4-[(4-Methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)-2-butanone as a convenient precursor for a new formal synthesis of KDO

Article abstract of DOI:10.1016/S0040-4020(02)00998-5

The application of 4-[(4-methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)-2-butanone, a readily available four-carbon building block, to the synthesis of 3-deoxy-D-manno-2-octulosonic acid (KDO) is described.

Full text of DOI:10.1016/S0040-4020(02)00998-5

Tetrahedron 58 (2002) 8553–8558
4-[(4-Methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)-2-
butanone as a convenient precursor for a new formal synthesis
of KDO
c
b
Achille Barco,a Lucio Bassetti,b Simonetta Benetti,a Valerio Bertolasi, Carmela De Risi,
,
*
Paolo Marchettib and Gian Piero Pollinib
a
`
Dipartimento di Chimica, Universita di Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy
`
`
Dipartimento di Chimica, Centro di Strutturistica Diffrattometrica, Universita di Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy
b
Dipartimento di Scienze Farmaceutiche, Universita di Ferrara, Via Fossato di Mortara 19, 44100 Ferrara, Italy
c
`
Dedicated to Professor Paola Vita Finzi, Universita di Pavia, on the occasion of her 70th birthday
Received 28 May 2002; revised 16 July 2002; accepted 8 August 2002
Abstract—The application of 4-[(4-methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)-2-butanone, a readily available four-carbon
building block, to the synthesis of 3-deoxy-D-manno-2-octulosonic acid (KDO) is described. q 2002 Elsevier Science Ltd. All rights
reserved.
1. Introduction
We describe here a novel approach to the synthesis of
this popular target based on the utilization of 4-[(4-
methylphenyl)sulfonyl]-1-(triphenylphosphoranylidene)-2-
butanone 2, a readily available four-carbon building block,
which we have recently introduced10 as a versatile tool for
the construction of substituted carbon atom frameworks,
since it can be functionalized at either end.
The biological importance of carbohydrates in living cells
justifies the interest in the development of procedures for the
synthesis of natural and unnatural sugars containing six,
seven or more carbon atoms. The 3-deoxy-D-manno-2-
octulosonic acid (KDO) 1, for example, is an essential
component of lipopolysaccharides contained in the outer
membrane of Gram-negative bacteria.1–3
2. Results and discussion
Considering the KDO molecule as the target, we envisaged
that the Wittig reaction of (R)-2,3-O-isopropylidene glycer-
aldehyde with the stabilized ylide function of 2 could serve
a twofold purpose, i.e. (i) the 3-carbon atom elongation of
the chain containing a conjugated double bond, in turn
susceptible to hydroxylation or epoxidation for the installa-
tion of the required oxygenated functions and (ii) the
introduction of a stereogenic center of known configuration
as a handle to induce asymmetry in the synthetic pathway.
In addition the sulfone moiety could be useful both (i) to add
the lacking carbon atom through deprotonation and reaction
with a suitable one carbon electrophile and (ii) for the final
conversion into a carbonyl group by oxidative desulfonyl-
ation11 (Scheme 1).
Accordingly, the chemical synthesis of this molecule and its
analogues has been largely studied to obtain enough
substance for biological studies and as a lead in designing
potential anti-infection agents. To date, continuous efforts
have been invested in developing efficient synthetic
approaches to KDO and related compounds including
homologation of lower monosaccharides, mainly D-man-
nose and D-arabinose,4–7 enzymatic syntheses8 and, less
frequently, de novo syntheses.9
With this in mind, the reaction between the stabilized ylide
2 and (R)-2,3-O-isopropylidene glyceraldehyde produced
exclusively the trans seven-carbon Wittig-adduct 3,10
containing both the conjugated double bond and the chiral
Keywords: 3-deoxy-D-manno-2-octulosonic acid; carbohydrates;
diastereoselection; keto sulfones.
