Dimethylsulfoxide-promoted Strecker reaction of N-tosylaldimines with cyanoformate

Article abstract of DOI:10.1055/s-0030-1258447

A metal-free method for performing the Strecker reaction of N-tosylaldimines with ethyl cyanoformate in dimethylsulf-oxide (DMSO) has been developed. Various types of N-tosyl-aldimines undergo the cyanation to provide the N-protected -amino nitriles. This

Full text of DOI:10.1055/s-0030-1258447

PAPER
919
Dimethylsulfoxide-Promoted Strecker Reaction of N-Tosylaldimines with
Cyanoformate
D
MSO-Promo
a
ted Strecke
n
r
Reaction
o
t
f
N
-Tos
o
ylaldimines
s
w
ith
C
yan
h
oformate T. Kadam, Ponnaboina Thirupathi, Sung Soo Kim*
Department of Chemistry, Inha University, Incheon 402-751, South Korea
Fax +82(32)8675604; E-mail: sungsoo@inha.ac.kr
Received 24 December 2010; revised 20 January 2011
types (alkyl, aryl, allylic, and acetylenic) of Grignard and
organolithium compounds.8 However, few reports have
appeared for the addition of TMSCN to sulfonyl ald-
imine.9 Wang et al. successfully employed ethyl cyano-
Abstract: A metal-free method for performing the Strecker reac-
tion of N-tosylaldimines with ethyl cyanoformate in dimethylsulf-
oxide (DMSO) has been developed. Various types of N-tosyl-
aldimines undergo the cyanation to provide the N-protected a-amino
nitriles. This uncatalyzed protocol requires neither elevated temper- formate in the asymmetric Strecker reaction of aldimine.10
ature nor high pressure for the cyanations.
However, the use of ethyl cyanoformate as a cyanating
agent in the racemic Strecker reaction of N-tosylaldimines
is yet to be reported.
Key words: N-tosylaldimine, ethyl cyanoformate, a-amino nitriles,
Strecker reaction
N-Tosylaldimines are stable compounds that can further
react with various types of nucleophiles. They are pre-
pared by condensation of the corresponding aldehydes, p-
toluene sulfonamide, and sodium benzenesulfinate in the
presence of formic acid (Scheme 1).11
The addition of carbon-centered nucleophiles to carbonyl
compounds and imines is a powerful method for the con-
struction of carbon–carbon bonds. The cyanide anion it-
self adds to imines to form a-amino nitriles, which can
transfer their functionality into bioactive and natural prod-
ucts.1 a-Amino nitriles can be readily converted into a-
amino acids and various nitrogen-containing heterocy-
cles, such as imidazoles and thiadiazoles.2 a-Amino acids
manifest biological and economical significance due to
their application in chemistry and biology.3 Hydrogen cy-
anide and trimethylsilyl cyanide (TMSCN) are the most
commonly used cyanide sources for the Strecker reaction,
however, although remarkable results have been accom-
plished, some problems including high cost, toxicity, or
volatility are still associated with these approaches. To
overcome these problems, attention has been given to the
development of alternative cyanide sources that are rela-
tive cheap, less toxic, and easier to handle. In this regard,
the development of other cyanide sources has been ex-
plored, including the use of tributyltin cyanide,4a diethyl
phosphorocyanated (DEPC),4b acetyl cyanide,4c diethyl
aluminum cyanide,4d benzoyl cyanide,4e and carbonyl cy-
anide.4f Ethyl cyanoformate (CNCOOEt) has attracted at-
tention due to its stability, lower toxicity, and ready
availability.5
TsNH2
O
NHTs
SO2Ar
NTs
ArSO2Na
aq NaHCO3
CH2Cl2, r. t.
R
H
R
R
H
aq HCO2H
r. t.
1
2
3
R = aryl
Ar = p-tolyl
Scheme 1 Synthesis of N-tosylaldimines
With increasing environmental concern, the need for metal-
free and environmentally benign methods has become of
significant importance. According to the principle of
green chemistry, synthetic methods should be designed to
minimize the energy input by running the reaction at am-
bient temperature with lower amounts of reagent and/or
catalyst.12 Accordingly, efficient cyanation of aldimines
without the use of a metal catalyst is desirable.
