Palladium-Catalyzed Multi-Component Reactions of N-Tosylhydrazones, 2-Iodoanilines and CO2towards 4-Aryl-2-Quinolinones

Article abstract of DOI:10.1002/chem.201604256

A palladium-catalyzed three-component reaction between N-tosylhydrazones, 2-iodoanilines and atmospheric pressure CO₂was developed whereby a tandem carbene migration insertion/lactamization strategy afforded 4-aryl-2-quinolinones in moderate to good yields. Notably, a wide range of functional groups were tolerated in this procedure. This protocol features the simultaneous formation of four novel bonds; two C?C, one C=C and one C?N (amide), representing an efficient methodology for incorporation of CO₂into heterocycles.

Full text of DOI:10.1002/chem.201604256

A Journal of
Accepted Article
Title: Palladium-Catalyzed Multi-Component Reactions of N-
Tosylhydrazones, 2-Iodoanilines and CO2 towards 4-Aryl-2-
Quinolinones
Authors: Jiang Cheng, Song Sun, Wei-Ming Hu, and Ning Gu
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To be cited as: Chem. Eur. J. 10.1002/chem.201604256
Link to VoR: http://dx.doi.org/10.1002/chem.201604256
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10.1002/chem.201604256
Chemistry - A European Journal
DOI: 10.1002/chem.201xxxxxx
█ CO2 Fixation
Palladium-Catalyzed Multi-Component Reactions of N-Tosylhydrazones,
2-Iodoanilines and CO2 towards 4-Aryl-2-Quinolinones
Song Sun, Wei-Ming Hu, Ning Gu, Jiang Cheng*
Dedication ((optional)
tosylhydrazone chemistry,[8-9] the reaction of N-tosylhydrazones
with aryl- halides generates corresponding olefins whereby
Abstract: A palladium-catalyzed three-component reaction
between N-tosylhydrazones, 2-iodoanilines and atmospheric
sequential
carbene
migration
insertion/β-H
elimination
procedure.[10] Therefore, in the case of 2-iodoaniline, ortho-(1-
phenylvinyl)aniline is formed,[10c] which is a potential substrate to
incorporate CO2 towards 2-quinolinones developed by Yu[11a] and
others recently.[11] Thus, a three-component reaction between N-
tosylhydrazones, 2-iodoanilines and CO2 was highly expected in
the construction of 2-quinolinones, which did not require the time-
consuming procedure for the isolation of the intermediates ortho-
(1-phenylvinyl)anilines. As part of our continuing studies on the
transformation of CO2,[12] we herein present an unprecedented
strategy towards 4-aryl-2-quinolinones by a three-component
coupling reaction of N-tosylhydrazones, 2-iodoanilines and CO2
catalyzed by a Pd(II)/phosphine system (Scheme 1d). Such
frameworks were ubiquitous in drugs, bioactive natural products,
photoelectric materials, and important intermediates in organic
synthesis.[13]
pressure of CO2 was developed whereby a tandem carbene
migration insertion/lactamization strategy to afford 4-aryl-2-
quinolinones in moderate to good yields. Notablely, a wide
range of functional groups were tolerated in this procedure.
This protocol features with simultaneous formation of four
novel bonds i.e. two C–C, one C=C and one C-N bonds in
amide, representing an efficient methodology for
incorporation of CO2 into heterocycles.
Recently, the incorporation of the entire “CO2” moiety or its
“C=O” fragment via multi-component reactions towards carbonyl-
containing compounds,[1-2] especially heterocycles,[3] represents a
great advance and greener approach by avoiding the use of
hazardous carbonylation reagents such as carbon monoxide and
phosgene. With this regard, Kobayashi, Kunai, as well as others
independently reported elegant cascade reaction of in situ formed
benzyne with a nucleophile and CO2 towards a series of carbonyl-
containing heterocycles (Scheme 1a).[4] The sequential
carboxylation/cyclization reaction of propargylic alcohols (or
amines), CO2 and
a third component allows to facilely
construction of oxazolidinones or other useful heterocyclic
frameworks.[5] For instance, Li developed a four-component
reaction of aldehydes, primary amines, alkynes, and CO2 leading
to oxazolidinones (Scheme 1b).[6] Jiang reported copper-
catalyzed domino reaction of readily available propargylic
alcohols, CO2 and nitriles to access highly substituted 3(2H)-
furanones (Scheme 1c).[7] However, despite much progress has
been made in this field, the development of procedures involving
either new reaction partners or new target molecules in the
fixation of CO2 remains an area of synthetic interest.
