Palladium-catalyzed carbonylative synthesis of aryl esters fromp-benzoquinones and aryl triflates

Article abstract of DOI:10.1039/d1ob01400e

A palladium-catalyzed dicarbonylation ofp-benzoquinones with aryl triflates has been developed. Using Cr(CO)₆as the CO source, the reaction proceeds smoothly and efficiently to give a series of aryl esters in moderate to good yields (up to 90%).

Full text of DOI:10.1039/d1ob01400e

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Palladium-catalyzed carbonylative synthesis of aryl
esters from p-benzoquinones and aryl triflates†
Cite this: Org. Biomol. Chem., 2021,
19, 7353
Siqi Wang,a Jian-Shu Wang,a Zhengjie Le,a Jun Ying *a and Xiao-Feng Wu
*
b,c
Received 19th July 2021,
Accepted 6th August 2021
DOI: 10.1039/d1ob01400e
rsc.li/obc
A palladium-catalyzed dicarbonylation of p-benzoquinones with various useful organic molecules.3 However, examples of the
aryl triflates has been developed. Using Cr(CO)6 as the CO source, direct synthesis of aryl esters from p-benzoquinone are still
the reaction proceeds smoothly and efficiently to give a series of limited.4–7 For instance, Ison and co-workers reported an
aryl esters in moderate to good yields (up to 90%).
iridium-catalyzed C–H functionalization of benzoic acids and
p-benzoquinone for the rapid construction of a series of benzo
[c]chromen-6-ones in 2011 (Scheme 1a).4 In 2015, Mal and
Bose developed a direct cross redox coupling of aldehydes or
alcohols and p-benzoquinone in the presence of Cu(OAc)2·H2O
and TBHP to afford a variety of aryl esters (Scheme 1b).5
p-Benzoquinones as a class of key structural motifs are preva-
lent in numerous pharmaceuticals, natural products, and bio-
logically active molecules, which are found to exhibit diverse
pharmacological properties such as anti-inflammatory, anti-
tumor, anti-viral, and so on.1,2 In addition, p-benzoquinone
derivatives are also versatile building blocks in the synthesis of
Table 1 Screening of the reaction conditionsa
Entry
[Pd]
Ligand
Base
Solvent
Yield (%)
1
2
3
4
5
6
7
8
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
Pd(TFA)2
Pd(PPh3)2Cl2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PPh3
PCy3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
K3PO4
Et3N
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
MeCN
n.r.
Trace
56
45
35
16
43
49
34
28
81
5
61
75
75
0
0
56
DPPF
DPPP
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
DPPF
9
Dioxane
DMF
10
11b
12b
13b
14b
15b,c
16b,d
17b,e
18b, f
Scheme 1 Aryl ester synthesis from p-benzoquinones.
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
aDepartment of Chemistry, Key Laboratory of Surface & Interface Science of Polymer
Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou 310018,
China. E-mail: yingjun@zstu.edu.cn
bDalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, 116023 Dalian, Liaoning, China
cLeibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Straβe
29a, 18059 Rostock, Germany. E-mail: xiao-feng.wu@catalysis.de
†Electronic supplementary information (ESI) available: General comments, a
general procedure, analytical data, and NMR spectra. See DOI: 10.1039/
d1ob01400e
a Reaction conditions: 1a (0.2 mmol), 2b (3.5 equiv.), Cr(CO)6 (1.5
equiv.), catalyst (10 mol%), ligand (20 mol%), base (2.0 equiv.), H2O
(4.0 equiv.), solvent (1.5 mL), 90 °C, 24 h, isolated yield. b 1a
(0.2 mmol) and 2b (1.0 equiv.); the yield was calculated based on
0.1 mmol of 2b. c H2O (2.0 equiv.). d Mo(CO)6 instead of Cr(CO)6.
e Fe2(CO)9 instead of Cr(CO)6. f TFBen instead of Cr(CO)6. DPPF: bis
(diphenylphosphino)ferrocene.
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Transition-metal-catalyzed carbonylative reactions have MeCN, dioxane, and DMF afforded reduced yields of 3ab
emerged as one of the most powerful and straightforward (Table 1, entries 8–10). To our delight, the yield was signifi-
approaches to establish valuable carbonyl-containing cantly improved to 81% when the amount of 2b employed
compounds.8,9 To the best of our knowledge, there has been (Table 1, entry 11) was changed. Subsequently, a series of pal-
no report on the direct carbonylative synthesis of aryl esters ladium catalysts were investigated, and the reactions all gave
from p-benzoquinone. Recently, our group developed a palla- decreased yields (Table 1, entries 12–14). Using a reduced
dium-catalyzed double carbonylative cyclization of propargyl amount of H2O slightly decreased the reaction yield (Table 1,
alcohols and aryl triflates to construct 4-aroyl-furan-2(5H)-ones entry 15). Additionally, no product was observed when Mo
with Cr(CO)6 as the CO surrogate.10 p-Toluquinone was needed (CO)6 or Fe2(CO)9 was used as the carbonyl source (Table 1,
to assist the CO release from Cr(CO)6 and stabilize the palla- entries 16 and 17). It was found that the reaction utilizing
dium intermediates. During the study process of this reaction, benzene-1,3,5-triyl triformate (TFBen) as the CO source led to
a trace amount of ester from p-toluquinone and aryl triflates 3ab in 56% yield (Table 1, entry 18). Notably, a monoester
was detected. As a part of our longstanding interest in product could be obtained as the by-product in this process.
carbonylation chemistry,11 we now disclose a palladium-cata-
