Preparation of N-protected allylic amines and α-methylene-β- amino acids from vinylalumination/Baylis-Hillman products via tandem S N2′ substitution-Overman rearrangement

Article abstract of DOI:10.1016/j.tetlet.2005.01.110

S_N2′ reaction on the acetates obtained from vinylalumination or Baylis-Hillman products, followed by in situ reduction afforded allylic alcohols. Upon conversion to trichloroacetimidates and [3,3]-sigmatropic rearrangement, the corresponding N-protected β-substituted allylic amines were obtained in good yields. Utilization of hydroxy group as the nucleophile furnished allylic hydroxy esters, which were converted to protected α-methylene-β-amino acids via Overman rearrangement.

Full text of DOI:10.1016/j.tetlet.2005.01.110

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 2121–2124
Preparation of N-protected allylic amines and a-methylene-b-amino
acids from vinylalumination/Baylis–Hillman products via
tandem SN20 substitution–Overman rearrangement
P. Veeraraghavan Ramachandran,* Thomas E. Burghardt and M. Venkat Ram Reddy
Department of Chemistry, Purdue University, 560 Oval Dr., West Lafayette, IN 47907-2084, USA
Received 6 January 2005; revised 20 January 2005; accepted 21 January 2005
Abstract—SN20 reaction on the acetates obtained from vinylalumination or Baylis–Hillman products, followed by in situ reduction
afforded allylic alcohols. Upon conversion to trichloroacetimidates and [3,3]-sigmatropic rearrangement, the corresponding N-pro-
tected b-substituted allylic amines were obtained in good yields. Utilization of hydroxy group as the nucleophile furnished allylic
hydroxy esters, which were converted to protected a-methylene-b-amino acids via Overman rearrangement.
ꢀ 2005 Elsevier Ltd. All rights reserved.
Allylic amines are very useful synthons in organic syn-
thesis.1 They are used in the preparation of various syn-
thetic intermediates; they are also attractive starting
materials for the synthesis of amino acids.1,2 Owing to
their importance, there have been many literature re-
ports1 for the preparation of allylic amines and [3,3]-sig-
matropic rearrangement of allylic trichloroacetimidates
(Overman rearrangement) is a well-established proto-
col.3 The resulting allylic amides can be conveniently
deprotected into the parent amines under either acidic
or basic conditions.4 Preparation of b-amino acids is
of particular interest to medicinal and bioorganic chem-
ists5 as various b-amino acid moieties can be found in
taxoids, b-lactam antibiotics, HIV-protease inhibitors,
and other compounds.6 Moreover, high proteolytic sta-
bility of b-amino acids makes them excellent substrates
for peptidomimetics.7
alternative to Baylis–Hillman protocol9 due to shorter
reaction times and tolerance of wider array of carbonyls.
Our ongoing work involving applications of the vinyl-
alumination products8a,10 prompted us to investigate the
preparation of N-protected-b-substituted allylic amines
from a-methylene-b-hydroxy esters. We envisaged the
protocol as a two-step synthesis, with the first step
involving the SN20 reaction of the acetates with various
nucleophiles, followed by an in situ reduction of the es-
ters to furnish primary allylic alcohols. In the second
step, the obtained allylic alcohols would be converted
to trichloroacetimidates and subjected to [3,3]-sigma-
tropic rearrangement to afford the allylic amides. The
retrosynthetic analysis is shown in Scheme 1. Among
the chosen representative nucleophiles, only SN20 addi-
tion of carbon is well recognized.9,11 The other, viz.
nitrogen,9,12 hydride,13 and sulfur14 are known, but
remain rather obscure. Herein we report the results
of our investigation.
Vinylalumination8 using [a-(ethoxycarbonyl)vinyl]di-
isobutylaluminum, prepared from ethyl propiolate and
diisobutylaluminum hydride (DIBAL-H) in the presence
of 4-methylmorpholine-N-oxide (NMO), is an attractive
Vinylalumination or Baylis–Hillman reaction of acetal-
dehyde and benzaldehyde provided the allylic alcohols
in high yields. The obtained alcohols were acetylated
Keywords: b-Amino acids; Allylic amines; SN20 reaction; Allylic alco-
hols; Vinylalumination; Baylis–Hillman reaction.
