Palladium/Sensory Component-Catalyzed Homocoupling Reactions of Aryl Halides

Article abstract of DOI:10.1055/s-0040-1707214

A novel and efficient catalyst system was developed for homocoupling reactions of aryl halides. The catalyst system consists of Pd(OAc) ₂and the peppery sensory component of tobacco leaves. This is the first time that a sensory component has been used in an organic reaction. Experiments using the catalyst system showed that the reactions proceeded smoothly under air in the absence of both an additional ligand and a reductant. Furthermore, the catalyst system can be applied to the coupling reactions of hetaryl iodides. Many functional groups (including a hydroxy group) are tolerated.

Full text of DOI:10.1055/s-0040-1707214

SYNLETT
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Georg
Thieme Ver-
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Synlett
F. Bao et al.
Letter
Palladium/Sensory Component-Catalyzed Homocoupling Reac-
tions of Aryl Halides
Fengyu Baoa
Zhikai Liub
Haixin Baia
Pd(OAc)2 (catalyst)
sensory component
2
Ar
X
Ar Ar
Ar = aryl, hetaryl, X = I, Br
25 examples, 19–91% yield
Haiyan Zhanga
Pengfei Liu*b
First application of a sensory component
in organic reactions
Natural feedstock
Qidong Zhangc
Guobi Chai*c
Additional ligand and reductant free
Homocoupling reactions in air
a
College of Science, Henan Agricultural University, Zhengzhou 450002,
P. R. of China
baofengyu@henau.edu.cn
College of Tobacco, Henan Agricultural University, Zhengzhou 450002,
b
P. R. of China
liupengfei523@126.com
Zhengzhou Tobacco Research Institute, Zhengzhou 450001, P. R. of China
c
chaigb@ztri.com.cn
Dedicated to Ms. Gailian Xiao
Received: 06.03.2020
Accepted after revision: 25.06.2020
Published online: 29.07.2020
reductive coupling reaction between two electrophilic re-
agents (Scheme 1b). The Ullmann reaction provides a direct
way to synthesize biaryl compounds from aryl halides ex-
clusively. However, harsh reaction conditions restrict its ap-
plication. To relax the reaction conditions, a palladium-cat-
alyzed Ullmann-type reaction has been developed and at-
tracts more and more attention, as palladium is one of the
most versatile catalysts. Most previous studies in this field
DOI: 10.1055/s-0040-1707214; Art ID: st-2020-k0133-l
Abstract A novel and efficient catalyst system was developed for ho-
mocoupling reactions of aryl halides. The catalyst system consists of
Pd(OAc) and the peppery sensory component of tobacco leaves. This is
2
the first time that a sensory component has been used in an organic
reaction. Experiments using the catalyst system showed that the reac-
tions proceeded smoothly under air in the absence of both an addition-
al ligand and a reductant. Furthermore, the catalyst system can be ap-
plied to the coupling reactions of hetaryl iodides. Many functional
groups (including a hydroxy group) are tolerated.
have focused on the development of new heterogeneous
palladium catalysts6 or the use of various reducing re-
7
8
9
agents, such as alcohols, poly(ethylene glycol), glucose,
10
11
12
13
benzoin, agarose hydrogel, amine, DMSO, hydroqui-
none,14 boronic esters, formate salt, a formate-based
15
16
Key words palladium catalyst, sensory component, homocoupling,
aryl halides, biaryls
17
6b,18
room-temperature ionic liquid, ascorbic acid,
a qui-
19
20
21
noid produced by electroreduction, hydrogen, indium,
zinc,22 magnetic nanoparticles, tert-butyllithium, and
23
24
Sensory components or compounds attract extensive
1,2
25
attention, as they play a vital role in human olfaction,
taste sense, and chemesthesis. Many sensory components
from various foods have been identified and characterized
hydrazine hydrate. Additional ligands and/or reducing re-
agents are necessary for most homocoupling reactions.
However, the use of phosphine ligands7
c,10,13–15
can have an
1
by means of sensomic studies. Recently, several sensory
environmental impact, and pollution might be increased
when additional reducing reagents are used. Furthermore,
many homocoupling reactions that use reducing reagents
are carried out under anaerobic and/or anhydrous condi-
tions. Consequently, their applications in the syntheses of
biaryl compounds are limited. Homocoupling reactions un-
components of tobacco leaves have been identified and iso-
2
lated. Although sensory components from food or tobacco
have been extensively studied, their applications in organic
reactions have not previously been reported.
