Iron-Catalyzed Regioselective Decarboxylative Alkylation of Coumarins and Chromones with Alkyl Diacyl Peroxides

Article abstract of DOI:10.1055/s-0037-1611864

A facile iron-catalyzed decarboxylative radical coupling of alkyl diacyl peroxides with coumarins or chromones has been developed, affording a highly efficient approach to synthesize a variety of α-alkylated coumarins and β-alkylated chromones. The reaction proceeded smoothly without adding any ligand or additive and provided the corresponding products containing a wide scope of functional groups in moderate to excellent yields. This protocol was highlighted by its high regioselectivity, readily available starting materials, and operational simplicity.

Full text of DOI:10.1055/s-0037-1611864

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2019, 30, A–G
letter
A
en
C. Jin et al.
Letter
Synlett
Iron-Catalyzed Regioselective Decarboxylative Alkylation of
Coumarins and Chromones with Alkyl Diacyl Peroxides
b
Can Jin*a
Xun Zhanga
Bin Sun*b
Zhiyang Yana
Tengwei Xua
b
a
R
H
a
O
O
O
O
O
O
25 examples
O
R
Fe(OTf)3
– CO2
+
R
O
b
O
R
b
H
O
Excellent regioselective
a
a
Inexpensive catalyst
a College of Pharmaceutical Sciences, Zhejiang University of
Technology, Hangzhou 310014, P. R. of China
jincan@zjut.edu.cn
b Collaborative Innovation Center of Yangtze River Delta Region
Green Pharmaceuticals, Zhejiang University of Technology,
Hangzhou 310014, P. R. of China
Decarboxylative coupling
C(sp2)–C(sp3) bond formation
O
O
8 examples
sunbin@zjut.edu.cn
Received: 01.05.2019
Accepted after revision: 26.05.2019
Published online: 26.06.2019
achieved under metal-free conditions by the Antonchick
and Jafarpour group.9,10 Although great progress has been
obtained in preparing alkylated coumarin or chromone
compounds, some drawbacks such as the use of excess
amounts of chemical oxidants, poor regioselectivity, and
low conversions or yields are still the issues limiting the
further application. Moreover, the method for preparation
of primary alkyl-substituted coumarins or chromones is
still an enormous challenge. Very recently, our group devel-
oped a visible-light-induced decarboxylative coupling reac-
tion between coumarins and NHP esters mediated by visi-
ble light using expensive iridium as photocatalyst.11 Apply-
ing this strategy, though primary alkylated coumarins were
synthesized successfully, whereas the pursuit of cost-effec-
tive system to achieve C–H alkylation of coumarin or chro-
mone is always an ongoing interest in our lab.
DOI: 10.1055/s-0037-1611864; Art ID: st-2019-l0245-l
Abstract A facile iron-catalyzed decarboxylative radical coupling of al-
kyl diacyl peroxides with coumarins or chromones has been developed,
affording a highly efficient approach to synthesize a variety of -alkylat-
ed coumarins and -alkylated chromones. The reaction proceeded
smoothly without adding any ligand or additive and provided the corre-
sponding products containing a wide scope of functional groups in
moderate to excellent yields. This protocol was highlighted by its high
regioselectivity, readily available starting materials, and operational
simplicity.
