Palladium-Catalyzed Oxidative Cycloisomerization of 2-Cinnamyl-1,3-Dicarbonyls: Synthesis of Functionalized 2-Benzyl Furans

Article abstract of DOI:10.1002/chem.201502781

A new palladium-catalyzed intramolecular oxidative cycloisomerization of readily available starting materials, 2-cinnamyl-1,3-dicarbonyls, has been demonstrated for the creation of structurally diverse 2-benzyl furans. The cycloisomerization occurs by a regioselective 5-exo-trig pathway. The reaction shows a broad substrate scope with good to excellent yields. Furthermore, a one-pot procedure has been executed by using readily available cinnamyl alcohols and 1,3-diketones. Cinnamyl verit: Palladium-catalyzed intramolecular oxidative cycloisomerization of readily available 2-cinnamyl-1,3-dicarbonyls affords structurally diverse 2-benzyl furans. The cycloisomerization occurs by a regioselective 5-exo-trig pathway, with a broad substrate scope in good to excellent yields. Furthermore, a one-pot procedure is executed by using readily available cinnamyl alcohols and 1,3-diketones

Full text of DOI:10.1002/chem.201502781

DOI: 10.1002/chem.201502781
Communication
&
Cycloisomerization
Palladium-Catalyzed Oxidative Cycloisomerization of 2-Cinnamyl-
1,3-Dicarbonyls: Synthesis of Functionalized 2-Benzyl Furans
Rajender Nallagonda, Reddy Rajasekhar Reddy, and Prasanta Ghorai*[a]
Abstract: A new palladium-catalyzed intramolecular oxi-
dative cycloisomerization of readily available starting ma-
terials, 2-cinnamyl-1,3-dicarbonyls, has been demonstrated
for the creation of structurally diverse 2-benzyl furans. The
cycloisomerization occurs by a regioselective 5-exo-trig
pathway. The reaction shows a broad substrate scope
with good to excellent yields. Furthermore, a one-pot pro-
cedure has been executed by using readily available cin-
namyl alcohols and 1,3-diketones.
Scheme 1. Oxidation (a) and oxidative cycloisomerization (b) of 2-cinnamyl-
Substituted furans are endowed with a broad spectrum of bio-
logically active natural products and pharmaceuticals.[1] They
have been extensively used as building blocks in organic syn-
thesis[2] and materials science.[3] Consequently, there has been
a long-standing interest in rapid and reliable construction of
functionalized furans, aimed at achieving a greater level of mo-
lecular complexity in a convergent and atom-economical fash-
ion from readily accessible starting materials.[4–6] Among vari-
ous approaches for the synthesis of furans, considerable atten-
tion has been paid to develop the intramolecular cycloisomeri-
zation of 2-substituted-carbonyl precursors, particularly from 2-
alkynyl-[4] or 2-allenylcarbonyl species.[5] Despite the tremen-
dous progress in Pd-catalyzed oxidative addition of carbonyls
to alkenes,[7] the aforementioned transformation of 2-alkenyl-
carbonyls by oxidative cycloisomerization has rarely been re-
ported. Nevertheless, alkenyl species are more readily accessi-
ble and manipulable than alkynes or allenes. The pioneering
oxidative cycloisomerization of 2-alkenyl-1,3-dione reported by
Han and Widenhoefer is the sole example in this regard.[8]
However, the method has limited substrate scope with respect
to both 1,3-dicarbonyls and their allyl counterparts.
1,3-dicarbonyls.
