L-proline catalyzed unprecedented synthesis of novel naphtho-bis[1,3]oxazines under solvent-free conditions

Article abstract of DOI:10.1080/00397911.2020.1719423

An unprecedented l-proline-mediated one-pot sequential synthesis of novel 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphtho[1,2-e:4,3-e′]bis[1,3]oxazine derivatives from 2,3-dihydroxynaphthalene, formaldehyde, and anilines under solvent-free conditions has been reported. Under the optimized reaction conditions, a broad range of substituted anilines and 2,3-dihydroxynaphthalene were found to participate in this transformation, thus affording new 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphtho[1,2-e:4,3-e′]bis[1,3]oxaz-ines in good to excellent yields. This green procedure offers several advantages such as high atom economy, mild reaction conditions, short reaction time, easy workup and column chromatography-free method with a wide range of functional group tolerance.

Full text of DOI:10.1080/00397911.2020.1719423

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
L-proline catalyzed unprecedented synthesis of
novel naphtho-bis[1,3]oxazines under solvent-free
conditions
Amol Maruti Jadhav, Sandip Gangadhar Balwe, Byung Gwon Cho, Kwon Taek
Lim & Yeon Tae Jeong
To cite this article: Amol Maruti Jadhav, Sandip Gangadhar Balwe, Byung Gwon Cho, Kwon
Taek Lim & Yeon Tae Jeong (2020): L-proline catalyzed unprecedented synthesis of novel
naphtho-bis[1,3]oxazines under solvent-free conditions, Synthetic Communications, DOI:
10.1080/00397911.2020.1719423
To link to this article: https://doi.org/10.1080/00397911.2020.1719423
View supplementary material
Published online: 28 Jan 2020.
Submit your article to this journal
Article views: 15
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/10.1080/00397911.2020.1719423
L-proline catalyzed unprecedented synthesis of novel
naphtho-bis[1,3]oxazines under solvent-free conditions
Amol Maruti Jadhav, Sandip Gangadhar Balwe, Byung Gwon Cho, Kwon Taek Lim,
and Yeon Tae Jeong
Department of Image Science and Engineering, Pukyong National University, Busan, Republic of Korea
ABSTRACT
ARTICLE HISTORY
Received 31 October 2019
An unprecedented L-proline-mediated one-pot sequential synthesis
of novel 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphtho[1,2-e:4,3-
e0]bis[1,3]oxazine derivatives from 2,3-dihydroxynaphthalene, formal-
dehyde, and anilines under solvent-free conditions has been
reported. Under the optimized reaction conditions, a broad range of
substituted anilines and 2,3-dihydroxynaphthalene were found to
participate in this transformation, thus affording new 3,10-diphenyl-
2,3,4,9,10,11-hexahydronaphtho[1,2-e:4,3-e0]bis[1,3]oxaz-ines in good
to excellent yields. This green procedure offers several advantages
such as high atom economy, mild reaction conditions, short reaction
time, easy workup and column chromatography-free method with a
wide range of functional group tolerance.
KEYWORDS
Multicomponent reaction;
naphtho-bis[13]oxazines;
one-pot synthesis;
polyheterocycles
GRAPHICAL ABSTRACT
R
R
NH2
OH
OH
N
N
N
R
O
O
OH
O
HO
L-proline (10 mol%)
Neat, 80 ºC, 20-40 min
L-proline (10 mol%)
Neat, 80 ºC, 20-40 min
O
O
N
H
H
R
R
Broad substrate scope
Clean synthetic method
C-C, C-O and C-N bond formation
Excellent atom economy
Column chromatography-free
23 examples up to 96% yields
Introduction
The design and synthesis of pharmaceutically important molecules from simple, cheap,
and available starting materials is the most challenging work in modern synthetic and
medicinal chemistry.[1] Multicomponent reactions (MCRs) constitute an especially
attractive synthetic strategy due to the fact that the products are formed in a single step
and diversity can be achieved simply by varying the reacting components.[2] In recent
decades, there has been significant importance attached to combinatorial synthesis, and
CONTACT Yeon Tae Jeong
ytjeong@pknu.ac.kr
Department of Image Science and Engineering, Pukyong
National University, Busan, Republic of Korea.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
A. M. JADHAV ET AL.
Figure 1. Biologically active molecules containing naphtho-bis[1,3]-oxazine derivatives.
