Stereocontrolled preparation of stereocomplementary regioisomeric tricarbonyliron complexes in enantiopure form

Article abstract of DOI:10.1016/S0040-4020(99)01110-2

The use of ultrasound to form ferralactone complexes from an enantiomerically pure allylic epoxide with an adjacent hydroxymethyl substituent affords a pair of stereocomplementary isomers that offer a regioconvergent route to the same chiral pentadienyliron complex. The enantiomeric purity, CD properties, and absolute configurations of intermediate η⁴-diene complexes are reported, and X-ray diffraction analysis of a pair of rearranged ferralactone complexes establishes their relative stereochemistries, and confirms their absolute stereochemistries. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(99)01110-2

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 2273±2281
Stereocontrolled Preparation of Stereocomplementary
Regioisomeric Tricarbonyliron Complexes in Enantiopure Form
²
Christopher E. Anson, Gaurang Dave and G. Richard Stephenson
*
School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK
Accepted 7 December 1999
AbstractÐThe use of ultrasound to form ferralactone complexes from an enantiomerically pure allylic epoxide with an adjacent hydroxy-
methyl substituent affords a pair of stereocomplementary isomers that offer a regioconvergent route to the same chiral pentadienyliron
complex. The enantiomeric purity, CD properties, and absolute con®gurations of intermediate h4-diene complexes are reported, and X-ray
diffraction analysis of a pair of rearranged ferralactone complexes establishes their relative stereochemistries, and con®rms their absolute
stereochemistries. q 2000 Elsevier Science Ltd. All rights reserved.
Introduction
via ferralactones is attractive because the allylic epoxide
starting materials are themselves easily obtained by asym-
metric induction using the widely applicable Sharpless
epoxidation and dihydroxylation methods. Unfortunately,
there is a dif®culty with the approach as the iron-mediated
opening of the epoxide typically lacks diastereoselectivity,
so that the chirality of the epoxide is not ef®ciently relayed
to control the planar chirality in the binding of the iron
moiety to the ligand. Modi®cation of the complexation
procedure to give access, not to mixtures of diastereo-
isomers, but to mixtures of regioisomers, however, would
ultimately allow stereoconvergent utilisation of the products
via cationic h5 intermediates of type 2 (Scheme 1).
The tricarbonyliron control group offers powerful stereo-
direction and activation effects, but its use in enantio-
selective organic synthesis requires ef®cient methods to
prepare optically pure diene and dienyl complexes. Origin-
ally, classical resolution procedures1 were employed, and
strategies for kinetic resolution of racemic complexes2 and
asymmetric induction during complexation of prochiral
ligands3 have been examined. With acyclic complexes, the
use of chiral allylborane4 and alkylzinc5 reagents and bio-
logical esteri®cation and reduction procedures6 have proved
particularly effective, while in the cyclic (cyclohexadiene)
series, asymmetric delivery of Fe(CO)3 from chiral azadiene
complexes to prochiral dienes,7 and an approach based on
the biodioxygenation of arenes followed by diastereo-
selective complexation of the resulting diene ligand, have
given good results.8,9 In this way, a derivative of the
simplest of the chiral cyclohexadienyl complex [tri-
carbonyl(h5-1-methylcyclohexadienyl)iron(11) PF6(12)]
has been obtained in optically pure form.8 Although this
procedure requires a separation of regioisomers, the corre-
sponding preparation9 of the 1-tri¯uoromethyl analogue was
fully controlled.
Results and Discussion
We report here the results of an initial study of the enantio-
selective preparation of tricarbonyl(h5-1-methylpenta-
dienyl)iron(11) PF6(12)
2
(RˆMe), the acyclic
counterpart to tricarbonyl(h5-1-methylcyclohexadienyl)-
iron(11) PF6(12). Racemic h4 dienol complexes are easily
In a recent development, ferralactone complexes have been
shown10,11 to be important as intermediates to non-racemic
h4 tricarbonyliron complexes of dienes as well as valuable
control groups12,13 and important as synthetic inter-
mediates14 in their own right. Access to diene complexes
Keywords: tricarbonyliron; dienyl complexes; ferralactone; enantioselec-
tive synthesis; circular dichroism; absolute con®guration.
* Corresponding author. Tel.: 144-1603-592019; fax: 144-1603-592710;
e-mail: g.r.stephenson@uea.ac.uk
Present address: Institut fuÈr Anorganische Chemie, Universitat Karls-
ruhe, Engesserstrasse Geb 30.45, 76131 Karlsruhe, Germany.
²
È
Scheme 1.
0040±4020/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(99)01110-2

2274
C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
Scheme 2.
made by direct complexation with Fe(CO)5 or Fe2(CO)9, but
an important alternative has been described by Aumann15
isomers are dif®cult to separate, so the mixture was
converted directly into the corresponding h4 diene
complexes by the normal procedure15 by treatment with
barium hydroxide. In this way, (1)-6 and (2)-7 were
obtained in a combined yield of 80% (37 and 43% yields,
respectively) in a convenient and straightforward fashion.
Â16
Bohner, Hampel and Schobert through the opening of
and more recently by Ley, Meek, Metten and Pique and
È
17
alkenylepoxides with Fe2(CO)9. The required (2E,4R,5R)-
epoxide 3 was obtained in enantiopure form as described by
Sharpless,18,19 using asymmetric dihydroxylation of the
benzoate of 1 (RˆMe) as the starting point (Sharpless
asymmetric epoxidation is unsatisfactory with dienols20).
Following this route (Scheme 2), using AD-mix-b, we can
prepare the epoxide starting material in a convenient way. In
practice, the optical purity of the product varies slightly
from run to run (we have observed [a]D values in the
range 48±53), but a typical large scale preparation of 3
gave a sample with [a]Dˆ153.3 (cˆ2, CHCl3), which has
proved adequate to give access to optically pure metal
complexes. Ley, Burkhardt, Cox and Meek,21 working in
the racemic series (obtained by direct epoxidation of ethyl
sorbate), have described an important anomalous complexa-
tion of 3 which affords a rearranged secondary alcohol as
well as the normal pair of endo and exo primary alcohols.
