Stereoselective synthesis of functionalized vinyl ethers from allyl bromides activated by triethylamine

Article abstract of DOI:10.1080/00397911.2017.1420801

An efficient coupling reaction of allyl bromides with various alcohols as nucleophiles activated by triethylamine, leading to functionalized vinyl ethers in good yields and with full stereoselectivity.

Full text of DOI:10.1080/00397911.2017.1420801

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Stereoselective synthesis of functionalized
vinyl ethers from allyl bromides activated by
triethylamine
Aïcha Arfaoui, Fatma Saâdi, Asma Bourafai Aziez, Hammouda Chebbi,
Catherine Fressigné, Julien Legros, Hassan Oulyadi, Jacques Maddaluno &
Hassen Amri
To cite this article: Aïcha Arfaoui, Fatma Saâdi, Asma Bourafai Aziez, Hammouda Chebbi,
Catherine Fressigné, Julien Legros, Hassan Oulyadi, Jacques Maddaluno & Hassen Amri
(2018) Stereoselective synthesis of functionalized vinyl ethers from allyl bromides activated by
triethylamine, Synthetic Communications, 48:6, 705-713, DOI: 10.1080/00397911.2017.1420801
To link to this article: https://doi.org/10.1080/00397911.2017.1420801
Published online: 13 Feb 2018.
Article views: 26
View supplementary material
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=lsyc20

SYNTHETIC COMMUNICATIONS®
2018, VOL. 48, NO. 6, 705–713
https://doi.org/10.1080/00397911.2017.1420801
Stereoselective synthesis of functionalized vinyl ethers from
allyl bromides activated by triethylamine
Aïcha Arfaouia,b, Fatma Saâdia, Asma Bourafai Aziezc, Hammouda Chebbid,
Catherine Fressignéb, Julien Legrosb, Hassan Oulyadic, Jacques Maddalunob, and
Hassen Amria
aLaboratoire de Synthèse Organique Sélective et Hétérocyclique-Evaluation de l’Activité Biologique,
Faculté des Sciences de Tunis, Université de Tunis El Manar, Tunis, Tunisia; bINSA Rouen, UNIROUEN, CNRS,
c
COBRA Laboratory (UMR 6014 & FR3038), Normandie Université, Rouen, France; Normandie Université,
COBRA, UMR6014 and FR3038 CNRS, Université de Rouen, INSA de Rouen, Mont-Saint-Aignan, France;
dLaboratoire de Matériaux, Cristallochimie et Thermodynamique Appliquée, Faculté des Sciences, Université de
Tunis El Manar, Tunis, Tunisia
ABSTRACT
ARTICLE HISTORY
Received 10 November 2017
An efficient coupling reaction of allyl bromides with various alcohols
as nucleophiles activated by triethylamine, leading to functionalized
vinyl ethers in good yields and with full stereoselectivity.
KEYWORDS
Allyl bromides; oxygen
nucleophiles; triethylamine;
vinyl ethers
GRAPHICAL ABSTRACT
Introduction
The search for efficient synthetic methods to build C–O bonds is of great interest in organic
chemistry, and vinyl ethers have attracted considerable attention for their potential applica-
tions: monomers for the synthesis of functional polymer materials,[1] precursors of active
pharmaceutical ingredients,[2] and synthons for the formation of hemilabile mono-[3] and
diphosphine ligands.[4] Moreover, such enol ethers can efficiently contribute in various reac-
tions, such as cyclization,[5] metathesis,[6] Claisen rearrangement,[7] addition of diverse X–H-
acids[8] Heck reactions,[9] and arylation.[10] Among the existing methods to access vinyl ethers,
the most recent progresses propose metal-catalyzed cross-coupling between vinyl(pseudo)
halides and alcohols as a formal SN2 reaction.[11–13] Herein we report the SN20 reaction
between alcohols and an allyl bromide 1 activated by Et3N affording enol ethers (Scheme 1).
Results and discussion
Dimethyl α-(bromomethyl)fumarate 1 has been used in the synthesis of alkenyl itaconic
acids[14] and organocatalytic α-alkylation of aldehydes.[15] In this context, we have
CONTACT Aïcha Arfaoui
Campus-2092, Tunis, Tunisia.
acha.arfaoui@gmail.com
Faculty of Science of Tunis, El Manar University, Universitary
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data (synthetic procedure for vinyl ethers 2, vinyl ethers 4, dimethyl 2-(bromomethyl)-3-phenoxymaleate
5, methyl 1-benzyl-4-(benzylamino)-2,5-dihydro-5-oxo-1H-pyrrole-3-carboxylate 6 and copies of NMR spectra of compounds
2, 4, 5, and 6) can be accessed on the publisher’s website.
© 2018 Taylor & Francis

