Rh(III)?catalyzed synthesis of isoquinolines from N-hydroxyoximes and alkynes in γ-valerolactone

Article abstract of DOI:10.1080/00397911.2020.1819326

A Rh (III)?catalyzed synthesis of isoquinoline derivatives from N-hydroxyoximes and alkynes via C–H activation/annulation process in biomass-derived γ-valerolactone (GVL) has been developed. A series of functional groups were well tolerated, affording the desired products in good to excellent yields.

Full text of DOI:10.1080/00397911.2020.1819326

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Rh(III)−catalyzed synthesis of isoquinolines from
N-hydroxyoximes and alkynes in γ-valerolactone
Kuan-Chang Jiang , Liang Wang , Qun Chen , Ming-Yang He , Ming-Gui Shen &
Zhi-Hui Zhang
To cite this article: Kuan-Chang Jiang , Liang Wang , Qun Chen , Ming-Yang He , Ming-Gui Shen
& Zhi-Hui Zhang (2020): Rh(III)−catalyzed synthesis of isoquinolines from N-hydroxyoximes and
alkynes in γ-valerolactone, Synthetic Communications, DOI: 10.1080/00397911.2020.1819326
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https://doi.org/10.1080/00397911.2020.1819326
Rh(III)ꢀcatalyzed synthesis of isoquinolines from
N-hydroxyoximes and alkynes in c-valerolactone
Kuan-Chang Jianga, Liang Wanga,b, Qun Chena, Ming-Yang Hea, Ming-Gui Shenc,
and Zhi-Hui Zhanga
aSchool of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials and
b
Technology, Changzhou University, Changzhou, China; School of Chemical and Pharmaceutical
c
Engineering, Changzhou Vocational Institute of Engineering, Changzhou, China; National Engineering
Laboratory for Biomass Chemical Utilization, Key and Open Laboratory on Forest Chemical Engineering,
Key Laboratory of Biomass Energy and Material, Institute of Chemical Industry of Forest Products,
Nanjing, China
ABSTRACT
ARTICLE HISTORY
Received 23 June 2020
A
Rh (III)ꢀcatalyzed synthesis of isoquinoline derivatives from
N-hydroxyoximes and alkynes via C–H activation/annulation process
in biomass-derived c-valerolactone (GVL) has been developed. A ser-
ies of functional groups were well tolerated, affording the desired
products in good to excellent yields.
KEYWORDS
Annulation; C–H activation;
isoquinolines; green
solvent; ketoximes
GRAPHICAL ABSTRACT
Introduction
Isoquinoline derivatives are very important heterocycles that have found wide applica-
tions in natural products and pharmaceuticals.[1] They also serve as useful ligands in
synthetic organic chemistry.[2] Traditionally, synthesis of isoquinolines required the use
of functionalized starting materials or strong acids.[3] These approaches usually suffered
from some drawbacks including poor yields, poor regioselectivity and harsh reac-
tion conditions.
In recent years, transition-metal-catalyzed C–H bond activation has emerged as a
practical and useful method for the construction of complex molecular scaffolds.[4]
Particularly, the C–H activation/annulation strategy is appealing from a synthetic per-
spective since it allows the rapid formation of highly valuable cyclic products from
CONTACT Liang Wang
lwcczu@126.com
School of Petrochemical Engineering, Jiangsu Key Laboratory of
Advanced Catalytic Materials and Technology, Changzhou University, Changzhou 213164, China; School of Chemical and
Pharmaceutical Engineering, Changzhou Vocational Institute of Engineering, Changzhou 213164, China; Zhi-Hui Zhang
zhangzh@cczu.edu.cn
School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic
Materials and Technology, Changzhou University, Changzhou 213164, China.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
K.-C. JIANG ET AL.
Scheme 1. Transition-metal-catalyzed synthesis of isoquinolines. (a) Previous work. (b) This work.
readily available substrates.[5] In this context, the synthesis of isoquinoline derivatives
using such strategy has been widely reported and great advance has been achieved.
Previously, such reactions proceeded under oxidative conditions, thus stoichiometric
amount of external oxidants were required for the regeneration of active catalytic spe-
cies.[6–10] To overcome these drawbacks, oxidizing directing groups such as N–O,[11–31]
N–N,[32–37] N–S[38] and N–Cl[39] were employed. They could served as internal oxi-
dants, thereby enabling the reaction proceed under redox-neutral conditions
(Scheme 1a).
Despite these significant advances, there are still some issues need to be addressed.
For example, although various oxidizing directing groups have been developed, the use
of oxime as the directing group undoubtedly has some advantages since oximes are
cheap, readily available, and water is generated as the byproduct in such reaction.
Moreover, the reported protocols were usually conducted in volatile and toxic organic
solvents, making them environmentally unfriendly. Finally, only a handful of reports
exist using 1,3-diynes as the substrates in the synthesis of isoquinolines. Regioselectivity
(3-alkynylation or 4-alkynylation) and chemoselective (mono- and difunctionalization)
are also big challenges.[29,30]
Considering these facts, it is still highly desirable to develop a protocol for the syn-
thesis of isoquinolines using simple substrates in green solvent. Recently, the use of
c-valerolactone (GVL) as reaction medium has become a hot field.[40] GVL is recog-
nized as a sustainable solvent due to its advantages such as high boiling and flash
points, good chemical stability and low toxicity. To our best knowledge, reports on the
C–H activation reactions in GVL are few. Herein, we report a Rh(III)-catalyzed synthe-
sis of isoquinoline derivatives from oximes and alkynes in GVL. Different oximes sur-
vived well under the reaction conditions, and good regioselectivity and chemoselective
was observed when 1,3-diynes were utilized as the substrates (Scheme 1b).