NHR
OH
OH
*
Corresponding author. Tel.: +1 765494 3503; fax: +1 765494
0239; e-mail: chandran@purdue.edu
R
R
RCHO
COOEt
R
Present address: Department of Organic and Medicinal Chemistry,
University of Minnesota, 1039 University Dr., Duluth, MN 55812,
USA.
Nu
Nu
Scheme 1. Retrosynthetic analysis.
0040-4039/$ - see front matter ꢀ 2005Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.01.110

2122
COOEt
P. V. Ramachandran et al. / Tetrahedron Letters 46 (2005) 2121–2124
afforded the alcohols 3c and 4c, respectively (Table 1,
DIBAL-H / NMO
THF, 1 h, 0 oC
RCHO
entries 5and 6). (4-Methoxyphenyl)methanethiol added
easily to the acetates 1 and 2 in the presence of triethyl-
amine to give quantitative yields of the expected allylic
thioether esters. However, upon reduction with LiAlH4,
only the starting thiol was recovered in 96% yield. For-
tunately, treatment of the SN20-substitution products
with DIBAL-H at ꢁ18 ꢁC furnished 3d and 4d, albeit
in somewhat diminished yields (Table 1, entries 7 and 8).
4 h, RT
85-90%
OH
COOEt
R
RCHO, DABCO
COOEt
R = Me, Ph
neat, 7-14 days, RT
75-85%
OH
OAc
The allylic alcohols 3a–d and 4a–d were converted to
the corresponding trichloroacetimidates by the treat-
ment with 0.1 equiv of sodium bis(trimethylsilyl)amide
(NaHMDS) in THF at ꢁ42 ꢁC, followed by the addition
of trichloroacetonitrile and warming to room temperature.
Although in the vast majority of the literature reports
the acetimidates are prepared using DBU or NaH as
the base,3 we found that, in our system, the best results
were obtained with NaHMDS. The use of catalytic
amounts of the solid NaH was quite inconvenient for
small scale preparations and DBU was required in a
stochiometric amount and provided the trichloro-
acetimidates along with the unreacted base, which
necessitated purification hence leading to diminished
yields. On the other hand, NaHMDS solution was easy
to add in catalytic amounts and furnished clear reaction
mixtures that did not require rigorous purification. After
removal of the solvent under reduced pressure, the ob-
tained crude acetimidates were diluted with xylene and
AcCl
pyridine,
a. Nu
b. LiAlH4 or
DIBAL-H
COOEt
R
R
CH2Cl2,
0 oC, 1 h,
99%
Nu
1:R=Me
2:R=Ph
3a: R = Me, Nu = NBn2, 77%
4a: R = Ph, Nu = NBn2, 78%
3b: R = Me, Nu = H, 71%
4b: R = Ph, Nu = H, 72%
3c: R = Me, Nu = Et, 71%
4c: R = Ph, Nu = Et, 73%
3d: R = Me, Nu = SPMB, 61%
4d: R = Ph, Nu = SPMB, 63%
Scheme 2. Synthesis of allylic alcohols.
to give quantitative yields of the corresponding acetates
1 and 2 (Scheme 2).
The reaction of dibenzylamine with 1 and 2, in the pres-
ence of triethylamine, followed by in situ reduction with
LiAlH4 at 0 ꢁC furnished the desired hydroxy amines 3a
and 4a in good yields (Table 1, entries 1 and 2). The
reductions with DIBAL-H were sluggish and required
over 6 h at rt. Analysis of the obtained amino alcohols
with 1H NMR spectroscopy revealed that 3a and 4a
were obtained as ꢀ1:1 mixtures of E- and Z-isomers,
which could be separated on silica gel. We were not con-
cerned about the isomer ratio since both 3a and 4a were
rearranged to a terminal methylene later. Hydride nucleo-
phile was installed by the treatment of 1 and 2 with
LiAlH4 to give the corresponding alcohols 3b and 4b
in good yields (Table 1, entries 3 and 4).13 This treatment
resulted in a simultaneous reduction of the ester moiety.