these types of reactions have attracted greater attention because the formation of car-
bon–carbon and carbon–heteroatom bonds in a powerful one-pot method would be
adopted in drug discovery as well as in total synthesis.[3] It is well known that six-
membered nitrogen and oxygen-containing 1,3-oxazines are an important class of het-
erocycles, which has attracted much synthetic interest due to their potential biological
and pharmacological activities such as anti-HIV,[4] antibacterial,[5] antitumor,[6] anal-
gesic,[7] antihypertensive,[8] antithrombotic,[9] and antiulcer[10] activities. In addition,
naphthoxazine derivatives have exhibited therapeutic potential for the treatment of
Parkinson’s disease.[11] Some 1,3-naphthoxazines are used as intermediates in the syn-
thesis of N-substituted amino alcohols,[12] and bioactive natural products.[13] Similarly,
some biologically active naphtho-bis[1,3]-oxazine derivatives as shown in (Fig. 1).[14]
In recent years, L-proline has drawn much interest in different organic reactions due
to its experimental simplicity, ease of handling, cost-effectiveness and excellent solubility
in water and organic solvents. L-Proline has been found to be a very efficient catalyst in
different transformations like enamine based direct catalytic asymmetric aldol
condensation,[15] a-amination reaction,[16] Mannich reaction,[17] Diels–Alder reac-
tion,[18] and as an excellent promoter for the copper-catalyzed coupling reactions.[19]
Moreover, L-proline and solvent-free combination reactions are well known as
environmentally benign methods that also usually provide improved selectively,
enhanced reaction rates, cleaner products and manipulative simplicity in organic trans-
formation.[20] We, therefore, became interested in devising more general and green
methods for the synthesis of novel 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphtho[1,2-
e:4,3-e0]bis[1,3]oxazine derivatives.
As part of continuing research in our laboratory toward the development of a new
reaction methodology,[21] for the first time herein, we disclosed a highly efficient,
approach for the synthesis of novel 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphththo[1,2-
e:4,3-e0]bis[1,3]oxazine derivatives from 2,3-dihydroxynaphthalene, formaldehyde, and
anilines using a L-proline as a catalyst through a one-pot multicomponent cascade
under solvent-free reaction condition (Scheme 1).

R
SYNTHETIC COMMUNICATIONSV
3
N
O
OH
5 (expected product)
NH2
OH
OH
O
-proline (10 mol%)
L
H
H
Solvent-free, 80 °C
20-40 min
N
O
1a
2a
3a
O
N
4a (obtained product)
Scheme 1. Synthesis of novel 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphtho[1,2-e:4,3-e]bis[1,3]oxazine
derivatives catalyzed by L-proline under solvent-free condition.
Result and discussion
For our initial investigation, the reaction of 2,3-dihyroxynaphthalene (1a, 1mmol), formal-
dehyde (2a, 4 mmol), and anilines (3a, 2 mmol), was chosen as a model reaction to opti-
mize the reaction conditions and the results are summarized in (Table 1). The reaction was
first carried out under catalyst-free reaction condition in ethanol at 80 ꢀC for 18h, only a
trace amount of product was detected (Table 1, entry 1). Next, the reaction was performed
in the presence of 10 mol % p-TsOH, this reaction afforded the desired product 4a in 68%
1
yield. (Table 1, entry 2). The structure of 4a was assigned with the help of H NMR, 13C
NMR, and HRMS data. Encouraged by this result, we attempted to optimize the yield of
the reaction by screening the same set of reaction with various Lewis acid catalysts such as,
AcOH, InCl3, Cu(OTf)2, Sc(OTf)3 and L-proline were screened, and the results of these
experiments are summarized in (Table 1, entries 2–7). Among all the screened catalysts, L-
proline was found superior with respect to reaction time and product yield (Table 1, entry
12). Then, we investigated the influence of various organic solvents such as CHCl3,
CH3CN, Toluene, and THF on the model reaction (Table 1, entries 8–11). We found that
the rate of the reaction was sparingly slow and resulted in lower product yields (Table 1,
entries 8–11). Therefore, ethanol is a choice of solvent for this conversion with respect to
the reaction rate and the product yield (Table 1, entry 7).
