Synthesis of γ-lactones and unsaturated bis γ-lactones via Cu-Fe-mediated reductive cyclization of di- and tri-α-halogenated carboxylic esters

Article abstract of DOI:10.1016/S0022-328X(00)00056-5

A new synthetic route to γ-substituted γ-butyrolactones from alkenes and α-dichloro ester, in the presence of CuCl (catalytic) and Fe(0) (stoichiometric) in acetonitrile, was established. A study of this reaction has demonstrated that the overall process consists of the following reaction steps: (a) addition of the dichloro ester to the olefin via CuCl catalysis; (b) selective reduction of the α-chloro atom in the resulting adduct by Fe(0); (c) cyclization of the resulting γ-chloro ester to γ-butyrolactone. Yields were improved by first carrying out step (a), then steps (b) and (c) in one pot. Selectivity was improved in the presence of a small amount of water. α-Trichloro esters also generated the γ-substituted γ-butyrolactone, albeit in lower yields and selectivity. The latter reaction gave rise to the formation of interesting by-products, namely new unsaturated bis-lactones.

Full text of DOI:10.1016/S0022-328X(00)00056-5

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 601 (2000) 153–159
Synthesis of g-lactones and unsaturated bis g-lactones via
Cu–Fe-mediated reductive cyclization of di- and tri-a-halogenated
carboxylic esters
Iris Somech, Youval Shvo *
School of Chemistry, Raymond and Be6erly Sackler Faculty of Exact Sciences, Tel A6i6 Uni6ersity, 69978 Tel A6i6, Israel
Received 28 October 1999; received in revised form 15 January 2000
Abstract
A new synthetic route to g-substituted g-butyrolactones from alkenes and a-dichloro ester, in the presence of CuCl (catalytic)
and Fe(0) (stoichiometric) in acetonitrile, was established. A study of this reaction has demonstrated that the overall process
consists of the following reaction steps: (a) addition of the dichloro ester to the olefin via CuCl catalysis; (b) selective reduction
of the a-chloro atom in the resulting adduct by Fe(0); (c) cyclization of the resulting g-chloro ester to g-butyrolactone. Yields were
improved by first carrying out step (a), then steps (b) and (c) in one pot. Selectivity was improved in the presence of a small
amount of water. a-Trichloro esters also generated the g-substituted g-butyrolactone, albeit in lower yields and selectivity. The
latter reaction gave rise to the formation of interesting by-products, namely new unsaturated bis-lactones. © 2000 Elsevier Science
S.A. All rights reserved.
Keywords: g-Butyrolactones; Bis-lactones; a-Chloro esters; Cu; Fe; Reductive cyclization
1. Introduction
recently reported [5]. The above reaction was promoted
by catalytic amounts of Fe(0).
The 1,2-addition reaction of a-poly halides to olefins
The addition of a-bromoalkanoic acids to various
alkenes, initiated by peroxides, have also been studied
[6]. In this case, the resulting addition products cyclized
to give g-butyrolactones in moderate to good yields.
Various radical initiators were used; however, CuCl
was found to be inactive with the above bromoalkanoic
acid substrates.
is formulated below:
R%CX3+R2CꢀCR2“R%C(X2)–C(R2)–CR2X
The reaction is known to be catalyzed by metal salts
[1] and metal complexes [2], as well as by free radical
initiators (Kharasch reaction [3]). Some of the reactive
catalysts are: Cu(I), RuCl2(PPh3)3, [CpMo(CO)3]2,
[CpFe(CO)2]2, Co2(CO)8, and Pd. While the peroxide-
initiated Kharasch reaction is frequently accompanied
by telomerization [4] of the olefins used, the metal-cata-
lyzed reactions are usually more selective. Taken to-
gether, this is a simple and useful one-step C–C
bond-forming reaction, valuable in organic synthesis.
The addition of several of a-dichloro methyl esters to
various terminal olefins, resulting in a,g-dichloro-sub-
stituted esters in moderate to good yields, has been
* Corresponding author. Fax: +972-3-640 9293.