Key words coumarins, chromones, C–C bond, iron-catalyzed, decar-
boxylation
Coumarin and chromone derivatives possessing carbon-
yl-conjugated olefin fragment in their structures exhibit a
broad range of notable activities such as antimicrobial,
anti-inflammatory, anticancer, and anti-HIV.1 In the past
decades, direct C–H functionalizations via a cross-coupling
pathway has become one of the most straightforward and
efficient methods for C–C or C–X bond formation because
this protocol is more atom economical and environmental-
ly friendly.2 With the assistance of precious metals, such as
Pd,3 Rh,4 Ru,5 considerable progress has been made in the
synthesis of aryl-substituted coumarin or chromone deriva-
tives. For example, Shafiee and coworkers developed a regi-
oselective arylation of chromenones via palladium-cata-
lyzed oxidative boron Heck-type reaction.3a Subsequently, a
more difficult task, that is alkylation of coumarins or chro-
mones, was also realized under transition-metal catalysis6–8
(Scheme 1, 1). In 2015, Ge’s group developed two novel re-
gioselective cross-dehydrogenation couplings of coumarins
and chromones with different ethers via C(sp3)–H function-
alization process under catalysis of copper or iron salts.7b In
addition, alkylation of coumarins and chromones was also
Alkyl diacyl peroxides which could be easily synthe-
sized from the corresponding carboxylic acids were demon-
strated to be effective alkyl sources because it can be easily
decomposed to give alkyl radicals in the presence of inex-
pensive metal catalysts, such as Cu and Fe, while elimina-
tion of CO2.12 Therefore, we reasonably postulated that it
should be possible to achieve the alkylation of coumarin or
chromone via decarboxylative alkylation by employing pri-
mary alkyl diacyl peroxides as alkyl source, providing a
practical and cheaper approach to offer the alkylated deriv-
atives. In continuation of our interest in the development of
C–H functionalization of coumarins or chromones, herein,
we present our recent work on this iron-catalyzed decar-
boxylative coupling reaction between alkyl diacyl peroxides
and coumarins or chromones for the synthesis of -alkylat-
ed coumarins and -alkylated chromones.
To begin our study, coumarin (1a) and lauroyl peroxide
(LPO, 2a) was chosen as the representative reactant to ex-
plore and optimize the decarboxylative coupling reaction
(Table 1). Initially, the reaction was carried out in MeCN un-
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G
Georg Thieme Verlag KG, Rüdigerstraße 14, 70469 Stuttgart, Germany

B
C. Jin et al.
Letter
Synlett
Previous works:
(1) Metal-catalyzed alkylation of coumarin and chromone
X
O
O
O
O
O
H
transition-metal-catalyzed
Fe, Cu, Co
X
(1) (ref. 6–8)
O
+
H
X = C, O
(ether or cycloalkane)
O
O
X
(2) Alkylation of coumarin and chromone
O
O
O
I(III)
, N3
Alkyl-H
(2) (ref. 9)
+
Alkyl
O
O
H
(secondary or tertiary alkyl)
H
O
X
X
TBHP
+
H
(3) (ref. 10)
O
O
X = C, O
(ether or cycloalkane)
This work:
R
O
stable radical
favored
R
O
O
O
– CO2
R
Fe(OTf)3
O
O
unfavored
cheaper;
catalytic amount;
environmentally friendly
O
O
O
O
R
R
O
O
δ–
O
O
O
δ+
δ–
δ+
1,4-conjugated addition
favored
O
O
O
R
– CO2
Fe(OTf)3
O
R
R
unfavored
O
Scheme 1 Strategies for the synthesis of alkylated chromone or coumarin derivatives
der the catalysis of various copper salts (5 mol%) at 60 °C for
8 h. Disappointingly, the experimental results indicated
that all of these screened copper catalysts, such as CuCl2,
CuBr2, Cu(OAc)2, or CuBr, were all ineffective for this trans-
formation (Table 1, entries 1–4). Fortunately, when the re-
action was performed in the presence of 5 mol% FeCl3, it
was pleased to find that the desired product 3aa could be
obtained in 25% yield (Table 1, entry 5). Encouraged by this
result, another two iron salts were also studied, and
Fe(OTf)3 proved to be best with 58% yield for coupling prod-
uct 3aa (Table 1, entries 6 and 7). Subsequently, several oth-
er solvents including dioxane, DCM, and DCE were probed,
and dioxane was proved to be the best choice (Table 1, en-
tries 8–10). A significant improvement was observed when
the temperature was elevated to 70 °C, however, we also
found that a further increase of reaction temperature could
not improve the efficiency of the reaction (Table 1, entries
11 and 12). Either increasing the amount of Fe(OTf)3 to 10
mol% or decreasing to 2 mol% all did not display positive ef-
fects on this transformation (Table 1, entries 13 and 14).
The optimization experiments also revealed that no desired
product 3aa was observed in absence of an iron catalyst,
and the yield dropped obviously when the reaction was con-
ducted under an air atmosphere (Table 1, entries 15 and 16).
After the reaction conditions were screened, it could be
concluded that the optimized reaction conditions should be
performed under the catalysis of 5 mol% Fe(OTf)3 at 70 oC in
dioxane under N2 atmosphere.