The use of solvents as a reagent without intervention of
catalyst has been reported for various organic transforma-
tions. Watahiki et al. reported the use of dimethylsulfox-
ide (DMSO) for the cyanobenzoylation of aldehydes with
benzyl cyanide.4e The combination of DMSO with hexane
was employed for the cyanosilylation of aldehydes13a as
well as for the synthesis of silyl ethers from alcohols and
tert-butyldimethylsilyl chloride.13b Similarly, Iwanami et
al. described the synthesis of cyanohydrin carbonates in
DMSO in the presence of molecular sieves.13c Consider-
ing the activity of polar solvents, ethyl cyanoformate may
be activated in a suitable solvent without using a metal
catalyst.
a-Amino nitriles have been prepared with imines and
TMSCN by use of numerous catalytic systems,6a,b such as
vanadyl triflate,6c rhodium iodide,6d [Fe(Cp)2PF6],6e ionic
liquid,6f b-cyclodextrin,6g thallium chloride,6h and io-
dine.6i
Sulfonyl imines are considered to be versatile substrates
in organic synthesis for industrial applications.7 The sul-
fonyl imines are highly electrophilic and react with all
In light of the success of developing several catalytic sys-
tems for the cyanation of carbonyl compounds and a-ami-
do p-tolylsulfones with TMSCN,14 we wish to report
herein a simple method for the cyanation of N-tosylald-
SYNTHESIS 2011, No. 6, pp 0919–0923
Advanced online publication: 24.02.2011
DOI: 10.1055/s-0030-1258447; Art ID: F55810SS
x
x
.
x
x
.2
0
1
1
© Georg Thieme Verlag Stuttgart · New York

920
S. T. Kadam et al.
PAPER
imines with ethyl cyanoformate in DMSO. The effect
of various solvents was examined for the cyanation of
N-tosyl-p-tolylaldimine (4) with ethyl cynaoformate (5;
Table 1). Solvents such as tetrahydrofuran, acetonitrile,
methanol, dichloromethane and dioxane did not give the
desired product under the present reaction conditions
(Table 1, entries 1, 3, 4, 6 and 8). However, nitromethane
and N,N-dimethylformamide generated the desired prod-
uct within ten hours reaction time (Table 1, entries 2 and
5), albeit in low yield (14 and 10%).
Table 2 DMSO-Promoted Cyanation of N-Tosylaldimines with
Ethyl Cyanoformatea
Ts
Ts
N
O
HN
DMSO
r.t.
NC
OEt
R
CN
+
R
7
5
9
R = aryl or heteroaryl
Entry R in 7
9
Time (h) Yield (%)b
1
2
9a
2
2
2
78
82
80
Table 1 Cyanation of N-Tosyl-p-tolylaldimines with Ethyl Cyano-
formate in Various Solventsa
Ts
Ts
HN
HN
9b
9c
O
solvent
r.t.
CN
+
NC
OEt
4
5
6
3
Entry
Solvent
THF
Time (h)
Yield (%)b
n.r.
MeO
1
2
10
10
10
10
10
10
2
4
9d
9e
9f
3
3
62
55
67
n.r.
42
MeNO2
MeCN
MeOH
DMF
14
Cl
3
n.r.
5
4
n.r.
Cl
5
10
6
CH2Cl2
DMSO
n.r.
6
3
7
80
Br
8
1,4-dioxane
DMSO
10
6
n.r.
7
9g
9h
12
12
9
69c
O2N
10
DMSO
2
80d
8
a Reaction conditions: 4 (0.5 mmol), ethyl cyanoformate (1 mmol),
solvent (2 mL), r.t.
NC
b Isolated yield of the products; n.r. = no reaction.
c DMSO (1 mL) was used.
O
9
9i
9j
6
58
d MS (4 Å, 100 mg) were used in DMSO (2 mL).
10
12
n.r.