Biaryl structures are found in numerous natural prod-
ucts, polymers, pharmaceuticals, agrochemicals, dyes, and
der air in the absence of additional ligands or reductants are
3
7e,8
ligands. The Suzuki–Miyaura coupling reaction and the
still rare.
In addition, all the reagents used in these reac-
Negishi coupling reaction are typical methods for the syn-
thesis of biaryl compounds in which a nucleophilic re-
tions are industrial products. No studies have investigated
the use of biodegradable sensory components in organic re-
actions, although these originate from natural feedstocks.
Sensory components are readily available and environmen-
tally benign and renewable; consequently, their use in or-
4
agent, often obtained from aryl halide, is coupled with an
electrophilic reagent to give the biaryl product (Scheme 1a).
5
Another representative method is the Ullmann reaction, a
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2020. Thieme. All rights reserved. Synlett 2020, 31, A–F
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
Synlett
F. Bao et al.
Letter
a)
[Pd] cat.
Suzuki–Miyaura reaction (M = B)
Negishi reaction (M = Zn)
Ar1
M
+
Ar2
X
Ar1 Ar2
nucleophilic reagent
obtained from Ar X
electrophilic reagent
1
b)
Cu
Ar1
X
+
Ar2
X
Ar1 Ar2
Ullmann reaction
electrophilic reagent
electrophilic reagent
Scheme 1 Classical methods for the synthesis of biaryl compounds
ganic reactions is promising. From the point of view of
green synthesis, there is an urgent need to develop novel
homocoupling reactions with natural feedstocks under air
without additional ligands or reductants. Because sensory
components from tobacco leaves contain oxygen atoms, ni-
trogen atoms, and hydroxy groups, it is reasonable to as-
sume that these components might be useful in reductive
coupling reactions. Here, we report a Pd/sensory compo-
nent-catalyzed homocoupling reactions of aryl halides un-
der air in the absence of additional ligands or reductants.
This paper presents the first example of the use of sensory
components in organic reactions.
reaction was conducted without base, no product was de-
tected (entry 12). The effects of solvents on the reaction
were also studied. With dimethyl sulfoxide (DMSO) as sol-
vent, 2a was obtained in 11% yield (entry 13). When tolu-
ene or 1,4-dioxane was used as the solvent, 2a could not be
detected (entries 14 and 15).
Table 1 Screening of Sensory Components, Bases, and Solvents in the
Homocoupling of 1-Iodonaphthalene
I
Pd(OAc)2 (10 mol%)
sensory component
As a model for optimization of the reaction conditions,
we chose the homocoupling of 1-iodonaphthalene (1a). The
reaction was efficiently catalyzed by combinations of
Pd(OAc) and sensory components in the presence of K CO ,
2
base (2 equiv)
DMF, 100 °C, 24 h
1a
2a
2
2
3
b
and generated 1,1′-binaphthalene (2a) in high yields (Table
). The procedure for the isolation of the sensory compo-
Entry
Sensory componenta
Base
Yield (%)
1
1
2
peppery component
sour-tasting component
sweet-tasting component
bitter-tasting component
no sensory component
peppery component
peppery component
peppery component
peppery component
peppery component
peppery component
peppery component
peppery component
peppery component
peppery component
K
K
K
2
2
2
CO
CO
CO
3
3
3
87
87
67
73
ND
51
10
84
11
ND
ND
ND
11
ND
ND
nents was as follows. The sensory components were ex-
tracted from flue-cured tobacco leaves and subjected to gel
permeation chromatography to give four fractions that
were characterized by taste (peppery, sour, sweet, bitter).
