Novel asymmetric Wittig reaction: Synthesis of chiral allenic esters

Article abstract of DOI:10.1002/ejoc.200400413

Wittig reactions between 10-(phenylsulfonyl)isobornyl (triphenylphosphoranylidene)acetates (1 and 6) and ketenes resulted in asymmetric induction, with the selective synthesis of allenes with axial chirality. Use of the (1R)-(-)-10-(phenyl-sulfonyl)isoborneol unit allows the synthesis of allenes with S configuration, whereas use of the (1S)-(+)-10-(phenylsulfonyl)isoborneol unit produces allenes with R configuration. The structure of (1R)-(-)-10-(phenylsulfonyl)isobornyl (S)-5,5-dimethylhexa-2,3-dienoate (2e) was determined by X-ray crystallography. Chirooptical studies of the allenic esters were carried out, confirming that two sets of enantiomeric derivatives were obtained. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejoc.200400413

FULL PAPER
Novel Asymmetric Wittig Reaction: Synthesis of Chiral Allenic Esters
[a]
[a]
[a]
´
Teresa M. V. D. Pinho e Melo,* Ana L. Cardoso, Antonio M. d’A. Rocha Gonsalves,
[b]
[c]
[c]
´
˜
˜
Joao Costa Pessoa, Jose A. Paixao, and Ana M. Beja
Keywords: Asymmetric Wittig reaction / Chiral allenic esters / Chiral phosphorus ylides
Wittig reactions between 10-(phenylsulfonyl)isobornyl (tri-
The structure of (1R)-(−)-10-(phenylsulfonyl)isobornyl (S)-
phenylphosphoranylidene)acetates (1 and 6) and ketenes re- 5,5-dimethylhexa-2,3-dienoate (2e) was determined by X-ray
sulted in asymmetric induction, with the selective synthesis
of allenes with axial chirality. Use of the (1R)-(−)-10-(phenyl-
sulfonyl)isoborneol unit allows the synthesis of allenes with
S configuration, whereas use of the (1S)-(+)-10-(phenylsul-
crystallography. Chirooptical studies of the allenic esters
were carried out, confirming that two sets of enantiomeric
derivatives were obtained.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
fonyl)isoborneol unit produces allenes with R configuration. Germany, 2004)
Introduction
chiral allenic esters.[5] A phosphorus ylide bearing a (1R)-
(Ϫ)-10-(phenylsulfonyl)isoborneol unit (1) reacted with
methylketene to give a selective synthesis of an allene with
axial chirality corresponding to a S configuration. In view
of the observed high selectivity, a more extensive study of
this reaction has been carried out with the goal of ex-
panding the scope of this synthetic methodology.
Allenes are important and versatile building blocks in
organic chemistry,[1] the inherent instability associated with
the cumulated double bond having been widely exploited
for synthetic purposes. This structural feature makes ad-
dition to allenes very favourable, since it involves a relief in
strain. Allenes can be obtained by various synthetic meth-
ods, but the use of the Wittig reaction[2] or the
HornerϪWadsworthϪEmmons reaction[3] are of particular
interest since they allow regio- and stereocontrol of the
carbonϪcarbon double bond formation.
Results and Discussion
We have described the reaction between the chiral phos-
Little attention has been paid to the synthesis of chiral phorus ylide 1 and ketene to give two products: the chiral
allenes through asymmetric Wittig-type reactions,[4] but op- allene 2a in 63% yield, and the ylide 3a in 3% yield. A more
tically active 4,4-disubstituted allenecarboxylates have been relevant result was obtained when ylide 1 was treated with
prepared by treatment of ketenes Ϫ generated in situ from methylketene, generated in situ from propionyl chloride and
phenyl acetates
Ϫ with chiral HornerϪWadsworthϪ triethylamine, to afford allene 2b with axial chirality in 64%
Emmons reagents.[3c,3d] On the other hand, Tömösközi and yield. The structure of (1R)-(Ϫ)-10-(phenylsulfonyl)isobor-
Bestmann have reported reactions between phosphorus yl- nyl (S)-penta-2,3-dienoate (2b) was determined by X-ray
ides containing chiral alcohol units and acid chlorides to crystallography (Scheme 1).[5]
afford chiral allenes, although neither the absolute configu-
Cleavage of the chiral auxiliary was achieved by alkaline
rations of the products nor the levels of asymmetric induc- hydrolysis[3b] of allene 2b. Penta-2,3-dienoic acid[6] was iso-
tion were determined.[2f] The same authors also reported lated with an [α]D25 value of ϩ98. The signs of the optical
reactions between racemic phosphorus ylides and chiral rotation values may be predicted and a rough estimation
acid chlorides to give enantiomerically enriched allenes.[2g]
may be accomplished. In fact, the concept of an asymmetric
In a preliminary communication we have described a no- screw pattern of polarisability at a chiral centre has been
vel asymmetric Wittig reaction that allows the synthesis of applied by Lowe[7a] and Brewster[7b] to work out an empiri-
cal rule for assigning the absolute configuration of optically
[a]
´
Departamento de Quımica, Universidade de Coimbra,
active allenes. Therefore, according to the LoweϪBrewster
rule, the penta-2,3-dienoic acid with S configuration should
be dextrorotatory, as is indeed the case.
In order to evaluate the scope of this asymmetric Wittig
reaction it was essential to study the reactivity of phos-
phorus ylide 1 with a range of ketenes bearing progressively
3004Ϫ535 Coimbra, Portugal
Fax: (internat.) ϩ 351-239-826068
E-mail: tmelo@ci.uc.pt
[b]
[c]
´
´
Centro de Quımica Estrutural, Instituto Superior Tecnico,
1049-001 Lisboa, Portugal
´
Departamento de Fısica, Universidade de Coimbra,
3004-516 Coimbra, Portugal
4830
© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200400413
Eur. J. Org. Chem. 2004, 4830Ϫ4839

Synthesis of Chiral Allenic Esters
FULL PAPER
Scheme 1
bulkier substituents. This could allow us to determine
whether the steric factor is limiting in the selectivity.
A different outcome was observed when ylide 1 was
treated with phenylketene (Scheme 2). In this case a mixture
A selection of monosubstituted acetyl chlorides was of diastereoisomers was obtained, as shown clearly in the
made, and included butyryl chloride, 3-methylbutyryl chlo- 1H NMR and 13C NMR spectra.
ride, 3,3-dimethylbutyryl chloride, 3-phenylbutyryl chloride
and phenylacetyl chloride. These acid chlorides were used bulky groups in the reacting ketene does not affect the selec-
for the in situ generation of the corresponding ketenes. tivity of Wittig reactions of the ylide 1, the chiral allenic
Our results allowed us to conclude that the presence of
Treatment of ylide 1 with ethylketene, isopropylketene, esters being obtained with high selectivity even with tert-
tert-butylketene and benzylketene was carried out and in all butylketene or benzylketene. In the case of the ketene with
these cases the corresponding allenic ester with axial chiral- a conjugative phenyl group, however, no selectivity was ob-
ity was obtained selectively and in good yield (Scheme 1). served.
In some cases, ylide 3, the result of the acylation of 1, was
also formed. H NMR spectra of the allenes 2 showed sig- esters with axial chirality corresponding to a S configura-
A synthetic methodology for the preparation of allenic
1
nals corresponding to single diastereoisomers, and the chi- tion having been established, it was important to ascertain
ral allenes 2 showed positive optical rotation values.
whether the use of a phosphorus ylide bearing a chiral
The structure of (1R)-(Ϫ)-10-(phenylsulfonyl)isobornyl auxiliary enantiomeric with the isoborneol unit of phos-
(S)-5,5-dimethylhexa-2,3-dienoate (2e) was determined by phorus ylide 1 would permit the selective synthesis of all-
X-ray crystallography (Figure 1).
enes of R configuration.
Figure 1. ORTEPII plot of compound 2e with anisotropic displacement ellipsoids calculated at the 30% probability level; the angle
between the least-squares planes C2ϪC3ϪC4ϪC5 and C4ϪC3ϪC2ϪC1 is 89.04(18)°; the absolute configurations of chiral carbon atoms
were determined by the Flack method [η ϭ 0.039(18)] by use of the anomalous scattering of the sulfur atom at the Cu-Kα wavelength,
confirming the S,R,S absolute configurations of C9, C10 and C13
Eur. J. Org. Chem. 2004, 4830Ϫ4839
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T. M. V. D. Pinho e Melo et al.
FULL PAPER
(7bϪ7f) with axial chirality corresponding to a R configura-
tion (Scheme 3). This was also confirmed by chirooptical
studies (see below).
The stereochemical outcome of this asymmetric Wittig-
type reaction can be explained by the assumption that the
presence of the chiral 10-(phenylsulfonyl)isoborneol unit in
the starting phosphorus ylide determines the geometry of
approach of the ketene, thus allowing for asymmetric induc-
tion.