*
Corresponding author. Tel.: þ39-532-291174; e-mail: bns@dns.unife.it
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)00998-5

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A. Barco et al. / Tetrahedron 58 (2002) 8553–8558
Scheme 1.
center of known configuration for the stereoselective
functionalization of the entire molecule. Thus, sodium
borohydride reduction of the carbonyl group in the presence
of cerium chloride12 proceeded highly stereoselectively
affording the corresponding allylic alcohol 4 as a single
diastereoisomer, as indicated by analytical HPLC of the
crude product. It is likely that the chiral auxiliary influences
the stereochemical outcome in the reductive step, a
vinylogous version of Cram’s rule being right to explain
the observed high level of 1,4-stereocontrol across the
existing E double bond. Based on literature examples on the
addition of nucleophiles to enones bearing a chiral center in
Figure 1.
Scheme 2.

A. Barco et al. / Tetrahedron 58 (2002) 8553–8558
8555
Figure 2. An ORTEP14 view of compound 9 displaying the thermal ellipsoids at 30% probability.
g-position,13 we assumed that the a,b-unsaturated ketone 3
reacts via its s-cis conformation, the Lewis acid reasonably
forcing the enone to adopt this particular conformation
through complexation both to the carbonyl oxygen atom and
the C-4 oxygen atom of the dioxolanyl substituent. Thus, the
hydride attack must occur preferentially from the bottom
face of the ketone group (Fig. 1).
chemistry we oxidized the alcohol 8, obtained by removal of
the acetyl group, with pyridinium chlorochromate to the
ketone 9. X-Ray analysis allowed us to unequivocally assign
the absolute configuration of the three contiguous asym-
metric centers as 2R,3R,4S (Fig. 2).
Moreover, sodium borohydride reduction of the carbonyl
group of the ketone 9 in the presence of cerium chloride12
afforded the corresponding alcohol 10 as a single diastereo-
isomer, which gave rise by acetylation to the corresponding
acetyl derivative 11, an epimer of 7. The stereochemical
outcome of the reduction could be predicted on the basis of a
chelate Felkin–Ahn model,15 the hydride attack occurring
preferentially from the re face to produce the S configur-
ation at the newly created stereogenic centre.
Based on this assumption, we assigned the absolute
configuration at the C-3 carbon atom in compound 4 as R,
this assignment being confirmed at a later stage of the
synthesis. Transformation of the allylic alcohol 4 into the
acetate 5 by treatment with acetic anhydride and pyridine
(Scheme 2) and subsequent oxidation of 5 with the osmium
tetroxide/N-methylmorpholine N-oxide system gave a 4:1
mixture of isomeric diols which was protected as iso-
propylidene derivatives by a standard procedure and
separated by flash-chromatography, the major isomer 7
being a solid.
The attractive intermediate 8 possesses both the correct
framework and stereochemistry for KDO 1. Thus, the
reaction of the bisanion of 8, prepared by action of LDA at
2788C, with ethyl chloroformate (Scheme 3) produced a
mixture of epimeric esters 12, a fact of no consequence
because the final oxidative desulfonylation generated the
required carbonyl group. This operation was carried out
Unfortunately, we were unable to obtain suitable crystals for
X-ray analysis in spite of numerous attempts of crystal-
lization in a variety of solvents. To assign the stereo-
Scheme 3.

8556
A. Barco et al. / Tetrahedron 58 (2002) 8553–8558
following Hwu’s protocol11 involving the action of
bistrimethylsilylperoxide16a on the bisanion produced by
means of LDA on the mixture of epimeric esters 12 which
was eventually transformed into the known diacetonide-
protected KDO ethyl ester 13 already taken to KDO by
Whitesides et al.17 thus establishing a new formal
synthesis of this target. Our own methodology advan-
tageously compares with the reported one, allowing to
obtain the key intermediate 13 in 25% overall yield based
on 3.
