Reaction of Catalytic Olefination of Hydrazones with Polyhaloalkanes. Investigation of Alkene Formation Chemoselectivity

Article abstract of DOI:10.1023/A:1026007801456

Hydrazones of carbonyl compounds at treatment with polyhaloalkanes in the presence of CuCl as catalyst are converted into substituted alkenes with formation of a new C=C bond.

Full text of DOI:10.1023/A:1026007801456

Russian Journal of Organic Chemistry, Vol. 39, No. 4, 2003, pp. 527 531. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 4, 2003,
pp. 562 567.
Original Russian Text Copyright
2003 by Korotchenko, Shastin, Nenaidenko, Balenkova.
Dedicated to Full Member of the Russian Academy of Sciences
I. P. Beletskaya on occasion of her jubilee
Reaction of Catalytic Olefination of Hydrazones
with Polyhaloalkanes. Investigation of Alkene Formation
Chemoselectivity
V. N. Korotchenko1, A. V. Shastin2, V. G. Nenaidenko1, and E. S. Balenkova1
1Lomonosov Moscow State University, Moscow, Russia
2Institute of Problems of Chemical Physics, Russian Academy of Sciences
142432, Chernogolovka, Moscow oblast, Russia e-mail: shastin@icp.ac.ru
Received November 25, 2002
Abstract Hydrazones of carbonyl compounds at treatment with polyhaloalkanes in the presence of CuCl as
catalyst are converted into substituted alkenes with formation of a new C=C bond.
We recently found a new reaction for olefinating
carbonyl compounds: Catalytic Olefination Reaction
(COR) [1 7]. It was demonstrated that the treating of
N-unsubstituted hydrazones of aromatic aldehydes
and ketones with carbon tetrachloride in the presence
of catalytic amounts of CuCl afforded the correspond-
ing , -dichlorostyrenes [2, 7]. Thus a new carbon-
carbon double bond is created as a result of redox
reaction. This approach to olefination of carbonyl
compounds is totally new and has no published
analogs. It was shown that catalytic olefination is a
general process. Alongside the carbon tetrachloride as
olefination reagents are suitable the other polyhalo-
alkanes: carbon tetrabromide [5, 7], bromoform
[4, 7], Freones CF3CCl3 and CF2Cl CFCl2 [6]. The
corresponding polyhaloalkanes in the reaction play
the role of C1- and C2-building blocks. It turned out
that variation of haloalkanes in reaction with hydr-
azone provided different types of di-, tri-, and tetra-
substituted alkenes; therewith the structure of arising
alkenes II depended on the character of the halogen-
containing reagent. Alongside alkenes the COR
affords symmstrical azines III (Scheme 1).
This method of alkene synthesis has obvious
advantages of simple apparatus and easy isolation of
the reaction products, mild conditions and high yields
of the target substances. These features characterize
the new reaction as very promising and easy for use
in the organic synthesis.
Formal result of the reaction is a elimination of
two halogen atoms from the molecule of the poly-
haloalkane. Under COR conditions occurs the rupture
of C Br [4, 5], C Cl [2, 3], and even C F [6] bonds
in the molecule of the initial halogen-containing com-
pound although the energies and bond lengths of
C Hlg bonds significantly differ: C Br, bond length
1
1.938 , bond energy 70 kcal mol ; C Cl, bond
1
length 1.767 , bond energy 83.5 kcal mol ; C F,
bond length 1.379 , bond energy 108 kcal mol 1 [8].
Consequently, in the presence of different halogen
atoms in a molecule the competitive elimination
thereof under reaction conditions is possible which
might provide different alkene types. Thus the
establishing of factors governing the laws of halogens
elimination and the reaction chemoselectivity is of
fundamental theoretical and practical importance.
Scheme 1.
II, Hlg = Y = X = Cl (a); X = Br, Y = Hlg = Cl (b); Hlg = Y = X = Br (c); X = H, Y = Hlg = Cl (d);
X = F = Br (e); X = F, Y = Hlg = Cl (f); X = CF3, Y = Hlg = Cl (g); X = F, Y = CClF2, Hlg = Cl (h).
1070-4280/03/3904-0527$25.00 2003 MAIK Nauka/Interperiodica

