Highly regioselective diels-alder reaction of 9-substituted anthracenes with citraconic anhydride

Article abstract of DOI:10.1055/s-0033-1340629

The regioselectivity in the Diels-Alder reaction of 9-substituted anthracenes having electron-releasing substituents with citraconic anhydride has been investigated. The ortho regioisomer is preferred in all the cases with good yield. The reaction proceed

Full text of DOI:10.1055/s-0033-1340629

696▌
LETTER
letter
Highly Regioselective Diels–Alder Reaction of 9-Substituted Anthracenes with
Citraconic Anhydride
Diels–Alder Reaction of 9-Substituted Anthracenes
Ruhima Khan, Thokchom Prasanta Singh, Moirangthem Dhaneshwar Singh*
Department of Chemistry, Manipur University, Canchipur 795 003, Manipur, India
Fax +91(385)2435145; E-mail: moirangthemds@yahoo.co.in
Received: 25.11.2013; Accepted after revision: 19.12.2013
O
Abstract: The regioselectivity in the Diels–Alder reaction of 9-
substituted anthracenes having electron-releasing substituents with
R
O
O
citraconic anhydride has been investigated. The ortho regioisomer
is preferred in all the cases with good yield. The reaction proceeded
best under conventional heating conditions in toluene.
O
R
solvent
O
+
72–96 h
Key words: Diels–Alder reaction, regioselective, diastereoselec-
tivity, cycloaddition, solvent effects
O
1a–f
2
3a–f
ortho
Scheme 1 Diels–Alder reaction of 9-substituted anthracenes with
citraconic anhydride
The Diels–Alder reaction is one of the most useful and re-
liable synthetic strategies for obtaining structural and ste-
reochemical complexity.1,2 This has been proved by its
various applications in total synthesis3,4 and asymmetric
synthesis.5,6 Various works had been reported which im-
prove the scope, reactivity, and selectivity that makes the
Diels–Alder reaction an extremely powerful and versatile
synthetic tool.7 The Diels–Alder reaction of nonsymmet-
rical 1,3-diene with unsymmetrical dienoplies has tremen-
dous interest to organic chemists due to regio- and
stereochemistry involved in the reaction.8,9 Among the
various organic compounds containing nonsymmetrical
1,3-diene moiety, the use of chiral 9-substituted anthra-
cenes in diastereoselective Diels–Alder cycloadditions
with maleimide and related dienophiles are well estab-
lished.10–16 Further, chiral C9-substituted anthracenes un-
dergo selective cycloadditions with various symmetric
and nonsymmetric dienophiles under thermal and Lewis
acid promoted conditions.17 The Diels–Alder reaction of
9-substituted anthracenes with unsymmetrical dieno-
philes results into the formation of two regioiosomers –
the ortho and the meta adducts. However, in most cases
the ortho adduct has been found to be the major product.
The regioselectivity has been attributed to kinetic rea-
sons.18 High meta selectivity in the Diels–Alder reactions
of 9-substituted anthracenes and 2-acetamidoacrylate has
also been reported.19
9-Substituted anthracenes of type 1 represent a 1,3-diene
system having an electron-releasing group as substituent
at the 1-position. The Diels–Alder reactions of 9-substi-
tuted anthracenes with unsymmetrical olefinic dieno-
philes usually give the ortho regioisomer as the major
adduct as compared to the meta isomer. However, in the
case of 9-substituted chiral anthracenes having consider-
ably bulky groups, the Diels–Alder reactions with non-
symmetrical dienophiles give preferentially the meta
adduct. In the present investigation, we wish to study the
stereochemical outcome of the Diels–Alder reaction of 9-
methoxymethylanthracene and its derivatives with citra-
conic anhydride. The different 9-substituted anthracenes
were prepared from the 9-anthraldehyde using different
conditions and requisite reagents.24–27 Then, initial studies
were focused on the one-pot condensation of 9-methoxy-
methylanthracene and citraconic anhydride at refluxing
conditions for 96 hours in different polar/aprotic solvents
using the Lewis acid AlCl3. The results are summarized in
Table 1.