The acetates 1 and 2, upon reaction with ethylmagne-
sium bromide, followed by the reduction with LiAlH4,
15
refluxed in the presence of K2CO3 for 4–10 h (reac-
tions monitored by TLC), furnishing the desired b-
substituted allylic amides 5a–d and 6a–d in good yields
(Scheme 3). The preparation of N-protected allylic
amines is summarized in Table 1.
Since direct installation of the oxygen nucleophile was
not facile, as a surrogate we used SN20 Mitsunobu con-
ditions16 for the aliphatic substrate and rearrangements
of the acetate devised by Foucault and Le Guemmout17
for the aromatic acetate 2 to obtain the allylic hydroxy
esters 7e and 8e, respectively (Scheme 4; Table 1, entries
9 and 10).
Due to the importance of b-amino acids,5–7 we chose to
convert hydroxy esters 7e and 8e to N-protected a-meth-
ylene-b-amino acids. Thus, they were subjected to Over-
Table 1. Synthesis of protected b-substituted allylic amines
Entry
Acetate
Nu
Alcohol
Yld, %a
Amide
Yld, %a
O
#
R
#
#
1. a. NaHMDS (0.1 eq)
b. Cl3CCN
OH
Nu
HN
CCl3
Nu
1
2
1
2
1
2
1
2
1
2
1
2
Me
Ph
NBn2
NBn2
H
3a
4a
3b
4b
3c
4c
3d
4d
7e
8e
77b
78b
71
5a
5a
5b
6b
5c
6c
5d
6d
9e
10e
73
72
78
77
76
75
70
73
71
73
R
R
3
Me
Ph
2. K2CO3, xylene, ∆
4
H
Et
72
71
5
Me
Ph
3a-d, 4a-d
5a: R=Me, Nu=NBn2, 73%
6a: R=Ph, Nu=NBn2, 72%
5b: R=Me, Nu=H, 78%
6b: R=Ph, Nu=H, 77%
5c: R=Me, Nu=Et, 76%
6c: R=Ph, Nu=Et, 75%
5d: R=Me, Nu=SPMB, 70%
6d: R=Ph, Nu=SPMB, 73%
6
Et
73
7
Me
Ph
SPMB
SPMB
ÔOHÕd
ÔOHÕd
61c
63c
65
8
9
10
Me
Ph
70
a All yields are of isolated, pure products.
b Obtained as ꢀ1:1 mixtures of separable E- and Z-isomers.
c Reduction with DIBAL-H at ꢁ18 ꢁC was required.
d The hydroxy nucleophile was inserted via other routes (see text).
Scheme 3. Synthesis of N-protected b-substituted allylic amines.

P. V. Ramachandran et al. / Tetrahedron Letters 46 (2005) 2121–2124
2123
1) Ph3P, DEAD,
warm to rt over 0.5h, when it was quenched with aq
10% HCl (5mL). The product was extracted with
Et2O (3 · 30 mL), washed with brine, concentrated in
vacuo, and purified on silica gel (ethyl acetate/hexanes
2:8) to furnish 0.75g of (2 E)-2-methyl-3-phenylprop-2-
en-1-ol (4b) (5.1 mmol, 72% yield). 1H NMR
(300 MHz, CDCl3, d): 1.98 (br s, 1H), 1.91 (s, 3H),
4.20 (s, 2H), 6.54 (s, 1H), 7.24–7.3 (m, 5H); 13C NMR
(75MHz, CDCl 3, d): 15.3, 69.0, 125.0, 126.4, 128.2,
128.9, 137.6, 137.7. Carbon nucleophile: To a solution
of 2 (0.9 g, 3.6 mmol) in Et2O (15mL) cooled to
ꢁ18 ꢁC was added EtMgBr (3 M in Et2O; 1.2 mL,
3.6 mmol) and the reaction was stirred for 2 h at 0 ꢁC.
