Catalytic olefination of carbonyl compounds. Effect of the structure of the carbonyl compound on the reaction

Article abstract of DOI:10.1023/A:1023499925287

The mechanism of the novel reaction of catalytic olefination of carbonyl compounds was studied. The reaction involves the transformation of hydrazones of aromatic aldehydes and ketones into the corresponding dichloroalkenes and symmetrical azines by the treatment with carbon tetrachloride in the presence of CuCl as a catalyst. The stability of intermediate diazoalkanes is the main factor determining the direction of the reaction. In the case of sufficiently stable diazoalkanes, other products can be formed under the reaction conditions along with the products of catalytic olefination.

Full text of DOI:10.1023/A:1023499925287

492
Russian Chemical Bulletin, International Edition, Vol. 52, No. 2, pp. 492—497, February, 2003
Catalytic olefination of carbonyl compounds. Effect
of the structure of the carbonyl compound on the reaction
a
V. N. Korotchenko,a A. V. Shastin,b V. G. Nenaidenko,a and E. S. Balenkova
ꢀ
aDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119992 Moscow, Russian Federation.
Eꢀmail: nen@acylium.chem.msu.ru
bInstitute of Problems of Chemical Physics, Russian Academy of Sciences,
14 Institutskii prosp., 142432 Chernogolovka, Moscow Region, Russian Federation.
Eꢀmail shastin@icp.ac.ru
The mechanism of the novel reaction of catalytic olefination of carbonyl compounds was
studied. The reaction involves the transformation of hydrazones of aromatic aldehydes and
ketones into the corresponding dichloroalkenes and symmetrical azines by the treatment with
carbon tetrachloride in the presence of CuCl as a catalyst. The stability of intermediate
diazoalkanes is the main factor determining the direction of the reaction. In the case of
sufficiently stable diazoalkanes, other products can be formed under the reaction conditions
along with the products of catalytic olefination.
Key words: catalysis, copper salts, carbonyl compounds, hydrazones, diazoalkanes, carbenes,
alkenes, olefination.
10
10
Olefination of carbonyl compounds, being the transꢀ
CBr4,7,9 and Freons CF3CCl3 and CF2ClCFCl2 can
be used as C1ꢀ and C2ꢀbuilding blocks in syntheses of the
corresponding substituted alkenes. We used hydrazones
of aromatic and heteroaromatic aldehydes4—6,8—10 and
alkyl aryl ketones7 as carbonyl components. The method
proposed for alkene synthesis has such unambiguous adꢀ
vantages as simplicity of experimental design and isolaꢀ
tion of products, mild conditions and easiness of the reacꢀ
tions, and high yields of target products. These features
make this reaction very promising and convenient for use
in organic synthesis.
formation of the carbonyl group into the double carbonꢀ
carbon bond, is one of the most convenient and universal
method for the preparation of alkenes.1 Great diversity
and accessibility of carbonyl compounds allows olefination
to be used for syntheses of a wide scope of substituted
alkenes. The Wittig reaction and its modifications2 and
the synthesis using equimolar amounts of metals as reꢀ
ducing agents3 are classical approaches to olefination.
However, searching for new catalytic routes for this
transformation remains important because considerable
amounts of phosphorous reagents and/or metals should
be usually used and drastic requirements are imposed on
the conditions of this reaction.
The purpose of this work is to study the influence of
the structure of carbonyl compounds and their derivaꢀ
tives on the regularities and direction of the reaction.
Hydrazones 2a—h of substituted benzaldehydes and
acetophenones were chosen for the study. Substrates with
both electronꢀdonating and electronꢀwithdrawing subꢀ
stituents in the aromatic cycle were studied. In the series
of hydrazones 2a—h, steric shielding of the hydrazone
group increases on going from aldehydes to alkyl aryl
ketones and further to diaryl ketones, which should deꢀ
crease its reactivity. Unlike the previously studied types of
hydrazones, compounds 2g and 2h have two aromatic
substituents at the carbonyl group. The behavior of such
substrates has not previously been studied under the COR
conditions.
Results and Discussion
We have recently found the novel catalytic olefination
reaction (COR) of carbonyl compounds 1. It has been
shown that Nꢀunsubstituted hydrazones 2 of aromatic alꢀ
dehydes can be transformed into dichloroalkenes 3 by the
treatment with ССl4 in the presence of catalytic amounts
of copper(I) chloride (Scheme 1).4—6 The reaction is acꢀ
companied by nitrogen evolution, and alkenes 3 are
formed along with symmetrical azines 4.
The further studies showed that the discovered reacꢀ
tion is of general character, and a wide scope of comꢀ
pounds with the general formula CHal2XY can be used as
olefination agents. For example, CCl4,4—7 CHBr3,7,8
Hydrazones 2a—h were treated with CCl4 chosen as
model polyhaloalkane under the standard olefination conꢀ
ditions.5 The reaction was carried out in DMSO using
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 469—474, February, 2003.
1066ꢀ5285/03/5202ꢀ492 $25.00 © 2003 Plenum Publishing Corporation