Surprisingly, polar aprotic DMSO acts as an effective sol-
vent for the cyanation, leading to product formation with
good yield (80%) in two hours (Table 1, entry 7). De-
creasing the amount of solvent (1 mL) led to lower yield
and the reaction required an extended time (Table 1, entry
9). Cyanation of N-tosyl-p-tolylaldimine with ethyl cy-
anoformate in the presence of molecular sieves (4 Å) nei-
ther increased the yield nor decreased the reaction time
(Table 1, entry 10). Accordingly, 2 mL of DMSO and 2.0
equivalents of ethyl cyanoformate were established as op-
timal for the cyanation of N-tosyl-p-tolylaldimine under
the present conditions.
11
12
9k
9l
12
12
n.r.
n.r.
a Reaction conditions: N-tosylaldimines (0.5 mmol), ethyl cyano-
formate (1 mmol), DMSO (2 mL), r.t.
b Isolated yield of products; n.r. = no reaction.
A range of aromatic N-tosylaldimines were examined in
the cyanation with ethyl cyanoformate in DMSO without
catalyst (Table 2). With electron-donating R substituents
in 7, good yields of the cyanation product were obtained
within two hours reaction time (Table 2, entries 2 and 3).
Substrates with halogen substituents on the benzene ring
of the N-tosylaldimines underwent cyanation with moder-
ate yield (Table 2, entries 4–6). p-Chloro-substituted ald-
imines substrates gave the desired products in 62% yield,
while o-chloro-substituted substrates gave 55% yield of
Synthesis 2011, No. 6, 919–923 © Thieme Stuttgart · New York

PAPER
DMSO-Promoted Strecker Reaction of N-Tosylaldimines with Cyanoformate
921
O
the corresponding cyanation products. Bromo substitu-
ents on the aldimine provided the product in 67% yield
under the reaction conditions (Table 2, entry 6). With an
electron-withdrawing group located in the phenyl ring of
7 (Table 2, entries 7 and 8), the yield was either zero or
much lower than in the case of substrates with electron-
donating groups (entries 2 and 3). This phenomenon is
consistent with other, similar, reactions,14l,15 and may in-
dicate that p-electrons of the benzene ring play some role
in the reaction mechanism.
Me
S
O
EtO
Me
CN
Me
r.t.
+
CN
Me
EtO
O
O
S
10
Ts
N
R
O
Ts
N-Tosylaldimines derived from acid-sensitive heterocy-
clic 2-furfuraldehyde underwent the reaction smoothly to
give the products in moderate yields (Table 2, entry 9). N-
Tosylaldimine, prepared form cinnamaldehyde, did not
give the corresponding cyanation product under the reac-
tion conditions (Table 2, entry 10), and the 2-naphthyl
imine was also found to be unsuitable, which may be due
to the steric hindrance of the naphthyl moiety (Table 2,
entry 11). The reaction of aliphatic N-tosylisobutyl ald-
imine gave no yield of the desired product after 12 hours
reaction time (Table 2, entry 12).
Ts
work-up
HN
EtO
N
R
CN
R
CN
11
Scheme 2 Proposed reaction pathway
moter. The various types of N-tosylaldimines derived
from aromatic and heteroaromatic aldehydes react with
ethyl cyanoformate to give the N-protected a-amino ni-
triles in good yield. The major advantages of the method
are the mild, metal-free reaction conditions and easy
work-up.
The scope of the present protocol was explored with vari-
ous cyanating agents to give the corresponding cyanation
products (Table 3).
1H NMR (200 MHz) spectra were recorded in CDCl3 with a Varian
Gemini 4000 spectrometer. Chemical shifts are reported in ppm,
with tetramethylsilane (TMS) as the internal standard. 13C NMR
data were collected with a Varian Gemini 2000 spectrometer (50
MHz).
Table 3 DMSO-Promoted Cyanation of N-Tosyl-p-tolylaldimins
with Various Cyanide Sourcesa
Entry
Cyanide source
TBACN
Time (h)
Yield (%)b
1
2
3
12
12
2
n.r.
n.r.
