Synthesis of 1,3-diaryl butanones from acetophenones via a tandem reaction

Article abstract of DOI:10.1080/00397911.2020.1755871

A tandem reaction for the simple construction of 1,3-diaryl butanones from acetophenones was developed. Anhydrous HI was generated in situ by the promotion of the [Rh]- complex with molecular hydrogen and iodine. The acetophenones undergo aldol reactions

Full text of DOI:10.1080/00397911.2020.1755871

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Synthesis of 1,3-diaryl butanones from
acetophenones via a tandem reaction
Sida Li, Ronibala Devi Laishram, Guoli Shen, Xuexin Zhang, Yong Yang,
Jianxiao Ni, Yong Zhan, Yongyun Zhou & Baomin Fan
To cite this article: Sida Li, Ronibala Devi Laishram, Guoli Shen, Xuexin Zhang, Yong Yang,
Jianxiao Ni, Yong Zhan, Yongyun Zhou & Baomin Fan (2020): Synthesis of 1,3-diaryl butanones
from acetophenones via a tandem reaction, Synthetic Communications
To link to this article: https://doi.org/10.1080/00397911.2020.1755871
View supplementary material
Published online: 27 Apr 2020.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=lsyc20

R
SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2020.1755871
Synthesis of 1,3-diaryl butanones from acetophenones via
a tandem reaction
Sida Lia, Ronibala Devi Laishrama, Guoli Shena, Xuexin Zhanga, Yong Yangb,
Jianxiao Nia, Yong Zhanb, Yongyun Zhoua,c, and Baomin Fana,c
aKey Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission and
b
Ministry of Education, Yunnan Minzu University, Kunming, China; Chongqing Academy of Chinese
c
Materia Medica, Chongqing, China; School of Chemistry and Environment, Yunnan Minzu University,
Kunming, China
ABSTRACT
ARTICLE HISTORY
Received 23 December 2019
A tandem reaction for the simple construction of 1,3-diaryl buta-
nones from acetophenones was developed. Anhydrous HI was gen-
erated in situ by the promotion of the [Rh]- complex with molecular
hydrogen and iodine. The acetophenones undergo aldol reactions
by anhydrous HI firstly, and then hydrogenation reactions by the
same [Rh]-complex to generate the corresponding 1,3-diaryl buta-
nones in one pot.
KEYWORDS
Acetophenones; aldol
reaction; anhydrous HI;
molecular hydrogen;
molecular iodine
GRAPHICAL ABSTRACT
Introduction
Arylated ketones are important motifs found in bioactive natural products and are
important synthetic intermediates of many industrial products like pharmaceuticals, cos-
metics, or agrochemicals.[1–7] In this article, a kind of particular arylated ketones viz
1,3-diaryl butanones has been paid attention. These ketones are useful as important pre-
cursors for the preparation of NK2 and NK3 receptor antagonists for the treatment of
asthma,[8] GABAB receptor agonist (R)-baclofen hydrochloride,[9,10] matrix metallopro-
tease inhibitors for tumor cell invasion,[11] anti-inflammatory agents,[12] inhibitors of
stomach acid secretion,[13] and as a solvent for inks and lacquers.[14] Generally, 1,3-dia-
ryl butanones were reported to be prepared by methods like the selective coupling
of alcohols using both heterogeneous[15–17] and homogeneous catalyst,[18,19] Friedel-
Crafts-type reactions,[20] Wittig olefination,[21] Heck arylation.[22,23] Most of these
reaction procedures suffer from one or other limitations like the use of elevated tem-
perature, generation of large amounts of by-products, use of expensive substrates. Thus,
CONTACT Yong Yang
Baomin Fan FanBM@ynni.edu.cn
neimen@163.com
Chongqing Academy of Chinese Materia Medica, Chongqing, China;
Key Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs
Commission and Ministry of Education, Yunnan Minzu University, Kunming, China
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
S. LI ET AL.
there is still a need for the development of new methodologies for the synthesis of 1,3-
diaryl butanones. Among them, the aldol reaction was also attracted as a powerful
method for the synthesis of 1,3-diaryl butanones.[24–26] Much effort has been devoted to
developing more convenient and efficient strategies for these kinds of reactions.