We then turned our attention to the potential for the
preparation of trisubstituted allenes. (1R)-(Ϫ)-10-(phenyl-
sulfonyl)isobornyl 3-oxo-2-(triphenylphosphoranylidene)-
butanoate (3a, 93%) was prepared from ylide 1 and acetyl
chloride in the presence of BSA (N,O-bis(trimethylsilyl)-
acetamide] by the general procedure described in the litera-
ture (Scheme 4).[9] Treatment of ylide 3a with methylketene,
ethylketene and benzylketene was carried out. However, the
products were again stereoselectively obtained disubstituted
allenes with S axial chirality .
Scheme 2
The (1S)-(ϩ)-10-(phenylsulfonyl)isoborneol (4)[8] reacted
with bromoacetyl bromide to give the corresponding ester
5 (91%), and treatment of this with triphenylphosphane
gave the new chiral phosphorus ylide 6 in 69% yield. Wittig
Attempts were made to promote this type of reaction
reactions between this phosphorus ylide 6 Ϫ bearing a (1S)- starting from phosphorus ylide 9. In this case, however, no
(ϩ)-10-(phenylsulfonyl)isoborneol unit Ϫ and a range of reaction between ylide 9 and the ketene generated in situ
ketenes including ketene, methylketene, ethylketene, isopro- from propionyl chloride and triethylamine was observed,
pylketene, tert-butylketene and benzylketene were studied. and only starting ylide could be recovered.
Allenes 7 were obtained selectively and in good yields, and
The synthesis of allenes 2b, 2c and 2f from ylide 3a could
the 1H NMR spectra of compounds 7 showed signals corre- be explained in terms of the in situ generation of phos-
sponding to single diastereoisomers. When compared, these phorus ylides with the general structure 3, which might have
allenes could not be distinguished from the corresponding acted as intermediates. To check this hypothesis, ylide 3b
allenes derived from ylide 1 by their 1H NMR and 13C was prepared and treated with triethylamine. No reaction
NMR spectra. On the other hand, the allenic esters 7bϪ7f was observed, however, thus indicating that ylides 3 are not
showed negative values for their optical rotations, indicating involved in the process. Another possibility would be the
that these allenes were enantiomers of the corresponding elimination of acetyl chloride ion from 3a by reaction with
allenes 2. We concluded that we had obtained allenic esters triethylammonium chloride. This would afford ylide 1,
Scheme 3
4832
© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2004, 4830Ϫ4839

Synthesis of Chiral Allenic Esters
FULL PAPER
Isotropic UV and CD Spectra
The CD and UV spectra of the enantiomeric allenes
2bϪ2f and 7bϪ7f and of the allenes 2a and 7a were re-
corded. Compounds 2aϪ2f and 7aϪ7f each have three ster-
eogenic carbon centres in the isobornyl moiety, while in
2bϪ2f and 7bϪ7f there is an additional chirality source,
characterised by two orthogonal CϭC chromophores, in
the form of the allenic group. Allenes 2a and 7a have no
axial chirality in the allenic group.
The UV spectra of 2aϪ2f and 7aϪ7f are similar, mostly
dominated by the πǞπ* benzenic and allenic transitions,
some of the transitions corresponding to double excitation
bands.[11Ϫ13] Vibronic progressions of about 1000 cmϪ1 are
seen in the 245Ϫ275 nm region. These may be associated
with the symmetric CϭCϭC stretch[13] and/or the benzene
B-band.
The perturbations of molecular electronic states by alkyl
groups, particularly the ϪCH3 group, are normally small
and, as mentioned by Runge et al.,[12] would not be ex-
Scheme 4
which would give allenes 2 on reaction with the ketenes. pected to be very important in the allenic derivatives. This
When 3a was treated with triethylammonium chloride, how- is why the UV spectra of 2bϪ2e and 7bϪ7e are quite simi-
ever, we were unable to observe the formation of 1.
lar, a very slight decrease in ε values in the 245Ϫ275 nm
We imagine that the synthesis of 2 from 3a involves the range being observed over the sequence of substituents tBu,
initial addition of the ketene to give the oxaphosphetane iPr, Et, Me. Compounds 2f and 7f, containing the Bzl moi-
11. This intermediate undergoes nucleophilic attack by the ety, shows some significant differences, but the pattern of
chlorine ion, resulting in the generation of the carbanion the UV spectra is similar to those of 2bϪ2e and 7bϪ7e.
12. Protonation of 12 with facial diastereoselectivity would
The CD spectra of compounds 2aϪ2f and 7aϪ7f follow
give 13, followed by elimination of triphenylphosphane ox- a similar pattern (Figure 2). The allenic groups in 2a and
ide to give allenes 2 (Scheme 5).
7a have no axial chirality, but the CD signal, in the
Scheme 5
Eur. J. Org. Chem. 2004, 4830Ϫ4839
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T. M. V. D. Pinho e Melo et al.
FULL PAPER
Figure 2. CD spectra for chiral allenic esters 2bϪ2f and 7bϪ7f
250Ϫ275 nm range, is reasonably strong, and the vibronic ried out, confirming that two sets of enantiomeric deriva-
progressions are also clearly observed. The overall optical tives were obtained.
activity is due to the isobornyl moiety, but the measured
CD spectra indicate that the chirality is efficiently trans-
Experimental Section
mitted throughout the whole molecule. As expected gener-
ally, the CD signal increases its intensity as the size of the
substituent increases. This is clearly observed in the se-
quence 2a,7a (R ϭ H), 2b,7b (R ϭ Me), 2c,7c (R ϭ Et),
2d,7d (R ϭ iPr), 2e,7e (R ϭ tBu) where there is an increase
in the |∆ε| values corresponding to an increase in the polar-
izability of the substituent. In the cases of 2f and 7f (R ϭ
Bzl), however, the ε and ∆ε values are even lower than
those of 2b and 7b. The allenes of set 2 are enantiomers of
the corresponding allenes of set 7 and they show CD spec-
tra consistent with this.
1
General Remarks: H NMR spectra were recorded with a Bruker
AMX 300 instrument operating at 300 MHz and 500 MHz. 13C
spectra were recorded with a Bruker AMX 300 instrument op-
erating at 75.5 MHz and 125 MHz. The solvent was deuteriochlor-
oform except where indicated otherwise. IR spectra were recorded
on a PerkinϪElmer 1720X FTIR spectrometer. Mass spectra were
recorded with a HP GC 6890/MSD5973 instrument or in a Trio
1000 GC mass spectrometer, either by electron impact (EI) or by
chemical ionisation with ammonia (CI), through GC inlet or direct
inlet for thermally labile products. Mass spectra were also recorded
in a LCQ Advantage, Thermo Finnigan mass spectrometer by ESϩ
where indicated. Optical rotations were measured on an Optical
Activity AA-5 electrical polarimeter. The circular dichroism spectra
were run with a Jasco 720 spectropolarimeter in the 200Ϫ400 nm
range, with use of the appropriate UV/Vis (170Ϫ700 nm) photo-
multiplier. Isotropic absorption spectra were run between 200 and
400 nm with a Hitachi U2000 spectrophotometer. Microanalyses
were carried out at the University of Coimbra on a Fisons EA
1108-CHNS-O instrument. M.p.s were recorded with a Reichert
hot stage and are uncorrected. Flash column chromatography was
carried out on Merck 9385 silica as the stationary phase. Ylide 3a
(93%) was prepared from ylide 1 and acetyl chloride in the presence
of BSA by the general procedure described in the literature.[9]
Conclusion
In this work we describe a new asymmetric Wittig reac-
tion that allows the synthesis of allenic esters with axial
chirality. Treatment of (1R)-(Ϫ)-10-(phenylsulfonyl)isobor-
nyl (triphenylphosphoranylidene)acetate (1) with methylke-
tene, ethylketene, isopropylketene, tert-butylketene and
benzylketene, each generated in situ from the corresponding
acid chloride and triethylamine, allowed the selective syn-
thesis of allenes with S configurations. Only with phenylke-
tene was no selectivity observed. On use of a phosphorus
ylide bearing a chiral auxiliary enantiomeric with the iso-
borneol unit of phosphorus ylide 1, (1S)-(ϩ)-10-(phenylsul-
fonyl)isobornyl (triphenylphosphoranylidene)acetate (6),
the formation of allenes with R configurations was
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl Bromoacetate: Bromoacetyl
bromide (4.8 mL, 54.4 mmol) was added dropwise to a stirred solu-
tion
of
(1R)-(Ϫ)-10-(phenylsulfonyl)isoborneol[14]
(8.01 g,
27.2 mmol) in dichloromethane. The mixture was stirred under ni-
trogen at room temperature for 12 h. The solution was washed with
achieved. Chirooptical studies of the allenic esters were car- an aqueous solution of sodium hydroxide and dried (MgSO4), and
4834 © 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjoc.org
Eur. J. Org. Chem. 2004, 4830Ϫ4839

Synthesis of Chiral Allenic Esters
FULL PAPER
the solvents were evaporated off to give (1R)-(Ϫ)-10-(phenylsulfon- zoyl chloride (8.04 mmol, 1.0 mL) in dry tetrahydrofuran was ad-
yl)isobornyl bromoacetate as an oil (10.6 g, 25.6 mmol, 94%). 1H ded dropwise. The mixture was stirred under nitrogen at room tem-
NMR: δ ϭ 0.87 (s, 3 H), 0.99 (s, 3 H), 1.20Ϫ1.25 (m, 1 H), perature for 12 h and filtered, and the filtrate was washed with
1.65Ϫ2.05 (m, 6 H), 2.99 (d, J ϭ 13.9 Hz, 1 H), 3.58 (d, J ϭ water, dried (MgSO4) and concentrated under vacuum. The prod-
13.9 Hz, 1 H), 3.79 (d, J ϭ 12.8 Hz, 1 H), 3.84 (d, J ϭ 12.8 Hz, 1
uct was purified by flash chromatography [ethyl acetate/hexane
H), 4.97Ϫ4.99 (m, 1 H), 7.55Ϫ7.60 (m, 2 H, Ar-H), 7.64Ϫ7.69 (m, (1:1)] to give 9 in 81% yield (4.58 g, 6.53 mmol). Compound 9 was
1 H, Ar-H), 7.93Ϫ7.96 (m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 19.8, obtained as a solid, m.p. 196.4Ϫ198.0 °C. 1H NMR: δ ϭ 0.13 (s, 3
20.2, 26.2, 27.0, 29.7, 39.0, 43.9, 49.6, 49.9, 54.9, 79.5, 127.7, 129.2,
H), 0.63 (s, 3 H), 0.94Ϫ1.02 (m, 1 H), 1.25Ϫ1.72 (m, 6 H), 2.61 (d,
133.6, 141.0, 165.4 ppm. CI-MS: m/z (%) ϭ 434 (54) [M ϩ NH4] J ϭ 13.9 Hz, 1 H), 3.04 (d, J ϭ 13.9 Hz, 1 H), 4.77 (t, J ϭ 3.6 Hz,
ϩ, 432 (40), 278 (18), 277 (88).
