. b Reaction was performed at 130 °C. c Isoquinoline-4-boronic acid pinacol ester (0.2 mmol, 2.0 equiv.) and CuCl2 (1.2 equiv.) were used.
Yields are isolated yields. Product isolation is based on the combination of 2 parallel reaction tubes.
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With these results in mind, we subsequently explored the benzyl alcohol were used for annulation with isoquinoline,
generality of the protocol in the synthesis of pyrido-fused qui- affording the corresponding heterocyclic products in high
nazolinones (Scheme 3). First, a series of isoquinolines and yields (3ba, 3ca, 3da, and 3ea).
pyridines were examined for the transformation with 2-amino-
Additionally, the dehydrogenative cross-coupling of 2-ami-
benzyl alcohol. Under standard conditions, 3aa was obtained noarylmethanols with tetrahydroisoquinolines was investi-
in 78% isolated yield. Bromo-substituted isoquinolines readily gated (Scheme 4). Initially, the annulation of 2-aminobenzyl
reacted with 2-aminobenzyl alcohol, producing 3ab and 3ac in alcohol (1a) and tetrahydroisoquinoline (4a) to form 5,6-
81% and 83% yields, respectively. Isoquinolin-5-amine and its dihydro-8H-isoquinolino[1,2-b]quinazolin-8-one (5aa) was
derivatives were less reactive towards the transformation, addressed. The reaction conditions were screened to maximize
though 3ad, 3ae, and 3af were generated in 52%, 68%, and the yield of 5aa, concerning temperature, catalyst, additive,
42% yields, respectively. Similarly, the reaction of pyrrolyl-sub- reactant molar ratio, and solvent (see Table S2† for detailed
stituted isoquinolines proceeded with difficulty, affording 3ag data). Different from the formation of 3aa, CuBr should be
and 3ah in 50% and 38% yields, respectively. In contrast, pyra- used instead of CuCl2 for the synthesis of 5aa. The best result
zolyl-substituted isoquinolines are more reactive, with 3ai and was achieved for the reaction conducted in DMF at 100 °C for
3aj being obtained in 76% and 78% yields, respectively. 12 h under oxygen, utilizing 3 equivalents of tetrahydroisoqui-
Compared to other reactants, 5-((4-chlorophenyl)thio)isoquino- nolines, in the presence of 20 mol% CuBr and 20 mol%
line emerged as the most reactive candidate, forming 3ak in TsOH·H2O. Under these conditions, 86% GC yield of 5aa was
75% yield. Nitro- and sulfonic acid-substituted isoquinolines detected (entry 42, Table S2†), and 80% isolated yield of 5aa
and pyridines exhibited lower reactivity in this transformation, was achieved. Several derivatives of 5aa were also synthesized
presumably due to their low basicity (3al, 3am, 3an, and 3ao). utilizing the standard reaction conditions (Scheme 3).
Interestingly, utilizing 4-(4,4,5,5-tetramethyl-1,3,2-dioxaboro- Substituted 2-aminobenzyl alcohols were reactive in the reac-
lan-2-yl)isoquinoline in the presence of excess CuCl2 led to a tion with 4a, producing the corresponding products in high
mixture of 3aa and 3ap in 37% and 46% yields, respectively. In yields (5ba, 5ca, 5ea, 5fa, 5ga, 5ha and 5ia). (2-Aminopyridin-3-
the next series of experiments, several derivatives of 2-amino- yl)methanol was less reactive than 1a, though 5da was
Scheme 4 Annulation of 2-aminoarylmethanols with tetrahydroisoquinolines. Reaction conditions: 2-aminoarylmethanols 1 (0.1 mmol, 1.0 equiv.);
tetrahydroisoquinolines 4 (0.3 mmol, 3.0 equiv.); CuBr (20 mol%); TsOH·H2O (20 mol%); DMF (0.5 mL); 100 °C; 12 h. Yields are isolated yields.
Product isolation is based on the combination of 2 parallel reaction tubes.