Catalytic olefination of carbonyl compounds
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
493
Scheme 1
VN (% of theor.)
2
18
16
14
12
10
8
2a
2b
2c
2d
2e
2f
6
2g
2h
4
2
20
40
60
80
τ/s
Fig. 1. Nitrogen evolution upon treatment of hydrazones 2a—h
with CCl4 (initial step of the reaction).
shielding of the hydrazone group also affects the reaction
rate, although to a less extent. For example, for hydrꢀ
azone 2h the complete conversion occurs approximately
within 30 days (TLC monitoring), while the complete
conversion of hydrazones 2a—g takes 3—24 h. This beꢀ
havior of hydrazone 2h can be attributed to both the greatꢀ
est steric shielding of the hydrazone group in this series of
substrates and a change in the electronic factors. Based
on the obtained experimental data, we found that the rate
of transformations of the hydrazones under the COR conꢀ
ditions decreases in the series 2a ≈ 2d > 2b ≈ 2c ≈ 2e ≈
≈ 2f >> 2g >> 2h.
R2 = H (a, b, c), Me (d, e, f); R3 = MeO (a, d), Cl (b, e), NO2 (c, f)
We examined in detail the products of transformaꢀ
tion of hydrazones 2a—h under the reaction conditions
(Table 1). In the case of hydrazones 2a—f, the total yield
of two expected products, viz., corresponding dichloroꢀ
alkenes 3 and symꢀazines 4, is almost 100%. However,
already for fluorenone hydrazone 2g, "anomalous" prodꢀ
5 equiv. of CCl4 in the presence of a base (aqueous amꢀ
monia) and 10 mol.% of CuCl as a catalyst. By analogy to
the earlier studies of catalytic olefination, we can assume
that the main products of transformation of hydrazones 2
are the corresponding dichloroalkenes 3 and symmetrical
azines 4 of carbonyl compounds.
Table 1. Yields (%) of the products of transformation of
hydrazones 2a—h under the reaction conditions
Catalytic olefination is accompanied by nitrogen evoꢀ
lution. The reactivity of substrates toward CCl4 can be
estimated by measuring the rate of nitrogen evolution. It
turned out (Fig. 1) that in the series of substrates of the
same type, viz., hydrazones 2a—c of paraꢀsubstituted
benzaldehydes and hydrazones 2d—f of paraꢀsubstituted
acetophenones, the enhancement of the donating ability
of the substituent in the aromatic ring increases the rate of
nitrogen evolution. For example, in the case of hydrazones
2a and 2d containing the methoxy group, the rate of nitꢀ
rogen evolution is maximal. It is seen (see Fig. 1) that in
the pairs of substrates 2a and 2d, 2b and 2e, 2c and 2f the
rates of gas evolution are close. This fact suggests that in
the series of aromatic aldehydes and aryl methyl ketones
the electronic factors exert the highest effect on the rate
of the reaction of hydrazones with polyhaloalkanes. Steric
Hydrꢀ
azone
Products
"Anomalous"
products
3a—h
4a—h 3a—h + 4a—h
2a
2b
2c
2d
2e
2f
49
74
79
88
82
58
37
44
19
17
7
14
32
0
93
93
96
95
96
90
37
—
—
—
1d*
1e,* 7e,* 8e*
1f*
6g (21), 7g (7),
1g,* 8g*
1h (37), 8h*
2g
2h
0
0
0
* The product was detected in trace amounts by GLCꢀMS specꢀ
trometry.

