Effect of the Grignard reagent on the X→Csp, migration of the MR3 group in HC ≡ CCH2XMR3 compounds

Article abstract of DOI:10.1023/A:1013895817461

The effect of the Grignard compounds (EtMgBr, PhMgBr, t-BuMgCl, cyclo-C₆H₁₁MgBr, and PhC≡CMgBr) on the isomerization of HC≡CCH₂XMR₃ into R₃MC≡CCH₂XH (M = Si, Ge; X = O, S) was studied. The efficiency of the 1,4-(X→C_sp)-migration of the R₃M group was shown to depend on the nucleophilicity of the Grignard compound and nature of the M-X bond.

Full text of DOI:10.1023/A:1013895817461

Russian Journal of Organic Chemistry, Vol. 37, No. 11, 2001, pp. 1549 1552. Translated from Zhurnal Organicheskoi Khimii, Vol. 37, No. 11, 2001,
pp. 1625 1628.
Original Russian Text Copyright
2001 by Novokshonov, Medvedeva, Mareev.
Effect of the Grignard Reagent on the X Csp Migration
of the MR3 Group in HC CCH2XMR3 Compounds*
V. V. Novokshonov, A. S. Medvedeva, and A. V. Mareev
Irkutsk Institute of Chemistry, Siberian Division, Russian Academy of Sciences,
ul. Favorskogo 1, Irkutsk, 664033 Russia
fax: (8395)396046; e-mail: amedved@irioch.irk.ru
Received February 7, 2001
Abstract The effect of the Grignard compounds (EtMgBr, PhMgBr, t-BuMgCl, cyclo-C6H11MgBr, and
PhC CMgBr) on the isomerization of HC CCH2XMR3 into R3MC CCH2XH (M = Si, Ge; X = O, S) was
studied. The efficiency of the 1,4-(X Csp)-migration of the R3M group was shown to depend on the nucleo-
philicity of the Grignard compound and nature of the M X bond.
We previously reported [1 4] on a new method for
formation of an M Csp bond via isomerization of
the terminal propynes HC CC(R1R2)XMR3 into
R3MC CC(R1R2)XH (X = O, S; M = Si, Ge) by the
action of Grignard compounds. We studied the effect
of the structure of heteroelement-containing propynes
(the presence of substituents at the carbon atoms of
trimethylsilyl alkynyl ethers and the nature of hetero-
elements X and M) on the ability of the MR3 group
to migrate from the X atom to Csp [2 5]. An inter-
molecular mechanism of the process was proposed
and substantiated [2]. The goal of the present work
was to examine the effect of the Grignard compound
on the isomerization. The following Grignard com-
pounds were used: ethylmagnesium bromide, phenyl-
magnesium bromide, cyclohexylmagnesium bromide,
phenylethynylmagnesium bromide, and tert-butyl-
magnesium chloride. The substrates were terminal
propynes HC CCH2XMR3 (I III), where X = O, S;
M = Si, Ge. The isomerization process can be illus-
trated by Scheme 1.
The data in table show that the efficiency of
isomerization of compounds I III strongly depends
on the nature of the Grignard compound. With the use
of ethylmagnesium bromide the yield of 3-trimethyl-
silyl-2-propyn-1-ol (IV) from 1-trimethylsiloxy-2-
propyne (I) was 85% (tetrahydrofuran, 9 h under
reflux) [2]. Under similar conditions, but in the
presence of phenylmagnesium bromide, the yield of
alcohol IV was 54% (83% on the reacted ether).
These findings indicate that the isomerization slows
down on replacement of EtMgBr by PhMgBr. The
effect of RMgBr is seen most clearly in the isomeriza-
tion of propynes II and III containing Ge O and
Si S bonds. Under conditions optimal for the
isomerization of ether I, the yield of 3-triethylgermyl-
2-propyn-1-ol (V) from 1-triethylgermoxy-2-propyne
(II) was as low as 12.5% [5]. On the other hand, in
the presence of a softer nucleophile, phenylmagne-
sium bromide, the yield of 3-triethylgermyl-2-propyn-
1-ol (V) increases almost fourfold (48%). The iso-
merization induced by PhMgBr successfully occurs at
room temperature, the reaction time being prolonged
by a factor of 1.5. An analogous effect of the
Grignard compound nature was observed in the
isomerization of 1-trimethylsilylthio-2-propyne (III).
Replacement of ethylmagnesium bromide [4] by
phenylmagnesium bromide increases the yield of the
Scheme 1.
I, IV, R3M = Me3Si, X = O; II, V, R3M = Et3Ge, X = O;
III, VI, R3M = Me3Si, X = S; Y = Br, R1 = Et, Ph, cyclo-
C6H11, PhC C; Y = Cl, R1 = t-Bu.
____________
*
This study was financially supported by the Russian Founda-
tion for Basic Research (project no. 98-03-32931a).
1070-4280/01/3711-1549$25.00 2001 MAIK Nauka/Interperiodica

