Transformation of (+)-thiomicamine into the p-methylthio analogue of (+)-5-epi-cytoxazone

Article abstract of DOI:10.1016/j.tetasy.2006.06.009

(2S,3S)-(+)-Thiomicamine 3, a commercially available aminodiol, was transformed into (4R,5S)-5-hydroxymethyl-4-(p-methylthiophenyl)-2-oxazolidinone 10, a compound related to cytoxazone-type biologically active natural products. The synthetic strategy of t

Full text of DOI:10.1016/j.tetasy.2006.06.009

Tetrahedron: Asymmetry 17 (2006) 1749–1753
Transformation of (+)-thiomicamine into the p-methylthio
analogue of (+)-5-epi-cytoxazone
Maria D. Rozwadowska*
Faculty of Chemistry, Adam Mickiewicz University, ul. Grunwaldzka 6, 60-780 Poznan´, Poland
Received 23 May 2006; accepted 2 June 2006
Abstract—(2S,3S)-(+)-Thiomicamine 3, a commercially available aminodiol, was transformed into (4R,5S)-5-hydroxymethyl-4-(p-meth-
ylthiophenyl)-2-oxazolidinone 10, a compound related to cytoxazone-type biologically active natural products. The synthetic strategy of
the highly regio- and stereoselective synthesis was based upon the reversal of the position of the hydroxyl and amine functionalities in 3,
accomplished via azidolysis of the key intermediate, epoxide 6.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
chiral cinnamic acid derivatives or by the construction of the
carbon framework by formation of a carbon–carbon bond
between two building blocks, chiral pool approach included.
More than 20 different syntheses of (ꢀ)-cytoxazone 1 and
its stereoisomers, for example, 2 (Fig. 1) have been
reported since the isolation of this cytokine modulator
from Streptomyces sp. by Osada et al. in 1998.1,2 The
synthesis of (ꢀ)-cytoxazone and its congeners appears to
be attractive to many research teams in view of the possibil-
ity of developing novel immunotherapeutic agents and also
because the 4,5-disubstituted 2-oxazolidinone ring system
provides an interesting objective for various asymmetric
synthesis strategies.
In syntheses in which E-p-methoxycinnamic acid deriva-
tives such as esters, amides or cinnamic alcohol were used
as substrates, the 2-hydroxy-3-amino functionalities were
introduced either via a two-step procedure, involving cata-
lytic asymmetric Sharpless dihydroxylation followed by
azidolysis3–5 or straightforwardly, by Sharpless amino-
hydroxylation.6 A one-pot amidation/oxidation7 or epoxi-
dation/azidolysis8 process was applied to the cinnamic acid
derivatives as well. Racemic cytoxazone rac-1 and
4-epi-cytoxazone rac-2 were also prepared from methyl
p-methoxyphenyl glycidate and resolved by enzymatic
methods.9
Since the oxazolidinone ring is conveniently constructed
from b-aminoalcohols, in all the syntheses performed so
far, efforts have been made to prepare these key intermedi-
ates in high enantiomeric purity. This has been accom-
plished in two ways: either by the enantioselective
introduction of hydroxy and amino functionalities into pro-
The C–C bond forming methodology, which relies on the
chiral pool approach, uses commercially available amino
acids10,11 and carbohydrates12,13 as substrates. Homolo-
gation can then be achieved by the addition of Grignard
reagents10,12,13 or cyanohydrin formation11 via the
corresponding aldehydes. The aldol-type reaction was also
successfully applied in C–C bond forming methodology.
Thus, p-methoxybenzylidene amines, both chiral14,15 and
O
O
HN
HN
O
O
OH
OH
CH3O
CH3O
prochiral,16,17 were treated with carbon nucleophiles in dia-
2
1
16
stereoselective14,15,17 and enantioselective
syntheses. A
(-)-cytoxazone
(+)-5-epi-cytoxazone
diastereoselective aldol reaction followed by Curtius rear-
rangement18,19 and the diastereoselective imino 1,2-Wittig
rearrangement of hydroximates20–22 were another way of
the synthesis of b-aminoalcohols.
Figure 1.