Recently, Akazome’s group has reported a novel solvent-free reaction of acetophenone
derivatives for the generation of a-alkylated compounds by using anhydrous HI gas. They
prepared safe laboratory scale anhydrous HI gas before the reaction.[27] In their method-
ology, HI acts as both acid and as a reducing agent. Commercially available HI is only
55–57 wt% aqueous solution. So, many researchers have used anhydrous HI in different
reactions by preparing with various methods, such as the combination of tetrahydronaph-
thalene and I2,[28] RSH and I2,[29–31] ROH and I2,[32–34] RCOOH and I2,[35,36] BI3:N,N-
diethylaniline complex and acetic acid.[37] Although direct use of HI in some reaction has
been introduced,[38,39] but still are limited. Very recently, our group developed the rho-
dium catalyzed direct preparation of anhydrous HI from molecular hydrogen and iodine;
and successfully utilized in the formation of iodoalkanes from alkenes, aldehydes, alcohols,
and ethers,[40] and alkynes.[41] Inspired with this we describe herein the tandem reaction
for the construction of 1,3-diaryl butanones, which is initiated by the in situ generation of
HI, aldol condensation and then hydrogenation. The anhydrous HI was generated in situ
by the Rh(CO)2(acac)/dppb promoted reaction of molecular iodine and hydrogen. The in
situ generated HI resulted in the condensation of acetophenones to generate enone inter-
mediates. The [Rh]-complex then catalyzed hydrogenation of the enones to give the 1,3-
diaryl butanones as final product via a tandem reaction.
Result and discussion
As initiation of screening for tandem reaction, acetophenone 1a was chosen as the
model substrate using Rh activated with carbon as a catalyst with molecular hydrogen
and iodine (100 mol%) in DCE at room temperature (rt) for 72 h. The reaction
afforded the desired product in 22% yield (see the supporting information Table 1).
Other carbon activated catalysts of Pd, Ru, and Pt were also studied but provided poor
yield or no reaction (see supplementary Table 1). Among the different catalytic systems
studied, Rh(CO)2(acac)/dppb was identified as the best catalyst for the tandem reaction
of acetophenone in DCE at rt (entry 5, Table 1). Other Rh complexes with dppb were
also studied, but the results were not appreciable (entries 1–4, Table 1). The complexes
of Rh(CO)2(acac) with other ligands like PPh3, dppp, dppm were also studied, but the
yield of the reaction could not be improved (see supplementary Table 1). Solvents like
DCM, CHCl3, CH3CN, and toluene were also tested for the reaction to enhance the
reactivity and yield, but the results were poor (entries 6–9, Table 1). The temperature
was also checked but increasing the temperature lowered the reactivity of the reaction
(entry 10, Table 1). Therefore, rt was chosen as optimal temperature for the studies.
Notably, increasing catalytic loading of I2 to 1.5 equiv increased the yield of the reaction
giving the desired product in 72% yield (entry 11, Table 1). Further increasing or lower-
ing the loading of I2 did not improve the reaction (see supplementary Table 1).
Therefore, we optimized the I2 loading at 1.5 equiv.

R
SYNTHETIC COMMUNICATIONSV
3
Table 1. Screening of catalyst and the reaction conditions for the transformation of 1,3-diphenyl
butanone from acetophenone.a
Entry
Catalyst (5 mol%)
[Rh(COD)Cl]2/dppb
Solvent
I2 loading (equiv)
Yield (%)b
1
2
3
4
5
6
7
8
DCE
DCE
DCE
DCE
DCE
DCM
CHCl3
MeCN
Toluene
DCE
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.5
11
13
26
20
58
40
18
N.R.
