Mechanically induced solvent-free esterification method at room temperature

Article abstract of DOI:10.1039/d0ra09437d

Herein, we describe two novel strategies for the synthesis of esters, as achieved under high-speed ball-milling (HSBM) conditions at room temperature. In the presence of I2 and KH2PO2, the reactions afford the desired esterification derivatives in 45% to 91% yields within 20 min of grinding. Meanwhile, using KI and P(OEt)3, esterification products can be obtained in 24% to 85% yields after 60 min of grinding. In addition, the I2/KH2PO2 protocol was successfully extended to the late-stage diversification of natural products showing the robustness of this useful approach. Further application of this method in the synthesis of inositol nicotinate was also discussed. This journal is

Full text of DOI:10.1039/d0ra09437d

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Mechanically induced solvent-free esterification
method at room temperature†
Cite this: RSC Adv., 2021, 11, 5080
c
Lei Zheng,a Chen Sun,a Wenhao Xu,ab Alexandr V. Dushkin,c Nikolay Polyakov,
ab
Weike Su
and Jingbo Yub
*
Herein, we describe two novel strategies for the synthesis of esters, as achieved under high-speed ball-
milling (HSBM) conditions at room temperature. In the presence of I2 and KH2PO2, the reactions afford
the desired esterification derivatives in 45% to 91% yields within 20 min of grinding. Meanwhile, using KI
and P(OEt)3, esterification products can be obtained in 24% to 85% yields after 60 min of grinding. In
addition, the I2/KH2PO2 protocol was successfully extended to the late-stage diversification of natural
products showing the robustness of this useful approach. Further application of this method in the
synthesis of inositol nicotinate was also discussed.
Received 6th November 2020
Accepted 12th January 2021
DOI: 10.1039/d0ra09437d
rsc.li/rsc-advances
an important role in pharmaceutical chemistry with esterica-
tion reactions being among the most commonly used reactions
in medicinal chemistry.6 Natural products modied by esteri-
cation reactions show better biological activity than before
modication, but these reactions oen require large amounts of
environmentally harmful solvents and catalysts.7
Introduction
Mechanochemistry has been a popular topic in recent decades
because it is a solution-free and energy-efficient approach,
which complies with green chemistry. High-speed ball-milling
(HSBM) is a green mechanical technique used in organic
synthesis and has opened unique opportunities in synthetic
organic chemistry.1 HSBM facilitates reactions with insoluble
reactants, and enables solvent-free synthetic procedures to
successfully avoid the use of environmentally harmful and toxic
solvents, among other advantages.2 What's more, HSBM can
directly break or stretch chemical bonds because the role of
mechanical action is usually to provide better contact between
the reagents.3 More experimental results indicate that solvent-
free milling can lead to different product compositions or
catalyst combinations compared to those obtained by analo-
gous solution-based protocols. The Faraday Discussion Mech-
anochemistry which took place 2014 in Montreal have indicated
that the importance of mechanical processing in the context of
pharmaceuticals materials science.3b For these reasons, much
catalysts can be used in high-speed ball-milling to optimize
organic reactions.4
In recent years, many researchers have devoted themselves
to exploring green and efficient esterication reactions.
Common strategies of transition metal catalysis and pre-
functionalization are reported for the synthesis of ester groups.
Previously, Buchwald et al. described a method for the prepa-
ration of phenyl esters from aryl chlorides via palladium-
catalysed carbonylation (Scheme 1a).8 In 2011, Robles et al.
demonstrated a mild and regioselective method of esterication
and amidation using Gregg-Samuelson-type conditions
(Scheme 1b).9 In 2018, Szostak and coworkers reported an
alternative transition-metal-free method for esterication of
amides (Scheme 1c).10 Recently, Lee and coworkers developed
a new disconnection approach for the formation of aryl esters
by a nickel-catalysed radical cross-coupling reaction of a redox-
active ester with an aryl zinc reagent (Scheme 1d).11 When
transition metals are used in drug synthesis, the purication of
the reaction becomes tedious. Prefunctionalization will reduce
atom economy and increase the experimental procedures. We
have currently been focusing on the development of novel,
atom-economical, environmentally friendly methods for ester-
ication under HSBM conditions.