1 H), 7.18Ϫ7.22 (m, 2 H, Ar-H), 7.28Ϫ7.33 (m, 1 H, Ar-H),
7.44Ϫ7.59 (m, 12 H, Ar-H), 7.67Ϫ7.71 (m, 2 H, Ar-H), 7.83Ϫ7.91
(m, 8 H, Ar-H) ppm. 13C NMR: δ ϭ 19.45, 20.06, 26.92, 29.85,
36.94, 43.96, 49.07, 49.13, 54.50, 69.10 (d, 1JC,P ϭ 114 Hz), 125.40,
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (Triphenylphosphoranylidene)-
acetate (1): Triphenylphosphane (4.35 g, 16.58 mmol) was added to
a stirred solution of (1R)-(Ϫ)-10-(phenylsulfonyl)isobornyl bromo-
acetate (6.5 g, 15.65 mmol) in toluene. The mixture was heated un-
der reflux for 12 h. Filtration of the solution gave the correspond-
ing phosphonium salt, which was dissolved in water (170 mL). The
solution was neutralised by the addition of aqueous sodium hy-
droxide (10.9 g, 330 mL of water). The resulting solid was collected
by filtration and dried to give 1 (8.16 g, 13.7 mmol, 87%). Com-
pound 1 was obtained as a solid, m.p. 201Ϫ202 °C (from ethyl
acetate/hexane). 1H NMR: δ ϭ 0.84 (s, 3 H), 0.94 (s, 3 H),
3
4
128.57 (d, JC,P ϭ 12.5 Hz), 131.65 (d, JC,P ϭ 2.7 Hz), 133.32 (d,
3
2JC,P ϭ 9.82 Hz), 141.56, 143.63 (d, JC,P ϭ 9.66 Hz), 167.07 (d,
2
2JC,P ϭ 15.4 Hz), 192.60 (d, JC,P ϭ 6.0 Hz) ppm. FAB-MS: m/z
(%) ϭ 701 (66) [Mϩ], 551 (6), 460 (9), 407 (100). HRMS (ESϩ):
701.2491. C43H42O5PS, [M ϩ H]ϩ requires 701.2506. C43H41O5PS
(700.8): calcd. C 73.69, H 5.9; found C 73.62, H 6.05. [α]2D0 ϭ ϩ47.6
(c ϭ 0.1, CH2Cl2).
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl
3-Oxo-2-(triphenylphos-
1.45Ϫ1.50 (m, 1 H), 1.65Ϫ1.93 (m, 6 H), 2.94 (d, J ϭ 13.9 Hz, 1 phoranylidene)pentanoate (3b): This compound was prepared from
H), 3.79 (d, J ϭ 13.9 Hz, 1 H), 4.46 (m, 1 H), 7.25Ϫ7.30 (m, 2 ylide 1 and acetyl chloride in the presence of BSA by the general
H, Ar-H), 7.36Ϫ7.38 (m, 1 H, Ar-H), 7.44Ϫ7.51 (m, 6 H, Ar-H),
procedure described in the literature.[9] Compound 3b was obtained
7.53Ϫ7.59 (m, 3 H, Ar-H), 7.64Ϫ7.72 (m, 6 H, Ar-H), 7.93Ϫ7.96 as a yellow solid (93%), m.p. 187.7Ϫ188.8 °C (from diethyl ether/
1
(m, 2 H, Ar-H) ppm. CI-MS: m/z (%) ϭ 597 (20) [M], 294 (19), hexane). IR (KBr): ν˜ ϭ 1633 and 2955 cmϪ1. H NMR: δ ϭ 0.86
277 (100), 281 (61), 207 (97), 73 (33). HRMS (ESϩ): 597.2217. (s, 3 H), 0.93 (s, 3 H), 0.96 (approx. t, J ϭ 7.4 Hz, 3 H), 1.13Ϫ1.21
C36H38O4PS [M ϩ H]ϩ requires 597.2228. C36H37O4PS (597.7):
calcd. C 72.5, H 6.3; found C 71.9, H 6.4. [α]2D0 ϭ ϩ48.7 (c ϭ
0.1, CH2Cl2).
(m, 1 H), 1.61Ϫ1.94 (m, 6 H), 2.65Ϫ2.73 (m, 1 H), 2.80Ϫ2.88 (m,
1 H), 3.00 (d, J ϭ 13.8 Hz, 1 H), 3.63 (d, J ϭ 13.8 Hz, 1 H), 4.99
(dd, J ϭ 3.7, J ϭ 7.9 Hz, 1 H), 7.38Ϫ7.55 (m, 12 H, Ar-H),
7.68Ϫ7.75 (m, 6 H, Ar-H), 7.88Ϫ7.91 (m, 2 H, Ar-H) ppm. 13C
NMR: δ ϭ 9.8, 20.3, 20.4, 27.0, 30.0, 39.8, 44.0, 49.6, 49.7, 55.5,
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl Bromoacetate (5): Bromoace-
tyl bromide (4.8 mL, 54.4 mmol) was added dropwise to a stirred
solution of the alcohol 4[8] (8.01 g, 27.2 mmol) in dichloromethane.
The mixture was stirred under nitrogen at room temperature for
12 h. The solution was washed with an aqueous solution of sodium
3
77.4, 126.1, 127.3, 127.5, 128.4 (d, JC,P ϭ 12.5 Hz), 129.1, 131.4
4
3
(d, JC,P ϭ 2.8 Hz), 132.9 (d, JC,P ϭ 9.7 Hz), 133.3, 141.6, 166.6
2
2
(d, JC,P ϭ 17.8 Hz), 196.3 (d, JC,P ϭ 3.7 Hz) ppm. ES-MS: m/z
(%) ϭ 653 (100) [Mϩ].
hydroxide and dried (MgSO4), and the solvents were evaporated
1
off to give 5 as oil (10.3 g, 24.8 mmol, 91%). H NMR: δ ϭ 0.87 General Procedure for the Synthesis of Allenes 2 and Phosphorus
(s, 3 H), 0.99 (s, 3 H), 1.20Ϫ1.21 (m, 1 H), 1.65Ϫ2.06 (m, 6 H),
Ylides 3 Starting from Ylide 1: A solution of acid chloride
2.99 (d, J ϭ 14.0 Hz, 1 H), 3.58 (d, J ϭ 14.0 Hz, 1 H), 3.79 (d, J ϭ (7.54 mmol) in tetrahydrofuran was added dropwise to a stirred
14.0 Hz, 1 H), 3.84 (d, J ϭ 14.0 Hz, 1 H), 4.96Ϫ5.00 (m, 1 H), solution of the ylide 1 (7.54 mmol) and triethylamine (1.8 mL) in
7.54Ϫ7.60 (m, 2 H, Ar-H), 7.63Ϫ7.69 (m, 1 H, Ar-H), 7.93Ϫ7.98
tetrahydrofuran. The mixture was stirred under nitrogen at room
(m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 19.8, 20.2, 26.2, 27.0, 29.7, temperature for 12 h and filtered, and the filtrate was concentrated
39.0, 43.9, 49.6, 49.9, 54.9, 79.5, 127.6, 129.3, 133.6, 141.1, 165.3 under vacuum. The crude oil was dissolved in CH2Cl2, washed with
ppm. CI-MS: m/z (%) ϭ 416 (11) [M ϩ H]ϩ, 277 (100), 135 (98).
water and dried (MgSO4), and the solvents were evaporated off.
