Studies on the silylation reaction of α,β-epoxy esters synthesized by Darzen's condensation reaction

Article abstract of DOI:10.1080/714040968

Me₃SiCl/Mg in HMPA was used for silylation of α,β-epoxy esters resulting in the corresponding β-silylated esters in a one pot reaction with reasonable yields.

Full text of DOI:10.1080/714040968

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Phosphorus, Sulfur, and Silicon and the Related
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Studies on the Silylation Reaction of α,β-Epoxy Esters
Synthesized by Darzen's Condensation Reaction
Mohammed Bolourtchian a , Manouchehr Mamaghani b & Abed Badrian b
a Chemistry and Chemical Engineering Research Center of Iran, Tehran, Iran
b Guilan University, Rasht, Iran
Published online: 18 Jun 2010.
To cite this article: Mohammed Bolourtchian , Manouchehr Mamaghani & Abed Badrian (2003) Studies on the Silylation
Reaction of α,β-Epoxy Esters Synthesized by Darzen's Condensation Reaction, Phosphorus, Sulfur, and Silicon and the Related
Elements, 178:12, 2545-2550, DOI: 10.1080/714040968
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Phosphorus, Sulfur, and Silicon, 178:2545–2550, 2003
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500390248042
STUDIES ON THE SILYLATION REACTION OF
α,β-EPOXY ESTERS SYNTHESIZED BY DARZEN’S
CONDENSATION REACTION
Mohammed Bolourtchian,a Manouchehr Mamaghani,b
and Abed Badrianb
Chemistry and Chemical Engineering Research Center of Iran,
Tehran, Irana and Guilan University, Rasht, Iranb
(Received May 6, 2003; accepted June 10, 2003)
Me3SiCl/Mg in HMPA was used for silylation of α,β-epoxy esters result-
ing in the corresponding β-silylated esters in a one pot reaction with
reasonable yields.
Keywords: Epoxidations; epoxides; esters; ring opening; silicon
RESULTS AND DISCUSSION
Since Si C bond forming reactions are the key for organosilicon chem-
istry and silicon industry, the search for a new Si C bond forming
reaction is an important task.1,2 Si C bond forming reactions such
as the direct synthesis,3 hydrosilylation,4 and general organometal-
lic reactions,5 are important methods for the preparation of various
organosilicon compounds. Another established Si C bond forming re-
action is the direct silylation of activated alkenes with trimethylsilyl-
chloride (TMSCl) in the presence of Mg and hexamethylphosphorictri-
amide (HMPA) as solvent.6−8 This reaction generally proceeds in good
yields, and the reaction conditions require stoichiometric amounts of
alkene and TMSCl. Furthermore, this reaction cannot be applied to
unactivated alkenes and all attempts to utilize TMSCl as silylating
agent have been unsuccessful.9 Our research has focused on the de-
velopments of new synthetic methods and reactions of organosilicon
We are grateful to the Iranian National Research Council for financial support of our
research program.
Address correspondence to Manouchehr Mamaghani, Department of Chemistry, Fac-
ulty of Sciences, Guilan University, P.O. Box 41335-1914, Rasht, Iran. E-mail: m-chem41@
guilan.ac.ir
2545