To the obtained crude ester was added LiAlH4 (1 M in
THF; 3.5mL, 3.5mmol) and the mixture was stirred
for 1 h, while it warmed to rt. After quenching with
10% aq HCl (5mL), the obtained material was extracted
with Et2O (3 · 30 mL), washed with brine, the volatiles
were removed under reduced pressure, and the product
as purified on silica gel (ethyl acetate/hexanes 2:8) to fur-
nish (2E)-3-phenyl-2-propylprop-2-en-1-ol (4c): (0.45g,
OH
4-MeO-(C6H4)-COOH
2) K2CO3, MeOH
COOEt
COOEt
Me
Ph
COOEt
OH
7e: R=Me, 65%
8e: R=Ph, 70%
R
1) DABCO, THF reflux
2) K2CO3, EtOH
OAc
2
Scheme 4. Preparation of allylic esters using oxygen nucleophile.
CCl3
COOEt
HN
Ph
O
1. a. NaHMDS (0.1 eq)
b. Cl3CCN
2. K2CO3, xylene, ∆
R
COOEt
OH
7e: R=Me
8e: R=Ph
9e: R=Me, 71%
10e: R=Ph, 73%
Scheme 5. Synthesis of protected a-methylene-b-amino acids.
1
man rearrangement as described above to furnish the
corresponding protected b-amino acids 9e and 10e in
good yields (Scheme 5; Table 1, entries 9 and 10).
2.6 mmol, 72% yield). H NMR (300 MHz, CDCl3, d):
0.96 (t, J = 7.4 Hz, 3H), 1.56 (m, 2H), 2.31 (t,
J = 7.96 Hz, 2H), 2.60 (s, 1H), 4.24 (s, 2H), 6.58 (s,
1H), 7.26–7.41 (m, 5H); 13C NMR (75MHz, CDCl 3,
d): 14.3, 21.7, 30.9, 68.8, 125,3, 126.5, 128.3, 128.7,
137.7, 142.3. Sulfur nucleophile: To a solution of 2
(0.3 g, 1.2 mmol) in CH2Cl2 (15mL) was added Et 3N
(0.14 mL, 1.1 mmol) and (4-methoxyphenyl)methaneth-
iol (0.25mL, 1.8 mmol) and the reaction was stirred
overnight at rt, followed by cooling to ꢁ18 ꢁC and the
addition of DIBAL-H (1 M in hexanes; 1.3 mL,
1.3 mmol). The reaction was allowed to warm to rt
and was stirred for 6 h, when it was quenched with
H2O (5mL). The product was extracted with CH 2Cl2
(1 · 10 mL) and Et2O (2 · 30 mL), the solvents were re-
moved under reduced pressure, and the material was
purified on silica gel (flash; ethyl acetate/hexanes 2:8)
to furnish (2Z)-2-{[(4-methoxybenzyl)thio]methyl}-3-
phenylprop-2-en-1-ol (4d; 0.23 g, 0.8 mmol, 63%
yield). 1H NMR (300 MHz, CDCl3, d): 2.94 (br s,
1H), 3.40 (s, 2H), 3.61 (s, 2H), 3.77 (s, 3H), 4.34 (s,
2H), 6.70 (s, 1H), 6.79 (d, J = 8.58 Hz, 2H), 7.08
(d, J = 8.52 Hz, 2H), 7.24–7.47 (m, 5H); 13C NMR
(75MHz, CDCl 3, d): 29.9, 36.2, 55.3, 66.3, 114.0,
127.1, 128.5, 128.8, 129, 130.1, 130.3, 136.7, 137.4,
158.6. MS (EI): 300 (M+), 205, 121 (MeO–(C6H4)–
CH2+), 107; (CI): 283 (M+HꢁH2O), 121 (MeO–
(C6H4)–CH2+); HRMS: 300.1184 (calcd), 300.1184 (ac-
tual). Oxygen nucleophile on aliphatic substrate: To ethyl
2-(1-hydroxyethyl)acrylate (1.7 g, 10.0 mmol) dissolved
in THF (30 mL) was added triphenylphosphine (3.5g,
13.3 mmol) and 4-nitrobenzoic acid (2.2 g, 13.2 mmol).