As shown in Table 1, our attempt to perform the model re-
action of 9-methoxymethylanthracene (1 mmol) and citra-
conic anhydride (3 mmol) in refluxing benzene did not
succeed. The reaction gives a mixture of products after 96
hours of refluxing (Table 1, entry 1). However, when 9-
methoxymethylanthracene and citraconic anhydride was
reacted in refluxing toluene (Table 1, entry 2), we ob-
served that the reaction was completed in 72 hours,
and the product was confirmed as 9-(methoxymethyl)-
15-methyl-9,10,11,15-tetrahydro-9,10-[3,4]furanoanthra-
cene-12,14-dione (3a). The product is exclusively an
ortho adduct with 75% yield of the two possible isomeric
products (o/m ratio = 99:1). Then reactivity of the two
substrates was examined with other organic solvents like
DMF, CH2Cl2, and MeCN. The reactions in DMF and
CH2Cl2 (Table 1, entries 3 and 4, respectively) did not
In continuation to our interest in substituted anthra-
cenes,20,21 we also reported the stereochemistry of the
Diels–Alder reaction of 1-subsituted anthracene with dif-
ferent dienophiles.22,23 Herein, we wish to report our stud-
ies on the Diels–Alder reaction of 9-substituted
anthracenes with citraconic anhydride in which the ad-
ducts are obtained with high regioselectivity and good
yields (Scheme 1).
SYNLETT 2014, 25, 0696–0700
Advanced online publication: 14.01.2014
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9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1340629; Art ID: ST-2013-B1084-L
© Georg Thieme Verlag Stuttgart · New York

LETTER
Diels–Alder Reaction of 9-Substituted Anthracenes
697
proceed even after 96 hours of refluxing, whereas the re- these observations, we came to the conclusion that the
action in MeCN gives the product in quantitative yield best optimal reaction conditions for the Diels–Alder reac-
(Table 1, entry 5). The effect of temperature was tested tion of 9-substituted anthracenes with citraconic anhy-
with toluene (150 °C, Table 1, entry 6), but the yield re- dride are refluxing in toluene for 72 hours without any
mained the same as that under refluxing conditions. How- acid catalyst.
ever, the reaction failed to proceed without any solvent
(Table 1, entry 7).
Table 2 Optimization of Diels–Alder Reaction of 9-Methoxymeth-
ylanthracene with Citraconic Anhydridea
Table 1 Diels–Alder Reaction of 9-Methoxymethylanthracene with
O
Citraconic Anhydride in Different Solventsa
O
MeO
O
O
O
OMe
MeO
O
O
O
O
OMe
OMe
1a
+
solvent
O
3a
+
AlCl3
72–96 h
1a
ortho
+
O
acid catalyst
O
3a
ortho
+
O
4a
meta
toluene
72–96 h
O
2
O
O
Entry
Solvent
Time (h)
Temp (°C)
Yield (%)b
O
2
O
OMe
1
2
3
4
5
6
7
benzene
toluene
DMF
96
72
96
96
96
72
96
reflux
reflux
reflux
reflux
reflux
150c
–
75
35
40
45
76
–
4a
meta
CH2Cl2
MeCN
Entry
Catalyst
Time (h) Ratio (o/m) Yield (%)b
toluene
solvent-free
1
2
3
4
5
6
AlCl3
96
96
96
72
72
72
>99:1
>99:1
>99:1
–
70
68
64
–
150
FeCl3
a 9-Methoxymethylanthracene (1 mmol), citraconic anhydride (3
mmol), AlCl3 (5 mol%), solvent (5 mL).
b Isolated yield.
ZnCl2
BF3·OEt2
TFA
c In a sealed tube.