afford the alcohol 4 (0.60 g, 81%) as a light yellow oil,
which was sufficiently pure (HPLC analysis) to be used in
the next step without further purification. The crude alcohol
was dissolved in CH2Cl2 (8 mL) containing pyridine
(0.18 mL, 2.35 mmol) and a catalytic amount of 4-N,N0-
dimethylaminopyridine. Acetic anhydride (0.24 mL,
2.35 mmol) was added, the mixture stirred at room
temperature for 3 h, then washed with H2O (10 mL) and
NaHCO3 solution (10 mL, sat. aq.). The organic phase was
separated, dried and the solvent evaporated. The residual oil
was purified by flash chromatography (eluent EtOAc–
cyclohexane 1:1), affording the title compound 5 (0.65 g,
81%) as an oil; [Found: C, 59.80; H, 6.70. C19H26O6S
requires C, 59.67; H, 6.85%]; [a]2D0¼þ9.5 (c 0.35, CHCl3).
3. Conclusions
n
max (liquid film) 1720, 1600 cm21; dH (200 MHz, CDCl3)
Our results emphasize once more the versatility of the
synthon 2 as a tool for the construction of functionalized
carbon frameworks and this strategy may be extended to the
synthesis of unnatural sugars with seven or more carbon
atoms. In particular, the versatile intermediate 2 has been
conveniently used to develop a new formal synthesis of
KDO, which is complementary to the already reported
chemical syntheses of this target.
1.39 (3H, s, Me), 1.41 (3H, s, Me), 2.01 (3H, s, COMe),
1.95–2.10 (2H, m, CH2CHOAc), 2.42 (3H, s, PhMe), 3.05–
3.17 (2H, m, CH2SO2), 3.50–3.60 (1H, m, CHaHbO),
4.05–4.15 (1H, m, CHaHbO), 4.40–4.50 (1H, m,
HCvCH–CHO), 5.20–5.30 (1H, m, CHOAc), 5.60–5.75
(2H, m, HCvCH), 7.40 (2H, d, J¼7.8 Hz, arom.), 7.80 (2H,
d, J¼7.8 Hz, arom.); dC (50 MHz, CDCl3) 20.9, 21.5, 25.7,
26.5, 27.3, 27.4, 52.2, 69.2, 75.7, 109.5, 128.0, 129.8, 131.3,
131.8, 135.7, 144.8, 169.7.
4. Experimental
4.1.2. (2R,3R,4S,5R)5-O-Acetyl-1,2,3,4-bis-O-isopropyl-
idene-7-[(40-methylphenyl)sulfonyl]-heptan-1,2,3,4,5-
pentaol (7). A solution of N-methylmorpholine N-oxide
(0.67 g, 4.49 mmol) in tert-butyl alcohol–H2O mixture
(50:5) (30 mL) containing a catalytic amount of OsO4 was
added dropwise to a stirred solution of 5 (0.61 g,
1.59 mmol) in THF (5 mL) (CAUTION: care should be
taken in handling osmium tetroxide.18 The vapor is toxic,
causing damage to eyes, respiratory tract and skin). The
reaction mixture was stirred at room temperature for 18 h,
the solvent was evaporated, the residue dissolved in a
mixture of acetone (10 mL) and 2,2-dimetoxy-propane
(10 mL), and p-toluenesulfonic acid was added in small
portions until pH¼5. After stirring the reaction mixture at
room temperature for 3 h, triethylamine was added until
pH¼8, then the solvent was concentrated in vacuo.