2546
M. Bolourtchian et al.
compounds. We are particularly interested in the modified direct syn-
thesis of organosilicon compounds via silylation reactions.
In the previous work, Bolourtchian and coworkers reported that,
β-silylated nitriles 2 can be produced by the silylation of α,β-
unsaturated nitriles 1 and cyanoepoxides 3 (Scheme 1).10,11 We also re-
ported that silylation of α,β-unsaturated esters could lead to the related
β-silyl esters (Scheme 2).13
SCHEME 1
SCHEME 2
In continuation of our interest for the synthesis of organosilicon com-
pounds and mechanistic studies of silylation reactions, herein we ex-
tend our methodology to the silylation of α,β-epoxy esters for production
of the corresponding β-silylated esters. The reaction of Me3SiCl/Mg with
α,β-epoxy esters in the presence of HMPA as solvent gave the related
β-silylesters (Table I). Ring cleavage at the β-position of the epoxy esrer
6, followed by the addition of TMS groups, leads to 7 that is a tetrasily-
lated compound, which is the results of the addition of two TMS groups
to the epoxide ring and two TMS groups to the carbonyl function. After
elimination of (Me3Si)2O, silylated enoxysilane 8 is obtained. Hydroly-
sis of 8 in acidic conditions gives β-silylated ester 9 (Scheme 3).
The mechanism of the reaction is depicted in Scheme 4. 2 The reac-
tion is initiated by one electron transfer from Mg metal to the epoxy
ester 6 to give the corresponding radical anion 10. The radical anion
10 is subjected to the electrophilic attack by TMSCl, generating the

Silylation of Epoxy Esters
2547
SCHEME 3
radical species 11, followed by the fast second electron transfer. Sub-
sequently, the anionic intermediate 12 reacts with another TMSCl to
produce O-trimethylsilyl β-silylated ester 13 (Scheme 4) which is sub-
jected to further silylation reaction at the carbonyl group to produce
the tetrasilylated product (7).
SCHEME 4
In this reactions, three roles for TMSCl may be postulated: activation
of the epoxide ring as electrophiles by coordination to the oxygen atom
of the epoxide, stabilization of the anion intermediates, and activation
of Mg metal. The prepared α,β-epoxy esters and β-silylated esters are
summarized in Table I. The reactions also were examined in different

2548
M. Bolourtchian et al.
TABLE I Silylation of α,β-Epoxy Esters
Entry
Epoxy ester 6
Products 9
Yieldsa (%)
60
a
b
c
65
58
70
d
e
53
aIsolated yields.
solvent media by using DMF which resulted in radical coupling and
reduced the yields of silylated products.
In the research undertaken epoxy esters 6a–c, which were prepared
by Darzen’s methodology, were produced as a mixture of cis/trans iso-
mers (6a: 43/57; 6b: 32/68; 6c: 39/61). In a silylation reaction on isomeric
mixture of 6c, examination of the isolated disilylated intermediate (13)
by 1HNMR showed that the cis isomer reacts much faster than the trans
isomer, leaving appreciable amount of trans isomer unreacted.
Therefore the epoxy ester isomers (6a–c) were separated by an enzy-
matic method using Pig’s liver esterase (PLE) as a catalyst in phosphate
buffer (0.1M, pH = 8) at room temperature. The enzyme hydrolyzed the
trans-isomer leaving the cis-isomer intact. The silylation reaction was
conducted on the cis isomer. In this respect, the research is underway.
In conclusion a practical and convenient protocol has been de-
veloped for the silylation of α,β-epoxy esters to give β-silylated es-
ters. This reaction appears to be general for activated alkenes and
epoxide systems. It can be applied to the synthesis of multiple-point

