Silver (I)-promoted asymmetric halohydrin reaction of chiral N-enoyl-2-oxazolidinones: Scope and limitations

Article abstract of DOI:10.1016/j.tet.2005.01.053

The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br₂/I₂) and water were efficiently carried out in aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diaste

Full text of DOI:10.1016/j.tet.2005.01.053

Tetrahedron 61 (2005) 2279–2286
Silver (I)-promoted asymmetric halohydrin reaction of chiral
N-enoyl-2-oxazolidinones: scope and limitations
*
Saumen Hajra, Ananta Karmakar and Manishabrata Bhowmick
Department of Chemistry, Indian Institute of Technology, Salua road, Kharagpur 721 302, India
Received 7 October 2004; revised 21 December 2004; accepted 14 January 2005
Available online 1 February 2005
Abstract—The halohydrin reaction of chiral N-enoyl-2-oxazolidinones 1 by halogen (Br2/I2) and water were efficiently carried out in
aqueous organic solvent promoted by silver(I) with high anti- and regioselectivity and moderate to good diastereoselectivities. The alkenoyl,
cinnamoyl and electron-deficient cinnamoyl substrates smoothly underwent bromohydrin reaction in aqueous acetone but no iodohydrin
reaction, where as electron-rich cinnamoyl substrates preferred to undergo iodohydrin reaction in aqueous acetone with moderate
diastereoselectivity and enhanced diastereoselectivity was observed in aqueous THF.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
suitable aldehydes provide selectively both anti- and syn-a-
halo-b-hydroxycarboxylic acid derivatives.7 Genet et al.
reported the catalytic asymmetric hydrogenation of
a-chloro-b-ketocarboxylic acid esters for the enantioselec-
tive synthesis of a-chloro-b-hydroxycarboxylic acid esters.8
Under controlled reaction conditions, epoxide ring opening
of b-alkyl-a,b-epoxycarboxylic acids/derivatives provide
stereoselectively a-halo-b-hydroxy-, as well as a-hydroxy-
b-halocarboxylic acids/derivatives.9 However, epoxide ring
opening of the b-aryl-a,b-epoxycarboxylic acid derivatives
with halides give either poor regioselectivity or selectively
a-hydroxy-b-halocarboxylic acid derivatives.9b,d
Carboxyhalohydrins especially a-halo-b-hydroxycar-
boxylic acid derivatives are versatile and useful synthetic
intermediates because of their facile transformation to a
variety of important compounds. These moieties are present
in precursors to many biologically active compounds.1
Carboxyhalohydrins are also good precursors for stereo-
selective radical reactions.2 A potentially straightforward
method for the synthesis of carboxyhalohydrins is the
stereoselective halohydrin reaction of a,b-unsaturated
carboxylic acid derivatives.3 Only few reports on the
asymmetric halohydrin reaction are known in literature.4–6
Henry et al. first reported palladium(II)-catalyzed enantio-
selective hydroxychlorination of terminal alkenes with a
metal chloride—mechanistically it is a hydroxychlorination
to alkenes and there is no involvement of halonium (XC)
intermediate.4 Sudalai et al. described NaIO4 mediated
oxidative enantioselective halohydrination of alkenes
(encapsulated in b-cyclodextrin) using alkali metal halides
with moderate enantioselectivity.5 Barluenga et al. reported
a highly diastereoselective iodohydrination of terpene
derivatives using Py2IBF4.6
In this paper we report in full the silver(I)-promoted
asymmetric halohydrin reaction of chiral N-enoyl-2-oxazo-
lidinones 1,10 in which high regio- and diastereoselectivities
up to 82:18 of anti-a-halo-b-hydroxy carbonyls 3 and 4 with
good yields are demonstrated.
2. Results and discussion
Initially (4S)-N-cinnamoyl-4-(1-methylethyl)-2-oxazolidi-
nones were selected as substrates for the development of
the diastereoselective halohydrin reaction. It was assumed
that the b-aryl group of the three-member halonium
intermediate 2 would enhance the electrophilicity towards
the water nucleophile to achieve high regioselectivity
(Scheme 1; RZAr and R0Zi-Pr) and also these carboxy-
halohydrins are very important precursors to many biologi-
cally active compounds.1 Moreover our research group is
involved in the chelation controlled stereoselective radical
There are only a few methods, other than halohydrin
reaction, for the stereoselective synthesis of the a-halo-b-
hydroxycarboxylic acid derivatives.7–9 Reagent controlled
aldol reaction of chiral a-halogenated imide enolates with
Keywords: Asymmetric; Halohydrin; Silver (I); Halogen (Br2/I2); N-enoyl-
2-oxazolidinones; a-Halo-b-hydroxy carboxylic acid derivatives.
* Corresponding author. Tel.: C91 3222 283340; fax: C91 3222 255303;
e-mail: shajra@chem.iitkgp.ernet.in
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.01.053

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S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
and 6:1, it gave O95:05 of carboxybromohydrins; lower as
well as higher amount of water enhanced the formation of
5a. The compound 5a was characterized by the 1H and 13
C
NMR spectra analysis and compared with the authentic
dibromo compound, prepared on reaction of 1a with Br2 in
CCl4. It was also found that there was no reaction in 50%
aqueous acetone and no appreciable change in the product
distribution when the concentrations of the reaction medium
were varied between 0.1 M and 0.5 M in a 4:1 (v/v) acetone/
water ratio. All halohydrin reactions were performed in
aqueous organic solvent (solvent: H2O, 4:1 v/v) at 0.2 M
concentration.
To establish suitable reaction conditions, initially AgNO3-
promoted halohydrin reactions of three electronically
different cinnamoyl substrates 1a–1c, containing (4S)-4-
(1-methylethyl)-2-oxazolidinone as chiral auxiliary were
studied (Table 1). When a solution of 1a in aqueous acetone
(acetone/water 4:1) was treated with AgNO3 (1.2 equiv) and
Br2 (1.2 equiv) at rt (25 8C), it gave the desired carboxy-
bromohydrin with poor diastereoselectivity (dr 52:48;
entry 1) and the diastereomeric ratio was increased to
65:35 (entry 2) when the reaction was performed at 0–5 8C.