With the optimized conditions in hand, different sets of
experiments were carried out to investigate the scope and
limitation of this reaction. Initially, a series of coumarins
were investigated via the decarboxylative coupling reaction
with LPO (2a) under the optimized conditions. As given in
Scheme 2, this method was found to be applicable to a wide
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G

C
C. Jin et al.
Letter
Synlett
Table 1 Optimization of the Reaction Conditionsa
O
C11H23
catalyst
O
n-C11H23
+
n-C11H23
O
solvent, N2, 8 h
O
O
O
O
O
2a
3aa
1a
Entry
Catalyst
Solvent
Temp (°C)
Yield (%)b
1
2
CuCl2
CuBr2
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
60
60
60
60
60
60
60
60
60
60
70
80
60
60
60
60
N.D.
N.D.
N.D.
N.D.
25
3
Cu(OAc)2
CuBr
4
5
FeCl3
6
Fe(OTf)2
Fe(OTf)3
Fe(OTf)3
Fe(OTf)3
Fe(OTf)3
Fe(OTf)3
Fe(OTf)3
Fe(OTf)3
Fe(OTf)3
–
53
7
58
8
dioxane
DCM
65
9
50
10
11
12
13c
14d
15
16e
DCE
60
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
83
67
82
75
N.D.
65
Fe(OTf)3
a Reaction conditions: unless otherwise noted, all reactions were performed with 1a (0.6 mmol), 2a (1.2 mmol), and catalyst (0.03 mmol) in dioxane (3 mL)
under N2 atmosphere for 8 h.
b Isolated yield.
c Fe(OTf)3(10 mol%).
d Fe(OTf)3 (2 mol%)
e Under air atmosphere.
range of coumarins (1a–n), giving the corresponding prod-
ucts 3aa–na in 40–83% yields. Coumarins bearing electron-
donating groups at 6-position of aromatic ring, such as
methyl (1b) or methoxy (1c) could provide the desired
products 3ba and 3ca in 81% and 78% yields, respectively.
Meanwhile, the coumarins containing electron-withdraw-
ing groups at 6-position of the aromatic ring, even though
the strong-withdrawing group (nitro), were also well toler-
ated for this decarboxylative coupling reaction, affording
the corresponding -substituted products 3da–fa in 51–
71% yields. Subsequently, coumarins with substituents at
different positions of the benzene ring were also tested. The
experiment results indicated that this decarboxylative cou-
pling reaction was not very sensitive to the substituted po-
sitions of functional groups. Coumarins bearing either elec-
tron-donating groups or electron-withdrawing groups at
the 7 or 8-position of the aromatic ring were all suitable for
this transformation and gave the desired product
3ga,ha,ia,ka,la in 58–78% yields. To our delight, unprotect-
ed 7-hydroxycoumarin 1j was also well compatible with
these reaction conditions, giving the corresponding product
3ja in moderate yield. In addition, it was worth noting that
4-methyl-substituted coumarins 1m or 1n also could un-
dergo this decarboxylative coupling process well, achieving
the target products 3ma and 3na in high efficiency, where-
as C(sp3)–H bonds were unaffected. Compared with the pre-
vious photocatalytic method,12 this strategy possessed a
wider scope of coumarins, including the nitro-substituted
1f, unprotected substrate 1j, and 4-methyl-substituted 1m
or 1n, that were all tolerated for this transformation.
After the scope of coumarins was examined, we then
turned our attention to explore the scope of alkyl diacyl
peroxides via decarboxylative coupling reaction with cou-
marin (1a). The results are summarized in Scheme 3. This
method was found to be applicable to a variety of alkyl dia-
cyl peroxides, which were able to undergo the decarboxyl-
ative coupling process to provide the desired -position-
substituted alkylated coumarin derivatives 3ab–ak in mod-
erate to good yields. Initially, a series of simple primary al-
kyl-substituted diacyl peroxides 2b–e bearing n-octyl, n-
propyl, 3-methylbutyl, and 2,2-dimethylpropyl were
probed, and these substrates all showed good tolerance for
this reaction, affording the corresponding products 3ab–ae
in 58–79% yields. Moreover, alkyl diacyl peroxides with ad-
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G