Figure 1. a) Bioactive 2-benzyl furans; b) an array of highly functionalized
furans are accessible by the current strategy.
lective 5-exo-trig cyclisation pathway (Scheme 1b). However,
the competitive formation of a,b,g,d-dienones instead of annu-
lation to provide the furan poses a formidable challenge
(Scheme 1a).[12]
2-Benzyl furans are important privileged scaffolds in many
bioactive molecules (Figure 1a).[13] However, although this core
skeleton is useful, a limited number of strategies for its synthe-
sis from easily available precursors are currently known.[14] Fur-
thermore, because of its inherent low reactivity, functionaliza-
tion at the 3-position of furans has proven difficult,[15] and the
synthesis of tetrasubstituted furans remains a challenge.[16]
In our initial attempt to synthesize the furans, we probed
a 2-step sequence by using a model reaction of 2-cinnamyl-
1,3-dione 1j (Table 1). In the presence of benzoquinone (BQ) as
oxidant and DMF as solvent, PdII catalysts, such as Pd(OAc)2,
PdCl2, and [PdCl2(CH3CN)2], were tested, the last of which pro-
viding the best conversions into the desired product 3j
(Table 1, entries 1–3). To further improve the yield,
[PdCl2(CH3CN)2] catalyst was examined in the presence of a vari-
ety of additives (Table 1, entries 4–9) and solvents (entries 9–
14). Interestingly, acids played a vital role here and p-toluene-
sulfonic acid monohydrate (PTS) was found to be better than
Intrigued by the easy accessibility of 2-cinnamyl-1,3-dicar-
bonyls, from cinnamyl alcohol (Scheme 1) or cinnamyl bromide
and commercially available 1,3-dicarbonyls,[9,10] as well as our
continuing interest in developing oxidative cycloisomerization
reactions,[11] we embarked on the study of palladium-catalyzed
oxidative cycloisomerizations of 2-cinnamyl-1,3-dicarbonyls for
the synthesis of highly functionalized 2-benzyl furans by a se-
[a] R. Nallagonda, R. R. Reddy, Dr. P. Ghorai
Department of Chemistry
Indian Institute of Science Education and Research Bhopal
Bhauri, Indore By-pass Road, Bhopal-462066 (India)
E-mail: pghorai@iiserb.ac.in
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201502781.
Chem. Eur. J. 2015, 21, 14732 – 14736
14732
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Table 1. Catalyst optimization.
Entry
Catalyst
Additive
Oxidant
Solvent
Yield [%][a]
(1 equiv) (1 equiv)
1
2
3
4
5
6
7
8
Pd(OAc)2
PdCl2
–
–
–
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
BQ
O2
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DCE
MeOH
dioxane
toluene
THF
THF
THF (RT)
THF
<5
<5
17
46
19
21
<5
7
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
[PdCl2(CH3CN)2]
–
PTS
AcOH
TFA
PivOH
LiCl
K2CO3
PTS
PTS
PTS
PTS
PTS
-
PTS
PTS
PTS
PTS
TfOH
TfOH
9
0
10
11
12
13
14
15
16
17
18
19
20
21
28
59
77
16
85 (79)[b]
23
32
<5
9
Cu(OAc)2
Ag2O
BQ
THF
THF
THF
THF
–
82
0
BQ
[a] The yields were determined based on 1H NMR spectra of the reaction
mixture using diphenylacetonitrile as internal standard; [b] value in pa-
rentheses refer to yield of product isolated by column chromatography.
acetic acid, trifluoroacetic acid (TFA), and pivalic acid (PivOH;
Table 1, entries 4–7). Benzoquinone (BQ) was a better oxidant
than O2, Cu(OAC)2, and Ag2O (Table 1, entries 17–19 vs.
entry 14). After the above screening, 5 mol% of [PdCl2(CH3CN)2]
catalyst, 1 equivalent of BQ as the oxidant and 1 equivalent of
PTS as the additive in THF solvent at 808C were chosen as the
optimal reaction conditions (Table 1, entry 14). Under these
conditions, 3j was obtained in 79% yield. Another stronger
acid, TfOH, was also examined for the current cyclization pro-
cess, and the desired furan was formed in a similar manner
(entry 20). However, the reaction did not work at all in the ab-
sence of Pd catalyst (entry 21).