1550
NOVOKSHONOV et al.
Effect of the Grignard compound on the isomerization
R3M
X
R1MgBr
Solvent
Temperature,
C
Time, h
Yield, %
Reference
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Me3Si
Et3Ge
Et3Ge
Et3Ge
Et3Ge
Me3Si
Me3Si
O
O
O
O
O
O
O
O
O
O
O
S
EtMgBr
EtMgBr
PhMgBr
PhMgBr
t-BuMgCl
cyclo-C6H11
PhC CMgBr
EtMgBr
PhMgBr
PhMgBr
Ether
THF
Ether
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
35 36
64 65
25
64 65
64 65
64 65
64 65
64 65
64 65
25
9
9
15
9
9
9
9
9
9
9
24.5
85
[2]
[2]
22
54 (83a)
3.5
12.5
23b
12.5
48
43
[5]
[5]
[5]
PhC CMgBr
EtMgBr
PhMgBr
25
25
25
15
5
6
12
31c (17)d
48d
[4]
S
a
b
c
Calculated on the reacted ether.
1-Phenyl-2-trimethylsilylacetylene was also isolated in 20% yield.
Isolated as Me3SiC CCH2SMe.
d
Isolated as Me3SiC CCH2SEt.
isomerization product almost threefold (the product
was isolated as the corresponding S-ethyl derivative,
Me3SiC CCH2SEt). These data indicate a greater
efficiency of using phenylmagnesium bromide in the
isomerization of propynes II and III; the Ge O and
Si S bonds in the latter are more sensitive to organo-
magnesium compounds than the Si O bond in I.
Unlike phenylmagnesium bromide, ethylmagnesium
bromide as a stronger nucleophile readily cleaves the
Ge O and Si S bonds in compounds II and III,
thus reducing the yield of isomerization products
V and VI.
formation of product VII is explained by participation
of the trimethylsilyl group of initial ether I in the
Csp-silylation of phenylacetylene. The reaction mix-
ture also contained phenylacetylene, 2-propynyl
alcohol, and hexamethyldisiloxane (GLC).
Scheme 2.
tert-Butylmagnesium chloride and cyclohexyl-
magnesium bromide showed a weak activity in the
isomerization under study. In the presence of these
Grignard compounds the yield of alcohol IV from
ether I was 3.5 and 12.5%, respectively. A possible
reason for the low yields of the isomerization product
is heterolytic cleavage of the Si O bond by the action
of t-BuMgCl and cyclo-C6H11MgBr which are
stronger bases than EtMgBr.
Phenylethynylmagnesium bromide as nucleophile
gave rise to different results of the rearrangements
of trimethylsilyl and triethylgermyl 2-propynyl ethers
I and II. The reaction of ether I with PhC CMgBr
in THF gave 23% of expected alcohol IV and 20% of
phenyltrimethylsilylacetylene VII (Scheme 2). The
The reaction of germanium analog II with phenyl-
ethynylmagnesium bromide under the conditions
favoring the isomerization (THF, room temperature,
15 h) gave 3-triethylgermyl-2-propyn-1-ol (V) in 12%
yield (Scheme 3). According to the GLC data, the
reaction mixture also contained phenylacetylene,
2-propynyl alcohol, and hexaethyldigermoxane, while
no phenyltriethylgermylacetylene (VIII) was detected.
It could be expected that heterolytic cleavage of the
Ge O bond in ether II by the action of PhC CMgBr
with formation of compound VIII would occur more
readily than in the case of silyl analog I. The obtained
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 11 2001