–
–
catalyst-free
>99:1
76
To evaluate the catalytic activity in the Diels–Alder reac-
tion of 9-substituted anthracenes with citraconic anhy- a 9-Methoxymethylanthracene (1 mmol), citraconic anhydride (3
mmol), toluene (5 mL).
dride, we carried out the model reaction with different
acids such as AlCl3, FeCl3, ZnCl2, BF3·OEt2, and TFA (5
b Isolated yield.
mol%) in refluxing toluene for 72–96 hours. But there was
no improvement in the reaction yield and regioselectivity
of the Diels–Alder reaction using Lewis acids (Table 2,
entries 1–3). But the reactions using BF3·OEt2 and TFA
(Table 2, entries 4 and 5) did not proceed to the expected
product but gave a tarry mixture.
To extend the scope of this reaction, different 9-substitut-
ed anthracene derivatives were then examined for their re-
actions with citraconic anhydride (2) under the optimized
conditions (Table 3). For different precursors, the reaction
proceeded very smoothly in all cases (Table 3, entries 1,
2, 4–6). However, for the precursor where the aromatic
ring with the electron-withdrawing substituent the yield
was little less (Table 3, entry 3) as compared to other de-
rivatives. Importantly, the reaction of 2 with different 9-
substituted anthracenes generates the ortho isomer as the
only product with good yield (71–82%). The configura-
tion was confirmed through 1H NMR and 13C NMR spec-
tra and thin-layer chromatography.
Next, we performed the model reaction in refluxing tolu-
ene for 72 hours without any acid catalyst and to our de-
light, the product was obtained in 76% yield with high
regioselectivity (o/m ratio = 99:1). This shows that Lewis
acids like AlCl3, FeCl3, and ZnCl2 are not effective in in-
creasing the yield or the regioselectivity of the Diels–
Alder reaction of 9-methoxymethylanthracene with citra-
conic anhydride, and acids such as BF3·OEt2 and TFA
hindered the reaction which might be due to a competitive
ring opening and subsequent decarboxylation of the citra-
conic anhydride moiety in strong acidic solution. From
In the 1H NMR spectrum of compound 3a, the protons at
C10 and the bridge are shown by the singlet peaks at δ =
4.31 and 3.14 ppm, respectively, as the dihedral angle is
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 696–700

698
R. Khan et al.
LETTER
Table 3 Diels–Alder Reactions of Citroconic Anhydride and 9-Sub-
close to 90° between these two protons. The proton-
decoupled 13C NMR spectrum of compound 3a showed
19 distinct resonances. The spectrum showed different
peaks for the two carbonyl groups at δ = 174.8 and 169.1
ppm. The high regioselectivity of the ortho product was
further authenticated from the single-crystal X-ray crys-
tallography of product 3a (CCDC-940801) as shown in
Figure 1.
stituted Anthracenes under Thermal Conditionsa (continued)
O
O
R
O
O
R
toluene
+
O
reflux, 72 h
O
3a–f
ortho
Table 3 Diels–Alder Reactions of Citroconic Anhydride and 9-Sub-
1a–f
2
stituted Anthracenes under Thermal Conditionsa
O
Entry R
Product
Ratio mp
(o/m) (°C)
Yield
(%)b
O
R
O
O
O
R
toluene
+
O
O
O
O
reflux, 72 h
Me
O
C
O
5
OCOMe
>99:1 221–223 75
3a–f
1a–f
2
ortho
3e
Entry R
Product
Ratio mp
(o/m) (°C)
Yield
(%)b
3e
O
O
O
O
O
O
OH
OMe
6
OH
>99:1 176–179 80
1
OMe
>99:1 189–192 76
3a
3f
3a
a Reaction conditions: 9-substituted anthracene (1 mmol), 2 (3 mmol),
toluene (5 mL; reflux for 72 h).
O
b Isolated yield.
O
O
OC2H5
2
3
4
OEt
>99:1 196–198 82
>99:1 163–165 71
>99:1 203–205 78
3b
O
O
O
Br
Figure 1 ORTEP diagram for the compound 3a
Br
In conclusion, we developed a procedure for the Diels–
Alder reaction of 9-substituted anthracenes with citracon-
ic anhydride. The reaction proceeds under thermal condi-
tions without any catalyst. Citraconic anhydride having a
methyl group is successfully used as a dienophile in the
Diels–Alder reaction with 9-substituted anthracenes giv-
ing exclusively the ortho isomer.