Scheme 2. Variation of cinnamyl moiety. Reaction conditions: 2-Cinnamyl-
1,3-dione (0.15 mmol), [PdCl2(CH3CN)2] (5 mol%), BQ (1 equiv), PTS (1 equiv),
THF (1.0 mL). Yields refer to products isolated by column chromatography.
With the optimized conditions in hand (Table 1, entry 14),
the scope of this reaction with respect to the cinnamyl moiety
was examined (Scheme 2). The dimethyl-1,3-dicarbonyl unit at-
tached to various symmetrical diaryl–cinnamyl functionalities
gave the corresponding 2-benzyl-3-aryl-4-acyl-5-methyl furans
(3a–i) in good yields. Besides H (3a), electron-rich substituents
on the aryl moiety, such as Me (3b), MeO (3c), and tBu (3d), as
well as electron-deficient halide substituents, such as Cl (3e),
Br (3 f), and F (3g), were well tolerated, affording the desired
furans in 57–75% yields. Fortunately, halide substituents Br
(3 f) and Cl (3e), which are sensitive to palladium-catalyzed re-
actions and are also potential substrates for further transition
metal-catalyzed functionalizations, did not give rise to any
complications under such mild reaction conditions. Other
types of aryl moiety, such as 1-naphthyl (3h), and heteroaryl
moiety, such as 2-thiophene (3i), were equally applicable to
provide the functionalized furans in good yields. By retaining
the same 1,3-dicarbonyl moiety in the 2-cinnamyl-1,3-dicarbon-
yl substrate, various unsymmetrical cinnamyl groups were em-
ployed for the current furan synthesis. Corresponding 2-
benzyl-3-alkyl-4-acyl-5-methyl furans (3j–o) were efficiently
synthesized in good yields. Apart from 2-benzyl furans, the cor-
responding 2-alkyl furans can potentially be synthesized by
using the same reaction conditions, as shown in cases of 3q
and 3r.
To further explore the substrate scope, various 1,3-dicarbon-
yl moieties of the 2-cinnamyl-1,3-dicarbonyl substrates were
Chem. Eur. J. 2015, 21, 14732 – 14736
www.chemeurj.org
14733
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
To test the practicality of this approach, a gram-scale synthe-
sis of 3j from the corresponding 2-cinnamyl-1,3-dicarbonyl
species 1j was performed (Scheme 5a). Furthermore, a gram-
scale synthesis of 3e was carried out from the corresponding
allyl alcohol and acetylacetone, also catalyzed by
[PdCl2(CH3CN)2] (Scheme 5b).
A proposed reaction pathway for the oxidative cycloisomeri-
zation of 2-cinnamyl-1,3-dicarbonyls to form functionalized 2-
benzyl furans, based on the aforementioned results, is depict-
ed in Scheme 6. An acid-mediated tautomerization of 2-cin-
namyl-1,3-dicarbonyl 1 generates the enol tautomer 1’ which
reacts with the PdII species to provide palladium–enolate I.
Then, I undergoes intramolecular 5-exo-trig cyclization to give
species II. However, PdII might also act as a p-acid to activate
the C=C bond for the intramolecular 5-exo-trig cyclization to
generate species II. Subsequently, II can be transformed into
the desired product by b-hydride elimination to give inter-
Scheme 3. Variation of 1,3-Dicarbonyl Counterpart. Reaction conditions: 2-
Cinnamyl-1,3-dione (0.15 mmol), [PdCl2(CH3CN)2] (5 mol%), BQ (1 equiv), PTS
(1 equiv), THF (1.0 mL). Yields refer to products isolated by column chroma-
tography.
then investigated (Scheme 3). 1,3-Dicarbonyls bearing aryl/aryl
(5a,b), aryl/alkyl (5c), heteroaryl/alkyl (5d) and alkyl/alkyl (5e)
substituents delivered the corresponding furans in good yields.