The ester bond is found in a plethora of naturally occurring
and pharmaceutically relevant molecules.5 This bond occupies
aKey Laboratory for Green Pharmaceutical Technologies and Related Equipment of
Ministry of Education, College of Pharmaceutical Sciences, Zhejiang University of
Technology, Hangzhou 310014, P. R. China. E-mail: pharmlab@zjut.edu.cn
bNational Engineering Research Center for Process Development of Active
Pharmaceutical Ingredients, Collaborative Innovation Center of Yangtze River Delta
Region Green Pharmaceuticals, Zhejiang University of Technology, Hangzhou
310014, P. R. China
cInstitute of Solid State Chemistry and Mechanochemistry, Novosibirsk, Russia
† Electronic supplementary information (ESI) available: Experimental procedures,
characterization data, NMR spectra. See DOI: 10.1039/d0ra09437d
Herein, we report two novel strategies for the synthesis of
ester groups under solvent-free milling (Scheme 1e). Through
modication of the reaction conditions, modes of reactivity
have been observed that are different from those in solution.
Compared with the preceding procedures of esterication, I2/
KH2PO2 system and KI/P(OEt)3 system are solvent-free,
transition-metal-free and prefunctionalization no need.
5080 | RSC Adv., 2021, 11, 5080–5085
© 2021 The Author(s). Published by the Royal Society of Chemistry

View Article Online
Paper
RSC Advances
Table 1 Optimization of the reaction conditionsa
Entry
Additive
Phosphines
Yieldb (%)
1
2
3
I2
—
I2
—
PPh3
PPh3
n.d.
n.d.
84
4
5
6
7
8
9
10
11c
12d
13
14
15
16
17
18
19e
20f
21g
22h
KI
NaI
CuI
FeI2
I2
I2
I2
I2
I2
KI
KI
KI
I2
KI
—
KI
KI
KI
KI
PPh3
PPh3
PPh3
PPh3
66
52
n.d.
12
n.d.
34
91
67
83
63
32
41
83
n.d.
Trace
75
44
33
K3PO4
NaH2PO2
KH2PO2
KH2PO2
KH2PO2
P(OEt)3
P(OMe)3
P(OBut)3
P(OEt)3
—
P(OEt)3
P(OEt)3
P(OEt)3
P(OEt)3
P(OEt)3
Scheme 1 Mechanically induced synthetic of derivatives containing
an ester group. (a) Buchwald's work; (b) Robles's work; (c) Szostak's
work; (d) Lee's work; (e) this work; (f) mechanosynthesis of inositol
nicotinate.
Moreover, KH2PO2 and P(OEt)3 can be easily removed as effec-
tive substitutes of PPh3. In addition, we discuss the advantages
of this method in the synthesis of inositol nicotinate
(Scheme 1f).
n.d.
a
Unless otherwise noted, all reactions were carried out with 1a (0.5
mmol), 2a (0.6 mmol), additive (0.5 mmol), phosphine (0.5 mmol),
and anhydrous sodium sulfate (0.4 g) at 25 Hz for 30 min, using two
stainless steel balls (f ¼ 1.2 cm, FMB ¼ 0.036) in 50 mL stainless steel
Results and discussion
At the outset, reactions between benzoic acid 1a and phenol 2a
were evaluated with different combinations of additives and
phosphine, where anhydrous sodium sulfate was chosen as
a helpful grinding auxiliary for better substrate mixing on the
basis of our previous research; the selected results were
summarized in Table 1. To our delight, both I2 and KI additives
could afford desired product 3aa in good yields aer 30 min of
grinding, where I2 worked better than KI (Table 1, entries 1–7).
We optimized both the I2 and KI strategies in order to discuss
the different reaction efficiencies and reaction mechanisms of
similar additives under the mechanochemistry process. Next,
several kinds of phosphines were tested (Table 1, entries 8–16).
The I2 with KH2PO2 gave the best result of 91%, while other
phosphines gave lower yields under the same conditions (Table
1, entries 2–10). For KI, the reaction with P(OEt)3 as phosphine
gave the most satisfactory result, while others were inferior
(Table 1, entries 13–15). To further optimize the reaction
conditions, we tested the amount of additives and phosphines.
The best yield of 75% was given by adding 0.75 mmol KI and
0.5 mmol P(OEt)3 (Table 1, entry 17). Decreasing additive and
phosphate loadings led to erosion in yield (Table 1, entries 11–
13, 19 and 20). From the experimental results, the corre-
sponding products were difficultly obtained without iodine or
potassium iodide as additives (Table 1, entries 2 and 18).