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3
Table 1. Optimization of reaction conditions.a
Entry
Catalyst
Additive 1
AgSbF6
–
AgBF4
AgSbF6
–
–
–
–
–
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
AgSbF6
Additive 2 (equiv.)
Solvent
Yield (%)b
ꢁ
1
2
3
4
5
6
7
8
[RhCp Cl2]2
–
–
–
GVL
GVL
GVL
GVL
GVL
GVL
GVL
GVL
GVL
80
0
63
84
55
0
56
61
46
88
58
46
15
60
36
73
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
Cu(OAc)2ꢃH2O
Cu(OAc)2ꢃH2O
CuCl2ꢃH2O
CsOAc
KOAc
NaOAc
KOAc
KOAc
KOAc
KOAc
KOAc
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
ꢁ
9
[RhCp Cl2]2
ꢁ
10
11
12
13
14
15
16
17
18
[RhCp Cl2]2
GVL
ꢁ
[RhCp Cl2]2
DMF
CH3CN
DMSO
DCE
THF
HFIP
H2O
GVL
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
KOAc
KOAc
KOAc
KOAc
ꢁ
[RhCp Cl2]2
ꢁ
[RhCp Cl2]2
20
[RhCp Cl2]2
45c, 77d
ꢁ
aReaction conditions: 1a (0.2 mmol), 2a (0.2 mmol), catalyst (2 mol%), additive 1 (8 mol%), additive 2 (0.2 equiv.), solvent
(2 mL), 80 ꢂC for 12 h in a sealed tube.
bIsolated yields.
cAt 60 ꢂC.
dAt 100 ꢂC.
Results and discussion
At the outset of our studies, we chose acetophenone oxime 1a and 1,2-diphenylethyne
2a as the model substrates to screen the reaction conditions ꢂin the presence of
ꢁ
[RhCp Cl2]2 (2 mol%) and AgSbF6 (8 mol%) in GVL (2 mL) at 80 C for 12 h (Table 1,
entry 1).
Encouragingly, the desired product 3a was obtained in 80% yield under above
reaction conditions. The reaction did not occur in the absence of any additive (entry
2). Switching AgSbF6 to AgBF4 gave the desired product in relative lower yield
(63%, entry 3). The addition of Cu(OAc)2ꢃH2O slightly improve the yield, indicating
an external oxidant was not necessary (entry 4). It was also worth noting that a
moderate yield of 3a could be obtained in the presence of Cu(OAc)2ꢃH2O, while no
product was observed when CuCl2ꢃH2O was used as the additive. It was assummed
that OAc anion might promote the reaction (entries 5 and 6). A series of additives
including CsOAc, KOAc and NaOAc were then tried alone, however, only moderate
yields were obtained (entries 7–9). Instead, the combination of AgSbF6/KOAc
afforded 3a in 88% yield (entry 10). Other solvents were also evaluated. Reactions in
N,N-dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), 1,2-
dichloroethane (DCE) and tetrafuran (THF) gave unsatisfactory yields (entries

