Cyclomagnesation of olefins with ethylmagnesium bromide in the presence of titanium complexes

Article abstract of DOI:10.1007/s11178-005-0169-z

Cyclomagnesation of terminal and cyclic olefins and 1,2-dienes with RMgHlg and R₂Mg in the presence of dichloro(dicyclopentadienyl)titanium(IV) gives non-Grignard cyclic and acyclic organomagnesium compounds. The reaction direction depends on t

Full text of DOI:10.1007/s11178-005-0169-z

Russian Journal of Organic Chemistry, Vol. 41, No. 3, 2005, pp. 352–357. Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005,
pp. 363–368.
Original Russian Text Copyright © 2005 by Dzhemilev, D’yakonov, Khafizova, Ibragimov.
Cyclomagnesation of Olefins with Ethylmagnesium Bromide
in the Presence of Titanium Complexes
U. M. Dzhemilev, V. A. D’yakonov, L. O. Khafizova, and A. G. Ibragimov
Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Bashkortostan, Russia
e-mail: ink@anrb.ru
Received July 22, 2004
Abstract—Cyclomagnesation of terminal and cyclic olefins and 1,2-dienes with RMgHlg and R2Mg in the
presence of dichloro(dicyclopentadienyl)titanium(IV) gives non-Grignard cyclic and acyclic organomagnesium
compounds. The reaction direction depends on the structure of unsaturated initial compound. The most
probable reaction mechanism is discussed.
In 1989, we reported [1] on the cyclomagnesation
of olefins with RMgR' (R' = Alk, Hlg) in the presence
of Cp2ZrCl2 as catalyst, which afforded 1,4-dimagne-
sium compounds and/or magnesacyclopentanes. These
studies were subsequently developed in [2–9]. Accord-
ing to the data of [3, 6, 8], depending on the condi-
tions, the cyclomagnesation process can be accom-
panied by carbomagnesation [10–14] which involves
formation of zirconacyclopentane intermediates. The
yields and ratio of cyclo- and carbomagnesation prod-
ucts depends on the solvent nature, temperature, and
initial reactant ratio [3, 8]. As a rule, the reaction is
catalyzed by zirconium complexes [1–14]. We have
found no published data on the use of coordination
compounds derived from other transition metals to
catalyze cyclomagnesation.
listed olefins were performed with the use of Cp2TiCl2
as catalyst.
Depending on the substrate nature, the reactions
with EtMgBr and Et2Mg in the presence of Cp2TiCl2
gave cyclo-, carbo-, and hydromagnesation products.
Styrene reacted with EtMgBr in the presence of
Cp2TiCl2 (20°C, 20 h, THF, PhCH=CH2–EtMgBr–[Ti]
ratio 1:2:0.05) to afford a mixture of mono- and
diphenyl-substituted magnesacyclopentanes and/or (in
keeping with the Schlenk equilibrium) 1,4-dimagne-
sium derivatives I–III [3, 8]. Deuterolysis of the
latter led to formation of 1,4-dideuterobutanes IV–VI
at a ratio of ~3 : 2 : 1 in an overall yield of ~75%
(Scheme 1). In each experiment, unidentifiable high-
molecular compounds were formed (~15%) in addition
to the above products. When the reaction of styrene
was performed with Et2Mg instead of EtMgBr, other
conditions being equal, the products were magnesa-
cyclopentanes and/or 1,4-dimagnesium derivatives
I–III (ratio ~5:1:2) in an overall yield of ~60%; in
this case, no high-molecular products were formed.
The reaction of endo-dicyclopentadiene (tricyclo-
[5.2.1.02,6]deca-3,8-diene) with EtMgBr (20°C, 50 h,
THF, substrate–EtMgBr–[Ti] ratio 1:2:0.05) involved
the double bond in the norbornene moiety and afforded
a ~1:1 mixture of regioisomeric carbomagnesation
products VIIIa and VIIIb in ~70% yield. As shown
in [15], addition of chemically activated magnesium
changes the chemoselectivity of the process, and the
reaction gives a mixture of cyclo-, carbo-, and hydro-
magnesation products VII–IX (~5:2:2) in an overall
yield of ~75%, the endo-configuration of the cyclo-
With the goal of extending the scope of application
of catalytic cyclomagnesation of unsaturated com-
pounds with organomagnesium reagents and searching
for new catalysts capable of promoting such reactions,
we examined reactions of ethylmagnesium bromide
and diethylmagnesium (EtMgR; R = Br, Et) with
olefins (1-octene, allylbenzene, styrene, and endo-di-
cyclopentadiene) in the presence of catalytic systems
on the basis of Ti, Hf, Fe, Co, Ni, Pd, and Rh, i.e.,
transition metals whose coordination compounds are
widely used to catalyze various transformations of
olefins, dienes, and acetylenes. Preliminary experiments
showed that the maximal yields of the cyclomagnesa-
tion products are attained in the presence of titanium
complexes, in particular Cp2TiCl2. Therefore, all sub-
sequent experiments on cyclomagnesation of the above
1070-4280/05/4103-0352 © 2005 Pleiades Publishing, Inc.