Therefore, we investigated the scope of this reaction using solvent-free reaction con-
ditions. To our delight, under solvent-free reaction conditions, we observed higher
yields (96%) in shorter reaction time (Table 1, entry 12). Then, the catalyst loading on
the model reaction was investigated (Table 1, entries 12–14). We found that there is no
noticeable improvement in the yield of the desired product was observed after increas-
ing the catalyst loading from 10 to 20 mol% (Table 1, entry 13). Notably, the decrease

4
A. M. JADHAV ET AL.
Table 1. Optimization of reaction conditions for the synthesis of novel 3,10-diphenyl-2,3,4,9,10,11-
hexahydronaphtho[1,2-e:4,3-e]-bis[1,3]oxazine (4a).a
N
NH2
OH
OH
O
O
O
Catalyst, Temperature
H
H
Solvent or,
Solvent-free
20-40 min
N
1a
2a
3a
4a
Entry
Catalyst (mol%)
Solvent
Temp (ꢀC)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
–
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
CHCl3
CH3CN
Toluene
THF
Solvent-free
Solvent-free
Solvent-free
Solvent-free
80
80
80
80
80
80
80
Reflux
Reflux
Reflux
Reflux
80
18
8
8
6
8
6
3
4
4
trace
68
64
60
58
60
84
56
62
50
42
92
91
78
92
p-TSA (10%)
AcOH (10%)
InCl3(10%)
Cu(OTf)2(10%)
Sc(OTf)3(10%)
L-Proline (10%)
L-Proline (10%)
L-Proline (10%)
L-Proline (10%)
L-Proline (10%)
L-Proline (10%)
L-Proline (20%)
L-Proline (5%)
L-Proline (10%)
9
10
11
12
13
14
15
6
6
20 min
20 min
40 min
20 min
80
80
100
aReactions were performed with 2,3-dihydroxynaphthalene (1a, 1 mmol), formaldehyde (2a, 4 mmol) and aniline (3a,
2 mmol), in the presence of 10 mol% L-proline, solvent or under solvent-free conditions at 80 ꢀC.
bIsolated yields.
in the catalyst loading to 5 mol%, decrease in the yields were observed (Table 1, entry
14). Therefore, 10 mol% of L-proline was sufficient and optimal quantity for the com-
plete conversion of the reactants into the desired products. We also carried out the
reaction at higher temperatures, but yields were not improved by increasing the tem-
perature (Table 1, entries 15). From all these establishments, we concluded that the best
reaction conditions were obtained by using 10 mol % of L-proline as a catalyst under
solvent-free condition at 80 ꢀC for 20 min to afford the desired product 4a in 96% yield
(Table 1, entry 12).
The scope of this three-component reaction under the optimized reaction conditions
was studied using dihydroxynaphthalenes, formaldehyde and various anilines and results
are summarized in (Table 2). Initially, we investigated the scope of dihydroxynaphtha-
lene, formaldehyde with various anilines. We found that various aromatic and hetero-
aromatic anilines take part in this one-pot cascade and provided the corresponding
products with good to excellent yields (Table 2, entries 4a–4w).
Interestingly, a variety of functional groups substituted at the aromatic ring of the
aniline substrate, including electron-withdrawing such as, halides (Table 2, entries 4h,
4i, and 4ai) and electron-donating such as, methoxy and methyl (Table 2, entries
4b–4g, 4m, 4n, 4o, 4r, 4s, 4t, and 4w) groups, were well tolerated. Moreover,

R
SYNTHETIC COMMUNICATIONSV
5
Table 2. Substrate scope.a,b
R
N
O
NH2
OH
O
L-proline (10 mol %)
R
H
H
OH
O
Solvent-free, 80 °C
20-40 min
N
R
1a or 1b
2a
3a
(4a-4w)
OMe
Me
N
N
Me
N
N
N
N
N
O
O
O
O
O
O
O
O
N
Me
OMe
Me
(4b), 88%, 26 min
(4a), 92%, 20 min
(4c), 84%, 30 min
(4d), 89%, 32 min
Me
Me
Br
Me
Me
Me
Me
Me
N
O
N
O
OMe
N
N
N
O
O
O
O
O
N
O
N
N
OMe
Me
Me
Br
Me
(4f), 88%, 36 min
(4h), 86%, 20 min
(4e), 85%, 26 min
(4g), 90%, 40 min
COOH
OH
N
O
N
O
O
N
N
O
O
O
O
N
O
N
O
N
N
O
COOH
OH
(4i), 89% 34 min
(4i), 84% 34 min
(4i), 90% 34 min
(4l), 87%, 38 min

6
A. M. JADHAV ET AL.
Table 2. Contined.