E-mail address: shvoy@ccsg.tau.ac.il (Y. Shvo)
Scheme 1.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S 0 0 2 2 - 3 2 8 X ( 0 0 ) 0 0 0 5 6 - 5

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I. Somech, Y. Sh6o / Journal of Organometallic Chemistry 601 (2000) 153–159
Table 1
Experimental data for the reaction of 3 with various reagents and stainless steel (SS-304) a
Experiment
SS-304 (g)
CuCl (mol%)
bipy (mol%)
Water (mol%)
Time (h)
Conv. (%) GC area (%)
GC area (%)
(1)
(2)
0
1
2
3
4
5
0
5
5
–
–
–
–
5
5
5
–
–
–
21
21
21
22.5
18
0
0.5
0.5
0.66
–
–
–
–
–
100
100
100
0
37
51
43
0
45
28
42
0
0.5
570
23.5
100
84
2
a Reaction conditions: all reactions were performed in acetonitrile (15 ml) in a glass-lined, magnetically-stirred, closed reactor (25 ml) in an oil
bath at 140°C. [3]=1.8 M.
Table 2
Experimental data for the reaction of 3 with Fe(0) in acetonitrile
Experiment
3:Fe
(mol ratio)
[3] (M)
Water (mol%)
Time (h)
Temperature
(oC)
Conv. (%) GC area (%) (1) GC area (%) (2)
1
2
3
1:1
1.3:1
2:1
1.8
1.6
1.6
622
649
622
23.5
24
23
141
140
140
100
100
90
94
93
82
2
1
1
2. Results and discussion
The results of experiments in which the stainless steel
was replaced with iron powder are compiled in Table 2.
The data (Table 2) reveal that it is the iron in the
stainless steel that has reacted with 3, thus generating
the butyrolactone (1). Here too, the presence of water
gave rise to high selectivity towards the lactone (1), as
only traces of 2 were observed in all experiments.
Practically quantitative conversions were realized with a
3:Fe molar ratio range of 1–1.3.
At this stage it was realized that 4-substituted butyro-
lactones, of importance to the fragrance industry, can
be readily prepared from simple starting materials,
either by a one-step reaction in the presence of both
Cu(I) (catalytic) and Fe(0) (stoichiometric), or by a
two-step sequence, reacting the pre-prepared ester 3
with a stoichiometric amount of Fe(0).
Extensive corrosion of metal parts of a stainless-steel
reactor was noted at the end of a reaction of methyl
dichloroacetate with 1-octene in the presence of CuCl
in acetonitrile at 140°C. The crude reaction mixture,
which had a strong peach odor, was distilled to yield
4-hexyl butyrolactone (1) (40%), and methyl-3-
hexenoate (2) (11%). The former is a commercial peach
odor fragrance.
As shown in Scheme 1, we presume that it must be 3,
generated by Cu(I)-catalyzed addition of the dichloro
ester to 1-octene, that has reacted with the reactor’s
metal, to give the lactone (1) and the ester (2). Com-
pound 3 was, therefore, independently prepared in a
glass vessel, isolated, identified, and then exposed to
stainless-steel shavings in a glass vessel in acetonitrile
under a variety of reaction conditions (Table 1).
The experiments presented in Table 1 clearly demon-
strate that it is the stainless steel that is responsible for
the formation of 1 and 2 from 3. Significantly, no
lactone formation occurred prior to the reduction of
the a C–Cl bond by the stainless steel, which was
absent in experiment 0. Noteworthy is the result of
experiment 5, whereby the added water substantially
suppressed the formation of the alkenoic acid ester (2).
Interim analyses at 4.5 h of the reaction mixtures in
experiments 3 and 5, revealed 90% and 22% conversion,
respectively. Thus, although water imparts better selec-
tivity toward lactone formation, it does slow the reac-
tion rate. It has been claimed that a water molecule in
the coordination sphere of an iron complex intermedi-
ate suppresses the reduction rate (see Ref. [7]).
3. Reaction scope
In light of the above results, we have decided to
study the scope of the reaction. To that end, several
esters of type 3 were prepared by adding methyl
dichloroacetate, or methyl trichloroacetate, to various
alkenes in the presence of CuCl (catalytic). The addi-
tion products were isolated, purified, identified, and
then subjected to the reducing conditions of Fe(0) in
CH3CN, in the presence of traces of water. These
reactions were studied with esters 4–7 (Scheme 2). The
experimental conditions and the results of the Fe pro-
moted reduction reactions are presented in Table 3. In
all cases g-butyrolactones were obtained.