*
Tel.: +48 618291322; fax: +48 618658008; e-mail: mdroz@amu.edu.pl
0957-4166/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2006.06.009

1750
M. D. Rozwadowska / Tetrahedron: Asymmetry 17 (2006) 1749–1753
To complete the synthesis of cytoxazone 1 and its congen-
ers the prepared chiral b-aminoalcohols were then sub-
jected to standard functional group manipulations,
including cyclization either of the N-Boc derivatives or
directly from aminoalcohols and phosgene equivalents.
temperature for 18 h, to afford the quaternary salt 5 (mp
194–195.5 °C, [a]D = +46.1) in excellent yield. The next
step of the synthesis, the formation of epoxide 6, turned
out to be very unreliable. It was strongly dependent upon
the reaction conditions, in particular on the reaction tem-
perature and the work-up procedure. Since the synthetic
strategy undertaken was built up on the success of the
epoxide formation step, several experiments were carried
out to overcome this difficulty.
Herein we report another approach to the synthesis of
cytoxazone derivatives. It is based upon (+)-thiomicamine
3, 2-amino-1-(4-methylthiophenyl)-1,3-propanediol, which
is a commercially available industrial waste product. (+)-
Thiomicamine 3 was used as the substrate and trans-
formed into (+)-10, the p-methylthio analogue of (+)-5-
epi-cytoxazone 2, in a highly stereoselective synthesis in
It was established that on treatment of a suspension of 5 in
THF with an excess of sodium hydride in a strong stream
of argon, it was very important to maintain the reaction
temperature precisely at 65 °C, to prevent decomposition
of the product. It was also important to cool the reaction
mixture (ice-bath) immediately after the clear solution
had formed (after ca. 2.5 h) and quench it with a sodium
hydroxide/sodium chloride solution. Under these condi-
tions, epoxide 6 (mp 77.5–79.0 °C, [a]D = +41.6) was pro-
duced in a quantitative yield. As expected, in the process
of epoxidation, complete inversion of configuration at
C-2 took place, giving epoxide 6 as a single diastereomer.24
It should be noted that among the strategies applied for the
asymmetric synthesis of cytoxazone and congeners, a
related epoxide was used as the intermediate.8
44% overall yield, involving
a seven-step reaction
sequence. The synthetic strategy applied is summarized
in Scheme 1.
2. Results and discussion
In order for (+)-thiomicamine 3 to be used in the synthesis,
the position of the amino and hydroxy groups had to be
reversed. To achieve this, epoxide 6 was considered to be
the key intermediate in the synthesis and was expected to
be easily prepared by an (Scheme 1) intramolecular substitu-
tion of the amine function by the secondary hydroxyl group.
For the regioselective introduction of the amine functiona-
lity into the benzylic position of various intermediates en
route to cytoxazone or analogues, azidolysis with sodium
azide in DMF,25 dioxane,9 acetonitrile26 or acetone13 was
reported. Under these conditions however, long reaction
times, elevated temperatures, and the presence of additives
were often needed. Here, in this synthesis, excellent results
were achieved when epoxide 6 in methoxyethanol/water
(8:1) was reacted with (2.5:1) sodium azide/ammonium
chloride27 at 65 °C, affording azidodiol 7 (mp 92.0–
93.5 °C, [a]D = ꢀ200.2) in high yield, as a single diastereo-
mer.24 Once again, an inversion of configuration took place
at the second stereocenter, C-3.
Therefore a straightforward procedure as described by
Castedo et al.23 was chosen, in which 2-amino-1-phenyl-
1,3-propanediol was reacted with dichlorocarbene to give
the corresponding epoxide in a simple operation. In our
case, however, an inseparable mixture of products was
formed. A two-step transformation of the primary amine
into a good leaving group by its quaternization was under-
taken. Thus, (+)-thiomicamine 3 was converted into
methiodide 5 via N,N-dimethylthiomicamine 4 (mp 89.5–
90.5 °C, [a]D = +35.6) prepared by refluxing 3 in a formic
acid/formaldehyde mixture for 5 h, followed by N-methyl-
ation of 4 with methyl iodide in acetonitrile at room
OH
OH
a
OH
OH
b
NH2
NMe2
CH3S
CH3S
3
4
6
OH
O
OH
NMe3
d
c
I
OH
CH3S
CH3S
5
O
N3
HN
O
f
OR
OR
CH3S
OR
CH3S
7 R = H
8 R = COOPh
e
9 R = COOPh
10 R = H
g
Scheme 1. Reagents and conditions: (a) HCOOH/CH2O (85%); (b) CH3I/CH3CN (98%); (c) NaH/THF (99%); (d) NaN3/NH4Cl/CH3OCH2CH2OH
(94%); (e) ClCOOC6H5/PyH/CH2Cl2 (90%); (f) P(C6H5)3/THF/H2O (71%); (g) K2CO3/CH3OH/H2O (88%).