Cl
N
MeO
Me
Me
OMe
OMe
N
OH
OH
N
N
N
N
O
O
O
O
O
O
O
O
N
N
OMe
MeO
Me
Me
OMe
Cl
(4m), 84%, 24 min (4n), 85%, 36 min
(4p), 84%, 24 min
(4o), 88%, 20 min
OMe
Me
N
Me
N
N
N
O
O
O
O
O
O
O
O
N
N
N
N
Me
Me
OMe
(4q), 86%, 28 min
(4s), 84%, 35 mi
(4t), 89%, 30 min
(4r), 90%, 30 min
Me Me
O
N
N
N
O
O
O
O
O
N
O
N
N
O
Me
Me
(4u), 87%, 38 min
(4v), 86%, 26 min
(4w), 91%, 32 min
aReactions were performed with dihydroxynaphthalenes (1 mmol), formaldehyde (4 mmol) and anil-
ine (2 mmol), in the presence of 10 mol% L-proline under solvent-free conditions at 80 °C.
bIsolated yields.
substituted dihydroxynaphthalenes like 2,3 and 2,6-dihydroxynaphthalene participate in
this reaction and afforded good to excellent yields (Table 2, entries 4a–4w). In addition,
heteroaryl anilines such as furan-2-ylmethyl provided the desired products in good
yields without affecting the heterocyclic moieties (Table 2, entries 4k and 4v). In gen-
eral, the reactions were clean and no side products were detected. In all cases, the reac-
tions proceeded efficiently at 80 ꢀC under solvent-free conditions and with 10 mol% of
the L-proline catalyst, and the pure products can be obtained by recrystallization of the
crude products in ethanol to avoid tedious work-up and column-chromatography-free

R
SYNTHETIC COMMUNICATIONSV
7
O
COOH
COO
Mannich condensation
N
N
H
H
H
-H2O, L-proline
N
H
H
NH2
L-proline
2
H
H
3
Schiff base
5
N
H
O
HO
HO
H
O
Nuclophilic addition
N
H
H
H
O
H
5
1
N
6
H
N
OH
OH
N
H
H
Intramolecular
cyclization
O
O
O
O
Mannich condensation
-2H2O
N
N
H
7
4
Scheme 2. Possible reaction mechanism for the synthesis of 3,10-diphenyl-2,3,4,9,10,11-hexahydro-
naphtho[1,2-e:4,3-e0]bis[1,3]oxazine derivatives 4.
method. Therefore, the present protocol has general applicability and accommodates a
variety of substitution patterns. All the structures of newly synthesized compounds
1
(4a–4w) have been ascertained on the basis of H NMR, 13C NMR and HRMS analyses.
We have proposed a plausible reaction mechanism (Fig. 2). Initially, the condensation
of formaldehyde 2 and aniline in the presence of L-proline leads to the formation of
Schiff base 5. Next, the 2,3-dihydroxynaphthalene 3 undergoes nucleophilic addition
with Schiff base 5 to form intermediate 6. The intermediate 6 reacts with the second
molecule of formaldehyde 2 to give the intermediate 7. Then intermediate 7 undergoes
intramolecular cyclization followed by water elimination to afford the desired product
naphtho-bis[1,3]oxazines (4) in good to excellent yield (Scheme 2).
Conclusion
We have successfully developed an unprecedented simple and efficient strategy for the
synthesis of 3,10-diphenyl-2,3,4,9,10,11-hexahydronaphtho[1,2-e:4,3-e0]bis[1,3]oxazine
de-rivatives under solvent-free reaction conditions. The main advantages of this one-pot

8
A. M. JADHAV ET AL.
process are operational simplicity, excellent yields, shorter reaction time, ease of chro-
matography, and environmental friendliness. We believe, our present methodology may
become a very helpful device for the synthetic as well as medicinal chemists.