Furthermore, a simple comparison of the KI/P(OEt)3 induced
reaction under solvent-based conditions was conducted (Table
b
c
d
vial. Yield based on 1a. 0.5 equiv. I2 was used. 0.5 equiv. KH2PO2
was used. 1.5 equiv. KI was used. 0.5 equiv. KI was used. 0.5
equiv. P(OEt)3 was used. Yield of the comparative experiment: 1a
e
f
g
h
(0.5 mmol), 2a (0.6 mmol), KI (0.5 mmol), P(OEt)3 (0.5 equiv.), and
CH2Cl2 (20 mL) at room temperature.
at room temperature, which veried our hypothesis that HSBM
may induce high activity when using KI/P(OEt)3. To the best of
our knowledge, there was no report of inorganic iodine salts or
inorganic phosphorus salts promoted esterication reactions,
which inspired our interest in probing these two systems.
The mechanochemistry process parameters usually have
a strong inuence on the outcomes, as previously shown by us
and others.12 Thus, a combined assessment of the grinding time
and vibration frequency was carefully carried out; the results of
Fig. 1 Influence of milling time and frequency on the reaction. (a) Path
1, entries 19 and 22), and the reaction could hardly be promoted a; (b) path b.
© 2021 The Author(s). Published by the Royal Society of Chemistry
RSC Adv., 2021, 11, 5080–5085 | 5081

View Article Online
RSC Advances
Paper
Table 2 Esterification between carboxylic acid and alcoholab
be obtained by milling at 30 Hz within 30 min (93% yield).
However, the yield under optimal conditions did not change
much from that conducted at 25 Hz with 20 min. For compre-
hensive energy consumption and environmental friendliness,
we chose 25 Hz and 20 min as the subsequent experimental
conditions. When we recorded the results of the KI/P(OEt)3
strategy (Fig. 1b), the best result was obtained by milling at
25 Hz within 60 min (82% yield). Of note, further increase the
vibration frequency (30 Hz) led to a decrease of yield (76%).
Since the reaction substrates are the same in these two systems,
we speculate that distinct intermediates with inconsistent
sensitivity to reaction energy would be presence.
With the optimal conditions in hand, there was a large
difference in yield between the two different reaction systems,
so substrate expansion was divided into two parts for elucida-
tion. The scopes and limitations of this I2/KH2PO2 promoted
methodology were investigated rst by using various benzoic
acids. The results are presented in Table 2. The electronic
properties of the phenyl ring substituents of the carboxylic acids
had some effect on the reaction. Generally, carboxylic acids
possessing electron-withdrawing groups produced esters with
lower yields (3ad, 3ae, and 3af). Carboxylic acids possessing
electron-donating groups produced esters with higher yields
(3ag, 3ah, and 3ai). The procedure tolerated a range of func-
tional groups, such as chloro, bromo, naphthalene, and pyri-
dine groups. The compatibility of halogen groups was
synthetically useful since the products could easily be further
modiable (3ab and 3ac). Notably, 2-naphthoic acid and nico-
tinic acid ran smoothly under the standard conditions,
producing esters in 85 and 83% yields, respectively (3aj and
3ak). Furthermore, butyric acid was explored. This reaction
generated 3al in moderate yields; the reason for the lower yield
might be the volatility of fatty acids. Then, the esterication of
benzoic acid with several phenols and alcohols was investi-
gated. Gratifyingly, p-cresol and 4-(tert-butyl) phenol produced
p-tolyl benzoate 3ba and 4-(tert-butyl) phenyl benzoate 3bb in 87
and 76% yields, respectively. As expected, the triuoromethyl
and halogen groups on the phenyl ring of phenol derivatives
were well compatible under the standard procedure (3bc–3bf).
The ortho steric hindrance will reduce the yield of the product,
even with a prolonged reaction time (3bj and 3bk). Phenolic
compounds with electron withdrawing groups can produce
corresponding esters in medium to good yields (3bg, 3bh, and
3bi). Methanol, ethanol, and butyl alcohol afforded the ester in
63%, 72% and 75% yield, respectively (3ca–3cc). Notably, the
solketal could obtain the product 3cd in a medium yield.