M. D. Rozwadowska / Tetrahedron: Asymmetry 17 (2006) 1749–1753
1751
With the position of the two functional groups reversed,
the synthesis was then continued by treatment of azidodiol
7 with an excess of phenylchloroformate/pyridine in meth-
ylene chloride at ice-bath temperature to give dicarbonate 8
(oil, [a]D ꢀ44.7), which was obtained in satisfactory yield.
The construction of the 2-oxazolidinone ring was then per-
formed in one-pot by treatment of 8 with triphenylphos-
phine in aqueous THF at 50 °C, during which the azide
reduction and cyclization took place simultaneously. The
desired 2-oxazolidinone carbonate 9 (mp 135.5–137.0 °C,
[a]D = +72.2) was isolated in moderate yield as a single
isomer.24 Removal of the phenyloxycarbonyl group in 9
occurred via hydrolysis with potassium carbonate in
aqueous methanol. The final product, (4R,5S)-(+)-
5-hydroxymethyl-4-(p-methylthiophenyl)-2-oxazolidinone,
(+)-10 (mp 174.5–175.0 °C, [a]D = +30.8) was obtained as
an enantiomerically pure compound24 in 44% overall yield,
based on (+)-thiomicamine 3.
were washed with water, dried, and concentrated under re-
duced pressure. The residue was dissolved in methanol/iso-
propyl ether to give crystalline N,N-dimethylthiomicamine
4 in 85% yield. Mp 89.0–90.5 °C; [a]D = +35.6 (c 1.0,
1
methanol). H NMR (CDCl3): d ca. 1.7 (s, 1H, disappears
on treatment with D2O, OH), 2.47 (s, 3H, SCH3), 2.51 (s,
6H, NCH3), 2.64 (ddd, J = 4.1, 7.6, 9.8 Hz, 1H, H-2),
3.40 (dd, J = 4.1, 11.5 Hz, 1H, H-3), 3.51 (dd, J = 7.6,
11.5 Hz, 1H, H-30), 4.35 (d, J = 9.9 Hz, 1H, H-1), ca.
4.50 (br s, 1H, disappears on treatment with D2O, OH),
7.20–7.29 (m, 4H, Ar–H). MS m/z (%): 241 (M+, <1),
178 (2), 151 (3), 137 (4), 109 (4), 91 (1), 89 (5), 88 (100).
Found: C, 59.68; H, 8.62; N, 5.81; S, 13.24. C12H19NO2S
(241.1) req.: C, 59.72; H, 7.94; N, 5.81; S, 13.26.
4.3. (1S,2S)-2-Dimethylamino-1-(4-methylthiophenyl)-1,3-
propanediol methiodide 5
Compound 4 (1.75 g, 7.26 mmol) in acetonitrile (28 ml) and
methyl iodide (2 ml) was stirred at room temperature for
20 h. The precipitate was filtered off, washed with ethyl
ether and recrystallized from methanol to deposit methio-
dide 5 (2.7 g, 98%). Mp 195.5–196.5 °C; [a]D = +46.1 (c
0.98, methanol). 1H NMR (DMSO-d6): d 2.48 (s, 3H,
SCH3), 3.15 (m, 1H, H-2), 3.36 (3s, 9H, NCH3), 3.61 (m,
1H, H-3), 3.87 (m, 1H, H-30), 5.12 (d, J = ca. 10 Hz, 1H,
disappears on treatment with D2O, CHOH), 5.39 (t,
J = 4.0 Hz, 1H, disappears on treatment with D2O,
CH2OH), 6.39 (d, J = 3.6 Hz, 1H, H-1), 7.29–7.40 (m,
4H, Ar–H). MS m/z (%): 193 (3), 152 (4), 151 (70), 142
(39), 137 (8), 127 (16), 110 (4), 89 (6), 88 (100). Found:
C, 40,69; H, 5.96; N, 3.60; S, 8.29. C13H22NO2SI (383.0)
req.: C, 40.72; H, 5.79; N, 3.67; S, 8.35.