4
K.-C. JIANG ET AL.
ꢁ
Figure 1. Reaction scope. Reaction conditions: 1 (0.2 mmol), 2 (0.2 mmol), [RhCp Cl2]2 (2 mol%),
AgSbF6 (8 mol%), KOAc (0.2 equiv.), GVL (2 mL), 80 ꢂC for 12 h in a sealed tube, isolated yields.

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5
Scheme 2. Plausible mechanism.
11–15). On the contrary, reaction in hexafluoroisopropanol (HFIP) provided 3a in
73% yield (entry 16). We also tried the reaction in water, while only 20% yield was
obtained (entry 17). Other reaction parameters were also checked. It was found that
the reaction was performed efficiently at 80 ꢂC, while the yield dropped to 45% at
60 ꢂC and 77% at 100 ꢂC, respectively (entry 18).
Next, the scope of the substrates under the optimized reaction conditions was
explored. Initially, a series of ketoximes were evaluated (Figure 1). Generally, acetophe-
none oximes containing both electron-withdrawing groups and electron-donating
groups reacted with 1,2-diphenylethyne 2a smoothly to give the desired products in
good to excellent yields (3a–3h). For the para-substituted acetophenone oximes, a series
of functional groups including alkyl, methoxy, chloro, nitro and cyano were tolerated
well. No obvious steric hindrance effect was observed for 2-methyl-substituted acetophe-
none oxime. In the case of meta-substituted oxime, regioisomeric mixtures were
obtained. The reaction occurred preferentially at the less hindered site (3ha and 3hb).
Other ketoximes derived from ketones such as propiophenone, benzophenone and 1-
(naphthalen-1-yl)ethan-1-one also showed good reactivities, affording the corresponding
products 3i–3k in good yields. In addition, ketoxime of heterocyclic ketone also reacted
smoothly to give the desired product 3l in 75% yield. Finally, we extended the substrate
2 to 1,3-diynes. To the best of our knowledge, the formation of 3-alkynylated hetero-
cycles from 1,3-diynes has been well documented,[41] while only one report gave the
4-alkynylated isoquinolines.[29] In the present protocol, reactions between 1a and 1,4-
diphenylbuta-1,3-diyne, 1,4-di-p-tolylbuta-1,3-diyne or 1,4-bis(4-methoxyphenyl)buta-
1,3-diyne provided the 4-alkynylated isoquinolines 3m, 3n and 3o in moderate yields