Next, the KI/P(OEt)3 promoted esterication reaction was
examined. Unfortunately, it was observed that the KI/P(OEt)3
a
Path A reaction conditions: 1 (0.5 mmol), 2 (0.6 mmol), I2 (0.5 mmol),
KH2PO2 (0.5 mmol) and anhydrous sodium sulfate (0.4 g) at 25 Hz in
mixer mill, using two stainless steel balls (f ¼ 1.2 cm, FMB ¼ 0.036)
b
in 50 mL stainless steel vial. Yield based on 1. Path B reaction
conditions: 1 (0.5 mmol), 2 (0.6 mmol), KI (0.75 mmol), P(OEt)3 (0.5
mmol) and anhydrous sodium sulfate (0.4 g) at 25 Hz in mixer mill,
using two stainless steel balls (f ¼ 1.2 cm, FMB ¼ 0.036) in 50 mL
stainless steel vial. c 1 (2.0 mmol). d 2 (1.8 mmol).
I2/KH2PO2 system strategy are summarized in Fig. 1a. The yields
increased gradually as the frequency was increased from 15 to
20 Hz. However, in contrast to the apparent inuence of
frequency, variation in the grinding time did not show any
obvious difference from 20 to 30 Hz, where the best result could
Scheme 2 Mechanosynthesis of inositol nicotinate.
5082 | RSC Adv., 2021, 11, 5080–5085
© 2021 The Author(s). Published by the Royal Society of Chemistry

View Article Online
Paper
RSC Advances
Table 3 Chiral substratea
solketal could not afforod product 3cd under these conditions,
and butyric acid failed to deliver the desired ester. The KI/
P(OEt)3 esterication reaction had serious substrate restric-
tions, which may be related to its possible reaction mechanism.
Aer that, the chiral molecule phenylethanol was tried.
Phenylethyl benzoate could be obtained under two
a
See Table 1. b 1 (1.0 mmol), 2 (0.5 mmol), I2 (1.0 mmol), KH2PO2 (1.0
mmol) and anhydrous sodium sulfate (0.4 g) at 15 Hz within 60 min in
c
mixer mill. 1 (1.0 mmol), 2 (0.5 mmol), KI (1.50 mmol), P(OEt)3 (1.0
mmol) and anhydrous sodium sulfate (0.4 g) at 15 Hz within 120 min
in mixer mill.
did not show better reaction efficiency than the I2/KH2PO2
system. As shown in Scheme 2, the varied substrate scope was
evaluated. Compared with I2/KH2PO2, the yield of esterication
reaction through KI/P(OEt)3 is reduced. Compared with that
under I2/KH2PO2 conditions, the activity of methanol, ethanol
and n-butanol in the conversion to corresponding esters was
greatly weakened under KI/P(OEt)3 conditions (3ca–3cc). The
Table 4 Late-stage diversificationa
Scheme 3 Control experiments. (a) Mechanistic study of KI/P(OEt)3-
strategy; (b) mechanistic study of I2/KH2PO2 strategy; (c) the synthesis
of N-benzamide; (d) the sythesis of S-(m-tolyl) benzothioate; (e) the
capture of possible intermediates in the I2/KH2PO2 strategy; (f) verifi-
cation of radical mechanism; (g) reaction kinetics.
a
b
See Table 1. 1 (2.0 mmol). c 2 (3.0 mmol).
© 2021 The Author(s). Published by the Royal Society of Chemistry
RSC Adv., 2021, 11, 5080–5085 | 5083

View Article Online
RSC Advances
Paper
esterication conditions, but it was interesting that the incorporation, demonstrating oxygen transfer from the acid to
congurations of the product were different (Table 3, 3da). the ester (Scheme 3b). Aer that, we veried the reaction
Whatever, the expansion of amino acid substrates was not mechanism by aniline and m-methylthiophenol. In the pres-
smooth, even if we reduced the milling frequency and pro- ence of KI and P(OET)3, the yields of N-benzamide and S-(m-
longed the reaction time, poor yield was achieved (Table 3, 3db tolyl) benzothioate were higher than that of I2/KH2PO2 strategy
and 3dc).