706
A. ARFAOUI ET AL.
Scheme 1. Background (a) and the objective (b) of the current work.
previously described a simple and stereoselective synthesis of allyl bromide 1,[16]
a
trifunctional alkene from the addition of bromine to dimethyl itaconate, followed by
dehydrobromination using triethylamine (Scheme 2).
Recently, we have reported a general methodology for the selective synthesis of allyl
ethers[17] from the use of 1,4-diazabicyclo[2.2.2]octane[18,19] in the direct nucleophilic sub-
stitution of the brominated derivative 1.[16] Alcoholysis of the resulting quaternary
ammonium salt produce the functionalized allyl ethers in the presence of triethylamine
in SN20 reaction in good yields (Scheme 1). We have also examined the sequence involving
the use of the ammonium salt previously described with quite bulky secondary amines in
methanol to afford allyl amines.[20] On the basis of this work, it has been observed that 1,4-
diazabicyclo[2.2.2]octane (DABCO) plays an important role in the stereoselectivity of the
obtained product either, allyl amines or allyl ethers, by the formation of a co-nucleophile
Scheme 2. A convenient pathway for synthesis of allyl bromide 1.
Scheme 3. Vinylic etherification of brominated derivative 1.

SYNTHETIC COMMUNICATIONS®
707
which can be easily dislodged by conjugate addition of heteroatom nucleophiles. In
continuation of this study, we enhance herein the reaction shown in Scheme 1 by imple-
menting an effective protocol for the synthesis of α,β-difunctionalized vinyl ethers 2 by the
Table 1. Stereoselective synthesis of E-vinyl ethers.
Entry
1
R
Vinyl ethers
Time (h)
2
Yieldsa (%)
95
C6H5
2
p-MeOC6H4
1
90
3
4
p-NO2C6H4
m-OHC6H4
1,5
1,5
92
70
5
CF3CH2
11
60
6
7
Me
Et
17
22
65
51
8
9
nPr
76
48
45
nBu
144
10
tBu
no reaction
144
–
aIsolated yields after purification by column chromatography on silica gel.

708
A. ARFAOUI ET AL.
combination of allyl bromide 1 with various alcohols without addition of DABCO. A
mixture of two regioisomers has been formed after being stirred for 5 min which allyl
ethers disappeared in favor of vinyl ethers by spontaneous isomerization.[21] The coupling
reaction was activated by the use of triethylamine leading to the formation of vinyl ethers 2
with total stereoselectivity in favor of E-isomer with good yields ranging from 45 to 92%.
The vinyl ethers 2 could be used as monomers for the synthesis of polyamides or polye-
sters. Geometry of the resulting multisubstituted vinyl ethers 2 was examined by NOE
experiments by considering the trend of the through-space coupling between two atom
groups OR and methyl to develop a rational criterion for the structural assignment of
the vinyl ethers 2 as well are significantly in favor of the corresponding E-configuration
(Scheme 3).
Substituents at the meta and para positions of the aryl group of substituted phenol deri-
vatives have shown that they are more reactive than the aliphatic alcohols such as MeOH,
EtOH, n-PrOH, and n-BuOH and the corresponding vinyl ethers 2a–d have been obtained
in good yields with low reaction time (1–2 h) (Table 1).
Notably, the reaction seems to be inhibited by the size of the alkyl primary alcohol
groups. The use of a bulky tertiary alcohol (such as tert-butyl alcohol) as an oxygen nucleo-
phile is ineffective even after 144 h of stirring at reflux. It seems to be affected by the steric
hindrance of the alcohol which attenuates its nucleophilicity (entry 10, Table 1).
To expand the field of the reactivity of allylic bromides toward oxygen nucleophiles, we
have tried the coupling reaction of ethyl 2-(bromomethyl)-3-cyanoacrylate 3[18] as a mix-
ture of two isomers Z and E with a series of aliphatic and aromatic alcohols activated by the
presence of triethylamine. A mixture of two regioisomers was observed and a complete iso-
merization of allyl ethers into vinyl ethers 4 was formed in E-configuration with good
yields (Scheme 4).
The aryl-substituted phenol has shown that they are more reactive than the aliphatic
alcohols such as n-PrOH and n-BuOH and the corresponding vinyl ethers 4a–d have been
obtained in good yields with moderate reaction time (5–10 h) (Table 2). Moreover, the
steric hindrance of the alcohol attenuates its nucleophilicity in the case of (o,o0,p)-
tribromophenol and (o,o0,p)-trinitrophenol (entries 8 and 9—Table 2). The very low
reactivity of HC≡C–CH2OH (entries 7—Table 2) is attributed to the attracting effect of
the two hybridized carbons sp.
Theoretical calculations have been made on the ethyl 3-cyano-2-phenoxybut-2-enoate
4a show that the configuration E is more stable compared to the corresponding Z-isomer.
The geometry optimizations in vacuo, were performed with Jaguar 7.6[22] at the DFT level,
using the B3P86[23] hybrid density functional, the basis set used for computations was
6 − 31 þ g**.[24] As expected, the E-isomer 4a has the lowest energy and therefore the most
stable structure (Fig. 1).
Such functionalized enol ethers can be of interest as building blocks to synthesize
elaborated molecules. Thus we have used compound phenoxymaleate 2a as starting
Scheme 4. Direct synthesis of vinyl ethers 4.