71
Synthesis of N-Protected a-Amino Nitriles; General Procedure
N-Tosylaldimine (0.5 mmol) was added at r.t. to a mixture of ethyl
cyanoformate (1.0 mmol) and DMSO (2 mL), and the progress of
the reaction was monitored by TLC. Upon completion of the reac-
tion, the mixture was quenched with H2O (2 mL), extracted with
CH2Cl2 (3 × 5 mL) and dried with anhydrous Na2SO4. The solvent
was evaporated and the resulting viscous mass was subjected to sil-
ica gel flash column chromatography to obtain the pure compound.
TBDMSCN
TMSCN
a Reaction conditions: N-tosylaldimine (0.5 mmol), cyanide source
(1.0 mmol), DMSO (2 mL).
b Ioslated yield; n.r. = no reaction.
All products were characterized by H, 13C NMR, IR and GC-MS
1
data, which were consistent with literature values.9d,17 HRMS val-
The cyanation of N-tosyl-p-tolylaldimines with tetrabutyl-
ammonium cyanide (TBACN) or tert-butyldimethylsilyl
cyanide (TBDMSCN) failed to produce the product even
after 12 hours reaction time (Table 3, entries 1 and 2),
which may be due to steric hindrance of the reagents. In
contrast, the reaction with trimethylsilyl cyanide
(TMSCN) gave the corresponding cyanation products in
71% yield.
ues for the new products are given below (9e).
Compound 9a
Colorless solid; mp 153–154 °C.
IR (KBr): 3330, 3132, 2245, 1608, 1245, 1062, 788 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.77 (d, J = 8.0 Hz, 2 H), 7.38–
7.29 (m, 4 H), 7.16 (d, J = 8.0 Hz, 2 H), 5.40 (d, J = 9.2 Hz, 1 H),
5.31 (d, J = 9.2 Hz, 1 H), 2.20 (s, 3 H).
A possible reaction mechanism and the proposed role of 13C NMR (50 MHz, CDCl3): d = 21.1, 47.7, 116.1, 127.0, 127.2,
129.0, 130.4, 140.1, 144.3.
GC–MS: m/z = 286 [M+·].9d,e,15
DMSO are shown in Scheme 2. The oxygen atom of
DMSO can coordinate with ethyl cyanoformate to give
the cationic species 10 and the cyanide anion.13c The cya-
nide anion can then react with N-tosylaldimines to offer
the corresponding product through formation of 11.16 This
environmentally friendly, metal-free protocol could thus
be a convenient method for the cyanation of N-tosylald-
imines.
Compound 9b
Colorless solid; mp 155–156 °C.
IR (KBr): 3270, 3032, 2233, 1602, 1275, 1162, 738 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.80 (d, J = 8.0 Hz, 2 H), 7.32–
7.23 (m, 4 H), 7.18 (d, J = 8.0 Hz, 2 H), 5.42 (d, J = 9.2 Hz, 1 H),
5.20 (d, J = 9.2 Hz, 1 H), 2.40 (s, 3 H), 2.32 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 21.1, 21.6, 47.9, 116.5, 127.0,
127.3, 129.1, 130.0, 140.0, 144.2.
In conclusion, a very simple method has been developed
for the synthesis of N-protected a-amino nitriles from N-
tosylaldimines in DMSO as the solvent as well as the pro-
Synthesis 2011, No. 6, 919–923 © Thieme Stuttgart · New York

922
S. T. Kadam et al.
PAPER
GC–MS: m/z = 300 [M+·].9d,e
1 H), 5.22 (d, J = 9.1 Hz, 1 H), 5.10 (d, J = 9.1 Hz, 1 H), 2.44 (s,
3 H).
Compound 9c
Colorless solid; mp 129 °C.
IR (KBr): 3366, 3028, 2133, 1654, 1285, 1068, 738 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.79 (d, J = 8.0 Hz, 2 H), 7.35–
7.31 (m, 4 H), 6.89 (d, J = 8.0 Hz, 2 H), 5.39 (d, J = 9.0 Hz, 1 H),
5.15 (d, J = 9.0 Hz, 1 H), 3.79 (s, 3 H), 2.1 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 21.6, 42.2, 110.3, 110.9, 127.2,
129.9, 135.9, 144.0, 144.4, 144.6.