(Scheme 3c and d). Next, we examined changes to the additive
The broad synthetic utility of this process is further high- under HSBM conditions. Aer HSBM of I2 and KH2PO2, the 31
P
lighted by the late-stage diversication of natural products. To chemical shi of KH2PO2 at 7.00 ppm was vanished, while a new
our delight, thymol, paeonol and eugenol were tolerated, peak at 1.00 ppm was formed, which was regarded as complex A,
producing the resulting esters in medium yields (3da, 3db, and but not available in solution (Scheme 3e). We hypothesize that
3dc).13–15 We were pleased to nd that the direct esterication of complex A (31P 1.00 ppm) can be produced in the HSBM envi-
cholesterol (3dd),16 a cyclopentane polyhydrophenanthrene ronment, which is not available in solution. Both esterication
derivative necessary for the human body; and oleanolic acid methods were completely still underwent in the presence of
(3de),17 a medicine for treating infectious acute jaundice hepa- radical
scavengers,
2,2,6,6-tetramethylpiperidine-1-oxyl
titis, furnished the esterication products in low to medium (TEMPO) or 2,6-di-tert-butyl-4-methyl-phenol (BHT), to give
yields, demonstrating the synthetic advantage of the I2/KH2PO2 3aa in good yield (Scheme 3f). The difference of reaction
protocol (Table 4). However, the KI/P(OEt)3 protocol, delivered kinetics was further studied by sampling in the rst 15 minutes
the esterication products only in trace amounts.
(the amount of 3aa was detected by HPLC). KI/P(OEt)3 reaction
Aerwards, we explored the practicability of this method, was almost carried out at a uniform rate. In the rst 4 min, there
which was exemplied through the synthesis of the anti- was no obvious product formation in I2/KH2PO2 reaction, and
hyperlipidaemic agent inositol nicotinate (Scheme 2).18 This the formation of 3aa product was accelerated aer 6 min
method can afford inositol nicotinate in moderate yield without (Scheme 3g).
purication by column chromatography.
Based on the above results and Denton's work,20a a possible
To shed light on the pathways of the two system dehydration mechanistic pathway is proposed for the I2/KH2PO2 strategy
platforms, several control experiments were performed. Firstly, (Path A). First, activated additive A is formed by the mechano-
we carried out mechanistic studies beginning with an isotope chemical reaction of potassium hypophosphite and iodine.
labelling experiment, whereby benzoic acid and 18O enriched Then, as in the classical Mitsunobu reaction,20b,c the counter
phenol were subjected to the reaction conditions (Scheme 3a).19 anion associated with phosphonium salt B may engage in
In the presence of KI and P(OEt)3, the ester product was ob- nonproductive, reversible bonding and exchange at the phos-
tained with high 18O incorporation, which indicated oxygen phorus atom, but ultimately, intercepting phenol 1b to afford
transfer from the alcohol to the ester. In contrast, using I2 and the conventional intermediate, the phenoxyphosphonium-
KH2PO2, the ester product was obtained with high 16O nucleophile ion pair C. Subsequent nucleophilic substitution
between phenoxyphosphonium salt C and intermediate B
afforded the substitution product 3aa (Scheme 4a). Next, the
mechanism of the KI/P(OEt)3 strategy is proposed through the
results of GC-MS (Fig. S3†). The benzoic acid in the KI/P(OEt)3
system undergoes Michel–Arbuzov reaction to obtain diethyl
benzoylphosphonate.21a,b According to previous reports, diethyl
benzoylphosphonate can easily react with phenol to obtain the
target product 3aa (Scheme 4b).21c
Conclusions
In conclusion, we have disclosed two protocols under HSBM
conditions that facilitated facile esterication of carboxyl and
hydroxyl groups. The I2/KH2PO2 strategy successfully replaced
organic phosphorus (PPh3) with inorganic phosphorus salts
(KH2PO2), while KI/P(OEt)3 strategy enabled the esterication
with an easily removable P(OEt)3. Both methods are solvent-free
and transition metal-free. Additionally, the feasibility of I2/
KH2PO2 strategy was demonstrated by application to the ester-
ication of natural products and the synthesis of inositol nic-
otinate. In addition, we discussed the different reaction
mechanisms of the two systems through control experiment.
Further investigation of environmentally friendly green chem-
Scheme 4 Plausible reaction mechanism: (a) path A; (b) path B.
5084 | RSC Adv., 2021, 11, 5080–5085
istry reaction under HSBM conditions is underway in our lab.
© 2021 The Author(s). Published by the Royal Society of Chemistry

View Article Online
Paper
RSC Advances
E. L. Parksa, A. H. Cocolasa, A. Weavera, N. P. Seeramb and
G. E. Henrya, Inorg. Chim. Acta, 2020, 505, 119495–119502; (c)
Y. Yua, Y. Liub, R. Shic, D. Zhanga, C. Lia and J. Shib, Bioorg.
Chem., 2020, 98, 103644–103649.