3. Conclusion
In conclusion, enantiomerically pure (4R,5S)-(+)-10, the
sulfur analogue of (4R,5S)-(+)-5-epi-cytoxazone 2, has
been synthesized in 44% overall yield in seven steps starting
from (+)-thiomicamine 3. The key step of the synthesis, the
reversal of the position of the hydroxyl and amine func-
tional groups occurred via a highly stereo- and regioselec-
tive epoxidation/azidolysis process, involving inversion of
configuration of both stereogenic centers.
It should be noted that in the synthesis described herein an
industrial waste product has been used as a substrate and
transformed into a compound related to natural products
of potent biological activity.
4.4. (2R,3S)-2,3-Epoxy-3-(4-methylthiophenyl)-1-propanol 6
In a stream of argon, a suspension of methiodide 5 (0.76 g,
2 mmol) in tetrahydrofuran (80 ml) and sodium hydride
(0.19 g, 8 mmol) was heated at 65 °C, while care was taken
to keep the temperature at 65 °C itself. The moment of the
solution became clear, ca. 2–2.5 h, the mixture was imme-
diately cooled in ice-water bath and slowly treated with
10% sodium hydroxide containing 10% sodium chloride.
The phases were separated and the organic phase concen-
trated under reduced pressure. The residue was partitioned
between ethyl ether and 20% ammonium chloride, the
organic layer separated, dried and the solvent evaporated
to leave a TLC pure, pale-yellow precipitate (0.38 g, 99%,
100:0 dr24), which was used for the next step as such.
4. Experimental
4.1. General methods
Melting points were determined on a Koffler block and are
uncorrected. IR spectra: Bruker FT-IR IFS 113V. NMR
spectra: Varian Gemini 300, with TMS as the internal
standard. Mass spectra (EI): AM D402. Optical rotation:
Perkin–Elmer polarimeter 242B. Elemental analysis: Vario
EL III. Merck Kieselgel 60 (70–230 mesh) was used for
column chromatography and Merck DC-Alufolien Kieselgel
60254 for TLC. Analytical HPLC: Waters HPLC system
with Mallinkrodt–Baker Chiralcel OD-H column, hexane–
isopropanol (9:1). (+)-Thiomicamine was purchased from
Aldrich Chemical Co., and used as received.
A sample was digested with benzene/hexane (1:1) giving 6
as a cream-colored solid. Mp 77.5–79.0 °C, [a]D = +41.6
1
(c 0.97, methanol). H NMR (DMSO-d6): d 2.47 (s, 3H,
4.2. (1S,2S)-2-Dimethylamino-1-(4-methylthiophenyl)-1,3-
propanediol 4
SCH3), 3.20–3.30 (m, 3H, H-2, H-1, H-10), 4.13 (d,
J = 3.8 Hz, 1H, H-3), 4.88 (t, J = 4.9 Hz, 1H, disappears
on treatment with D2O, CH2OH), 7.20–7.37 (m, 4H, Ar–
H). 1H NMR (DMSO-d6/D2O): d 2.46 (s, 3H, SCH3),
3.22 (dd, J = ca. 7, 12.7 Hz, 1H, H-1), 3.33 (dd, J = 4.3,
12.7 Hz, 1H, H-10), 3.29–3.34 (m, 1H, H-2), 4.16 (d,
J = 4.0 Hz, 1H, H-3), 7.26–7.38 (m, 4H, Ar–H). 13C
NMR (DMSO-d6): d 14.61 (CH3), 55.76 (CH), 58.29
(CH2), 58.92, 125.54, 126.89 (CH), 131.82, 137.44 (C).
A mixture of (+)-thiomicamine 3 (2.13 g, 10 mmol), formic
acid (5 ml) and 37% aqueous formaldehyde (5 ml) was
heated at reflux for 5 h. This was then cooled to room tem-
perature rendered alkaline with 20% sodium hydroxide and
stirred for 1 h, then extracted with ethyl ether until Dra-
gendorff test was negative. The combined organic extracts

1752
M. D. Rozwadowska / Tetrahedron: Asymmetry 17 (2006) 1749–1753
MS m/z (%): 196 (M+, 100), 179 (26), 178 (52), 177 (22),
167 (31), 166 (66), 165 (62), 152 (22), 151 (48), 150 (24),
137 (67), 136 (31), 135 (77), 121 (61), 91 (38), 89 (26).
Found: C, 61.17; H, 6.08; S, 16.20. C10H12O2S (196.1)
req.: C, 61.20; H, 6.17; S, 16.31.