EFFECT OF THE GRIGNARD REAGENT ON THE X Csp MIGRATION
1551
Scheme 3.
EXPERIMENTAL
The IR spectra were recorded on a Specord 75IR
spectrometer. GLC analysis was performed on
an LKhM-80 chromatograph equipped with a thermal
conductivity detector; carrier gas helium; column
1500 3.0 mm; stationary phase 10% of polymethyl-
siloxane on Chromaton.
Isomerization of 1-trimethylsiloxy-2-propyne (I).
A. By the action of PhMgBr. a. 1-Trimethylsiloxy-2-
propyne, 5.13 g (0.04 mol), was added to the Grignard
compound prepared from 1.94 g (0.08 mol) of magne-
sium and 6.28 g (0.04 mol) of freshly distilled phenyl
bromide in 50 ml of THF (the solution was filtered
from excess magnesium), and the mixture was re-
fluxed for 9 h. The solvent was distilled off, and the
residue was treated with 5% hydrochloric acid and
extracted with ether. The extract was dried over
anhydrous MgSO4 and evaporated to obtain 4.9 g
of the residue which was analyzed by GLC using
an authentic sample of 3-trimethylsilyl-2-propyn-1-ol.
The yield of alcohol IV was 54% (83% on the reacted
ether I).
b. Ether I, 2.1 g (0.016 mol), was quickly added
to the Grignard compound prepared from 0.48 g
(0.02 mol) of magnesium and 3.14 g (0.02 mol) of
phenyl bromide in 20 ml of THF. The mixture was
stirred for 15 h at 20 C and was then treated as
described above. The residue, 1.9 g, contained 22% of
alcohol IV (GLC).
results may be explained as follows. In both cases
phenylethynylmagnesium bromide acts as a weak
metalating agent which converts ethers I and II into
the corresponding Iotsitch compounds. Taking into
account that the isomerization of propyne I is a rela-
tively slow process (see table), concurrent heterolysis
of the Si O bond by the action of phenylethynyl-
magnesium bromide leads to formation of compound
VII. The rearrangement of germanium-containing
analog II is faster, so that its bromomagnesium
derivative is removed from the reaction, favoring
metalation of the triple bond of the substrate. Presum-
ably, just the higher rate of isomerization, i.e., of
heterolytic cleavage of the Ge O bond by the Iotsitch
reagent derived from ether II rather than by phenyl-
ethynylmagnesium bromide (to give phenyltriethyl-
germylacetylene VIII), is responsible for the observed
reaction pattern.
We can conclude that efficient 1,4-migration of
a heteroelement-containing group R3M from hetero-
atom X to the terminal Csp atom requires proper
B. By the action of t-BuMgCl. 1-Trimethylsiloxy-
2-propyne, 2.83 g (0.022 mol), was added to the
Grignard compound prepared from 0.97 g (0.04 mol)
of magnesium and 3.7 g (0.04 mol) of tert-butyl
chloride in 40 ml of THF (activation with iodine;
yield 55%, according to the data of titration with
0.1 N hydrochloric acid [6]), and the mixture was
refluxed for 9 h. The solvent was distilled off, and
the residue was hydrolyzed with 5% hydrochloric
acid. After appropriate treatment, 2.3 g of a residue
was obtained. According to the GLC data, it was
a mixture of 2-propynyl alcohol, hexamethyldisil-
oxane, and 3-trimethylsilyl-2-propyn-1-ol (IV); the
yield of the latter was 4%.
C. By the action of cyclo-C6H11MgBr. A solution
of 5 g (0.04 mol) of 1-trimethylsiloxy-2-propyne (I)
in 5 ml of THF was added to the Grignard compound
prepared from 1.94 g (0.08 mol) of magnesium and
6.52 g (0.04 mol) of cyclohexyl bromide in 40 ml of
THF (the solution was filtered from excess magne-
sium under nitrogen). The mixture was treated as
described above to isolate 4.2 g of a residue. Accord-
ing to the GLC data, the residue was a mixture of
choice of Grignard compound. The main requirement
is the stability of the X M bond in terminal alkyne
I III toward organomagnesium halide. The use of
phenylmagnesium bromide as a less basic nucleophile
than ethylmagnesium bromide is preferable in the
isomerization of propynes in which the X M bond
readily undergoes heterolytic cleavage. More nucleo-
philic Grignard compounds, such as tert-butylmagne-
sium chloride and cyclohexylmagnesium bromide,
give rise to cleavage of even stronger Si O bond in
the ethers under study by those reagents rather than
by the corresponding Iotsitch compounds. Phenyl-
ethynylmagnesium bromide is a weak metalating
agent in the formation of Iotsitch compounds from
1-trimethylsiloxy- and 1-triethylgermoxy-2-propynes,
which is responsible for unsatisfactory yields of the
rearrangement products. Trimethylsilyl 2-propynyl
ether undergoes concurrent heterolysis of the Si O
bond by the action of PhC CMgBr, leading to forma-
tion of phenyltrimethylsilylacetylene.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 11 2001

