FeCl3-Assisted Niobium-Catalyzed Cycloaddition of Nitriles and Alkynes: Synthesis of Alkyl- and Arylpyrimidines Based on Independent Functions of NbCl5 and FeCl3 Lewis Acids

Article abstract of DOI:10.1021/acs.orglett.7b02708

NbCl₅-catalyzed [2 + 2 + 2] cycloaddition of nitriles with alkynes was used to synthesize pyrimidine derivatives. In this reaction, the use of individual Lewis acids, namely NbCl₅ and FeCl₃, is a key strategy for achieving the reaction using a catalytic amount of NbCl₅. The roles of the two Lewis acids were investigated using FT-IR spectroscopy. The results showed that NbCl₅ served as an efficient Lewis acid catalyst for nitrile activation, whereas FeCl₃ showed stronger Lewis acidity toward pyrimidines, releasing NbCl₅ into the catalytic cycle.

Full text of DOI:10.1021/acs.orglett.7b02708

Letter
pubs.acs.org/OrgLett
FeCl3‑Assisted Niobium-Catalyzed Cycloaddition of Nitriles and
Alkynes: Synthesis of Alkyl- and Arylpyrimidines Based on
Independent Functions of NbCl5 and FeCl3 Lewis Acids
Maito Fuji and Yasushi Obora*
Department of Chemistry and Material Engineering, Faculty of Chemistry, Materials and Bioengineering, Kansai University, Suita,
Osaka 564-8680, Japan
S
* Supporting Information
ABSTRACT: NbCl5-catalyzed [2 + 2 + 2] cycloaddition of nitriles with alkynes was used to synthesize pyrimidine derivatives. In
this reaction, the use of individual Lewis acids, namely NbCl5 and FeCl3, is a key strategy for achieving the reaction using a
catalytic amount of NbCl5. The roles of the two Lewis acids were investigated using FT-IR spectroscopy. The results showed that
NbCl5 served as an efficient Lewis acid catalyst for nitrile activation, whereas FeCl3 showed stronger Lewis acidity toward
pyrimidines, releasing NbCl5 into the catalytic cycle.
contributed to the development of niobium-catalyzed [2 + 2 +
2] cycloadditions.7 We reported the cycloaddition of two alkynes
with one alkene to give 1,3-cyclohexadiene derivatives using the
following systems: NbCl3(DME),7b−d NbCl5/hydrosilane,7e and
an external-additive-free NbCl5/alkene−solvent.7f In addition, a
Nb(OEt)5/Grignard reagent system catalyzed isocyanate cyclo-
trimerization.7g We have also reported cycloadditions involving
nitriles; a NbCl5/Zn/alkoxysilane system gives pyridine
derivatives via cycloaddition of two alkynes with one nitrile
molecule.7h
The [2 + 2 + 2] cycloaddition of two nitrile moieties with one
alkyne moiety is one of the most efficient methods in terms of
atom and step economy for preparing tetra- or trisubstituted
pyrimidine derivatives.8 This reaction traditionally required use
of an alkali metal8a or a large amount of a strong protonic acid
(TfOH or H3PO4/BF3).8b−e Transition-metal-mediated/cata-
lyzed reactions have been developed in recent years (Scheme 1).
Liu et al. reported pyrimidine synthesis using a zirconium-
mediated cycloaddition of aryl- or silyl-nitriles.8f However, an
excess of the zirconium reagent was required. Rosenthal et al.
reported the catalytic synthesis of pyrimidines using a seven-
membered zirconium complex (eq 1).8g Louie et al. reported the
synthesis of bicyclic pyrimidines using alkynenitriles and
cyanamides in an FeI2/Zn system (eq 2).8h Liu et al. reported
the synthesis of aminopyrimidines from ynamides and nitriles
(eq 3).8i However, the method cannot be used with simple
monoalkynes such as diphenylacetylene and phenylacetylene.
yrimidine derivatives are present as scaffolds in numerous
1a−f
Pnatural products and bioactive products.