D
C. Jin et al.
Letter
Synlett
R2
R2
O
O
C11H23
Fe(OTf)3 (5 mol%)
R1
O
n-C11H23
R1
+
n-C11H23
O
dioxane (3 mL), N2, 70 °C
O
O
O
O
2a
1
3
C11H23
C11H23
O
C11H23
O
O
O
O
O
O
3aa, 83%
3ba, 81%
3ca, 78%
Cl
C11H23
Br
C11H23
O2N
C11H23
O
O
O
O
O
O
3da, 71%
3ea, 69%
3fa, 51%
C11H23
C11H23
C11H23
O
O
O
Cl
O
O
F
O
O
3ga, 74%
3ha, 64%
3ia, 58%
C11H23
C11H23
C11H23
O
O
O
O
HO
O
O
O
Cl
3ja, 40%
3ka, 68%
3la, 78%
C11H23
C11H23
O
O
O
O
O
O
O
3na, 63%
3ma, 48%
Scheme 2 Substrate scope of coumarins. All reactions were performed with 1 (0.6 mmol), 2a (1.2 mmol), and Fe(OTf)3 (0.03 mmol) in dioxane (3 mL)
at 70 °C under N2 atmosphere for 8 h.
ditional functional groups, such as cyclopentyl (2f), phenyl
(2g), and alkenyl (2h), were also well tolerated for this
transformation, and the desired products 3af–ah could be
obtained in satisfied yields. Subsequently, we explored
whether the secondary alkyl diacyl peroxides could adapt
to this reaction. To our delight, 1-methylpropyl diacyl per-
oxide (2i), cyclopentyl diacyl peroxide (2j), and cyclohexyl
diacyl peroxide (2k) all could be well tolerated, and the
alkylated products 3ai,aj,ak were isolated in 55%, 58%, and
50% yields, respectively. Apart from primary or secondary
alkyl diacyl peroxides, tertiary alkyl diacyl peroxide (2l)
was also employed to react with the coumarin (1a) under
the optimized conditions. However, it failed to give the de-
sired product 3al mainly due to the poor stability of tertiary
alkyl diacyl peroxides compared with the primary or sec-
ondary alkyl diacyl peroxides.
or electron-donating groups (methyl, methoxy) on the 6- or
7-positions of the benzene ring were all able to undergo
this decarboxylative coupling process well, giving the alkyl-
substituted chromone derivatives 5a–h in moderate yields.
Noticeably, the electron-rich alkyl radical was more
prone to add to the electron-deficient -position of the
chromone, rather than the relatively electron-rich -posi-
tion, regioselectively providing the -substituted alkylated
chromone derivatives.
To gain the insight into the mechanism of the reaction,
several control experiments were carried out as shown in
Scheme 5. Firstly, in order to determine if radicals were in-
volved in these two decarboxylative coupling reactions, 1,1-
diphenylethylene was used as radical scavenger adding into
the reaction system, and the transformation was complete-
ly suppressed (Scheme 5, 1). As expected, the correspond-
ing product 3aa or 5a was not found by ESI-MS. Subse-
quently, the further step confirmed the formation of alkyl
radical, and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)
was then added into the decarboxylative coupling reaction
between coumarin (1a) and LPO (2a) under the standard
Applying the optimized reaction conditions found
above, various chromones containing a wide scope of func-
tional groups on the benzene ring were also reacted with
LPO (2a) as depicted in Scheme 4. Expectedly, chromones
bearing either electron-withdrawing (fluoro, chloro, bromo)
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G

E
C. Jin et al.
Letter
Synlett
R
O
O
O
H
O
O
O
O
Fe(OTf)3 (5 mol%)
dioxane, N2, 70 °C, 8 h
O
R
+
Fe(OTf)3 (5 mol%)
R
O
+
O
O
LPO
R
R
dioxane, N2, 70 °C, 8 h
O
1a
3
C11H23
2
H
2a
5
4
O
O
O
O
O
O
3ac, 67%
O
3ab, 79%
O
C11H23
O
C11H23
O
C11H23
5a, 56%
5b, 60%
5c, 64%
O
O
MeO
O
O
O
O
O
O
O
3ad, 62%
3ae, 58%
3af, 80%
O
C11H23
MeO
Br
C11H23
O
C11H23
O
5d, 54%
5f, 45%
5e, 53%
O
O
O
O
O
O
O
O
Cl
3ag, 65%
3ah, 69%
3ai, 55%
F
O
C11H23
O
C11H23
5h, 50%
5g, 43%
Scheme 4 Substrate scope of chromones. All reactions were per-
formed with 4 (0.6 mmol), 2a (1.2 mmol), and Fe(OTf)3 (0.03 mmol) in
dioxane (3 mL) at 70 °C under N2 atmosphere for 8 h.