52
[Rh(NBD)Cl]2/dppb
Rh(COD)2SbF6/dppb
Rh(COD)2BF4/dppb
Rh(CO)2(acac)/dppb
Rh(CO)2(acac)/dppb
Rh(CO)2(acac)/dppb
Rh(CO)2(acac)/dppb
Rh(CO)2(acac)/dppb
Rh(CO)2(acac)/dppb
Rh(CO)2(acac)/dppb
9
10c
11
40/50/24
72
DCE
aReaction conditions: Metal (0.01 mmol) and ligand (0.012 mol) in solvent (1 mL) were stirred at rt for 30 min under Ar.
Acetophenone 1a (0.4 mmol) and I2 were added. The reaction mixture was stirred in a hydrogen atmosphere at rt for
c
72 h). bIsolated yield. Reaction at 40, 50 and 60 °C.
Bold indicates the optimal condition of the reaction
With the optimum conditions in hand, we explored the scope and limitation of the
reaction of various acetophenone derivatives using the catalytic system of
Rh(CO)2(acac)/dppb with H2 and I2 (Table 2). We were delighted that our reaction
conditions could provide tandem products across the various acetophenones. However,
for the substituted aryl moiety inꢀthe ketones, the yields were low at rt. So, the reaction
temperature was elevated to 50 C to get higher yields. The alkyl substituents in the
aryl ring of the ketones also gave the desired product in moderate yields. These might
be due to increased electron density at the carbonyl carbon which will lower the nucleo-
philicity. Among the methyl substituted aryl moiety substrates, the para-substituted
gave the highest yield 69% while the ortho-substituted gave only trace, these might be
due to the steric-effect of the substituent (entries 2–4, Table 2). The bulkier alkyl sub-
stituents like ethyl and t-butyl in the para-position also gave the desired products in
moderate yields (entries 5–6, Table 2). Notably, upon substitution of the stronger elec-
tron-donating group such as methoxy either at the para- or meta- position, no desired
products were observed (entries 7 and 8, Table 2). Higher yields were expected from
the halogen substituents like fluoro, chloro and bromo in the para-position of the phe-
nyl ring due to the increased nucleophilicity at the carbonyl carbon but the yields were
only moderates (entries 9–11, Table 2). The relatively low yield of the naphthyl methyl
ketone 14% (entry 12, Table 2) might be attributed to the sterically hindered effects
from the coordination of the catalyst with the substrate. Alkyl ketone and heterocyclic
ketone were also studied but could not get the desired products (entries 13 and 14,
Table 2).
We also tried with different acetophenones having different electronic properties
like para-fluoro acetophenone and para-methyl acetophenone in the same reaction to
furnish the cross-aldol hydrogenated product. But, mixtures of cross-aldol and

4
S. LI ET AL.
Table 2. Scope for the transformation of 1,3-diaryl butanones from
acetophenones.a
Entry
1[c]
Ar
Yield (%)[b]
72
1a
1b
1c
2
3
4
69
52
Trace
1d
1e
5
6
55
52
1f
1g
lh
7
NR
8
9
NR
44
1i
10
11
49
56
1j
1k
1l
12
13
14
14
Complex mixture
Complex mixture
1m
1n
aReaction conditions: Rh(CO)2(acac) (0.01 mmol) and dppb (0.012 mol) in DCE (1 mL)
were stirred at rt for 30 min under Ar. Ketones (1a–1n) (0.4 mmol) and iodine (0.3
mmol) were added. The reaction mixt-ure was stirred in a hydrogen atmosphere at
c
50 ꢀC for 72 h. bIsolated yield. Reaction at rt.
self-condensed aldol products were obtained (Scheme 1). In all of the reactions,
unreacted starting materials were the main reason for the moderate or low yields. Only
a few impurities were observed and confirmed from GC-MS. Since the products have a
chiral carbon, we tried the asymmetric version of the reaction to get the enantiomeric
products by using chiral ligands. We tried with (R)-DIOP but unfortunately, no
enantiomeric product was obtained (see supporting information). Other chiral ligands
were also tested and still under investigation.