The bromohydrin reaction of 1a in aqueous acetonitrile was
comparable (entry 3) with aqueous acetone. However, there
was no bromohydrin reaction in aqueous DMF, DMSO and
THF (entry 4). Iodohydrin reaction of 1a under the same
reaction conditions gave !5% of the desired compounds
(entry 5), also there was no improvement even with the use
of excess reagents and under different reaction conditions.
While the bromohydrin reaction of 1b was performed under
the same reaction conditions, it gave mixture of products
(entry 6). However, 1b smoothly underwent iodohydrin
reaction with 70:30 diastereoselectivity (entry 8) in aqueous
acetone. There is no appreciable change in diastereomeric
ratio and yield when the reaction was performed at rt (25 8C)
(entry 7). Unlike 1a, 1b underwent iodohydrin reaction in
aqueous THF with improved diastereoselectivity of 80:20
(entry 9). Bromohydrin reaction was also studied for the
Scheme 1.
reaction of chiral b-aryl-a-halo-b-oxycarboxylic acid esters
for the enantioselective synthesis of lignans.11 However,
there is no suitable method, other than the aldol reaction,7
for the synthesis of the chiral b-aryl-a-halo-b-oxycarb-
oxylic acid derivatives.
There are only a few reports for the halohydrin reactions of
a,b-unsaturated carbonyls.2d,3,12 By screening these
methods, we found that halogen (Br2/I2) and silver nitrate
(AgNO3) is an effective combination for the halohydrin
reaction of N-cinnamoyl-2-oxazolidinoes 1 over aromatic
electrophilic substitutions. Halohydrin reaction of 1a (RZ
Ph and R0Zi-Pr) with Br2 and AgNO3 in aqueous acetone
gave the desired carboxybromohydrine, along with a minor
amount of a non-separable mixture of diastereoisomers
(dr 60:40) of a dibromo compounds -anti-(4S)-3-(20,30-
dibromo-30-phenyl-propionyl)-4-(1-methylethyl)-2-oxazo-
lidinone (5a). The formation of 5a varied with the amount of
water in the reaction media. A systematic study showed that
when the acetone/water ratio was maintained between 4:1
Table 1. AgNO3-promoted halohydrin reactions of 1 under different reaction conditions
Substrate
R
R1
Solvent
X
Ratioa (3:4)
Yieldb (%)
1c
2
3
4
1a
1a
1a
1a
Ph
Ph
Ph
Ph
i-Pr
i-Pr
i-Pr
i-Pr
Acetone
Acetone
CH3CN
DMF or DMSO
or THF
Br
Br
Br
Br
52:48 (55:45)
65:35 (66:34)
64: 36 (62:38)
88
92
82
NR
5
1a
Ph
i-Pr
Acetone or THF
or CH3CN
Acetone
Acetone
Acetone
THF
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
I
ND
!5%d
e
6
1b
1b
1b
1b
1c
1c
1c
1d
1e
1f
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
2-ClC6H4
2-ClC6H4
2- ClC6H4
Ph
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
i-Pr
Ph
Br
I
I
ND
7c
8
65:35 (68:32)
70:30 (70:30)
80:20 (82:18)
62:38 (65:35)
52:48
86
89
92
91
87
9
I
10
11c
12
13
14
15
16
Br
Br
I
Br/I
Br/I
Br/I
Br/I
NR
e
ND
ND
ND
ND
e
e
e
Ph
4-MeOC6H4
4-MeOC6H4
Ph2CH
Ph
Ph2CH
1 g
a Determined from the 1H NMR spectrum of the crude reaction mixture. Ratio in the parentheses refer to the ratio of isolated 3 and 4 after column
chromatography.
b Combined isolated yields of 3 and 4 after chromatography.
c Reaction at room temperature (25 8C).
d O90% of 1a was recovered.
e Mixture of products. ND: Not determined; NR: No reaction.

S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
2281
Figure 1. ORTEP diagram of 3c and 4c.
electron-deficient substrate 1c, obtaining moderate dia-
stereoselectivity with good yield (entry 10). Like 1a, when
the bromohydrination of 1c was performed at rt, it also
showed poor diastereoselectivity (entry 11) as well as not
responding to the iodohydrin reaction (entry 12). The
configurational assignments for the diastereomeric carb-
oxyhalohydrins 3 and 4 were made by confirming the
stereochemistry of 3a and 4a on comparison with the
literature data.7d,13 This was confirmed by the single crystal
X-ray analysis14 of 3c and 4c (Fig. 1), crystallized from
CHCl3.
Recently, Barluenga et al. found that phenyl group present
in the terpene moiety undergoes halocarbocyclization
during the iodohydrination of alkenes tethered in terpene
derivatives with Py2IBF4.6 Spectral analysis of the unde-
sired compounds were found to be bromo-carbocyclized
product, but the regio- and stereochemistry of the bromo-
carbocylized products could not be confirmed. Our several
attempts were also failed to get single crystal X-ray
difraction quality crystals.16
To assess whether the counter anion of the Ag(I) salt affects
the diastereoselctivity of the halohydrin reactions, product
studies were carried out employing the electronically
different cinnamoyl substrates 1a–1c, using AgOAc and
Ag2O instead of AgNO3 as a promoter, under a variety of
reaction conditions (Table 2). AgNO3 (Eq. 1) and AgOAc
(Eq. 2) produce acids on reaction with a halogen in water,
whereas Ag2O does not produce any acid (Eq. 3) under the
same reaction conditions. When the halohydrin reactions of
1a-1c were performed in the presence of AgOAc instead of
AgNO3, similar results were obtained, that is, 3 was
produced as the major diastereoisomer (Table 2; entries
1–3). But in the case of Ag2O-mediated reactions, 1a and
the electron-deficient 1c showed very poor diastereoselec-
tivities (entries 4 and 6), whereas 1b still showed 3b as the
Since, the (4S)-4-(1-methylethyl)-2-oxazolidinone chiral
auxiliary gave moderate to good diastereoselectivities, we
also examined other oxazolidinone chiral auxiliaries viz
(4S)-4-phenyl- and (4S)-4-(diphenylmethyl)-2-oxazolidi-
nones.10,15 Unfortunately, halohydrin reaction of substrates
1d–1e, having different oxazolidinone chiral auxiliaries
(R0ZPh, Ph2CH) using Br2 and/or I2, gave mixture of
products. Only 12% of an undesired compound was
obtained in pure form from the bromohydrin reaction of
1d. The same compound was obtained in 56% yield, along
with minor amount (26%) of another undesired product,
when 1d was treated with AgNO3 and Br2 in dry acetone i.e.
in the absence of any external nucleophile at 0–5 8C.