We have found that use of sonication22 to effect reaction of
(1)-3 with Fe2(CO)9 affords only two products, the endo
complex (2)-4 and the regioisomeric secondary alcohol
(1)-5 in roughly equal amounts (47:53 by nmr). Thus
under the ultrasound conditions, the formation of the
rearranged product is far more favoured than is the case
with the standard conditions23 (we obtained 4 in 43%
yield by ultrasound, compared to 20% reported
previously21). As described earlier,21 these ferralactone
The alcohols 6 and 7 were converted (Scheme 3) into their
acetate derivatives (1)-8 and (1)-9 to establish the optical
purity of these products. The determination of the enantio-
meric excess of the acetate 8 by 1H NMR in the presence of
tris[3-(hepta¯uoropropylhydroxymethylene)-(1)-camphor-
ato]europium(III) [Eu(hfc)3] has been described by
Howell,24 and in this way, we proved by integration of
signals from the acetate methyl group that the enantiomeric
excess of the sample of 8 furnished by the asymmetric
dihydroxylation/ferralactone route was at least 99%. The
use of the chiral shift reagent with the acetate (1)-9 has
not been reported before. Our dihydroxylation-derived
sample showed only one singlet for the acetate in the
presence of the shift reagent. An authentic racemic sample
of 9 was needed to check the validity of the analysis and this
was obtained by Freidel±Crafts acetylation of (butadiene)-
Fe(CO)3,25 reduction of the resulting ketone, and acetylation
of the alcohol. This complex showed the expected two
1
singlets when the H NMR spectrum was measured under
the same conditions with the same quantity of the shift
reagent. Furthermore, when a small portion of racemic 9
was added to the nmr sample of (1)-9 in the presence of
Eu(hfc)3, small peaks corresponding to the pair of signals
Scheme 3.

C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
2275
Figure 1. Circular dichroism (CD) curves of tricarbonyliron diene complexes.
from the OAc group of the minor enantiomer were seen to
appear. These experiments prove that the epoxide opening,
the isomerisation to form 7, and the rearrangement of the
ferralactones to the h4 products, all proceed with no signi®-
cant racemisation of the intermediates.
(h4-diene)Fe(CO)3 complexes, so in the disubstituted
diene complex 10 the effects of the two substituents should
be distinguishable. As the aldehyde and ketone functional
groups should in¯uence the CD curves in a similar fashion,
comparison of these two complexes can be expected to yield
a more clear-cut conclusion. The CD curves (Fig. 1) were
now much more similar, with the crucially diagnostic29 high
wavelength bands showing a maximum at 398 nm (De
11.6, cˆ0.038 M) for 10 and a minimum at 384 nm (De
24.4, cˆ0.036 M) for 11. As with the acetates, the two
complexes had opposite signs for De in the 400 nm region.
This band at around 400 nm is typical of tricarbonyl(h4-1,3-
diene)iron(0) complexes with aldehyde and ketone substi-
tuents at C1,28 indicating that the complexes 10 and 11 must
have their electron withdrawing substituents at opposite
ends of the chiral h4-diene moiety (see Fig. 2), allowing
the absolute con®guration of the planar chiral element in
(1)-11 to be assigned as S.30
Since the absolute con®guration of the acetate 826 is known,
the stereochemical course of the route from (1)-3 can be
established with certainty. The con®guration of the second-
ary alcohol 7 is not known. Circular dichroism (CD) spectra
(Fig. 1) were measured for the two acetates 8 and 9, but the
forms of these two curves were not suf®ciently similar for
the absolute con®guration of (1)-9 to be assigned by
comparison with (1)-8. However, the signs of the highest
wavelength bands in the CD curves were opposite, suggest-
ing that the two complexes might have different absolute
con®gurations in the h4 region. The similarity between the
substituents at the two ends of the diene in 8 makes a clear
comparison of these two CD spectra dif®cult. This problem
was overcome by oxidation of the alcohols (1)-6 and (2)-7
to afford the aldehyde (2)-10 and the ketone (1)-11. The
speci®c rotation for the sample of (2)-10 {[a]Dˆ2114
(cˆ1.5, CHCl3)} was consistent with the value reported
by Howell27 for a sample {[a]Dˆ2112} with an ee of
99%. Electron withdrawing substituents are known28,29 to
exert a large in¯uence on the chiroptical properties of
The availability of 11 allowed the relative con®guration
between the secondary alcohol and the metal-bound diene
to be examined. Reduction of 11 (Scheme 3) was performed
with sodium borohydride in the same manner as described
earlier in the preparation of racemic 9, and afforded a single
1
diastereoisomer in 99% yield. Comparison of the H NMR
spectra of the reduction product and that of the sample of 9
Figure 2. Typical CD curves in the 320±470 nm range for the enantiomers of 1-acylbutadiene complexes of Fe(CO)3 (numbering based on (1-4h)-butadiene
not on (2-5-h)-pentadien-1-one structures).

2276
C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
Scheme 3. Since hydride should thus be delivered trans to
the metal, the stereochemistry of (2)-7 can be assigned as
2R,3S, as drawn in Scheme 2. The con®guration of the C2
centre was shown in this way to be identical to that at the
corresponding position in the ferralactone complex (1)-5
(determined by X-ray crystallography, see below). As
expected, the Ba(OH)2 step has not in¯uenced the stereo-
chemistry at this position. These results are consistent with
the generally accepted mechanisms for the formation of
ferralactone complexes21 and the stereochemical course of
their conversion into h4 diene complexes by the action of
barium hydroxide,15 which proceeds with a syn, anti isomer-
isation of terminal substituents at the metal complex. The
de®nition of the stereochemical course of these reactions
was con®rmed by separation of a small portion of the
mixture of ferralactone complexes. The faster eluting
isomer (2)-4 (Fig. 3)33 {[a]Dˆ2173 (cˆ1, CHCl3)}
showed the expected doublet for the C6 methyl group in
1
the H NMR spectrum and was identi®ed as one of the
stereoisomers initially reported34 in racemic form by Ley
and Meek. As a ®nal check, 4 was oxidised with PDC to
obtain the corresponding aldehyde {[a]Dˆ1356}, which
had identical nmr properties to those reported.21,34 The
secondary alcohol (1)-5 was recrystallised from hexane
as orthorhombic colourless crystals (mp 130±1338C;
[a]Dˆ155, c 1, CHCl3), and X-ray diffraction analysis
proved the relative stereochemisty (Fig. 4) which had
not been established in the earlier investigations21 of the
racemate. The absolute con®guration was also con®rmed
through this procedure. Working on a small scale, the
conversion of 4 into 6, and 5 into 7, respectively, was
checked using pure samples of each complex.