The sensory component was necessary for the coupling re-
action, as no product was detected when the reaction was
carried out in its absence (Table 1, entry 5). When the pep-
pery component was used, 2a was obtained in 87% yield
3
4
K2CO3
5
K
2
3
CO
3
6
K
PO
4
7
KOH
8
KOAc
t-BuOK
DBU
TMG
–
(entry 1). The sour-tasting component produced 2a in the
same yield (entry 2), whereas the sweet- and bitter-tasting
components gave lower yields (entries 3 and 4). The effects
of inorganic and organic bases on the reaction were then
studied. Replacement of the inorganic base K CO by K PO
9
10
1
1
1
1
1
2
3
3
4
2
decreased the yield from 87 to 51% (entry 6). Strong inor-
ganic bases, as represented by KOH, suppressed the homo-
coupling reaction (entry 7). When the organic base KOAc
was used, 2a was obtained in a high yield (entry 8). The
strong organic base t­BuOK also suppressed the homocou-
pling reaction (entry 9). When organic bases containing ni-
trogen atoms, such as 1,8-diazabicyclo[5.4.0]undec-7-ene
3c
4d
K
K
K
CO
CO
CO
2
2
2
3
3
3
15e
a
b
c
8 mg.
Isolated yield; ND = not detected by TLC.
DMSO as solvent.
With toluene as solvent.
d
e
(DBU) or 1,1,3,3-tetramethylguanidine (TMG), were used,
With 1,4-dioxane as solvent.
no product was detected (entries 10 and 11). This phenom-
enon indicates that organic bases containing nitrogen at-
Further screening of the Pd compounds and the amount
oms are unsuitable for the Pd(OAc) /peppery component-
of peppery component shows that a combination of 10
2
catalyzed homocoupling reaction. Additionally, when the
mol% of Pd(OAc) and 8 mg peppery component was the
2
©
2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

C
Synlett
F. Bao et al.
Letter
best catalyst (Table 2). A decrease in the amount of
screening during optimization, in which the nitrogen-con-
taining bases DBU and TMG inhibited the reaction. Interest-
ingly, the homocoupling reaction of the protected aniline,
tert-butyl (4-iodophenyl)carbamate, gave 2j in 19% yield
(entry 9). Iodobenzenes bearing fluoro (entries 10 and 11),
chloro (entry 12), or trifluoromethyl (entries 13–15) sub-
stituents are suitable substrates, and the coupling reactions
proceeded smoothly to produce the corresponding prod-
ucts. When a fluoro or trifluoromethyl substituent was
present in the ortho-position of the iodobenzene, the yields
were lower than those for the corresponding para-substi-
tuted reactants (entries 10, 11, 13, and 15). This is probably
because of steric hindrance by a substituent in the ortho-
position, which might lead to difficulties in forming aryl-
palladium complexes.1 Iodobenzenes bearing electron-
withdrawing substituents in the para-position coupled effi-
ciently to produce the corresponding biaryls (entries 15, 17,
18, 23, and 24). Notably, the homocoupling reactions of aryl
bromides, which are cheaper and more readily available,
Pd(OAc) resulted in a lower yield (entries 2 and 3). When
2
the reaction was attempted without a Pd compound, no
product was detected (entry 4), indicating that the peppery
component is not the catalyst. Tris(dibenzylideneace-
tone)dipalladium [Pd (dba) ] and PdCl (PPh ) generated 2a
2
3
2
3 2
in very low yields (entries 5 and 6). When a combination of
Pd(PPh ) and peppery component was used as the catalyst,
3
4
2
a could not be detected (entry 7). Pd(PPh ) gave 2a in a
3 4
very low yield (entry 8). Increasing the amount of peppery
component slightly improved the yield from 87 to 91% (en-
try 9), whereas a decrease in the amount of peppery re-
duced the yield from 87 to 61% (entry 10).
2c
Table 2 Screening of Pd Compounds and the Amount of Peppery
Component in the Homocoupling of 1-Iodonaphthalene
I
Pd catalyst
peppery component
2
were also catalyzed by a combination of Pd(OAc) and the
K2CO3 (2 equiv)
2
DMF, 100 °C, 24 h
peppery component (entries 19 and 25). We also noted that
a nitro group was not reduced to an amino group by the
catalyst system. The dicarboxylic acid 2y was not detected
by TLC, whereas diester 2x was obtained in 76% yield. Cou-
pling of 2-iodopyridine gave 2u in 77% yield. 2-Iodopyri-
dine might not disturb the oxidative addition of the aryl io-
dide to the Pd(0) species, whereas DBU, TMG, and aniline
might coordinate to the Pd center, disturbing the subse-
quent oxidative addition of the aryl iodide to the Pd(0) spe-
cies; consequently, the homocoupling reaction of 2-iodopy-
ridine proceeds well, whereas DBU, TMG, and aniline inhib-
it the reaction. The formation of 2u and 2v indicates that a
1
a
2a
a
Entry
Pd compound (mol%)
Peppery component (mg) Yield (%)
1
2
3
4
5
6
7
8
9
Pd(OAc)
Pd(OAc)
Pd(OAc)
–
2
2
2
(10)
(5)
8
8
87
73
(5)
16
8
45
ND
<10
23
Pd
2
(dba)
3
(10)
8
PdCl
2
(PPh
3
)
2
(10)
8
Pd(PPh
Pd(PPh
3
3
)
)
4
4
(10)
(10)
(10)
(10)
8
ND
<10
91
combination of Pd(OAc) and the peppery component can
2
–
be applied to the coupling reactions of aromatic heterocy-
cles.