Particularly, 1,3-dicarbonyls bearing an ester functionality, such
as ethyl (5 f), allyl (5g) and benzyl (5h) esters, provided the de-
sired furans without any problem. Notably, allyl and benzyl
esters, which are generally sensitive to palladium-catalyzed re-
action conditions, did not give rise to any complications under
such mild reaction conditions. In the case of tert-butyl ester,
the desired oxidative cyclization occurred, but the tert-butyl
group was deprotected, providing the corresponding carboxyl-
ic acid-substituted furan 5i. 1,3-Dicarbonyls bearing unsym-
metrical alkyl groups, such as methyl/ethyl, led to product mix-
tures containing two regioisomers (5j/j’ and 5k/k’). When, in-
stead of 1,3-dicarbonyls, a 2-cyanocarbonyl species was utilized
under the current reaction conditions, encouragingly, the de-
sired furan 5l was formed, along with a dearylated analogue
5l’, as an inseparable mixture.
Scheme 4. One-pot reaction. Reaction conditions: Alcohol (0.15 mmol), 1,3-
dicarbonyl compound (0.15 mmol), [PdCl2(CH3CN)2] (5 mol%), BQ (1 equiv),
PTS (1 equiv), THF (1.0 mL). Yields refer to products isolated by column chro-
matography.
Next, we examined the one-pot, sequential C-alkylation of
1,3-dicarbonyls with cinnamyl alcohols followed by oxidative
cyclization for the palladium-catalyzed synthesis of furans
(Scheme 4). Various tetrasubstituted furans were synthesized in
good yields.
Scheme 5. Gram-scale syntheses of 3j (a) and 3e (b). Yields refer to products
isolated by column chromatography.
Chem. Eur. J. 2015, 21, 14732 – 14736
www.chemeurj.org
14734
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
Huang, Z. Li, H. Jiang, Org. Lett. 2012, 14, 616; d) M. G. Nilson, R. L.
Funk, J. Am. Chem. Soc. 2011, 133, 12451; e) L. Liu, Y. Gao, C. Che, N.
Wu, D. Z. Wang, C.-C. Li, Z. Yang, Chem. Commun. 2009, 662; f) E. Pavla-
kos, T. Georgiou, M. Tofi, T. Montagnon, G. Vassilikogiannakis, Org. Lett.
2009, 11, 4556; g) J.-Q. Dong, H. N. C. Wong, Angew. Chem. Int. Ed.
2009, 48, 2351; Angew. Chem. 2009, 121, 2387; h) J. Robertson, S. Naud,
Org. Lett. 2008, 10, 5445; i) I. Margaros, G. Vassilikogiannakis, J. Org.
Chem. 2008, 73, 2021; j) X. Zhou, W. Wu, X. Liu, C.-S. Lee, Org. Lett.
2008, 10, 5525; k) K. L. Jackson, J. A. Henderson, J. C. Morris, H. Mo-
toyoshi, A. J. Phillips, Tetrahedron Lett. 2008, 49, 2939; l) J. N. Abrams,
R. S. Babu, H. Guo, D. Le, J. Le, J. M. Osbourn, G. A. O’Doherty, J. Org.
Chem. 2008, 73, 1935; m) J. Bi, V. K. Aggarwal, Chem. Commun. 2008,
120.
[3] a) O. Gidron, L. J. W. Shimon, G. Leitus, M. Bendikov, Org. Lett. 2012, 14,
502; b) O. Gidron, A. Dadvand, Y. Sheynin, M. Bendikov, D. F. Perepichka,
Chem. Commun. 2011, 47, 1976; c) U. H. F. Bunz, Angew. Chem. Int. Ed.
2010, 49, 5037; Angew. Chem. 2010, 122, 5159; d) O. Gidron, Y. Diskin-
Posner, M. Bendikov, J. Am. Chem. Soc. 2010, 132, 2148.
Scheme 6. Proposed mechanism for current process.