Scheme 1. Some typical examples of multi-component reactions
On the other hand, thanks to the well-developed N-
involving carbon dioxide towards carbonyl-containing heterocycles.
Initially, we tested the reaction of N-tosylhydrazone 1a (0.3
mmol), 2-iodoaniline 2a (0.2 mmol), and atmospheric pressure of
CO2 (Table 1). To our delight, this three-component reaction took
place in the presence of Pd(OAc)2 (10 mol%) and NaOtBu (1.2
[]
[a] Dr. S. Sun, W.-M. Hu, N. Gu, and Prof. Dr. J. Cheng
School of Petrochemical Engineering, Jiangsu Key Laboratory of
Advanced Catalytic Materials & Technology, and Jiangsu Province
Key Laboratory of Fine Petrochemical Engineering, Changzhou
University, Gehu Road 1, Changzhou, 213164, P. R. China
E-mail: jiangcheng@cczu.edu.cn
Homepage: www.chengjiangjs.com
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201xxxxxx.
o
mmol) under atmospheric pressure of CO2 in diglyme at 140 C
for 24 h, producing 4-phenyl-2-quinolinone 3a in 27% yield (Table
1, entry 1). The employment of phosphine ligands increased the
reaction efficiency dramatically, and PPh3 was the best (65%,
Table 1, entries 2-4) (for details, see Supporting Information). The
efficiency of the reaction was further increased to 68% by
1
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Chemistry - A European Journal
DOI: 10.1002/chem.201xxxxxx
replacing Pd(OAc)2/PPh3 with Pd(PPh3)2Cl2 (Table 1, entries 5-7).
Among the bases tested, NaOtBu was the best (68%, Table 1,
entries 7-9). The solvent had a profound effect on the reaction
and diglyme (68%) was superior to 1, 4-dioxane (53%), while
DMSO almost inhibited the reaction (Table 1, entries 7, 10-11).
Notablely, in the presence of 6 equivalents of NaOtBu, 3a was
isolated in 75% yield (1a: 2a = 1.7: 1, Table 1, entry 12).
Increasing the pressure of CO2 did not have any positive effect for
this transformation (Table 1, entry 13).
Table 1. Selected results for screening the optimized reaction
conditions[a]
Entry
[Pd]
Ligand
Base
Isolated Yield [%]
1
2
Pd(OAc)2
Pd(OAc)2
--
NaOtBu
NaOtBu
27
51
Xphos
3
4
Pd(OAc)2
Pd(OAc)2
Ph2P(2-Py)
NaOtBu
NaOtBu
NaOtBu
NaOtBu
NaOtBu
LiOtBu
62
PPh3
PPh3
--
65
Scheme 2. Scope of N-tosylhydrazones. Reaction conditions: 1 (0.34 mmol), 2a
(0.2 mmol), Pd(PPh3)2Cl2 (0.02 mmol), NaOtBu (1.2 mmol), diglyme (3.0 mL), at
140 oC under atmospheric pressure of CO2 for 24 h, in a sealed Schlenk tube.
5
PdCl2
64
6
Pd(PPh3)4
45
7
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
Pd(PPh3)2Cl2
--
68
Next, the scope of 2-iodoanilines was also investigated. As
shown in Scheme 3, the substituted 2-iodoanilines proceeded
smoothly with N-tosylhydrazone (1a) and atmospheric pressure of
CO2 to afford 4-aryl-2-quinolinones with substituents on the 6-, 7-
and 8- position in moderate to good yields. To our delight, the
substrates bearing strong electron-withdrawing groups such as
cyano, nitro groups also ran smoothly under the standard
conditions to afford products 4g and 4h in 57% and 45% yields,
respectively.