Pd(OAc)
Pd(OAc)
2
16
4
10
2
61
Reports in the literature suggest that the sour-tasting
component of tobacco contains lactic acid, levulinic acid,
malic acid, fumaric acid, and citric acid;2a the sweet-tasting
component contains fructose, sucrose, glucose, and inosi-
tol;2b and the peppery component contains nicotine.
Therefore, the main components of the sour-tasting and
sweet-tasting components contain hydroxy groups, where-
as the main component of the peppery component is an
a
solated yield; ND = not detected by TLC.
With the optimized reaction conditions [10 mol%
Pd(OAc) , 8 mg peppery component, 2 equiv of K CO ], we
2c
2
2
3
further investigated the scope of the homocoupling reac-
tions (Table 3). The coupling reactions of both electron-de-
ficient and electron-rich iodoarenes proceeded well and
produced the corresponding biaryl compounds. Electron-
donating substituents such as methyl (entry 2), tert-butyl
Ar Ar
ArX
Pd (0)
(entry 4), methoxy (entry 5), and hydroxy (entry 7) in the
para-position were tolerated. GC analysis of the homocou-
pling reaction of 1-iodo-3-methylbenzene (1d) showed that
Ar Pd
Ar
Ar Pd
X
23% of the dehalogenated product was formed and 20% of
III
I
1d remained unreacted. Note that polymethoxy substitu-
HX
+
O
H
ents were also tolerated, and the corresponding biaryl com-
pound 2g was obtained in 58% yield (entry 6). However, 4-
iodoaniline did not produce 2i (entry 8), probably because
the amine functionality coordinates to and poisons the cat-
alyst. This finding is in line with the results from the base
base
+
N
HNMe2
MeN CH2
HX
Ar Pd
NMe2
ArX
II
Scheme 2 A possible mechanism for the homocoupling reactions
©
2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

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F. Bao et al.
Letter
amine. It is reasonable to assume that all the sensory com-
intermediate II by dimethylamine generated in situ by the
reaction of DMF with the base.26 For the formation of inter-
mediate III from intermediate II, we propose a path that in-
volves the interaction of intermediate II with ArX, because
in the ethanol-promoted homocoupling of aryl halides, it
has been reported that a similar interaction of an Ar–Pd–
OEt intermediate with ArX generates an Ar–Pd–Ar interme-
diate.7 The reductive elimination of intermediate III gives
the biaryl product, along with regeneration of Pd(0) spe-
cies. Indeed, 2a was not detected in the absence of a base
(Table 1, entry 12). Dimethylamine might not be formed in
the absence of a base, and consequently the catalytic cycle
could not be completed.
ponents can act as reducing reagents to reduce Pd(OAc) to
2
Pd(0) species. Because 2a could not be detected in the ab-
sence of the Pd compound or the sensory component (Table
2, entry 4 and Table 1, entry 5), and a combination of
Pd(OAc) and the peppery component produced 2a in high
2
yield (Table 1, entry 1), we propose the following mecha-
nism. The reaction of Pd(OAc)2 and peppery component
generates a Pd(0) species that initiates the catalytic cycle
d
(Scheme 2). Indeed, we found that the homocoupling of 1a
could be catalyzed by a combination of Pd(OAc) and nico-
2
tine (Scheme 3). Oxidative addition of ArX to Pd(0) species
produces intermediate I. Intermediate I is converted into
Table 3 Homocoupling Reactions of Aryl Halidesa
Pd(OAc)2 (10 mol%)
peppery component (8 mg)
2
Ar
I
Ar Ar
K2CO3 (2 equiv)
DMF, 100 °C
1
2
Entry
1
Product, yield
Entry
14
Product, yield
F3C
CF3
2
2
b, 81%
c, 49%
2o, 58%
2
3
15
16
F3C
CF3
O
2p, 66%
O
2
d, 48%
2q,19%
NC
4
5
t-Bu
t-Bu
17
18
CN
2
e, 55%
2r,61%
MeO
OMe
OHC
CHO
2
f, 76%
2s, 89%
MeO
MeO
MeO
OMe
OMe
OMe
6
7
19
20
OHC
CHO
2
g, 58%
2s, 45%d
OHC
HO
OH
CHO
2
h, 53%c
2t,64%
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2020. Thieme. All rights reserved. Synlett 2020, 31, A–F

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F. Bao et al.