GC–MS: m/z = 276 [M+·].9d,e
Acknowledgment
13C NMR (50 MHz, CDCl3): d = 21.6, 47.7, 55.4, 116.5, 124.0,
The authors thank The Center for Biological Modulators of the
KRICT for financial support. Thanks are also due to BK 21 admini-
strated by the Korea Research Foundation.
127.3, 128.5, 130.0, 136.0, 144.5.
GC–MS: m/z = 316 [M+·].9d,e
Compound 9d
Colorless solid; mp 134–135 °C.
References
IR (KBr): 3268, 3020, 2135, 1664, 1285, 1088, 731 cm–1.
(1) Shafran, Y. M.; Bakulev, V. A.; Mokrushin, V. S. Russ.
Chem. Rev. 1989, 58, 148.
1H NMR (200 MHz, CDCl3): d = 7.75 (d, J = 8.0 Hz, 2 H), 7.37–
7.32 (m, 4 H), 7.21 (d, J = 8.0 Hz, 2 H), 5.51 (d, J = 9.1 Hz, 1 H),
5.40 (d, J = 9.1 Hz, 1 H), 2.44 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 21.5, 47.48, 115.9, 127.1, 128.4,
129.4, 130.0, 130.5, 135.7, 135.8, 144.8.
(2) Strecker, A. Ann. Chem. Pharm. 1850, 75, 27.
(3) (a) Weinstock, L. M.; Davis, P.; Handelsman, B.; Tull, R.
J. Org. Chem. 1967, 32, 2823. (b) Matier, W. L.; Owens, D.
A.; Comer, W. T.; Deitchman, D.; Ferguson, H. C.;
Seidehamel, R. J.; Young, J. R. J. Med. Chem. 1973, 16,
901. (c) Williams, R. M. Synthesis of Optically Active a-
Amino Acids; Pergamon: Oxford, 1989. (d) O’Donnell, M.
J. Tetrahedron 1988, 44, 5253. (e) Duthaler, R. O.
Tetrahedron 1994, 50, 1539. (f) Najera, C.; Sansano, J. M.
Chem. Rev. 2007, 107, 4584.
(4) (a) Ishitiani, H.; Komiyama, S.; Kobayashi, S. Angew.
Chem. Int. Ed. 1998, 37, 3186. (b) Harusawa, S.; Hamada,
Y.; Shioiri, T. Tetrahedron Lett. 1979, 4663. (c) Pan, S. C.;
List, B. Org. Lett. 2007, 9, 1149. (d) Nakamura, S.; Sato,
N.; Sugimoto, M.; Toru, T. Tetrahedron: Asymmetry 2004,
15, 1513. (e) Watahiki, T.; Ohba, S.; Oriyama, T. Org. Lett.
2003, 5, 2679. (f) Tian, S. K.; Deng, L. J. Am. Chem. Soc.
2001, 123, 6195.
GC–MS: m/z = 320, 318 [M+·].9d,e
Compound 9e
Colorless solid; mp 118–119 °C.
IR (KBr): 3266, 3028, 2133, 1654, 1285, 1068, 738 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.60 (d, J = 8.4 Hz, 2 H), 7.21–
7.17 (m, 2 H), 7.12 (d, J = 7.0 Hz, 2 H), 7.08–7.05 (m, 2 H), 4.49
(m, 2 H), 2.4 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 21.5, 46.0, 115.9, 127.1, 127.7,
129.5, 129.8, 130.4, 131.3, 133.0, 135.1, 144.5.
HRMS-FAB: m/z [M]+ calcd for C15H14N2O2Cl: 321.0465; found:
(5) (a) Belokon, Y. N.; Blacker, A. J.; Carta, P.; Clutterbuck, L.
A.; North, M. Org. Lett. 2003, 5, 4505. (b) Belokon, Y. N.;
Blacker, A. J.; Carta, P.; Clutterbuck, L. A.; North, M.