CYCLOMAGNESATION OF OLEFINS WITH ETHYLMAGNESIUM BROMIDE
353
Scheme 1.
Ph
Ph
Ph
[Ti]
MgR
MgR
MgR
MgR
MgR
MgR
Ph CH CH2
+
EtMgR
+
+
Ph
Ph
III
I
II
Ph
Ph
Ph
DCl, D2O
D
D
D
D
D
D
I–III
+
+
Ph
Ph
VI
IV
V
R = Br, Et.
pentene fragment being retained. Presumably, activat-
ed magnesium reduces Cp2TiCl2 to [Cp2Ti] which is
responsible for formation of titanacyclopentane inter-
mediates [16, 17]. The structure of organomagnesium
compounds VII–IX was established by analysis of the
corresponding deuterolysis products XI–XIII. Treat-
ment of compounds VIIa and VIIb with methyl
formate gave cyclopentanols Xa and Xb [18], provid-
ing an additional support to the assumed structure of
magnesacyclopentanes (Scheme 2).
2:5:6 (Scheme 3). In the reaction with Et2Mg, the
ratio of deuterolysis products XVIIa–XVIIIa–XIXa
was 4:7:1. In experiments with allylbenzene, the sub-
strate underwent partial isomerization to 2-propenyl-
benzene (~30%) [19]. We failed to effect cyclo-
magnesation of internal olefins with inactivated doubly
or triply substituted double bonds (such as cyclo-
hexene, 1,5,9-trimethyl-1,5,9-cyclododecatriene, and
5-ethyl-5-decene).
Cyclomagnesation of 1,2-dienes with 2 equiv of
EtMgBr in the presence of chemically activated mag-
nesium and a catalytic amount (5 mol %) of Cp2TiCl2
(THF, 20°C, 8 h) gave 2,5-dialkylidenemagnesacyclo-
pentanes XXa–XXd and dimagnesium derivatives
XXIa–XXId, the ratio XXa–XXIa being equal to
Terminal olefins, namely 1-octene and allylben-
zene, reacted with EtMgBr in the presence of Cp2TiCl2
(~20°C, 20 h, THF, olefin–EtMgBr–[Ti] molar ratio
1:4:0.05) to give a mixture of cyclo-, carbo-, and
hydromagnesation products XIV–XVI at a ratio of
Scheme 2.
Et
H
MgR
[Ti], Mg
–MgX2
+
EtMgR
+
+
MgR
MgR
MgR
VIIa, VIIb
VIIIa, VIIIb
IXa, IXb
HCOOMe, [Ni]
VIIa, VIIb
OH
Et
Xa, Xb
H
D
DCl, D2O
VII–IX
+
+
D
D
D
XIa, XIb
XIIa, XIIb
XIIIa, XIIIb
[Ti] = Cp2TiCl2; [Ni] = Ni(acac)2 + 2Ph3P; X = Cl, Br; R = Br, Et.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 3 2005