R
SYNTHETIC COMMUNICATIONSV
5
Scheme 1. Cross-aldol hydrogenation.
Scheme 2. Control experiments.

6
S. LI ET AL.
Scheme 3. Plausible mechanism of the reaction.
To better understand the reaction pathway, sets of control experiments were carried
out as shown in Scheme 2. First, the condensation was carried out at three different
reaction times under the same optimal conditions using acetophenone 1a as a model
substrate (Scheme 2a). After 12 h it gave the condensation product E in 13% yield with
a trace amount of hydrogenated product 2a. And as the reaction continued for 24 h the
yield of E increased to 24% and that of 2a to 3%. While continuing the reaction for 48
h the yield of E decreased and that of 2a increased. Thus, confirmed the formation of E
followed by the hydrogenation to give the desired hydrogenated product 2a. Next, the
reduction of E was carried out using the same catalytic conditions without I2 for 72 h,
it gave the hydrogenated product 2a in 62% yield (Scheme 2b). For the stronger support
of the reaction pathway we further carried out the condensation reaction of 1a in the
absence of [Rh]-complex (Scheme 2c). Firstly, the reaction was carried out by passing
HI gas (1 atm) released from the reaction of NaI and phosphoric acid to the solution of
acetophenone 1a in DCE. But it cannot bring the condensation of acetophenone to the
desired product; it might be due to the low concentration of HI in DCE which cannot
promote the condensation of the acetophenone to give the aldol product. Similar result
was reported in the supporting information of Brown’s work where, they used acetophe-
none 1a (1 equiv) and phosphoric acid (2 equiv) and refluxed for 3 days to get 9% yield
of enone E.[42] This explains enone intermediate E cannot be generated in the solution
with low concentration of HI. Next, the tandem reaction for preparation of 1,4-buta-
nones was performed using acetophenone 1a in [Rh]-complex without H2 and I2
(Scheme 2d). To our anticipation, no product was formed confirming the initial forma-
tion of intermediate E by the in situ generated HI followed by hydrogenation with
[Rh]-complex to give the hydrogenated aldol product.

R
SYNTHETIC COMMUNICATIONSV
7
Based on control reactions a plausible mechanism for the transformation of the 1,3-
diaryl butanone (2a) was developed as shown in Scheme 3. The coordination of rho-
dium precursor with dppb generates the complex A, which then added H2 followed by
I2 to give C with the generation of HI. This HI generated in situ activated the acetophe-
none to enol and proceeded the aldol reaction by reacting another molecule of aceto-
phenone to give D which on dehydration to give a,b-unsaturated ketone E. The
rhodium complex B reduced E to furnished the product (2a) with the regeneration of
rhodium compound A. Based on the proposed mechanism, the final product was
obtained by the hydrogenation of the aldol product catalyzed by rhodium complex,
unlike the earlier reported mechanism.[27]
Conclusion
In summary, we developed a tandem reaction for the preparation of 1,3-diaryl buta-
nones using simple and readily available starting material acetophenones. The method-
ology also showed the in situ generations of anhydrous HI from the Rh(CO)2(acac)/
dppb promoted reaction of molecular iodine and hydrogen in the presence of the sub-
strate. The HI thus generated initiated the condensation of acetophenones. Thus, this
methodology opens up the applications of this conveniently generated anhydrous HI in
other reactions.
Experimental
Materials
The reactions and manipulations were performed under an atmosphere of argon by
using standard Schlenk techniques and glovebox (Mikrouna, Supper1220/750).
Anhydrous toluene was distilled from sodium benzophenone ketyl prior to use.