6
K.-C. JIANG ET AL.
(57%, 55% and 54%, respectively). In the sharp contrast, 3-alkynylated isoquinolines 3p
was observed as the major product for 1-(4-chlorophenyl)ethan-1-one oxime.
Based on the above literatures, we proposed a mechanism for this transformation. As
shown from Scheme 2, initially, rhodium catalyst coordinates to the nitrogen of the
ketoxime 1, then C–H activation occurs, presumably facilitated by OAc anion, to give
the 5-membered rhodacycle A. The rhodacycle A coordinates to an equivalent of alkyne
2, followed by migratory insertion of an alkyne to give C. Finally, reductive elimination
delivers product 3. Meanwhile, the catalytically active species are regenerated by the
internal oxidant via NꢀO bond cleavage.
Conclusion
In summary, we have developed a Rh (III)-catalyzed synthesis of isoquinolines deriva-
tives from N-hydroxyoximes and alkynes via C–H activation/annulation process in
c-valerolactone. The present C–H activation/annulation reaction allows the rapid forma-
tion of isoquinolines from readily available substrates. The reaction conditions are mild,
and a series of functional groups were tolerated well, providing the desired products in
good to excellent yields. 1,3-Diynes also show good reactivities and regioselectivities.
Moreover, GVL is derived from lignocellulosic biomasses and is highly soluble in water.
Thus, the use of GVL instead of conventional organic solvents as the reaction medium
can ease its biodegradation and reduce its environmental impact.
Experimental
General remarks
All reagents were obtained from local commercial suppliers and used without further
purification. The reaction was monitored by TLC using analytical-grade silica gel plates
1
(GF254) under UV light. H NMR, 13C NMR and spectra were recorded at ambient
temperature on a 300 NMR spectrometer (75 MHz for 13C). Chemical shifts are given
in parts per million (d, ppm) and were referenced to CDCl3 (7.26 or 77.0 ppm). The
coupling constants J are given in Hz. Mass spectrometry was performed on an LCMS-
2010 EV (Shimadzu) instrument with an ESI source. High-resolution mass spectrometry
(HRMS) was performed on an Agilent 6540 Q-TOF MS instrument with an ESI source.
Melting points (m.p.) are determined with an Optimelt MPA 100 apparatus and are
not corrected.
General procedure for synthesis of isoquinolines
In a 10 mL of Schlenk tube equipped with a stir bar was charged with ketoxime 1
ꢁ
(0.2 mmol, 1.0 equiv), alkyne 2 (0.2 mmol, 1.0 equiv), [RhCp Cl2]2 (2 mol%), AgSbF6
(8 mol%), KOAc (0.2 equiv.) in GVL (2 mL). The tube was sealed and the reaction mix-
ture was stirred at 80 ꢂC for 12 h in oil bath. After the completion of the reaction, the
mixture was extracted by EtOAc and washed with water for several times. The organic
layer was then dried over anhydrous Na2SO4, concentrated in vacuum, and the residue

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SYNTHETIC COMMUNICATIONSV
7
was purified by flash column chromatography on silica gel with petroleum ether and
EtOAc as the eluent to give the pure acridine products.
Selected data: 1-Methyl-3,4-diphenylisoquinoline (3a).[28] Yellow solid; m.p.
1
156–158 ꢂC. H NMR (300 MHz, CDCl3) d 8.20–8.16 (m, 1H), 7.65 (dt, J ¼ 6.9, 3.5 Hz,
1H), 7.59–7.54 (m, 2H), 7.37 (d, J ¼ 7.4 Hz, 2H), 7.35–7.28 (m, 3H), 7.24–7.20 (m, 2H),
7.21–7.13 (m, 3H), 3.07 (s, 3H); 13C NMR (75 MHz, CDCl3) d 157.5, 149.2, 140.9,
137.4, 135.8, 131.2, 130.1, 129.8, 129.0, 128.0, 127.4, 127.0, 126.8, 126.4, 126.1, 126.0,
125.34, 22.6; MS (ESI) m/z 296 [M þ H]þ.
Funding
We gratefully acknowledge the China Postdoctoral Science Foundation [2018M632289], the
Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology [BM2012110], the
Priority Academic Program Development (PAPD) of Jiangsu Higher Education Institutions, and
Jiangsu Key Laboratory of Biomass Energy and Material [JSBEM201806] for the finan-
cial support.
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