Regioselective palladium(II)-catalyzed desulfitative heck-type reaction: Access to α-benzyl-β-keto esters from Baylis-Hillman adducts and sodium sulfinates

Article abstract of DOI:10.1055/s-0033-1339663

A new palladium(II)-catalyzed desulfitative Heck-Type arylation from sodium arenesulfinates and Baylis-Hillman adducts for the synthesis of highly functionalized α-benzyl-β-keto ester derivatives in good to excellent yields has been developed. This methodology is simple and mild, it can utilize halogen bearing building blocks, and it has excellent regioselectivity. Georg Thieme Verlag Stuttgart ? New York.

Full text of DOI:10.1055/s-0033-1339663

PAPER
▌2867
paper
Regioselective Palladium(II)-Catalyzed Desulfitative Heck-Type Reaction:
Access to α-Benzyl-β-keto Esters from Baylis–Hillman Adducts and Sodium
Sulfinates
Palladium(II)-Catalyzed Desulfitative Heck-Type Reaction
Kammari Bal Raju, Vellakkaran Mari, Kommu Nagaiah*
Organic & Biomolecular Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad-500007, India
Fax +91(40)27191659; E-mail: nagaiah@iict.res.in
Received: 10.06.2013; Accepted after revision: 01.08.2013
structural motif with various important applications in or-
Abstract: A new palladium(II)-catalyzed desulfitative Heck-Type
ganic synthesis, and they have been extensively used in
arylation from sodium arenesulfinates and Baylis–Hillman adducts
the construction of natural products and other biologically
for the synthesis of highly functionalized α-benzyl-β-keto ester de-
rivatives in good to excellent yields has been developed. This meth-
active heterocyclic molecules (Scheme 1).2 Many efforts
odology is simple and mild, it can utilize halogen bearing building have been made to achieve efficient preparation of these
blocks, and it has excellent regioselectivity.
scaffolds through palladium-catalyzed Heck reaction be-
tween Baylis–Hillman adducts3 and various aryl sources4
Key words: Heck reaction, Baylis–Hillman adducts, palladium,
desulfitative, α-benzyl-β-keto esters
[Scheme 2 (a)].
However, these methods suffer limited scope despite good
yields, they require long reaction times at reflux, and they
have a small methodological scope which lacks chemo-
and regioselectivity. Recently, our group has reported a
method for synthesis of α-benzyl-β-keto esters with good
yields from arylboronic acids used as arylpalladium(II)
precursors with Baylis–Hillman adducts.5
The development of synthetic organic chemistry mostly
depends on reactions involving the formation of new C–C
bonds. The Heck reaction is one of the most important
versatile C–C bond forming reactions catalyzed by a tran-
sition metal.1 α-Benzyl-β-keto esters are a predominant
R
O
H
N
NH
O
NH
N
N
N
O
H
O
ref. 2k
inhibitors of hepatitis C
virus polymerase
ref. 2j
HIV 1 reverse transcriptase inhibitors
anti-hepatitis B activity
O
O
OR
ref. 2h
Me
O
Me
O
N
ref. 2i
O
Me
N
OR
O
O
O
Me
O
insecticides
tumor necrosis factor inhibitors
Scheme 1 Synthetic applications of α-benzyl β-keto esters
SYNTHESIS 2013, 45, 2867–2874
Advanced online publication: 15.08.2013
0
0
3
9
-
7
8
8
1
1
4
3
7
-
2
1
0
X
DOI: 10.1055/s-0033-1339663; Art ID: SS-2013-Z0394-OP
© Georg Thieme Verlag Stuttgart · New York

2868
K. B. Raju et al.
PAPER
previous works
OH
O
OH
O
O
O
R1
OR2
Ha
O
Pd
R1
OR2
HO
R1
R1
OR2
1
OR2
+
+
(a)
Hb
X
Pd(II)
Ar
Ar
Ar
Ar
2
3
3′
Hb
X = Br, I, N2+BF4
–
this work
OH
O
Ha
O
O
O
HO
R1
R1
OR2
PdII
OR2
R1
OR2
(b)
1
Pd(II)
+
Ar
Ar
SO2Na
3
Ar
2
R
1 = alkyl, aryl, heterocycle
R2 = Me, Et, n-Bu
Scheme 2 Palladium-catalyzed synthesis of α-benzyl-β-keto esters from Baylis–Hillman adducts
In recent years, desulfitative coupling for the construction when palladium(II) chloride was used as the palladium(II)
of C–C bonds by using arenesulfinic acids,6 sodium precursor (entry 22) instead of palladium(II) acetate (en-
arenesulfinates,7 and, less frequently, arenesulfonyl try 10) and copper(II) chloride was used as the oxidant;
chlorides8 as aryl sources via the extrusion of SO2 has at- this gave 3a in a good 86% yield (entry 23); Increasing the
tracted increasing attention. Sulfinic acid salts are gener- amount of catalyst from 5 mol% to 10 mol% gave 3a in
ally used as sulfonylation reagents in the preparation of excellent yield (entry 24). Under the optimized reaction
compounds containing sulfonyl groups.9 Most recently, conditions (entry 24) products of Hb-hydride elimination
the palladium-catalyzed desulfitative C–C bond forming 3′ [Scheme 2 (a)] or decarboxylation were not observed13
reactions of sodium arenesulfinates with alkenes, nitriles, indicating total regioselectivity in the respective migrato-
and aldehydes have been reported.10 We have chosen so- ry aryl insertion and hydride elimination (Ha) steps in the
dium arenesulfinates as arylpalladium(II) precursors be- catalytic cycle [Scheme 2 (b)].
cause they are stable in air and easy to handle; thus,
With the optimized reaction conditions (Table 1, entry 24)
sodium arenesulfinates are ideal aryl sources.6,10a,11 Here-
in hand, the palladium-catalyzed desulfitative addition re-
in, we report the first regioselective desulfitative Heck-
type coupling of Baylis–Hillman adducts with sodium
sulfinates [Scheme 2 (b)].