Table 2. AgOAc- and Ag2O-promoted halohydrin reaction of 1a
Entry
Substrate
Ag(I) salt
Additive
X
Ratiob (3:4)
Yieldc (%)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1a
1b
1c
1a
1b
1c
AgOAc
AgOAc
AgOAc
Ag2O
Ag2O
Ag2O
Ag2O
Ag2O
Ag2O
None
None
None
None
None
None
HNO3
HNO3
HNO3
Br
I
Br
Br
I
Br
Br
I
65:35
80:20
60:40
50:50
65:35
50:50
67:33 (66:34)
79:21 (77:23)
61:39 (62:38)
94
91
90
97
88
94
96 (95)
90 (87)
94 (91)
Br
a Halohydrin reactions were performed using 0.7 equiv of Ag2O and 1.2 equiv of halogen (X2) in aqueous organic solvent (1a and 1c in aqueous acetone and 1b
in aqueous THF) at 0–5 8C for 30 min.
b Determined from the 1H NMR spectrum of the crude reaction mixture.
c Isolated yields: ratios in parentheses refer to the reactions in the presence of AcOH.

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S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
major diastereomer with dr of 65:35 (Table 2; entry 5).
When the Ag2O-promoted halohydrin reactions of 1a–1c
were performed in the presence of either HNO3 or AcOH as
an additive, these showed diastereoselectivities (Table 2;
entries 7–9) similar to either AgNO3- or AgOAc-promoted
reactions (Table 1, entries 2, 9 and 10 and Table 2, entries
1–3).
either AgNO3 or AgOAc promoted reactions, the HC-
chelated S-cis-syn-dipole conformation 10 might be
involved in the halohydrin reaction. The preferred attack
of XC from the Re-face of conformation 10 and subsequent
opening of the halonium intermediate 20 by anti-nucleo-
philic attack of H2O at the b-position yielded 3 as the major
diastereoisomer (Scheme 2). The poor diastereoselectivities
of the cinnamoyl- and electron-deficient cinnamoyl sub-
strates 1a and 1c in Ag2O-promoted reactions i.e. under
unchelated conditions (Table 2; entries 4 and 6) might be
accounted for by the involvement of both the equilibrated S-
cis- and S-trans-anti-dipole conformations 1 and 100. The
iodohydrination of electron-rich cinnamoyl substrate 1b
promoted by Ag2O, that is, under unchelated conditions still
showed carboxyhalohydrin 3b a major diastereoisomer.
This could be due to the extensive conjugation of the
electron-donating substituent at the p-position with the
a,b-unsaturated carbonyls, equilibrium might be shifted
more towards the unchelated S-trans-anti-dipole confor-
mation 100 and involve the Re-face of S-trans-anti-dipole
conformation 100, providing 3b as the major diastereoisomer.
This was supported by the Ag2O-mediated reactions
performed in the presence of either HNO3 or AcOH as an
additive (Table 2; entries 7–9).
AgNO3 CX2 CH2O/AgXYCHOX CHNO3
AgOAc CX2 CH2O/AgXYCHOX CAcOH
Ag2O C2X2 C2H2O/2AgXYC2HOX
(1)
(2)
(3)
Unchelated N-cinnamoyl-2-oxazolidinone usually exists in
the S-cis-anti-dipole conformation 1,17 so it was also
expected to give carboxyhalohydrin 4 as a major dia-
stereoisomer for the above halohydrin reactions, but that
was not observed. So it might be concluded here that in
It was found that either AgNO3 or AgOAc as a promoter and
(4S)-4-(1-methylethyl)-2-oxazolidinone as a chiral auxiliary
are a better combination for the Ag(I)-promoted halohydrin
reaction. So, to generalize this asymmetric halohydrin
reaction, the reaction was further studied for a variety of
enoyl substrates containing (4S)-4-(1-methylethyl)-2-oxa-
zolidinone as a chiral auxiliary (Table 3). Substrate 1h
possessing strong electron-withdrawing substituents, for
example, –NO2 group on the aromatic ring, smoothly
underwent bromohydrin reaction in aqueous acetone under
the same reaction conditions with moderate diastereoselec-
tivity (entry 1). Similar to 1c, no iodohydrin reaction was
observed for 1h. Substrate 1i with an electron-donating
substituent on the aromatic ring efficiently underwent
iodohydrin reaction under the same reaction conditions in
aqueous acetone with moderate diastereoselectivity (entry
2). Like 1b, the iodohydrin reaction of 1i in aqueous THF
provided improved diastereoselectivity (entry 3). Another
two electron-rich cinnamoyl substrates 1j and 1k also
responded to the iodohydrin reaction in aqueous THF with
dr of 82:18 and 78:22, respectively (entries 4 and 5).
However, due to instability of the minor isomers 4j and 4k
in silica-gel during column chromatography, they could not
Scheme 2.
Table 3. AgNO3-promoted halohydrin reaction of different substrates 1
Substrate
R
Solvent
X
Ratioa (3:4)
Yieldb (%)
1
2
3
4
5
6
7
8
1 h
1i
1i
2-NO2C6H4
4-BnOC6H4
4-BnOC6H4
3, 4-MeOC6H3
4-BnO-3-MeOC6H3
3, 5-Br-4-BnOC6H2
2-naphthyl
Acetone
Acetone
THF
THF
THF
Acetone
Acetone
Acetone
Br
I
I
I
I
Br
I
Br
60:40
64:36
80:20
82:18
78:22
65:35
68:32
62:38d
86
91
92
1j
77c
74c
87
1k
1 l
1m
1n
88
86e
CH3
a Determined from the 1H NMR spectrum of the crude reaction mixture.
b Combined isolated yields of 3 and 4 after chromatography otherwise it is noted.
c Isolated yield of the isomer 3.
d Along with 15% of other regio-isomers
e Combined isolated yield of 3n, 4n and the other regio-isomers.

