New method for cycloalumination of disubstituted acetylenes with 1,2-dichloroethane

Article abstract of DOI:10.1134/S1070428008060018

A new procedure has been developed for the synthesis of 2,3-dialkyl(phenyl)aluminacyclopent-2-enes by Cp₂TiCl ₂-catalyzed cycloalumination of disubstituted acetylenes with EtAlCl₂ in the presence of ethylene generated in situ from 1,2-dichloroethane and activated magnesium.

Full text of DOI:10.1134/S1070428008060018

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 6, pp. 781–784. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © I.R. Ramazanov, A.G. Ibragimov, U.M. Dzhemilev, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 6,
pp. 793–796.
New Method for Cycloalumination of Disubstituted Acetylenes
with 1,2-Dichloroethane
I. R. Ramazanov, A. G. Ibragimov, and U. M. Dzhemilev
Institute of Petroleum Chemistry and Catalysis, Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Bashkortostan, Russia
e-mail: ink@anrb.ru
Received October 30, 2007
Abstract—A new procedure has been developed for the synthesis of 2,3-dialkyl(phenyl)aluminacyclopent-
2-enes by Cp2TiCl2-catalyzed cycloalumination of disubstituted acetylenes with EtAlCl2 in the presence of
ethylene generated in situ from 1,2-dichloroethane and activated magnesium.
DOI: 10.1134/S1070428008060018
We previously discovered a new class of cyclic
organoaluminum compounds, aluminacyclopropenes I,
that are formed by cycloalumination of disubstituted
acetylenes with EtAlCl2 in the presence of magnesium
and a catalytic amount of Cp2TiCl2 in tetrahydrofuran
[1]. A probable reaction mechanism includes reduction
of Cp2TiCl2 to coordinatively unsaturated [Cp2Ti]
species, complex formation of the latter with disubsti-
tuted acetylene, and transmetalation of titanacyclo-
propene intermediate thus formed with EtAlCl2.
Aluminacyclopropenes show a weaker reactivity than
do titanacyclopropenes A, so that it is difficult to in-
volve them in subsequent transformations.
tion of titanacyclopropene intermediate A via inser-
tion into the Ti–C bond of an unsaturated molecule
which is inert toward the initial organoaluminum com-
pound. Such unsaturated compound may be ethylene
which can be readily generated in situ by reaction of
1,2-dichloroethane with magnesium, the latter being
used in the cyclometalation process. Insertion of ethyl-
ene molecule into the Ti–C bond should give titana-
cyclopentene B whose transmetalation with initial di-
haloalane could produce the target aluminacyclo-
pentenes II (Scheme 1).
The efficiency of this approach was demonstrated
by us previously while developing a new procedure for
the synthesis of aluminacyclopentanes [2] and 1,2-di-
phenyl-1,4-dialuminabut-1-ene [3] and intermolecular
Therefore, we tried to effect some chemical trans-
formations, e.g., ring expansion, at the stage of forma-
Scheme 1.
Mg
Et Al
MgCl2
Cp2TiCl2
R
R
II
[Cp2Ti]
R
EtAlCl2
R
Cp2Ti
R
R
R
Cp2Ti
B
R
A
C2H4
ClCH2CH2Cl + Mg
MgCl2
781