The mixture was cooled to ꢁ78 ꢁC and diethylazodi-
carboxylate (2.1 mL, 13.2 mmol) was added slowly.
The mixture was allowed to warm to rt over 3 h, when
it was quenched with satd aq NaHCO3 (10 mL), the
product was extracted with Et2O (3 · 30 mL), washed
with brine, evaporated, and purified on silica gel (ethyl
acetate/hexanes 1:8) to give (2E)-2-(ethoxycarbonyl)-
benzoate in 66% yield (1.9 g, 6.5mmol). The obtained
ester was dissolved in MeOH (65mL), and treated with
K2CO3 (1.0 g, 7.2 mmol) for 1 h at rt. The reaction was
In conclusion, we have developed a simple and reliable
two-step procedure for the preparation of b-substituted
allylic amides and a-methylene-b-amino esters from the
acetates of readily accessible vinylalumination or Bay-
lis–Hillman products. We believe that the simplicity of
the protocol, tolerance of a wide range of nucleophiles,
and the importance of allylic amines make this proce-
dure attractive and it will find applications in organic
syntheses.
Representative experimental procedures
Nitrogen nucleophile: To a solution of ethyl 2-[(acetyl-
oxy)(phenyl)methyl]acrylate (2; 0.9 g, 3.6 mmol) in
CH2Cl2 (30 mL) was added triethylamine (0.5mL,
3.5mmol) and dibenzylamine (1.0 mL, 7.2 mmol) and
the reaction was stirred for 4 h at rt, followed by cooling
to 0 ꢁC and addition of LiAlH4 (1 M in THF; 3.6 mL,
3.6 mmol). After stirring at rt for 1 h, followed by
quenching with H2O (5mL), the product was extracted
with Et2O (3 · 50 mL). After removal of the volatiles,
the residue was purified on silica gel (flash; ethyl ace-
tate/hexanes 1:9) to provide a mixture of separable
(2E) and (2Z)-2-{[dibenzylamino]methyl}-3-phenyl-
prop-2-en-1-ol (4a) (52:48 E/Z ratio; 0.95g, 2.8 mmol,
77% combined yield). For the E-isomer: 1H NMR
(300 MHz, CDCl3, d): 1.32 (br s, 1H), 3.42 (s, 2H),
3.51 (s, 4H), 4.33 (s, 2H), 6.77 (s, 1H), 7.21–7.43 (m,
15H); 13C NMR (75MHz, CDCl 3, d): 35.3, 57.4, 57.8,
67.6, 125.9, 126.3, 127.2, 127.4, 127.5, 127.8, 127.9,
128.0, 128.3, 129.0, 135.7, 136.9, 137.0. MS (EI): 343
(M+), 194, 91 (C7H7+); (CI): 344 (M+H), 210, 147. Hy-
dride nucleophile: To LiAlH4 (0.3 g, 7.9 mmol) diluted
with Et2O (30 mL) and cooled to 0 ꢁC was slowly added
EtOH (0.46 mL, 7.9 mmol). The mixture was transferred
via canula to a solution of 2 (1.8 g, 7.3 mmol) in Et2O
(30 mL) cooled to ꢁ78 ꢁC. Reaction was allowed to

2124
P. V. Ramachandran et al. / Tetrahedron Letters 46 (2005) 2121–2124
Jumnah, R.; Williams, A. C.; Williams, J. M. J. J. Chem.
Soc., Perkin Trans. 1 1997, 1411; (d) Burgess, K.; Liu, L.
T.; Pal, B. J. Org. Chem. 1993, 58, 4758; (e) Trost, B. M.;
Van Vranken, D. L. J. Am. Chem. Soc. 1993, 115, 444.