action was then extended to a wide array of sodium arene-
sulfinates 2 and Baylis–Hillman adducts 1 to explore the
scope and limitation of the reaction (Table 2). The halo-
At the outset of our study, the regioselective desulfitative gen-bearing Baylis–Hillman adducts and sodium arene-
Heck-type arylation was investigated with butyl 2-[hy- sulfinates gave the desired products 3b–i in good yields
droxy(4-tolyl)methyl]acrylate (1a) and sodium benzene- and excellent chemoselectivity without concomitant for-
sulfinate (2a) as the model substrates (Table 1). The use mation of competitive palladium(0)-catalyzed Heck and
of palladium(II) acetate or chloride in presence of various dehalogenation byproducts. 1-Heteroaryl Baylis–Hillman
ligands12 and oxidants gave the product 3a in low yields adducts gave the corresponding products 3i–l in reason-
(entries 1–9). However, in the absence of a ligand, the re- able yields. Even the 1-alkyl-substituted substrates gave
action gave 3a in a moderate 45% yield (entry 10). Next, the corresponding coupling products 3m,n in excellent
we examined conditions without a ligand by replacing the yields. The 2-methylphenyl-substituted Baylis–Hillman
oxidant copper(II) acetate monohydrate with other oxi- adduct undergoes efficient coupling with sodium ben-
dants such as copper(II) acetate, copper(I) bromide, cop- zenesulfinate to give 3r in 78% yield. Finally, electron-
per(II) bromide, silver carbonate, silver(I) acetate, and deficient or electron-rich Baylis–Hillman adducts and so-
oxygen, this gave 3a in unsatisfactory 18–34% yields (en- dium arenesulfinates afforded 3o–w in good to excellent
tries 11–16). The effect of solvent was also investigated yields.
by the replacement of 1,4-dioxane with other solvents like
An incomplete reaction was observed, when arenesulfo-
acetic acid, acetonitrile, dimethylformamide, 1,2-dichlo-
nyl chlorides were used as the aryl source in the Heck re-
roethane, and toluene; this furnished 3a in poor <5–25%
action with a Baylis–Hillman adduct, and in the presence
yields (entries 17–21). An improved yield was observed
of strong base with high temperature (>160 °C) the corre-
Synthesis 2013, 45, 2867–2874
© Georg Thieme Verlag Stuttgart · New York

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Palladium(II)-Catalyzed Desulfitative Heck-Type Reaction
2869
Table 1 Optimization of the Reaction Conditionsa
O
O
OH
O
Pd(II)
oxidant
SO2Na
OBu
OBu
+
solvent
8 h
1a
2a
3a
Entry
Pd(II)
Oxidant
Solvent (°C)
Yieldb (%)
1
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
CuBrc
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
AcOH (100)
<5
<5
<5
<5
<5
8
2
CuBrd
c
3
Cu(OAc)2
4
Cu(OAc)2·H2Oc
Cu(OAc)2·H2Od
Cu(OAc)2·H2Oe
Cu(OAc)2·H2Oc
Cu(OAc)2·H2Od
Cu(OAc)2·H2Oe
Cu(OAc)2·H2O
Cu(OAc)2
5
6
7
10
12
11
45
33
22
34
25
20
18
<5
20
25
23
20
65
86
97
11
8
PdCl2
9
PdCl2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24f
25f
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
CuBr
CuBr2
Ag2CO3
PdCl2
AgOAc
PdCl2
O2
PdCl2
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
Cu(OAc)2·H2O
CuCl2
PdCl2
MeCN (90)
PdCl2
DMF (100)
PdCl2
DCE (80)
PdCl2
toluene (90)
PdCl2
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
1,4-dioxane (90)
PdCl2
PdCl2
CuCl2
PdCl2
a Unless specified, the reaction was carried out with: 1a (0.5 mmol), 2a (0.6 mmol), Pd catalyst (0.05 equiv), solid oxidant (1.0 equiv) or O2
balloon (1 atm); solvent (3.0 mL); 8 h.
b Isolated yield (average of 2 runs).
c 1,10-Phenanthroline (0.1 equiv).
d 2,9-Dimethyl-1,10-phenanthroline (0.1 equiv).
e 2,2′-Bipyridyl.
f Pd (0.1 equiv).
sponding α-benzyl-β-keto ester 3a was formed in 65% A plausible mechanism to rationalize this transformation
isolated yield (Scheme 3). From this domino effect, it is is illustrated in Scheme 4. Although the mechanism is not
apparent that sodium arenesulfinates are ideal aryl well understood at this stage, on the basis of above obser-
sources.
vations, we proposed that a plausible catalytic route could
consist the following steps: (a) coordination of sodium
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2013, 45, 2867–2874

2870
K. B. Raju et al.
PAPER
O
O
OH
O
SO2Cl
(20%)
OBu
OBu
+
b, c
(65%)
3a
4
1a
Scheme 3 Palladium-catalyzed synthesis of α-benzyl-β-keto esters from Baylis–Hillman adducts with arenesulfonyl chlorides (a) standard
condition: 1a (0.5 mmol), 4 (0.6 mmol), PdCl2 (0.1 equiv), CuCl2 (1.0 equiv), 1,4-dioxane (3.0 mL), 90 °C, 8.0 h, 20% yield; (b) 1a (0.5 mmol),
4 (0.6 mmol), PdCl2 (0.1 equiv), CuCl2 (1.0 equiv), Na2CO3 (1.0 equiv), 1,4-dioxane (3.0 mL), 160 °C, 16.0 h, 65% yield; (c) 1a (0.5 mmol),
4 (0.6 mmol), PdCl2 (0.1 equiv), without CuCl2, Na2CO3 (1.0 equiv), 1,4-dioxane (3.0 mL), 160 °C, 8.0 h, 0% yield.
arenesulfinate to palladium(II) to give complex A; (b) de-
sulfitative reaction of the sulfinic acid salt to generate the
arylpalladium complex B; (c) oxidative addition of the
olefinic group to form complex C; (d) reductive elimina-
tion followed by enol isomerization to produce the desired
product D. When an oxidant was not used, incomplete re-
action was observed and this supports the formation of
palladium(0) and the necessity of the oxidant to regener-
ate the palladium(II) species in the catalytic cycle (Table
1, entry 25). A detailed experimental and theoretical in-
vestigation of mechanistic insight is in progress.