3c
O
O
O
O
O
C
OCOPh
General Experimental Methods
3d
All the commercial reagents were used without further purification.
All solvents were HPLC grade. Column chromatography was per-
formed on silica gel (100–200 mesh). TLC was carried out with sil-
3d
1
ica gel 60-F-254 plates. The H NMR and 13C NMR spectra were
recorded on a 400 MHz Jeol ECS-400 (100 MHz for 13C) spectrom-
Synlett 2014, 25, 696–700
© Georg Thieme Verlag Stuttgart · New York

LETTER
Diels–Alder Reaction of 9-Substituted Anthracenes
699
eter using either residual solvent signals as an internal reference or
from internal TMS on the δ scale (for CDCl3: δH = 7.24 ppm, δC =
77.0 ppm; for DMSO-d6: δH = 2.52 ppm, δC = 41.23 ppm). The
chemical shifts (δ) are reported in ppm. The following abbreviations
are used: m (multiplet), s (singlet), br s (broad singlet), d (doublet),
t (triplet) dd (doublet of doublet). FTIR spectra were obtained using
FTIR spectrophotometer as KBr disc and reported in cm–1. All melt-
ing points were measured in open glass capillary and values are un-
corrected using a melting point apparatus. Crystal structures were
recorded on a single-crystal X-ray diffractometer.
Anthracen-9-ylmethylbenzoate (1f)
To a solution of 9-anthracenemethanol (200 mg, 0.96 mmol) in dry
CH2Cl2 (10 mL) were added pyridine (152 μL, 7.2 mmol), DMAP
(12 mg, 0.10 mmol), and benzoyl chloride (223 μL, 1.92 mmol) at
0 °C, and the solution was stirred at same temperature for 1 h. The
solvent was removed under removed pressure to obtain a residue
which was purified by column chromatography over silica gel (10%
EtOAc in PE) to furnish the pure compound 1f as pale yellow solid
(180 mg, 67%); mp 118–119 °C. 1H NMR (CDCl3): δ = 8.47 (s, 1
H), 8.38 (d, J = 8.8 Hz, 2 H), 7.99 (d, J = 8.4 Hz, 2 H), 7.92 (d, J =
8.3 Hz, 2 H), 7.43–7.53 (m, 5 H), 7.19–7.29 (m, 2 H), 6.33 (s, 2 H).
13C NMR (CDCl3): δ = 166.8, 133.0, 131.4, 131.2, 130.0, 129.7,
129.2,129.1, 128.5, 128.3, 127.9, 126.7, 126.2, 125.1, 124.0, 123.7,
121.4, 59.4. IR (KBr): 3067, 3002, 2880, 1789, 1603, 1424, 1296,
936 cm–1; Anal. Calcd for C22H16O2: C, 84.59; H, 5.16; O, 10.24.
Found: C, 84.50, H, 5.09, O, 10.21.
9-Anthracenemethanol (1a)
Pale yellow solid; yield: 990 mg (98%); mp 159–162 °C (lit.24 162–
64 °C). 1H NMR (CDCl3): δ = 8.50 (s, 1 H), 8.45 (d, J = 7.5 Hz, 2
H), 8.06 (d, J = 7.5 Hz, 2 H), 7.63–7.52 (m, 4 H), 5.72 (s, 2 H), 1.59
(br s, 1 H) ppm. 13C NMR (CDCl3): δ = 131.6, 131.0, 130.2, 129.2,
128.4, 126.50, 125.1, 123.9, 57.5 ppm. IR (KBr): 3452, 3045, 2961,
2910, 1622, 1443, 1277, 983, 739 cm–1. Anal. Calcd for C15H12O:
C, 86.51; H, 5.81; O, 7.68. Found: C, 86.31; H, 5.79; O, 7.65.