Figure 3. Molecular structure of ferralactone (2)-4 [Fe(1)-C(4)ˆ1.986 (4),
Fe(1)-C(7)ˆ2.100 (5), Fe(1)-C(8)ˆ2.057(5), Fe(1)-C(9)ˆ2.194(5), C(7)-
Ê
C(8)ˆ1.412(7), C(8)-C(9)ˆ1.385(6) A; C(7)-C(8)-C(9)ˆ124.2 (4)8].
formed by the Ba(OH)2 reaction, showed the two complexes
to be identical. Unlike aldehydes,31 ketones adjacent to
tricarbonyl(h4-diene)iron complexes react with nucleo-
philes in a stereochemically controlled fashion. The stereo-
directing in¯uence of the metal is known from results
reported32 for a selection of nucleophiles, with attack occur-
ring from the face opposite to the tricarbonyliron group
when the ketone is in the cissoid conformation drawn in
Finally, a preliminary investigation of the formation of
h5-dienyl complexes was performed. Because of the posi-
tion of the OH groups in each case, the same con®guration
of the dienyl product would be expected, starting from either
Figure 4. Molecular structure of ferralactone (1)-5 [Fe(1)-C(4)ˆ1.985(4), Fe(1)-C(7)ˆ2.201(5), Fe(1)-C(8)ˆ2.077(5), Fe(1)-C(9)ˆ2.098(5), C(7)-
Ê
C(8)ˆ1.392(7), C(8)-C(9)ˆ1.416(7) A; C(7)-C(8)-C(9)ˆ122.4(4)8].

C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
2277
6 or 7. This opens the way for straightforward stereo-
selective access to enantiopure dienyl complexes without
the need to separate isomers35 by a reaction sequence
utilising sharpless dihydroxylation, ferralactone regio-
isomer formation by the ultrasound procedure, conversion
into h4-diene complexes, and acid mediated h4±h5 inter-
conversion by dehydroxylation. Simple conversion of either
6 or 7 into (h5-hexadienyl)Fe(CO)3 (2, RˆMe) by reaction
with HPF6 gave the expected product but in racemic form.
Reaction of 6 with the minimum quantity of HPF6 following
Howell's procedure,36 however, afforded a sample of the
salt with an [a]D of approximately 219 (cˆ1, CH3CN)
(this decreased gradually during the measurement).
Reaction starting with 7 was slower but afforded the same
enantiomer of the product, [a]Dˆ224 (cˆ1, CH3CN).
Engineering and Physical Sciences Research Council
(EPSRC) National Mass Spectrometry Service Centre at
the University of Wales, Swansea. CD spectra were
recorded using Jasco J-600 spectrometer, and [a]D
measurements were performed on a Jasco DIP/360
polarimeter. X-ray data was collected on Rigaku AFC7R
diffractometer.
(1)-(2E,4R,5R)-4,5-Epoxyhex-2-en-l-ol (3). Starting from
the dienol 1 (RˆMe), Schotten±Baumann benzoylation37
followed by the standard AD-mix asymmetric dihydroxyla-
tion procedure and a version of the representative procedure
for the conversion of unactivated diols into epoxides as
described by Kolb and Sharpless19 affords (3). (2E,4E)-
hexa-2,4-dien-l-ol (1, RˆMe) (4.9 g, 50 mmol) was
dissolved in pyridine (75 ml). Benzoyl chloride (25 ml)
was added gradually while the temperature of the reaction
mixture was maintained below 508C. The mixture was then
stirred at rt for 15 h. Hexane (300 ml) was added and the
mixture was quenched with 5% aqueous sodium hydrogen
carbonate (2£300 ml). The hexane layer was dried with
anhydrous MgSO4 and the solvent removed under reduced
pressure. The residue was a colourless oil which was
puri®ed either by distillation under reduced pressure (bp
1308C/1 mmHg) or by ¯ash chromatography (30 to 70%
ethyl acetate in hexane, gradient). (2E,4E)-2,4-Hexadienyl
benzoate (9.7 g, 96%) solidi®ed on cooling. mp 168C,
(Found: C, 77.07; H, 6.72; C13H14O2 requires C, 77.20; H,
6.98%); nmax(®lm)/cm21 1717 (CvO), 1662 and 1600
(diene), 1451, 1271, 1115, 990 (trans CHvCH), 711 (Ph);
dH(CDC13) 1.76 (3 H, d, Jˆ6 Hz, Me), 4.8 (2 H, d, Jˆ6 Hz,
CH2), 5.8 (2 H, m, outer-CH), 6.1 (1 H, m, inner-CH), 6.3 (1
H, dd, Jˆ11 Hz, 15, inner-CH) 7.42±8.04 (5 H, m, Ph).
dC(CDC13) 18 (CH3), 65 (CH2), 124±135 (9£CH), 166
(CvO); m/z 202 (M1, 19%), 105 (PhCO, 100), 77 (Ph,
16). This product (0.808 g, 4 mmol) was added to a solution
of AD-mix-b (5.6 g) and methyl sulfonamide (0.380 g,
4 mmol) in 1:1 v/v t-butyl alcohol:water (40 ml) at 08C.