Conflicts of interest
There are no conicts to declare.
13 (a) K. M. Adki and Y. A. Kulkarni, Life Sci., 2020, 250, 117544–
117561; (b) Y. S. Hu, X. Han, P. J. Yu, M. M. Jiao, X. H. Liu and
J. B. Shi, Bioorg. Chem., 2020, 98, 103735–103748; (c)
H. Zhang, X. Geng, Z. Li, Y. Li, K. Xu, H. Wu, J. Xie, P. Sun,
S. Wei and M. Qiao, Front. Psychiatr., 2020, 11, 295–308; (d)
Y. Peng, X. Zheng, Z. Fan, H. L. Zhou, X. X. Zhu,
G. J. Wang and Z. H. Liu, Phytomedicine, 2019, 68, 1–48.
14 (a) C. S. Jia, D. D. Cao, S. P. Ji, X. M. Zhang and B. Muhoza,
Food Hydrocolloids, 2020, 104, 105717–105769; (b)
H. G. Bilgicli, A. Kestane, P. Taslimi, O. Karabay, A. Bytyqi-
Damoni, M. Zengin and I. Gulcin, Bioorg. Chem., 2019, 88,
102931–102937; (c) M. Govindarajan, M. Rajeswary,
S. L. Hoti, A. Bhattacharyya and G. Benelli, Parasitol. Res.,
2016, 115, 807–815.
15 (a) A. Rohatgi, A. Khera, J. D. Berry, E. G. Givens, C. R. Ayers,
K. E. Wedin, I. J. Neeland, I. S. Yuhanna, D. R. Rader, J. A. de
Lemos and P. W. Shaul, N. Engl. J. Med., 2014, 371, 2383–
2393; (b) S. R. Pfeffer, J. Biol. Chem., 2019, 294, 1706–1709;
(c) B. M. Castellano, A. M. Thelen, O. Moldavski, M. Feltes,
R. E. N. Van der Welle, L. Mydock-McGrane, X. Jiang,
R. J. Van Eijkeren, O. B. Davis, S. M. Louie, R. M. Perera,
D. F. Covey, D. K. Nomura, D. S. Ory and R. Zoncu, Science,
2017, 355, 1306–1311.
Acknowledgements
We gratefully acknowledge the National Natural Science Foun-
dation of China (No. 21978270).
Notes and references
1 (a) E. Boldyreva, Chem. Soc. Rev., 2013, 42, 7719–7738; (b)
L. Takacs, Chem. Soc. Rev., 2013, 42, 7649–7659; (c)
J. L. Howard, Q. Cao and D. L. Browne, Chem. Sci., 2018, 9,
3080–3094.
´
2 (a) J. G. Hernandez and C. Bolm, J. Org. Chem., 2017, 82,
4007–4019; (b) S. Tabasso, D. Carnaroglio, E. C. Gaudino
and G. Cravotto, Green Chem., 2015, 17, 684–693; (c)
R. B. N. BaigandR and S. Varma, Chem. Soc. Rev., 2012, 41,
1559–1584.
3 (a) L. Takacs, Prog. Mater. Sci., 2002, 47, 355–414; (b)
´
T. Friscic, S. L. James, E. V. Boldyreva, C. Bolm, W. Jones,
J. Mack, J. W. Steedh and K. S. Suslick, Chem. Commun.,
2015, 51, 6248–6256.
4 (a) J. B. Yu, Y. Zhang, Z. J. Jiang and W. K Su, J. Org. Chem.,
´
2016, 81, 11514–11520; (b) H. C Cheng, J. G. Hernandez
and C. Bolm, Org. Lett., 2017, 19, 6284–6287; (c) H. Xu,
H. W Liu, K. Chen and G. W Wang, J. Org. Chem., 2018, 83,
6035–6049.
16 (a) T. B. Ayeleso, M. G. Matumba and E. Mukwevho,
Molecules, 2017, 22, 1915–1930; (b) J. Pollier and
ˇ
5 (a) A. Zapf and M. Beller, Top. Catal., 2002, 19, 101–109; (b)
J. Stetter and F. Lieb, Angew. Chem., Int. Ed., 2000, 39,
1724–1728; (c) N. Marion, S. Diez-Gonzalez and S. P. Nolan,
Angew. Chem., Int. Ed., 2007, 46, 2988–3000.