528
KOROTCHENKO et al.
Reaction of hydrazone I with polyhaloalkanes
Yield of reaction products, %
DMSO aqueous ammonia ethanol ethylenediamine
Polyhaloalkane
alkene (II)
Molar ratio
of productsa
azine (III)
alkene (II)
Molar ratio
of productsa
azine (III)
CCl4
CBrCl3
CBr2Cl2
CBr4
CHCl3
CHBrCl2
CHBr2Cl
CHBr3
CFCl3
CCl3-CF3
CCl2F-CClF2
74
71
82
89
0
44
41
67
Traces
63
IIa
21
20
10
7
56
52
53
26
30
21
21
92
54
78
55
0
32
41
30
58
64
49
IIa
5
IIa, IIb (98: 2)
IIa, IIb (95: 5)
IIc
IIa
IIa, IIb (71: 29)
IIc
37
17
23
73
55
41
65
17
33
44
IId, IIe (98: 2)
IId, IIe (84: 16)
IIe
IIe, IIe (71: 29)
IIe
IIg
IIh
IIi
IIe
IIg
IIh
IIi
20
a
According to the data of 1H NMR spectra.
We have chosen 4-chlorobenzaldehyde hydrazone
(I) as a model compound for investigation of factors
affecting the chemoselectivity of COR. A wide range
of polyhaloalkanes of different character was used
as olefinating reagents: tetrahalomethanes CBrnCl4 n
(n = 0, 1, 2, 4; products of successive replacement
of chlorine with bromine in carbon tetrachloride:
CCl4, CBrCl3, CBr2Cl2, CBr4); haloforms
CHBrnCl3 n (n = 0, 1, 2, 3; products of successive
replacement of chlorine with bromine in chloroform:
CHCl3, CHBrCl2, CHBr2Cl, CHBr3); Freons CCl3F,
CCl3CF3, CCl2F CClF2, CBr2F2.
structures of the formed alkenes IIa I were studied
by GC-MS method and H NMR spectroscopy.
1
It was established that the treatment of hydrazone I
with tetrahalomethanes in all cases afforded , -di-
halostyrenes (IIa c) and azine III as only products.
The overall yield of the two COR products, alkene
IIa c and azine III, was close to quantitative yield
(see the table).
The thorough investigation of reaction mixtures
composition revealed that at the use bromotrichloro-
methane CBrCl3 and dibromodichloromethane
CBr2Cl2, which contained simultaneously chlorine
and bromine, alongside the main product, dichloro-
alkene IIa, arose also some bromochloroalkene IIb.
It was demonstrated that at successive replacement of
bromine for chlorine the fraction of alkene IIb
increased. Consequently, under COR conditions in
the reagent molecule are cleaved prevailingly the
C Br bonds in keeping with the strength of the
C Hlg bonds.
We formerly showed that the character of solvent
and of base used in the reaction significantly affected
the yield of the target alkenes. Two types of optimal
reaction conditions were selected for different poly-
haloalkanes. When polychloro- and polybromo-
methanes CCl4, CBr4, CHBr3 were applied the best
yields of the target alkenes were obtained at reaction
in DMSO with aqueous ammonia used as base [2]. In
reaction with Freons optimal solvent and base were
respectively ethanol and 1,2-ethylenediamine [6].
Thus these two reaction systems supplement each
other and cover the whole range of halogen-contain-
ing COR reagents we have studied. Therefore the
reactions with the model hydrazone I were performed
in both systems.
The treating of hydrazone I with tetrahalomethanes
in the reaction system ethanol ethylenediamine were
obtained the same products (see the table). However
in
reaction
with
dibromodichloromethane
CBr2Cl2 the chemoselectivity sharply decreased as
compared with the process in DMSO, and bromo-
chloroalkene IIb was obtained in 29% yield.
The reaction was cariied out in the presence of
CuCl as catalyst (10 mol%). Polyhaloalkenes were
used in 5-fold excess with respect to hydrazone I. The
Similarly occurs reaction between haloforms and
hydrazone I in the presence of CuCl. Therewith the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 4 2003

