Cyclic α-acylvinyl anionic synthons: A novel synthesis of 2-trimethylsilyl-3-methyl-cyclohexenone by the Wurtz-Fittig coupling reaction

Article abstract of DOI:10.1080/00397910802432196

2-Trimethylsilyl-3-methyl-cyclohexen-1-one: a cyclic α-acyl anionic synthon was prepared in good yield by the Wurtz-Fittig coupling reaction of 6-bromo-7-methyl-1,4-dioxaspiro[4,5]-6-decene with metallic sodium and chlorotrimethylsilane in anhydrous ether solvent. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802432196

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Cyclic α-Acylvinyl Anionic
Synthons: A Novel Synthesis
of 2-Trimethylsilyl-3-methyl-
cyclohexenone by the
Wurtz–Fittig Coupling Reaction
Divya Jyothi a & S. HariPrasad a
a Department of Chemistry, Central College Campus,
Bangalore University, Bangalore, India
Version of record first published: 29 Jan 2009.
To cite this article: Divya Jyothi & S. HariPrasad (2009): Cyclic α-Acylvinyl Anionic
Synthons: A Novel Synthesis of 2-Trimethylsilyl-3-methyl-cyclohexenone by the
Wurtz–Fittig Coupling Reaction, Synthetic Communications: An International Journal
for Rapid Communication of Synthetic Organic Chemistry, 39:5, 875-879
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Synthetic Communications1, 39: 875–879, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802432196
Cyclic a-Acylvinyl Anionic Synthons: A Novel
Synthesis of 2-Trimethylsilyl-3-methyl-
cyclohexenone by the Wurtz–Fittig Coupling
Reaction
Divya Jyothi and S. HariPrasad
Department of Chemistry, Central College Campus, Bangalore University,
Bangalore, India
Abstract: 2-Trimethylsilyl-3-methyl-cyclohexen-1-one: a cyclic a-acyl anionic
synthon was prepared in good yield by the Wurtz–Fittig coupling reaction of
6-bromo-7-methyl-1,4-dioxaspiro[4,5]-6-decene with metallic sodium and chloro-
trimethylsilane in anhydrous ether solvent.
Keywords: Cyclic a-acylvinyl anionic synthons, substituted cyclic vinyl silanes,
a-trimethylsilyl-b-methyl-cyclohexenone, Wurtz–Fittig reaction
INTRODUCTION
Cyclic vinylsilanes form an important class of compounds in synthetic
organic chemistry.[1] Reports of cyclic vinyl silanes that have been
functionalized are few, though the variously substituted acyclic vinyl
silanes have been well documented.[2]
An important class of functionalized cyclic vinylsilanes are the
a-trimethylsilyl-a,b-unsaturated cycloalkenones. These compounds are
cyclic a-acylvinyl anionic synthons.[3] The most common route for the pre-
paration of the a-trimethylsilyl-a,b-unsaturated cycloalkenones is the
reaction of n-butyl lithium with the corresponding 6-halo-1,4-dioxaspiro
Received May 7, 2008.
Address correspondence to S. HariPrasad, Department of Studies in
Chemistry, Central College Campus, Bangalore University, Dr. B. R. Ambedkar
Veedhi, Bangalore 560 001, India. E-mail: hariprasad@bub.ernet.in
875