Some
pyrimidine-containing polymers or π-conjugated pyrimidines1g
have been used as semiconductors,1h,i fluorescent molecules,1j
liquid crystalline materials,1k and photovoltaic materials,1l,m
while alkylpyrimidines are important synthetic intermediates.2
Various methods for the formation of pyrimidine rings have been
reported,1−4 e.g., the well-known Pinner3a and Bredereck3b
syntheses, involving cyclocondensations of 1,3-dicarbonyl
compounds with amidines and formamide, respectively.
However, preparation of the starting materials is not always
easy. In addition, few methods for alkylpyrimidine synthesis have
been reported, despite their simple structures.
Ramsey (in 1876) and Reppe (in 1949) reported metal-
catalyzed [2 + 2 + 2] cycloaddition reactions for the production
of pyridine5a or benzene.5b Since then, [2 + 2 + 2] cycloaddition
reactions have become widely used because of their economy and
efficiency in constructing three bonds in a single step from
various unsaturated substrates, without byproduct formation.
Transition-metal-catalyzed [2 + 2 + 2] cycloaddition reactions
are powerful tools for forming various six-membered carbocycles
such as benzenes and cyclohexadienes, or heterocycles such as
pyridines and pyrimidines. Many transition-metal catalysts have
been studied.5
In 1991, Plessis et al. reported that a low-valent niobium
species generated from NbCl5/C2H6AlCl2 catalyzed the [2 + 2 +
2] cycloaddition of three alkyne molecules to form benzene
derivatives.6a Niobium species are thermally stable and have high
reductive abilities and Lewis acidities, therefore their use in many
organic reactions has been reported.6 Recently, we have
Received: August 30, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b02708
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Scheme 1. Transition-Metal-Mediated/Catalyzed Synthesis of
Pyrimidine Derivatives
Table 1. Cycloaddition of 3-Hexyne and Benzonitrile under
Various Conditions
a
b
entry
1
catalyst
additive
conv (%)
yield (%)
13
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
NbCl5
none
none
42
81
78
91
87
91
90
80
11
99
54
79
85
54
47
>99
c
2
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3
AlCl3
FeBr3
CuCl
TMSCl
FeCl3
FeCl3
FeCl3
FeCl3
FeCl3
TfOH
19
47
d
3
e
f
4
86 [83 , 65 ]
g
5
cg
,
63
6
7
8
9
60
60
28
n.d.
11
10
11
12
13
14
15
16
22
AlCl3
44
TaCl5
ZrCl4
47
21
Nb(OEt)5
NbCl5
trace
75
a
Reaction conditions: 1a (0.50 mmol), 2a (1.0 mL), catalyst (0.10
mmol), and additive (1.0 mmol) were stirred at 60 °C for 4 h under
b
Ar. Conversions and yields were determined by GC based on 1a
c
d
used. FeCl3 (0.50 mmol) was used. FeCl3 (0.75 mmol) was used.
e
f
Isolated yield. Isolated yield from larger scale reaction (1a: 1.0
mmol). NbCl5 (0.05 mmol) was used.
g
We investigated the scopes and limitations of various
substrates under the optimized conditions (Table 2). Sym-
metrical internal alkynes such as 3-hexyne (1a), 4-octyne (1b),
and 5-decyne (1c) gave the corresponding pyrimidine derivatives
3a−c with excellent selectivities. The unsymmetrical alkynes 1d
and 1e gave the corresponding products in good yields as a
mixture of regioisomers, i.e., 3d,3e and 3d′,3e′. The product
regioselectivities were affected by steric hindrance. Methylphe-
nylacetylene (1f) gave 3f as the sole product. The terminal alkyne
phenylacetylene (1g) and 1-hexyne (1h) gave excellent
selectivities and yields.
Next, we investigated the reaction of 1a with various nitriles.
The reaction with an electron-rich nitrile, p-tolylnitrile (2b), gave
the product 3i in 43% yield. An electron-deficient nitrile, p-
fluorobenzonitrile (2c), also reacted and gave the product 3j in
57% yield.