The products were isolated by flash chromatography [ethyl acetate/
hexane (1:1)]. In some cases allene 2 was the only product, whereas
in other cases ylide 3 was also formed.
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (Triphenylphosphoranylidene)-
acetate (6): Triphenylphosphane (4.35 g, 16.58 mmol) was added to
a stirred solution of 5 (6.5 g, 15.65 mmol) in toluene. The mixture
was heated under reflux for 12 h. Filtration of the solution gave (1R)-(؊)-10-(Phenylsulfonyl)isobornyl Buta-2,3-dienoate (2a) and
the corresponding phosphonium salt, which was dissolved in water
(170 mL). The solution was neutralised by the addition of aqueous
sodium hydroxide (10.9 g, 330 mL of water). The resulting solid
was collected by filtration and dried to give 6 (6.47 g, 10.8 mmol,
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl
phoranylidene)butanoate (3a)
3-Oxo-2-(triphenylphos-
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl Buta-2,3-dienoate (2a): 2a
was obtained as an oil (1.71 g, 63%). IR (film): ν˜ ϭ 1715, 1940,
1968 cmϪ1. Ϫ1H NMR: δ ϭ 0.87 (s, 3 H), 0.93 (s, 3 H), 1.19Ϫ1.29
(m, 1 H), 1.58Ϫ2.0 (m, 6 H), 2.99 (d, J ϭ 14.1 Hz, 1 H), 3.59 (d,
J ϭ 14.1 Hz, 1 H), 4.78 (dd, J ϭ 3.3, J ϭ 9.3 Hz, 1 H), 5.07 (dd,
J ϭ 6.5, J ϭ 14.4 Hz, 1 H), 5.18 (dd, J ϭ 6.5, J ϭ 14.4 Hz, 1 H),
5.56 (approx. t, J ϭ 6.5 Hz, 1 H), 7.52Ϫ7.68 (m, 3 H, Ar-H),
7.88Ϫ7.92 (m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 20.2, 20.7, 27.5,
1
69%). H NMR: δ ϭ 0.84 (s, 3 H), 0.89Ϫ1.13 (m, 4 H), 1.22Ϫ2.04
(m, 6 H), 2.94 (d, J ϭ 13.8 Hz, 1 H), 3.79 (d, J ϭ 13.8 Hz, 1 H),
4.48Ϫ4.51 (m, 1 H), 7.15Ϫ7.33 (m, 2 H, Ar-H), 7.37Ϫ7.57 (m, 10
H, Ar-H), 7.62Ϫ7.73 (m, 6 H, Ar-H), 7.93Ϫ7.98 (m, 2 H, Ar-H)
ppm. ES-MS: m/z (%) ϭ 597 (100) [Mϩ], 279 (10).
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl 3-Oxo-3-phenyl-2-(triphenyl-
phosphoranylidene)propanoate (9): A solution of ylide 1 (4.8 g, 29.9, 39.9, 44.5, 49.9, 50.3, 55.5, 78.4, 79.1, 88.8, 128.1, 129.6,
8.04 mmol) and triethylamine (1.9 mL) in dry tetrahydrofuran 133.9, 142.8, 164.2, 216.3 ppm. CI-MS: m/z (%) ϭ 378 (69) [M ϩ
(1.0 mL) was stirred at room temperature while a solution of ben- NH4]ϩ, 361 (5) [Mϩ], 294 (39), 277 (100). HRMS (CI): 378.1744.
Eur. J. Org. Chem. 2004, 4830Ϫ4839
www.eurjoc.org
© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4835

T. M. V. D. Pinho e Melo et al.
FULL PAPER
C20H28O4PS [M ϩ NH4]ϩ requires 378.1739. [α]2D0 ϭ ϩ144 (c ϭ
1, CH2Cl2).
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl 5-Methyl-3-oxo-2-(triphenyl-
phosphoranylidene)hexanoate (3d): 3d was obtained as a yellow oil
(0.26 g, 5%). 1H NMR: δ ϭ 0.74 (d, J ϭ 2.8 Hz, 3 H), 0.76 (d, J ϭ
2.8 Hz, 3 H), 0.97 (d, J ϭ 6.5 Hz, 6 H), 0.98Ϫ2.32 (m, 8 H), 2.53
(dd, J ϭ 6.6 Hz, J ϭ 15.5 Hz, 1 H), 2.76 (dd, J ϭ 7.5 Hz, 15.5 Hz,
1 H), 3.02 (d, J ϭ 13.8 Hz, 1 H), 3.64 (d, J ϭ 13.8 Hz, 1 H), 4.99
(dd, J ϭ 3.8 Hz, J ϭ 7.9 Hz, 1 H), 7.38Ϫ7.55 (m, 12 H, Ar-H),
7.70Ϫ7.77 (m, 6 H, Ar-H), 7.91Ϫ7.94 (m, 2 H, Ar-H) ppm. ES-
MS: m/z (%) ϭ 681 (100) [Mϩ], 405 (14).
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl
3-Oxo-2-(triphenylphos-
phoranylidene)butanoate (3a): 3a was obtained as an oil (0.14 g,
1
3%). IR (film): ν˜ ϭ 1657, 1549, 1286 cmϪ1. H NMR: δ ϭ 0.85 (s,
3 H), 0.95 (s, 3 H), 1.13Ϫ1.26 (m, 1 H), 1.68Ϫ1.91 (m, 6 H), 2.35
(s, 3 H), 2.99 (d, J ϭ 13.9 Hz, 1 H), 3.64 (d, J ϭ 13.9 Hz, 1 H),
4.98 (dd, J ϭ 3.7, J ϭ 7.9 Hz, 1 H), 7.42Ϫ7.55 (m, 12 H, Ar-H),
7.63Ϫ7.76 (m, 6 H, Ar-H), 7.91Ϫ7.94 (m, 2 H, Ar-H) ppm. 13C
NMR: δ ϭ 20.7, 20.8, 27.5, 30.4, 30.6, 40.2, 44.5, 50.1, 50.2, 56.0,
72.7 (d, 1JC,P ϭ 115 Hz), 78.0, 126.3, 127.3, 128.0, 128.9 (d, 3JC,P ϭ
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-5,5-Dimethylhexa-2,3-di-
enoate (2e) and (1R)-(؊)-10-(Phenylsulfonyl)isobornyl 5,5-Dimethyl-
3-oxo-2-(triphenylphosphoranylidene)hexanoate (3e)
4
2
12.2 Hz), 129.0, 129.6, 131.9 (d, JC,P ϭ 2.8 Hz), 133.5 (d, JC,P
ϭ
2
2
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-5,5-Dimethylhexa-2,3-di-
enoate (2e): The general procedure was followed, with ylide 1
(7.54 mmol) and triethylamine (1.8 mL) and 3,3-dimethylbutyryl
chloride (11.31 mmol). Compound 2e was obtained as a white solid
(2.42 g, 77%), m.p. 134.5Ϫ135.6 °C (from diethyl ether/hexane). IR
9.7 Hz), 167.2 (d, JC,P ϭ 17.6 Hz), 193.4 (d, JC,P ϭ 4.1 Hz) ppm
CI-MS: m/z (%) ϭ 639 (17) [M ϩ H]ϩ, 638 (2) [Mϩ], 379 (4), 294
(11), 277 (70).
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-Penta-2,3-dienoate (2b):
This compound was obtained as a white solid (1.81 g, 64%), m.p.
96.0Ϫ97.6 °C (from diethyl ether/hexane). IR (film): ν˜ ϭ 1715,
1
(KBr): ν˜ ϭ 1715, 1955 cmϪ1. H NMR: δ ϭ 0.87 (s, 3 H), 0.95 (s,
3 H), 1.05 (s, 9 H), 1.17Ϫ1.29 (m, 1 H), 1.57Ϫ2.02 (m, 6 H), 2.99
(d, J ϭ 14.0 Hz, 1 H), 3.59 (d, J ϭ 14.0 Hz, 1 H), 4.69Ϫ4.73 (m,
1 H), 5.47 (d, J ϭ 6.1 Hz, 1 H), 5.57 (d, J ϭ 6.1 Hz, 1 H),
7.51Ϫ7.57 (m, 2 H, Ar-H), 7.60Ϫ7.67 (m, 1 H, Ar-H), 7.88Ϫ7.92
(m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 20.1, 20.2, 27.1, 29.3, 29.5 (3
ϫ C), 32.5, 39.5, 44.0, 49.4, 49.84, 54.8, 77.8, 90.2, 106.3, 127.7,
129.1, 133.5, 141.1, 164.5, 209.8 ppm. CI-MS: m/z (%) ϭ 417 (40)
[M ϩ H]ϩ, 277 (100), 135 (77). HRMS (CI): 417.2103. C24H33O4S
[M ϩ H]ϩ requires 417.2099. [α]2D0 ϭ ϩ180 (c ϭ 0.5, CH2Cl2).