The mixture was stirred at 08C for 2 h and then the tempera-
ture was allowed to increase to 158C. The progress of the
reaction was monitored by TLC (silica gel, 7:3 ethyl acetate:
hexane, Rf 0.25 for the diol) and continued until the starting
material had disappeared (2 h). The colour of the reaction
mixture had changed from orange to lemon yellow at the
end of the reaction. The mixture was cooled to 58C and
anhydrous sodium sul®te (6.0 g, 48 mmol) was added with
vigorous stirring. The suspension was warmed to rt. After
45 min, the product was extracted with ethyl acetate
(4£20 ml), the combined extracts were dried with
MgSO4 and concentrated. Flash chromatography (silica
gel, 40:60 ethyl acetate: hexane) gave two isomeric diols
(0.821 g, 88% total yield) [lit.18 91%]. The isomer ratio
was 75:13 (lit.18 83:7). The faster eluting diol, a white
solid, mp 54±568C, [a]2D5ˆ112.7 (cˆ2, CHCl3) was
discarded. Continued elution afforded (1)-(2E,4R,5R)-2,3-
dihydroxyhex-2-enyl benzoate, [a]2D5ˆ17.7 (cˆ2, CHC13)
[lit.18, 12.2 (c 2, CHCl3)]. Found: C, 65.50; H, 6.95;
C13H16O4 requires C, 66.09; H, 6.83%; nmax(®lm)/cm21
3399 (OH, br), 3063 (Ph), 2974±2883 (CH) 1717 (CO),
1601 and 1585 (Ph), 1451, 1274, 1113, 978 (CHvCH),
711 (Ph); [lit.18 (neat) nmax/cm21 3402 (br. s) 2968±2876,
1702, 1602, 1443, 1254, 1111, 969, 711]; dH(CDCl3) 1.16 (3
H, d, Jˆ6 Hz, Me), 2.70±3.20 (2 H, br, OH, variable), 3.65
Conclusions
Starting from a readily available enantiopure hydroxy-
methyl-substituted allylic epoxide, we have shown that by
the use of ultrasound to effect ferralactone formation, pairs
of stereocomplementary regioisomers can be obtained and
converted into the corresponding tricarbonyliron diene
complexes without loss of optical purity. The route onwards
to the synthetically important cationic h5 complexes is less
straightforward but we have demonstrated that a single
stereoisomer (5S) is formed from each of the two products
from the 4R,5R epoxide. We have shown in this study that
diverting the normally non-diastereoselective epoxide
opening to give regioisomeric products, provides a suitable
strategy for a regioconvergent approach to non-racemic
hexadienyl complexes, which does not rely on the need
for separation of isomers, and we have fully de®ned the
stereochemical processes in these reaction sequences and
determined the absolute con®gurations of the intermediate
complexes. Because of their completely stereoselective
reactions with nucleophiles, organometallic complexes of
this class in both the cyclic and acyclic series are valuable
in enaniopure form for the asymmetric synthesis of chiral
target structures. Our work in this area aims to make such
complexes more readily available.
Experimental
All experiments were carried out in ¯ame or oven dried
glassware, under an environment of dry, oxygen-free nitro-
gen or argon. Ether and THF were dried by distillation from
sodium metal and benzophenone, and CH2Cl2 by distillation
from calcium hydride. The dried solvents were stored over
activated 4A molecular sieves. Pyridine was distilled from
potassium hydroxide. Column chromatography was
performed using silica gel (Silica Matrex 60, 70±200 microns,
Fisons) and analytical thin-layer chromatography was
performed on aluminium backed silica plates, Merck
5554. IR spectra were recorded as thin ®lms or in solution,
using a Perkin±Elmer 1720X FTIR spectrometer. NMR
spectra were recorded on JEOL EX270 FT NMR. Mass
spectra were determined on a Kratos MS 25 spectrometer
and microanalyses were carried out using Carlo Erba
EA1108 by Mr A. W. R. Saunders of the University of East
Anglia. High resolution mass spectra were measured at the

2278
C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
(1 H, m, CHOH), 3.90 (1 H, t, Jˆ6 Hz, CHOH), 4.81 (2 H,
d, Jˆ6 Hz, CH2), 5.83 (1 H, dd, Jˆ6 Hz, 15.5, CH), 5.96 (1
H, m, CH), 7.7±8.1 (5 H, m, Ph); [lit.18 dH (400 MHz,
CDCl3) 1.16 (3 H, d, Jˆ6.4 Hz), 2.72 (1 H, s), 2.85 (1 H,
s), 3.64 (1 H, t, Jˆ6.4 Hz), 3.90 (1 H, m), 4.81 (2 H, d,
C, 42.59; H, 3.57%; dC & DEPT (CDCl3) 22 (CH3), 62
(CH2), 74, 78, 82 and 88 (CH), 207 (CO) (Lit.21 209, 207,
206, 203, 88, 82, 78, 74, 62, 22), and (1)-(3E,2S,4S,5R)-[1-
(carbonyloxy-kC)-5-hydroxy-(2,3,4-h)-hex-3-en-2-yl)]tri-
carbonyliron(0) (5). (slow eluting): mp 130±1338C,
[a]2D5ˆ155 (cˆ1, CHCl3); dC & DEPT (CDC13) 25
(CH3), 65 (CH2), 67, 70, 88 and 90 (CH), 208 (CO) (Lit.21
209, 208, 207, 204, 90, 88, 71, 67, 65, 26). Single crystals of
5 were grown as follows: ferralactone 5 (,50 mg) was
dissolved in minimum volume of dry acetone. This solution
(contained in an open ¯ask) was placed in a closed vessel
charged with dry ether (100 ml). The system was left at rt
for 5 days and the light yellow crystals were collected, dried
under vacuum, and analysed by X-ray diffraction. Crystal
data for (1)-5: C10H10O6Fe; Mˆ282.03; orthorhombic,
Jˆ6 Hz), 5.97 (1 H, m), 7.42±8.02 (5 H, m, Ph)]; dC
&
DEPT (CDCl3) 18.9 (Me), 64 (CH2), 70, 76, 126, 128,
129, 130, 133, 133 (Ph), 166 (CO); m/z 219 (M1217,
0.4%), 123 (PhCOOH, 37), 105 (PhCO, 100) 77 (Ph, 23),
70 (C5H10, 70). To a mixture of this product (1.050 g,
4.45 mmol), pyridinium p-toluene sulfonate (10.5 mg,
0.045 mmol) and dry CH2Cl2 (6 ml) at rt, was added
trimethyl orthoacetate (0.67 ml, 5.4 mmol) by micro-
syringe. The mixture was stirred for 15 min, then evapo-
rated and residual methanol removed under vacuum
(0.1 mmHg) for 2 min. The residue was taken up in dry
CH2Cl2 (6 ml) triethylamine (12 ml, 0.09 mmol) was
added followed by acetyl bromide (0.4 ml, 5.37 mmol)
over 4 min during which the solution was cooled occasion-
ally to maintain temperature below 408C. After 30 min,
when all the diol had been consumed, (TLC, silica gel,
2:1 ethyl acetate: hexane) the solvent was removed, the
residue was dissolved in methanol (18 ml) and K2CO3
(1.07 g, 7.7 mmol) was added to vigorously stirred solution.