Aliphatic nitriles such as acetonitrile (2d) and octanonitrile
(2e) reacted with 1a and gave the corresponding alkylpyr-
imidines, i.e., 3k and 3l, in moderate yields. Acrylonitrile (2f) was
a good substrate and the vinyl group remained intact throughout
the reaction; the divinylpyrimidine 3m was obtained in good
yield.
We used FT-IR analysis to clarify the roles of the two Lewis
acids. A weak Lewis base such as acetonitrile or pyridine can be
used to evaluate the Lewis acidities of ionic liquids and metal
chlorides by FT-IR analysis.9 The shifts to higher wavenumbers
of the CN stretching or ring vibrations are related to the acidity.
This is because the lone pair of the nitrogen in acetonitrile or
pyridine interacts with Lewis acid sites. We used this method to
support our hypothesis. First, we monitored the CN stretching
vibrations of PhCN (Figure 1A). Pure PhCN gave a band at 2228
cm−1 arising from CN stretching.10a FeCl3/PhCN caused only a
We reported the synthesis of pyrimidine derivatives via [2 + 2 +
2] cycloaddition of readily available alkynes and arylnitriles using
NbCl5 as a Lewis acid.7i However, a greater than stoichiometric
amount of NbCl5 had to be added several times to the reaction
system.
In a previous study of pyrimidine synthesis, we found that the
cycloaddition of nitriles and alkynes could be achieved by
addition of NbCl5 (1.2 equiv) in six batches to the reaction
system (eq 4). The reason is as follows. The Lewis acidic niobium
species was poisoned by the pyrimidine product, which is a Lewis
base. We hypothesized that this problem could be solved by
addition of another Lewis acid to capture the product, enabling
regeneration of the active niobium species (eq 5).
Initially, we selected 3-hexyne (1a) and benzonitrile (2a) as
model substrates to test our hypothesis. Table 1 shows the effects
of various Lewis acid combinations in the cycloaddition. When
1a (0.5 mmol) was reacted with 2a (1 mL) in the presence of a
catalytic amount of NbCl5 (20 mol %), the pyrimidine derivative
3a was obtained in 13% yield (entry 1). This reaction was
promoted by addition of FeCl3 and 3a was obtained in 86% yield
(entries 2−4). The product was obtained in an acceptable yield
even when NbCl5 (10 mol %) was used (entries 5 and 6). AlCl3
also promoted the reaction (entry 7). However, other additives
such as FeBr3, CuCl, and TMSCl were not suitable for this
reaction (entries 8−10).
In the absence of a catalyst, the reaction gave only 22% yield
(entry 11). When AlCl3 and TaCl5 were used instead of NbCl5,
the yields were significantly lower (entries 12 and 13). ZrCl4 had
no catalytic activity (entry 14). Nb(OEt)5 inhibited the reaction
(entry 15). The use of TfOH8d,e instead of FeCl3 led to decrease
the yield of 3a under these conditions (entry 16).
B
DOI: 10.1021/acs.orglett.7b02708
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
(Figure 1B). The vibration peak for pure 3b appeared at 1585
cm−1.1f,10b Mixtures of FeCl3/3b and NbCl5/3b were examined.
The peak for FeCl3/3b was at a higher wavenumber than that for
NbCl5/3b. This shows that FeCl3 interacted more strongly than
NbCl5 with the pyrimidine ring. These outcomes are consistent
with a reaction mechanism in which the two Lewis acids have
different roles. The use of a mixture of NbCl5/FeCl3/PhCN was
also investigated. FT-IR analysis showed negligible interactions
between NbCl5 and FeCl3 (Figure S2), i.e., NbCl5 (which
activated the nitriles) and FeCl3 (which coordinated with the
pyrimidine and led to release of NbCl5 into the catalytic cycle)
performed independent Lewis acid functions in the catalytic
cycle.