SYNTHETIC COMMUNICATIONS®
709
Table 2. Total stereoselective synthesis of vinyl ethers.
Entry
1
R
Vinyl ethers
Time (h)
10
Yieldsa (%)
C6H5
82
2
p-MeOC6H4
5
80
3
4
m-OHC6H4
6
60
75
C6H5CH2
10
5
6
n-C3H7
n-C4H9
24
20
50
55
7
8
9
C3H3
No reaction
No reaction
No reaction
60
65
70
–
–
–
o,p,o0-Br3C6H2
o,p,o0-NO2C6H2
aIsolated yields after purification by column chromatography on silica gel.
Figure 1. Calculated energy difference for Z- and E-4a isomers.

710
A. ARFAOUI ET AL.
Figure 2. X-ray crystal structure of Z-5. CCDC 1548610.[27]
Scheme 5. Efficient synthesis of 3,4-disubstituted pyrrolin-2-one 6.
material to access caspase-3 inhibitors with a pyrrolinone scaffold.[25] For this, we first per-
formed radical bromination of 2a with N-bromosuccinimide under classical conditions (in
refluxing tetrachloride with benzoyl peroxide[26] as initiator) to give allyl bromide Z-5
in 71% yield (Scheme 4). The stereochemistry of the functionalized allyl bromide 5 was
determined based on the X-ray diffraction analysis (Fig. 2). The molecular structure
shows that the double bond in 5 is in Z-configuration, and the phenoxyl group is attached
to the β-carbon of the carbonyl group and the methylene bromide atom is connected to the
α-carbon, which suggests that the bromination of 2a is achieved in a syn-fashion. It can be
deduced that the vinyl ether 2 has an E-configuration by analogy with the preceding result.
Therefore Z-3, was reacted with an excess of benzylamine, to undergoes two consecutive
transformations: aza-Michael addition-cyclization reactions to produce the target bioactive
3,4-disubstituted pyrrolin-2-one 6[25] (Scheme 5).
Experimental
All reagents and solvents were purchased from commercial sources and used as received
without further purification. Reactions were routinely performed under nitrogen
atmosphere with magnetic stirring. All reactions were monitored by TLC on silica gel
plates (Fluka silica gel 60 F254, Merck) and visualized by a 254 nm UV lamp and potassium
permanganate aqueous solution. The crude products were purified using column
1
chromatography on silica gel; Fluka silica gel 70-230 mesh was used. H, 13C NMR, and
NOESY spectra were recorded on a Bruker AC 400 MHz spectrometer at 400 and
77 MHz, for 1H, 13C, and NOESY respectively in deuterated chloroform as solvent and tet-
ramethylsilane as internal standard. The chemical shifts (δ) and coupling constants (J) are
respectively, expressed in parts per million (ppm) and Hertz (Hz). All NMR spectra were