Purification of the residual oil by flash cromatography
(eluent EtOAc–cyclohexane 1:3) allowed to obtain the title
compound 7 (0.47 g, 65%), the more abundant isomer, as a
white solid, mp 81–828C (ether–petroleum ether 1:1);
[Found: C, 58.25; H, 7.15. C22H32O8S requires C, 57.88; H,
7.06%]; [a]2D0¼þ12.66 (c 0.30, CHCl3); nmax (KBr) 3300,
1735, 1600 cm21; dH (200 MHz, CDCl3) 1.38 (6H, s, 2Me),
1.40 (3H, s, Me), 1.60 (3H, s, Me), 2.09 (3H, s, COMe),
2.05–2.20 (2H, m, CH2CHOAc), 2.50 (3H, s, PhMe), 3.10–
3.21 (2H, m, CH2SO2), 3.70–3.80 (1H, m, CHaHbO), 3.85–
3.95 (2H, m, CHO), 3.96–4.04 (m, 1H, CHO), 4.09–4.20
(m, 1H, CHaHbO), 5.10–5.20 (1H, m, CHOAc), 7.40 (2H, d,
J¼7.8 Hz, arom.), 7.80 (2H, d, J¼7.8 Hz, arom.); dC
(50 MHz, CDCl3) 21.1, 21.7, 23.9, 25.4, 26.6, 27.2, 27.3,
52.6, 67.7, 71.4, 79.3, 81.0, 110.0, 110.2, 128.1, 130.0,
136.0, 144.9, 170.2.
4.1. General remarks
Melting points were determined on a Bu¨chi–Tottoli
apparatus and are uncorrected. Infrared (IR) spectra were
recorded on a FT-IR Paragon 500 spectrometer. Nuclear
magnetic resonance (1H NMR and 13C NMR) spectra were
taken on a Bruker AC spectrometer at 200 and 50 MHz,
respectively, for solutions in CDCl3 unless otherwise noted.
Chemical shifts are given in parts per million downfield
from tetramethylsilane as the internal standard and coupling
constants are given in Hertz. Optical rotations were
measured with a Perkin–Elmer 241 MC Polarimeter.
Diastereomeric ratios were determined through HPLC
analyses: in normal phase on silica gel and isopropanol–
water 80:20 as eluant, in reverse phase on C18 and
acetonitrile–water concentration gradient. Organic
solutions were dried over anhydrous magnesium sulfate
and evaporated with a rotary evaporator. Light petroleum
refers to the fractions boiling in the range 40–608C and
ether to diethyl ether. Flash-chromatography was carried out
with Merck silica gel (230–400 mesh). All reactions were
performed under N2 or Ar atmosphere. Elemental analyses
were effected by the microanalytical laboratory of
Dipartimento di Chimica, University of Ferrara.
Compound 3 was prepared according to the literature.10
4.1.1. (3R)3-Acetoxy-1-(2,2-dimethyl-1,3-dioxolan-4-yl)-
5-[(40-methylphenyl)sulfonyl]-1-pentene (5). To a well-
stirred and cooled (2108C) solution of ketone 310 (0.75 g,
2.21 mmol) in MeOH (10 mL) containing CeCl3·7H2O
(0.82 g, 2.21 mmol), NaBH4 (0.1 g, 2.60 mmol) was added
in one portion. Stirring was continued for 30 min, then the
excess of NaBH4 was destroyed with acetone. The reaction
mixture was concentrated in vacuo, diluted with aqueous
NaCl (7 mL), and extracted with ethyl acetate (3£25 mL).
The combined organic extracts were dried and evaporated to
4.1.3. (2R,3R,4S,5R)1,2,3,4-Bis-O-isopropylidene-7-[(40-
methylphenyl)sulfonyl]-heptan 1,2,3,4,5-pentaol (8). A
solution of 7 (0.5 g, 1.1 mmol) and sodium carbonate
(0.18 g, 1.7 mmol) in a 1:1 mixture of MeOH–H2O (15 mL)
was stirred at room temperature for 24 h. Most of the solvent

A. Barco et al. / Tetrahedron 58 (2002) 8553–8558
8557
was evaporated in vacuo and the residual slurry extracted
with EtOAc (3£15 mL). After usual work-up, the title
compound 8 (0.4 g, 88%) was obtained as an oil which was
used without further purification in the next step. nmax
(liquid film) 3450, 1600 cm21; dH (200 MHz, CDCl3) 1.25
(3H, s, Me), 1.35 (3H, s, Me), 1.37 (3H, s, Me), 1.41 (3H, s,
Me), 2.04–2.09 (2H, m, CH2CHOH), 2.44 (3H, s, PhMe),
3.25–3.35 (2H, m, CH2SO2), 3.57–3.63 (1H, m, CHaHbO),
3.65–3.69 (3H, m, 2CHO and OH), 4.06–4.15 (1H, m,
CHaHbO), 4.15–4.20 (1H, m, CHOH), 7.40 (2H, d,
J¼7.8 Hz, arom.), 7.80 (2H, d, J¼7.8 Hz, arom.).