I. Somech, Y. Sh6o / Journal of Organometallic Chemistry 601 (2000) 153–159
155
same lactone (1), it was in substantially lower yield and
selectivity. In this experiment, a mixture of bis-lactones,
8 and 9, accompanied 1. The bis-lactone mixture was
readily separated from lactone (1) by column chro-
matography. Their structure was established as 8 and 9
by elemental analysis, MS, IR and NMR spectra. While
lactones 8 and 9 were not previously reported, the
unsubstituted trans isomer was prepared in 20% yield
It should be pointed out that esters 3, 6, and 7 were
obtained as diastereomeric mixtures, as indicated by the
close multiplicity of their GC signals, and were reacted
with Fe–acetonitrile as such. The results, presented in
Table 3 and Scheme 2, are discussed below.
4-Hexyl-butyrolactone (1) was obtained in a good
yield and selectivity (Table 3) from methyl dichloroac-
etate (3). Although, methyl trichloroacetate (4) gave the
Scheme 2. All the reactions in this were promoted by Fe filings in acetonitile–water solution. The yields are given in Table 3.
Table 3
Experimental data for synthesis of butyrolactones from esters 3–7 a
Ester (mmol)
Water (mmol)
CH3CN (ml)
Time (h)
Conv. (%)
Products
GC area (%)
Yields (%)
3 (9.8)
4 (3.47)
61.1
36.0
5.5
3.0
21.5
5.5
100
98
1
1
97
37
40
86
50
50
66
15
71
15
16
42
23
22
10
5
8+9
10
11
12
11
5 (7.09)
6 (8.93)
72.2
53.6
6.0
5.0
20
21.5
100
100
7 (7.75)
72
6.0
42.5
100
13–16
a All reactions were carried out in sealed glass ampoules at an oil bath temperature of 140°C with a Fe:substrate molar ratio of 1:1. Coarse iron
filings were used.

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I. Somech, Y. Sh6o / Journal of Organometallic Chemistry 601 (2000) 153–159
plane of symmetry. Indeed, GC analysis of the
purified bis-lactones mixture gave rise to four sig-
nals, in agreement with the above argument.
1
3. The H-NMR chemical shifts of the ring junction
allylic H atoms in the various isomers may serve as
indicators for the double-bond configuration (see
Section 2 for the stereochemistry of 8 and 9). Two
1H-NMR signals at l=3.6 and 3.9 ppm were as-
signed to two trans isomers, 13 and 14. An addi-
tional broad signal at l=2.8 ppm was assigned to
the cis isomers, 15 and 16.
Scheme 3.
Obviously, the formation of lactone dimers disturbs
the selectivity towards the bicyclic lactone 11, when
using the trichloro ester 7. Better yield of 11 could be
obtained from the dichloro ester 6 (Table 3). Neverthe-
less, the one-step synthesis of these novel bis-lactone
compounds from simple starting materials is attractive
in its own right. g-Butyrolactone are known for their
biological activity [10].
1
from a-diazo-g-butyrolactone [8]. In its H-NMR spec-
trum, the allylic ring H atoms were found to resonate
as multiplets at 3.54 ppm. Since the mixture of 8 and 9
exhibited two multiplets at 2.25–3.01 and 3.51–3.63
ppm (allylic H atoms), the latter signal can be assigned
to the trans isomer, in analogy with the above unsubsti-
tuted trans bis-lactone. No attempt was made to sepa-
rate the two isomers of the bis-lactones.
4-Phenyl-butyrolactone (10) was obtained with very
good selectivity but in modest yield (42%) from 5
(Table 3).
4. Mechanism aspects
The cyclohexene adduct 6 possesses three stereocen-
ters. According to GC analysis, four diastereomers, in
the ratio of 22:13:33:32, were formed. During the re-
ductive cyclization reaction of the mixture, one stere-
ocenter (a-Cl C atom) is lost. The intramolecular
cyclization is an SN2 type reaction (vide infra) [9].
Therefore only the trans isomer of 6 can cyclize to give
the lactone, cis-7-oxabicyclo[4.3.0]nonan-8-one (11).
Compound 12 is the HCl elimination product of cis-6,
which due to the kinetic stereochemical constraints
mentioned above, is incapable of undergoing cycliza-
tion [9].