Tetrahedron 2004, 60, 10433. (c) Yamagiwa, N.; Tian, J.;
Matsunaga, S.; Shibasaki, M. J. Am. Chem. Soc. 2005, 127,
3413. (d) Belokon, Y. N.; Ishibashi, E.; Nomura, H.; North,
M. Chem. Commun. 2006, 1775. (e) Belokon, Y. N.; Clegg,
W.; Harrington, R. W.; Ishibashi, E.; Nomura, H.; North, M.
Tetrahedron 2007, 63, 9724.
(6) (a) Groger, H. Chem. Rev. 2003, 103, 2795. (b) Merino, P.;
Marques-Lopez, E.; Tejero, T.; Herrera, R. P. Tetrahedron
2009, 65, 1219. (c) De S, K.; Gibbs, R. A. J. Mol. Catal. A:
Chem. 2005, 232, 123. (d) Majhi, A.; Kim, S. S.; Kadam, S.
T. Tetrahedron 2008, 64, 5509. (e) Khan, N. H.; Agrawal,
S.; Kureshy, R. I.; Sayed, H. R. A.; Singh, S.; Eringathodi,
S.; Raksh, V. J. Tetrahedron Lett. 2008, 49, 640. (f) Yadav,
J. S.; Reddy, B. V. S.; Eswaraiah, B.; Srinivas, M.;
Vishnumurthy, P. New J. Chem. 2003, 27, 462.
321.0464.
Compound 9f
Colorless solid; mp 150–151 °C.
IR (KBr): 3279, 3120, 2235, 1664, 1185, 1088 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.74 (d, J = 8.0 Hz, 2 H), 7.50 (d,
J = 8.0 Hz, 2 H), 7.27–7.32 (m, 4 H), 5.20 (d, J = 9.1 Hz, 1 H), 5.40
(d, J = 9.1 Hz, 1 H), 2.45 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 21.7, 47.6, 115.9, 124.1, 127.2,
128.7, 130.1, 131.1, 132.5, 135.7, 144.8.
GC–MS: m/z = 363, 365 [M+·].15
Compound 9h
Colorless solid; mp 121–123 °C.
IR (KBr): 3366, 3028, 2133, 1654, 1285, 1068, 738 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.60 (d, J = 8.0 Hz, 2 H), 7.58–
7.31 (m, 6 H), 5.49 (d, J = 9.0 Hz, 1 H), 5.38 (d, J = 9.0 Hz, 1 H),
2.40 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 21.6, 47.0, 115.9, 117.6, 126.3,
127.1, 129.6, 130.5, 130.8, 131.4, 133.3, 135.0, 135.1, 144.2.
(g) Surendra, K.; Krishnaveni, N. S.; Mahesh, A.; Rao, K. R.
J. Org. Chem. 2006, 71, 2532. (h) Majhi, A.; Kim, S. S.;
Kadam, S. T. Appl. Organomet. Chem. 2008, 22, 705.
(i) Royer, L.; De S, K.; Gibbs, A. R. Tetrahedron Lett. 2005,
46, 4595.
GC–MS: m/z = 311 [M+·].9d,e,15
(7) (a) Ishitani, H.; Nagayama, S. J. Org. Chem. 1996, 61, 1902.
(b) Prakash, G. K. S.; Mandal, M.; Olah, G. A. Synlett 2001,
77. (c) Davis, F. A.; Reddy, R. T.; Weismiller, M. C. J. Am.
Chem. Soc. 1989, 111, 5964.
Compound 9i
Colorless solid; mp 99–100 °C.
(8) (a) Joseph, S.; Steven, W. M. J. Org. Chem. 1990, 55, 393.
(b) Chan, T.; Jiang, S.; Turos, E. Tetrahedron Lett. 1994, 35,
8325. (c) Bloch, R. Chem. Rev. 1998, 98, 1407.
(9) (a) Fukuda, Y.; Maeda, Y.; Kondo, K.; Aoyama, T. Synthesis
2006, 1937. (b) Huang, X.; Huang, J.; Wen, Y.; Feng, Z.