Silylation of Epoxy Esters
2549
pharmacophores of bioorganosilicon compounds and also of carbon-
silicon bond formation.
EXPERIMENTAL
General
Chemicals were purchased from Merck and Fluka. IR spectra were de-
1
termined on a Shimadzo IR-470 spectrometer. H NMR spectra were
recorded on a Brucker AC, FT-NMR (80 MHZ) in deuteriochloroform
(CDCl3) with tetramethylsilane (TMS). Preparative thin layer chro-
matography was prepared from Merck Kieselgel 60 H, F254, Art No
7730. GC was carried out using Buck Scientific 910 (capillary column,
MXT-5, 15 m). All solvents used were dried and distilled according to
standard procedures.
General Procedure for Silylation of Epoxy Esters
To a three-necked flask Mg powder (2.5 equiv) and TMS-Cl (5 equiv)
in HMPA (20-mL mmol−1) was added. The flask was heated and the
temperature of the solution was kept at 60◦C. Then the epoxy ester 6
(1 equiv) was added dropwise during 60 min under Argon. The result-
ing solution was stirred for an additional 48 h at the same tempera-
ture. The mixture was poured into 20 mL of cold water. Hydrolysis of
the compounds was carried out with saturated NaHCO3 solution. The
aqueous layer was extracted three times with diethylether. The ethe-
real layer was dried over Na2SO4 and the solvent was evaporated. The
crude product was distillated under reduced pressure (10 mmHg) to
give β-silylated ester 9 as an oil. The isolated yield for each product
1
is given in parentheses and the IR, H NMR data for the compounds
11a–e are given below.
6a: Colorless oil (60%, 140◦C/10 mmHg); (Found: C, 64.15; H, 8.61;
O, 16.91; Si, 10.1. C14H22O2Si requires C, 64.28; H, 8.57; O, 17.1; Si,
10.00%); IR (liquid film); 3030, 1755, 1254, 845 cm−1; 1H NMR (CDCl3);
δ, 0.0 (s, 9H), 0.2 (t, J 6.3 Hz, 3H), 1.0–1.18 (t, J 6.1 Hz, 3H), 2.74 (d, J
6.1 Hz, 2H), 3.84–4.2 (q, J 7.1 Hz, 2H), 7.1–7.2 (m, 5H) ppm.
6b: Colorless oil (65%, 146◦C/10 mmHg); (Found: C, 64.20; H, 8.50;
O, 17.21; Si, 10.19. C15H24O3Si requires C, 64.28; H, 8.57; O, 17.1; Si,
10.00%); IR (liquid film); 3029, 1753, 1256, 847 cm−1; 1H NMR (CDCl3);
δ, 0.0 (s, 9H), 0.15 (t, J 6.3 Hz, 1H), 1.0–1.2 (t, J 6.1 Hz, 3H), 2.74 (d,
J 6.2 Hz, 2H), 3.5 (s, 3H), 3.8–4.18 (q, J 7.1 Hz, 2H), 6.5–7.2 (m, 5H)
ppm.

2550
M. Bolourtchian et al.
6c: Colorless oil (58%, 130◦C/10 mmHg); (Found: C, 68.10; H, 9.05;
O, 12.21; Si, 10.71. C15H24O2Si requires C, 68.18; H, 9.09; O, 12.12; Si,
1
10.60%); IR (liquid film); 3032, 2972, 1760, 1253, 847 cm−1; H NMR
(CDCl3); δ, −0.9 (s, 9H), 0.7 (s, 3H), 1.1–1.21 (t, J 6.1 Hz, 3H), 2.69 (s,
2H), 3.9–4.2 (q, J 7.1 Hz, 2H), 7.2 (m, 5H) ppm.
6d: Colorless oil (70%, 155◦C/10 mmHg); (Found: C, 73.68; H, 8.05; O,
9.78; Si, 8.59. C20H26O2Si requires C, 73.61; H, 8.09; O, 9.82; Si, 8.62%);
IR (liquid film); 3030, 2952, 1762, 1253, 844 cm−1; 1H NMR (CDCl3); δ,
−0.1 (s, 9H), 1.0–1.2 (t, J 6.1, 3H), 2.70 (s, 2H), 3.8–4.2 (q, J 7.1, 2H),
7.1–7.4 (m, 10H) ppm.
6e: Colorless oil (53%, 130◦C/10 mmHg); (Found: C, 64.50; H, 10.71;
O, 13.41; Si, 11.38. C13H26O2Si requires C, 64.46; H, 10.74; O, 13.22; Si,
1
11.57%); IR (liquid film); 3050, 2962, 1750, 1252, 845 cm−1; H NMR
(CDCl3); δ, 0.0 (s, 9H), 0.9–1.1 (t, J 6.1. Hz, 3H), 1.2–1.5 (m, 10H), 2.71
(s, 2H), 3.82–4.2 (q, J 7.1 Hz, 2H)., 2H), 3.8–4.2 (q, J 7.1 Hz, 2H). 7.1–7.4
(m, 10H) ppm.
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