S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
2283
be obtained in pure form. While the bromohydrin reaction of
1i–1k were performed under the same reaction conditions;
these gave a mixture of products. We have also studied the
halohydrin reaction of electronically different cinnamoyl
substrates, where 1l behaved like an electron-deficient
cinnamoyl substrate, that is, responded to the bromohydrin
reaction in aqueous acetone (entry 6) but no iodohydrin
reaction. On the other hand, 1m acted as an electron-rich
cinnamoyl substrate and smoothly underwent iodohydrin
reaction in aqueous acetone (entry 7), whereas bromohydrin
reaction gave mixture of products. We have also studied
the halohydrin reaction of alkenoyl substrate 1n. This
responded to the bromohydrin reaction with moderate
diastereoselectivity (entry 8), along with 15% of other
regio-isomers, minor isomer 4n was always obtained as a
non-separable mixture with regio-isomers.
Commercial grade reagents were used without further
purification. Solvents are used after distillation following
usual protocols. For the halohydrin reaction distilled water
is used. Flash chromatography was carried out using Acme
silica gel (230–400 mesh). Substrates 1 were synthesized
following the literature procedures.10,18
4.1. General experimental procedure for the halohydrin
reaction
To a solution of the substrate 1 (1 mmol) in aqueous organic
solvent (20 ml; acetone or THF; organic solvent/H2O 4:1)
Ag(I) (for AgNO3 and AgOAc 1.2 mmol and Ag2O
(0.7 mmol) and halogen (Br2 or I2, 1.2 mmol) were added,
respectively, at 0–5 8C and allowed to stir for 20–30 min.
The reaction mixture was extracted with Et2O at least three
times, washed with water, dried over Na2SO4. The organic
solution was filtered through a small cellite pad (otherwise
locking problem or poor base line was found in the 1H NMR
of the crude mixture) and the filtrate was concentrated under
vacuum. Flash column chromatography of the crude
mixture using petroleum ether-EtOAc as eluent gave
desired carboxyhalohydrins in pure form.
3. Conclusion
In conclusion, we have described Ag(I)-promoted asym-
metric halohydrin reaction of chiral N-enoyl-2-oxazolidi-
nones 1 with high regio- and anti-selectivity and moderate
to good diastereoselectivity in good yields. Alkenoyl,
cinnamoyl and electron-deficient cinnamoyl substrates
smoothly undergo bromohydrin reactions but no iodohydrin
reactions, whereas electron-rich cinnamoyl substrates prefer
to undergo iodohydrin reactions. AgNO3 and AgOAc are
found to be better promoters than Ag2O for promoting
diastreoselectivity. It was found that the acids produced on
reactions of AgNO3 and AgOAc with halogen in aqueous
media were responsible for the involvement of the
HC-chelated S-cis-syn-dipole conformation and provided
better diastereoselectivity for the halohydrin reactions of
N-enol-2-oxazolidinoes. It was also found that the oxazo-
lidinone chiral auxiliary should contain alkyl substituents,
more specifically non-nucleophilic substituents; otherwise
that would act as a competitive nucleophile. This method-
ology, that is, the direct use of halogen and water promoted
by Ag(I), offers an alternative method for the asymmetric
synthesis of carboxyhalohydrins, that is, anti-a-halo-b-
hydroxycarboxylic acid derivatives. We are currently
applying the concept of halohydrin reaction to other halo-
nucleophilic (XC NuK) addition reactions for the asym-
metric 1,2-hetero-bifunctionalization of alkenes.
4.1.1. anti-(4S, 20S, 30S)-3-[30-Hydroxy-20-iodo-30-(4-
methoxyphenyl)-propionyl]-4-(1-methylethyl)-2-oxazo-
lidinone (3b). Gummy liquid, [a]2D1 C88.48 (c 1.0, CHCl3);
FTIR (KBr) 3459 (br, OH), 2963, 2837, 1778, 1694, 1612,
1586, 1515, 1484, 1463, 1387, 1303, 1250, 1205, 1178,
1142, 1103, 1022, 971, 835, 789, 768, 728, 694, 565 cmK1
;
1H NMR (200 MHz, CDCl3) d 7.33 (d, JZ8.6 Hz, 2H), 6.89
(d, JZ8.6 Hz, 2H), 6.13 (d, JZ7.9 Hz, 1H), 5.15 (d, JZ
7.9 Hz, 1H), 4.47 (m, 1H), 4.30–4.20 (m, 2H), 3.80 (s, 3H),
3.40 (br s, 1H), 2.5–2.33 (m, 1H), 0.95 (t, JZ6.3 Hz, 6H);
13C NMR (50 MHz, CDCl3) d 170.9, 159.7, 152.9, 131.7,
128.3 (2C), 113.9 (2C), 75.4, 63.4, 58.2, 55.2, 27.9, 25.0,
17.7, 15.0. Anal. Calcd for C16H20INO5: C, 44.36; H, 4.65;
N, 3.23. Found: C, 44.18; H, 4.45; N, 2.92%.
4.1.2. anti-(4S, 20R, 30R)-3-[30-Hydroxy-20-iodo-30-(4-
methoxyphenyl)-propionyl]-4-(1-methylethyl)-2-oxazo-
lidinone (4b). Gummy liquid; [a]2D2 C8.68 (c 1.0, CHCl3);
FTIR (KBr) 3473 (br OH), 2962, 2929, 1777, 1697, 1611,
1514, 1485, 1463, 1386, 1303, 1250, 1202, 1177, 1120,
1030, 972, 830, 789, 769, 694, 562 cmK1 1H NMR
;
(200 MHz, CDCl3) d 7.33 (d, JZ8.7 Hz, 2H), 6.87 (d, JZ
8.7 Hz, 2H), 6.18 (d, JZ7.0 Hz, 1H), 5.10 (d, JZ7.0 Hz,
1H), 4.49–4.11 (m, 3H), 3.79 (s, 3H), 2.37–2.12 (m, 1H),
0.85 (d, JZ7.0 Hz, 3H), 0.65 (d, JZ7.0 Hz, 3H); 13C NMR
(50 MHz, CDCl3) d 171.2, 159.7, 153.0, 131.6, 128.0 (2C),
113.9 (2C), 75.8, 63.4, 59.0, 55.3, 28.5, 23.8, 17.8, 14.3.
Anal. Calcd for C16H20INO5: C, 44.36; H, 4.65; N, 3.23.
Found: C, 44.54; H, 4.86; N, 3.02%.