4.1.6. (2R/S,4R,5S,6R,7R)Ethyl 2-[(40-methylphenyl)sul-
fonyl]-4,5,6,7,8-pentahydroxy-5,6,7,8-bis-O-isopropyli-
dene-octanoate (12). A solution of diisopropylamine
(0.24 mL, 1.73 mmol) in dry THF (5 mL) was treated with
n-butyl lithium (1.08 mL, 1.6 M in hexane) at 2788C. After
stirring for 15 min, a solution of 8 (0.3 g, 0.72 mmol) in dry
THF (1 mL) was added in one portion. The dark red solution
was stirred for 20 min, then freshly distilled ethyl
chloroformate (0.082 g, 0.86 mmol) in dry THF (1 mL)
was added. The mixture was stirred at 2788C for 30 min,
then the temperature was slowly raised at 2208C and
stirring was continued for 15 min at this temperature. The
reaction mixture was diluted with ammonium chloride
solution (10 mL, sat. aq.), extracted with EtOAc (3£10 mL),
the organic extracts dried and evaporated. The residual oil
was purified by flash chromatography (eluent EtOAc–
cyclohexane 2:1) to give the title compound 12 (0.27 g,
77%) as an epimeric mixture (positive response to FeCl3
test); [Found: C, 56.85; H, 7.10. C23H34O9S requires C,
56.77; H, 7.04%]; nmax (liquid film) 3450, 1720, 1690, 1645,
1600 cm21; dH (200 MHz, CDCl3) 1.20–1.40 (15H, m),
2.00–2.05 (2H, m), 2.44 (3H, s), 3.50–4.40 (10H, m), 7.40
(2H, m), 7.80 (2H, m).
4.1.4. (2R,3R,4S)1,2,3,4-Bis-O-isopropylidene-7-[(40-
methylphenyl)sulfonyl]-1,2,3,4-tetrahydroxy-heptan-5-
one (9). A solution of the alcohol 8 (0.4 g, 0.96 mmol) in
dry CH2Cl2 (4 mL) was quickly added to a well-stirred
suspension of PCC (0.3 g, 1.38 mmol), sodium acetate
˚
(0.12 g, 1.4 mmol) and 4 A molecular sieves (0.25 g) in dry
CH2Cl2 (4 mL). After 3 h, ether (40 mL) was added and
the mixture passed through a short column of florisil.
Evaporation of the solvent in vacuo afforded the title
compound 9 (0.34 g, 87%) as a white solid, mp 98–998C
(hexane); [Found: C, 58.35; H, 6.70. C20H28O7S requires C,
58.23; H, 6.84%]; [a]2D0¼þ1.41 (c 0.55, CHCl3); nmax
(KBr) 1705, 1600 cm21. dH (200 MHz, CDCl3) 1.40 (3H, s,
Me), 1.42 (3H, s, Me), 1.60 (6H, s, 2Me), 2.44 (3H, s,
PhMe), 3.15–3.20 (2H, m, CH2SO2), 3.39–3.42 (2H, m,
CH2CO), 3.95–4.01 (1H, m, CHaHbO), 4.15–4.18 (3H, m,
2CHO and CHaHbO), 4.39 (1H, d, J¼7.0 Hz, OCH–CO),
7.40 (2H, d, J¼7.8 Hz, arom.), 7.80 (2H, d, J¼7.8 Hz,
arom.).