General Procedure for the Cycloaddition Reactions of Citro-
conic Anhydride and 9-Substituted Anthracenes under Ther-
mal Conditions
To a 25 mL round-bottom flask, citroconic anhydride (2, 3 equiv),
and 9-substituted anthracenes 1a–f (1 equiv) were dissolved in tol-
uene (5 mL, c 0.23 M) and stirred at reflux temperature in an oil
bath. After stirring for 72 h, TLC showed completion of reaction.
The solvent was evaporated under reduced pressure, and the residue
was purified by column chromatography using 10% EtOAc in PE to
afford the corresponding adducts in good yields (71–82%).
9-Methoxymethyl Anthracene (1b)
Yellow crystalline solid; yield: 210 mg (70%); mp 89–91 °C (lit.25
92–93 °C). 1H NMR (DMSO-d6): δ = 8.47 (s, 1 H), 8.02 (d, J = 7.8
Hz, 2 H), 7.91 (d, J = 7.8 Hz, 2 H), 7.54–7.39 (m, 2 H), 7.33 (d, J =
7.2 Hz, 2 H), 5.34 (s, 2 H), 3.47 (s, 3 H). 13C NMR (DMSO-d6): δ =
131.5, 130.3, 128.5, 128.2, 127.8, 125.9, 124.5, 124.1, 66.2, 58.1.
IR (KBr): 3023, 2977, 2924, 1623, 1447, 1344, 1188, 1087, 940,
894, 738, 729 cm–1. Anal. Calcd for C16H14O: C, 86.45; H, 6.35; O,
7.20. Found: C, 86.41; H, 6.24; O, 7.15.
9-(Methoxymethyl)-15-methyl-9,10,11,15-tetrahydro-9,10-
[3,4]furanoanthracene-12,14-dione (3a)
Colorless crystalline solid; yield: 342 mg (76%). 1H NMR (CDCl3):
δ = 7.46 (d, J = 7.6 Hz, 1 H), 7.22–7.32 (m, 2 H), 7.06–7.21 (m, 5
H), 4.59–4.65 (q, 2 H), 4.31 (s, 1 H), 3.64 (s, 3 H), 3.14 (s, 1 H), 1.22
(s, 3 H). 13C NMR (CDCl3): δ = 174.8, 169.1, 140.0, 139.5, 138.1,
127.5, 127.4, 127.1, 126.5, 125.9,125.5, 124.0, 122.0, 68.8, 59.4,
53.2, 51.5, 49.1, 22.7. IR (KBr): 3073, 2963, 2930, 2845, 1841,
1745, 1439, 1235, 918, 751 cm–1. Anal. Calcd for C21H18O4: C,
75.43; H, 5.43; O, 19.14. Found: C, 75.25; H, 5.40; O, 19.03.
9-Ethoxymethyl Anthracene (1c)
To a solution of 9-anthracenemethanol (300 mg, 1.44 mmol) in an-
hydrous THF (10 mL) was added NaH (150 mg, 8.6 mmol), and the
solution was stirred at r.t. for 3 min. Then iodoethane (347 μg, 4.32
mmol) was added at r.t. The mixture was stirred for 12 h at r.t. and
then poured in the H2O. The aqueous layer was extracted with EtO-
Ac (3 × 10 mL). The combined organic layers were washed with
brine (20 mL) and dried over Na2SO4. The solvent was removed un-
der reduced pressure to obtain a residue which was purified by col-
umn chromatography over silica gel (eluent: 2% EtOAc in PE) to
furnish the pure compound 1c as yellow solid (300 mg, 88%); mp
101–103 °C. 1H NMR (CDCl3): δ = 7.53 (d, J = 15.4 Hz, 1 H), 7.32
(d, J = 7.1 Hz, 1 H), 7.28 (t, J = 4.3 Hz, 1 H), 7.22 (d, J = 4.6 Hz, 2
H), 7.11–7.20 (m, 4 H), 4.67 (s, 1 H), 3.82–3.89 (q, 2 H), 1.36 (t, J
= 7.3 Hz, 3 H). 13C NMR (CDCl3): δ = 139.3, 137.8, 129.7, 129.5,
128.2, 128.0, 127.4, 127.3, 127.0, 126.5, 126.2, 126.0, 125.2, 124.1,
71.2, 67.2,15.2. IR (KBr): 3023, 3012, 2934, 2922, 2843, 1403,
1223, 915, 723 cm–1. Anal. Calcd for C17H16O: C, 86.40; H, 6.82;
O, 6.77. Found: C, 86.21; H, 6.70; O, 6.65.