Table 2. Cycloadditions of Various Alkynes and Nitriles
Figure 2 shows a plausible reaction mechanism based on our
hypothesis and these experiments. Initially, a nitrile reacts with
a
Reaction conditions: 1 (0.50 mmol), 2 (1.0 mL), NbCl5 (0.10
mmol), and FeCl3 (1.0 mmol) were stirred at 60 °C for 4 h under Ar.
b
c
Selectivity of regioisomers. The values in parentheses show the
d
selectivity. Reaction time was 6 h.
Figure 2. Plausible reaction mechanism for cycloaddition of nitriles with
alkynes.
another nitrile activated by NbCl5 to form a 1,3-diaza-1,3-
butadiene scaffold (B). Subsequently, B undergoes cycloaddition
with an alkyne to form a pyrimidine scaffold (C).4i The
pyrimidine scaffold migrates from niobium to FeCl3, regenerat-
ing the niobium catalyst. After the reaction, D is decomposed by
quenching and pyrimidines are obtained.
In conclusion, we developed a niobium-catalyzed [2 + 2 + 2]
cycloaddition of one alkyne with two nitrile molecules, leading to
pyrimidine derivatives. In this reaction, independent Lewis acid
functions of NbCl5 and FeCl3 achieved a “catalytic version” of the
NbCl5-catalyzed cycloaddition of alkynes with nitriles to give
pyrimidines, which had previously only been achieved using
stoichiometric amounts of NbCl5.
Further investigations with regard to the scrutiny the detailed
functions of NbCl5 and FeCl3 are underway.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.7b02708.
Figure 1. FT-IR spectra of (A) pure PhCN, PhCN + NbCl5 (0.5 M),
and PhCN + FeCl3 (0.5 M) and (B) pure 3b, 3b + NbCl5 (2:1 by
weight) and 3b + FeCl3 (2:1 by weight).
Figures S1−S3, experimental procedures, and compound
characterization data (PDF)
slight change. However, NbCl5/PhCN significantly shifted the
peak to 2268 cm−1. The shift to higher wavenumber of the CN
bond vibration indicates the nitrile acidity. NbCl5 has a higher
affinity for the nitrile than FeCl3. Next, we monitored the
pyrimidine ring vibration mode of 3b using the same method
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: obora@kansai-u.ac.jp.
C
DOI: 10.1021/acs.orglett.7b02708
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
ORCID
Letter
2015, 265−286. (f) Lledo,
́
A.; Pla- Quintana, A.; Roglans, A. Chem. Soc.
Rev. 2016, 45, 2010−2023. (g) Hapke, M. Tetrahedron Lett. 2016, 57,
5719−5729. (h) Domínguez, G.; Perez-Castells, J. Chem. - Eur. J. 2016,
22, 6720−6739. (i) Yamamoto, K.; Nagase, H.; Tsurugi, H.; Mashima,
ez-
Yasushi Obora: 0000-0003-3702-9969
Notes
́
K. Dalton Trans. 2016, 45, 17072−17081. (j) Domínguez, G.; Per
́
The authors declare no competing financial interest.
Castells, J. In Comprehensive Organic Synthesis II; Knochel, P., Molander,
G. A., Eds.; Elsevier: Amsterdam, 2014; Vol. 5, pp 1537−1581.
ACKNOWLEDGMENTS
■
(6) (a) Plessis, J. A. K. D.; Viljoen, J. S.; Toit, C. J. D. J. Mol. Catal. 1991,
64, 269−275. (b) Andrade, C. K. Z.; Rocha, R. O. Mini-Rev. Org. Chem.
2006, 3, 271−280. (c) Lacerda, V., Jr.; dos Santos, D. A.; da Silva-Filho,
L. C.; Greco, S. J.; dos Santos, R. B. Aldrichimica Acta 2012, 45, 19−27.
(d) Oshiro, P. B.; Lima, P. S. D. S. G.; de Menezes, M. L.; da Silva-Filho,
L. C. Tetrahedron Lett. 2015, 56, 4476−4479. (e) Zakerinasab, B.;
Nasseri, M. A.; Kamali, F. Iran. Chem. Commun. 2015, 3, 335−347.