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D. Jyothi and S. HariPrasad
[4,n]cycloalkenes at ꢀ78 ꢁC, followed by quenching of the resulting anion
with chlorotrimethylsilane. Subsequent workup yields the a-trimethylsilyl-
a,b-unsaturated cycloalkenone.[4]
RESULTS AND DISCUSSION
We had earlier prepared a wide variety of novel cyclic vinyl silanes like
the 1,2-bis(trimethylsilyl)cycloalkenes, 2-trimethylsilyl-1-halocyclopen-
tenes, and a-amino-trimethylsilylcycloalkenes by the simple Wurtz–Fittig
coupling reaction of the corresponding 1-halocycloalkene with sodium
and chlorotrimethylsilane in different anhydrous solvents.[5]
In continuation of our studies, we now report the synthesis of 2-
trimethylsilyl-3-methyl-cyclohexen-1-one (4), which may be used as a cyc-
lic a-acyl anionic synthon by the simple Wurtz–Fittig coupling reaction
(Scheme 1). Surprisingly, this route using metallic sodium has not been
reported in the literature, even though there is one report of use of metal-
lic lithium for the creation of the anion.[6]
The starting compound 1 was prepared by the microwave irradiation
of ethylacetoacetate with paraformaldehyde, followed by hydrolysis.[7]
Bromination of 3-methyl-2-cyclohexenone followed by dehydrogenation
with triethylamine yielded the 2-bromo-3-methylcycloalkenone 2 in
56% yields. Subsequent ketalization and azeotropic removal of water
with ethylene glycol and p-toluene sulphonic acid=benzene gave the 6-
bromo-7-methyl-1,4-dioxaspiro[4,5]dec-6-ene 3 in 70% yield.[8]
The bromo compound 3 was then subjected to the Wurtz–Fittig cou-
pling reaction with slight excess quantities of metallic sodium (2.5 equiva-
lents) and chlorotrimethylsilane (4 equivalents) in anhydrous ether
solvent. The reactants were added at ꢀ40 ꢁC, followed by a slow rise to
ambient temperature. The reaction was followed using gas chromatogra-
phy. After complete disappearance of 3, as indicated by the chromato-
grams, the reaction mixture was worked up, concentrated, and distilled
Scheme 1. Reagents and conditions: (a) Br2=CCl4; Et3N, 0 ꢁC, 56%;
(b) (CH2OH)2, PTSA, C6H6, 70%; (c) (i) Na, Et2O, TMS-Cl, ꢀ40 ꢁC ! rt, 24 h;
(ii) NaHCO3, workup (76–82%).

2-Trimethylsilyl-3-methyl-cyclohexenone
877
to isolate the 2-trimethylsilyl-3-methyl-cyclohexenone (4). The reaction
was carried out 10 times with the isolated yields of 4 in the range of
76–82%.
EXPERIMENTAL
2-Trimethylsilyl-3-methyl-cyclohexenone (4)
Chlorotrimethylsilane (1.3 mL, 1.113 g, 10.25 mmol) was added to a
stirred solution of finely cut sodium pieces (0.15 g, 6.52 ꢂ 10ꢀ3 g atoms)
suspended in 5 mL anhydrous diethyl ether. The reaction flask was
cooled in a cryolator to ꢀ 40 ꢁC. Ice cold 6-bromo-7-methyl-1,4-dioxas-
piro[4,5]-6-decene (3) (0.59 g, 2.532 mmol) in 1 mL anhydrous ether was
added to the mixture, and the stirring continued for another hour. The
mixture was then allowed to attain room temperature overnight, when a
blue coloration developed. Further stirring for 24 h indicated complete
disappearance of 3 when monitored by gas chromatography (GC). The
precipitated solids and unreacted sodium were filtered out on a plug of
glass wool and washed with dry ether (2 ꢂ 5 mL). The combined ethe-
real extracts were washed with ice-cold saturated NaHCO3 solution
(20 mL) and brine (20 mL) and then dried (MgSO4). Vacuum concentra-
tion and distillation yielded 0.35 g (76%) of the product 4. IR (neat)
1
2955, 1662, 1584 and 1253 cmꢀ1; H NMR (400 MHz, CDCl3): d 2.33
(t, 2H, J ¼ 6.4 Hz), 2.28 (t, 2H, J ¼ 6.5 Hz), 1.99 (s, 3 H), 1.89 (qn,
2H, J ¼ 6.4 Hz) and 0.1968 (s, 9H); 13C NMR (400 MHz, CDCl3): d
203.172 (C¼O), 169.459 (C), 136.510 (CH), 36.958 (CH2), 34.615
(CH2), 24.404 (CH3), 22.099 (CH2), 1.653 (SiMe3); GC-MS (m=e, rel.
abund.) 182 (2.06, Mþ), 167 (100), 154 (5.1), 139 (10.3), 111 (5.15),
and 91 (4.1).
ACKNOWLEDGMENT
We are thankful to the Organic Chemistry and NMR departments,
Indian Institute of Science, Bangalore, for NMR facilities. Grateful
thanks are due to University Grants Commission–India and Department
of Science and Technology–India for financial assistance.
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