4.1.7. (4R,5S,6R,7R)Ethyl 2-oxo-4,5,6,7,8-pentahydroxy-
5,6,7,8-bis-O-isopropylidene-octanoate (13). A solution of
diisopropylamine (0.07 mL, 0.5 mmol) in dry THF (4 mL)
was treated with n-butyl lithium (0.31 mL, 1.6 M in hexane)
at 2788C. After stirring for 15 min, a solution of 12 (0.1 g,
0.20 mmol) in dry THF (1 mL) was added in one portion.
The dark red solution was stirred for 15 min, then neat bis-
(trimethylsilyl)peroxyde (BTMSPO)16a (0.89 g, 5 mmol)
was added (CAUTION: the reaction must be carried out in
safety cupboards and behind blast shields.16b Indeed, it has
been reported that BTMSPO could give rise to explosions
especially in the presence of metal needles, cannulas, etc.).
The color of the solution turned to light brown while stirring
was continued at room temperature for 12 h. The reaction
mixture was poured in ice-cold ammonium chloride
solution (10 mL, sat. aq.), extracted with EtOAc
(2£10 mL), the extracts dried and evaporated. The residual
oil was purified by flash chromatography (eluent EtOAc–
cyclohexane 1:1) to give the title compound 1317 (0.05 g,
70%) as an oil; [Found: C, 55.60; H, 7.40. C16H26O8
requires C, 55.48; H, 7.57%]; nmax (liquid film) 3450, 1745,
1730 cm21; dH (200 MHz, CDCl3) 1.30 (12H, s, 4Me), 1.35
(3H, t, J¼7.0 Hz, CH3CH2O), 3.05 (1H, dd, J¼16.5, 7.7 Hz,
COCHaHb), 3.20 (1H, dd, J¼16.5, 4.8 Hz, COCHaHb), 3.40
(1H, s, OH, exchange with D2O), 3.67–3.74 (1H, m,
CHaHbO), 3.80 (1H, t, J¼7.4 Hz, OCH–CHOH), 3.85–3.90
(1H, m, CHOH), 4.00–4.20 (2H, m, CHO and CHaHbO),
4.19–4.25 (1H, m, CHO), 4.30 (2H, q, J¼7.0 Hz,
CH3CH2O).
4.1.5. (2R,3R,4S,5S)5-O-Acetyl-1,2,3,4-bis-O-isopropyl-
idene-7-[(40-methylphenyl)sulfonyl]-heptan-1,2,3,4,5-
pentaol (11). To a well-stirred and cooled (2108C) solution
of ketone 9 (0.11 g, 0.26 mmol) in MeOH (10 mL)
containing CeCl3·7H2O (0.10 g, 0.26 mmol), NaBH4
(0.01 g, 0.26 mmol) was added in one portion. Stirring
was continued for 30 min, then the excess of NaBH4 was
destroyed with acetone. The reaction mixture was concen-
trated in vacuo, diluted with sodium chloride solution
(5 mL, sat. aq.) and extracted with EtOAc (3£15 mL). Usual
work-up of the dried organic extracts afforded 10 (0.10 g,
90%) as a light yellow oil. The crude alcohol 10 was
dissolved in CH2Cl2 (4 mL) containing pyridine (0.029 mL,
0.35 mmol), acetic anhydride (0.03 mL, 0.35 mmol) and a
catalytic amount of 4-N,N0-dimethylaminopyridine. After
stirring at room temperature for 3 h, the reaction mixture
was washed with H2O (10 mL) and NaHCO3 solution
(10 mL, sat. aq.). The organic phase was separated, dried
and evaporated in vacuo. The residual oil was purified by
flash cromatography (eluent EtOAc–cyclohexane 1:1),
affording the title compound 11 (0.097 g, 89%) as an oil;
[Found: C, 57.70; H, 7.18. C22H32O8S requires C, 57.88; H,
7.06%]; [a]2D0¼þ4.31 (c 1.16, CHCl3); nmax (liquid film)
1720, 1600 cm21. dH (200 MHz, CDCl3) 1.35 (3H, s, Me),
1.36 (3H, s, Me), 1.40 (3H, s, Me), 1.41 (3H, s, Me), 2.15
(3H, s, COMe), 2.15–2.18 (2H, m, CH2CHOAc), 2.44 (3H,
s, PhMe), 3.15–3.25 (2H, m, CH2SO2), 3.60–3.66 (1H, m,
CHaCHbO), 3.95–4.05 (1H, m, CHO), 4.10–4.15 (2H, m,
2CHO), 4.15–4.20 (1H, m, CHaHbO), 5.05–5.12 (1H, m,
CHOAc), 7.40 (2H, d, J¼7.8 Hz, arom.), 7.80 (2H, d,
J¼7.8 Hz, arom.).