Experimental
General procedure for the synthesis of 3,10-diphenyl-2,3,4,9,10,11-
hexahydronaphtho[1,2-e:4,3-e0]bis[1,3]oxazine (4a)
A mixture of 2,3-dihydroxynaphthalene (1a, 1 mmol), formaldehyde (2, 4 mmol) and
aniline (3a, 2 mmol) and 10 mol% L-proline was added, and the mixture was stirred at
80 ꢀC under solvent-free conditions. The progress of the reaction was monitored by
TLC. After completion of the reaction, the reaction mixture was cooled to room tem-
perature, water was added, and the mixture was stirred for 5 min. The solid obtained
was removed by filtration and recrystallized from ethanol to afford the pure white prod-
uct 4a (92%) yield. Compounds 4a–4w were also synthesized by adopting
this procedure.
1
It was obtained as white solid; Yield 92%; white solid; Mp: 220–222 ꢀC; H NMR
(400 MHz, CDCl3) d 7.67–7.62 (m, 2H), 7.45–7.40 (m, 2H), 7.25 (m, 4H), 7.17–7.13 (m,
4H), 6.92 (m, 2H), 5.49 (s, 4H), 4.94 (s, 4H), 13C NMR (101 MHz, CDCl3) d 148.60,
143.61, 129.42, 126.03, 124.67, 121.85, 121.56, 118.71, 112.64, 80.07, 48.15; HRMS (ESI,
m/z): calcd for C26H22N2O2 (M þ Hþ) 394.1681, found: 394.1683.
1
Full experimental detail, H and 13C NMR spectra have been provided in Supporting
information.
ORCID
Yeon Tae Jeong
http://orcid.org/0000-0002-2943-6954
References
[1] (a) Ramachandran, G.; Karthikeyan, N. S.; Giridharan, P.; Sathiyanarayanan, K. Org.
Biomol. Chem. 2012, 10, 5343–5346. DOI: 10.1039/c2ob25530h. (b) Ruijter, E.; Scheffelaar,
R.; Orru, R. V. A. Angew. Chem. Int. Ed. 2011, 50, 6234–6246. DOI: 10.1002/anie.
€
€
201006515. (c) Wangelin, A. J. V.; Neumann, H.; Gordes, D.; Klaus, S.; Strubing, D.;
Beller, M. Chem. Eur. J. 2003, 9, 4286–4294. DOI: 10.1002/chem.200305048. (d) Reza
Naimi-Jamal, M.; Mashkouri, S.; Sharif, A. Mol. Divers. 2010, 14, 473–477. DOI: 10.1007/
s11030-010-9246-5.
[2] (a) Domling, A.; Ugi, I. Angew. Chem. Int. Ed. Engl. 2000, 39, 3168–3210. DOI: 10.1002/
€
€
1521-3773(20000915)39:18<3168::aid-anie3168>3.0.co;2-u. (b) Ugi, I.; Domling, A.; Horl,
W. Endeavour. 1994, 18, 115–122. DOI: 10.1016/S0160-9327(05)80086-9. (c) Heck, S.;
Domling, A. Synlett. 2000, 3, 424–426. (d) Balwe, S. G.; Kim, J. S.; Kim, Y. I.; Jeong, Y. T.
Tetrahedron. 2019, 75, 797–807. DOI: 10.1016/j.tet.2018.12.066.
[3] (a) Kumar, A.; Siddharth, S.; Ram, A. M.; Jayant, S. J. Comb. Chem. 2010, 12, 20–24.
DOI: 10.1021/cc100007a. (b) Almstetter, M.; Weber, L.; Illgen, K. Synlett. 1999, 3,
366–374. DOI: 10.1055/s-1999-2612. (c) Domling, A.; Terrett, N. K. Chem. Rev. 2006, 106,
17–89.(d) Balwe, S. G.; Jeong, Y. T. Org. Chem. Front. 2018, 5, 1628–1632. DOI: 10.1039/
C8QO00071A. (e) Balwe, S. G.; Jeong, Y. T. Org. Biomol. Chem. 2018, 16, 1287–1296.
DOI: 10.1039/C7OB02933K.

R
SYNTHETIC COMMUNICATIONSV
9
[4] Cocuzza, A. J.; Chidester, D. R.; Cordova, B. C.; Jeffrey, S.; Parsons, R. L.; Bacheler, L. T.;
Erickson-Viitanen, S.; Trainor, G. L.; Ko, S. S. Bioorg. Med. Chem. Lett. 2001, 11,
1177–1179. DOI: 10.1016/S0960-894X(01)00192-5.