Letter
Table 3 (continued)
Entry
Product, yield
Entry
21
Product, yield
8
2
H N
NH2
N
N
2
i, NDb
2u, 77%
S
t
NHCO2tBu
9
BuO CHN
22
2
S
2
2
j, 19%
2v, 35%
1
0
1
23
24
2
O N
NO2
F
F
k, 54%
2w, 68%
1
F
F
MeO C
2
CO Me
2
2
2
2
l, 67%
2x, 76%
Cl
1
2
25
26
MeO C
CO Me
2
2
Cl
m, 36%
2x, 32%e
F3C
1
3
HO2C
CO2H
CF3
n,23%
2y, NDb
a
b
c
Isolated yield.
ND = not detected by TLC.
Reflux, 48 h.
From 4-bromobenzaldehyde as the aryl halide.
From methyl 4-bromobenzoate as the aryl halide.
d
e
In conclusion, the sensory component from a natural
I
feedstock that is cheap and easily cultivated on a large scale
was used in a Pd-catalyzed homocoupling of aryl halides to
catalyst (10 mol%)
nicotine (8 mg)
2
27
K CO (2 equiv)
synthesize biaryl compounds under air. This is a green al-
ternative to many existing methods. The reactions proceed-
ed smoothly in the absence of any additional ligand or re-
ductant. Many functional groups were tolerated. To the best
of our knowledge, this is the first example of the use of a
sensory component in organic reactions.
2
3
0
.5 mmol
DMF, 100 °C, 24 h
1a
2a
cat. = Pd(OAc)2, 38%
cat. = Pd(PPh ) , 11%
3
4
Scheme 3 A control experiment for homocoupling of 1a using nico-
tine instead of the peppery component
Funding Information
This work was supported by Henan Science and Technology Commit-
tee (182102110194) and Young Elite Scientists Sponsorship Program
Supporting Information
by CAST (2017QNRC001).
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Supporting information for this article is available online at
https://doi.org/10.1055/s-0040-1707214.
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Thieme. All rights reserved. Synlett 2020, 31, A–F

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F. Bao et al.
Letter
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selected examples of Suzuki–Miyaura reactions see: (c) Qian,
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Dai, Y. Eur. J. Org. Chem. 2017, 2017, 1337. (d) Qian, H.; Zhang,
T.; Yin, Z.; Wang, Q.; Yuan, Q.; Jiang, R.; Yan, S.; Zhao, X.
J. Organomet. Chem. 2016, 824, 124.
(
2
2
003, 68, 9867. (d) Venkatraman, S.; Li, C.-J. Tetrahedron Lett.
000, 41, 4831. (e) Venkatraman, S.; Huang, T.; Li, C.-J. Adv.
Synth. Catal. 2002, 344, 399.
(
5) Fanta, P. E. Synthesis 1974, 9.
(23) Zheng, J.; Lin, S.; Jiang, B.-W.; Marder, T. B.; Yang, Z. Can. J. Chem.
(
6) For selected examples see: (a) Zeng, M.; Du, Y.; Qi, C.; Zuo, S.; Li,
X.; Shao, L.; Zhang, X.-M. Green Chem. 2011, 13, 350. (b) Zhang,
L.; Wang, A.; Miller, J. T.; Liu, X.; Yang, X.; Wang, W.; Li, L.;
Huang, Y.; Mou, C.-Y.; Zhang, T. ACS Catal. 2014, 4, 1546.
2
012, 90, 138.