4. Experimental
The 1H NMR spectra were measured on a Bruker-200
(200 MHz) and Bruker-500 (500 MHz) using CDCl3 as
solvent. The 13C NMR spectra were measured with Bruker-
200 (50 MHz) and Bruker-500 (125 MHz) using CDCl3 as
solvent. 1H NMR chemical shifts are expressed in parts per
million (d) downfield to CHCl3 (dZ7.26); 13C NMR
chemical shifts are expressed in parts per million (d)
relative to the central CDCl3 resonance (dZ77.0). Coupling
4.1.3. anti-(4S, 20S, 30S)-3-[20-Bromo-30-hydroxy-30-(2-
chlorophenyl)-propionyl]-4-(1-methylethyl)-2-oxazolidi-
none (3c). Mp 108–109 8C; [a]2D2 C69.98 (c 1.0, CHCl3);
FTIR (KBr) 3450 (br OH), 2964, 2920, 2849, 1782, 1702,
1464, 1439, 1386, 1302, 1203, 1120, 1049, 1024, 971, 763,
717, 686, 636, 599, 465 cmK1; 1H NMR (200 MHz, CDCl3)
d 7.55–7.51 (m, 1H), 7.42–7.24 (m, 3H), 6.12 (d, JZ7.3 Hz,
1H), 5.66 (br d, 1H), 4.44 (m, 1H), 4.23 (m, 2H), 3.72 (br s,
1H), 2.5–2.3 (m, 1H), 0.93 (d, JZ7.0 Hz, 6H); 13C NMR
1
constants in H NMR are in Hz. IR spectra were recorded
using Thermo Nicolet FT-IR spectroscopy. Elemental
analyses were carried out using Perkin–Elmer 2400-II
and mass spectra were analyzed by Waters LCT mass
spectrometer.

2284
S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
(50 MHz, CDCl3) d 169.0, 152.7, 136.5, 133.4, 129.8,
129.7, 128.4, 127.2, 71.7, 63.5, 58.3, 43.1, 28.0, 17.8, 14.8.
Anal. Calcd for C15H17BrClNO4: C, 46.12; H, 4.39; N, 3.59.
Found: C, 46.08; H, 4.18; N, 3.59%.
2.30 (m, 1H), 0.96 (quasi t, JZ5.90, 6.8 Hz, 6H); 13C NMR
(50 MHz, CDCl3) d 171.0, 159.0, 152.9, 136.8, 131.9, 128.5
(2C), 128.3 (2C), 128.0, 127.4 (2C), 114.9 (2C), 75.5, 70.1,
63.0, 58.2, 28.0, 24.9, 17.8, 15.1. Anal. Calcd for
C22H24INO5: C, 51.88; H, 4.75; N, 2.75. Found: C, 51.99;
H, 4.79; N, 2.67%.
4.1.4. anti-(4S, 20R, 30R)-3-[20-Bromo-30-hydroxy-30-(2-
chlorophenyl)-propionyl]-4-(1-methylethyl)-2-oxazolidi-
none (4c). Mp 123–124 8C; [a]2D1 K6.48 (c 1.0, CHCl3);
FTIR (KBr) 3455 (br OH), 2964, 2926, 1779, 1703, 1676,
1593, 1483, 1465, 1438, 1385, 1301, 1201, 1120, 1049,
4.1.8. anti-(4S, 20R, 30R)-3-[30-Hydroxy-20-iodo-30-(4-
benzyloxyphenyl)-propionyl]-4-(1-methylethyl)-2-oxa-
zolidinone (4i). Gummy liquid, [a]2D3 C8.68 (c 1.0, CHCl3);
FTIR (KBr) 3459 (br OH), 2962, 2925, 1777, 1695, 1609,
1512, 1485, 1463, 1454, 1384, 1302, 1202, 1175, 1120,
1
1023, 973, 755, 718, 684, 669, 632, 464 cmK1; H NMR
(200 MHz, CDCl3) d 7.60–7.45 (m, 1H), 7.40–7.20 (m, 3H),
6.22 (d, JZ6.5 Hz, 1H), 5.58 (d, JZ6.5 Hz, 1H), 4.42 (m,
1H), 4.33–4.14 (m, 2H), 2.30–2.15 (m, 1H), 0.86 (d, JZ
7.0 Hz, 3H), 0.60 (d, JZ7.0 Hz, 3H); 13C NMR (50 MHz,
CDCl3) d 169.1, 152.8, 136.5, 133.2, 129.7, 129.6, 128.2,
127.1, 72.3, 63.4, 58.9, 42.0, 28.3, 17.7, 14.3. Anal. Calcd
for C15H17BrClNO4: C, 46.12; H, 4.39; N, 3.59. Found: C,
46.34; H, 4.24; N, 3.54%.
1
1020, 829, 738, 697, 624, 558 cmK1; H NMR (200 MHz,
CDCl3) d 7.48–7.25 (m, 7H), 6.96 (d, JZ8.7 Hz, 2H), 6.19
(d, JZ7.0 Hz, 1H), 5.13–5.05 (m, 3H), 4.51–4.08 (m, 3H),
3.63 (br d, JZ7.0 Hz, 1H), 2.32–2.15 (m, 1H), 0.84 (d, JZ
7.0 Hz, 3H), 0.64 (d, JZ7.0 Hz, 3H); 13C NMR (50 MHz,
CDCl3) d 171.1, 158.9, 153.0, 136.8, 131.9, 128.5 (2C),
128.0 (2C), 127.9, 127.3 (2C), 114.9 (2C), 75.8, 70.0, 63.4,
58.9, 28.4, 23.7, 17.7, 14.3. Anal. Calcd for C22H24INO5: C,
51.88; H, 4.75; N, 2.75. Found: C, 51.93; H, 4.57; N, 2.75%.