After 70 min, saturated NH4Cl solution (35 ml) was added
and the product extracted with CH2Cl2 (3£30 ml). The
combined organic layers were dried with MgSO4, ®ltered
and evaporated. The residue was puri®ed by ®ltration
through a pad of silica gel and the pad was washed with
20% ethyl acetate in hexane. Evaporation of the ®ltrate
under vacuum gave the crude epoxide (0.792 g, 82%)
which was puri®ed by chromatography (0±70% ethyl
acetate in hexane gradient). (1)-(2E,4R,5R)-4,5-epoxyhex-
2-en-l-ol (3): [a]2D5ˆ153.3 (cˆ2, CHCl3) nmax(®lm)/cm21
3402 (OH, br. s), 1740 (CvO), 1447, 1379, 1092, 1009, 969
(CHvCH), 854; dH(CDCl3) 1.34 (3 H, d, Jˆ5 Hz, Me),
2.54 (1 H, s, OH), 2.93 (1 H, m, epoxy-CH), 3.1 0 (1 H,
dd, Jˆ2 Hz, 8, epoxy-CH), 4.14 (2 H, d, Jˆ5 Hz, CH2), 5.45
(1 H, m, cis-CH), 6.05 (1 H, m, cis-CH); dC & DEPT
(CDC13) 18 (Me), 56, 59 (2£CH), 62 (CH2), 127, 134
(2£CH); m/z 113 (M121, 2%), 97 (M1217, 8), 96
(M12H20, 23), 70 (36), 54 (35), 43 (100). A second epoxide
(,2% yield) was discarded.
Ê
P212121; aˆ11.572(3), bˆ12.934(4), cˆ7.674(2) A, Uˆ
Ê 3
23
1148.6(6) A ; Zˆ4; Dcˆ1.63 Mg m ; F(000)ˆ576; m(Mo-
Ka)ˆ1.33 mm21. Colourless crystal 0.10£0.15£0.25 mm;
Tˆ2808C; 1193 independent re¯ections measured on
Ê
Rigaku AFC7R diffractometer (Mo-Ka lˆ0.71073 A,
58,2u,508, v-scans). Re®nement on F2: wR2ˆ0.0740,
R1ˆ0.0415, Sˆ1.081 for all data; Flack xˆ0.02(4). Atomic
coordinates, bond lengths and angles, and thermal
parameters have been deposited at the Cambridge Crystal-
lographic Data Centre, reference 136760.
(1)-(2R,5S)-Tricarbonyl[(2,3,4,5-h)-hexa-2,4-dien-l-ol]-
iron(0) (6) and (2)-(2R,3S)-tricarbonyl[(3,4,5,6-h)-hexa-
3,5-dien-2-ol]iron(0) (7). Using the ultrasound procedure
described above, (1)-(2E,4R,5R)-4,5-epoxyhex-2-en-l-ol
(3) (1.14 g, 10 mmol) was converted into a crude mixture
of ferralactone complexes which were taken on into the next
step without puri®cation. By the method of Aumann,15 the
ferralactone complexes were dissolved in methanol (50 ml)
at rt. Saturated aqueous barium hydroxide (25 ml) was
added and the mixture was allowed to stand for 15 h.
Water was added and the product was extracted in pentane.
The combined extracts were dried with MgSO4, concen-
trated and ¯ash chromatography (silica, 20% ethyl acetate
in hexane) afforded (1)-(2R,5S)-tricarbonyl[(2,3,4,5-h)-
hexa-2,4-dien-l-ol]iron(0) (6). (0.99 g, 42%), and (2)-
(2R,3S)-tricarbonyl-[(3,4,5,6-h)-hexa-3,5-dien-2-ol]iron(0)
(7) (1.13 g, 48%). (1)-(2R,5S)-tricarbonyl[(2,3,4,5-h)-
hexa-2,4-dien-l-ol]iron(0) (6) (slow eluting): [a]2D5ˆ18.3
(c 1, CHCl3); Found: C, 45.7, H 4.15; C9H10O4Fe requires
C, 45.41; H, 4.23%; nmax(®lm)/cm21 3325 (OH), 2048, 1980
and 1970 (CO), 1442, 1380, 1101, 609, 568, [(lit.24 nmax
(®lm)/cm21 3340 (OH), 2049, 1982, 1975)]; dH(CDCl3)
1.10 (1 H, m, 2-H), 1.26 (1 H, q, Jˆ6 Hz, 5-H), 1.42 (3
H, d, Jˆ6 Hz, Me), 1.61 (1 H, br s, OH), 3.55±3.80 (2 H,
m, CH2), 5.0±5.20 (2 H, m, 3-H and 4-H); dC & DEPT
(CDCl3) 19 (CH3), 58 (CH2), 60, 65, 82, 86 (CH), 212
(CO). (2)-(2R,3S)-tricarbonyl[(3,4,5,6-h)-hexa-3,5-dien-2-
ol]iron(0) (7) (fast eluting): [a]2d5ˆ246.4 (c 1, CHCl3);
(Found: C, 45.74; H, 4.04; C9H10O4Fe requires C, 45.42;
H, 4.23%); nmax(CH2Cl2)/cm21 3605 (free OH), 2048,
1980 and 1968 (CO), 1374, 1147, 1085, 1034; dH(CDC13)
0.35 (1 H, dd, Jˆ2 Hz, 9, CHanti), 1.09 (1 H, t, Jˆ8 Hz, CH),
1.35 (3 H, d, Jˆ6 Hz, Me), 1.46 (1 H, br. s, OH), 1.81 (1 H,
ddd, Jˆ1, 2, 7 Hz, CHsyn), 3.78 (1 H, t, Jˆ6 Hz, HC±Me),
5.28 (2 H, m, CH-internal); dC & DEPT (CDCl3) 26 (CH3),
40 (CH2), 70, 71, 81 and 85 (CH), 211 (CO); m/z 238 (M1,
22%), 210 (M12CO, 55), 182 (M122CO, 34), 154
(2)-(4E,2R,3R,5R)-[2-(Carbonyloxy-kC)-6-hydroxy-(3,4,
5-h)-hex-4-en-3-yl]tricarbonyliron(0) (4) and (1)-(3E,
2S,4S,5R)-[1-(carbonyloxy-kC)-5-hydroxy-(2,3,4-h)-hex-
3-en-2-yl)]tricarbonyliron(0) (5). A mixture of (1)-
(2E,4R,5R)-4,5-epoxyhex-2-en-l-ol (3) (1.14 g, 10 mmol)
and Fe2(CO)9 (5.6 g, 18 mmol) in THF (200 ml) was soni-
cated in a 50 W ultrasound bath at rt for 3 h. The mixture
was ®ltered through a pad of Celite and evaporated under
reduced pressure. Flash chromatography (silica, gradient
from 10 to 70% ethyl acetate in hexane) of the residue
gave a mixture of two isomeric ferralactones (total 2.56 g,
91%), as a yellow oil which solidi®ed on cooling. The ratio
(nmr) of the ferralactones 4:5 was 47:53. Small portions
could be separated by repeated ¯ash chromatography
using the same conditions, to afford pure samples of the
two compounds: (2)-(4E,2R,3R,5R)-[2-(carbonyloxy-kC)-
6-hydroxy-(3,4,5-h)-hex-4-en-3-yl]tricarbonyliron(0) (4)33
(fast eluting): mp 81±838C (dec), [a]2D5ˆ2173 (c. 1.0,
CHC13); Found: C, 42.74; H, 3.38; C10H10O6Fe requires

C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
2279
(M123CO, 39), 136 (80), 134 (100), 81 (26); m/z (EI)
237.9928 (M1), C9H10O4Fe required 237.9928. By the
same procedure, small portions of puri®ed ferralactone
complexes could be converted into h4-diene complexes.