DZHEMILEV et al.
354
Scheme 3.
R
R
[Ti]
MgR'
MgR'
R
R
CH CH2
+
EtMgR'
+
+
MgR'
XVIa, XVIb
MgR'
Et
XIVa, XIVb
XVa, XVb
R
'
–MgR2
XIVa, XIVb
Mg
R
R
D
D
DCl, D2O
R
+
+
XIV–XVI
D
D
Et
XVIIIa, XVIIIb
XVIIa, XVIIb
XIXa, XIXb
[Ti] = Cp2TiCl2; R = C6H13 (a), Ph CH2 (b); R' = Br, Et.
~1:1 (according to the 13C NMR spectrum) [20].
Treatment of compounds XXI with D+/D2O furnished
more than 90% of 1,6-dialkyl-2,5-dideutero-1,5-hexa-
dienes XXIIa–XXIId (Scheme 4).
Thus our results showed that titanium complexes
successfully catalyze cyclomagnesation of olefins and
1,2-dienes with RMgHlg and R2Mg, which results in
formation of cyclic and acyclic organomagnesium
compounds in fairly high yields.
The selectivity of cyclomagnesation of allenes with
EtMgBr in the presence of Cp2TiCl2 as catalyst de-
pends on the initial 1,2-diene structure. For example,
the reaction of phenylallene under optimal conditions
resulted in formation of a complex mixture of unsa-
turated organomagnesium compounds. The reactions
performed in diethyl ether were characterized by poor
selectivity and poor yield.
EXPERIMENTAL
The deuterolysis products were analyzed by GLC
on a Chrom-5 chromatograph equipped with a 3-m×
3-mm column; stationary phase 5% SE-30); carrier gas
helium. The IR spectra were recorded on a Specord
75IR spectrometer from samples prepared as thin
films. The mass spectra (70 eV) were obtained on
an MKh-1306 mass spectrometer; ion source tempera-
Taking into account published data [19, 21, 22] and
the results of our experiments, the formation of cyclic
and acyclic organomagnesium compounds can be ra-
tionalized as shown in Scheme 5. According to this
scheme, the reaction of EtMgBr with olefins in the
presence of Cp2TiCl2 involves formation of such key
intermediates as titanacyclopropanes [16], titanacyclo-
pentanes [17], and alkyl and hydride titanium com-
pounds [19]; these intermediates undergo transmetala-
tion with EtMgX to give the final products.
1
ture 200°C. The H and 13C NMR spectra were
1
measured on Jeol FX-90Q (89.55 MHz for H and
22.5 MHz for 13C) and Bruker AM-300 instruments
(75.46 MHz for 13C and 300 MHz for 1H) using CDCl3
as solvent.
Tetrahydrofuran was dried over metallic sodium
and was distilled just before use. Solutions of EtMgBr
and Et2Mg in THF were prepared as described in [23].
Scheme 4.
R
R
R
[Ti], Mg
–MgX2
R
R
+
EtMgR
·
–MgEt2
R
Mg Mg
Mg
Et
Et
XXa–XXd
XXIa–XXId
R
DCl, D2O
D
D
XXIIa–XXIId
[Ti] = Cp2TiCl2; X = Cl, Br; R = C5H11 (a), C7H15 (b), 2-(3-cyclohexenyl)ethyl (c), PhCH2 (d).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 3 2005

CYCLOMAGNESATION OF OLEFINS WITH ETHYLMAGNESIUM BROMIDE
355
Scheme 5.
Cp2TiCl2
EtMgBr
Cp2TiEt
Cp2TiEt
[Cp2Ti]
MgBrCl, C2H5
C2H4
MgBrCl
C2H4 + C2H6
R–CH=CH2
Et
Cp2TiH
Cp2Ti
R–CH=CH2
R
R
R–CH=CH2
TiCp2
TiCp2
Cp2Ti
R
R–CH=CH2
Cp2TiEt
EtMgBr
EtMgBr
R
Et
BrMg
R
R
BrMg
R
R
Ti
Ti
Cp
Cp
Cp
Cp
Cp2TiEt2
EtMgBr
BrMg
EtMgBr
R
R
MgBr
BrMg
R
MgBr
–MgBr2
–MgBr2
R
R
R
Mg
Mg
R = Alk, Ph.
Dicloro(dicyclopentadienyl)titanium(IV) was syn-
thesized by the procedure described in [24].
styrene, 1-octene, or allylbenzene, and 0.5 mmol of
Cp2TiCl2. The mixture was allowed to warm up to
room temperature, stirred for 20 h using a magnetic
stirrer, treated with a 10–12% solution of DCl in D2O,
and extracted with diethyl ether or hexane. The extract
was dried over MgSO4 and evaporated, and the residue
was subjected to fractional distillation under reduced
pressure.
The yields of organomagnesium compounds were
determined by GLC analysis of the corresponding
deuterium derivatives. Compounds IV–VI [25], Xa,
Xb, XIa, XIb [26], XIIIa, XIIIb [27], XVIIa [28],
XVIIb [29], XIXa, XIXb, [30], and XXIIa–XXIId
[20] were identified by comparing their physical
properties and spectral parameters with those of
authentic samples.
Reaction of terminal olefins with EtMgBr and
Et2Mg in the presence of Cp2TiCl2. A glass reactor
was charged at 0°C under dry argon with 20 mmol of
EtMgBr or Et2Mg (a solution in THF), 10 mmol of
3-Deuteromethylnonane (XVIIIa). bp 55–56°C
1
(10 mm). H NMR spectrum, δ, ppm: 0.85 m (8H,
13
CH3, CH2D), 1.15–1.50 m (13H, CH, CH2). C NMR
spectrum, δC, ppm: 11.40 (C1), 14.11 (C9), 18.91 t
(JCD = 19.5 Hz), 22.72 (C8), 27.10 (C5), 29.51 (C2),
29.71 (C6), 31.99 (C7), 34.36 (C4), 37.11 (C3). Found,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 41 No. 3 2005