(f) Yaragorla, S.; Kumar, G. S. Indian J. Chem., Sec. B 2015, 54, 240−244.
This work was supported partly by JSPS KAKENHI Grant
Number 16K05784. High-resolution mass spectra were
performed at Global Facility Center, Hokkaido University.
REFERENCES
■
(1) (a) De Coen, L. M.; Heugebaert, S. A. T.; García, D.; Stevens, C. V.
Chem. Rev. 2016, 116, 80−139. (b) Ashid, M.; Yogi, P.; Katariya, D.;
Agarwal, P.; Joshi, A. World J. Pharm. Pharm. Sci. 2016, 5, 990−1009.
(c) Dudas, N. A.; Putz, M. V. Int. J. Chem. Model. 2014, 6, 95−114.
(d) Sharma, V.; Chitranshi, N.; Agarwal, A. K. Int. J. Med. Chem. 2014,
2014, 1−31. (e) Dongre, R. S.; Bhat, A. R.; Meshram, J. S. Am. J.
PharmTech Res. 2014, 4, 138−155. (f) Avupati, V. R.; Yejella, R. P. World
(g) Blasing, K.; Ellinger, S.; Harloff, J.; Schulz, A.; Sievert, K.; Taschler,
̈
̈
C.; Villinger, A.; Zur Taschler, C. Chem. - Eur. J. 2016, 22, 4175−4188.
̈
(h) Simon, C.; Amatore, M.; Aubert, C.; Petit, M. Org. Lett. 2015, 17,
844−847. (i) Bian, J.; Qian, X.; Fan, J.; Li, X.; Sun, H.; You, Q.; Zhang, X.
Tetrahedron Lett. 2015, 56, 397−400. (j) da Silva Barbosa, J.; da Silva, G.
V. J.; Constantino, M. G. Tetrahedron Lett. 2015, 56, 4649−4652.
(k) Andrade, A.; Santos, G. C.; Silva-Filho, L. C. J. Heterocyclic Chem.
2015, 52, 273−277. (l) de Souza Siqueira, M.; da Silva-Filho, L. C.
Tetrahedron Lett. 2016, 57, 5050−5052. (m) da Silva, B. H. S. T.;
Bregadiolli, B. A.; Graeff, C. F. D. O.; da Silva-Filho, L. C.
ChemPlusChem 2017, 82, 261−269. (n) Wised, K.; Nomura, K.
Organometallics 2016, 35, 2773−2777. (o) Saito, K.; Umi, T.;
Yamada, T.; Suga, T.; Akiyama, T. Org. Biomol. Chem. 2017, 15,
1767−1770.
́
J. Pharm. Pharm. Sci. 2014, 3, 1563−1587. (g) Achelle, S.; Ple, N. Curr.
Org. Synth. 2012, 9, 163−187. (h) Gunathilake, S. S.; Magurudeniya, H.
D.; Huang, P.; Nguyen, H.; Rainbolt, E. A.; Stefan, M. C.; Biewer, M. C.
Polym. Chem. 2013, 4, 5216−5219. (i) Kanbara, T.; Kushida, T.; Saito,
N.; Kuwajima, I.; Kubota, K.; Yamamoto, T. Chem. Lett. 1992, 21, 583−
586. (j) Achelle, S.; Nouira, I.; Pfaffinger, B.; Ramondenc, Y.; Ple,
Lopez, J. R. J. Org. Chem. 2009, 74, 3711−3717. (k) Petrov, V. F. Mol.
Cryst. Liq. Cryst. 2006, 457, 121−149. (l) Achelle, S.; Baudequin, C.
Targets Heterocycl. Syst. 2013, 17, 1−34. (m) El Aslaoui, Z.; Karzazi, Y. J.
Mater. Environ. Sci. 2017, 8, 1291−1300.
́
N.;
́
(7) (a) Satoh, Y.; Obora, Y. Eur. J. Org. Chem. 2015, 2015, 5041−5054.