[4] Synthesis of furans from 2-alkynyl-carbonyls: a) Y. Ma, S. Zhang, S. Yang,
F. Song, J. You, Angew. Chem. Int. Ed. 2014, 53, 7870; Angew. Chem.
2014, 126, 8004; b) J. Gonzµlez, L. A. Lopez, R. Vicente, Chem. Commun.
2014, 50, 8536; c) B. Song, L.-H. Li, X.-R. Song, Y.-F. Qiu, M.-J. Zhong, P.-
X. Zhou, Y.-M. Liang, Chem. Eur. J. 2014, 20, 5910; d) D. Nitsch, T. Bach, J.
Org. Chem. 2014, 79, 6372; e) F. Hu, Y. Xia, C. Ma, Yan. Zhang, J. Wang,
Org. Lett. 2014, 16, 4082; f) C. He, S. Guo, J. Ke, J. Hao, H. Xu, H. Chen,
A. Lei, J. Am. Chem. Soc. 2012, 134, 5766; g) R. Vicente, J. Gonzalez, L.
Riesgo, J. Gonzalez, L. A. Lopez, Angew. Chem. Int. Ed. 2012, 51, 8063;
Angew. Chem. 2012, 124, 8187; h) W.-h. Ji, Y.-m. Pan, S.-y. Zhao, Z.-p.
Zhan, Synlett 2008, 3046; i) X.-H. Duan, X.-Y. Liu, L.-N. Guo, M.-C. Liao,
W.-M. Liu, Y.-M. Liang, J. Org. Chem. 2005, 70, 6980; j) Z.-P. Zhang, X.-B.
Cai, S.-P. Wang, J.-L. Yu, H.-J. Liu, Y.-Y. Cui, J. Org. Chem. 2007, 72, 9838;
k) T. Yao, X. Zhang, R. C. Larock, J. Org. Chem. 2005, 70, 7679; l) T. Yao, X.
Zhang, R. C. Larock, J. Am. Chem. Soc. 2004, 126, 11164.
mediate III, followed by isomerization. Furthermore, Pd0 was
assumed to be oxidized by benzoquinone to regenerate the
active PdII catalyst. In the one-pot protocol, the PdII species
also catalyzes the dehydrative coupling between 1,3-dicarbon-
yls and cinnamyl alcohols to form the product 1. The alternate
pathway, whereby a,b,g,d-dienones are generated from sub-
strate 1 followed by cyclization to provide the furans, is ruled
out based on the control experiment (see the Supporting In-
formation).
In summary, a versatile catalytic method for the synthesis of
highly functionalized 2-benzyl furans through palladium-cata-
lyzed intramolecular oxidative annulation of 2-cinnamyl-1,3-di-
carbonyls has been disclosed. A one-pot, sequential synthesis
of 2-cinnamyl-1,3-dicarbonyls, starting from the corresponding
cinnamyl alcohols and 1,3-dicarbonyls, has also been demon-
strated. In view of the high pharmaceutical importance of the
functionalized 2-benzyl furans, this simple and practical syn-
thetic strategy should be valuable to both pharmaceutical and
agrochemical industries. Furthermore, it will significantly
impact the step economy in the synthesis of bioactive com-
pounds.
[5] Synthesis of furans from 2-allenyl-carbonyls: a) M. H. Suhre, M. Reif, S. F.
Kirsch, Org. Lett. 2005, 7, 3925; b) Y. Xia, Y. Xia, R. Ge, Z. Liu, Q. Xiao, Y.
Zhang, J. Wang, Angew. Chem. Int. Ed. 2014, 53, 3917; Angew. Chem.
2014, 126, 3998; c) A. Palisse, S. F. Kirsch, Eur. J. Org. Chem. 2014, 7095;
d) C. Cheng, S. Liu, G. Zhu, Org. Lett. 2015, 17, 1581.