O
O
O
O
O
O
3aj, 58%
3ak, 50%
3al, N.D.
Scheme 3 Substrate scope with alkyl diacyl peroxides. All reactions
were performed with 1a (0.6 mmol), 2 (1.2 mmol), and Fe(OTf)3(0.03
mmol) in dioxane (3 mL) at 70 °C under N2 atmosphere for 8 h.
Based on the control-experiment results and previous
reports,12 a plausible mechanism has been proposed in
Scheme 6. Bao’s group has demonstrated that the Fe(III)
was initially reduced by alkyl radical to afford the Fe(II).
Then Fe(II) could be oxidized by the alkyl diacyl peroxide to
provide the alkyl radical by releasing a molecule of carbon
dioxide, accompanied with oxidation of Fe(II) to Fe(III) via a
SET process. Subsequently, the alkyl radical could attack the
-position of coumarin, generating a thermodynamically
stable radical D, which could be transformed into the de-
sired product 3 via a SET process, followed by elimination of
AlkylCOOH. Because the -position of chromone possessed
a higher electron density than the -position, the electron-
conditions. The experiment result indicated that no desired
product 3aa was found, meanwhile, the radical trapping
product 6 was detected by ESI-MS and isolated in 64% yield
(Scheme 5, 2). The similar result was obtained when TEMPO
was added into another coupling reaction between chro-
mone 5a and LPO 2a. These experiment results indicated
that radicals were involved in both two decarboxylative
coupling reactions.
C11H23
O
O
O
O
O
1a
4
3aa, N. D. (not detected by ESI-MS)
standard conditions
(1)
O
1,1-diphenylethylene
3.0 eq.
O
O
C11H23
5a, N. D. (not detected by ESI-MS)
C11H23
O
standard conditions
N
C11H23
(2)
+
LPO
+
TEMPO (3.0 eq.)
O
O
O
O
6, 64%
(ESI-MS, found: 312.3)
3aa, N. D.
(not detected by ESI-MS)
2a
1a
Scheme 5 Control experiments
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G

F
C. Jin et al.
Letter
Synlett
rich alkyl radical exhibited some nucleophilicity and was
prone to react at the electron-deficient -position of chro-
mone instead of the -position, generating the radical in-
termediate C. After a SET process and elimination of Alkyl-
COOH, radical C was finally transformed into the desired
product 5.
References and Notes
(1) (a) Musa, M. A.; Cooperwood, J. S.; Khan, M.; Omar, F. Curr. Med.
Chem. 2008, 15, 2664. (b) Spino, C.; Dodier, M.; Sotheeswaran, S.
Bioorg. Med. Chem. Lett. 1998, 8, 3475. (c) Wang, X. H.; Bastow,
K. F.; Sun, C. M.; Lin, Y. L.; Yu, H. J.; Don, M. J.; Wu, T. S.;
Nakamura, S.; Lee, K. H. J. Med. Chem. 2004, 47, 5816.
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S. Chem. Soc. Rev. 2011, 40, 5068. (d) Sun, B.; Wang, Y.; Li, D. Y.;
Jin, C.; Su, W. K. Org. Biomol. Chem. 2018, 16, 2902. (e) Sun, B.;
Yin, S.; Zhuang, X. H.; Jin, C.; Su, W. K. Org. Biomol. Chem. 2018,
16, 6017. (f) Sun, B.; Deng, J. C.; Li, D. Y.; Jin, C.; Su, W. K. Tetrehe-
dron Lett. 2018, 59, 4364. (g) Sun, B.; Yan, Z. Y.; Jin, C.; Su, W. K.
Synlett. 2018, 29, 2432. (h) Lv, Y. H.; Li, Y.; Xiong, T.; Lu, Y.; Liu,
Q.; Zhang, Q. Chem. Commun. 2014, 50, 2367. (i) Vogl, O.;
Rondestvedt, C. S. J. Am. Chem. Soc. 1954, 77, 3067. (j) Zhao, W.