1
1961 cmϪ1. H NMR: δ ϭ 0.85 (s, 3 H), 0.87 (s, 3 H), 1.24Ϫ1.29
(m, 1 H), 1.69Ϫ2.04 (m, 9 H), 2.99 (d, J ϭ 14.1 Hz, 1 H), 3.60 (d,
J ϭ 14.1 Hz, 1 H), 4.69 (dd, J ϭ 3.2 Hz, J ϭ 8.4 Hz, 1 H),
5.43Ϫ5.47 (m, 2 H), 7.51Ϫ7.57 (m, 2 H, Ar-H), 7.62Ϫ7.64 (m, Ar-
H, 1 H), 7.89Ϫ7.91 (m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 12.7,
19.7, 20.3, 27.1, 29.3, 39.4, 44.0, 49.4, 49.9, 55.0, 77.5, 88.1, 89.7,
127.7, 129.2, 133.5, 141.1, 164.2, 213.1 ppm. CI-MS: m/z (%) ϭ
375 (28) [M ϩ H]ϩ, 277 (100) , 135 (95). HRMS (CI): 375.1634.
C21H27O4S [M ϩ H] requires 375.1630. [α]2D0 ϭ ϩ149 (c ϭ 1,
ϩ
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl
5,5-Dimethyl-3-oxo-2-(tri-
CH2Cl2).
phenylphosphoranylidene)hexanoate (3e): 3e was obtained as an oil
1
(52 mg, 1%). H NMR: δ ϭ 0.86 (s, 3 H), 0.93 (s, 3 H), 1.05 (s, 9
H), 1.11Ϫ1.15 (m, 1 H), 1.59Ϫ1.99 (m, 6 H), 2.42 (d, J ϭ 13.6 Hz,
1 H), 2.94 (d, J ϭ 13.6 Hz, 1 H), 2.97 (d, J ϭ 13.8 Hz, 1 H), 3.62
(d, J ϭ 13.8 Hz, 1 H), 5.00 (dd, J ϭ 3.9, J ϭ 8.0 Hz, 1 H),
7.40Ϫ7.48 (m, 12 H, Ar-H), 7.70Ϫ7.78 (m, 6 H, Ar-H), 7.90Ϫ7.93
(m, 2 H, Ar-H) ppm.
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-Hexa-2,3-dienoate (2c):
This compound was obtained as a white solid (2.11 g, 72%), m.p.
76.0Ϫ77.3 °C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1711,
1
1956 cmϪ1. H NMR: δ ϭ 0.87 (s, 3 H), 0.93 (s, 3 H), 0.98Ϫ1.05
(m, 3 H), 1.19Ϫ1.26 (m, 1 H), 1.64Ϫ1.96 (m, 6 H), 2.05Ϫ2.12 (m,
2 H), 2.99 (d, J ϭ 14.0 Hz, 1 H), 3.60 (d, J ϭ 14.0 Hz, 1 H),
4.69Ϫ4.72 (m, 1 H), 5.50Ϫ5.61 (m, 2 H), 7.51Ϫ7.57 (m, 2 H, Ar-
H), 7.61Ϫ7.66 (m, 1 H, Ar-H), 7.88Ϫ7.91 (m, 2 H, Ar-H) ppm.
13C NMR: δ ϭ 12.9, 19.7, 20.3, 27.1, 29.3, 39.5, 44.0, 49.4, 49.9,
55.0, 77.6, 89.3, 96.6, 127.7, 129.2, 133.5, 141.1, 164.4, 212.0 ppm.
CI-MS: m/z (%) ϭ 389 (10) [M ϩ H]ϩ, 277 (90), 135 (100). HRMS
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-5-Phenylpenta-2,3-dieno-
ate (2f) and (1R)-(؊)-10-(Phenylsulfonyl)isobornyl 3-Oxo-5-phenyl-
2-(triphenylphosphoranylidene)pentanoate (3f)
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-5-Phenylpenta-2,3-dieno-
ate (2f): 2f was obtained as a white solid (2.58 g, 76%), m.p.
101.4Ϫ102.7 °C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1711,
(CI): 389.1793. C22H29O4S [M ϩ H]ϩ requires 389.1786. [α]2D0
ϩ180 (c ϭ 0.5, CH2Cl2).
ϭ
1
1957 cmϪ1. H NMR: δ ϭ 0.85 (s, 3 H), 0.89 (s, 3 H), 1.15Ϫ1.26
(m, 1 H), 1.59Ϫ1.98 (m, 6 H), 2.96 (d, J ϭ 14.0 Hz, 1 H),
3.38Ϫ3.44 (m, 2 H), 3.56 (d, J ϭ 14.0 Hz, 1 H), 4.72Ϫ4.76 (m, 1
H), 5.52Ϫ5.56 (m, 2 H), 7.16Ϫ7.32 (m, 5 H, Ar-H), 7.48Ϫ7.52 (m,
2 H, Ar-H), 7.57Ϫ7.62 (m, 1 H, Ar-H), 7.86Ϫ7.89 (m, 2 H, Ar-H)
ppm. 13C NMR: δ ϭ 19.8, 20.2, 27.0, 29.4, 33.9, 39.5, 44.0, 49.4,
49.8, 54.9, 77.8, 89.0, 94.5, 126.6, 127.6, 128.2, 128.5, 129.1, 133.5,
138.3, 141.1, 164.0, 212.4 ppm. CI-MS: m/z (%) ϭ 451 (25) [M ϩ
H]ϩ, 277 (100), 135 (92). HRMS (CI): 451.1948. C27H31O4S [M ϩ
H]ϩ requires 451.1943. [α]2D0 ϭ ϩ160 (c ϭ 0.5, CH2Cl2).
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-5-Methylhexa-2,3-dieno-
ate (2d) and (1R)-(؊)-10-(Phenylsulfonyl)isobornyl 5-Methyl-3-oxo-
2-(triphenylphosphoranylidene)hexanoate (3d)
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl (S)-5-Methylhexa-2,3-dieno-
ate (2d): 2d was obtained as a white solid (2.28 g, 75%), m.p.
89.3Ϫ90.0 °C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1708,
1
1956 cmϪ1. H NMR: δ ϭ 0.88 (s, 3 H), 0.95 (s, 3 H), 1.02Ϫ1.07
(m, 6 H), 1.20Ϫ1.25 (m, 1 H), 1.61Ϫ2.00 (m, 6 H), 2.38Ϫ2.44 (m,
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl 3-Oxo-5-phenyl-2-(triphenyl-
1 H), 3.00 (d, J ϭ 14.0 Hz, 1 H), 3.60 (d, J ϭ 14.0 Hz, 1 H), phosphoranylidene)pentanoate (3f): 3f was obtained as an oil (0.66 g,
1
4.71Ϫ4.74 (m, 1 H), 5.49Ϫ5.58 (m, 2 H), 7.53Ϫ7.58 (m, 2 H, Ar-
H), 7.63Ϫ7.65 (m, 1 H, Ar-H), 7.89Ϫ7.92 (m, 2 H, Ar-H) ppm.
12%). H NMR: δ ϭ 0.70 (s, 3 H), 0.76 (s, 3 H), 1.11Ϫ1.15 (m, 1
H), 1.57Ϫ2.06 (m, 6 H), 2.77Ϫ2.81 (m, 2 H), 2.88 (d, J ϭ 13.8 Hz,
13C NMR: δ ϭ 19.9, 20.2, 22.0, 22.1, 27.0, 27.6, 29.4, 39.5, 44.0, 1 H), 2.92Ϫ3.00 (m, 1 H), 3.14Ϫ3.20 (m, 1 H), 3.49 (d, J ϭ
49.4, 49.8, 54.8, 77.6, 89.8, 102.0, 127.7, 129.1, 133.5, 141.1, 164.3,
13.8 Hz, 1 H), 5.00 (dd, J ϭ 3.8 Hz, J ϭ 8.0 Hz, 1 H), 6.97Ϫ7.00
(m, 2 H, Ar-H), 7.10Ϫ7.29 (m, 3 H, Ar-H), 7.38Ϫ7.54 (m, 12 H,
210.9 ppm. CI-MS: m/z (%) ϭ 403 (35) [M ϩ H] ϩ, 277 (100),
135 (92). HRMS (CI): 403.1941. C23H31O4S [M ϩ H]ϩ requires Ar-H), 7.66Ϫ7.73 (m, 6 H, Ar-H), 7.86Ϫ7.89 (m, 2 H, Ar-H) ppm.
403.1943. [α]2D0 ϭ ϩ140 (c ϭ 0.5, CH2Cl2).
ES-MS: m/z (%) ϭ 729 (100) [M]ϩ, 409 (5), 279 (4).