Then, the scope of aryl triflates 2 in the reaction with p-tolu-
lyzed dicarbonylation of p-benzoquinones and aryl triflates quinone 1a was investigated under the optimal reaction con-
using Cr(CO)6 as the CO source, and various aryl esters were ditions (Table 1, entry 11) as shown in Scheme 2. For sub-
produced in moderate to good yields (Scheme 1c).
strates bearing para-electron-donating or -withdrawing groups,
Initially, p-toluquinone 1a was treated with p-tolyl triflate 2b the reaction gave the corresponding products 3aa–ah in mod-
in the presence of Pd(OAc)2 as the catalyst and various phos- erate to high yields (55–83%). It was found that the reaction
phine ligands in toluene at 90 °C for 24 h (Table 1, entries with meta-substituted phenyl triflates afforded the desired pro-
1–4). It was found that the reaction with DPPF gave the highest ducts 3ai–al in 63–90% yields. Also, ortho-Me and -OMe substi-
yield (56%) of the desired product 3ab (Table 1, entry 3). Then, tuted phenyl triflates were successfully transformed to pro-
several bases were examined, and lower yields were achieved ducts 3am and 3an in 83% and 71% yield, respectively.
(Table 1, entries 5–7). The reaction with other solvents such as Furthermore, good yields of products 3ao–aq were obtained
Scheme 2 Scope of aryl triflates. Reaction conditions: 1a (0.2 mmol), 2 (0.2 mmol), Cr(CO)6 (1.5 equiv.), Pd(OAc)2 (10 mol%), DPPF (20 mol%),
K2CO3 (2.0 equiv.), H2O (4.0 equiv.), toluene (1.5 mL), 90 °C, 24 h, isolated yield and calculated based on 0.1 mmol of 2. a PhI (0.2 mmol) was used.
b PhBr (0.2 mmol) was used. c 2t (0.8 equiv.).
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when disubstituted compounds were tested. Additionally, the
reaction with 2-naphthyl triflate and 1-naphthyl triflate led to
the expected product 3ar and 3as in high yields. It is note-
worthy that the vinyl triflate 2t can be smoothly converted to
product 3at in 57% yield as well. Decreased yields were
obtained when iodobenzene or bromobenzene was applied.
Subsequently, we turn to test a couple of p-benzoquinone
derivatives 1 in the reaction with p-tolyl triflate 2b (Scheme 3).
The reaction with benzoquinone 1b in the presence of TFBen
as the CO surrogate furnished product 3bb in 59% yield. It was
shown that a good yield (80%) of product 3cb was achieved
when 2,5-dimethyl-benzoquinone 1c was subjected to the reac-
tion system. Also, the reaction with 2,6-dimethyl-benzo-
quinone 1d worked well to give product 3db in 70% yield.
Moreover, 53% yield of product 3eb was obtained in the reac-
tion with naphthoquinone 1e. Interestingly, with Cr(CO)6 and
TFBen as the co-carbonyl sources, tBu-benzoquinone 1f was
transformed to the mono-carbonylated product 3fb in 40%
yield, which was attributed to the steric hindrance of the tBu
group on 1f.
Scheme 4 Scale-up reaction and control experiments.
In order to show the scalability of this method, a scale-up
reaction was performed. When 1 mmol p-toluquinone 1a was
tested in the reaction with p-tolyl triflate 2b, 72% yield of the
desired product 3ab was achieved (Scheme 4a). Moreover, the
reaction with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)
under the standard conditions proceeded smoothly to give 3ab
in 61% yield, which indicated that the reaction pathway did
not involve a radical intermediate (Scheme 4b). Additionally,
when 2-methylhydroquinone 4 was treated with p-tolyl triflate
2b under the standard conditions, the target product 3ab was
obtained in 59% yield (Scheme 4c). This suggested that
2-methylhydroquinone 4 was probably the key intermediate in Scheme 5 Plausible mechanism.
this reaction.
On the basis of previous reports,7–10 a plausible mechanism
for palladium-catalyzed dicarbonylation of p-benzoquinones
and aryl triflates is proposed (Scheme 5). Initially, the active
Pd(0) catalyst, formed from the reaction of Pd(II) with DPPF,
undergoes oxidative addition with p-tolyl triflate 2b to generate
the Pd(II) species A. Meanwhile, CO is released from Cr(CO)6
and inserted to A, leading to the acyl Pd(II) complex B.
Subsequently, reduction of p-toluquinone 1a in the presence
of Cr(CO)6 and H2O might generate 2-methylhydroquinone 4.
Nucleophilic substitution of 4 with two molecules of B gives
the Pd(II) intermediate C. Finally, reductive elimination of C
furnishes the final product 3ab and regenerates the active Pd
(0) species for the next catalytic cycle.
In conclusion, we have developed a facile method for the
synthesis of aryl esters via palladium-catalyzed dicarbonylation
of p-benzoquinones and aryl triflates with Cr(CO)6 as the CO
source. A variety of aryl esters were prepared in moderate to
good yields in this protocol.
Scheme 3 Scope of p-benzoquinone derivatives. Reaction conditions:
1 (0.2 mmol), 2b (0.2 mmol), Cr(CO)6 (1.5 equiv.), Pd(OAc)2 (10 mol%),
DPPF (20 mol%), K2CO3 (2.0 equiv.), H2O (4.0 equiv.), toluene (1.5 mL),
90 °C, 24 h, isolated yield and calculated based on 0.1 mmol of 2b.
a TFBen (2.5 equiv.), 90 °C, 36 h. b Et3N (3.0 equiv.), 120 °C, 24 h. c 2b Conflicts of interest
(0.8 equiv.), Cr(CO)6 (1.5 equiv.), TFBen (5.0 equiv.), Et3N (3.0 equiv.),
120 °C, 24 h.
There are no conflicts to declare.
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