Upon subjecting the trichloro ester 7 (diastereomeric
mixture) to the reducing conditions (Fe–CH3CN), the
expected bicyclic lactone 11 (identical to that obtained
from 6) was obtained, however in lower yield. It was
accompanied again by butyrolactone dimers, to which
structures 13–16 were assigned (Scheme 2), on the basis
of elemental analysis, MS, IR and NMR spectra. The
dimer mixture (GC), was separated from the bicyclic
lactone 11 by column chromatography and was ob-
tained as a colorless solid. No attempt was made to
separate this mixture. We propose the following stereo-
chemical analysis for the four isomeric bis-lactones
13–16 in the purified mixture.
The mechanism of the reductive cyclization reaction,
described in Scheme 3, can be readily rationalized. The
CuCl-catalyzed addition of methyl dichloro acetate to
an alkene yields the a,g-dichlor ester A. Reaction of A
with Fe–CH3CN (stoichiometric) results in the selective
reduction of the a-Cl atom (B). Such a reduction may
proceed via oxidative addition of Fe to the more reac-
tive a C–Cl bond, and coordination of a water
molecule to the Fe atom [7]. With the g-Cl atom being
intact, a well-known neighboring group displacement
reaction (thermal) of the g-Cl atom by the ester car-
bonyl group ensues[11]. The products (Scheme 3) are a
lactone and MeCl (identified). Reduction must precede
cylization, as methyl 4-chlorooctanoate, identified by
GC–MS, was observed as a transient reaction interme-
diate. This must be due to the diminished basicity of
the a-chloro ester carbonyl group in A, which functions
as a nucleophile in the cyclization reaction.
In the absence of added water the Fe reduction
reaction mixture was found to generate methyl chlo-
ride, which was collected in chloroform from the gas
phase of the reaction mixture, and identified by NMR.
However, in the presence of water, no MeCl could be
detected, and instead, methanol only was observed in
the reaction mixture (NMR). It stands to reason that
the methanol was generated during the reaction (140°C)
by hydrolysis of the methyl ester (rather than MeCl
hydrolysis). The carboxylic acid formed in the presence
of water must cyclize faster than the ester in the ab-
sence of water. Therefore, the improved selectivity to-
wards lactone formation versus HCl elimination (in the
presence of water) may now be ascribed to the above
differential rate effect, i.e. the cyclization rate increased
relative to elimination.
1. The lactone and the cyclohexane rings in all isomers
must be cis-fused due to the kinetic stereochemical
constraints of the cyclization reaction, as previously
explained.
2. Such a situation generates four diastereomers, two
meso, 14 and 15, and two racemates, 13 and 16,
which are depicted in Scheme 2. It should be noted
that while 14 has point symmetry, 15 possesses a

I. Somech, Y. Sh6o / Journal of Organometallic Chemistry 601 (2000) 153–159
157
complex bis-lactone structures is an attractive synthetic
route, in spite of the low yield.
The source of H atoms that participate in the reduc-
tion of the C–Cl bond prior to cyclization was briefly
studied. Reductive cyclization of 3 in the presence of
added D2O resulted in the formation of a-d1-4-hexyl-g-
1
butyrolactone. Its H-NMR spectrum was compared to
5. Experimental
that of 4-hexyl-g-butyrolactone (see Section 5). A signal
at l=2.5 ppm, with a different multiplicity, clearly
indicated the presence of only one H atom a to a
carbonyl. In a second experiment, cyclization of 3 was
carried out (no added water) with Fe and CD3CN as
solvent (dried over molecular sieves). No deuterium
incorporation into lactone 1 could be detected by
1NMR. Thus, the a-H atoms of acetonitrile do not
participate in the reduction of the a-C–Cl bond of the
esters in the presence of Fe. Therefore, when present,
water serves as H donor for the above Fe promoted
reduction, when absent, the source of H atom for the
reduction reaction is presently unclear.
The proposed mode of formation of the bis-lactone
compounds is outlined in Scheme 4. It should be noted
that only adducts of methyl trichloroacetate, such as
17, generated significant quantities of the bis-lactones.
This can be attributed to the greater stability of the
chloro substituted radical intermediate 18 versus H
substituted radical, generated from methyl dichloroac-
etate, in the reaction with Fe(0). Radical 18 may un-
dergo intermolecular coupling to give 19, followed by
iron promoted vicinal elimination of Cl atoms, generat-
ing cis- and trans-20. The resulting maleate–fumarate
intermediate (20) then undergoes cyclization, as previ-
ously described, to the bis-lactone (21), with the elimi-
nation of MeCl (Scheme 4).