[5] Mathew, B. P.; Kumar, A.; Sharma, S.; Shukla, P. K.; Nath, M. Eur. J. Med. Chem. 2010,
45, 1502–1507. DOI: 10.1016/j.ejmech.2009.12.058.
[6] Chylinska, J. B.; Urbanski, T.; Mordarski, M. J. Med. Chem. 1963, 6, 484–487. DOI: 10.
1021/jm00341a004.
[7] Kurz, T. Tetrahedron. 2005, 61, 3091–3096. DOI: 10.1016/j.tet.2005.01.039.
[8] Kajino, M.; Shibouta, Y.; Nishikawa, K.; Meguro, K. Chem. Pharm. Bull. 1991, 39,
2896–2905. DOI: 10.1248/cpb.39.2896.
[9] Buckman, B. O.; Mohan, R.; Koovakkat, S.; Liang, A.; Trinh, L.; Morrissey, M. M. Bioorg.
Med. Chem. Lett. 1998, 8, 2235–2240. DOI: 10.1016/S0960-894X(98)00386-2.
[10] Katsura, Y.; Nishino, S.; Takasugi, H. Chem. Pharm. Bull. 1991, 39, 2937–2943. DOI: 10.
1248/cpb.39.2937.
[11] Joyce, J. N.; Presgraves, S.; Renish, L.; Borwege, S.; Osredkar, T.; Hagner, D.; Replogle, M.;
PazSoldan, M.; Millan, M. J. Exp. Neurol. 2003, 184, 393–407. DOI: 10.1016/S0014-
4886(03)00353-4.
[12] (a) Cimarelli, C.; Palmieri, G.; Volpini, E. Tetrahedron. 2001, 57, 6089–6096. DOI: 10.
1016/S0040-4020(01)00589-0. (b) Dong, Y.; Sun, J.; Wang, X.; Xu, X.; Cao, L.; Hu, Y.
Tetrahedr Asymm. 2004, 15, 1667–1672. DOI: 10.1016/j.tetasy.2004.04.006. (c) Lu, J.; Xu,
X.; Wang, S.; Wang, C.; Hu, Y.; Hu, H. J. Chem. Soc. Perkin Trans. 2002, 1, 2900–2903.
DOI: 10.1039/B204534F.
[13] (a) Wang, X.; Dong, Y.; Sun, J.; Xu, X.; Li, R.; Hu, Y. J. Org. Chem. 2005, 70, 1897–1900.
DOI: 10.1021/jo0480444. (b) Yamazaki, N.; Ito, T.; Kibayashi, C. Org. Lett. 2000, 2,
465–467. DOI: 10.1021/ol990389z. (c) Cheng, G.; Wang, X.; Su, D.; Liu, H.; Liu, F.; Hu, Y.
J. Org. Chem. 2010, 75, 1911–1916. DOI: 10.1021/jo902615u.
[14] (a) Cananzi, S.; Merlini, L.; Artali, R.; Beretta, G. L.; Zaffaroni, N.; Dallavalle, S. Bioorg.
Med. Chem. 2011, 19, 4971–4984. DOI: 10.1016/j.bmc.2011.06.056. (b) Arai, A. C.;
Kessler, M.; Rogers, G.; Lynch, G. Mol. Pharmacol. 2000, 58, 802–813. DOI: 10.1124/mol.
58.4.802. (c) Olianas, M. C.; Onali, P. Life Sci. 1999, 65, 2233–2240. DOI: 10.1016/S0024-
€
3205(99)00488-9. (d) Bohme, T. M.; Augelli-Szafran, C. E.; Hussein, H.; Pugsley, T.; Serpa,
K.; Schwarz, R. D. J. Med. Chem. 2002, 45, 3094–3102. DOI: 10.1021/jm011116o.
[15] (a) Alcaide, B.; Almendros, P.; Luna, A.; Torres, M. S. J. Org. Chem. 2006, 71, 4818–4822.
DOI: 10.1021/jo0604235. (b) Zotova, N.; Franzke, A.; Armstrong, A.; Blackmond, D. G. J.