8
--
48
9
--
KOtBu
< 5
10[b]
11[c]
12
13[h]
--
NaOtBu
NaOtBu
NaOtBu
NaOtBu
53
--
0
51[d] 71[e] 75[f] 72[g]
41
--
--
[a] Reaction conditions: 1a (0.3 mmol), 2a (0.2 mmol), [Pd] (0.02 mmol), ligand
(0.04 mmol), base (1.2 mmol), diglyme (3.0 mL), at 140 oC under atmospheric
pressure of CO2 for 24 h, in a sealed Schlenk tube, unless otherwise noted. [b]
in 1, 4-dioxane, at 100 oC. [c] in DMSO. [d] NaOtBu (1.0 mmol). [e] NaOtBu (1.4
mmol). [f] NaOtBu (1.2 mmol), 1a (0.34 mmol). [g] NaOtBu (1.2 mmol), 1a (0.4
mmol). [h] CO2 (2.5 MPa). Xphos
biphenyl]-2-yl)phosphine.
= dicyclohexyl(2',4',6'-triisopropyl-[1,1'-
With the optimized reaction conditions in hand, we then
explored the scope and limitation of the N-tosylhydrazones as
shown in Scheme 2. Generally, except the 4-CF3 substituted
analogue (3g, 33%), the reaction efficiency was not sensitive to
the electronic property of the groups on the phenyl ring of N-
tosylhydrazones as substrates bearing both electron-donating
(3b-3c, 3h-3k, 58-76%) and electron-withdrawing groups (3d-3f,
62-71%) worked well to deliver the desired products in moderate
to good yields. In the cases of substrates with ortho- hindrance on
the phenyl, 3h-3j were isolated in acceptable 58%, 61% and 65%
yields, respectively. Notably, some functional groups, such as
methyl (3b, 3h, 3j), fluoro (3d), chloro (3e), and cyano (3f) groups,
which were suitable for potential further functionalization, survived
well in these reactions. Importantly, the diversity of the product
was further increased as this procedure allow to access 4- (2-
naphthyl) (3l, 46%), 3- methyl (3m, 71%; 3n, 73%), propyl (3o,
70%) and phenyl (3p, 56%) of 4-aryl-2-quinolinones in moderate
to good yields. In particular, the procedure was applicable to the
construction of fused cyclic product. For instance, 3q could be
isolated in 60% yield.
Scheme 3. The substrate scope of 2-iodoanilines. Reaction conditions: 1a (0.34
mmol), 2 (0.2 mmol), Pd(PPh3)2Cl2 (0.02 mmol), NaOtBu (1.2 mmol), diglyme
(3.0 mL), at 140 oC under atmospheric pressure of CO2 for 24 h, in a sealed
Schlenk tube.
Some control experiments were conducted to get some
insights into this transformation. Firstly, 2-(1-phenylprop-1-en-1-
yl)aniline 5 (Z/E = 3/2)[14] was employed to react with 1 atm of
CO2 in the presence of 6 equivalents of NatOBu and the 3-methyl-
4-phenyl-2-quinolinone 3n was isolated in 96% yield, indicating
2
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10.1002/chem.201604256
Chemistry - A European Journal
DOI: 10.1002/chem.201xxxxxx
both Z and E isomers took part in this transformation (Scheme
4a). This was consistent with the 6π-electrocyclic reaction
group to the carbenic carbon gives intermediate C, which
encounters β-hydride elimination to deliver amine and
E
pathway
proceeding
with
isocyanate
intermediate.[15]
regenerates the Pd0 catalyst in the presence of base. Then, with
the assistance of base, the amine E reacts with CO2 rapidly,
leading to carbamate F, which converts to isocyanate
intermediate G by dehydration.[16] Finally, the 6π- electrocyclic
reaction in G takes place towards intermediate H, which affords
4-aryl-2-quinolinone I via [1,5]-σ-hydrogen shift in H. Alternatively,
before the 6π- electrocyclic reaction of G, pathway involving
intermediate 6 could not be thoroughly ruled out at the current
stage. (for details, see Supporting Information)
Subsequently, 1-iodo-2-isocyanatobenzene (6) was employed to
react with 1a in the presence of Pd(PPh3)2Cl2 (10 mol%) and
o
NaOtBu (3 equiv) under N2 in diglyme at 140 C for 24 h, and 3a
was isolated in 43% yield (Scheme 4b), indicating the possibility
of 6 serving as an intermediate (for details, see Supporting
Information). Moreover, the intermolecular kinetic isotopic
experiment confirmed the kH/kD in methyl was 1.3. Thus, the β-
hydride elimination was not the rate determining step during this
transformation (Scheme 4c).