Compound 3b
Colorless solid; yield: 362 mg (82%). 1H NMR (CDCl3): δ = 7.52
(d, J = 7.8 Hz, 1 H), 7.27–7.33 (m, 2 H), 7.22 (d, J = 4.6 Hz, 1 H),
7.11–7.20 (m, 4 H), 4.63–4.70 (q, 2 H), 4.32 (s, 1 H), 3.84–3.90 (q,
2 H), 3.17 (s, 1 H), 1.35 (t, J = 6.9 Hz, 3 H), 1.25 (s, 3 H). 13C NMR
(CDCl3): δ = 174.9, 169.1, 140.3, 140.1, 139.6, 138.3, 127.5, 127.4,
127.0, 126.5, 125.8, 125.4, 124.2, 122.1, 67.2, 66.6, 53.2, 53.1,
51.5, 49.1, 22.7, 15.2. IR (KBr): 3083, 3061, 2949, 2932, 2872,
1843, 1759, 1423, 1229, 921, 753 cm–1. Anal. Calcd for C22H20O4:
C, 75.84; H, 5.79; O, 18.37. Found: C, 75.34; H, 5.70; O, 18.27.
Compound 3c
9-Bromomethylanthracene (1d)
Colorless crystalline solid; yield: 299 mg (71%). 1H NMR (CDCl3):
δ = 7.63 (s, 1 H), 7.34 (d, J = 6.8 Hz, 1 H), 7.18–7.28 (m, 6 H), 4.91
(br s, 1 H), 4.51 (br s, 1 H), 4.33 (s, 1 H), 3.40 (s, 1 H), 1.29 (s, 3 H).
13C NMR (CDCl3): δ = 174.9, 168.1, 140.5, 139.8, 138.5, 127.9,
127.4, 127.2, 126.8, 126.1, 125.5, 124.8, 122.3, 53.1, 51.4, 48.1,
44.0, 22.7. IR (KBr): 3079, 2961, 2934, 2861, 2853, 1840, 1762,
1430, 1215, 925, 750 cm–1. Anal. Calcd for C20H15BrO3: C, 62.68;
H, 3.95; Br, 20.85; O, 12.52. Found: C, 62.61; H, 3.75; Br, 20.35;
O, 12.42.
Yellow solid (1.6 g, 82%); mp 145–147 °C (lit.26 143–146 °C). 1H
NMR (DMSO-d6): δ = 7.89 (s, 1 H), 7.27–7.65 (m, 8 H), 5.11 (s, 2
H). 13C NMR (DMSO-d6): δ = 131.8, 130.2, 128.5, 127.3, 125.9,
125.7,125.2, 31.0. IR (KBr): 3067, 2958, 2832, 1605, 1462, 1380,
1197, 912 cm–1. Anal. Calcd for C15H11Br: C, 66.44; H, 4.09; Br,
29.47. Found: C, 66.23; H, 4.11; Br, 29.35.
Anthracen-9-ylmethylacetate (1e)
Yellow crystalline solid; yield: 240 mg (67%); mp 114–115 °C
(lit.27 115–116 °C). 1H NMR (DMSO-d6): δ = 8.47 (s, 1 H), 8.29 (d,
J = 9.2 Hz, 2 H), 7.99 (d, J = 8.8 Hz, 2 H), 7.43–7.55 (m, 4 H), 6.11
(s, 2 H), 2.04 (s, 3 H). 13C NMR (DMSO-d6): δ = 171.3, 131.4,
131.0, 129.2, 129.1, 126.7, 126.2, 125.1, 123.9, 58.8, 21.0. IR
(KBr): 3206, 2316, 1658, 1605, 1462, 1380, 1197, 912, 735 cm–1;
Anal. Calcd for C17H14O2: C, 81.58; H, 5.64; O, 12.78. Found: C,
81.50; H, 5.56; O, 12.70.