4.1.5. anti-(4S, 20S, 30S)-3-[20-Bromo-30-hydroxy-30-(2-
nitrophenyl)-propionyl]-4-(1-methylethyl)-2-oxazolidi-
none (3h). Mp 155–156 8C; [a]2D3 C113.68 (c 1.0, CHCl3);
FTIR (KBr) 3381 (br OH), 2965, 1748, 1707, 1529, 1488,
1403, 1393, 1364, 1300, 1281, 1227, 1217, 1143, 1119,
4.1.9. anti-(4S, 20S, 30S)-3-[30-Hydroxy-20-iodo-30-(3,4-
dimethoxyphenyl)-propionyl]-4-(1-methylethyl)-2-oxa-
zolidinone (3j). Mp 164–165 8C; [a]2D3 C54.68 (c 1.0,
CHCl3); FTIR (KBr) 3473 (br OH), 3024, 2964, 1761, 1702,
1607, 1591, 1517, 1484, 1465, 1448, 1438, 1421, 1388,
1365, 1332, 1298, 1262, 1236, 1218, 1201, 1160, 1137,
1119, 1105, 1071, 1052, 1024, 1002, 969, 889, 835, 761,
1043, 1018, 972, 853, 780, 749, 719, 674, 608, 504 cmK1
;
1H NMR (200 MHz, CDCl3) d 7.95 (dd, JZ8.0, 0.9 Hz,
1H), 7.85–7.60 (m, 2H), 7.57–7.45 (m, 1H), 6.08 (d, JZ
8.0 Hz, 1H), 5.93 (d, JZ8.0 Hz, 1H), 4.49 (m, 1H), 4.35–
4.18 (m, 2H), 3.75 (br s, 1H), 2.50–2.33 (m, 1H), 0.94
(d, JZ7.0 Hz, 3H), 0.92 (d, JZ7.0 Hz, 3H); 13C NMR
(50 MHz, CDCl3) d 168.4, 152.8, 149.1, 133.7, 133.3,
129.4, 129.3, 124.6, 69.6, 63.6, 58.3, 43.8, 28.0, 17.7, 14.7.
Anal. Calcd for C15H17BrN2O6: C, 44.90; H, 4.27; N, 6.98.
Found: C, 44.60; H, 4.03; N, 6.73%.
1
700, 655, 618, 576 cmK1; H NMR (200 MHz, CDCl3) d
7.10–6.70 (m, 3H), 6.17 (d, JZ7.6 Hz, 1H), 5.13 (d, JZ
7.6 Hz, 1H), 4.45 (m, 1H), 4.25 (m, 2H), 3.90 (s, 3H), 3.88
(s, 3H), 2.51–2.30 (m, 1H), 0.95 (t, JZ6.5 Hz, 6H); 13C
NMR (50 MHz, CDCl3) d 171.0, 152.8, 149.0, 148.9, 131.9,
119.4, 110.9, 109.8, 75.6, 63.3, 58.1, 55.9, 55.8, 27.8, 24.6,
17.8, 15.0. Anal. Calcd for C17H22INO6: C, 44.07; H, 4.79;
N, 3.02. Found: C, 44.11; H, 4.77; N, 2.85%.
4.1.6. anti-(4S, 20R, 30R)-3-[20-Bromo-30-hydroxy-30-(2-
nitrophenyl)-propionyl]-4-(1-methylethyl)-2-oxazolidi-
none (4h). Gummy liquid; [a]2D2 K39.18 (c 1.0, CHCl3);
FTIR (KBr) 3453 (br OH), 2964, 2927, 2876, 1779, 1704,
1608, 1580, 1529, 1485, 1464, 1386, 1351, 1300, 1203,
4.1.10. anti-(4S, 20S, 30S)-3-[30-Hydroxy-20-iodo-30-(4-
benzyloxy-3-methoxyphenyl)-propionyl]-4-(1-methyl-
ethyl)-2-oxazolidinone (3k). Gummy liquid: [a]2D3 C64.38
(c 1.0, CHCl3); FTIR (KBr) 3455 (br OH), 2963, 2929,
2875, 1778, 1694, 1594, 1514, 1485, 1463, 1454, 1422,
1386, 1303, 1262, 1203, 1141, 1102, 1020, 971, 912, 857,
1142, 1120, 1052, 1020, 972, 853, 786, 750, 713, 672 cmK1
;
1H NMR (200 MHz, CDCl3) d 7.97 (dd, JZ8.0, 0.9 Hz,
1H), 7.87–7.60 (m, 2H), 7.57–7.42 (m, 1H), 6.16 (d, JZ
7.4 Hz, 1H), 5.90 (d, JZ7.4 Hz, 1H), 4.43 (m, 2H), 4.40–
4.15 (m, 2H), 2.48–2.15 (m, 1H), 0.89 (d, JZ7.0 Hz, 3H),
0.71 (d, JZ7.0 Hz, 3H); 13C NMR (50 MHz, CDCl3) d
168.6, 152.9, 148.9, 134.1, 133.4, 129.3, 129.0, 124.8, 70.6,
63.6, 59.1, 42.6, 24.4, 17.7, 14.5. Anal. Calcd for
C15H17BrN2O6: C, 44.90; H, 4.27; N, 6.98. Found: C,
44.67; H, 4.13; N, 6.73%.
1
804, 767, 734, 697, 648, 617, 563, 456 cmK1; H NMR
(200 MHz, CDCl3) d 7.50–725 (m, 7H), 6.94 (s, 1H), 6.87
(m, 2H), 6.15 (d, JZ7.6 Hz, 1H), 5.14 (m, 3H), 4.48–4.35
(m, 1H), 4.29–4.16 (m, 2H), 3.90 (s, 3H), 3.57 (br s, 1H),
2.50–2.31 (m, 1H), 0.94 (t, JZ6.6 Hz, 6H), 13C NMR
(50 MHz, CDCl3) d 170.9, 152.7, 149.5, 148.1, 136.8,
132.4, 128.4 (2C), 127.4, 127.1 (2C), 119.2, 113.5, 110.3,
75.6, 70.8, 63.2, 58.0, 55.9, 27.7, 24.5, 17.7, 14.9. Anal.
Calcd for C23H26INO6: C, 51.22; H, 4.86; N, 2.60. Found:
C, 51.06; H, 4.91; N, 2.68%.