Table 2 Preparative Scope of α-Benzyl-β-keto Esters from Baylis–
Hillman Adducts
O
O
SO2Na
OH
O
R1
OR2
PdCl2, CuCl2
R1
OR2
1,4-dioxane, 90 °C
R3
R3
1
2
3
R1
R2
R3
Product
Yield (%)
4-NCC6H4
4-O2NC6H4
4-MeOC6H4
4-BrC6H4
Ph
Bu
Bu
Bu
Bu
Et
Cl
Br
Br
Me
Br
H
3b
3c
3d
3e
3f
83
81
93
87
92
87
91
79
86
80
92
96
94
87
92
80
78
95
89
92
92
95
O
S
Ar
ONa
CuX2
Pd0
PdX2
O
HX
S
Ar
A
O
4-BrC6H4
Ph
Bu
Et
3g
3h
3i
XPd
Cl
Br
H
HPdX
2-thienyl
2-furyl
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Bu
Et
SO2
O
O
O
B
ArPdX
OH
H
3j
O
HO
R1
R1
OR2
OR2
PdX
2-furyl
Me
H
3k
3l
R1
OR2
D
Ar
2-thienyl
(CH2)4Me
(CH2)6Me
4-NCC6H4
4-MeOC6H4
4-O2NC6H4
2-MeC6H4
Ph
Ar
C
H
3m
3n
3o
3p
3q
3r
3s
Scheme 4 Proposed reaction pathway
H
In summary, a new and efficient method for palladi-
um(II)-catalyzed desulfitative Heck-Type arylation was
demonstrated from sodium arenesulfinates and Baylis–
Hillman adducts to access highly functionalized α-benzyl-
β-keto ester derivatives in good to excellent yields. This
reaction took place under mild conditions and it tolerates
a wider range of functionalities than previously possible;
methyl, bromo, and chloro on the sodium arenesulfinate
were all well tolerated under these reaction conditions.
Therefore this methodology offers an alternative to palla-
dium-catalyzed aryl halide, arenediazonium tetrafluoro-
borate salts, and arylboronic acids addition to Baylis–
Hillman adducts. Further investigation of the scope,
mechanism, and synthetic applications of this reaction are
in progress.
Me
H
H
H
Me
Me
H
Ph
Me
Bu
Bu
Bu
3t
4-i-PrC6H4
Ph
3u
3v
3w
H
Ph
Me
Synthesis 2013, 45, 2867–2874
© Georg Thieme Verlag Stuttgart · New York

PAPER
Palladium(II)-Catalyzed Desulfitative Heck-Type Reaction
2871
All solvents and reagents were used, as received. TLC was per-
formed on Merck Kiesel gel 60, F254 plates; 0.25-mm thickness.
Column chromatography was performed on silica gel (100–200
mesh) with a EtOAc–hexane gradient. Melting points were deter-
mined on a Fisher Johns melting point apparatus and are uncorrect-
ed. IR spectra were recorded on a Perkin-Elmer RX-1 FT-IR
system. 1H NMR spectral data were collected at 300, 400, and 500
MHz, while 13C NMR were recorded at 75, 100 and 150 MHz.
HRMS (ESI) spectral data were collected using an ORBITRAP
high resolution mass spectrometer.
13C NMR (75 MHz, CDCl3): δ = 192.9, 168.4, 150.5, 140.6, 136.8,
131.7, 130.6, 129.5, 123.9, 120.9, 65.8, 56.5, 33.8, 30.3, 18.9, 13.5.
MS (ESI): m/z = 434 [M + H]+, 456 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C20H20BrNNaO5: 456.0462;
found: 456.04010.
Butyl 2-(4-Bromobenzyl)-3-(4-methoxyphenyl)-3-oxopropano-
ate (3d)
Colorless liquid; yield: 0.194 g (93%).
IR (neat): 2959, 2928, 1732, 1677, 1599, 1511, 1216, 1171, 1070,
1029, 841, 771, 667 cm–1.
α-Benzyl-β-keto Esters 3 from Baylis–Hillman Adducts; Gener-
al Procedure
1H NMR (300 MHz, CDCl3): δ = 8.01–7.91 (m, 2 H), 7.41–7.36 (m,
2 H), 7.12 (d, J = 8.4 Hz, 2 H), 6.96–6.91 (m, 2 H), 4.55 (t, J = 7.4
Hz, 1 H), 4.05 (t, J = 6.6 Hz, 2 H), 3.88 (s, 3 H), 3.28 (d, J = 7.4 Hz,
2 H), 1.54–1.41 (m, 2 H), 1.18 (d, J = 14.8 Hz, 2 H), 0.84 (t, J = 7.3
Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 192.3, 169.3, 163.9, 137.6, 131.5,
131.1, 130.7, 129.1, 120.5, 113.9, 65.4, 55.6, 34.1, 30.4, 29.7, 18.9,
13.5.
A mixture of sulfinic acid sodium salt 2 (0.60 mmol), PdCl2 (0.10
equiv), Baylis–Hillman adduct 1 (0.50 mmol), and CuCl2 (1.0
equiv) was dissolved in 1,4-dioxane (3.0 mL) in a 10-mL round-
bottomed flask. The mixture was vigorously stirred at 90 °C for 8 h.
After cooling to r.t., the mixture was partitioned between EtOAc
(25.0 mL) and H2O (25.0 mL) and filtered through a celite pad. The
filtrate was transferred to a separatory funnel, and the organic layer
was washed with H2O and brine, dried (anhyd Na2SO4), and con-
centrated in vacuo. The resulting residue was purified by column
chromatography (gradient, hexane–EtOAc) to afford the pure prod-
uct.