[6] Other recent strategies for the synthesis of furans: For Review: a) A. V.
Gulevich, A. S. Dudnik, N. Chernyak, V. Gevorgyan, Chem. Rev. 2013, 113,
3084; For recent literature: b) L. Chen, Yi. Du, X.-P. Zeng, T.-D. Shi, F.
Zhou, J. Zhou, Org. Lett. 2015, 17, 1557; c) I. I. Roslan, J. Sun, G.-K.
Chuah, S. Jaenicke, Adv. Synth. Catal. 2015, 357, 719; d) Z.-L. Wang, H.-L.
Li, L.-S. Ge, X.-L. An, Z.-G. Zhang, X. Luo, J. S. Fossey, W.-P. Deng, J. Org.
Chem. 2014, 79, 1156; e) L. Xia, Y. R. Lee, Eur. J. Org. Chem. 2014, 3430;
f) Y. Lian, T. Huber, K. D. Hesp, R. G. Bergman, J. A. Ellman, Angew. Chem.
Int. Ed. 2013, 52, 629; Angew. Chem. 2013, 125, 657; g) M. Zheng, L.
Huang, W. Wu, H. Jiang, Org. Lett. 2013, 15, 1838; h) Y. Yang, J. Yao, Y.
Zhang, Org. Lett. 2013, 15, 3206; i) H. Cao, H. Zhan, J. Cen, J. Lin, Y. Lin,
Q. Zhu, M. Fu, H. Jiang, Org. Lett. 2013, 15, 1080; j) X. Zheng, S. Lu, Z. Li,
Org. Lett. 2013, 15, 5432; k) L. Zhou, M. Zhang, W. Li, J. Zhang, Angew.
Chem. Int. Ed. 2014, 53, 6542; Angew. Chem. 2014, 126, 6660.
Acknowledgements
This work has been supported by DST, India and IISER Bhopal.
R.N. is grateful to CSIR and R.R.R. is thankful to IISER Bhopal for
research fellowships.
[7] For PdII-catalyzed oxidative cyclization: a) S. Shin, D. Kang, W. H. Jeon,
P. H. Lee, Beilstein J. Org. Chem. 2014, 10, 1220; b) X. Zeng, Chem. Rev.
2013, 113, 6864; c) T. Hosokawa, S. Murahashi, Acc. Chem. Res. 1990, 23,
49.
[8] X. Han, R. A. Widenhoefer, J. Org. Chem. 2004, 69, 1738.
Keywords: cycloisomerization
oxidation · palladium
·
furans
·
heterocycles
·
[9] Synthesis of 2-cinnamyl-1,3-dicarbonyls: a) R. Kumar, E. V. van der Eyck-
en, Chem. Soc. Rev. 2013, 42, 1121; b) P. Kothandaraman, W. Rao, X.
Zhang, P. W. H. Chan, Tetrahedron 2009, 65, 1833; c) W. Huang, J. Wang,
Q. Shena, X. Zhou, Tetrahedron Lett. 2007, 48, 3969; d) M. Rueping, B. J.
Nachtsheim, A. Kuenkel, Org. Lett. 2007, 9, 825; e) M. Yasuda, T. Somyo,
A. Baba, Angew. Chem. Int. Ed. 2006, 45, 793; Angew. Chem. 2006, 118,
807.
[10] a) W. Yang, L. Huang, H. Liu, W. Wang, H. Li, Chem. Commun. 2013, 49,
4667; b) Y. Jiang, C.-M. Park, T.-P. Loh, Org. Lett. 2014, 16, 3432; c) J.
Tummatorn, S. Ruchirawat, P. Ploypradith, Chem. Eur. J. 2010, 16, 1445.
[11] a) R. Nallagonda, M. Rehan, P. Ghorai, Org. Lett. 2014, 16, 4786; b) M.
Rehan, G. Hazra, P. Ghorai, Org. Lett. 2015, 17, 1668.