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obtained in 42% yield. The reaction of 1a and 6,7-dimethoxy- was formed via copper-catalyzed oxidation of the alcohol
1,2,3,4-tetrahydroisoquinoline hydrochloride proceeded to moiety under atmospheric oxygen.38,39 The product 3aa was
70% yield of 5ab under standard conditions. Interestingly, fol- formed via annulation reaction between 2-aminobenzaldehyde
lowing this protocol, bioactive naturally occurring alkaloid (6) and isoquinoline (2a), followed by oxidation to furnish the
rutaecarpine (5ad) was obtained in 63% yield. These obser- quinazolinone ring.36 A similar pathway for the formation of
vations were comparable to those previously reported in the lit- 5aa from tetrahydroisoquinoline (4a) is also possible, with the
erature, where a nanocobalt catalyst was employed for similar cyclic imine 9 being the active intermediate.40 In both cases,
transformations.22
the significant basicity of isoquinoline or the dihydroisoquino-
Control experiments were performed to probe the elemen- line nitrogen triggered the Csp2–H amination step. This was
tary steps of the transformation (Scheme 5). A plausible reac- activated by a proton source, as evidenced from the control
tion pathway for the formation of (tetrahydro)isoquinolino- reaction using isoquinoline hydrochloride (Scheme 5c). An
fused quinazolinone is proposed in Scheme 6. The active inter- alternative mechanism for the formation of 5aa is also pro-
mediate was believed to be 2-aminobenzaldehyde (6), which vided, due to the observation of an amidine intermediate by
Scheme 5 Control experiments.
Scheme 6 Proposed reaction pathway.
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GC-MS during the reaction progress. The cyclic amidine 8 was dried over anhydrous Na2SO4, and analyzed by GC with refer-
susceptible to oxidation when exposed to an oxygen atmo- ence to diphenyl ether. To isolate the pyrido-fused quinazoli-
sphere.41 Additionally, the reaction of 6 with 2a in the absence none product, the combined organic extracts were concen-
of the copper catalyst did not result in any trace amount of trated in vacuo and purified by column chromatography on
3aa. In contrast, 5aa was detected by GC-MS for the reaction of silica gel with a hexane/ethyl acetate solvent system to afford
6 with 4a in the absence of the copper catalyst. In both cases, the pure product. The product identity was further confirmed
intermediates B and E were not detected by GC-MS under by GC-MS, 1H NMR and 13C NMR.
these conditions due to their low stability. These observations
imply that the conversion of B to 3aa required the copper cata-
lyst, while E could be converted to 5aa without the copper Conflicts of interest
species. Nevertheless, the presence of the copper catalyst accel-
There are no conflicts to declare.
erated the formation of 5aa from E. Indeed, further investi-
gation is needed to elucidate the mechanism of the
transformation.
Acknowledgements
This work is fully funded by The Viet Nam National
Conclusions
Foundation for Science and Technology Development
(NAFOSTED) under the Project code 104.01-2019.340 (PI: Nam
T. S. Phan). Khang X. Nguyen acknowledges Vingroup Joint
Stock Company and the Domestic Master/PhD Scholarship
Programme of Vingroup Innovation Foundation (VINIF),
Vingroup Big Data Institute (VINBIGDATA) for the scholarship
he has received.
In summary, a new route to pyrido-fused quinazolinones via
copper-catalyzed cascade C(sp2)–H amination and annulation
of 2-aminoarylmethanols with isoquinolines or pyridines was
developed. The transformation proceeded readily in the pres-
ence of a commercially available copper salt catalyst, utilizing
molecular oxygen as a green oxidant. Among a series of copper
salts, CuCl2 offered the best catalytic activity. An acidic additive
was required, and p-toluenesulfonic acid monohydrate
emerged as the best candidate for the formation of the pyrido-
fused quinazolinones. Broad substrate scope with good toler-
ance of functionalities was observed under the optimized reac-
tion conditions. Moreover, the dehydrogenative cross-coupling
of 2-aminoarylmethanols with tetrahydroisoquinolines was
investigated under similar conditions, in which CuBr exhibited
higher catalytic activity than CuCl2. Several ring-fused quinazo-
linones were obtained following this protocol. The remarkable
feature of this protocol is that complicated heterocyclic struc-
tures are readily achieved in a single synthetic step from easily
accessible reactants and catalysts. This pathway to pyrido-
fused quinazolinones would be complementary to existing
methods, and would be significant to pharmaceutical chem-
istry, materials science, and industrial chemistry.
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