MS (ESI): m/z = 419 [M + H]+, 441 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C21H23BrNaO4: 441.08269;
found: 441.08368.
Butyl 2-Benzyl-3-oxo-3-(4-tolyl)propanoate (3a)
Butyl 3-(4-Bromophenyl)-2-(4-methylbenzyl)-3-oxopropano-
ate (3e)
Colorless liquid; yield: 0.158 g (97%).
IR (neat): 3026, 2960, 2930, 1733, 1681, 1606, 1454, 1273, 1215,
1181, 909, 748, 698, 666, 595 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.88 (d, J = 8.3 Hz, 1 H), 7.36–
7.13 (m, 8 H), 4.62 (t, J = 7.3 Hz, 1 H), 4.05 (t, J = 6.5 Hz, 2 H),
3.34 (d, J = 7.3 Hz, 2 H), 2.42 (s, 3 H), 1.56–1.40 (m, 2 H), 1.18 (m,
2 H), 0.83 (t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 194.1, 169.5, 144.4, 138.5, 133.7,
129.4, 128.9, 128.8, 128.5, 126.6, 65.3, 56.1, 34.7, 30.4, 21.6, 18.8,
13.5.
Colorless liquid; yield: 0.175 g (87%).
IR (neat): 2959, 2926, 1735, 1688, 1584, 1515, 1455, 1378, 1271,
1220, 1172, 1070, 1008, 931, 841, 810, 772, 653, 571 cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.95 (d, J = 8.5 Hz, 1 H), 7.85–
7.78 (m, 2 H), 7.63–7.56 (m, 2 H), 7.43 (d, J = 8.3 Hz, 1 H), 7.09
(q, J = 8.2 Hz, 2 H), 4.55 (t, J = 7.4 Hz, 1 H), 4.05 (t, J = 6.6 Hz, 2
H), 3.30 (d, J = 7.3 Hz, 2 H), 2.30 (s, 3 H), 1.54–1.41 (m, 2 H), 1.18
(dt, J = 14.8, 7.3 Hz, 2 H), 0.84 (t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 193.6, 169.1, 136.2, 135.1, 132.1,
130.2, 130.1, 129.2, 128.7, 127.1, 65.5, 56.3, 34.2, 30.3, 21.1, 18.9,
13.5.
MS (ESI): m/z = 325 [M + H]+, 347 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C21H25O3: 325.17976; found:
MS (ESI): m/z = 403 [M + H]+, 425 [M + Na]+.
325.17982.
HRMS (ESI): m/z [M + Na]+ calcd for C21H23BrNaO3: 425.07228;
found: 425.07176.
Butyl 2-(4-Chlorobenzyl)-3-(4-cyanophenyl)-3-oxopropanoate
(3b)
Colorless solid; yield: 0.154 g (83%); mp 76–80 °C.
Ethyl 2-(4-Bromobenzyl)-3-oxo-3-phenylpropanoate (3f)
Colorless liquid; yield: 0.167 g (92%).
IR (neat): 3020, 2961, 2232, 1734, 1692, 1492, 1216, 1093, 1015,
931, 848, 817, 771, 667 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.06–7.99 (m, 2 H), 7.80–7.73 (m,
2 H), 7.30–7.22 (m, 2 H), 7.20–7.12 (m, 2 H), 4.56 (t, J = 7.4 Hz, 1
H), 4.05 (t, J = 6.6 Hz, 2 H), 3.32 (d, J = 7.4 Hz, 2 H), 1.48 (m, 2
H), 1.28–1.10 (m, 2 H), 0.84 (t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 193.1, 168.4, 139.1, 136.3, 132.6,
130.3, 128.9, 128.8, 117.7, 116.8, 65.8, 56.3, 33.7, 30.3, 18.8, 13.5.
MS (ESI): m/z = 370 [M + H]+, 392 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C21H20ClNO3: 392.10239;
IR (neat): 3021, 2982, 2929, 2871, 1733, 1686, 1596, 1488, 1446,
1403, 1368, 1302, 1268, 1215, 1181, 1153, 1100, 966, 931, 852,
813, 746, 688, 665, 620 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.95 (d, J = 7.8 Hz, 2 H), 7.57 (t,
J = 7.3 Hz, 1 H), 7.45 (t, J = 7.7 Hz, 2 H), 7.37 (d, J = 8.3 Hz, 2 H),
7.11 (d, J = 8.3 Hz, 2 H), 4.58 (t, J = 7.3 Hz, 1 H), 4.12–4.07 (t, J =
6.9 Hz, 2 H), 3.28 (d, J = 7.3 Hz, 2 H), 1.11 (t, J = 7.1 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 194.1, 169.1, 137.4, 136.1, 133.7,
131.6, 130.7, 128.8, 128.6, 120.5, 61.6, 55.9, 34.1, 13.9.
found: 392.10268.
MS (ESI): m/z = 363 [M + H]+, 385 [M + Na]+.
Butyl 2-(4-Bromobenzyl)-3-(4-nitrophenyl)-3-oxopropanoate
(3c)
Colorless solid; yield: 0.175 g (81%); mp 89–92 °C.
HRMS (ESI): m/z [M + Na]+ calcd for C18H17BrNaO3: 385.02976;
found: 385.02978.
Butyl 2-Benzyl-3-(4-bromophenyl)-3-oxopropanoate (3g)
Colorless liquid; yield: 0.168 g (87%).
IR (neat): 3020, 1735, 1695, 1528, 1346, 1215, 1071, 1012, 931,
852, 743, 667, 624 cm–1.
IR (neat): 2958, 2927, 1736, 1689, 1584, 1488, 1454, 1396, 1273,
1219, 1180, 1071, 1008, 940, 840, 771, 699 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.86–7.75 (m, 2 H), 7.58 (d,
J = 8.4 Hz, 2 H), 7.31–7.15 (m, 5 H), 4.56 (t, J = 7.3 Hz, 1 H), 4.02
(t, J = 15.1, 8.5 Hz, 2 H), 3.32 (d, J = 7.4 Hz, 2 H), 1.54–1.39 (m, 2
H), 1.21 (m, 2 H), 0.82 (t, J = 7.4 Hz, 3 H).