(b) Obora, Y.; Takeshita, K.; Ishii, Y. Org. Biomol. Chem. 2009, 7, 428−
431. (c) Obora, Y.; Satoh, Y.; Ishii, Y. J. Org. Chem. 2010, 75, 6046−
6049. (d) Satoh, Y.; Obora, Y. Org. Lett. 2011, 13, 2568−2571.
(e) Satoh, Y.; Obora, Y. J. Org. Chem. 2011, 76, 8569−8573. (f) Kamei,
M.; Watanabe, K.; Fuji, M.; Obora, Y. Chem. Lett. 2016, 45, 943−945.
(g) Ozaki, M.; Obora, Y.; Tada, Y.; Ishii, Y. J. Organomet. Chem. 2013,
741, 109−113. (h) Satoh, Y.; Obora, Y. J. Org. Chem. 2013, 78, 7771−
7776. (i) Satoh, Y.; Yasuda, K.; Obora, Y. Organometallics 2012, 31,
5235−5238. (j) Obora, Y.; Kimura, M.; Tokunaga, M.; Tsuji, Y. Chem.
Commun. 2005, 901−902. (k) Obora, Y.; Kimura, M.; Ohtake, T.;
Tokunaga, M.; Tsuji, Y. Organometallics 2006, 25, 2097−2100.
(l) Yasuda, K.; Obora, Y. J. Organomet. Chem. 2015, 775, 33−38.
(8) (a) Cairns, T. L.; Sauer, J. C.; Wilkinson, W. K. J. Am. Chem. Soc.
1952, 74, 3989−3992. (b) Pourzal, A. A. Synthesis 1983, 1983, 717−718.
(c) Martinez, A. G.; Fernandez, A. H.; Alvarez, R. M.; Losada, M. C. S.;
Vilchez, D. M.; Subramanian, L. R.; Hanack, M. Synthesis 1990, 1990,
881−882. (d) Yang, L.; Hua, R. Chem. Lett. 2013, 42, 769−771.
(e) Chen, P.; Song, C.; Wang, W.; Yu, X.; Tang, Y. RSC Adv. 2016, 6,
80055−80058. (f) You, X.; Yu, S.; Liu, Y. Organometallics 2013, 32,
5273−5276. (g) Burlakov, V. V.; Becker, L.; Bogdanov, V. S.; Andreev,
M. V.; Arndt, P.; Spannenberg, A.; Baumann, W.; Rosenthal, U. Eur. J.
Inorg. Chem. 2014, 2014, 5304−5310. (h) Lane, T. K.; Nguyen, M. H.;
D’Souza, B. R.; Spahn, N. A.; Louie, J. Chem. Commun. 2013, 49, 7735−
7737. (i) Karad, S. N.; Liu, R. S. Angew. Chem., Int. Ed. 2014, 53, 9072−
9076.
(2) (a) Yamanaka, H.; Edo, K.; Shoji, F.; Konno, S.; Sakamoto, T.;
Mizugaki, M. Chem. Pharm. Bull. 1978, 26, 2160−2166. (b) Yamanaka,
H.; Sakamoto, T. Yuki Gosei Kagaku Kyokaishi 1985, 43, 951−961.
(c) Martínez, A. G.; Herrera, A.; Martínez, A.; Teso, E.; García, A.; Osío,
J.; Pargada, L.; Unanue, R.; Subramanian, L. R.; Hanack, M. J. Heterocycl.
Chem. 1988, 25, 1237−1241. (d) Tsuritani, T.; Shinokubo, H.; Oshima,
K. Chem. Lett. 2004, 33, 122−123. (e) Delia, T. J. J. Heterocyclic Chem.
2013, 50, 735−745. (f) Mai, W. P.; Sun, B.; You, L. Q.; Yang, L. R.; Mao,
P.; Yuan, J. W.; Xiao, Y. M.; Qu, L. B. Org. Biomol. Chem. 2015, 13,
2750−2755.
(3) (a) Pinner, A. Ber. Dtsch. Chem. Ges. 1893, 26, 2122−2125.