RAMAZANOV et al.
782
Cycloalumination of disubstituted acetylenes with EtAlCl2 in the presence of magnesium and 1,2-dichloroethane using
Cp2TiCl2 as catalyst
Yield,a %
Conversion
of acetylene, %
Run no.
Initial acetylene
Oct-4-yne
II
I
III
1
2
3
4
5
6
55
65
50
45
50
55
20
15
20
05
10
15
20
20
10
–
100
100
080
050
070
075
Dec-5-yne
Dec-1-en-4-yne
1,2-Diphenylethyne
Pent-4-en-1-yn-1-ylbenzene
Pent-1-yn-1-ylbenzene
–
05
a
The yields were determined for the corresponding hydrolysis products.
cycloalumination of disubstituted acetylenes and ter-
minal olefins [4].
and III was fairly large (up to 40% for oct-4-yne; see
table, run nos. 1–3). Moreover, cycloalumination of
dec-1-en-4-yne gave a mixture of regioisomeric alu-
minacyclopentenes IIf and IIg at a ratio of 1:1.
Taking into account the above stated, we performed
cycloalumination of a series of disubstituted acetylenes
with EtAlCl2 in the presence of activated magnesium
and Cp2TiCl2 as catalyst. The reactions were carried
out by slowly adding a mixture of 1,2-dichloroethane
and disubstituted acetylene to a solution of EtAlCl2 in
THF (molar ratio acetylene–C2H4Cl2–EtAlCl2–Mg–
Cp2TiCl2 = 1:2:4:3:0.05). The process was complete
in 10 h at room temperature. Apart from aluminacyclo-
pentenes II, the reaction mixture contained alumina-
cyclopropenes I and aluminacyclopentadienes III;
their yields and ratios depended on the substituent
nature in the acetylenic substrate. The reactions with
dialkyl-substituted acetylenes (oct-4-yne and dec-5-
yne) and 1-allyl-2-pentylacetylene (dec-1-en-4-yne)
were not selective, and the fraction of by-products I
The reactions were more selective when 1-alkyl-
(allyl)-2-phenylacetylenes and diphenylacetylene were
used as substrates. In these cases, the yield of the
corresponding aluminacyclopentenes II was 45–65%,
and the amount of aluminacyclopropenes I was as
small as 5–15% (see table, run nos. 4–6). The presence
of a phenyl group at the triple bond favors regio-
selective process with predominant formation of one
isomer (~9:1) in which the phenyl group occupies the
α-position with respect to the aluminum atom (com-
pounds IIf and IIg).
Unsymmetrically substituted acetylenes (dec-1-en-
4-yne, pent-1-yn-1-ylbenzene) gave rise to 10% of
a mixture of regioisomeric aluminacyclopentadienes
Scheme 2.
EtAlCl2
R1
+
Mg
+
R1
R2
R1
R2
R1
R1
R2
R2
R2
R2
ClCH2CH2Cl
[Cp2TiCl2], THF, 20°C
+
+
+
+
Al
Et
R1
R2
R2
R2
R1
R1
R1
Al
Et
Al
Et
Al
Et
Al
Et
IIa–IIg
R2
Ia–Ic, Ie–Ig
R2
IIIa–IIIc, IIIg
R1
R1
R1
R2
R2
R2
R1
H3O+ (D3O+)
R2
R2
R2
R1 R1
+
R1
H(D)
+
+
+
R1
(D)H
(D)H
H(D)
(D)H
H(D)
H(D)
H(D)
H(D)
H(D)
IVa–IVg
(Va–Vg)
VIa–VIc, VIe–VIg
(VIIa–VIIc, VIIe–VIIg)
VIIIa–VIIIc, VIIIg (IXa–IXc, IXg)
R1 = R2 = Pr (a), Bu (b), Ph (d); R1 = C5H11, R2 = CH2=CHCH2 (c); R1 = CH2=CHCH2, C5H11 (d);
R1 = Ph, R2 = CH2=CHCH2 (f), Pr (g).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 6 2008

NEW METHOD FOR CYCLOALUMINATION OF DISUBSTITUTED ACETYLENES
783
III at a ratio of 1:1:1 (for dec-1-en-4-yne) or to 5% of
preferentially one isomer (for pent-1-yn-1-ylbenzene).
turned out to be almost inactive (the concentration of
IVa in the hydrolysis products was as low as 5%). The
reaction successfully occurs in ethers (THF, diethyl
ether). Aliphatic (hexane, cyclohexane) and aromatic
solvents (benzene, toluene) promoted oligomerization
of disubstituted acetylenes.
The configuration of the double bond in cyclic
organoaluminum compounds I–III does not change
upon hydrolysis or deuterolysis. The cycloalumination
of disubstituted acetylenes was found to occur with
1
high stereoselectivity (>95%, according to the H and
D
D
13C NMR data). Thus the hydrolysis of the products
resulted in the formation of cis-olefins IVa–IVg, VIa–
VIc, and VIe–VIg and trans,trans-dienes VIIIa–VIIIc
and VIIIg (Scheme 2). The reactions with dec-1-en-4-
yne and pent-1-yn-1-ylbenzene under the given condi-
tions were not accompanied by cycloalumination in-
volving the double bond in the substrate.
4
5
6
7
2
3
H21C
9
8
10
Me
VIIc
D
D
D
D
4
2
5
1
4
6
6
2
7
7
Qualitative analysis of steric factors affecting the
formation of titanacyclopentene intermediate B and the
observed ratio of regioisomers obtained from 1-alkyl-
2-phenyl-substituted acetylenes suggest that the reac-
tion regioselectivity is determined mainly by electronic
factors. The rate of catalytic cycloalumination of phen-
ylacetylenes is lower due mainly to steric hindrances
related to approach of the titanacene fragment to bulky
phenyl substituent. Steric factors are also responsible
for the reduced fraction of aluminacyclopentadienes
III formed in the reactions with 1-alkyl(allyl)-2-
phenylacetylene as a result of coordination of the
second acetylene molecule by titanacyclopropene
intermediate A and subsequent transmetalation of
titanacyclopentadiene with EtAlCl2. Our results indi-
cate higher reactivity of titanacyclopropene interme-
diate A generated in situ toward ethylene derived from
1,2-dichloroethane rather than toward initial disubsti-
tuted acetylene.
3
3
5
Me
H21C
8
8
9
9
VIIf
VIIg
The structure of cyclic organoaluminum com-
pounds I–III was determined on the basis of the
1H and C NMR and mass spectra of the correspond-
13
ing deuterolysis products. The H and 13C NMR
1
parameters of compounds V, VII, and IX were com-
pared with previously reported data for Va, Vb, Ve [5],
Vc, Vd, Vf, Vg [6], VIIa, VIIe [1], VIIb [3], IXa [1],
13
and IXb [7]. Signals in the C NMR spectra of VIIc,
VIIf, and VIIg were assigned taking into account
known spectral parameters of their undeuterated ana-
logs [8]. Compounds IXc, IXd, and IXg were iden-
tified by mass spectrometry and GLC (by comparing
with retention times of dienes VIIIc and VIIIg
obtained by hydrolysis of aluminacyclopentadienes
which were formed in the cycloalumination of the cor-
responding acetylenes with EtAlCl2 in the presence of
Cp2ZrCl2 [7]).
A very important condition is slow addition of
a mixture of 1,2-dichloroethane and disubstituted ace-
tylene to the reaction system. The presence of excess
1,2-dichloroethane induces strong heat evolution
which favors side processes leading to aluminacyclo-
pentadienes III and cyclotrimerization products of
initial acetylene.
EXPERIMENTAL
1
13
The H and C NMR spectra were measured from
solutions in CDCl3 on a Jeol FX-90Q spectrometer at
90 and 22.5 MHz, respectively, using tetramethylsilane
By studying cyclometalation of dec-5-yne with
EtAlCl2 using chloride ion acceptor (Mg) and ethylene
donor (1,2-dichloroethane) in the presence of Ti, Zr,
and Hf complexes we found that Cp2TiCl2 showed the
highest catalytic activity. Titanium(IV) alkoxides like
Ti(OBu)4 and Ti(OPr-i)4 ensured considerably lower
selectivity. Dicyclopentadienylzirconium dichloride
Cp2ZrCl2 favored predominant formation of alumina-
cyclopentadiene III (the yield of compound IVa was
17% according to the GLC data), while Cp2HfCl2
(1H) or the solvent (13C) as internal reference. The C
13
NMR spectra were recorded with complete decoupling
from protons and using INEPT (Insensitive Nuclei
Enhanced by Polarization Transfer) pulse sequence.
The products were analyzed by gas–liquid chromatog-
raphy on a Carlo Erba instrument equipped with
a flame ionization detector and an Ultra-1 (25 m×
0.2 mm) glass capillary column; oven temperature 50–
170°C; carrier gas helium. The mass spectra (electron
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 6 2008