In conclusion, we have developed an efficient palladium-
catalyzed three-component reaction between N-tosylhydrazones,
2-iodoanilines and CO2, allowing to quick access a series of 4-
aryl-2-quinolinones in moderate to good yields with diversity. This
procedure tolerates some functional groups well. This protocol
features with simultaneous formation of four novel bonds i.e. two
C–C, one C-C double and one C-N bond in amide, representing
an efficient methodology for incorporation of CO2 into
heterocycles.
Experimental Section
Experimental Details: In
a glovebox, N-tosylhydrazone (0.34 mmol), 2-
iodoaniline (0.2 mmol), Pd(PPh3)2Cl2 (0.02 mmol, 14 mg), NaOtBu (1.2 mmol,
115.2 mg) and diglyme (3.0 mL) was added into a 20 mL Schlenk tube
equipped a Teflon cap. The reaction vessel was evacuated to about -0.1 MPa
(last 30 seconds per time) and backfilled with CO2 (1 atm) in three times. The
sealed Schlenk tube was stirred at 140 °C for the desired time. After the
reaction mixture was cooled to room temperature, 1 M HCl (1.5 mL) was added
to terminate the reaction. The reaction mixture was diluted with EtOAc and
washed with saturated brine water. The organic layer was dried over anhydrous
MgSO4 and concentrated in vacuum. The residue was purified by flash column
chromatography on silica gel with CH2Cl2-ethyl acetate as eluent to give the
desired product.
Scheme 4. Mechanism study.
Acknowledgements
We thank the National Natural Science Foundation of China (nos.
21272028 and 21572025), “Innovation
& Entrepreneurship
Talents” Introduction Plan of Jiangsu Province, the Key University
Science Research Project of Jiangsu Province (15KJA150001),
Jiangsu Key Laboratory of Advanced Catalytic Materials
&Technology (BM2012110) and Advanced Catalysis and Green
Manufacturing Collaborative Innovation Center for financial
supports. Sun thank the National Natural Science Foundation of
China (no. 21602019), Young Natural Science Foundation of
Jiangsu Province (BK20150263) for financial supports.
Keywords: carbon dioxide
• 4-aryl-2-quinolinone • N-
tosylhydrazone • multi-component reaction
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DOI: 10.1002/chem.201xxxxxx
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Revised: ((will be filled in by the editorial staff))
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4
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10.1002/chem.201604256
Chemistry - A European Journal
DOI: 10.1002/chem.201xxxxxx
COMMUNICATION
█ CO2 Fixation
Song Sun, Wei-Ming Hu, Ning Gu, Jiang
Cheng* ■■ – ■■
Palladium-Catalyzed Multi-Component
Reactions of N-Tosylhydrazones, 2-
Iodoanilines and
A
palladium-catalyzed three-component reaction between N-
tosylhydrazones, 2-iodoanilines and atmospheric pressure of CO2 was
developed whereby a tandem carbene migration insertion/lactamization
strategy to afford 4-aryl-2-quinolinones in moderate to good yields.
Notablely, a wide range of functional groups were tolerated in this
procedure. This protocol features with simultaneous formation of four novel
bonds i.e. two C–C, one C=C and one C-N bonds in amide, representing an
efficient methodology for incorporation of CO2 into heterocycles.
CO2 towards 4-Aryl-2-Quinolinones
5
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