(0.79 g, 3 mmol) was added and the mixture heated at
50 °C for 1 h under an argon atmosphere. The solvent
was evaporated and the wet residue extracted with ethyl
ether. The organic solution was washed with 5% sodium
hydroxide, 5% hydrochloric acid, and 20% ammonium
chloride, dried and the solvent removed under vacuum.
The oily residue was heated at reflux with iso-propyl ether
(ca. 35 ml) until a clear solution was obtained. After cool-
ing, the solid (0.29 g) was recrystallized two times from
methanol to give enantiomerically pure24 oxazolidinone
9 (0.14 g). An additional amount of 9 (0.13 g; total yield
71%) was recovered after column chromatography (silica
gel 1:10, methylene chloride) of the mother liquor. Mp
135.5–137.5 °C, [a]D = +72.2 (c 0.64, methanol). IR
4.5. (2S,3R)-3-Azido-3-(4-methylthiophenyl)-1,2-propane-
diol 7
To a stirred solution of epoxide 6 (0.43 g, 2.2 mmol) in
(8:1) 2-methoxyethanol/water (13.5 ml), sodium azide
(0.72 g, 11 mmol) was added followed by ammonium chlo-
ride (0.23 g, 4.4 mmol) and the mixture was heated at
100 °C for 3 h. It was concentrated under reduced pressure
and the residue extracted with ethyl ether. The organic ex-
tract was washed with 20% ammonium chloride, dried, and
the solvent evaporated to deposit oily 7 (0.51 g, 98%,
97.8:2.2 dr24), that solidified on standing. After crystalliza-
tion from methylene chloride–carbon tetrachloride, crystal-
line 7 in 94% yield and with 99.7:0.3 dr24 was collected. Mp
92–93.5 °C; [a]D = ꢀ200.2 (c 0.98, methanol). IR (KBr)
cmꢀ1: 3459, 3218 (br), 2107. 1H NMR (DMSO-d6): d
2.48 (s, 3H, SCH3), 3.19 (dd, J = 5.5, 11.0 Hz, 1H, H-1),
3.28 (dd, J = ca. 5, 11.0 Hz, 1H, H-10), 3.67 (m, 1H, H-
2), 4.56 (d, J = 5.9 Hz, 1H, H-3), 4.70 (t, J = ca. 5 Hz,
1H, disappears on treatment with D2O, CH2OH), 5.30
(d, J = 5.6 Hz, 1H, disappears on treatment with D2O,
CHOH), 7.20–7.34 (m, 4H, Ar–H). 13C NMR (CDCl3): d
15.4 (CH3), 62.63 (CH2), 67.9, 74.8, 126.6, 128.0 (CH),
132.4, 139.7 (C). MS m/z (%): 239 (M+, 23), 178 (22),
151 (38), 150 (100), 137 (13), 135 (19), 123 (19). Found:
C, 50.21; H, 5.44; N, 17.57; S, 13.39. C10H13N3O2S
(239.1) req.: C, 50.19; H, 5.48; N, 17.57; S, 13.37.
1
(KBr) cmꢀ1: 3257, 1760, 1726. H NMR (DMSO-d6): d
2.47 (s, 3H, SCH3), 4.40–4.56 (m, 3H, CH2, H-5), 4.75
(d, J = 6.0 Hz, 1H, H-4), 7.23–7.48 (m, 10H, Ar–H).
MS m/z (%): 359 (M+, 11), 277 (12), 222 (43), 221 (14),
179 (12), 178 (44), 174 (18), 165 (13), 151 (23), 150 (15),
132 (12), 94 (100), 77 (15). Found: C, 59.92; H, 4.85; N,
3.88; S, 8.99. C18H17NO5S (359.1) req.: C, 60.15; H,
4.77; N, 3.90; S 8.90.
4.8. (4R,5S)-5-Hydroxymethyl-4-(4-methylthiophenyl)-2-
oxazolidinone 10
A mixture of carbamate 9 (0.225 g, 0.64 mmol) in meth-
anol (23 ml), water (1.5 ml), and potassium carbonate
(0.29 g, 3 mmol) was stirred at room temperature for
1 h under an argon atmosphere. Methanol was removed
under reduced pressure and the aqueous residue extracted
with ethyl acetate. The organic solution was washed with
water, 20% ammonium chloride, dried, and the solvent
evaporated to give TLC pure 10 as a solid (0.13 g, 88
%). Recrystallization from methanol afforded enantiome-
rically pure24 10. Mp 175.5–176.5 °C, [a]D = +31.9 (c 0.9,
methanol). IR (KBr) cmꢀ1: 3449–2646 (br), 1747, 1720.