4836
© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2004, 4830Ϫ4839

Synthesis of Chiral Allenic Esters
FULL PAPER
(1R)-(؊)-10-(Phenylsulfonyl)isobornyl
4-Phenylbuta-2,3-dienoate (d, J ϭ 14.0 Hz, 1 H), 3.60 (d, J ϭ 14.0 Hz, 1 H), 4.69Ϫ4.72 (m,
(2g): This compound was obtained as an oil (0.83 g, 25%, 50:50
diastereoisomeric mixture). IR (film): ν˜ ϭ 1715, 1948 cmϪ1 13C (m, 1 H, Ar-H), 7.88Ϫ7.91 (m, 2 H, Ar-H) ppm. CI-MS: m/z (%) ϭ
NMR: δ ϭ 19.6, 19.7, 20.1, 20.2, 27.0, 27.1, 29.4, 29.6, 39.5, 44.0,
389 (55) [M ϩ H]ϩ, 277 (100), 135 (94) ppm. HRMS (CI):
49.4, 49.5, 49.9, 55.0, 60.4, 78.0, 92.2, 92.3, 98.3, 98.4, 127.2, 127.3, 389.1785. C22H29O4S [M ϩ H]ϩ requires 389.1786. [α]2D0 ϭ Ϫ180
1 H), 5.50Ϫ5.61 (m, 2 H), 7.51Ϫ7.57 (m, 2 H, Ar-H), 7.61Ϫ7.66
.
127.7, 128.1, 128.6, 128.8, 129.0, 129.2, 129.3, 133.2, 133.4, 133.6,
141.2, 163.3, 163.5, 214.6, 214.8 ppm. CI-MS: m/z (%) ϭ 437 (1)
[Mϩ ϩ H], 277 (97), 135 (100). HRMS (CI): 437.1781 C26H29O4S
[M ϩ H]ϩ requires 437.1786.
(c ϭ 0.5, CH2Cl2).
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl
3-Oxo-2-(triphenylphos-
phoranylidene)hexanoate (8c): 8c was obtained as an oil (0.75 g,
1
15%). H NMR: δ ϭ 0.75 (approx. t, J ϭ 7.4 Hz, 3 H), 0.86 (s, 3
Component I: 1H NMR: δ ϭ 0.80 (s, 3 H), 0.88 (s, 3 H), 1.13Ϫ1.18
H), 0.94 (s, 3 H), 1.04Ϫ1.17 (m, 1 H), 1.47Ϫ1.89 (m, 8 H),
(m, 1 H), 1.59Ϫ2.00 (m, 6 H), 2.87 (d, J ϭ 14.0 Hz, 1 H), 3.41 (d, 2.60Ϫ2.68 (m, 1 H), 2.68Ϫ2.85 (m, 1 H), 3.00 (d, J ϭ 13.8 Hz, 1
J ϭ 14.0 Hz, 1 H), 4.57 (dd, J ϭ 2.8, J ϭ 7.8 Hz, 1 H), 5.97 (d, H), 3.64 (d, J ϭ 13.8 Hz, 1 H), 4.99 (dd, J ϭ 3.8, J ϭ 8.0 Hz, 1
J ϭ 6.3 Hz, 1 H), 6.57 (d, J ϭ 6.3 Hz, 1 H), 7.16Ϫ7.32 (m, 5 H, H), 7.38Ϫ7.55 (m, Ar-H, 12 H), 7.68Ϫ7.78 (m, 6 H, Ar-H),
Ar-H), 7.47Ϫ7.50 (m, 1 H, Ar-H), 7.57Ϫ7.67 (m, 2 H, Ar-H), 7.89Ϫ7.92 (m, 2 H, Ar-H) ppm. ES-MS: m/z (%) ϭ 667 (100) [Mϩ].
7.82Ϫ7.84 (m, 2 H, Ar-H) ppm.
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-5-Methylhexa-2,3-dieno-
Component II: 1H NMR: δ ϭ 0.73 (s, 3 H), 0.78 (s, 3 H), 1.13Ϫ1.18 ate (7d) and (1S)-(؉)-10-(Phenylsulfonyl)isobornyl 5-Methyl-3-oxo-
(m, 1 H), 1.59Ϫ2.00 (m, 6 H), 2.93 (d, J ϭ 14.0 Hz, 1 H), 3.55 (d,
J ϭ 14.0 Hz, 1 H), 4.77 (dd, J ϭ 3.0, J ϭ 7.8 Hz, 1 H), 5.93 (d,
J ϭ 6.3 Hz, 1 H), 6.48 (d, J ϭ 6.3 Hz, 1 H), 7.16Ϫ7.32 (m, 5 H,
Ar-H), 7.47Ϫ7.50 (m, 1 H, Ar-H), 7.57Ϫ7.67 (m, 2 H, Ar-H),
7.91Ϫ7.94 (m, 2 H, Ar-H) ppm.
2-(triphenylphosphoranylidene)hexanoate (8d)
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-5-Methylhexa-2,3-dieno-
ate (7d): was obtained as a white solid (1.85 g, 61%), m.p.
86.9Ϫ87.5 °C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1708,
1955 cmϪ1. Ϫ1H NMR: δ ϭ 0.87 (s, 3 H), 0.94 (s, 3 H), 1.01Ϫ1.06
(m, 6 H), 1.19Ϫ1.23 (m, 1 H), 1.63Ϫ1.99 (m, 6 H), 2.34Ϫ2.40 (m,
1 H), 2.98 (d, J ϭ 14.0 Hz, 1 H), 3.60 (d, J ϭ 14.0 Hz, 1 H),
General Procedure for the Synthesis of Allenes 7 and Phosphorus
Ylides 8: A solution of acid chloride (7.54 mmol) in tetrahydrofu-
ran was added dropwise to a stirred solution of the ylide 6 4.69Ϫ4.71 (m, 1 H), 5.48Ϫ5.56 (m, 2 H), 7.51Ϫ7.57 (m, 2 H, Ar-
(7.54 mmol) and triethylamine (1.8 mL) in tetrahydrofuran. The H), 7.61Ϫ7.64 (m, 1 H, Ar-H), 7.88Ϫ7.91 (m, 2 H, Ar-H) ppm.
mixture was stirred under nitrogen at room temperature for 12 h
and filtered, and the filtrate was concentrated under vacuum. The
CI-MS: m/z (%) ϭ 403 (72) [M ϩ H]ϩ, 277 (65), 105 (17). HRMS
(CI): 403.1932. C23H31O4S [M ϩ H]ϩ requires 403.1943. [α]2D0
ϭ
crude oil was dissolved in CH2Cl2, washed with water and dried Ϫ160 (c ϭ 0.5, CH2Cl2).
(MgSO4), and the solvents were evaporated off. The products were
isolated by flash chromatography [ethyl acetate/hexane (1:1)].
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl 5-Methyl-3-oxo-2-(triphenyl-
phosphoranylidene)hexanoate (8d): This compound was obtained as
an oil (1.33 g, 26%). H NMR: δ ϭ 0.73 (d, J ϭ 5 Hz, 3 H), 0.74
(d, J ϭ 5 Hz, 3 H), 0.96 (d, J ϭ 6.6 Hz, 6 H), 1.10Ϫ1.15 (m, 1 H),
1.58Ϫ2.11 (m, 7 H), 2.53 (dd, J ϭ 6.6 Hz, J ϭ 15.5, 1 H), 2.76 (dd,
1
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl Buta-2,3-dienoate (7a): This
compound was obtained as an oil (1.52 g, 56%). IR (film): ν˜ ϭ
1707, 1955 cmϪ1 1H NMR: δ ϭ 0.87 (s, 3 H), 0.94 (s, 3 H),
.
1.17Ϫ1.31 (m, 1 H), 1.59Ϫ1.98 (m, 6 H), 2.99 (d, J ϭ 14.1 Hz, 1 J ϭ 7.5 Hz, J ϭ 15.5, 1 H), 2.98 (d, J ϭ 13.8 Hz, 1 H), 3.63 (d,
H), 3.59 (d, J ϭ 14.1 Hz, 1 H), 4.78 (dd, J ϭ 3.3, J ϭ 9.3 Hz, 1 J ϭ 13.8 Hz, 1 H), 4.99 (dd, J ϭ 3.8, J ϭ 7.9 Hz, 1 H), 7.38Ϫ7.53
H), 5.07 (dd, J ϭ 6.5, J ϭ 14.4 Hz, 1 H), 5.18 (dd, J ϭ 6.5, J ϭ
(m, 12 H, Ar-H), 7.70Ϫ7.74 (m, 6 H, Ar-H), 7.89Ϫ7.92 (m, 2 H,
14.4 Hz, 1 H), 5.56 (approx. t, J ϭ 6.5 Hz, 1 H), 7.52Ϫ7.59 (m, 2 Ar-H) ppm. 13C NMR: δ ϭ 20.4, 20.9, 22.4, 22.5, 24.9, 25.5, 27.1,
H, Ar-H), 7.60Ϫ7.67 (m, 1 H, Ar-H), 7.89Ϫ7.93 (m, 2 H, Ar-H)
ppm. [α]2D0 ϭ Ϫ90 (c ϭ 0.5, CH2Cl2).