Compound 3d
Colorless crystalline solid; yield: 317 mg (78%). 1H NMR (CDCl3):
δ = 7.89(d, J = 7.6 Hz, 2 H), 7.20–7.40 (m, 11 H), 5.75 (d, J = 16.0
Hz, 1 H), 5.57 (d, J = 12.0 Hz, 1 H), 4.74 (s, 1 H), 2.97 (s, 1 H), 1.27
(s, 3 H). 13C NMR (CDCl3): δ = 173.1, 169.7, 166.4, 140.1, 138.3,
138.2, 138.1, 133.4, 129.8, 129.5, 128.5, 127.9, 127.8, 127.5, 127.1,
125.3, 125.2, 124.3, 124.2, 60.7, 57.5, 54.8, 51.1, 46.2, 20.8. IR
(KBr): 3075, 3020, 2934, 2863, 2839, 1842, 1786, 1673, 1453,
1289, 915, 743 cm–1. Anal. Calcd for C27H20O5: C, 76.40; H, 4.75;
O, 18.85. Found: C, 76.10; H, 4.25; O, 18.80.
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 696–700

700
R. Khan et al.
LETTER
Compound 3e
(5) Kazutaka, S.; Kentaro, F.; Fumito, K.; Seiji, I.; Hisashi, Y.
J. Am. Chem. Soc. 2010, 132, 5625.
(6) (a) Futatsugi, K.; Yamamoto, H. Angew. Chem. Int. Ed.
2005, 44, 1484. (b) Liu, D.; Canales, E.; Corey, E. J. J. Am.
Chem. Soc. 2007, 129, 1498.
(7) Corey, E. J. Angew. Chem. Int. Ed. 2002, 41, 1650.
(8) Mehta, G.; Uma, R. Acc. Chem. Res. 2000, 33, 278.
(9) Kanishchev, O. S.; Sanselme, M.; Bouillon, J. P.
Tetrahedron 2013, 69, 1322.
Colorless solid; yield: 325 mg (75%). 1H NMR (CDCl3): δ = 7.31–
7.40 (m, 4 H), 7.18–7.25 (m, 4 H), 5.36 (t, J = 8.8 Hz, 2 H), 4.37 (s,
1 H), 3.07 (s, 1 H), 2.20 (s, 3 H), 1.30 (s, 3 H). 13C NMR (CDCl3):
δ = 172.0, 169.5, 166.2, 140.2, 139.8, 139.3, 138.3, 128.2, 127.2,
127.0, 126.6, 125.7, 125.0, 123.8, 122.0, 65.2, 58.5, 57.3, 53.8,
51.0, 46.2, 20.2. IR (KBr): 3083, 2978, 2939, 2874, 1840, 1777,
1729, 1459, 1251, 932,735 cm–1. Anal. Calcd for C22H18O5: C,
72.92; H, 5.01; O, 22.08. Found: C, 72.52; H, 5.23; O, 22.10.
(10) Liu, X.; Snyder, J. K. J. Org. Chem. 2008, 73, 2935.
(11) Burgess, K. L.; Corbett, M. S.; Eugenio, P.; Lajkiewicz, N.
J.; Liu, X.; Sanyal, A.; Yan, W.; Yuan, Q.; Snyder, J. K.
Bioorg. Med. Chem. 2005, 13, 5299.
(12) Sanyal, A.; Yuan, Q.; Snyder, J. K. Tetrahedron Lett. 2005,
46, 2475.
(13) Burgess, K. L.; Lajkiewicz, N. J.; Sanyal, A.; Yan, W.;
Snyder, J. K. Org. Lett. 2005, 7, 31.