Anhydrous CH3CN (acetonitrile), DCE (dichloroethane), DCM (dichloromethane) were
distilled from calcium hydride. Acetophenones were purchased from Sigma Aldrich and
1
used without further purification. H NMR and 13 C NMR spectra were recorded on
Bruker-Avance 400 MHz spectrometer. CDCl3 was used as solvent. Chemical shifts (d)
were reported in ppm with tetramethylsilane as internal standard and J values were
given in Hz, abbreviation were used to denoted signals multiplicities (s ¼ singlet, d ¼
doublet, t ¼ triplet, q ¼ quartet, m ¼ multiplate). Melting points were measured on X-
4 melting point apparatus and uncorrected. High resolution mass spectra (HRMS) were
performed on a VGAutospec-3000 spectrometer. Column chromatography was per-
formed with silica gel using petroleum ether and ethyl acetate as eluents.
General procedure for the synthesis of 2a
Rh(CO)2(acac) (0.01 mmol), dppb (0.012 mol) and 1 mL of DCE were added to a
Schlenk tube under an argon atmosphere in a glovebox. The mixture was stirred at
room temperature for 30 min. Then acetophenone 1a (0.4 mmol) and iodine (0.3
mmol) were added. The reaction mixture was stirred in a hydrogen atmosphere at rt
for 72 h. After vacuum evaporation of the solvent, the residue was purified by silica gel

8
S. LI ET AL.
column chromatography to provide the desired product 2a. The compounds 2b–2n
were also synthesized by using this procedure.
Compound 2a was obtained as colorless oil, 72% yield; 1H NMR (400 MHz,
Chloroform-d) d 7.93–7.91 (m, 2H), 7.54 (t, J ¼ 7.3 Hz, 1H), 7.44 (t, J ¼ 7.8 Hz, 2H),
7.31–7.25 (m, 4H), 7.21–7.16 (m, 1H), 3.54–3.46 (m, 1H), 3.30 (dd, J ¼ 16.4, 5.7 Hz,
1H), 3.18 (dd, J ¼ 16.5, 8.3 Hz, 1H), 1.34 (d, J ¼ 6.9 Hz, 3H). 13 C NMR (101 MHz,
Chloroform-d) d 199.2, 146.6, 137.2, 133.1, 128.6, 128.6, 128.2, 126.9, 126.4, 47.1, 35.6,
22.0. HRMS(EIþ): m/z calcd for C16H16O [M]þ: 224.1213. Found 224.1210.
Experimental details, 1H, 13 C NMR and HRMS spectra have been provided in
supporting information.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
We gratefully thank the National Natural Science Foundation of China [21572198], the Applied
Basic Research Project of Yunnan Province [2018FB021, 2017FA004], the Chongqing Science &
Technology Commission [cstc2017zdyfX0013] and Yunnan Provincial Key Laboratory
Construction Plan Funding of Universities for their financial support.
References
[1] Murthy, Y. V. S. N.; Meah, Y.; Massey, V. J. Am. Chem. Soc. 1999, 121, 5344–5345. DOI:
10.1021/ja990908t.
[2] Ducki, S.; Hadfield, J. A.; Hepworth, L. A.; Lawrence, N. J.; Liu, C.-Y.; McGown, A. T.
Bioorg. Med. Chem. Lett. 1997, 7, 3091–3094. DOI: 10.1016/S0960-894X(97)10147-0.
[3] Borejsza-Wysocki, W.; Hrazdina, G. Phytochemistry. 1994, 35, 623–628. DOI: 10.1016/
S0031-9422(00)90575-2.
[4] Morimoto, C.; Satoh, Y.; Hara, M.; Inoue, S.; Tsujita, T.; Okuda, H. Life Sci. 2005, 77,
194–204. DOI: 10.1016/j.lfs.2004.12.029.