1H NMR (300 MHz, CDCl3): δ = 8.30 (d, J = 8.8 Hz, 2 H), 8.08 (d,
J = 8.8 Hz, 2 H), 7.39 (d, J = 8.3 Hz, 2 H), 7.10 (d, J = 8.3 Hz, 2 H),
4.57 (t, J = 7.4 Hz, 1 H), 4.04 (t, J = 6.6 Hz, 2 H), 3.30 (t, J = 7.2
Hz, 2 H), 1.52–1.40 (m, 2 H), 1.26–1.10 (m, 2 H), 0.82 (t, J = 7.3
Hz, 3 H).
© Georg Thieme Verlag Stuttgart · New York
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13C NMR (75 MHz, CDCl3): δ = 193.5, 169.1, 138.2, 135.1, 132.1,
MS (ESI): m/z = 315 [M + H]+, 337 [M + Na]+.
130.1, 128.8, 128.6, 126.7, 65.5, 56.2, 34.6, 30.4, 18.9, 13.5.
MS (ESI): m/z = 389 [M + H]+, 411 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C19H22NaO4: 337.14103;
found: 337.14072.
HRMS (ESI): m/z [M + H]+ calcd for C20H22O3Br: 389.07528;
found: 389.07468.
Butyl 2-Benzyl-3-oxo-3-(thiophen-2-yl)propanoate (3l)
Pale yellow oil; yield: 0.145 g (92%).
IR (neat): 2959, 2928, 1732, 1661, 1516, 1454, 1412, 1356, 1274,
1221, 1148, 1063, 847, 772, 726, 699, 595 cm–1.
Ethyl 2-(4-Chlorobenzyl)-3-oxo-3-phenylpropanoate (3h)
Colorless liquid; yield: 0.144 g (91%).
IR (neat): 3063, 3024, 2981, 2927, 2852, 1732, 1684, 1596, 1492,
1446, 1408, 1368, 1324, 1267, 1227, 1180, 1151, 1092, 1058, 1015,
966, 931, 896, 851, 815, 739, 688, 639, 600 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.96 (d, J = 7.8 Hz, 2 H), 7.57 (t,
J = 7.2 Hz, 1 H), 7.45 (t, J = 7.6 Hz, 2 H), 7.27–7.13 (m, 4 H), 4.59
(t, J = 7.3 Hz, 1 H), 4.10 (t, J = 6.7 Hz, 2 H), 3.29 (d, J = 7.3 Hz, 2
H), 1.11 (t, J = 7.1 Hz, 3 H).
1H NMR (300 MHz, CDCl3): δ = 7.79–7.66 (d, J = 7.1 Hz, 1 H),
7.68 (d, J = 4.9 Hz, 1 H), 7.31–7.18 (m, 5 H), 7.13 (dd, J = 8.6, 4.6
Hz, 1 H), 4.47 (t, J = 7.4 Hz, 1 H), 4.08 (t, J = 6.6 Hz, 2 H), 3.35 (d,
J = 7.4 Hz, 2 H), 1.58–1.45 (m, 2 H), 1.30–1.14 (m, 2 H), 0.85 (t,
J = 7.4 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 186.8, 169.1, 143.2, 138.5, 134.9,
133.1, 128.9, 128.5, 128.3, 126.7, 65.5, 57.4, 34.7, 30.4, 18.9, 13.6.
13C NMR (75 MHz, CDCl3): δ = 194.2, 169.1, 136.9, 136.1, 133.7,
MS (ESI): m/z = 317 [M + H]+, 339 [M + Na]+.
132.5, 130.4, 128.7, 128.6, 61.7, 55.9, 34.1, 13.9.
MS (ESI): m/z = 317 [M + H]+, 339 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C18H20NaO3S: 339.10254;
found: 325.10177.
HRMS (ESI): m/z [M + Na]+ calcd for C18H17ClNaO3: 339.34190;
found: 339.34186.
Butyl 2-Benzyl-3-oxooctanoate (3m)
Colorless liquid; yield: 0.145 g (96%).
IR (neat): 3029, 2958, 2929, 2871, 2255, 1738, 1713, 1604, 1495,
1456, 1360, 1312, 1243, 1164, 1064, 1029, 963, 908, 729, 699, 648,
594 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.26 (t, J = 7.3 Hz, 2 H), 7.21–7.13
(m, 3 H), 4.08 (t, J = 6.6 Hz, 2 H), 3.78 (t, J = 7.6 Hz, 1 H), 3.15 (t,
J = 7.2 Hz, 2 H), 2.51 (dt, J = 17.1, 7.4 Hz, 1 H), 2.32 (dd, J = 17.4,
7.3 Hz, 1 H), 1.58–1.45 (m, 4 H), 1.34–1.13 (m, 6 H), 0.86 (dt,
J = 19.1, 7.3 Hz, 6 H).
13C NMR (75 MHz, CDCl3): δ = 204.8, 169.3, 138.3, 128.8, 128.5,
126.6, 65.3, 60.5, 42.8, 34.1, 31.1, 30.5, 29.7, 23.1, 22.4, 19.1, 13.8,
13.6.
MS (ESI): m/z = 305 [M + H]+, 327 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C19H28NaO3: 327.19307;
Butyl 2-(4-Bromobenzyl)-3-oxo-3-(thiophen-2-yl)propanoate
(3i)
Colorless liquid; yield: 0.155 g (79%).