4.1.7. anti-(4S, 20S, 30S)-3-[30-Hydroxy-20-iodo-30-(4-ben-
zyloxyphenyl)-propionyl]-4-(1-methylethyl)-2-oxazolidi-
none (3i). Mp 163–164 8C; [a]2D2 C63.08 (c 1.0, CHCl3);
FTIR (KBr) 3465 (br OH), 3033, 2959, 2921, 2874, 1768,
1678, 1608, 1515, 1487, 1455, 1429, 1388, 1366, 1329,
1307, 1247, 1221, 1206, 1178, 1119, 1101, 1078, 1049,
1021, 1003, 970, 922, 857, 841, 821, 800, 760, 749, 729,
4.1.11. anti-(4S, 20S, 30S)-3-[20-Bromo-30-hydroxy-30-(4-
benzyloxy-3, 5-dibromophenyl)-propionyl]-4-(1-methyl-
ethyl)-2-oxazolidinone (3l). Mp 170–171 8C; [a]2D2 C45.68
(c 1.0, CHCl3); FTIR (KBr) 3448 (br OH), 2960, 2922,
2853, 1781, 1700, 1645, 1456, 1380, 1256, 1200, 1116,
1
702, 694, 626, 562, 509, 490 cmK1; H NMR (200 MHz,
CDCl3) d 7.50–7.25 (m, 7H), 6.97 (d, JZ8.7 Hz, 2H), 6.13
(d, JZ7.9 Hz, 1H), 5.16 (d, JZ7.9 Hz, 1H), 5.06 (s, 2H),
4.52–4.38 (m, 1H), 4.33–4.18 (m, 2H), 3.44 (br s, 1H), 2.51–
1047, 742, 701, 620, 532 cmK1 1H NMR (200 MHz,
;
CDCl3) d 7.65–7.55 (m, 4H), 7.51–7.32 (m, 3H), 5.74 (d,
JZ8.3 Hz, 1H), 5.12 (d, JZ8.3 Hz, 1H), 5.03 (s, 2H), 4.50

S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
2285
(m, 1H), 4.42–4.18 (m, 2H), 2.67 (br s, 1H), 2.52–2.25 (m,
1H), 0.99 (d, JZ7.1 Hz, 6H); 13C NMR (50 MHz, CDCl3) d
168.7, 152.9, 152.8, 137.8, 136.0, 131.6 (2C), 128.4 (5C),
118.5 (2C), 74.6, 73.3, 63.6, 58.3, 44.6, 28.0, 17.7, 14.7.
Anal. Calcd for C22H22Br3NO5: C, 42.61; H, 3.58; N, 2.26.
Found: C, 42.86; H, 3.42; N, 2.19%.
296.013 (MCHC2)C. Anal. Calcd for C10H16BrNO4: C,
40.83; H, 5.48; N, 4.76. Found: C, 40.48; H, 5.31; N, 4.75%.
4.1.16. anti-(4S, 20R, 30R)-3-(20-Bromo-30-hydroxy-butio-
nyl)-4-(1-methylethyl)-2-oxazolidinone (4n). Oily liquid,
[a]2D2 C18.48 (c 1.0, CHCl3); FTIR (KBr) 3445 (br OH),
1773, 1702, 1377, 1318, 1200, 1104, 1012, 767, 708,
4.1.12. anti-(4S, 20R, 30R)-3-[20-Bromo-30-hydroxy-30-(4-
benzyloxy-3, 5-dibromophenyl)-propionyl]-4-(1-methyl-
ethyl)-2-oxazolidinone (4l). Gummy liquid, [a]2D2 C6.888
(c 1.0, CHCl3); FTIR (KBr) 3473 (br OH), 3064, 3032,
2963, 2926, 2874, 1781, 1705, 1548, 1497, 1485, 1455,
1386, 1303, 1256, 1202, 1141, 1105, 1053, 1019, 970, 914,
875, 740, 697, 632, 537 cmK1; 1H NMR (200 MHz, CDCl3)
d 7.65–7.45 (m, 4H), 7.44–7.33 (m, 3H), 5.87 (d, JZ7.4 Hz,
1H), 5.09 (d, JZ7.4 Hz, 1H), 5.03 (s, 2H), 4.45 (m, 1H),
4.40–4.19 (m, 2H), 2.42–2.18 (m, 1H), 0.84 (d, JZ6.9 Hz,
3H), 0.75 (d, JZ6.9 Hz, 3H); 13C NMR (50 MHz, CDCl3) d
168.8, 153.0, 152.8, 137.9, 135.9, 131.4 (2C), 128.4 (5C),
118.6 (2C), 74.6, 73.8, 63.6, 59.0, 43.9, 28.4, 17.7, 14.4..
Anal. Calcd for C22H22Br3NO5: C, 42.61; H, 3.58; N, 2.26.
Found: C, 42.45; H, 3.52; N, 2.08%.
655 cmK1 1H NMR (200 MHz, CDCl3) d 5.35 (d, JZ
.
8.6 Hz, 1H); 4.45 (m, 1H); 4.30–4.17 (m, 5H); 2.70 (br S,
1H), 2.37–2.27 (m, 1H); 1.39 (d, JZ6.3 Hz, 3H); 0.87 (dd,
JZ2.4, 6.9 Hz, 6H). 13C NMR (50 MHz, CDCl3) d 169.6,
153.4, 68.8, 64.0, 58.7, 46.8, 28.5, 20.4, 18.2, 15.2. Anal.
Calcd for C10H16BrNO4: C, 40.83; H, 5.48; N, 4.76. Found:
C, 40.46; H, 5.17; N, 4.86%.
4.1.17. anti-(4S)-3-(20,30-Dibromo-30-phenyl-propionyl)-
4-(1-methylethyl)-2-oxazolidinone (5a). Non-seperable
mixture of diastereomers (60:40); light yellow solid, mp
1
76–80 8C; H NMR (200 MHz, CDCl3) d 7.60–7.26 (m,
5H), 6.58 (d, JZ11.6 Hz, 1H), 5.51 (d, JZ11.6 Hz, 1H),
4.65–4.50 (m, 1H), 4.47–4.20 (m, 2H), 2.60– 2.40 (m, 1H),
0.98 (d, JZ6.8 Hz, 1.8H), 0.97 (d,, JZ6.9 Hz, 2.4H), 0.95
(d, JZ6.8 Hz, 1.8H). 13C NMR (125 MHz, CDCl3): major d
167.6, 153.6, 138.0, 129.9, 129.4 (2C), 128.8 (2C), 64.1,
58.9, 50.6, 44.3, 28.5, 18.2, 15.3. minor d 167.8, 153.5,
137.9, 129.8, 129.3 (2C), 128.7 (2C), 63.9, 59.5, 51.2, 43.9,
28.7, 18.3, 15.2.