[5] Yokota, T.; Ikemoto, T.; Sasaki, M.; Horikoshi, T. J. Soc. Cosmet. Chem., 2001, 35,
120–126. DOI: 10.5107/sccj.35.2_120
[6] Boker, A.; Fischer, M.; Berger, R. G. Biotechnol. Prog. 2001, 17, 568–572. DOI: 10.1021/
bp010011b.
[7] Smets, J.; Denutte, H. R. G.; Pintens, A.; Stanton, D. T.; Aken, K.; Van, Laureyn, I. H. H.;
Denolf, B.; Vrielynck, F. A. C. US. 2009, 2009–628255.
[8] Giardina, G. A. M.; Grugni, M.; Graziani, D.; Raveglia, L. F. Chem. Abstr. 1998,
130–24978.
[9] Bowery, N. G. Trends Pharm. Sci. 1982, 3, 400–403. DOI: 10.1016/0165-6147(82)91205-6.
ꢀ
[10] Olpe, H. R.; DemieVille, H.; Baltzer, V.; Bencze, E. L.; Koella, W. P.; Wolf, P.; Haas, H. L.
Eur. J. Pharmacol. 1978, 52, 133–136. DOI: 10.1016/0014-2999(78)90032-8.
[11] Scott, W. J.; Popp, M. A.; Hartsough, D. S. Chem. Abstr. 1997, 128, 22719.
[12] Geronikaki, A.; Hadjipavlou-Litina, D.; Tzaki, M. Arzneimittelforschung. 2011, 50,
266–271. DOI: 10.1055/s-0031-1300197.
[13] Matuz, J.; Csehi, A.; Bihari, M.; Barta, S.; Gizella, S. I.; Szporny, L.; Ezer, E.; Saghy, K.;
Domany, G.; Hajos, G. Hun.gChem. Abstr. 1995, 124, 55943.
[14] Reith, W.; Dettmer, M.; Widdecke, H.; Fleisher, B. Stud. Surf. Sci. Catal. 1991, 59, 487.
DOI: 10.1016/S0167-2991(08)61157-X.

R
SYNTHETIC COMMUNICATIONSV
9
[15] Shimizu, K.-I.; Sato, R.; Satsuma, A. Angew. Chem. Int. Ed. 2009, 48, 3982–3986. DOI: 10.
1002/anie.200901057.
[16] Fischer, A.; Makowski, P.; Mu€ller, J.-O.; Antonietti, M.; Thomas, A.; Goettmann, F. Chem.
Sus. Chem. 2008, 1, 444–449. DOI: 10.1002/cssc.200800019.
[17] Yamada, Y. M. A.; Uozumi, Y. Org. Lett. 2006, 8, 1375–1378. DOI: 10.1021/ol060166q.
[18] Makarov, I. S.; Madsen, R. J. Org. Chem. 2013, 78, 6593–6598. DOI: 10.1021/jo4008699.
[19] Musa, S.; Ackermann, L.; Gelman, D. Adv. Synth. Catal. 2013, 355, 3077–3080. DOI: 10.
1002/adsc.201300656.
[20] Pan, X.; Li, M.; Gu, Y. Chem. Asian J. 2014, 9, 268–274. DOI: 10.1002/asia.201300956.
[21] Frattini, S.; Quai, M.; Cereda, E. Tetrahedron Lett. 2001, 42, 6827–6829. DOI: 10.1016/
S0040-4039(01)01384-3.
[22] Viviano, M.; Glasnov, T. N.; Reichart, B.; Tekautz, G.; Kappe, C. O. Org. Process Res. Dev.
2011, 15, 858–870. DOI: 10.1021/op2001047.
[23] Climent, M. J.; Corma, A.; Iborra, S.; Mifsud, M. Adv. Synth. Catal. 2007, 349, 1949–1954.
DOI: 10.1002/adsc.200700026.