IR (KBr): 3370, 3100, 2235, 1664, 1085 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.78 (d, J = 8 Hz, 1 H), 7.38 (d,
J = 2.0 Hz, 1 H), 7.32 (d, J = 8.4 Hz, 2 H), 6.48 (dd, J = 3.4, 1.6 Hz,
Synthesis 2011, No. 6, 919–923 © Thieme Stuttgart · New York

PAPER
DMSO-Promoted Strecker Reaction of N-Tosylaldimines with Cyanoformate
923
Adv. Synth. Catal. 2006, 348, 2579. (c) Fukuda, Y.; Konda,
407. (f) Kim, S. S.; Kadam, S. T. Bull. Korean Chem. Soc.
2008, 29, 1320. (g) Kim, S. S.; Kadam, S. T. Catal.
Commun. 2008, 9, 1342. (h) Kim, S. S.; Rajagopal, G.;
George, S. C. Appl. Organomet. Chem. 2007, 21, 798.
(i) Kim, S. S.; George, S. C.; Kadam, S. T. Appl. Organomet.
Chem. 2007, 21, 994. (j) Kim, S. S.; Rajagopal, G. Synthesis
2007, 215. (k) Kadam, S. T.; Kim, S. S. Appl. Organomet.
Chem. 2007, 23, 119. (l) Kadam, S. T.; Thirupathi, P.; Kim,
S. S. Tetrahedron 2010, 66, 1684.
K.; Aoyama, T. Synthesis 2006, 2649. (d) Kantam, L. M.;
Mahendar, K.; Sreedhar, B.; Choudary, B. M. Tetrahedron
2008, 64, 3351. (e) Das, B.; Balasubramanyam, P.;
Krishnaiah, M.; Veeraneyulu Reddy, G. C. Synthesis 2009,
3467.
(10) Wang, J.; Wang, W.; Li, W.; Hu, X.; Shen, K.; Tan, C.; Liu,
X.; Feng, X. Chem. Eur. J. 2009, 15, 11642.
(11) Chemla, F.; Hebbe, V.; Normant, J.-F. Synthesis 2000, 75.
(12) Anastas, P.; Warner, J. C. In Green Chemistry: Theory and
Practice; Oxford University Press: Oxford, 1998.
(13) (a) Cabirol, F. L.; Lim, A. E. C.; Hanefeld, U.; Sheldon, R.
A.; Lyapkalo, I. M. J. Org. Chem. 2008, 73, 2446.
(b) Watahiki, T.; Matsuzaki, M.; Oriyama, T. Green Chem.
2003, 5, 82. (c) Iwanami, K.; Hinakubo, Y.; Oriyama, T.
Tetrahedron Lett. 2005, 46, 5881.
(14) (a) Kim, S. S.; Kwak, J. M.; George, S. C. Appl. Organomet.
Chem. 2007, 21, 809. (b) Kim, S. S.; Lee, S. H.; Kwak, J. M.
Tetrahedron: Asymmetry 2006, 17, 1165. (c) Kim, S. S.;
Kwak, J. M. Tetrahedron 2006, 62, 49. (d) Kim, S. S.;
Song, D. H. Eur. J. Org. Chem. 2005, 1777. (e) Kim, S. S.;
Majhi, A.; Kim, H. S. Appl. Organomet. Chem. 2008, 22,
(15) (a) Kadam, S. T.; Kim, S. S. Tetrahedron 2010, 66, 5647.
(b) Kadam, S. T.; Kim, S. S. Tetrahedron 2009, 65, 6330.
(c) Kadam, S. T.; Thirupathi, P.; Kim, S. S. Tetrahedron
2009, 65, 10383. (d) Majhi, A.; Kim, S. S.; Kadam, S. T.
Tetrahedron 2008, 64, 5509.
(16) We tried to isolate the intermediate 11 (R in 7 is 4-MeC6H4;
Scheme 2) after 1 h of reaction time before and after work-
up procedure. Under these conditions, we observed the
formation of 9b instead of intermediate 11. This may mean
that a small amount of moisture in the reaction mixture is
sufficient to convert 11 into 9.
(17) Takahashi, E.; Fujisawa, H.; Yanai, T.; Mukaiyama, T.
Chem. Lett. 2005, 34, 318.
Synthesis 2011, No. 6, 919–923 © Thieme Stuttgart · New York