Am. Chem. Soc. 2007, 129, 15100–15101. DOI: 10.1021/ja0738881. (c) Chandrasekhar, S.;
Narsihmulu, C.; Reddy, R. N.; Sultan, S. S. Tetrahedron Lett. 2004, 45, 4581–4582. DOI:
10.1016/j.tetlet.2004.03.116. (d) Kumar, I.; Rode, C. V. Tetrahedr. Asymm. 2007, 18,
1975–1980. DOI: 10.1016/j.tetasy.2007.08.018. (e) Bernard, M. A.; Frongia, A.; Guillot, R.;
Piras, P. P.; Secci, F.; Spiga, M. Org. Lett. 2007, 9, 541–544. DOI: 10.1021/ol063084a.
(f) Chandrasekhar, S.; Narsihmulu, C.; Reddy, R. N.; Sultan, S. S. Chem. Commun. 2004,
2450–2451. DOI: 10.1039/b409053p.
[16] List, B.; Pojarliev, P.; Biller, W. T.; Martin, H. J. J. Am. Chem. Soc. 2002, 124, 827–833.
DOI: 10.1021/ja0174231.
[17] (a) Janey, J. M.; Hsiao, Y.; Armstrong, J. D. J. Org. Chem. 2006, 71, 390–392. DOI: 10.
1021/jo0519458. (b) Kantam, M. L.; Rajasekhar, C. V.; Gopikrishna, G.; Reddy, K. R.;
Choudary, B. M. Tetrahedron Lett. 2006, 47, 5965–5967. DOI: 10.1016/j.tetlet.2006.06.042.
€
(c) Hahn, B. T.; Frohlich, Roland.; Harms, Klaus.; Glorius, Frank. Angew. Chem. Int. Ed.
2008, 47, 9985–9988. DOI: 10.1002/anie.200803515.
[18] (a) Ramachary, D. B.; Chowdari, N. S.; Barbas, C. F. Angew. Chem. Int. Ed. 2003, 42,
4233–4237. DOI: 10.1002/anie.200351916. (b) Xie, H.; Zu, H. L.; Oueis, R.; Li, H.; Wang,
J.; Wang, W. Org. Lett. 2008, 10, 1923–1926. DOI: 10.1021/ol800417q.
[19] Guo, S. R.; Yuan, Y. Q. Synth. Commun. 2008, 38, 2722–2730. DOI: 10.1080/
00397910802222746.

10
A. M. JADHAV ET AL.
[20] Yadav, J. S.; Kumar, S. P.; Kondaji, G.; Rao, R. S.; Nagaiah, R. K. Chem. Lett. 2004, 33,
1168–1169. DOI: 10.1246/cl.2004.1168.
[21] (a) Balwe, S. G.; Jeong, Y. T. RSC Adv. 2016, 6, 107225–107232. DOI: 10.1039/
C6RA24183B. (b) Balwe, S. G.; Lim, K. T.; Cho, B. G.; Jeong, Y. T. Tetrahedron. 2017, 73,
3564–3570. DOI: 10.1016/j.tet.2017.05.047. (c) Balwe, S. G.; Shinde, V. V.; Jeong, Y. T.
Tetrahedron Lett. 2016, 57, 5074–5078. DOI: 10.1016/j.tetlet.2016.10.002. (d) Balwe, S. G.;
Shinde, V. V.; Rokade, A. A.; Park, S. S.; Jeong, Y. T. Catal. Commun. 2017, 99, 121–126.
DOI: 10.1016/j.catcom.2017.06.006. (e) Jadhav, A. M.; Balwe, S. G.; Lim, K. T.; Jeong, Y.
T. Tetrahedron. 2017, 73, 2806–2813. DOI: 10.1016/j.tet.2017.03.084. (f) Jadhav, A. M.;
Kim, Y. I.; Lim, K. T.; Jeong, Y. T. Tetrahedron Lett. 2018, 59, 554–557. DOI: 10.1016/j.
tetlet.2018.01.008. (g) Jadhav, A. M.; Balwe, S. G.; Kim, J. S.; Lim, K. T.; Jeong, Y. T.
Tetrahedron Lett. 2019, 60, 560–565. DOI: 10.1016/j.tetlet.2019.01.028. (h) Balwe, S. G.;
Rokade, A. A.; Park, S. S.; Jeong, Y. T. Catal. Commun. 2019, 128, 105703. DOI: 10.1016/
j.catcom.2019.05.010. (i) Balwe, S. G.; Lim, K. T.; Cho, B. G.; Jeong, Y. T. Syn. Commun.
2019, 49, 602–610. DOI: 10.1080/00397911.2019.1566475.