4.2. X-Ray crystal structure analysis of 9
C20H28O7S,
Mr¼412.48,
colorless
crystal
(0.15£0.32£0.40 mm3), monoclinic, space group P21 (no.
˚
4) with a¼5.6088(3), b¼20.3082(17), c¼9.5794(8) A,
3
23
˚
b¼92.785(5)8, V¼1089.8(1) A , Z¼2, Dc¼1.257 g cm
,
5941 reflections measured, 2843 independent, Rint¼0.048,
˚
(u,248, T¼295 K, Mo Ka radiation, l¼0.71073 A) on a
Nonius Kappa CCD diffractometer. The structure was

8558
A. Barco et al. / Tetrahedron 58 (2002) 8553–8558
solved by direct methods (SIR92)19 and refined on F 2
(SHELXL-97).20 Refinement converged at a final wR2 value
of 0.1192 (all reflections), R1¼0.0455 (for 2534 reflections
with I.2s(I)), S¼1.128, Flack21 parameter¼20.1(1). All
non-H atoms were refined anisotropically, all hydrogen
atoms were included on calculated positions, riding on their
carrier atoms. A final difference Fourier showed no residual
6. Barton, D. H. R.; DeAlmeida, M. V.; Liu, W.; Shinada, T.;
Jaszberenyi, J. Cs.; Dos Santos, H. F.; LeHyaric, M.
Tetrahedron 2001, 57, 8767–8771.
7. Sarabia, F.; Lopez-Herrera, F. J. Tetrahedron Lett. 2001, 42,
8805–8809.
8. Crestia, D.; Guerard, C.; Bolte, J.; Demuynck, C. J. Mol.
Catal. B: Enzym. 2001, 11, 207–212, and references quoted
therein.
density outside 20.17 and 0.19 A23. An ORTEP14 view of
˚
one of the molecules is shown in Fig. 2.
9. Hu, Y.-J.; Huang, X.-D.; Yao, Z.-J.; Wu, Y.-L. J. Org. Chem.
1998, 63, 2456–2461, and references quoted therein.
10. Barco, A.; Benetti, S.; De Risi, C.; Marchetti, P.; Pollini, G. P.;
Zanirato, V. Eur. J. Org. Chem. 2001, 975–986.
11. Hwu, J. R. J. Org. Chem. 1983, 48, 4432–4433.
12. Luche, J. L.; Gemal, A. L. J. Am. Chem. Soc. 1979, 101,
5848–5849.
Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic data
Centre as supplementary publication number CCDC
184660. Copies of the data can be obtained, free of charge,
on application to CCDC, Union Road, Cambridge CB2 1EZ,
UK [fax: þ44-1223-336033 or e-mail: deposit@ccdc.
cam.ac.uk].
13. Mitchell, H. J.; Nelson, A.; Warren, S. J. Chem. Soc., Perkin
Trans. 1 1999, 1899–1914.
14. Johnson, C. K. ORTEP II; Report ORNL-5138; Oak Ridge
National Laboratory: Oak Ridge, TN, 1976.
Acknowledgements
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