3. (a) Sato, H.; Oishi, T.; Chida, N. J. Synth. Org. Chem.
Jpn. 2004, 62, 693; (b) Overman, L. E. Acc. Chem. Res.
1980, 13, 218; (c) Overman, L. E. J. Am. Chem. Soc. 1974,
96, 597.
4. (a) Ramachandran, P. V.; Burghardt, T. E.; Reddy, M. V.
R. J. Org. Chem. 2005, 70, 0000; (b) Bey, P.; Gerhart, F.;
Jung, M. J. Org. Chem. 1986, 51, 2835; (c) Takano, S.;
Akiyama, M.; Ogasawara, K. J. Chem. Soc., Chem.
Commun. 1984, 770.
5. (a) Dougherty, D. A. Curr. Opin. Chem. Biol. 2000, 4, 645;
(b) Bittker, J. A.; Phillips, K. J.; Liu, D. R. Curr. Opin.
Chem. Biol. 2002, 6, 367; (c) Yodar, N. C.; Kumar, K.
Chem. Soc. Rev. 2002, 31, 335.
6. (a) Ojima, I.; Lin, S. N.; Wang, T. Curr. Med. Chem. 1999,
6, 927; (b) Enantioselective Synthesis of b-Amino Acids;
Juaristi, E., Ed.; Viley-VCH: London, 1997, and refer-
ences cited therein.
quenched with H2O (20 mL), the product was extracted
with Et2O (3 · 30 mL), washed with brine, and after
removal of the solvents under reduced pressure purified
on silica gel (flash; ethyl acetate/hexanes 1:7) to furnish
7e (0.85g, 6.5mmol, 65% yield from the alcohol). 1H
NMR (300 MHz, CDCl3, d): 1.39 (t, J = 7.12 Hz, 3H),
1.85(d, J = 7.35Hz, 3H), 2.8 (br s, 1H), 4.29 (s, 2H),
4.33 (q, J = 7.15Hz, 2H), 6.92 (q, J = 7.23 Hz, 1H);
13C NMR (75MHz, CDCl 3, d): 14.1, 14.7, 51.7, 56.4,
131.8, 141.0, 167.9. Oxygen nucleophile on aromatic sub-
strate: To a solution 2 (2.5g, 10.1 mmol) in THF
(20 mL) was added DABCO (0.8 g, 7.1 mmol) and the
reaction was refluxed for 14 h, followed by evaporation
of THF. The residue was dissolved in EtOH (100 mL)
and treated with K2CO3 (3.5g, 25mmol) for 14 h at
rt, when it was quenched with H2O (50 mL), the product
was extracted with Et2O (3 · 50 mL), washed with brine,
the solvent was evaporated, and the material was puri-
fied on silica gel (flash; ethyl acetate/hexanes 1:7) to give
8e (1.45g, 7.0 mmol, 70% yield) 1H NMR (300 MHz,
CDCl3, d): 1.39 (t, J = 7.12 Hz, 3H), 3.18 (br s, 1H),
4.30 (q, J = 7.15Hz, 2H), 4.52 (d, J = 5.1 Hz, 2H),
7.25–7.45 (m, 5H), 7.86 (s, 1H); 13C NMR (75MHz,
CDCl3, d): 14.1, 59.9, 57.5, 128.6, 129.3, 129.7, 131.0,
134.6, 142.8, 168.5. Representative procedure for the
rearrangement: To 4b (0.2 g, 1.3 mmol) dissolved in
THF (15mL) and cooled to ꢁ42 ꢁC was added sodium
bis(trimethylsilyl)amide (1 M in THF; 0.13 mL,
0.13 mmol) and the reaction was stirred for 0.2 h, fol-
lowed by the addition of trichloroacetonitrile
(0.15mL, 1.5mmol) and stirring for 1 h, while it
warmed to rt. The solvent was removed under reduced
pressure and the crude material was diluted with xylene
(5mL), K 2CO3 (0.18 g, 1.3 mmol) was added, and the
reaction was stirred for 6 h at reflux. After filtration
through Celite, the product was purified on silica gel
(flash; ethyl acetate/hexanes 1:99) to give 2,2,2-tri-
chloro-N-(2-methyl-1-phenylprop-2-enyl)acetamide (6b)
(0.3 g, 1.0 mmol, 78% yield). 1H NMR (300 MHz,
CDCl3, d): 1.72 (s, 3H), 5.08 (d, J = 14.01 Hz, 2H),
5.41 (d, J = 7.95Hz, 1H), 6.94 (d, J = 6.99 Hz, 1H),
7.35-7.56 (m, 5H); 13C NMR (75MHz, CDCl 3, d):
19.2, 59.2, 111.5, 126.3, 127.4, 128, 137.1, 141.5,
159.7.