IR (neat): 3019, 1733, 1664, 1413, 1215, 1070, 1012, 744, 667 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.76 (dd, J = 3.9, 1.0 Hz, 1 H),
7.68 (dd, J = 5.0, 1.0 Hz, 1 H), 7.41–7.34 (m, 2 H), 7.14–7.07 (m, 3
H), 4.45–4.35 (t, J = 7.3 Hz, 1 H), 4.06 (t, J = 6.6 Hz, 2 H), 3.28 (d,
J = 7.4 Hz, 2 H), 1.49 (ddd, J = 14.0, 8.8, 6.6 Hz, 2 H), 1.29–1.12
(m, 2 H), 0.84 (t, J = 7.5 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 186.5, 168.7, 143.3, 137.3, 135.1,
133.1, 131.6, 130.7, 128.3, 120.6, 65.6, 57.2, 34.1, 30.4, 18.9, 13.5.
MS (ESI): m/z = 395 [M + H]+, 417 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C18H19BrNaO3S: 417.01053;
found: 327.19208.
found: 417.01019.
Butyl 2-Benzyl-3-oxodecanoate (3n)
Colorless liquid; yield: 0.156 g (94%).
Butyl 2-Benzyl-3-(furan-2-yl)-3-oxopropanoate (3j)
Colorless liquid; yield: 0.130 g (86%).
IR (neat): 2957, 2927, 2856, 2255, 1740, 1713, 1604, 1495, 1456,
1376, 1310, 1262, 1202, 1163, 1065, 1028, 907, 729, 699, 648 cm–1.
IR (neat): 3322, 2943, 2831, 1669, 1450, 1414, 1219, 1020, 915,
772, 731, 645 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.26 (t, J = 7.3 Hz, 2 H), 7.18 (dd,
J = 16.5, 7.6 Hz, 3 H), 4.08 (t, J = 6.6 Hz, 1 H), 3.78 (t, J = 7.6 Hz,
2 H), 3.15 (dd, J = 7.5, 4.2 Hz, 2 H), 2.51 (dt, J = 17.1, 7.3 Hz, 1 H),
2.32 (dt, J = 17.2, 7.2 Hz, 1 H), 1.59–1.46 (m, 4 H), 1.33–1.17 (m,
10 H), 0.88 (dt, J = 11.5, 7.3 Hz, 6 H).
13C NMR (75 MHz, CDCl3): δ = 204.8, 169.2, 138.3, 128.8, 128.5,
126.6, 65.3, 60.5, 42.9, 34.1, 31.6, 30.5, 28.8, 28.9, 23.3, 22.6, 19.1,
14.1, 13.6.
1H NMR (300 MHz, CDCl3): δ = 7.60 (dd, J = 1.6, 0.7 Hz, 1 H),
7.34–7.09 (m, 6 H), 6.54 (dd, J = 3.6, 1.7 Hz, 1 H), 4.43 (t, J = 7.5
Hz, 1 H), 4.08 (t, J = 6.6 Hz, 2 H), 3.33 (d, J = 7.5 Hz, 2 H), 1.52
(m, 2 H), 1.23 (m, 2 H), 0.86 (t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 183.1, 169.1, 151.9, 146.9, 138.2,
128.9, 128.5, 126.6, 118.5, 112.5, 65.4, 56.3, 34.2, 30.4, 18.9, 13.6.
MS (ESI): m/z = 301 [M + H]+, 323 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C18H21O4: 301.14344; found:
MS (ESI): m/z = 333 [M + H]+, 355 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C21H32NaO3: 355.22437;
325.14323.
found: 355.22340.
Butyl 3-(Furan-2-yl)-2-(4-methylbenzyl)-3-oxopropanoate (3k)
Colorless liquid; yield: 0.127 g (80%).
Butyl 3-(4-Cyanophenyl)-2-(4-methylbenzyl)-3-oxopropanoate
IR (neat): 2960, 2928, 1733, 1676, 1566, 1515, 1464, 1391, 1216,
1155, 1015, 880, 771, 667, 592 cm–1.
(3o)
Colorless liquid; yield: 0.152 g (87%).
1H NMR (300 MHz, CDCl3): δ = 7.60 (dd, J = 1.6, 0.7 Hz, 1 H),
7.29–7.23 (m, 2 H), 7.10 (dd, J = 17.7, 8.1 Hz, 3 H), 6.54 (dd,
J = 3.6, 1.7 Hz, 1 H), 4.40 (t, J = 7.5 Hz, 1 H), 4.08 (t, J = 6.6 Hz, 2
H), 3.29 (d, J = 7.4 Hz, 2 H), 2.30 (s, 3 H), 1.51 (dt, J = 14.6, 6.7
Hz, 2 H), 1.31–1.16 (m, 2 H), 0.85 (t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 183.2, 169.1, 152.1, 146.9, 136.1,
135.2, 129.2, 128.8, 118.5, 112.5, 65.3, 56.4, 33.7, 30.4, 21.1, 18.9,
13.6.
IR (neat): 3021, 2960, 2930, 2232, 1734, 1692, 1515, 1460, 1404,
1269, 1218, 1113, 1063, 1018, 931, 850, 808, 770, 667 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.99 (d, J = 8.3 Hz, 2 H), 7.72 (d,
J = 8.3 Hz, 2 H), 7.06 (q, J = 8.1 Hz, 4 H), 4.55 (t, J = 7.3 Hz, 1 H),
4.04 (t, J = 6.6 Hz, 2 H), 3.29 (d, J = 7.3 Hz, 2 H), 2.27 (s, 3 H), 1.45
(dt, J = 13.3, 6.6 Hz, 2 H), 1.21–1.11 (m, 2 H), 0.82 (t, J = 7.4 Hz,
3 H).
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13C NMR (75 MHz, CDCl3): δ = 193.6, 168.7, 139.4, 136.4, 134.7,
132.5, 129.3, 128.9, 128.7, 117.7, 116.6, 65.6, 56.6, 34.2, 30.3,
21.1, 18.8, 13.5.
MS (ESI): m/z = 350 [M + H]+, 372 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C22H23NNaO3: 372.15701;
13C NMR (75 MHz, CDCl3): δ = 194.6, 169.3, 136.2, 136.2, 135.3,
133.5, 129.2, 128.8, 128.67, 61.5, 56.3, 34.3, 21.1, 13.9.