Ferralactone 4 (0.330 g, 1.17 mmol) in methanol (9 ml)
was treated with saturated aq. Barium hydroxide (4.5 ml)
to give the h4-complex 6 (0.262 g, 94%) as a brown oil.
Ferralactone 5 (0.332 g, 1.18 mmol) afforded corresponding
h4-complex 7 as bright yellow needles (0.126 g, 45%)
after crystallisation from hexane. mp 70±728C, (hexane)
(lit.38 658C, petroleum ether).
dC & DEPT (CDC13) 19 (CH3), 129, 130, 142 and 153
(CH), 194 (CHO).
(1)-(3S)-Tricarbonyl[(3,4,5,6-h)-hexa-3,5-dien-2-one]-
iron(0) (11). A slurry of pyridinium dichromate (PDC)
(0.131 g, 0.37 mmol) in CH2Cl2 (3 ml) was cooled to 08C
and tricarbonyliron complex 7 (0.060 g, 0.25 mmol) in
CH2Cl2 (1 ml) was added. The mixture was warmed to rt
and stirred for 2 h and then at 308C for further 2 h. After
addition of ether (50 ml) the mixture was ®ltered through a
pad of Celite and the ®ltrate was concentrated. The residue
was subjected to ¯ash chromatography (10% ether in
hexane) to afford yellow oil (0.054 g, 91%). [a]2D5ˆ1358
(cˆ1.5, CHCl3); nmax(hexane)/cm21 2065, 2005 and 1994
(CO), 1678 (CvO), 1465, 1357, 1310, 1180, 619, 598, 564;
dH(CDCl3) 0.73 (1 H, dd, Jˆ2 Hz, 10, 6anti), 1.25 (1 H, d,
Jˆ8 Hz, 3-H), 2.02 (1 H, dd, Jˆ2 Hz, 7, 6-Hsyn), 2.14 (3 H,
s, CH3), 5.4 (1 H, m, 5-H), 5.96 (1 H, dd, Jˆ6 Hz, 8, 4-H);
dC & DEPT (CDC13) 30 (CH3), 41 (CH2), 55, 85, 86 (CH),
203 (CO); m/z 236 (M1, 9%) 208 (M12CO, 17) 180
(M122CO, 34), 152 (M123CO, 100), 134 (43).
(2)-(5S)-Tricarbonyl[(1,2,3,4,5-h)-hexadienyl]iron(11)
hexa¯uorophosphate(12) (2). Using Howell's pro-
cedure,36 the diene complex (1)-6 (0.238 g, 1 mmol) was
dissolved in dry ether (50 ml) in a PTFE vessel, and the
solution was cooled to 08C. HPF6 (75% aq. solution,
0.12 ml, 1 mmol) was added and the mixture was stirred
for 2 h at 08C. The solid product was collected by ®ltration
and washed with ether. The ®ltrate was concentrated and
further precipitated material was collected. The combined
solids were dried under vacuum (0.306 g, 80%): [a]2D5ˆ219
(cˆ1, CH3CN). nmax(C2H6CO)/cm21 2115, 2065 (CO);
dH(C2D6CO) 1.88 (3 H, d, Jˆ6 Hz, Me), 2.62 (1 H, dd,
Jˆ3 Hz, 12, 1-Hanti), 3.78 (2 H, m, 5-H and 1-Hsyn), 6.26
and 6.24 (2 H, m, inner CH), 7.19, (1 H, t, Jˆ7 Hz,
middle CH); dC & DEPT (C2D6CO) 21 (Me), 64 (CH2),
92, 96, 105, 106 (CH). The same product {[a]2D5ˆ224
(cˆ1, CH3CN)} was obtained in 31% yield from (2)-7.
IR indicated that in this case the reaction did not proceed
to completion.
(1)-(2R,5S)-Tricarbonyl[(2,3,4,5-h)-1-acetoxyhexa-2,4-
diene]iron(0) (8). Using the procedure of Howell,36 the h4-
complex 6 (0.238 g, 1.0 mmol) was dissolved in dry
pyridine (3.5 ml) under nitrogen and cooled to 08C. Acetic
anhydride (0.106 ml, 1.1 mmol) was added and the reaction
stirred at rt overnight. After removal of the solvent, the
residue was puri®ed by ¯ash chromatography (20% ethyl
acetate in hexane) to give the acetate as a yellow oil
(0.250 g, 88.4%). [a]2D5ˆ118 [(lit.24 for enantiomer
[a]2D5ˆ217, cˆ1, CHCl3)]; nmax(®lm)/cm21 2043, 1964
(CO), 1740 (CvO), 1231, 1023, 610, 579; dH(CDCl3),
1.00 (1 H, q, Jˆ7 Hz, 2-H), 1.26 (1 H, m, 5-H), 1.42 (3
H, d, Jˆ6 Hz, CH3), 2.06 (3 H, s, COCH3), 4.08 (2 H,
Jˆ7 Hz, CH2), 5.06 (1 h, dd, Jˆ5 Hz, 9, 4-H), 5.20 (1 H,
dd, Jˆ5, 8 Hz, 3-H); [lit.,24 (C6H6), 0.6±0.8, (2 H, m, 2-H
and 5-H), 0.96 (1 H, d, Jˆ6 Hz, 6-H), 1.69 (3 H, s, OAc),
3.99 ((1 H, d, Jˆ8 Hz, 1 b-H), 4.28 (1 H, m, 4-H), 4.58 (1 H,
m, 3-H); dC and DEPT (CDCl3) 19 and 21 (CH3), 54 (CH2),
58, 66, 83 and 87 (CH), 171 (CvO), 211 (CO); m/z 280 (M1
1%), 252 (M12CO, 21), 224 (M122CO, 37), 196
(M123CO, 100), 181 (14), 136 (51), 134 (75), 81 (25).