1552
NOVOKSHONOV et al.
2-propynyl alcohol, hexamethyldisiloxane, and 3-tri-
methylsilyl-2-propyn-1-ol (IV) (13%).
(0.011 mol) of 1-trimethylsilylthio-2-propyne in
3 ml of THF was added at 0 6 C to the Grignard
compound prepared from 0.27 g (0.011 mol) of
magnesium and 1.75 g (0.011 mol) of phenyl bromide
in 7 ml of THF. The mixture was stirred for 1 h at
0 6 C, allowed to warm up to room temperature, and
stirred for 6 h. Ethyl iodide, 2.6 g (0.016 mol), was
added, and the mixture was left overnight. It was
decomposed with a saturated solution of NH4Cl, the
product was extracted into ether, and the extract was
dried over MgSO4. The solvent was removed, and the
residue, 3 g, was analyzed by GLC using an authentic
sample of 3-ethylthio-1-trimethylsilylpropyne (VI)
[4]. Yield 48%.
D. By the action of PhC CMgBr. Phenylacetylene,
8.17 g (0.08 mol), was added over a period of 5 min
to the Grignard compound prepared from 2 g
(0.08 mol) of magnesium and 9 g (0.08 mol) of ethyl
bromide in 80 ml of THF, and the mixture was stirred
for 0.5 h at room temperature. A solution of 10.26 g
(0.08 mol) of 1-trimethylsiloxy-2-propyne (I) in 10 ml
of THF was added, and the reaction mixture was
refluxed for 9 h. By appropriate treatment we obtained
17 g of a residue which, according to the GLC data,
contained 23% of 3-trimethylsilyl-2-propyn-1-ol (IV),
20% of 1-phenyl-2-trimethylsilylacetylene (VII),
phenylacetylene, 2-propynyl alcohol, and hexamethyl-
disiloxane, which were identified by comparing with
authentic samples.
Isomerization of 1-triethylgermoxy-2-propyne
(II) by the action of PhC CMgBr. A solution of
1 g (0.01 mol) of phenylacetylene in 3 ml of THF
was added over a period of 5 min to the Grignard
compound prepared from 0.21 g (9 mmol) of magne-
sium and 0.95 g (9 mmol) of ethyl bromide in 10 ml
of THF. The mixture was stirred for 0.5 h, 1.9 g
(9 mmol) of 1-triethylgermoxy-2-propyne (II) was
added, and the mixture was stirred for 15 h at room
temperature. The solvent was distilled off, and the
residue was decomposed with a saturated solution of
ammonium chloride and was then treated as described
above. According to the GLC data, the residue, 2.5 g,
contained 3-triethylgermyl-2-propyn-1-ol (12%),
phenylacetylene, 2-propynyl alcohol, and hexaethyl-
digermoxane.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 37 No. 11 2001