SYNTHETIC COMMUNICATIONS®
711
acquired at room temperature. Multiplicity of peaks is indicated by the following: s, singlet;
d, doublet; t, triplet; q, quartet; quint, quintuplet; sext, sextuplet, and m, multiplet. High
resolution mass spectroscopy data were recorded on a micromass quadrupole time-of-
flight) instrument with an electrospray source in the EI or ESI mode in the university of
Rouen and GC–MS analyses were performed with a GCMS-QP2010S (Shimadzu)
instrument with a GC-2010 equipped with a 30 m capillary column (Supelco, SLBTM-
5ms, fused silica capillary column, 30 m � 0.25 mm � 0.25 mm film thickness), which
was used with helium as the vector gas in the university of Rennes 1.
General procedure for the preparation of vinyl ethers 2
To a stirred solution of dimethyl α-(bromomethyl)fumarate 1 (0.5 g, 1.83 mmol) and
alcohols (1.83 mmol, 1 equiv.) was added dropwise triethylamine (0.5 mL, 3.66 mmol) in
DCM (5 mL) under a nitrogen atmosphere. The mixture was then stirred vigorously at
39.6 °C for 1–144 h. Next, the mixture was diluted with DCM (20 mL) and washed succes-
sively with 2N HCl solution and water. The organic layer was dried over anhydrous
Na2SO4 and concentrated in vacuo. The crude product, thus obtained was purified by
column chromatography on silica gel to afford pure vinyl ethers 2.
Dimethyl 2-methyl-3-phenoxymaleate 2a
Colorless liquid; yield: (0.26 g, 95%); eluent CH2Cl2/petroleum ether, 60:40; 1H NMR
(CDCl3, δ ppm, J Hz): 7.23 (t, 2H, J ¼ 8.00), 7.00 (t, 1H, J ¼ 8.00), 6.90 (d, 2H, J ¼ 8.00),
3.75 (s, 3H), 3.59 (s, 3H), 1.92 (s, 3H); 13C NMR (CDCl3, δ ppm): 168.3 (CO2Me), 163.0
=
=
=
=
(CO2Me), 155.9 (aromatic C), 144.2 ( C), 129.7 (2 aromatic CH), 126.6 ( C), 123.4 (aro-
=
=
matic CH), 116.3 (2 aromatic CH), 52.5 (OCH3), 52.4 (OCH3), 13.6 (CH3). HRMS calcd.
for [MþH]þ C13H15O5: 251.0905; found: 251.0902.
Typical procedure for the synthesis of vinyl ethers 4
General procedure for aryl alcohols
To a solution of ethyl (Z,E)-2-(bromomethyl)-3-cyanoacrylate 3 (0.3 g, 1.38 mmol) and aryl
alcohols (1.38 mmol, 1 equiv.) was added dropwise triethylamine (0.38 mL, 2.76 mmol) in
CH3CN (5 mL) under a nitrogen atmosphere. The mixture was then stirred vigorously at
25 °C for 5–10 h. Next, the excess of solvent was concentrated under reduced pressure, and
the organic residue obtained was purified by chromatography on silica gel using a mixture
of petroleum ether/AcO2Et (80:20) as eluent to provide ethyl (E)-3-cyano-2-methyl-3-
aryloxyacrylate 4.
Ethyl (e)-3-cyano-2-methyl-3-phenoxyacrylate 4a
1
Yellow liquid; yield: (0.26 g, 82%); H NMR (CDCl3, δ ppm, J Hz): 7.39 (t, 2H, J ¼ 8.00),
7.21 (t, 1H, J ¼ 8.00), 7.05 (d, 2H, J ¼ 8.00), 4.35 (q, 2H, J ¼ 8.00), 2.10 (s, 3H), 1,37
(t, 3H, J ¼ 8.00); 13C NMR (CDCl3, δ ppm): 164.7 (CO2Et), 154.3 (aromatic ¼C), 131.7
(¼C), 130.0 (aromatic ¼CH), 125.3 (¼C), 118.2 (aromatic ¼CH), 112.2 (CN), 62.1
(OCH2), 14.0 (CH3), 12.8 (CH3). HRMS calcd. for [M]þ C131H13NO3: 231.08954; found:
231.08914.

712
A. ARFAOUI ET AL.
Conclusion
In summary, we have developed a simple and convenient method for stereoselective
synthesis of functionalized enol ethers by Et3N-activated sequential SN20 reaction/
isomerization from various alcohols and allyl bromides obtained from Morita–Baylis–
Hillman adducts. This simple procedure involves simple starting materials and the
obtained vinyl ethers can offer an access to pyrrolinones.
Acknowledgments
The authors wish to thank Professor Pierre Dixneuf (Rennes 1 University in France) for logistical
help. Computations have been performed at the Centre Régional Informatique et d’Applications
Numériques de Normandie (CRIANN, Saint Etienne du Rouvray).
References
[1] (a) Iftene, F.; David, G.; Boutevin, B.; Auvergne, R.; Alaaeddine, A.; Meghabar, R. J. Polym.
Sci., Part A: Polym. Chem. 2012, 50, 2432–2443; (b) Kanazawa, A.; Kanaoka, S.; Aoshima, S.
Macromolecules 2014, 47, 6635–6644; (c) Sugihara, S.; Kawamoto, Y.; Maeda, Y.
Macromolecules 2016, 49, 1563–1574; (d) Kottisch, V.; Quentin Michaudel, Q.; Fors, B. P.
J. Am. Chem. Soc. 2016, 138, 15535–15538; (e) Kanazawa, A.; Kanaoka, S.; Aoshima, S.
J. Am. Chem. Soc. 2013, 135, 9330–9333.
[2] (a) Tejedor, D.; Cotos, L.; García-Tellado, F. J. Org. Chem. 2013, 78, 8853–8858; (b) André, M.;
Letribot, B.; Bayle, M.; Mounetou, E.; Chezal, J.-M. Tetrahedron Lett. 2012, 53, 6107–6110.
[3] Oparina, L. A.; Malysheva, S. F.; Gusarova, N. K.; Vysotskaya, O. V.; Stepanov, A. V.;
Belogorlova, N. A.; Albanov, A. I.; Trofimov, B. A. Synthesis 2009, 2009, 3427–3432.
[4] Oparina, L. A.; Gusarova, N. K.; Vysotskaya, O. V.; Kolyvanov, N. A.; Artem’ev, A. V.;
Trofimov, B. A. Synthesis 2012, 44, 2938–2946.
[5] (a) Ram, R. N.; Gupta, D. K.; Soni, V. K. J. Org. Chem. 2016, 81, 1665–1674; (b) Jin, S.; Jiang, C.;
Peng, X.; Shan, C.; Cui, S.; Niu, Y.; Liu, Y.; Lan, Y.; Liu, Y.; Cheng, M. Org. Lett. 2016, 18,
680–683; (c) Kim, C.-E.; Park, S.; Eom, D.; Seo, B.; Lee, P. H. Org. Lett. 2014, 16,
1900–1903; (d) Zhang, X.; Cividino, P.; Poisson, J.-F.; Shpak-Kraievskyi, P.; Laurent, M. Y.;
Martel, A.; Dujardin, G.; Py, S. Org. Lett. 2014, 16, 1936–1939; (e) Murai, M.; Hosokawa,
N.; Roy, D.; Takai, K. Org. Lett. 2014, 16, 4134–4137; (f) Oparina, L. A.; Vysotskaya, O. V.;
Stepanov, A. V.; Ushakov, I. A.; Apartsin, K. A.; Gusarova, N. K.; Trofimov, B. A. Russ. J.
Org. Chem. 2017, 53, 203–209.
[6] (a) Minenkov, Y.; Occhipinti, G.; Jensen, V. R. Organometallics 2013, 32, 2099–2111; (b) Meek,
S. J.; O’Brien, R. V.; Llaveria, J.; Schrock, R. R.; Hoveyda, A. H. Nature 2011, 471, 461–466.
[7] (a) Gille, A.; Rehbein, J.; Hiersemann, M. Org. Lett. 2011, 13, 2122–2125; (b) Tejedor, D.;
Leandro Cotos, L.; García-Tellado, F. Org. Lett. 2011, 13, 4422–4425; (c) Becker, J.; Butt, L.;
von Kiedrowski, V.; Mischler, E.; Quentin, F.; Hiersemann, M. J. Org. Chem. 2014, 79,
3040–3051; (d) Vidhani, D. V.; Cran, J. W.; Krafft, M. E.; Manoharan, M.; Alabugin, I. V.
J. Org. Chem. 2013, 78, 2059–2073.
[8] (a) Malysheva, V. F.; Gusarova, N. K.; Artem’ev, A. V.; Belogorlova, N. A.; Albanov, A. I.;
Borodina, T. N.; Smirnov, V. I.; Trofimov, B. A. Eur. J. Org. Chem. 2014, 2014, 2516–2521;
(b) Malysheva, S. F.; Gusarova, N. K.; Artem’ev, A. V.; Belogorlova, N. A.; Albanov,
A. I.; Borodina, T. N.; Smirnov, V. I.; Trofimov, B. A. Synthesis 2014, 46, 2656–2662; (c)
Oparina, L. A.; Artem’ev, A. V.; Vysotskaya, O. V.; Kolyvanov, N. A.; Bagryanskaya, Y. I.;
Doronina, E. P.; Gusarova, N. K. Tetrahedron 2013, 69, 6185–6195; (d) Pahadi, N. K.; Tunge,
J. A. Synlett 2009, 2009, 3135–3138.
[9] Gøgsig, T. M.; Kleimark, J.; Lill, S. O. N.; Korsager, S.; Lindhardt, A. T.; Norrby, P.-O.;
Skrydstrup, T. J. Am. Chem. Soc. 2012, 134, 443–452.

SYNTHETIC COMMUNICATIONS®
713
[10] (a) Ebe, Y.; Nishimura, T. J. Am. Chem. Soc. 2015, 137, 5899–5902; (b) Iwasaki, T.; Miyata, Y.;
Akimoto, R.; Fujii, Y.; Kuniyasu, H.; Kambe, N. J. Am. Chem. Soc. 2014, 136, 9260–9263.
[11] Jouvin, K.; Bayle, A.; Legrand, F.; Evano, G. Org. Lett. 2012, 14, 1652–1655.
[12] Kundu, D.; Maity, P.; Ranu, B. C. Org. Lett. 2014, 16, 1040–1043.
[13] Dehli, J. R.; Julien Legros, J.; Bolm, C. Chem. Commun. 2005, 2005, 973–986.
[14] Nishimura, H.; Sasaki, M.; Seike, H.; Nakamura, M.; Watanabe, T. Org. Biomol. Chem. 2012, 10,
6432–6442.
[15] Jiménez, J.; Landa, A.; Lizarraga, A.; Maestro, M.; Mielgo, A.; Oiarbide, M.; Velilla, I.; Palomo,
C. J. Org. Chem. 2012, 77, 747–753.
[16] Besbes, R.; Villiéras, J.; Amri, H. Indian J. Chem. Sect. B 1997, 36, 5–8.
[17] Arfaoui, A.; Saâdi, F.; Nefzi, A.; Amri, H. Synth. Commun. 2015, 45, 2627–2635.
[18] Arfaoui, A.; Amri, H. Tetrahedron 2009, 65, 4904–4907.
[19] Khamri, S.; Amri, H. Tetrahedron 2009, 65, 4890–4893.
[20] Arfaoui, A.; Béji, F.; Ben Ayed, T.; Amri, A. Synth. Commun. 2008, 38, 3717–3725.
[21] (a) Su, C.; Williard, P. G. Org. Lett. 2010, 12, 5378–5381; (b) Lim, H. J.; Smith, C. R.;
RajanBabu, T. V. J. Org. Chem. 2009, 74, 4565–4572.
[22] Jaguar, Version 7.6; Schrodinger, LLC: New York, 2009.
[23] (a) Perdrew, J. P. Phys. Rev. 1986, B33, 8822; (b) Becke, A. D. J. Chem. Phys. 1989, 90, 5622.
[24] (a) Petersson, G. A.; Bennett, A.; Tensfeldt, T. G.; Al-Laham, M. A.; Shirley, W. A.; Mantzaris, J.
J. Chem. Phys. 1988, 89, 2193–218; (b) Petersson, G. A.; Al-Laham, M. A. J. Chem. Phys. 1991,
94, 6081–6090; (c) Frisch, J. M.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80, 3265–3269;
(d) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. V. R. J. Comput. Chem. 1983, 4,
294–301.
[25] (a) Lv, L.; Zheng, S.; Cai, X.; Chen, Z.; Zhu, Q.; Liu, S. ACS Comb. Sci. 2013, 15, 183–192; (b)
Zhu, Q.; Gao, L.; Chen, Z.; Zheng, S.; Shu, H.; Li, J.; Jiang, H.; Liu, S. Eur. J. Med. Chem. 2012,
54, 232–238.
[26] (a) Greenwood, F. L.; Kellert, M. D.; Sedlak, J. Org. Synth. 1958, 38, 8–9; (b) Thapa, R.; Brown,
J.; Balestri, T.; Taylor, R. T. Tetrahedron Lett. 2014, 55, 6743–6746.
[27] CCDC 1548610 contains the supplementary crystallographic data of compound 3 for this
paper. These data can be obtained free of charge from the Cambridge Crystallographic Data
Centre via. http://www.ccdc.cam.ac.uk/data_request/cif.