5.1. Preparation of esters 3–7
Methyl 2,4-dichlorodecanoate (3) [2], methyl 2,2,4-
trichlorodecanoate (4) [2], methyl 4-phenyl-2,2,4-
trichlorobutanoate (5) [12] are known compounds.
All reactions were carried out under a nitrogen
blanket.
5.2. Methyl 2-chloro-2-(2-chlorocyclohexyl) acetate (6)
Cyclohexene (15.0 g, 0.183 mol), methyl dichloroac-
etate (dist. 26.1 g, 0.183 mol), benzonitrile (30 ml),
2,2%-bipyridine (1.426 g, 9.13 mmol) and CuCl (0.904 g,
9.13 mmol) were placed in a 100 ml glass vessel and
heated at 130°C and stirred under reflux for 23 h. A
total of 80 ml of CCl4 were added to the cooled
solution, and the catalyst was filtered. The filtrate was
subjected to evaporator distillation. Benzonitrile was
distilled at 72–76°C/15 mmHg followed by the product
1
(6), b.p. 95–100°C/1 mmHg, 6.07 g (15%). H-NMR
(l): 1.19–2.34 (m, 9H), 3.80, 3.81, 3.82 (3s, 3H), 3.87–
5.13 (m, 2H). MS: m/z (%): 189 (M+–35) (2), 108
(100), 81 (47). IR w (neat): 1748 cm−1
.
5.3. Methyl 2,2-dichloro-2-(2-chlorocyclohexyl) acetate
(7)
In conclusion, a new simple synthetic route to g-bu-
tyrolactones from simple starting materials was found.
Furthermore, novel unsaturated bis-lactones can now
be readily prepared from a-trichloro esters, albeit in
low yields (no optimization was attempted). The low
yield of the bis-lactones may be attributed to the multi-
step process, involving free radical intermediates, asso-
ciated with their formation, as depicted in Scheme 4.
The simple one-step synthesis access to these rather
Cyclohexene (6.15 g, 0.075 mol), methyl trichloroac-
etate (dist. 13.3 g, 0.075 mol), benzonitrile (12 ml),
2,2%-bipyridine (0.585 g, 3.75 mmol) and CuCl (0.371 g,
3.75 mmol) were placed in a 50 ml glass vessel in an oil
bath at 140°C under reflux with stirring for 22 h. The
reaction mixture was worked up as described above for
6. A liquid (7) was obtained, b.p.110°C/0.2 mmHg, 5.64
g (29%). 1H-NMR (l): 1.3–2.8 (m, 9H, (CH2)4CH),
Scheme 4.

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I. Somech, Y. Sh6o / Journal of Organometallic Chemistry 601 (2000) 153–159
3.87 (s, 3H, OCH3), 3.9–4.0 (m, 1H, CHCl. IR w (neat):
1750, 1764 cm−1. MS: m/z (%): 257 [M+–H] (1), 223
[M+–Cl] (10), 199 [M+–CO2CH3] (13), 185 (64), 163
(45), 142 (87), 68 (100).
solid (0.1 g, 16%) (8+9) was obtained which was
washed with cyclohexane, m.p. 112–118°C, followed by
0.09 g of 1, identical to that obtained using ester (3) as
starting material.
Elemental analysis for C20H32O4 (8+9). Anal.
Found: C, 71.12; H, 9.70. Calc.: C, 71.39; H, 9.59%.
Spectral data for the 8+9 mixture: H-NMR (l): 0.89
5.4. Reducti6e cyclization reactions (general procedure)
1
Methyl 2,4-dichlorooctanoate (3) (2.5 g, 9.8 mmol),
water (1.1 ml, 61.1 mmol), acetonitrile (5.5 ml), and
coarse iron filings (0.549g, 9.8 mmol) were charged into
a 20 ml glass sleeve with a magnetic bar. The sleeve was
placed in an stainless steel reactor, which was tightly
closed and placed in an oil bath. The reaction mixture
was kept at 141°C for 21.5 h with stirring. (The reac-
tion conditions and specific quantities of reactants for
the reductive cyclization of esters 4–7 are presented in
Table 3.) After cooling, the reactor’s content was taken
up with CCl4 (25 ml), the mixture filtered, the solvent
evaporated, and the residue chromatographed on silica
with CH2Cl2–petroleum ether (1:1). An oil was ob-
tained (1.18 g, 71%), identified as 4-hexylbutyrolactone
(1) [13].