[24] Luo, S.; Mi, X.; Zhang, L.; Liu, S.; Xu, H.; Cheng, J.-P. Tetrahedron. 2007, 63, 1923–1930.
DOI: 10.1016/j.tet.2006.12.079.
[25] Paul, S.; Gupta, M. Synth. Commun. 2005, 35, 213–222. DOI: 10.1081/SCC-200048425.
[26] DePorre, Y. C.; Annand, J. R.; Bar, S.; Schindler, C. S. Org. Lett. 2018, 20, 2580–2584.
DOI: 10.1021/acs.orglett.8b00507.
[27] Matsumoto, S.; Koitabashi, S.; Otani, Y.; Akazome, M. Tetrahedron Lett. 2015, 56,
4320–4323. DOI: 10.1016/j.tet.2017.11.009.
[28] Hoffman, C. J.; Heintz, E. A. Inorg. Synth. 1963, 7, 180. DOI: 10.1002/9780470132388.
ch48.
[29] Matsumoto, S.; Mori, T.; Akazome, M. RSC Adv. 2012, 2, 3379. DOI: 10.1039/c2ra20061a.
[30] Matsumoto, S.; Kishimoto, T.; Ogura, K. Chem. Lett. 2002, 31, 134–135. DOI: 10.1246/cl.
2002.134.
[31] Chervin, S. M.; Abada, P.; Koreeda, M. Org. Lett. 2000, 2, 369–372. DOI: 10.1021/
ol991312d.
[32] Kasashima, Y.; Uzawa, A.; Hashimoto, K.; Yokoyama, Y.; Mino, T.; Sakamoto, M.; Fujita,
T. J. Oleo Sci. 2010, 59, 607–613. DOI: 10.5650/jos.59.607.
[33] Kasashima, Y.; Uzawa, A.; Hashimoto, K.; Nishida, T.; Murakami, K.; Mino, T.; Sakamoto,
M.; Fujita, T. J. Oleo Sci. 2010, 59, 549–555. DOI: 10.5650/jos.59.549.
[34] Kasashima, Y.; Uzawa, A.; Nishida, T.; Mino, T.; Sakamoto, M.; Fujita, T. J. Oleo Sci.
2009, 58, 421–427. DOI: 10.5650/jos.58.421.
[35] Kasashima, Y.; Nishida, T.; Fujimoto, H.; Mino, T.; Sakamoto, M.; Fujita, T. J. Oleo Sci.
2007, 56, 189–193. DOI: 10.5650/jos.56.189.
[36] Broomfield, C. E. Org. Process Res. Dev. 1997, 1, 88–89. DOI: 10.1021/op9600116.
[37] Reddy, C. K.; Periasamy, M. Tetrahedron Lett. 1990, 31, 1919–1920. DOI: 10.1016/S0040-
4039(00)98817-8..
[38] Larock, R. C. Comprehensive Organic Transformations, 2nd Ed.; New York: John Wiley &
Sons, Inc., 1999; p. 629.
[39] Wade, L. G. Organic Chemistry, 5th Ed.; USA: Pearson Education, Inc., 2003, p. 317.
[40] Zeng, C.-Y.; Shen, G.-L.; Yang, F.; Chen, J.-C.; Zhang, X.-X.; Gu, C.-P.; Zhou, Y.-Y.; Fan,
B.-M. Org. Lett. 2018, 20, 6859–6862. DOI: 10.1021/acs.orglett.8b02980.
[41] Li, J.-Y.; Laishram, R. D.; Chen, J.-C.; Xu, D.-D.; Shi, G.-G.; Lv, H.-P.; Fan, R.-F.; Fan, B.-
M. Asian J. Org. Chem. 2020, 9, 73–76. (just accepted). DOI: 10.1002/ajoc.201900677.
[42] Kerr, W. J.; Mudd, R. J.; Brown, J. A. Chem. Eur. J. 2016, 22, 4738–4742. DOI: 10.1002/
chem.201504825.