(14) Corbett, M. S.; Liu, X.; Sanyal, A.; Snyder, J. K.
Tetrahedron Lett. 2003, 44, 931.
Compound 3f
Colorless crystalline solid; yield: 368 mg (80%). 1H NMR (CDCl3):
δ = 7.63 (d, J = 17.6 Hz, 1 H), 7.57 (d, J = 15.6 Hz, 1 H), 7.34 (d, J
= 6.4 Hz, 1 H), 7.11–7.30 (m, 5 H), 5.02 (d, J = 11.2 Hz, 1 H), 4.90
(d, J = 11.2 Hz, 1 H), 4.33 (s, 1 H), 3.17 (s, 1 H), 1.78 (br s, 1 H),
1.26 (s, 3 H). 13C NMR (CDCl3): δ = 173.9, 168.2, 140.0, 139.0,
137.9, 127.3, 127.2, 127.0, 126.3, 125.7, 125.3, 123.9, 122.0, 65.8,
56.5, 54.2, 48.2, 41.5, 22.3. IR (KBr): 3582, 3088, 3021, 2951,
1840, 1778, 1651, 1456, 1224, 926, 750, 526 cm–1. Anal. Calcd for
C20H16O4: C, 74.99; H, 5.03; O, 19.98. Found: C, 74.91; H, 5.01; O,
19.92.
(15) Jones, S.; Valette, D. Org. Lett. 2009, 11, 5358.
(16) (a) Adams, H.; Jones, S.; Ojea-Jimenez, I. Org. Biomol.
Chem. 2006, 4, 2296. (b) Adams, H.; Bawa, A. R.; Jones, S.
Org. Biomol. Chem. 2006, 4, 4206.
Acknowledgment
(17) Sanyal, A.; Snyder, J. K. Org. Lett. 2000, 2, 2527.
(18) Alston, P. V.; Ottenbrite, R. M.; Newby, J. J. Org. Chem.
1979, 44, 4939.
We thank the University Grant Commission (UGC), New Delhi, In-
dia for financial support.
(19) Yang, B. V.; Doweyko, L. M. Tetrahedron Lett. 2005, 46,
2857.
(20) Verma, S. M.; Singh, M. D. J. Org. Chem. 1977, 42, 3736.
(21) Singh, M. D.; Jay, S.; Silvio, E. B.; Kurt, M. J. Am. Chem.
Soc. 1987, 109, 3397.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
m
iotSrat
ungIifoop
r
t
(22) Singh, M. D.; Anjana, N. Indian. J. Chem., Sect. B: Org.
Chem. Incl. Med. Chem. 2010, 49, 789.
(23) Singh, M. D.; Anjana, N. Indian J. Chem. Sect. B, Org.
Chem. Incl. Med. Chem. 2010, 49, 77.
(24) Xie, F.; Sivakumar, K.; Zeng, Q.; Bruckman, M. A.; Hodges,
B.; Wand, Q. Tetrahedron 2008, 64, 2906.
(25) Zimmermman, C.; Mohr, M.; Zipse, H.; Eichberger, R.;
Schnabel, W. J. Photochem. Photobiol. A. 1999, 125, 47.
(26) Lan, P.; Berta, D.; Porco, J. A. Jr.; South, M. S.; Parlow, J.
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References and Notes
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(2) (a) Corey, E. J.; Guzman-Perez, A. Angew. Chem. Int. Ed.
1998, 37, 388. (b) Brocksom, T. J.; Nakamura, J.; Ferreira,
M. L.; Brocksom, U. J. Braz. Chem. Soc. 2001, 12, 597.
(3) Nicolaou, K. C.; Snyder, S. A.; Montagnon, T.;
Vassilikogiannakis, G. Angew. Chem. Int. Ed. 2002, 41,
1668.
(4) (a) Williams, R. M.; Stocking, E. M. Angew. Chem. Int. Ed.
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Synlett 2014, 25, 696–700
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