MS (ESI): m/z = 297 [M + H]+, 319 [M + Na]+
HRMS (ESI): m/z [M + Na]+ calcd for C19H20NaO3: 319.13047;
found: 319.12958.
found: 372.15659.
Methyl 2-(4-Methylbenzyl)-3-oxo-3-phenylpropanoate (3t)
Colorless liquid; yield: 0.125 g (89%).
Butyl 2-Benzyl-3-(4-methoxyphenyl)-3-oxopropanoate (3p)
Colorless liquid; yield: 0.156 g (92%).
IR (neat): 2924, 2254, 1737, 1686, 1596, 1581, 1515, 1446, 1329,
1273, 1231, 1148, 904, 809, 723, 648, 584 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.95 (d, J = 7.3 Hz, 2 H), 7.55 (d,
J = 7.3 Hz, 1 H), 7.44 (t, J = 7.5 Hz, 2 H), 7.15–7.01 (m, 4 H), 4.63
(t, J = 7.3 Hz, 1 H), 3.63 (s, 3 H), 3.29 (dd, J = 7.0, 3.3 Hz, 2 H),
2.28 (s, 3 H).
13C NMR (75 MHz, CDCl3): δ = 194.5, 169.8, 136.2, 136.1, 135.3,
133.6, 129.3, 128.7, 128.7, 128.4, 56.1, 52.5, 34.4, 21.1.
MS (ESI): m/z = 283 [M + H]+, 305 [M + Na]+.
HRMS (ESI): m/z [M + Na]+ calcd for C18H18NaO3: 305.11482;
IR (neat): 2959, 2927, 2871, 1732, 1676, 1575, 1510, 1456, 1420,
1310, 1258, 1222, 1116, 1062, 1026, 968, 940, 840, 698, 635, 600,
563 cm–1.
1H NMR (300 MHz, CDCl3): δ = 7.93 (d, J = 8.8 Hz, 2 H), 7.27–
7.11 (m, 5 H), 6.88 (d, J = 8.8 Hz, 2 H), 4.50 (t, J = 7.7 Hz, 1 H),
4.06–3.98 (t, J = 6.8 Hz, 2 H), 3.85 (s, 3 H), 3.30–3.26, (d, J = 3.4
Hz, 2 H), 1.51–1.43 (m, 2 H), 1.24–1.17 (m, 2 H), 0.84 (t, J = 7.4
Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 191.9, 169.1, 163.6, 138.6, 130.9,
129.3, 128.8, 128.4, 126.4, 113.7, 96.2, 64.9, 55.8, 55.2, 34.7, 30.4,
29.7, 18.9, 13.6.
found: 305.11386.
MS (ESI): m/z = 353 [M + H]+, 375 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C21H25O4: 353.21112; found:
Butyl 2-Benzyl-3-(4-isopropylphenyl)-3-oxopropanoate (3u)
Colorless liquid; yield: 0.161 g (92%).
325.21115.
IR (neat): 2962, 1733, 1681, 1604, 1457, 1273, 1217, 1057, 907,
847, 728, 698, 667 cm–1.
Butyl 2-Benzyl-3-(4-nitrophenyl)-3-oxopropanoate (3q)
Colorless solid; yield: 0.143 g (80%); mp 86–88 °C.
IR (neat): 3020, 1736, 1696, 1529, 1346, 1214, 742, 667 cm–1.
1H NMR (300 MHz, CDCl3): δ = 8.27 (d, J = 8.8 Hz, 2 H), 8.06 (d,
J = 8.8 Hz, 2 H), 7.33–7.12 (m, 5 H), 4.62 (t, J = 7.4 Hz, 1 H), 4.05
(t, J = 6.6 Hz, 2 H), 3.36 (d, J = 7.4 Hz, 2 H), 1.56–1.37 (m, 2 H),
1.28–1.09 (m, 2 H), 0.82 (t, J = 7.3 Hz, 3 H).
1H NMR (300 MHz, CDCl3): δ = 7.91 (d, J = 8.3 Hz, 2 H), 7.23
(ddd, J = 10.6, 8.3, 5.3 Hz, 7 H), 4.61 (t, J = 7.3 Hz, 1 H), 4.03 (t,
J = 6.5 Hz, 2 H), 3.32 (d, J = 7.3 Hz, 2 H), 2.94 (m, 1 H), 1.52–1.38
(m, 2 H), 1.25 (d, J = 6.9 Hz, 6 H), 1.14 (d, J = 7.4 Hz, 2 H), 0.80
(t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 193.9, 169.5, 155.2, 138.5, 134.1,
128.9, 128.5, 126.8, 126.6, 65.3, 56.1, 34.7, 34.3, 30.4, 29.7, 23.6,
18.9, 13.6.
13C NMR (75 MHz, CDCl3): δ = 193.4, 168.6, 150.5, 140.8, 137.8,
129.5, 128.9, 128.7, 126.6, 123.8, 65.7, 56.6, 34.5, 30.3, 18.8, 13.5.
MS (ESI): m/z = 356 [M + H]+, 378 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C20H22NO5: 356.14925;
MS (ESI): m/z = 353 [M + H]+, 375 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C23H29O3: 353.21112; found:
325.21115.
found: 356.14947.
Butyl 2-Benzyl-3-oxo-3-phenylpropanoate (3v)
Colorless liquid; yield: 0.143 g (92%).
Butyl 2-Benzyl-3-oxo-3-(2-tolyl)propanoate (3r)
Colorless liquid; yield: 0.127 g (78%).
IR (neat): 2959, 2929, 1733, 1684, 1450, 1220, 1181, 1148, 1078,
940, 772, 688, 576 cm–1.
IR (neat): 3023, 2960, 2929, 1733, 1690, 1606, 1454, 1258, 1216,
1160, 1061, 934, 909, 748, 666, cm–1.