7. Steer, D. L.; Lew, R. A.; Perlmutter, P.; Smith, A. I.;
Aguilar, M.-I. Curr. Med. Chem. 2002, 9, 811.
8. (a) Ramachandran, P. V.; Rudd, M. T.; Burghardt, T. E.;
Reddy, M. V. R. J. Org. Chem. 2003, 68, 9310; (b)
Ramachandran, P. V.; Reddy, M. V. R.; Rudd, M. T.
Chem. Commun. 1999, 1979; (c) Ramachandran, P. V.;
Reddy, M. V. R.; Rudd, M. T. Tetrahedron Lett. 1999, 40,
627; (d) Li, G. G.; Wei, H.-X.; Willis, S. Tetrahedron Lett.
1998, 39, 4607; (e) Ramachandran, P. V.; Reddy, M. V.
R.; Rudd, M. T.; de Alaniz, J. R. Tetrahedron Lett. 1998,
39, 8791.
9. (a) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem.
Rev. 2003, 103, 811; (b) Basavaiah, D.; Rao, P. D.; Hyma,
R. S. Tetrahedron 1996, 52, 8001.
10. Ramachandran, P. V.; Pratihar, D.; Biswas, D.; Srivast-
ava, A.; Reddy, M. V. R. Org. Lett. 2004, 6, 481.
11. (a) GowriSankar, S.; Lee, C. G.; Kim, J. N. Tetrahedron
Lett. 2004, 45, 6949; (b) Amri, H.; Rambaud, M.;
´
Villieras, J. J. Organomet. Chem. 1990, 384, 1; (c) Drewes,
S. E.; Emslie, N. D. J. Chem. Soc., Perkin Trans. 1 1982,
2079.
12. (a) Nilov, D.; Ra¨cker, R.; Reiser, O. Synthesis 2002, 2232;
(b) Hba¨ıeb, S.; Latiri, Z.; Amri, H. Synth. Commun. 1999,
29, 981.
13. Basavaiah, D.; Pakalah, K. S. S. J. Chem. Soc., Chem.
Commun. 1992, 955.
14. (a) Kamimura, A.; Morita, R.; Matsuura, K.; Omataa, Y.;
`
Shiraib, M. Tetrahedron Lett. 2002, 43, 6189; (b) Calo, V.;
Lopez, L.; Pesce, G. J. Organomet. Chem. 1988, 353,
405.
15. Nishikawa, T.; Asai, M.; Ohayabu, N.; Isobe, M. J. Org.
Chem. 1998, 63, 188.
References and notes
ˆ ´
16. (a) Charette, A. B.; Cote, B.; Monroc, S.; Prescott, S. J.
Org. Chem. 1995, 68, 6888; (b) Mitsunobu, O. Synthesis
1. Johannsen, M.; Jørgensen, K. A. Chem. Rev. 1998, 98,
1689.
2. (a) Ichikawa, Y.; Ito, T.; Nishiyama, T.; Isobe, M. Synlett
2003, 7, 1034; (b) Savage, I.; Thomas, E. J.; Wilson, P. D.
J. Chem. Soc., Perkin Trans. 1 1999, 3291; (c) Bower, J. F.;
1981, 1.
17. Foucaud, A.; Le Guemmout, F. Bull. Soc. Chim. Fr. 1989,
3, 403.