[1] a) H. N. C. Wong, X.-L. Hou, K.-S. Yeung, H. Huang in Five-Membered Het-
erocycles: Furan, (Eds.: J. Alvarez-Builla, J. J. Vaquero, J. Barluenga),
Wiley-VCH, Weinheim, 2011, Vol. 1, pp. 533–692; b) D. J. Mortensen,
A. L. Rodríguez, K. E. Carlson, J. Sun, B. S. Katzenellenbogen, J. A. Katze-
nellenbogen, J. Med. Chem. 2001, 44, 3838; c) S. Breyer, K. Effenberger-
Neidnicht, S. Knauer, R. Schobert, Bioorg. Med. Chem. 2011, 19, 1264;
d) D. A. Mulholland, A. Langlois, M. Randrianarivelojosia, E. Derat, J. M.
Nuzillard, Phytochem. Anal. 2006, 17, 87.
[2] a) B. H. Lipshutz, Chem. Rev. 1986, 86, 795; b) C. Wang, Y. Chen, X. Xie, J.
Liu, Y. Liu, J. Org. Chem. 2012, 77, 1915; c) B. Yin, G. Zeng, C. Cai, F. Ji, L.
[12] F.-Q. Yuan, F.-S. Han, Org. Lett. 2012, 14, 1218.
Chem. Eur. J. 2015, 21, 14732 – 14736
www.chemeurj.org
14735
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Communication
[13] a) M. G. Ford, D. R. Pert, Pestic. Sci. 1974, 5, 635; b) T. B. Gaines, R. E.
Linder, Fundam. Appl. Toxicol. 1986, 7, 299; c) United Nations FADINAP
(2002), Agrochemical Reports 2: 29.
[14] a) F.-Q. Yuan, L.-X. Gao, F.-S. Han, Chem. Commun. 2011, 47, 5289; b) T.
Wang, X.-L. Chen, L. Chen, Z.-P. Zhan, Org. Lett. 2011, 13, 3324; c) C. Ra-
ji Reddy, M. D. Reddy, J. Org. Chem. 2014, 79, 106; d) D. Schmidt, C. C.
Malakar, U. Beifuss, Org. Lett. 2014, 16, 4862; e) C. R. Reddy, G. Krishna,
M. D. Reddy, Org. Biomol. Chem. 2014, 12, 1664.
[16] For selected examples for the synthesis of tetrasubstituted furans: a) Y.
Xiao, J. Zhang, Angew. Chem. Int. Ed. 2008, 47, 1903; Angew. Chem.
2008, 120, 1929; b) Y. Xiao, J. Zhang, Adv. Synth. Catal. 2009, 351, 617;
c) R. Liu, J. Zhang, Chem. Eur. J. 2009, 15, 9303; d) W. Li, J. Zhang, Chem.
Commun. 2010, 46, 8839; e) W. Zhao, J. Zhang, Chem. Commun. 2010,
46, 4384; f) H. Gao, J. Zhang, Chem. Eur. J. Chem. -Eur. J. 2012, 18, 2777;
g) A. W. Sromek, M. Rubina, V. Gevorgyan, J. Am. Chem. Soc. 2005, 127,
10500; h) T.-T. Kao, S. Syu, Y.-W. Jhang, W. Lin, Org. Lett. 2010, 12, 3066.
[15] Functionalization at 3-position of furans: a) H. Yang, Z. Zheng, J. Zeng,
H. Liu, B. Yi, Bull. Korean Chem. Soc. 2012, 33, 2623; b) K. Si Larbi, H. Y.
Fu, N. Laidaoui, K. Beydoun, A. Miloudi, D. E. Abed, S. Djabbar, H.
Doucet, ChemCatChem 2012, 4, 815.
Received: July 15, 2015
Published online on August 28, 2015
Chem. Eur. J. 2015, 21, 14732 – 14736
www.chemeurj.org
14736
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim