A novel and efficient tandem aldol condensation-Diels-Alder reaction pathway for the direct synthesis of dehydrodecaline derivatives

Article abstract of DOI:10.1055/s-0031-1290438

An efficient direct synthesis of dehydrodecaline derivatives is reported via a tandem aldol condensation-Diels-Alder cycloaddition process under Lewis acidic conditions. Addition of dienophile moieties to conjugated dienes, formed in situ from the condens

Full text of DOI:10.1055/s-0031-1290438

LETTER
▌2073
lAetteNr ovel and Efficient Tandem Aldol Condensation–Diels–Alder Reaction
Pathway for the Direct Synthesis of Dehydrodecaline Derivatives
Direct Synthesis of Dehydrodecaline Derivatives
M. Saeed Abaee,*a Mohammad M. Mojtahedi,*a Farveh Saberi,a Ghazal Karimi,b M. Taghi Rezaei,b
A. Wahid Mesbah,a Klaus Harms,c Werner Massac
a
Department of Organic Chemistry, Chemistry and Chemical Engineering Research Center of Iran, P.O.Box 14335-186, Tehran, Iran
Fax +98(21)44580785; E-mail: abaee@ccerci.ac.ir; E-mail: mojtahedi@ccerci.ac.ir
b
Chemistry Department, Islamic Azad University, Saveh Branch, Saveh, Iran
c
Fachbereich Chemie der Philipps-Universität Marburg, Hans-Meerwein-Str., 35032 Marburg, Germany
Received: 13.05.2012; Accepted after revision: 18.06.2012
one pot as opposed to step-by-step sequence of traditional
reactions (Scheme 1).
Abstract: An efficient direct synthesis of dehydrodecaline deriva-
tives is reported via a tandem aldol condensation–Diels–Alder cy-
cloaddition process under Lewis acidic conditions. Addition of
dienophile moieties to conjugated dienes, formed in situ from the
condensation of enone 1 with aldehydes, lead to high-yield stereo-
selective synthesis of the final endo products in relatively short time
periods. Products precipitate upon concentration of the organic
phase and are purified by recrystallization.
O
O
X
O
TMSNEt2
LiClO4
O
X
O
O
X = O, NPh
Ar
3
4–5
Key words: tandem reaction, aldol condensation, Diels–Alder re-
action, endo addition, Lewis acid catalysis
1
Ar
O
2
O
3
Various condensation reactions of carbonyl compounds
bearing acidic hydrogens1 or active methylenes2 with al-
dehydes or ketones are among the most important carbon–
carbon bond formation reactions in synthetic organic
chemistry because the resulting conjugated products are
very useful intermediates to take part in other synthetic
manipulations.3 In situ engagement of these products in
other organic transformations in a tandem fashion has be-
come very popular in recent years due to the ability in con-
structing several carbon–carbon and carbon–heteroatom
bonds in a one-pot process.4 In particular, the incorpora-
tion of [4+2] Diels–Alder (DA) cycloadditions into tan-
dem processes is very beneficial for rapid construction of
complex target molecules and libraries of compounds.5
This is due to the ability of the DA reaction itself to yield
simultaneously two carbon–carbon bonds, a six-mem-
bered ring, and up to four stereogenic centers with predict-
able stereochemistry in a single-step process.6
Ar
12
Scheme 1
We first examined the conditions for the reaction of 1 with
benzaldehyde and maleic anhydride (3a, X = O), as shown
in Table 1.10 TLC experiments showed that in the pres-
ence of TMSNEt2 and LiClO4 the intermediate diene
formed efficiently by initial mixing of 1 and 2.11 Addition
of the dienophile to this mixture led to sole formation of
endo DA adduct 4a (X = O) in 80% yield within 120 min-
utes (Table 1, entry 1). Successful use of other aldehydes
showed the generality of the procedure. When 2-naphthal-
dehyde (Table 1, entry 2) or aldehydes with electron-rich
(Table 1, entries 3 and 4), electron-deficient (Table 1, en-
tries 5 and 6), or heterocyclic (Table 1, entries 7 and 8) ar-
omatic rings were subjected to the conditions, single endo
products 4b–h were formed in high yields in all cases
within relatively short time periods.
In the course of our investigations on aldol condensation
reactions,7 we recently reported the synthesis of a series of
styrylcyclohex-2-enone dienes,8 as the products of the
condensation of 1 with 2, which were further explored for
their DA reactivity.9 In continuation, we were persuaded
to combine the whole chemistry into a one-pot aldol con-
densation–DA process and examine the potential of this
approach for direct construction of dehydrodecalins start-
ing from isophorone, aldehydes, and dienophiles. Hereby,
we would like to report the results of this strategy that
leads to the synthesis of novel endo products obtained in
Molecular models generated by Chem3D program helped
assign the stereochemistry of the products in which the
newly formed π-bonds have rearranged to the more stable
tetrasubstituted conjugate enone position (Figure 1).
1
Analysis of the H NMR spectrum of a typical product
shows a ‘medium’ coupling constant of about 6 Hz for H-
3a as a result of being coupled to H-4. This key coupling
constant seems to be proportional to the endo structure.
Conversely, the exo isomer is expected to show a ‘large’
3JH,H coupling constant for the same proton. A support to
this analogy is the observation made by Fields et al. for a
closely related exo structure with 3JH,H of about 13 Hz for
SYNLETT 2012, 23, 2073–2076
Advanced online publication: 03.08.2012
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0031-1290438; Art ID: ST-2012-B0414-L
© Georg Thieme Verlag Stuttgart · New York

2074
M. S. Abaee et al.
LETTER
a similar proton.12 In order to verify the proposed stereo- Analysis of the reaction mixtures showed the presence of
chemistry, a single crystal of 4h was prepared and ana- a single product 12 in each case. Products 12 were isolated
lyzed by X-ray crystallography.13 The results are depicted and when subjected to react with 3a under the same con-
in Figure 2 and clearly support the formation of endo ste- ditions, again high yields of 4a–h were obtained within
reoisomer as the sole DA product of the reaction.
60–90 minutes. Alternatively, in refluxing toluene high-
yield formation of the same adducts was observed within
6–8 hours but along with exo isomers in ratios ranging
from 8:1 to 10:1 for the major and minor isomers, respec-
tively (Scheme 2).
Table 1 One-Pot Synthesis of 4
O
O
O
O
O
TMSNEt2
LiClO4
O
O
+
+
O
Ar
O
O
O
O
O
O
3a
Ar
1
2
4
O
+
O
Entry
Ar
Ph
Product Time (min) Yield (%)a
Ar
Ar
O
12
3a
4
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
120
120
105
75
80
80
84
86
78
72
80
80
Scheme 2
2-naphthyl
4-MeC6H4
4-MeOC6H4
4-ClC6H4
3-BrC6H4
1-furyl
To show the generality of the method, we extended the
procedure to the reactions of 1 with 3b (X = NPh) and dif-
ferent aldehydes (Table 2). Experiments showed that un-
der exactly the same conditions (TMSNEt2 and LiClO4)
the intermediate dienes added efficiently to the dienophile
to again solely produce endo DA adducts 5 in high yields
within 60–120 minutes. In all cases, no formation of exo
counterparts was detected under the Lewis acidic condi-
tions, as also was previously noticed for stepwise synthe-
sis of the same products.9
90
150
120
120
4g
4h
1-thienyl
a Isolated yields.
Table 2 One-Pot Synthesis of 5
O
O
NPh
O
NPh
O
TMSNEt2
LiClO4
O
O
+
+
Ar
O
3b
Ar
1
2
5
3
Figure 1 Diagnostic JH,H couplings in exo (left) and endo (right)
diastereomers. For a better perception, only H-3a and H-4 are shown.
Entry
Ar
Ph
Product
Yield (%)a
1
2
3
4
5
6
7
8
5a
5b
5c
5d
5e
5f
82
82
86
88
80
74
82
82
2-naphthyl
4-MeC6H4
4-MeOC6H4
4-ClC6H4
3-BrC6H4
1-furyl
5g
5h
1-thienyl
a Isolated yields.
To further explore the scope of the method, we are cur-
rently studying the incorporation of singly activated di-
enophiles into the reaction. So far, the stepwise process
has successfully been carried out. The process is regio-
and stereoselective, and more attempts on the tandem ver-
sion of the reaction are under way. Figure 3 shows the rep-
Figure 2 Crystal structure of 4h. Displacement ellipsoids at 50%
probability level.
To get a grasp of the mechanism, reactions were stopped
before the addition of the dienophile and after TLC
showed the complete consumption of 1 and the aldehydes.
Synlett 2012, 23, 2073–2076
© Georg Thieme Verlag Stuttgart · New York

LETTER
Direct Synthesis of Dehydrodecaline Derivatives
2075
the mixture. The mixture was diluted with Et2O and washed with
brine (2 × 10 mL). The organic phase was dried over Na2SO4, and
the volatiles were removed under reduced pressure. Upon concen-
tration, the mixture solidified, and the solid was recrystallized by
means of EtOAc to obtain the final product.
resentative products obtained from the reaction of three
typical dienes 12 with methyl acrylate along with the X-
ray depiction of one of the major endo adducts 6b.14
(3aS*,4S*,9bS*)-7,7-Dimethyl-4-(naphthalen-2-yl)-4,5,7,8-tet-
rahydronaphtho[1,2-c]furan-1,3,9(3aH,6H,9bH)-trione (4b)
Mp 143–145 °C. IR (KBr): 1863, 1780, 1728, 1654 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 7.94–7.84 (m, 3 H), 7.61–7.45 (m, 2 H),
7.40 (d, J = 8.0 Hz, 1 H), 7.02 (s, 1 H), 4.82 (d, J = 9.0 Hz, 1 H),
3.98–3.88 (m, 2 H), 2.95 (dd, J = 11.0, 17.0 Hz, 1 H), 2.57–2.37 (m,
5 H), 1.12 (s, 3 H), 1.09 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3):
δ = 195.7, 169.6, 169.1, 159.7, 136.5, 133.8, 133.5, 130.8, 129.6,
128.5, 126.7, 125.8, 125.3, 125.1, 121.6, 50.8, 46.1, 44.4, 39.9,
35.5, 33.5, 33.1, 29.1, 27.3 ppm. MS (70 eV): m/z = 374 [M+], 302,
246, 141, 128. Anal. Calcd for C24H22O4: C, 76.99; H, 5.92. Found:
C, 77.22; H, 6.11.
(3aS*,4S*,9bS*)-4-(4-Methoxyphenyl)-7,7-dimethyl-4,5,7,8-tet-
rahydronaphtho[2,1-c]furan-1,3,9(3aH,6H,9bH)-trione (4d)
Mp 197–199 °C. IR (KBr): 1859, 1722, 1645 cm–1. 1H NMR (300
MHz, CDCl3): δ = 7.08 (d, J = 8.5 Hz, 2 H), 6.85 (d, J = 8.5 Hz, 2
H), 4.49 (d, J = 9.0 Hz, 1 H), 3.7 (s, 3 H), 3.61–3.56 (dd, J = 6.0, 9.0
Hz, 1 H), 3.39 (dd, J = 6.0, 12.0 Hz, 1 H), 2.63–2.26 (m, 6 H), 1.13
(s, 3 H), 1.06 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 198.3,
177.3, 176.2, 158.6, 157.32, 132.5, 128.8, 128.4, 127.2, 114.2,
114.0, 55.2, 50.7, 47.2, 45.4, 44.0, 39.7, 33.6, 32.9, 29.1, 27.1 ppm.
MS (70 eV): m/z = 354 [M+], 282, 227, 108. Anal. Calcd for
C21H22O5: C, 71.17; H, 6.26. Found: C, 71.23; H, 6.33.
(3aS*,4S*,9bS*)-4-(3-Bromophenyl)-7,7-dimethyl-4,5,7,8-tet-
rahydronaphtho[1,2-c]furan-1,3,9(3aH,6H,9bH)-trione (4f)
Mp 111–113 °C. IR (KBr): 1722, 1649 cm–1. 1H NMR (300 MHz,
CDCl3): δ = 7.42 (d, J = 7.5 Hz, 1 H), 7.36 (s, 1 H), 7.27–7.14 (m,
2 H), 4.60 (d, J = 9.0 Hz, 1 H), 3.70 (dd, J = 6.0, 9.0 Hz, 1 H), 3.30–
3.24 (m, 1 H), 2.70–2.26 (m, 6 H), 1.08 (s, 3 H), 1.07 (s, 3 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 195.7, 170.1, 168.4, 157.9, 140.5,
130.9, 130.2, 126.4, 126.1, 125.0, 122.7, 50.8, 45.8, 45.4, 39.3,
38.2, 33.2, 32.8, 28.6, 27.6 ppm. MS (70 eV): m/z = 402 [M+], 332,
277, 175. Anal. Calcd for C20H19BrO4: C, 59.57; H, 4.75. Found: C,
59.63; H, 4.80.
Figure 3 DA adducts of 12 with methyl acrylate (top) and crystal
structure of 6b with displacement ellipsoids at 50% probability level
(bottom)
In conclusion, we have reported a convenient and efficient
tandem protocol for the synthesis of dehydrodecaline de-
rivatives. Products are prepared in high yields using a one-
pot procedure without separation of the intermediate di-
enes. Reactions with highly substituted and hetero dieno-
philes are under study in our laboratory. Investigations to
access milder reaction conditions are also in progress.
(3aS*,4S*,9bS*)-4-(Furan-2-yl)-7,7-dimethyl-4,5,7,8-tetrahy-
dronaphtho[1,2-c]furan-1,3,9(3aH,6H,9bH)-trione (4g)
Mp 193–195 °C. IR (KBr): 1855, 1722, 1649 cm–1. 1H NMR (300
MHz, CDCl3): δ = 7.32 (d, J = 2.0 Hz, 1 H), 6.30 (dd, J = 2.0, 3.0
Hz, 1 H), 6.10 (d, J = 3.0 Hz, 1 H), 4.43 (d, J = 8.5 Hz, 1 H), 3.63
(dd, J = 5.5, 8.5 Hz, 1 H), 3.56 (dd, J = 5.5, 11.0 Hz, 1 H), 2.71–2.26
(m, 6 H), 1.11 (s, 3 H), 1.04 (s, 3 H) ppm. 13C NMR (75 MHz,
CDCl3): δ = 195.9, 170.3, 168.2, 156.0, 151.2, 141.6, 124.2, 110.6,
107.9, 50.9, 45.6, 43.8, 38.2, 33.2, 33.1, 32.2, 28.2, 28.0 ppm. MS
(70 eV): m/z = 314 [M+], 242, 186. Anal. Calcd for C18H18O5: C,
68.78; H, 5.77. Found: C, 68.93; H, 6.01.
Melting points are uncorrected. FTIR spectra were recorded using
KBr disks on a Shimadzu Prestige-21 spectrometer. NMR spectra
were obtained on a FT-NMR Bruker Ultra ShieldTM (500 MHz) as
CDCl3 solutions using TMS as internal standard reference. Elemen-
tal analyses were performed using a Thermo Finnigan Flash EA
1112 instrument. MS spectra were obtained on a Fisons 8000 Trio
instrument at ionization potential of 70 eV. TLC experiments were
carried out on precoated silica gel plates using PE–EtOAc (4:1) as
the eluent. TMSNEt2 was synthesized using known procedures.15
All other chemicals and starting materials were purchased from
commercial sources. Aldehydes were redistilled or recrystallized
before being used. Products 4a,c,e16 and 5a–h8 are known and were
identified by the comparison of their spectroscopic data with those
available in the literature.
(3aR*,4S*,9bS*)-7,7-Dimethyl-4-(thiophen-2-yl)-4,5,7,8-tetra-
hydronaphtho[1,2-c]furan-1,3,9(3aH,6H,9bH)-trione (4h)
Mp 191–193 °C. IR (KBr): 1724, 1645 cm–1. 1H NMR (300 MHz,
CDCl3): δ = 7.20 (dd, J = 1.0, 5.0 Hz, 1 H), 6.95–6.88 (m, 2 H), 4.41
(d, J = 9.0 Hz, 1 H), 3.84 (dd, J = 5.5, 10.5 Hz, 1 H), 3.61 (dd, J =
5.5, 9.0 Hz, 1 H), 2.78–2.26 (m, 6 H), 1.15 (s, 3 H), 1.04 (s, 3 H)
ppm. 13C NMR (75 MHz, CDCl3): δ = 195.9, 170.5, 167.9, 155.8,
139.9, 127.1, 126.8, 126.7, 125.2, 51.0, 45.7, 45.6, 38.0, 35.9, 33.6,
33.3, 28.8, 27.6 ppm. MS (70 eV): m/z = 330 [M+], 257, 202, 173.
Anal. Calcd for C18H18O4S: C, 65.43; H, 5.49. Found: C, 65.66; H,
5.70.
Typical Procedure for Tandem Reactions
A mixture of an aldehyde (2.0 mmol), enone 1 (276 mg, 2.0 mmol),
N-(trimethylsilyl)diethylamine (416 μL, 2.2 mmol), and LiClO4
(213 mg, 2 mmol) was stirred at r.t. under an inert atmosphere until
TLC showed the consumption of the majority of the reactants. To
this mixture was added maleic anhydride (196 mg, 1 mmol), and the
stirring was continued while the course of the reaction was moni-
tored by TLC experiments until all the reactants disappeared from
(2′S*,3′R*)-Methyl 7′,7′-Dimethyl-5′-oxo-1′,2′,3′,4′,5′,6′,7′,8′-
octahydro-1,2′-binaphthyl-3′-carboxylate (6a)
1
Mp 89–91 °C. IR (KBr): 1732, 1654, 1444 cm–1. HNMR (300
MHz, CDCl3): δ = 8.00 (d, J = 8.0 Hz, 1 H), 7.88 (d, J = 1.5, 8.0 Hz,
© Georg Thieme Verlag Stuttgart · New York
Synlett 2012, 23, 2073–2076

2076
M. S. Abaee et al.
LETTER
1 H), 7.76 (d, J = 8.0 Hz, 1 H), 7.57–7.34 (m, 4 H), 4.10 (ddd, J =
4.5, 5.0, 9.0 Hz, 1 H), 3.34 (s, 3 H), 3.25 (ddd, J = 4.0, 4.5, 5.5 Hz,
1 H), 3.18 (dd, J = 9.5, 19.0 Hz, 1 H), 2.83–2.65 (m, 2 H), 2.54 (d,
J = 5.0, 19.0 Hz, 1 H), 2.36 (s, 2 H), 2.31 (s, 2 H), 1.11 (s, 6 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 198.7, 173.7, 154.5, 137.5, 133.9,
131.4, 129.2, 128.5, 127.6, 126.2, 125.5, 125.2, 123.6, 122.4, 51.4,
51.1, 45.3, 42.7, 34.9, 34.8, 33.3, 29.1, 27.4, 24.8 ppm. MS (70 eV):
m/z 362 [M+], 302, 246. Anal. Calcd for C24H26O3: C, 79.53; H,
7.23. Found: C, 79.68; H, 7.40.
1957. (g) Liu, Y.; Hu, H.-Y.; Liu, Q.-J.; Hu, H.-W.; Xu, J. H.
Tetrahedron 2007, 63, 2024.
(4) (a) Pellissier, H. Adv. Synth. Catal. 2012, 354, 237. (b) Oe,
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1996, 96, 195. (c) Nandaluru, P. R.; Bodwel, G. J. Org. Lett.
2012, 14, 310. (d) Strübing, D.; Neumann, H.; Klaus, S.;
Hübner, S.; Beller, M. Tetrahedron 2005, 61, 11333.
(6) (a) Fringuelli, F.; Taticchi, A. The Diels–Alder Reacion:
Selected Practical Methods; John Wiley and Sons:
Chichester, 2002, 1–25. (b) Oppolzer, W. In Comprehensive
Organic Synthesis, Vol. 5; Trost, B. M., Ed.; Pergamon
Press: New York, 1991. (c) Gioia, C.; Bernardi, L.; Ricci, A.
Synthesis 2010, 1612.
(7) (a) Mojtahedi, M. M.; Abaee, M. S.; Khakbaz, M.; Alishiri,
T.; Samianifard, M.; Mesbah, A. W.; Harms, K. Synthesis
2011, 3821. (b) Abaee, M. S.; Mojtahedi, M. M.; Pasha, G.
F.; Akbarzadeh, E.; Shockravi, A.; Mesbah, A. W.; Massa,
W. Org. Lett. 2011, 13, 5282. (c) Abaee, M. S.; Mojtahedi,
M. M.; Hamidi, V.; Mesbah, A. W.; Massa, W. Synthesis
2008, 2122. (d) Abaee, M. S.; Mojtahedi, M. M.; Zahedi, M.
M.; Sharifi, R.; Khavasi, H. Synthesis 2007, 3339. (e) Abaee,
M. S.; Mojtahedi, M. M.; Forghani, S.; Ghandchi, N. M.;
Forouzani, M.; Sharifi, R.; Chaharnazm, B. J. Braz. Chem.
Soc. 2009, 20, 1895.
(8) Mojtahedi, M. M.; Abaee, M. S.; Zahedi, M. M.; Jalali, M.
R.; Mesbah, A. W.; Massa, W.; Yaghoubi, R.; Forouzani, M.
Monatsh. Chem. 2008, 139, 917.
(9) Abaee, M. S.; Mojtahedi, M. M.; Rezaei, M. T.; Khavasi, H.
Acta Chim. Slov. 2011, 58, 605.
(10) As a result of a series of optimization reactions, the quoted
conditions were selected. Under other sets of conditions, the
yields of the desired intermediate dienes were low and
reactions did not proceed efficiently.
(2R*,3S*)-Methyl 6,6-Dimethyl-8-oxo-3-p-tolyl-1,2,3,4,5,6,7,8-
octahydronaphthalene-2-carboxylate (6b)
1
Mp 99–101 °C. IR (KBr): 1732, 1660, 1434 cm–1. H NMR (300
MHz, CDCl3): δ = 7.10 (d, J = 8.0 Hz, 2 H), 7.01 (d, J = 8.0 Hz, 2
H), 3.5 (s, 3 H), 3.46–3.42 (m, 1 H), 2.97–2.94 (m, 1 H), 2.74 (dd,
J = 5.0, 18.5 Hz, 1 H), 2.66–2.62 (m, 2 H), 2.48 (dd, J = 4.5, 18.5
Hz, 1 H) 2.35 (s, 2 H), 2.33 (s, 3 H), 2.29 (s, 2 H), 1.11 (s, 3 H), 1.09
(s, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 198.8, 174.2, 154.2,
139.1, 136.8, 129.6, 129.5, 127.8, 51.8, 51.7, 45.6, 44.1, 40.1, 36.8,
33.6, 29.0, 28.5, 22.7, 21.4 ppm. MS (70 eV): m/z = 326 [M+], 295,
266, 251, 210. Anal. Calcd for C21H26O3: C, 77.27; H, 8.03. Found:
C, 77.38; H, 7.92.
(2R*,3S*)-Methyl 3-(4-Chlorophenyl)-6,6-dimethyl-8-oxo-
1,2,3,4,5,6,7,8-octahydronaphthalene-2-carboxylate (6c)
Mp 129–131 °C. IR (KBr): 1732, 1662, 1521 cm–1. 1H NMR (300
MHz, CDCl3): δ = 7.22 (dd, J = 8.0 Hz, 2 H), 7.03 (d, J = 8.0 Hz, 2
H), 3.55 (s, 3 H), 3.43 (ddd, J = 4.0, 6.0, 10.0 Hz, 1 H), 2.95 (ddd,
J = 3.5, 4.0, 5.5 Hz, 1 H), 2.67–2.59 (m, 3 H), 2.46–2.40 (m, 1 H),
2.32 (s, 2 H), 2.25 (s, 2 H), 1.07 (s, 3 H), 1.05 (s, 3 H) ppm. 13C
NMR (75 MHz, CDCl3): δ = 198.3, 173.4, 153.2, 140.2, 132.7,
129.1, 128.8, 128.5, 51.4, 51.3, 45.1, 43.5, 39.4, 36.0, 33.2, 28.5,
28.0, 22.2 ppm. MS (70 eV): m/z = 346 [M+], 286, 230, 165, 125.
Anal. Calcd for C20H23ClO3: C, 69.26; H, 6.68. Found: C, 69.42; H,
6.50.
(11) For a review on the use of LiClO4 in catalysis of organic
reactions, see: Bartoli, G.; Locatelli, M.; Melchiorre, P.;
Sambri, L. Eur. J. Org. Chem. 2007, 2037.
(12) Fields, E. K.; Dunlap, R. W.; Bruck, M.; Podias, A.; Hall,
H. K. Jr. J. Org. Chem. 1989, 54, 2244.
Acknowledgment
Authors would like to thank Iran National Science Foundation
(INSF-88002449) for financial support of this work.
(13) Crystallographic data for 4h has been deposited with the
Cambridge Crystallographic Data Center as supplementary
publication no. CCDC-880918. Copies of these data can be
obtained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [fax: +44(1223)336033;
e-mail: deposit@ccdc.cam.ac.uk or via
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
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References and Notes
www.ccdc.cam.ac.uk/conts/retrieving.html].
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Synlett 2012, 23, 2073–2076
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