1H NMR (DMSO-d6): d 2.49 (s, 3H, SCH3), 3.54 (dd,
J = 4.7, 12.4 Hz, 1H, CHHO), 3.63 (dd, J = 3.8,
12.4 Hz, 1H, CHHO), 4.15 (td, J=4.1, 6.3 Hz, 1H, H-
5), 4.64 (d, J = 6.3 Hz, 1H, H-4), 5.24 (t, J = 5.8 Hz,
1H, disappears on treatment with D2O, CH2OH), 7.29
(s, 4H, Ar–H). 1H NMR (CD3OD): d 2.47 (s, 3H,
SCH3), 3.69 (dd, J = ca. 4, 12.6 Hz, 1H, CHHO), 3.81
(dd, J = 3.6, 12.6 Hz, 1H, CHHO), 4.32 (ddd, J = 3.6,
ca. 4, 6.6 Hz, 1H, H-5), 4.76 (d, J = 6.3 Hz, 1H, H-4),
7.30 (s, 4H, Ar–H). 13C NMR: d 15.6 (CH3), 58.6
(CH), 62.6 (CH2), 86.6, 127.9, 127.94 (CH), 138.5,
140.7 (C), 161.6 (CO). MS m/z (%): 239 (M+, 82), 196
(18), 178 (22), 165 (14), 152 (16), 151 (100), 150 (40),
137 (16), 135 (11), 132 (26), 124 (10), 121 (11), 118
(12), 91 (10). Found: C, 55.30; H, 5.61; N, 5.82; S,
13.38. C11H13NO3S (239.1) req.: C, 55.21; H, 5.48; N,
5.86; S, 13.37.
4.6. (2S,3R)-3-Azido-1,2-diphenyloxycarbonyloxy-3-
(4-methylthiophenyl)-propane 8
To a solution of azidodiol 7 (0.45 g, 1.86 mmol) in methyl-
ene chloride (15 ml), three portions each of a reagent com-
posed of pyridine (0.15 ml, 1.8 mmol) and phenyl
chloroformate (0.26 ml, 1.8 mmol) were added in 1 h inter-
vals, at ice-bath temperature, with stirring. After reaching
room temperature the reaction mixture was washed with
5% hydrochloric acid followed by 5% sodium hydroxide,
dried, and the solvent evaporated under reduced pressure.
The oily residue was chromatographed over silica gel
(1:10) with carbon tetrachloride/methylene chloride (1:1)
to give 8 as an oil (0.8 g, 90%); [a]D = ꢀ44.7 (c 0.86, meth-
1
anol). IR (neat) cmꢀ1: 2107, 1765. H NMR (CDCl3): d
2.50 (s, 3H, SCH3), 4.02 (dd, J = 5.2, 12.3 Hz, 1H, H-1),
4.54 (dd, J = 3.0, 12.3 Hz, 1H, H-10), 4.87 (d, J = 8.5 Hz,
1H, H-3), 5.21 (ddd, J = 3.0, 5.2, 8.5 Hz, 1H, H-2), 7.04–
7.16 (m, 14H, Ar–H). MS m/z (%): 479 (M+, 9), 220 (21),
178 (28), 176 (23), 164 (21), 150 (100), 135 (11), 123 (13),
94 (20), 77 (64). HRMS (M+) found: 479.11219.
C24H21N3O6S req.: 479.11511.
4.7. (4R,5S)-4-(4-Methylthiophenyl)-5-phenyloxycarbonyl-
oxy-2-oxazolidinone 9
Acknowledgements
This work was supported by a research grant from the
State Committee for Scientific Research in the years
2003-2006 (KBN Grant No. 4T09A 07824).
To azido dicarboxylate 8 (0.48 g, 1 mmol) in tetrahydro-
furan (10 ml) and water (0.2 ml), triphenylphosphine

M. D. Rozwadowska / Tetrahedron: Asymmetry 17 (2006) 1749–1753
1753
14. Sugiyama, S.; Arai, S.; Ishii, K. Tetrahedron: Asymmetry
2004, 15, 3149.
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