(t, 6H, CH3), 1.30–1.91 (m, 20H, CH2), 2.25–3.01 (m,
ꢀCCH2–, cis isomer), 3.51–3.63 (m, ꢀCCH2–, trans
isomer), 4.38–4.52 (m, –OCH–, cis isomer), 4.59–4.65
(m, –OCH–, trans isomer). 13C-NMR (l): 14.0, 22.5,
24.6, 27.1, 27.9, 28.9, 31.5, 33.5, 34.6, 36.3 (CH2/CH3),
78.2, 78.6, 79.1 (C–O), 133.4, 136.1, 136.5 (CꢀC),
163.9, 164.1, 170.0 (CꢀO). MS: m/z (%): 336 [M+] (51),
251 [M+–C6H13] (100), 222 (96), 153 [M+/2–CH3] (48).
IR w (CH2Cl2): 1720, 1746 cm−1
.
5.7. Bis-lactones 13–16
Methyl 2,2-dichloro-2-(2-chlorocyclohexyl)acetate (7)
(2.0 g, 7.75 mmol), iron powder (0.434 g, 7.75 mmol)
and water (1.30 g, 72.0 mmol) in acetonitrile (6 ml),
were heated at 140°C for 42.5 h and then treated as
described in the above procedure. Chromatography on
silica with methylene chloride–petroleum ether (3:1)
gave first a white solid, mixture of the dimers (13–16)
(0.054 g, 5%), that was purified by washing with cyclo-
hexane, m.p. 193–198°C. Elemental analysis for
C16H20O4. Anal. Found: C, 69.38; H, 7.45. Calc. C,
69.55; H, 7.30%. 1H-NMR (l): 1.02–2.31 (m, 16H),
2.83–2.92 (m, cis isomer, ꢀCCH), 3.56–3.68 and 3.85–
3.95 (m, trans isomer, ꢀCCH), 4.50 (m, 2H, OCH). MS:
m/z (%): 277 [MH+] (100). IR w (KBr): 1718, 1752
The lactones 1 [13], 10 [14], 11 [15] and the ester 12
[16] are known compounds, and their properties (MS,
IR, NMR) were in agreement with the literature data.
1H-NMR (l): 0.89 (t, 3H, CH3) 1.29–1.90 (m, 11H,
5CH2+1Hb to CO), 2.27–2.40 (m, 1Hb to CO), 2.49–
2.57 (m, 2H, CH6 2CO), 4.41–4.54 (m, 1H, OCH6 ).
1
A product with an identical H-NMR spectrum was
obtained by repeating the above reaction with CD3CN
as solvent, previously dried over molecular sieves.
5.5. 2-d1-4-Hexyl-k-butyrolactone
cm−1
.
The above procedure was repeated, replacing the
water with 1.1 ml of D2O. After heating for the spe-
cified period and workup as described above, the crude
product was chromatographed on silica. The product
emerged from the column with methylene chloride–
petroleum ether (1:1), 1.213 g (73%).
The next emerging compound was the bicyclic lac-
tone (11) (0.11g, 10%), identical with that obtained
from the reductive cyclization of 6.
1H-NMR (l): 0.89 (t, 3H, CH3) 1.29–1.88 (m, 11H,
5CH2+1Hb to CO), 2.27–2.39 (m, 1Hb to CO), 2.47–
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Methyl 2,2,4-trichlorooctanoate (4) (1.0 g, 3.47
mmol), acetonitrile (3 ml), water (0.648 g, 36 mmol)
and coarse iron filings (0.194 g, 3.47 mmol) were
charged into a 20 ml glass sleeve, placed in a stainless-
steel reactor, closed tightly and placed in an oil bath at
145°C for 5.5 h. After cooling, the reactor’s content was
taken up with CCl4 (25 ml), the mixture filtered, the
solvent evaporated, and the residue chromatographed
on silica with CH2Cl2–petroleum ether (1:1). A white

I. Somech, Y. Sh6o / Journal of Organometallic Chemistry 601 (2000) 153–159
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