(b) Pinner, A. Ber. Dtsch. Chem. Ges. 1884, 17, 2519−2520. (c) Ghosh,
U.; Katzenellenbogen, J. A. J. Heterocycl. Chem. 2002, 39, 1101−1104.
(d) Baran, P. S.; Ryan, A. S.; Nguyen, S. A. Heterocycles 2006, 70, 581−
586. (e) Cheng, G.; Li, S.; Li, S.; Hu, Y. Bioorg. Med. Chem. Lett. 2008, 18,
1177−1180. (f) Bredereck, H.; Gompper, R.; Morlock, G. Chem. Ber.
1957, 90, 942−952.
(4) (a) Wu, X. F.; Wang, Z. In Transition Metal Catalyzed Pyrimidine,
Pyrazine, Pyridazine and Triazine Synthesis; Elsevier: Oxford, 2017; pp
5−54. (b) Hill, M. D.; Movassaghi, M. Chem. - Eur. J. 2008, 14, 6836−
6844. (c) Radi, M.; Schenone, S.; Botta, M. Org. Biomol. Chem. 2009, 7,
2841−2847. (d) Arora, N.; Pandeya, S. N. J. Pharm. Res. Clin. Pract.
2011, 1, 105−115. (e) Gore, R. P.; Rajput, A. P. Drug Invent. Today
2013, 5, 148−152. (f) Merugu, R.; Garimella, S.; Balla, D.; Sambaru, K.
Int. J. PharmTech Res. 2015, 8, 88−93. (g) Dar, A. M.; Uzzaman, S. Eur.
Chem. Bull. 2015, 4, 249−259. (h) Mohana Roopan, S.; Sompalle, R.
(9) (a) Platero, E. E.; Mentruit, M. P.; Morterra, C. Langmuir 1999, 15,
5079−5087. (b) Yang, Y.; Kou, Y. Chem. Commun. 2004, 226−227.
(c) Mittal, N.; Nisola, G. M.; Chung, W. J. Tetrahedron Lett. 2012, 53,
3149−3155.
(10) (a) Bian, H.; Zhao, H.; Zheng, J. J. Chem. Phys. 2009, 131, 124501.
(b) Goya, S.; Takahashi, T.; Okano, T. Yakugaku Zasshi 1966, 86, 952−
957.
Synth. Commun. 2016, 46, 645−672. (i) Guzman
́
, A.; Romero, M.;
Talamas, F. X. J. Org. Chem. 1996, 61, 2470−2483. (j) Chu, X. Q.; Cao,
́
W. B.; Xu, X. P.; Ji, S. J. J. Org. Chem. 2017, 82, 1145−1154. (k) Yang, K.;
Dang, Q.; Cai, P. J.; Gao, Y.; Yu, Z. X.; Bai, X. J. Org. Chem. 2017, 82,
2336−2344. (l) Deibl, N.; Kempe, R. Angew. Chem., Int. Ed. 2017, 56,
1663−1666. (m) Zhou, Y.; Tang, Z.; Song, Q. Adv. Synth. Catal. 2017,
359, 952−958. (n) Mahfoudh, M.; Abderrahim, R.; Leclerc, E.;
Campagne, J. M. Eur. J. Org. Chem. 2017, 2017, 2856−2865.
(5) (a) Ramsay, W. Philos. Mag. 1876, 2, 269−281. (b) Reppe, W.;
Schichting, O.; Klager, K.; Toepel, T. Justus Liebigs Ann. Chem. 1948,
560, 1−92. (c) Chopade, P. R.; Louie, J. Adv. Synth. Catal. 2016, 348,
́
2307−2327. (d) Domínguez, G.; Perez-Castells, J. Chem. Soc. Rev. 2011,
40, 3430−3444. (e) Amatore, M.; Aubert, C. Eur. J. Org. Chem. 2015,
D
DOI: 10.1021/acs.orglett.7b02708
Org. Lett. XXXX, XXX, XXX−XXX