30.1, 39.7, 44.2, 49.1 (d, JC,P ϭ 7.2 Hz), 49.7 (d, JC,P ϭ 18.4 Hz),
3
55.4, 77.7, 126.4, 127.1, 127.6, 128.4 (d, JC,P ϭ 12.1 Hz), 129.2,
4
3
131.4 (d, JC,P ϭ 2.9 Hz), 133.0 (d, JC,P ϭ 9.8 Hz), 133.3, 141.8,
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-Penta-2,3-dienoate (7b):
This compound was obtained as a white solid (1.69 g, 60%), m.p.
2
2
166.6 (d, JC,P ϭ 18 Hz), 194.9 (d, JC,P ϭ 3.4 Hz) ppm. ES-MS:
ϩ
m/z (%) ϭ 681 (100) [M]
.
95.9Ϫ97.1 °C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1707,
1
1955 cmϪ1. H NMR: δ ϭ 0.87 (s, 3 H), 0.93 (s, 3 H), 1.24Ϫ1.29 (1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-5,5-Dimethylhexa-2,3-di-
(m, 1 H), 1.67Ϫ2.05 (m, 9 H), 2.99 (d, J ϭ 14.1 Hz, 1 H), 3.60 (d,
enoate (7e) and (1S)-(؊)-10-(Phenylsulfonyl)isobornyl 5,5-Dimethyl-
J ϭ 14.1 Hz, 1 H), 4.69 (dd, J ϭ 3.2, J ϭ 8.4 Hz, 1 H), 5.43Ϫ5.49 3-oxo-2-(triphenylphosphoranylidene)hexanoate (8e)
(m, 2 H), 7.51Ϫ7.57 (m, 2 H, Ar-H), 7.61Ϫ7.64 (m, 1 H, Ar-H),
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-5,5-Dimethylhexa-2,3-di-
enoate (7e): 7e was obtained as a white solid (2.29 g, 73%), m.p.
131.0Ϫ132.2 °C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1709,
7.88Ϫ7.91 (m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 12.7, 19.7, 20.3,
27.1, 29.3, 39.4, 44.0, 49.4, 49.9, 55.0, 77.5, 88.1, 89.7, 127.7, 129.2,
133.5, 141.1, 164.2, 213.1 ppm. CI-MS: m/z (%) ϭ 375 (25) [M ϩ
H]ϩ, 293 (7), 277 (100). HRMS (CI): 375.1638. C21H27O4S [M ϩ
H]ϩ requires 375.1630. [α]2D0 ϭ Ϫ150 (c ϭ 0.5, CH2Cl2).
1956 cmϪ1 1H NMR: δ ϭ 0.87 (s, 3 H), 0.95 (s, 3 H), 1.05 (s, 9
.
H), 1.17Ϫ1.29 (m, 1 H), 1.57Ϫ2.02 (m, 6 H), 2.99 (d, J ϭ 14.0 Hz,
1 H), 3.59 (d, J ϭ 14.0 Hz, 1 H), 4.69Ϫ4.73 (m, 1 H), 5.47 (d, J ϭ
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-Hexa-2,3-dienoate and 6.1 Hz, 1 H), 5.56 (d, J ϭ 6.1 Hz, 1 H), 7.51Ϫ7.57 (m, 2 H, Ar-
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl
phoranylidene)hexanoate (8c)
3-Oxo-2-(triphenylphos-
H), 7.61Ϫ7.64 (m, 1 H, Ar-H), 7.88Ϫ7.91 (m, 2 H, Ar-H) ppm.
CI-MS: m/z (%) ϭ 417 (77) [M ϩ H]ϩ, 277 (53), 105 (25). HRMS
(CI): 417.2091. C24H33O4S [M ϩ H]ϩ requires 417.2099. [α]2D0
Ϫ180 (c ϭ 0.5, CH2Cl2).
ϭ
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-Hexa-2,3-dienoate (7c):
7c was obtained as a white solid 7c (2.20 g, 75%), m.p. 75.4Ϫ76.3
°C (from diethyl ether/hexane). IR (KBr): ν˜ ϭ 1709, 1955 cmϪ1
.
(1S)-(؊)-10-(Phenylsulfonyl)isobornyl
5,5-Dimethyl-3-oxo-2-(tri-
1H NMR: δ ϭ 0.87 (s, 3 H), 0.93 (s, 3 H), 0.98Ϫ1.05 (m, 3 H),
1.19Ϫ1.26 (m, 1 H), 1.64Ϫ1.96 (m, 6 H), 2.05Ϫ2.12 (m, 2 H), 2.99 (0.58 g, 11%). H NMR: δ ϭ 0.86 (s, 3 H), 0.93 (s, 3 H), 1.05 (s, 9
phenylphosphoranylidene)hexanoate (8e): 8e was obtained as an oil
1
Eur. J. Org. Chem. 2004, 4830Ϫ4839
www.eurjoc.org
© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4837

T. M. V. D. Pinho e Melo et al.
FULL PAPER
H), 1.11Ϫ1.15 (m, 1 H), 1.59Ϫ1.99 (m, 6 H), 2.43 (d, J ϭ 13.7 Hz,
reflections measured, 4676 independent reflections and 4360 with
1 H), 2.93 (d, J ϭ 13.7 Hz, 1 H), 2.97 (d, J ϭ 13.8 Hz, 1 H), 3.62 I Ͼ 2σ(I), µ ϭ 1.415 mmϪ1, no absorption correction; structural
(d, J ϭ 13.8 Hz, 1 H), 5.00 (dd, J ϭ 3.9, J ϭ 8.0 Hz, 1 H), analysis by direct methods and full-matrix refinement with aniso-
7.38Ϫ7.56 (m, 12 H, Ar-H), 7.71Ϫ7.76 (m, 6 H, Ar-H), 7.90Ϫ7.92
tropic displacement parameters, H atoms placed at idealised posi-
(m, 2 H, Ar-H) ppm. 13C NMR: δ ϭ 20.4, 21.0, 27.1, 30.1, 31.6, tions and refined as riding on their parent atoms with shelxl97
39.6, 44.2, 47.5, 49.6, 49.8, 51.2 (d, JC,P ϭ 7.3 Hz), 55.2, 77.8, 126.5,
defaults except for the methyl H atoms, which were refined as a
rigid group with a free torsion angle, npar/nref ϭ 17.5, R ϭ 0.0451
and Rw ϭ 0.0109, GOF ϭ 1.03. The absolute configuration of the
molecule was determined by the Flack method from the anomalous
dispersion of the S atom, η ϭ 0.039(18) for 2010 Friedel pairs.
Programs used: SHELXS97 and SHELXL93.[15]
3
4
127.3, 127.6, 128.4 (d, JC,P ϭ 12.1 Hz), 129.2, 131.4 (d, JC,P
ϭ
2.9 Hz), 133.2 (d, 3JC,P ϭ 9.8 Hz), 141.8, 166.7 (d, 2JC,P ϭ 17.9 Hz),
194.8 ppm. ES-MS: m/z (%) ϭ 695 (100) [Mϩ].
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-5-Phenylpenta-2,3-dieno-
ate (7f) and (1S)-(؉)-10-(Phenylsulfonyl)isobornyl 3-Oxo-5-phenyl-
2-(triphenylphosphoranylidene)pentanoate (8f)
CCDC-241071 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html [or from the Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge
CB2 1EZ, UK; fax: (internat.) ϩ44-1223-336-033; E-mail:
deposit@ccdc.cam.ac.uk].
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl (R)-5-Phenylpenta-2,3-dieno-
ate (7f): This compound was obtained as a white solid (2.92 g,
86%), m.p. 102.0Ϫ103.3 °C (from diethyl ether/hexane). IR (KBr):
1
ν˜ ϭ 1711, 1956 cmϪ1. H NMR: δ ϭ 0.85 (s, 3 H), 0.89 (s, 3 H),
1.15Ϫ1.26 (m, 1 H), 1.59Ϫ1.98 (m, 6 H), 2.96 (d, J ϭ 14.0 Hz, 1
H), 3.38Ϫ3.44 (m, 2 H), 3.56 (d, J ϭ 14.0 Hz, 1 H), 4.72Ϫ4.76 (m,
1 H), 5.52Ϫ5.56 (m, 1 H), 5.65Ϫ5.72 (m, 2 H), 7.16Ϫ7.32 (m, 5
H, Ar-H), 7.48Ϫ7.52 (m, 2 H, Ar-H), 7.57Ϫ7.62 (m, 1 H, Ar-H),
7.86Ϫ7.89 (m, 2 H, Ar-H) ppm. CI-MS: m/z (%) ϭ 451 (59) [M ϩ
H]ϩ, 277 (69), 105 (59). HRMS (CI): 451.1942. C27H31O4S [M ϩ
H]ϩ requires 451.1943. [α]2D0 ϭ Ϫ180 (c ϭ 0.5, CH2Cl2).