A. Goossens, Phytochemistry, 2012, 77, 10–15; (c) L. Ziberna,
ˇ
D. Samec, A. Mocan, S. F. Nabavi, A. Bishayee,
A. A. Farooqi, A. Sureda and S. M. Nabavi, Int. J. Mol. Sci.,
2017, 18, 643–658.
6 (a) J. S. Carey, D. Laffffan, C. Thomson and M. T. Williams,
Org. Biomol. Chem., 2006, 4, 2337–2347; (b) R. W. Dugger,
J. A. Ragan and D. H. B. Ripin, Org. Process Res. Dev., 2005,
9, 253–258; (c) K. C. K. Swamy, N. N. B. Kumar,
E. Balaraman and K. V. P. P. Kumar, Chem. Rev., 2009, 109,
2551–2651; (d) T. Yuen, S. B. Sze and P. H. Toy, J. Am.
Chem. Soc., 2006, 128, 9636–9637.
7 (a) K. Ishihara, S. Ohara and H. Yamamoto, Tetrahedron,
2002, 58, 8179–8188; (b) N. Bhatt, A. Patel, P. Selvam and
K. Sidhpuria, J. Mol. Catal., 2007, 275, 14–24; (c)
N. Sanchez, M. Martinez, J. Aracil and A. Corma, J. Am. Oil
Chem. Soc., 1992, 69, 1150–1153; (d) E. Heykants,
W. H. Verrelst, R. F. Parton and P. A. Jacobs, Stud. Surf. Sci.
Catal., 1997, 105, 1277–1284.
8 D. A. Watson, X. X. Fan and S. L. Buchwald, J. Org. Chem.,
2008, 73, 7096–7101.
9 N. Iranpoor, H. Firouzabadi, D. Khalili and S. Motevalli, J.
Org. Chem., 2011, 76, 2277–2281.
10 G. C. Li, P. Lei and M. Szostak, Org. Lett., 2018, 20(18), 5622–
5625.
11 B. H. Shih, R. S. Basha and C. F. Lee, ACS Catal., 2019, 9,
8862–8866.
17 I. O. Poon, D. S. L. Chow and D. Liang, Am. J. Health-Syst.
Pharm., 2006, 63, 2128–2134.
18 (a) S. Tanii, M. Arisawa and M. Yamaguchi, Chem. Commun.,
2019, 55, 14078–14080; (b) A. N. Holding and J. B. Spencer,
ChemBioChem, 2008, 9, 2209–2214.
´
19 (a) R. H. Beddoe, K. G. Andrews, V. Magne, J. D. Cuthbertson,
J. Saska, A. L. Shannon-Little, S. E. Shanahan, H. F. Sneddon
and R. M. Denton, Science, 2019, 365, 910–914; (b)
O. Mitsunobu, Synthesis, 1981, 1–28; (c) O. Mitsunobu and
M. Yamada, Bull. Chem. Soc. Jpn., 1967, 40, 2380–2382; (d)
J. An, R. M. Denton, T. H. Lambert and E. D. Nacsa, Org.
Biomol. Chem., 2014, 12, 2993–3003.
20 (a) P. J. Garegg and B. Samuelsson, J. Chem. Soc., Chem.
Commun., 1979, 978–980; (b) E. D. Matveeva,
T. A. Podrugina, N. G. Sandakova and N. S. Zerov, Russ.
J. Org. Chem., 2004, 40, 1469–1472; (c) C. A. Tolman, Chem.
Rev., 1977, 77, 313–348.
21 (a) S. M. A. Kedrowski and D. A. Dougherty, Org. Lett., 2010,
12, 3990–3993; (b) A. K. Bhattacharya and G. Thyagarajan,
Chem. Rev., 1981, 81, 415–430; (c) M. Sekine, A. Kume and
T. Hata, Tetrahedron Lett., 1981, 22, 3617–3620.
12 (a) C. F. Bagamboula, M. Uyttendaele and J. Debevere, Food
Microbiol., 2004, 21, 33–42; (b) M. H. Havasia, A. J. Resslera,
© 2021 The Author(s). Published by the Royal Society of Chemistry
RSC Adv., 2021, 11, 5080–5085 | 5085