RAMAZANOV et al.
784
impact, 70 eV) were obtained on a Finnigan 4021 mass
spectrometer (ion source temperature 200°C). The
elemental compositions were determined using a Carlo
Erba 1106 analyzer. The boiling points were deter-
mined according to Sivolobov [9].
H+D 9.11. C11H10D2. Calculated, %: C 90.36; H 6.89;
D 2.75.
[(1Z)-(1,2-2H2)Pent-1-en-1-yl]benzene (VIIg).
1
Yield 55%, bp 94°C (14 mm). H NMR spectrum, δ,
ppm: 0.88 t (3H, CH3, J = 7 Hz), 1.2–1.45 m (2H,
CH2), 1.85–2.1 m (2H, CH2), 7.25–7.5 m (5H, Ph).
13C NMR spectrum, δC, ppm: 13.03 (C5), 21.54 (C4),
General procedure for the cycloalumination of
disubstituted acetylenes. A glass reactor was filled
with argon and charged with 5 ml of THF, 8 mmol of
magnesium powder, and 4 mmol of EtAlCl2. The
reactor was cooled in an ice bath, 2.5 mg (0.1 mmol)
of Cp2TiCl2 was added, the cooling bath was removed,
and a mixture of 4 mmol of 1,2-dichloroethane and
2 mmol of disubstituted acetylene in 5 ml of THF was
added dropwise under stirring over a period of 4 h.
When the reaction was complete, 5 ml of hexane was
added, and the mixture was treated with 10% hydro-
chloric acid or a 7% solution of DCl in D2O. The
organic phase was separated, the aqueous phase was
extracted with diethyl ether, and the extract was com-
bined with the organic phase, washed with a solution
of Na2CO3 until neutral reaction, and dried over CaCl2.
Individual products were isolated by vacuum dis-
tillation.
1
28.90 (C3), 129.91 (C1, JCD = 23.8 Hz), 118.02 (C2,
1JCD = 23.8 Hz), 126.70 (C7), 128.10 (C8), 132.60 (C9),
137.03 (C6). Mass spectrum: m/z 148 [M]+. Found, %:
C 88.89; H + D 11.11. C11H12D2. Calculated, %:
C 89.13; H 8.16; D 2.71.
This study was performed under financial support
by the Ministry of Science and Education of the Rus-
sian Federation (project no. NSh-7470.2006.3).
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1
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29.37 (C7), 31.58 (C8), 114.56 (C1), 126.31 (C4, 1JCD
=
1
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1
Yield 50%, bp 85°C (15 mm). H NMR spectrum, δ,
ppm: 2.75–2.85 m (2H, CH2), 4.9–6.05 m (3H,
13
CH2=CH), 7.25–7.45 m (5H, Ph). C NMR spectrum,
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1
δC, ppm: 31.82 (C3), 115.40 (C1), 125.93 (C4, JCD
=
=
1999.
1
23.6 Hz), 126.31 (C7), 127.41 (C8), 128.51 (C5, JCD
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spectrum: m/z 146 [M]+. Found, %: C 90.89;
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 6 2008