Acknowledgments
The authors wish to thank Susana Marca˜o (IST) for collaborating
in the chirooptical studies. Financial support from Chymiotechnon
(1S)-(؉)-10-(Phenylsulfonyl)isobornyl 3-Oxo-5-phenyl-2-(triphenyl-
phosphoranylidene)pentanoate (8f): 8f was obtained as an oil (0.39 g,
ˆ
and the Fundac¸a˜o para a Ciencia e a Tecnologia (POCTI/36137/
1
QUI/2000) is gratefully acknowledged.
7%). H NMR: δ ϭ 0.70 (s, 3 H), 0.76 (s, 3 H), 1.11Ϫ1.15 (m, 1
H), 1.59Ϫ1.99 (m, 6 H), 2.75Ϫ2.81 (m, 2 H), 2.88 (d, J ϭ 13.9 Hz,
1 H), 2.97Ϫ3.03 (m, 1 H), 3.16Ϫ3.22 (m, 1 H), 3.49 (d, J ϭ
13.9 Hz, 1 H), 5.00 (dd, J ϭ 3.9, J ϭ 8.0 Hz, 1 H), 6.85Ϫ7.00 (m,
2 H, Ar-H), 7.09Ϫ7.31 (m, 3 H, Ar-H), 7.39Ϫ7.56 (m, 12 H, Ar-
H), 7.67Ϫ7.71 (m, 6 H, Ar-H), 7.86Ϫ7.88 (m, 2 H, Ar-H) ppm.
[1] [1a]
[1b]
D. J. Pasto, Tetrahedron 1984, 40, 2805Ϫ2877.
M. E.
Jung, in Comprehensive Organic Synthesis (Eds.: B. M. Trost,
I. Fleming), Pergamon: Oxford, 1991, vol. 4, pp. 53Ϫ58. [1c]R.
Simmer, Synthesis 1993, 165Ϫ178. [1d] L. K. Sydnes, Chem. Rev.
2003, 103, 1133Ϫ1150.
[2] [2a]
13C NMR: δ ϭ 20.3, 20.4, 27.1, 30.1, 31.1, 39.7, 42.2 (d, JC,P
7.8 Hz), 44.1, 49.6, 49.8, 55.5, 77.7, 126.3, 126.9, 127.6, 128.1,
ϭ
3
4
128.3, 128.5 (d, JC,P ϭ 12.1 Hz), 129.2, 131.5 (d, JC,P ϭ 2.4 Hz),
H. J. Bestmann, G. Graf, H. Hartung, S. Kolewa, E.
[2b]
3
2
Vilsmaier, Chem. Ber. 1970, 103, 2794Ϫ2801. Ϫ
H. J.
133.1 (d, JC,P ϭ 9.6 Hz), 140.3, 141.8, 166.7 (d, JC,P ϭ 18 Hz),
194.3 ppm. ES-MS: m/z (%) ϭ 729 (100) [Mϩ].
Bestmann, H. Hartung, Chem. Ber. 1966, 99, 1198Ϫ1207. Ϫ
[2c]
R. W. Lang, H. J. Hansen, Helv. Chim. Acta 1980, 63,
[2d]
438Ϫ455.
J. A. Marshall, M. A. Wolf, E. M. Wallace, J.
General Procedure for the Synthesis of Allenes 2b, 2c and 2f Starting
from Ylide 3a: A solution of acid chloride (7.54 mmol) in tetra-
hydrofuran was added dropwise to a stirred solution of the ylide
3a (7.54 mmol) and triethylamine (1.8 mL) in tetrahydrofuran. The
mixture was stirred under nitrogen at room temperature for 12 h
and filtered, and the filtrate was concentrated under vacuum. The
crude oil was dissolved in CH2Cl2, washed with water and dried
(MgSO4), and the solvents were evaporated off. The products were
isolated by flash chromatography [ethyl acetate/hexane (1:1)]. All-
enes 2b, 2c and 2f were identified by comparison with the specimen
isolated earlier.
[2e]
Org. Chem. 1997, 62, 367Ϫ371.
L. Braga, Tetrahedron Lett. 2000, 41, 1867Ϫ1869.
Tömösközi, H. J. Bestmann, Tetrahedron Lett. 1964,
C. C. Silveira, P. Boeck, A.
[2f]
I.
[2g]
1293Ϫ1295.
H. J. Bestmann, I. Tömösközi, Tetrahedron
1968, 24, 3299Ϫ3319. [2h] W. Oppolzer, C. Chapuis, D. Dupuis,
M. Guo, Helv. Chim. Acta 1985, 68, 2100Ϫ2114.
[3] [3a]
W. Runge, G. Kresze, Justus Liebigs Ann. Chem. 1975,
1361Ϫ1378. [3b] S. Musierowicz, A. E. Wroblewski, Tetrahedron
´
1980, 36, 1375Ϫ1380. [3c] K. Tanaka, K. Fuji, Tetrahedron Lett.
[3d]
1996, 37, 3735Ϫ3738.
J. Yamazaki, T. Watanabe, K.
Tanaka, Tetrahedron: Asymmetry 2001, 12, 669Ϫ675.
T. Rein, T. M. Pedersen, Synthesis 2002, 579Ϫ594.
[4]
[5]
[5a] T. M. V. D. Pinho e Melo, A. L. Cardoso, A. M. d’A. Rocha
Gonsalves, R. C. Storr, J. Costa Pessoa, J. A. Paixa˜o, A. M.
Beja, M. Ramos Silva, Tetrahedron Lett. 2003, 44, 6409Ϫ6412.
Circular Dichroism: The solutions for CD were prepared with etha-
nol (Riedel-de Hae¨n Spectranal® grade). Spectra were run in
Hellma cylindrical 0.1-cm quartz cells at concentrations of ca. 10Ϫ3
m. Normally at least two accumulations were made when recording
each CD spectrum.
[5b]
Corrigendum: T. M. V. D. Pinho e Melo, A. L. Cardoso,
A. M. d’A. Rocha Gonsalves, R. C. Storr, J. Costa Pessoa, J.
A. Paixa˜o, A. M. Beja, M. Ramos Silva, Tetrahedron Lett.
2004, 45, 2259.
X-ray Crystallographic Study: Crystal data for (1R)-(Ϫ)-10-(phenyl-
[6]
R. J. Bushby, G. H. Whitham, J. Chem. Soc., (B) 1969, 67Ϫ73.
sulfonyl)isobornyl
(S)-5,5-dimethylhexa-2,3-dienoate
(2e):
[7] [7a]
[7b]
G. Lowe, J. Chem. Soc., Chem. Commun. 1965, 411Ϫ413.
C24H32O4S, M ϭ 6.57, unit cell dimensions [a ϭ 9.9948(4), b ϭ
J. H. Brewster, J. Am. Chem. Soc. 1959, 81, 5475Ϫ5483. [7c]
˚
11.4800(6), c ϭ 20.6039(8) A and α ϭ β ϭ γ ϭ 90°], Z ϭ 4, d ϭ
E. Ruch, Angew. Chem. Int. Ed. Engl. 1977, 16, 65Ϫ72.
W. Oppolzer, M. J. Kelly, G. Bernardinelli, Tetrahedron Lett.
1984, 25, 5889Ϫ5892.
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Tetrahedron Lett. 1992, 33, 6003Ϫ6006.
1.170, orthorhombic, P212121. Data collection: EnrafϪNonius
Mach3 diffractometer, radiation used (Cu-Kα), graphite mono-
chromator, crystal size 0.25 ϫ 0.20 ϫ 0.35 mm3, room temperature,
ω-2θ, 4.29° Յ θ Յ 72.42°, Ϫ14 Յ k Յ13, Ϫ25 Յ l Յ 25, 8479
[8]
[9]
4838
© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2004, 4830Ϫ4839

Synthesis of Chiral Allenic Esters
FULL PAPER
Van de Coolwijk, C. J. Elsevier, P. Vermeer, Chem. Phys. 1986,
105, 227Ϫ246.
H. F. Baumann, C. J. Elsevier, P. Vermeer, W. Runge, J. Chem.
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[10]
E. L. Eliel, S. H. Wilen, L. N. Mander, Stereochemistry of Or-
ganic Compounds; John Wiley & Sons, New York, 1994, chap-
[13]
[14]
[15]
ter 14, pp. 1119Ϫ1190.
For the phenylallenes the UV and CD spectra have been ex-
[11]
plained in terms of excited states in localised at the allenic and
benzene moieties.[12,13] The assignment of the bands of the UV
spectra of compounds 2aϪ2f and 7aϪ7f was carried out by
comparison with these compounds.
Prepared by the general procedure described in reference [8]
but starting from (1R)-(Ϫ)-10-camphorsulfonic acid.
G. M. Sheldrick, SHELXS97 and SHELXL97, University of
Göttingen, Germany, 1997.
[12]
W. Runge, H. F. Baumann, A. M. F. Hezemans, P. J. F. M.
Received June 11, 2004
Eur. J. Org. Chem. 2004, 4830Ϫ4839
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© 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4839