N.; Xu, L.; Ding, Y. C.; Niu, B.; Xie, P.; Bian, Z. G.; Zhang, D. H.;
Zhou, A. H. Eur. J. Org. Chem. 2016, 325.
(3) (a) Khoobi, M.; Alipour, M.; Zarei, S.; Jafarpour, F.; Shafiee, A.
Chem. Commun. 2012, 48, 2985. (b) Min, M.; Hong, S. Chem.
Commun. 2012, 48, 9613. (c) Jafarpour, F.; Barzegar, M.; Olia, A.;
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14, 6108. (c) Chen, G.; Tokunaga, N.; Hayashi, T. Org. Lett. 2005,
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Alkyl
Alkyl
O
– AlkylCOOH
SET
O
O
O
D
3
O
O
Alkyl
OCOAlkyl
Fe(III)
1a
4a
Alkyl
O
O
O
alkyl radical
Fe(II)
Fe(III)
O
+
Alkyl
+
CO2
O
SET
B
A
SET
O
O
O
– AlkylCOOH
O
Alkyl
O
Alkyl
5
C
Scheme 6 Proposed mechanism
In summary, we have succeeded in developing a novel
iron-catalyzed regioselective alkylation of coumarins and
chromones by employing cheap and available alkyl diacyl
peroxides as the alkyl source, preparing a variety of alkyl-
substituted derivatives with alkyl group on the -position
of coumarins and the -position of chromones.13 The use of
inexpensive and nontoxic iron salts as the catalyst made
this transformation environmentally friendly and practical.
Remarkably, this transformation has been proven to be
compatible with a wide range of alkyl diacyl peroxides, es-
pecially the primary alkyl-substituted peroxides, and a va-
riety of coumarins or chromones bearing various functional
groups also exhibited good tolerance for this transforma-
tion. Mechanistic studies have revealed that these two de-
carboxylative coupling reactions all proceed through a radi-
cal process.
(5) Kim, K.; Choe, H.; Jeong, Y.; Lee, J. H.; Hong, S. Org. Lett. 2015,
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N. T. S. RSC Adv. 2018, 8, 10736.
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Funding Information
We thank the National Natural Science Foundation of China (Grant
No. 21606202) for financial support. We are also grateful to the Col-
lege of Pharmaceutical Sciences, Zhejiang University of Technology
and Collaborative Innovation Center of Yangtze River Delta Region
Green Pharmaceuticals for the financial help.
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Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0037-1611864.
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(13) General Procedure for the Synthesis of 3 or 5 (3aa as an
Example)
A 10 mL Schlenk tube was charged with coumarin (1a, 88 mg,
0.6mmol), LPO (2a, 477 mg, 1.2 mmol), Fe(OTf)3 (15 mg, 0.03
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G

G
C. Jin et al.
Letter
Synlett
mmol), and dioxane (3.0 mL). The tube was evacuated and back-
filled with N2 for three times. The mixture was then heated at
70 ℃ and stirred for 8 h. After the reaction finished, the reaction
mixture was extracted with DCM (30 mL). The organic layer was
dried over Na2SO4 and concentrated under reduced pressure.
The crude product was purified by flash chromatography on
silica gel column (ethyl acetate/hexane, 1:80) to afford 3aa (149
mg, 83%) as a white solid.
Compound 3aa: white solid; mp 59.6–60.3 ℃, 83% (149 mg). 1H
NMR (400 MHz, CDCl3):  = 7.47 (s, 1 H), 7.45–7.42 (m, 2 H),
7.31 (d, J = 8.0 Hz, 1 H), 7.26 (d, J = 8.0 Hz, 1 H), 2.56 (t, J = 7.8 Hz,
2 H), 1.68–1.60 (m, 2 H), 1.39–1.25 (m, 16 H), 0.88 (t, J = 6.8 Hz,
3 H). 13C NMR (100 MHz, CDCl3):  = 161.8, 153.1, 138.3, 130.4,
130.1, 127.1, 124.2, 119.6, 116.4, 31.9, 30.8, 29.63, 29.60, 29.56,
29.4, 29.3, 28.0, 22.7, 14.1. HRMS: m/z calcd for C20H29O2 [M +
H]+: 301.2162; found: 301.2170.
© 2019. Thieme. All rights reserved. — Synlett 2019, 30, A–G