REACTION OF CATALYTIC OLEFINATION OF HYDRAZONES
529
corresponding vinyl halides IId and IIe and also azine
III are formed (see the table). At the use of chloro-
form in both reaction systems no -chlorostyrene was
detected, the only reation product was azine III.
However replacement of one chlorine by bromine
(at the use of CHBrCl2) resulted in a good yield of
the target alkene IIg; therewith the yield of product
in DMSO is higher than in ethanol. The E-isomer of
alkene prevailed in the product.
presence of CuCl gave rise to the same comounds:
alkenes II and azine III. As a rule the overall yield of
COR products is close to quantitative, no other
compounds resulting from hydrazone I transforma-
tions were found in the reaction mixtures. These facts
led us to an assumption that in all cases the reactions
between hydrazone I and the halogen-containing
reagents followed the same mechanism (Scheme 2).
We previously studied the COR mechanism and
explained the processes occurring in the system and
providing the reaction products, alkenes II and azine
III [2, 4, 7]. In the first stage hydrazone I is oxidized
by Cu(II) compounds arising in the system furnishing
the corresponding diazoalkane. Further decomposi-
tion of diazoalkane catalyzed by copper results in
formation of a copper-carbene complex A, a key
reaction intermediate. The reaction of the complex
with polyhaloalkanes affords alkenes II with
regeneration of Cu(II) thus starting the new catalytic
cycle (inner cycle). Complex A also reacts with
diazoalkane furnishing azine III (outer cycle).
The use of dichlorobromomethane CHBrCl2 as
olefinating reagent in COR opens a convenient
preparative route to -chlorostyrenes. In going from
CHBrCl2 to dibromochloromethane CHBr2Cl the
fraction of -bromostyrene IIf considerably increased
(see the table).
The chemoselectivity of reaction with compounds
containing fluorine, chlorine, and bromine was
studied on a series of Freons, namely on CCl3F,
CCl2F CClF2, CCl3 CF3, and CF2Br2. The same
systems were used for olefination. It turned out that
reaction of hydrazone I with chlorofluoroalkanes gave
rise to fluoroalkenes (IIf h) and azine III.
The relations found in elimination of halogens
from polyhaloalkanes containing simultaneously
various halogen atoms required that the mechanism
of alkene formation be supplemented. A more
detailed consideration of interaction between copper-
carbene complex A and polyhaloalkanes provides an
understanding of the observed chemoselectivity.
A reaction of CCl4 and other polyhaloalkanes addi-
tion to double carbon-carbon bonds in the presence
of CuCl furnishing 1: 1 adducts is studied in detail
and well documented [9 11]. Two possible
mechanisms were suggested for this reaction. The
reaction either proceeds along radical mechanism [11]
The formation of fluoroalkenes IIf h occurred
stereoslectively. The composition of reaction mix-
tures was additionally studied by GC-MS method.
The application for olefinating Freones CCl3F and
CCl3 CF3 afforded only alkenes IIf and IIg evidenc-
ing especially high selectivity of reaction with these
Freones. With Freon CCl2F CClF2 traces of alkene
IIi (m/z 256) were detected in the reaction mixture;
the product resulted from rupture of chlorine and
fluorine from the Freon molecule.
Reactions of hydrazone I with all polyhaloalkanes
studied in this work (excluding CBr2F2) in the
Scheme 2.
L = RNH2, Hlg .
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 4 2003