1H NMR (400 MHz, CDCl3): δ = 7.96 (d, J = 7.3 Hz, 2 H), 7.57 (dd,
J = 13.7, 6.5 Hz, 1 H), 7.44 (t, J = 7.5 Hz, 2 H), 7.30–7.16 (m, 5 H),
4.63 (t, J = 7.3 Hz, 1 H), 4.03 (t, J = 6.6 Hz, 2 H), 3.33 (d, J = 7.3
Hz, 2 H), 1.53–1.38 (m, 2 H), 1.32–1.09 (m, 2 H), 0.80 (t, J = 7.3
Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 194.4, 169.3, 138.5, 136.3, 133.5,
128.9, 128.6, 128.7, 128.5, 126.6, 65.6, 56.2, 34.7, 30.4, 18.8, 13.5.
1H NMR (300 MHz, CDCl3): δ = 7.55 (d, J = 7.7 Hz, 1 H), 7.37 (dd,
J = 10.9, 4.1 Hz, 2 H), 7.27–7.17 (m, 5 H), 7.01 (d, J = 6.9 Hz, 1 H),
4.54 (t, J = 7.5 Hz, 1 H), 4.17 (t, J = 6.5 Hz, 2 H), 3.33 (d, J = 6.4
Hz, 2 H), 2.44 (s, 3 H), 1.55–1.41 (m, 2 H), 1.28–1.12 (m, 2 H),
0.87–0.83 (t, J = 7.2 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 198.1, 169.4, 138.4, 131.9, 131.6,
128.9, 128.5, 128.3, 126.6, 125.6, 65.2, 58.6, 34.7, 30.4, 20.9, 18.8,
13.6.
MS (ESI): m/z = 311 [M + H]+, 333 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C20H23O3: 311.16417; found:
MS (ESI): m/z = 325 [M + H]+, 347 [M + Na]+.
HRMS (ESI): m/z [M + H]+ calcd for C21H25O3: 325.17982; found:
325.16400.
Butyl 2-(4-Methylbenzyl)-3-oxo-3-phenylpropanoate (3w)
Colorless liquid; yield: 0.154 g (95%).
325.17970.
IR (neat): 3021, 1733, 1687, 1515, 1448, 1217, 907, 728 cm–1.
Ethyl 2-(4-Methylbenzyl)-3-oxo-3-phenylpropanoate (3s)
Colorless liquid; yield: 0.140 g (95%).
1H NMR (300 MHz, CDCl3): δ = 7.96 (d, J = 7.4 Hz, 2 H), 7.56 (t,
J = 7.3 Hz, 1 H), 7.44 (t, J = 7.6 Hz, 2 H), 7.09 (dd, J = 18.0, 8.0 Hz,
4 H), 4.60 (t, J = 7.3 Hz, 1 H), 4.03 (t, J = 6.6 Hz, 2 H), 3.29 (d,
J = 7.3 Hz, 2 H), 2.28 (s, 3 H), 1.52–1.40 (m, 2 H), 1.16 (dt,
J = 14.7, 7.3 Hz, 2 H), 0.80 (t, J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): δ = 194.45, 169.38, 136.18, 136.08,
135.30, 133.44, 129.16, 128.73, 128.62, 65.27, 56.29, 34.23, 30.33,
20.97, 18.83, 13.51.
IR (neat): 2981, 2924, 2854, 2254, 1733, 1685, 1597, 1515, 1447,
1369, 1268, 1217, 1182, 1152, 1111, 1023, 906, 852, 808, 728, 689,
667, 649, 604 cm–1.
1H NMR (500 MHz, CDCl3): δ = 8.02–7.90 (d, J = 7.5 Hz, 2 H),
7.56 (t, J = 7.4 Hz, 1 H), 7.44 (t, J = 7.7 Hz, 2 H), 7.12 (d, J = 7.9
Hz, 2 H), 7.06 (d, J = 7.8 Hz, 2 H), 4.60 (t, J = 7.3 Hz, 1 H), 4.10 (t,
J = 7.1 Hz, 2 H), 3.32–3.26 (d, J = 6.2 Hz, 2 H), 2.29 (s, 3 H), 1.12
(t, J = 7.1 Hz, 3 H).
© Georg Thieme Verlag Stuttgart · New York
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MS (ESI): m/z = 325 [M + H]+, 347 [M + Na]+.
J. E.; Kim, J. N. Tetrahedron Lett. 2007, 48, 8619.
(f) Gowrisankar, S.; Lee, H. S.; Kim, J. M.; Kim, J. N.
Tetrahedron Lett. 2008, 49, 1670.
(4) (a) Bras, J. L.; Muzart, J. Synthesis 2011, 3581. (b) Muzart,
J. Tetrahedron 2005, 61, 4179. (c) Kumareswaran, R.;
Vankar, Y. D. Synth. Commun. 1998, 28, 2291.
HRMS (ESI) : m/z [M + Na]+ calcd for C21H24NaO3: 347.1617;
found: 347.1609.
Acknowledgment
(d) Basavaiah, D.; Muthukumaran, K. Tetrahedron 1998,
54, 4943. (e) Sunder, N.; Bhat, S. V. Synth. Commun. 1998,
28, 2311. (f) Coelho, F.; Ferreira, B. R. V.; Pirovani, R. V.;
Souza-Filho, L. G. Tetrahedron 2009, 65, 7712.
(g) Antunes, O. A. C.; Perez, R.; Veronese, D.; Coelho, F.
Tetrahedron Lett. 2006, 47, 1325. (h) Bennett, N. J.;
Goldby, A.; Pringle, R. Synlett 2010, 1688. (i) Hyun-Soo,
K.; Sang-Jin, L.; Boram, C.; Yoon, C. M. Synthesis 2012, 44,
3161.
We thank the Director of CSIR-Indian Institute of Chemical Tech-
nology (IICT) for the generous support. B.R. K thanks the Council
of Scientific and Industrial Research for a Senior Research Fellow-
ship and CSIR, New Delhi for financial support through the pro-
gramme ORIGIN of XII FVP (CSC0108).
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.SnuIomprifgtooatrinSugpIoi
n
nfomartit
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