The racemic tricarbonyliron complex (^)-6 (0.144 g,
0.6 mmol) was reacted with acetic anhydride in a similar
manner to afford the racemic acetate (^)-8 (0.105 g,
62%).
Racemisation during the preparation of tricarbonyl-
[(1,2,3,4,5-h)-hexadienyl]iron(11) hexa¯uoro-
phosphate(12) (2)
A solution of neutral h4-complex 7 (0.056 g, 0.23 mmol) in
acetic anhydride (3 ml) was cooled to 08C and HPF6 (60%
aqueous solution) was added in portions until the IR
spectrum of the reaction mixture no longer showed absorp-
tion bands at 2048 and 1975 cm21 (bands due to the neutral
complex). A total of 0.3 ml HPF6, solution was required.
The mixture was poured into dry ether (30 ml). The
precipitated salt was ®ltered, washed with ether and
dried (0.022 g, 25%). [a]2D5ˆ0.0 (cˆ0.15, CH3CN);
n
max(C2H6CO)/cm21 2116, 2065 (CO).
(2)-(2R,5S)-Tricarbonyl[(2,3,4,5-h)-hexa-2,4-dien-1-al]-
iron(0) (10). A slurry of pyridinium dichromate (PDC)
(0.131 g, 0.37 mmol) in CH2Cl2 (3 ml) was cooled to 08C
and tricarbonyliron complex (1)-6 (0.096 g, 0.4 mmol) in
CH2Cl2 (1 ml) was added. The mixture was warmed to rt
and stirred for 2 h and then at 308C for further 2 h. After
addition of ether (50 ml) the mixture was ®ltered through a
pad of Celite and the ®ltrate was concentrated. The residue
was subjected to ¯ash chromatography (10% ether in
hexane) to afford a yellow oil (0.036 g, 38%). [a]2D5ˆ
2114 (cˆ1.5, CHCl3) (lit.28 [a]2D5ˆ2112 at ,99% e.e. by
NMR) nmax(hexane)/cm21 2063, 2004, 1989 (CO), 1688
(CHvO), 1459, 1171, 1121, 605, 565; dH(CDCl3) 1.26
(1H, m, 2-H), 1.50 (3 H, d, Jˆ7 Hz, CH3),1.70 (1 H, m,
5-H), 5.30 (1 H, dd, Jˆ5 Hz, 9, 4-H), 5.78 (1 H, m, 3-H);
(1)-(2R,3S)-Tricarbonyl[(3,4,5,6-h)-2-acetoxyhexa-3,5-
diene]iron (9). h4-Complex (2)-7 (0.238 g, 1 mmol) was
reacted with acetic anhydride in a similar manner to that
used for the h4-complex 6 to afford the corresponding
acetate (1)-9 as a yellow oil (0.180 g, 65%) which crystal-
lised on cooling at 2208C. mp 44.5±46.58C; [a]2D5ˆ199 (c
1, CHCl3); nmax(®lm)/cm21 2048, 1972 and 1964 (3 CO),
1739 (CvO), 1372, 1240, 1048, 613, 572; dH(CDCl3) 0.30
(1 H, dd, Jˆ3, 8 Hz, 6-Hanti), 0.98 (1 H, t, Jˆ7 Hz, 3-H),
1.36 (3 H, d, Jˆ6 Hz, CH3), 1.75 (1 H, m, 6-Hsyn), 2.07 (3 H,
d, Jˆ1 Hz, COCH3), 4.91 (1 H, quintet Jˆ6 Hz, 2-H), 5.20
(2 H, m, 4-H and 5-H); dC(CDCl3) 21 & 22 (CH3), 41 (CH2),
62, 73, 83, 87, 170 (CO); m/z 252 (M12CO, 18%), 224
(M122CO, 31), 196 (M123CO, 100), 181 (12), 136 (35),
134 (50), M1 280.

2280
C. E. Anson et al. / Tetrahedron 56 (2000) 2273±2281
Synthesis of the racemic acetoxy h4-complex (^)-9 from
tricarbonyl(h4-butadiene)iron(0) by acylation and
reduction
McArdle, P.; Cunningham, D.; Stephenson, G. R.; Hastings, M.
Organometallics 1994, 13, 1806
2. Birch, A. J.; Kelly, L. F.; Narula, A. S. Tetrahedron 1982, 38,
1813; Pearson, A. J.; Khetani, V. D.; Roden, B. A. J. Org. Chem.
1989, 54, 5141.
Following the method described by Knox,39 a solution of
a Perrier complex in CH2Cl2 was prepared by gentle warm-
ing of acetyl chloride (1.2 ml) and anhydrous AlCl3
(2.94 g), followed by addition of CH2Cl2 (10 ml) to the
cooled melt. To a stirred solution of tricarbonyl(h4-buta-
diene)iron(0) (0.213 g, 1.1 mmol) in CH2Cl2 (10 ml) at
2788C, a portion Perrier complex solution (1 ml) was
added. At 30 min intervals, two further portions (1 ml) of
the Pierrer complex were added. After the last addition, the
mixture was stirred for 10 min, diluted with dry ether at
2788C, and poured onto ice. The organic layer was sepa-
rated, washed with water (4£15 ml), brine (20 ml), dried
with MgSO4 and solvent evaporated to give oily product
(0.149 g, 56%). nmax(®lm)/cm21 2065, 2005, 1994 (CO),
1677 (CvO); dH(CDCl3) 0.72 (1 H, dd, Jˆ2, 10 Hz,
6-Hanti), 1.25 (1 H, d, Jˆ7 Hz, 3-H), 2.04 (1 H, dd. Jˆ3,
8 Hz, 6-Hsyn) 2.14 (3 H, s, CH3), 5.4 (1 H, m, 5-H). 5.97 (1
H, q, Jˆ5, 7 Hz, 4-H). The product was reduced to
corresponding secondary alcohol complex (^)-7 with
NaBH4 and the alcohol was reacted with acetic anhydride/
pyridine as described earlier which gave racemic acetate
complex (^)-9.