(
24) (a) Buter, J.; Heijnen, D.; Vila, C.; Hornillos, V.; Otten, E.;
Giannerini, M.; Minnaard, A. J.; Feringa, B. L. Angew. Chem. Int.
Ed. 2016, 55, 3620. (b) Pinxterhuis, E. B.; Visser, P.; Esser, I.;
Gualtierotti, J.-B.; Feringa, B. L. Angew. Chem. Int. Ed. 2018, 57,
(c) Marina, N.; Lanterna, A. E.; Scaiano, J. C. ACS Catal. 2018, 8,
7593.
9452.
(
7) (a) Hassan, J.; Penalva, V.; Lavenot, L.; Gozzi, C.; Lemaire, M. Tet-
rahedron 1998, 54, 13793. (b) Penalva, V.; Hassan, J.; Lavenot, L.;
Gozzi, C.; Lemaire, M. Tetrahedron Lett. 1998, 39, 2559. (c) Zeng,
M.; Du, Y.; Shao, L.; Qi, C.; Zhang, X.-M. J. Org. Chem. 2010, 75,
(
25) Gong, X.; Wu, J.; Meng, Y.; Zhang, Y.; Ye, L.-W.; Zhu, C. Green
Chem. 2019, 21, 995.
26) Zawisza, A. M.; Muzart, J. Tetrahedron Lett. 2007, 48, 6738.
27) Bi(het)aryls 2a–y; General Procedure
(
(
2
556. (d) Shao, L.; Du, Y.; Zeng, M.; Li, X.; Shen, W.; Zuo, S.; Lu,
Y.; Zhang, X.-M.; Qi, C. Appl. Organomet. Chem. 2010, 24, 421.
e) Huang, Y.; Liu, L.; Feng, W. ChemistrySelect 2016, 1, 630.
8) Wang, L.; Zhang, Y.; Liu, L.; Wang, Y. J. Org. Chem. 2006, 71,
284.
The appropriate (het)aryl halide 1 (0.5 mmol) was added to a
mixture of Pd(OAc) (0.05 mmol, 10 mol%), sensory component
2
(
(8 mg), and K CO (1.0 mmol, 2 equiv) in DMF (10 mL), and the
2 3
(
(
mixture was stirred and heated in an oil bath at 100 °C for 24 h.
The mixture was then extracted with EtOAc (3 × 20 mL). The
combined organic phases were dried (MgSO ), filtered, concen-
trated under reduced pressure, and purified by column chroma-
tography (silica gel).
1
9) Monopoli, A.; Caló, V.; Ciminale, F.; Cotugno, P.; Angelici, C.;
4
Cioffi, N.; Nacci, A. J. Org. Chem. 2010, 75, 3908.
(
(
(
10) Park, B. R.; Kim, K. H.; Kim, T. H.; Kim, J. N. Tetrahedron Lett.
011, 52, 4405.
11) Firouzabadi, H.; Iranpoor, N.; Kazemi, F. J. Mol. Catal. A: Chem.
011, 348, 94.
12) (a) Brenda, M.; Knebelkamp, A.; Creiner, A.; Heitz, W. Synlett
2
3,3′,4,4′,5,5′-Hexamethoxy-1,1′-biphenyl (2g)
Prepared by the general procedure from 5-iodo-1,2,3-trime-
thoxybenzene (1g) and purified by column chromatography
2
[
silica gel, EtOAc–PE (1:3)] as a light-yellow solid; yield: 48 mg
1991, 809. (b) Kuroboshi, M.; Waki, Y.; Tanaka, H. Synlett 2002,
637. (c) Kuroboshi, M.; Waki, Y.; Tanaka, H. J. Org. Chem. 2003,
68, 3938.
1
(58%); mp 127.2 °C. H NMR (400 MHz, CDCl ):  = 6.72 (s, 4 H),
3
13
3.93 (s, 12 H), 3.89 (s, 6 H). C NMR (100 MHz, CDCl ):
3
+

= 153.4, 137.7, 137.6, 104.6, 61.0, 56.3. HRMS: m/z [M + H]
(
13) Qi, C.; Sun, X.; Lu, C.; Yang, J.; Du, Y.; Wu, H.; Zhang, X.-M.
calcd for C18H23O : 335.1494; found: 335.1491.
6
J. Organomet. Chem. 2009, 694, 2912.
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2020. Thieme. All rights reserved. Synlett 2020, 31, A–F