4.1.13. anti-(4S, 20S, 30S)-3-[30-Hydroxy-20-iodo-30-(2-
naphthyl)-propionyl]-4-(1-methylethyl)-2-oxazolidinone
(3m). Mp 90–91 8C; [a]D22 C118.38 (c 0.8, CHCl3); FTIR
(KBr) 3444 (br OH), 2963, 2925, 1779, 1693, 1601, 1386,
1304, 1202, 1142, 1122, 1049, 1019, 819, 749, 694,
1
479 cmK1; H NMR (200 MHz, CDCl3) d 7.90–7.75 (m,
4.2. Bromocarbocyclized product
4H), 7.55–7.45 (m, 3H), 6.30 (d, JZ7.6 Hz, 1H), 5.33 (d,
JZ7.6 Hz, 1H), 4.41 (m, 1H), 4.19 (m, 2H), 2.49–2.28 (m,
1H), 0.94 (t, JZ7.5 Hz, 6H); 13C NMR (50 MHz, CDCl3) d
171.0, 152.8, 136.8, 133.3, 133.0, 128.5, 128.2, 127.6,
126.6, 126.3 (2C), 124.2, 76.1, 63.4, 58.1, 27.9, 24.2, 17.7,
15.0. Anal. Calcd for C19H20INO4: C, 50.35; H, 4.45; N,
3.09. Found: C, 50.40; H, 4.42; N, 3.02%.
4.2.1. Major compound. White amorphous solid, mp 156–
158 8C. FTIR (KBr) 1760, 1706, 1450, 1382, 1304, 1187,
1109, 1008, 750, 693, 589, 532, 485 cmK1 1H NMR
.
(200 MHz, CDCl3) d 7.40–7.20 (m, 9H); 6.01 (d, JZ7.4 Hz,
1H); 4.45 (dd, JZ8.8, 3.4 Hz, 1H); 5.08 (d, JZ7.4 Hz, 1H);
4.74 (t, JZ8.7 Hz, 1H); 4.25 (dd, JZ8.8, 3.4 Hz, 1H). 13C
NMR (50 MHz, CDCl3) d 168.8, 152.5, 138.6, 137.7, 129.0
(3C), 128.3 (3C), 126.6 (2C), 125.2 (2C), 75.0, 69.9, 57.7,
44.1. MS (ESI; m/z) for C18H14BrNO3 calculated (MCH)C
372.024, found 371.996 (MCH)C, 373.995 (MCHC2)C.
Anal. Calcd for (C18H14BrNO3C1H2O): C, 55.40; H, 4.13;
N, 3.59. Found: C, 55.53; H, 4.04; N, 3.75%.
4.1.14. anti-(4S, 20R, 30R)-3-[30-Hydroxy-20-iodo-30-(2-
naphthyl)-propionyl]-4-(1-methylethyl)-2-oxazolidinone
(4m). Gummy liquid, [a]2D2 C14.48 (c 0.5, CHCl3); FTIR
(KBr) 3458 (br OH), 2963, 1777, 1694, 1601, 1463, 1385,
1303, 1272, 1199, 1120, 1056, 1019, 819, 750, 693,
1
479 cmK1; H NMR (200 MHz, CDCl3) d 7.90–7.78 (m,
4H), 7.55–7.45 (m, 3H), 6.35 (d, JZ6.7 Hz, 1H), 5.29 (d,
JZ6.7 Hz, 1H), 4.42–4.08 (m, 3H), 3.90 (br s, 1H), 2.19–
1.95 (m, 1H), 0.76 (d, JZ7.0 Hz, 3H), 0.37 (d, JZ7.0 Hz,
3H); 13C NMR (50 MHz, CDCl3) d 171.1, 152.9, 136.6,
133.2, 133.0, 128.4, 128.0, 127.5, 126.2 (2C), 126.1, 124.0,
76.2, 63.3, 58.8, 28.3, 22.8, 17.6, 13.9. Anal. Calcd for
C19H20INO4: C, 50.35; H, 4.45; N, 3.09. Found: C, 50.26;
H, 4.26; N, 3.03%.
4.2.2. Minor compound. White amorphous solid, mp 151–
153 8C, FTIR (KBr) 1777, 1696, 1460, 1399, 1338, 1224,
1130, 1076, 1040,766, 685, 604, 523 cmK1 1H NMR
.
(200 MHz, CDCl3) d 7.60–7.20 (m, 9H); 5.91 (d, JZ8.2 Hz,
1H); 5.44 (dd, JZ8.6, 4 Hz, 1H); 5.12 (d, JZ8.2 Hz, 1H);
4.68 (t, JZ9 Hz, 1H); 4.26 (dd, JZ8.6, 4 Hz, 1H) 13C NMR
(50 MHz, CDCl3) d 168.9, 153.1, 139.4, 138.1, 129.7 (2C),
129.4, 129.2, 129.0 (2C), 127.6 (2C), 126.1 (2C), 75.2, 70.5,
58.1, 45.5. Anal. Calcd for (C18H14BrNO3 C1H2O): C,
55.40; H, 4.13; N, 3.59. Found: C, 55.38; H, 3.98; N, 3.75%.
4.1.15. anti-(4S, 20S, 30S)-3-(20-Bromo-30-hydroxy-butio-
nyl)-4-(1-methylethyl)-2-oxazolidinone (3n). Gummy
liquid, [a]2D2 C60.78 (c 1.0, CHCl3); FTIR (KBr) 3442 (br
OH), 1783, 1708, 1389, 1333, 1215, 1117, 1028, 772,
714 cmK1 1H NMR (200 MHz, CDCl3) d 5.43 (d, JZ
.
8.3 Hz, 1H); 4.40 (m, 1H); 4.31–4.18 (m, 5H); 3.58 (br s,
1H), 2.39–2.27 (m, 1H); 1.40 (d, JZ6.3 Hz, 3H); 0.87 (d,
JZ7.0 Hz, 3H); 0.83 (d, JZ7.0 Hz, 3H). 13C NMR
(50 MHz, CDCl3) d 169.5, 153.8, 69.6, 64.2, 59.7, 47.0,
29.0, 20.5, 18.3, 15.1. MS (m/z) for C10H16BrNO4:
calculated (MCH)C 294.024, found 294.015 (MCH)C,
Acknowledgements
We thank CSIR, New Delhi and DST, New Delhi for
providing financial support and Dr. K. Biradha for the single
crystal X-ray analysis. A. K. thanks CSIR, New Delhi and
M. B. thanks IIT, Kharagpur for their fellowships.

2286
S. Hajra et al. / Tetrahedron 61 (2005) 2279–2286
8. Genet, J. P.; de Andrade, M. C. C.; Vidal, V. R. Tetrahedron
References and notes
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Fringuelli, F.; Pizzo, F.; Vaccaro, L. J. Org. Chem. 2001, 66,
4463.
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