DZHEMILEV et al.
356
%: C 83.54; H+D 15.79. C10H21D. Calculated, %:
C 83.83; H 14.78; D 1.39.
diethyl ether or hexane. The extract was dried over
CaCl2 and evaporated, and the residue was subjected to
column chromatography on silica gel (L 40/100 µm)
using hexane–diethyl ether 10:1) as eluent.
1-[2-(Deuteromethyl)butyl]benzene (XVIIIb).
1
bp 82–83°C (20 mm). H NMR spectrum, δ, ppm:
0.82 m (5H, CH3, CH2D), 1.10–1.58 m (1H, CH),
2.45 d (2H, CH2C6H5, J = 6.0 Hz), 7.05–7.50 m (5H,
C6H5). 13C NMR spectrum, δC, ppm: 11.50 (C4); 18.70 t
(JCD = 19.5 Hz); 29.91 (C3); 36.72 (C2); 43.53 (C1);
125.60, 128.15, 129.22, 141.61 (Carom). Found, %:
C 88.34; H+D 11.27. C11H21D. Calculated, %: C 88.53;
H 10.13; D 1.34.
Reaction of endo-tricyclo[5.2.1.02,6]deca-3,8-di-
ene with EtMgBr in the presence of activated
magnesium and Cp2TiCl2. Metallic magnesium,
20 mmol, was activated with EtBr in THF under dry
argon [15] in a glass reactor. The mixture was cooled
at 0°C, and a solution of 20 mmol of EtMgBr in THF,
10 mmol of endo-tricyclo[5.2.1.02,6]deca-3,8-diene,
and 0.5 mmol of Cp2TiCl2 were added. The mixture
was allowed to warm up to room temperature, stirred
for 50 h using a magnetic stirrer, treated with a 10–
12% solution of DCl in D2O, and extracted with
diethyl ether or hexane. The extract was dried over
MgSO4 and evaporated, and the residue was subjected
to fractional distillation.
Reaction of 1,2-dienes with EtMgBr in the
presence of activated magnesium and Cp2TiCl2.
Metallic magnesium, 20 mmol, was activated with
EtBr in THF under dry argon [15] in a glass reactor.
The mixture was cooled to 0°C, and a solution of
20 mmol of EtMgBr in THF, 10 mmol of the corre-
sponding 1,2-diene, and 0.5 mmol of Cp2TiCl2 were
added. The mixture was allowed to warm up to room
temperature, stirred for 10 h using a magnetic stirrer,
treated with a 10–12% solution of DCl in D2O, and
extracted with diethyl ether or hexane. The extract was
dried over MgSO4 and evaporated, and the residue
was subjected to fractional distillation under reduced
pressure.
2,5-Dihexylidenemagnesacyclopentane (XXa).
13C NMR spectrum (C6D6), δC, ppm: 14.18 (C11, C17),
22.72 (C10, C16), 28.67 (C3, C4), 28.71 (C7, C13), 29.50
(C8, C14), 32.00 (C9, C15), 142.84 (C6, C12), 188.30
(C2, C5).
(6Z,10Z)-7,10-Bis(ethylmagnesio)hexadeca-6,10-
diene (XXIa). 13C NMR spectrum (C6D6), δC, ppm:
–1.13 (MgCH2), 12.27 (MgCH2CH3), 14.18 (C1, C16),
19.89 (C8, C9), 22.72 (C2, C15), 28.71 (C5, C12), 29.50
(C4, C13), 32.00 (C3, C14), 142.84 (C6, C11), 166.36
(C7, C10).
exo-9-Deutero-8-ethyl-endo-tricyclo[5.2.1.02,6]-
dec-3-ene (XIIa) and exo-9-deutero-8-ethyl-endo-
tricyclo[5.2.1.02,6]dec-4-ene (XIIb) (mixture of
1
isomers). bp 76–78°C (5 mm). H NMR spectrum, δ,
ppm: 0.82 m (3H, CH3), 1.0–1.70 m (5H, CH2, CH,
CHD), 1.82–2.70 m (6H, CH, CH2CH=), 2.95 m (1H,
CHCH=), 5.48–5.66 m (2H, CH=CH). 13C NMR spec-
trum, δ, ppm: XIIa: 12.23, 29.11, 28.72 (C10), 37.10 t
(C9, JCD = 19.5 Hz), 40.91 (C5), 43.00 (C1), 43.51 (C8),
44.52 (C6), 47.82 (C7), 55.33 (C2), 131.90 (C3), 132.34
(C4); XIIb: 12.23, 28.82 (C10), 29.31, 36.80 t (C9,
JCD = 19.5 Hz), 40.91 (C3), 43.42 (C8), 43.80 (C2),
44.31 (C1), 44.93 (C7), 56.61 (C6), 131.90 (C5), 132.61
(C4). Found, %: C 88.16; H+D 11.39. C12H17D. Cal-
culated, %: C 88.28; H 10.49; D 1.23.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
nos. 03-03-33050, 02-03-97904, 04-03-97510).
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