530
KOROTCHENKO et al.
Scheme 3.
or through intermediate formation of Cu(III) com-
pounds [12, 13]. We assume that similarly reacts the
copper-carbene complex with polyhaloalkanes under
the COR conditions. In the first stage arises an
organocopper compound B either via addition of
polyhaloalkane to copper-carbene complex A by
insertion of copper into the C Hlg bond, or through
a preliminary one-electron transfer resulting in
formation of a pair cation-radical anion-radical
that subsequently undergoes dimerization in the
solvent cage (Scheme 3). Subsequent elimination of
Cu(II) salt from B intermediate results in alkene II
formation.
However the replacement of one more chlorine by
bromine in the reagent molecule causes increase in
the amount of bromine-containing alkenes out of
proportion. It seems that in the first stage almost
exclusively C Br bonds in the polyhaloalkane are
disrupted with Cu Br bond formation in keeping with
the published data on the bromochloroalkanes addi-
tion to olefins [9, 10]. Thus the first stage procceds
selectively: when the initial reagent contains a single
bromine atom the subsequent
-elimination of
CuBrCl from B intermediate results in the only
chlorocontaining alkene II. When the initial reagent
contained more than one bromine atom (CBr2Cl2,
CHBr2Cl) the subsequent elimination of Cu(II) salt
may occur by two routes affording two different
alkenes (Scheme 4). Therefore the overall chemo-
selectivity of the reaction depends on the decomposi-
tion of intermediate B. Apparently the elimination of
The chemoselectivity is very high in reactions with
polyhaloalkanes containing a single bromine atom
(CBrCl3, CHBrCl2): Only traces of bromine-contain-
ing alkenes IIb and IIe are formed (see the table).
Scheme 4.
X = H, Cl.
CuHlg2 from intermediate B occurs significantly
The excellent chemoselectivity of olefination with
Freons CCl3F, CCl3CF3 also originates from sig-
nificantly higher strength of the C F bond as
compared to that of C Cl bond. However unsym-
metrical Freon CCl2F CClF2 can react with copper-
carbene complex A at two different ends affording
two different intermediates B and C. The subsequent
elimination of CuHlg2 fom intermediates B and C
results in two different alkenes IIh and IIi although
the formation of compound IIi occurred as a minor
process (Scheme 5).
faster and less selectively, probably due low stability
of B.
The comparison of two reaction systems studied
(DMSO aqueous ammonia and ethanol ethylenedi-
amine) shows that in the latter system the reaction is
less chemoselective. The most probable cause thereof
is the higher nucleophilicity of ethylenediamine as
compared with ammonia. As a result the intermediate
B in the second system decomposes faster, and
consequently the reaction is less selective.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 4 2003

REACTION OF CATALYTIC OLEFINATION OF HYDRAZONES
531
Scheme 5.
EXPERIMENTAL
was performed similarly using a solution of CBr4
(3.32 g, 10 mmol) in ethanol (30 ml).
1H NMR spectra were registered on spectrometer
Varian VXR-400 (operating frequency 400 MHz) in
CDCl3, internal reference TMS. GC-MS measure-
ments were carried out on HP5890 instrument
(ionization by electron impact, 70 eV) using 5989x-G
detector. TLC analyses were carried out on Merck 60
F254 plates, column chromatography was performed
on silica gel Merck (63-200 mesh). 4-Chlorobenz-
aldehyde hydrazone (I) was prepared by procedure
[2]. Commercial polyhaloalkanes were used without
additional purification.
The study was carried out under financial support
of the Russian Foundation for Basic Research (grants
nos. 00-03-32760, 00-03-32763, and 02-03-06142).
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2. Shastin, A.V., Korotchenko, V.N., Nenajden-
ko, V.G., and Balenkova, E.S., Tetrahedron, 2000,
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Reaction of hydrazone (I) with polyhaloalkanes
in DMSO. To a solution of freshly prepared
hydrazone I (309 mg, 2 mmol) in DMSO (2ml) was
added a concn. aqueous ammonia (0.68 ml) and
freshly purified CuCl (20 mg, 0.2 mmol, 10 mol%)
and then the corresponding polyhaloalkane (10 mmol)
maintaining the temperature at 20 C. The reaction
mixture was stirred for 20 h and then poured in water
(200 ml). The reaction products were extracted into
dichloromethane (3 20 ml), the combined extract
were dried over sodium sulfate, the dichloromethane
was evaporated, and the reaction products were
separated by column chromatography on silica gel.
We failed to separate E- and Z-isomers of alkenes by
means of column chromatography.
3. Shastin, A.V., Korotchenko, V.N., Nenaiden-
ko, V.G., and Balenkova, E.S., Izv. Akad. Nauk,
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similarly using a solution of CBr4 (3.32 g, 10 mmol)
in DMSO (8 ml).
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vol. 35, p. 1339.
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Reaction of hydrazone (I) with polyhaloalkanes
in ethanol. To a solution of freshly prepared hydr-
azone I (309 mg, 2 mmol) in ethanol (20 ml) was
added ethylenediamine (10 mmol, 0.67 ml) and fresh-
ly purified CuCl (20 mg, 0.2 mmol, 10 mol%) and
then the corresponding polyhaloalkane (10 mmol)
maintaining the temperature at 20 C. The reaction
mixture was stirred for 24 h and then worked up as
described above. Reaction of hydrazone I with CBr4
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 4 2003