3. Birch, A. J.; Raverty, W. D.; Stephenson, G. R.; Organo-
metallics 1984, 3, 1075; Maywald, F.; Eilbracht, P. Synlett 1996,
È
380; Knolker, H.-J.; Hermann, H. Angew. Chem. Int. Ed. Engl.
1996, 35, 341.
4. Roush, W. R.; Park, J. C. Tetrahedron Lett. 1990, 31, 4707;
Roush, W. R.; Wada, C. K. J. Am. Chem. Soc. 1994, 116, 2151.
5. Takemoto, Y.; Baba, Y.; Honda, A.; Nakao, S.; Noguchi, I.;
Iwata, C.; Tanaka, T.; Ibuka, T. Tetrahedron 1998, 54, 15567;
Tanaka, K.; Watanabe, T.; Shimamoto, K.; Sahakitpichan, P.;
Fuji, K. Tetrahedron Lett. 1999, 40, 6599.
6. Alcock, N. W.; Crout, D. H. G.; Henderson, C. M.; Thomas,
S. E. J. Chem. Soc., Chem. Commun. 1988, 746; Uemura, M.;
Nishimura, H.; Yamada, S.; Hayashi, Y.; Nakamura, K.; Ishihara,
K.; Ohno, A. Tetrahedron Asym. 1994, 5, 1673; Howell, J. A. S.;
O'Leary, P. J.; Palin, M. G.; Jaouen, G.; Top, S. Tetrahedron
Asymmetry 1996, 7, 307.
È
7. Knolker, H.-J.; Herzberg, D. Tetrahedron Lett. 1999, 40, 3547.
8. Stephenson, G. R.; Howard, P. W. J. Organometal. Chem. 1989,
370, 97.
9. Stephenson, G. R.; Howard, P. W.; Taylor, S. C. J. Organo-
metal. Chem. 1985, 285, C17; Pearson, A. J.; Gelormini, A. M.;
Pinkerton, A. A. Organometallics 1992, 11, 936.
Â
10. Ley, S. V.; Cox, L. R.; Meek, G.; Metten, K.-H.; Pique, C.;
Circular dichroism measurements
Worrall, J. M. J. Chem. Soc., Perkin Trans. 1 1997, 3299.
11. Ley, S. V.; Cox, L. R. J. Chem. Soc., Perkin Trans. 1 1997,
3315.
Volumetric and spectroscopic measurements were
performed in air without special precautions. Accurately
weighed samples of the complexes (10±20 mg) were
dissolved in CHCl3, CH3OH or CH3CN in 2 ml volumetric
¯asks. CD spectra were recorded at 228C and with 0.2 cm
path-length, at a scan rate of 100 nm min21 at 0.2 nm
resolution and a 1 nm bandwidth at the following con-
centrations: 8: 0.032 M; 9: 0.018 M; 10: 0.038 M; 11:
0.2038 M. Plots of De (mol21 dm2) against l (nm) are
shown in Fig. 1.
12. Ley, S. V.; Cox, L. R. Chem. Commun. 1998, 227; Ley, S. V.;
Burckhardt, S.; Cox, L. R.; Worrall, J. M. Chem. Commun. 1998,
229.
13. Ley, S. V.; Cox, L. R.; Middleton, B.; Worrall, J. M.
Tetrahedron 1999, 55, 3515.
14. Ley, S. V.; Meek, G. J. Chem. Soc., Chem. Commun. 1995,
Â
Â
1751; Bates, R. W.; Fernandez-Megõa, E.; Ley, S. V.; Ru
K.; Tilbrook, D. M. G. J. Chem. Soc., Perkin Trans., 1 1997, 1917.
15. Aumann, R.; Ring, H.; Kruger, C.; Goddard, R. Chem. Ber.
1979, 112, 3644.
Èck-Braun,
Â
16. Ley, S. V.; Cox, L. R.; Meek, G.; Metten, K.-H.; Pique, C.
J. Chem. Soc., Chem. Commun. 1994, 1931.
Acknowledgements
È
17. Bohmer, J.; Hampel, F.; Schobert, R. Synthesis 1999, 661.
We thank the EPSRC for a QUOTA award to G. D., Dr
M. J. Riddout (Institute of Food Research, Norwich) for
assistance with CD spectroscopy, and the EPSRC National
Mass Spectrometry Service Centre (Swansea) for high
resolution mass spectrometric measurements.
18. Becker, H.; Soler, M. A.; Sharpless, K. B. Tetrahedron 1995,
51, 1345.
19. Kolb, H. C.; Sharpless, K. B. Tetrahedron 1992, 48, 10515.
20. Dave, G. PhD thesis; University of East Anglia: Norwich,
1997.
21. Ley, S. V.; Burckhardt, S.; Cox, L. R.; Meek, G. J. Chem. Soc.,
Perkin Trans. 1 1997, 3327.
22. Horton, A. M.; Ley, S. V. J. Organometal. Chem. 1985, 285,
C17.
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2281
 Â
28. Djedaini, F.; Gree, D.; Martelli, J.; Gree, R.; Leroy, L.; Bolard,
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Ê
Ê 3
gonal, P4I2I2; aˆ8.504(1), cˆ32.843(7) A, Uˆ2375.1(7) A ;
Zˆ8; Dcˆ 1.58 Mg m23; F(000)ˆ1152; m(Mo-Ka)ˆ1.28 mm21
.
30. The labels for absolute con®gurations are determined by
writing a formal s bond between each carbon bound to iron and
the metal atom, in the standard fashion for organometallic p
Pale yellow crystal 0.30£0.30£0.40 mm; Tˆ2408C; 1313 inde-
pendent re¯ections measured on Rigaku AFC7R diffractometer
Ê
(Mo-Ka lˆ0.71073 A, 2.58,2u,258, v-scans). Re®nement on
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È
For application to organoiron complexes, see: Birch, A. J; Raverty,
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relative stereochemistry in racemic complexes by the Rp,Sp
nomenclature.
 Â
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Â
Lett. 1984, 25, 3693; Teniou, A.; Toupet, L.; Gree, R. Synlett
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33. Note added in proof: The absolute con®guration of