494
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
Korotchenko et al.
ucts, viz., 9ꢀchlorofluorene (6g) and 9,9´ꢀbifluorenylidene
(7g), were obtained along with the expected 9ꢀdichloroꢀ
methylenefluorene (Scheme 2). The corresponding fluoreꢀ
none azine 4g was not isolated.
the same standard conditions using GLCꢀMS spectroꢀ
metry, which detects trace amounts of substances. In the
case of aldehyde hydrazones (hydrazones 2a—с), only
products of COR 3a—c and 4a—c were found in the reacꢀ
tion mixtures. On going to acetophenone hydrazones
(hydrazones 2d—f), the main products were found along
with "anomalous" products: ketones 1d—f, stilbenes 7d—f,
which are formal products of doubling the corresponding
carbenes, and 1ꢀarylethanols 8d—f. In the case of hydrꢀ
azone 2g, the formations of target alkene 3g and "anomaꢀ
lous" products compete. For substrate 2h, no products of
COR were found in the reaction mixture. However, oxyꢀ
genꢀcontaining products, viz., corresponding ketones 1g,h
and alcohols 8g,h, were detected in the GLCꢀMS spectra
of the reaction mixtures in the case of 2g and 2h.
Scheme 2
Thus, the gradual transition from the substrates that
enter into COR to the substrates involved in alternative
reactions occurs in the studied series of hydrazones of
aromatic carbonyl compounds 2a—h.
We have previously6—10 proposed the catalytic cycle
describing COR (Scheme 3). In the first step, hydrazone 2
is oxidized by CuII to form the corresponding diazoalꢀ
kane 5. The involvement of diazoalkanes as intermediates
of COR has reliably been proved earlier.5 The subsequent
copperꢀcatalyzed decomposition of diazoalkane 5 affords
copperꢀcarbene complex I, which is the key intermediate
of the reaction. The reactions of complex I with polyhaloꢀ
alkanes results in the corresponding dihaloalkenes 3 with
regeneration of CuII and beginning of a new catalytic
cycle. In addition to this, complex I reacts with diazoꢀ
alkane 5 to form azine 4.
In the case of benzophenone hydrazone 2h (at its 100%
conversion), the only isolated product was benzophenone
1h (37% yield), which forms due to the oxidative cleavage
of the С=N bond under the reaction conditions.11
Thus, in the case of hydrazones 2a—f, the results agree
well with the assumption, whereas the behavior of hydrꢀ
azones 2g and 2h containing two aromatic substituents
does not obey the general scheme of COR.
To reveal the dependence of the composition of the
formed products on the substrate structure, we studied
the products of transformation of hydrazones 2a—h under
The formation of products 1 and 6—8 from hydrazones
2g,h under the reaction conditions cannot be explained
by the earlier proposed catalytic cycle. We assumed that
Scheme 3

Catalytic olefination of carbonyl compounds
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
495
the difference observed for the behavior of the substrates
can be attributed to a change in the steric factors and
stability of intermediate diazoalkanes 5. Diazoalkanes are
widely used in the synthetic organic chemistry, and their
properties are described in fundamental reviews and
monograph.12 The published data on the enhancement of
the thermostability of diazoalkanes and their stability
toward decomposition in acidic media in the series
alkyldiazomethanes < PhC(Me)=N2 < PhCH=N2 <<
<< P h 2C=N2 < diazofluorene and on the stabilization of
aryldiazoalkanes with electronꢀwithdrawing substituents
in the aromatic cycle are available.12 At the same time,
steric shielding of the diazo group increases in the series
of diazoalkanes 5 formed from hydrazones studied in this
work: 4ꢀСlC6H4C(H)=N2 (5b) < 4ꢀСlC6H4C(Me)=N2
(5e) << diazofluorene (5g) < Ph2C=N2 (5h). According
to the mechanism proposed by us for the transformation
of hydrazones 2, nitrogen is evolved in the reaction meꢀ
dium upon diazoalkane decomposition. The data on the
rate of gas evolution can thus correlate with the stability
of diazoalkanes under these conditions. As can be seen in
Table 1, an increase in the amount of the "anomalous"
products correlates with an increase in the stability of
diazoalkanes.
To establish the mechanism of formation of products
1, 6—8, we scrutinized the transformations of diazoalkanes
in the reaction medium for the most stable diazofluorene
5g and diphenyldiazomethane 5h. With this purpose, we
studied the decomposition of preliminarily prepared
diazofluorene 5g (Table 2) and diphenyldiazomethane 5h
under standard conditions (DMSO as solvent, and aqueꢀ
ous ammonia as base).
We found that diazofluorene and diphenyldiazoꢀ
methane slowly decompose with nitrogen evolution upon
the treatment with CCl4 in a DMSO solution in the presꢀ
ence of aqueous ammonia even in the absence of CuCl.
Note that the decomposition of diazofluorene 5g occurs
several times more rapidly than the decomposition of
diphenyldiazomethane 5h (according to the data on gas
evolution), i.e., under these conditions, diphenyldiazoꢀ
methane is more stable than diazofluorene.
These data show that oxygenꢀcontaining products can
form due to noncatalytic transformations of diazofluorene
in the reaction mixture. It is known12,13 that alcohols and
carbonyl compounds are formed from diazoalkanes due
to the interaction of the latter with water and oxidants
(DMSO, oxygen) present in the system. It is likely that
similar processes also occur in this case.
Copper(I) chloride catalyzes the decomposition of
diazofluorene 5g in DMSO in the presence of aqueous
ammonia and in the absence of CCl4. 9,9´ꢀBifluorenylꢀ
idene 7g was isolated as the sole product, which agrees
with the published data14 on the formation of 9,9´ꢀbiꢀ
fluorenylidene due to the decomposition of diazoalkane
5g catalyzed by compounds of various transition metals,
such as copper, nickel, gold, and others.
9ꢀChlorofluorene 6g forms upon diazofluorene 5g deꢀ
composition as a result of the elimination of the halogen
atom from CCl4 in the presence of CuCl. Halogen atom
elimination is characteristic of carbenes generated from
diazoalkanes thermally, photochemically, or by transiꢀ
tion metal catalysis.12,15 For example, it is described15
that photolysis of diazofluorene in chlorineꢀcontaining
solvents is followed by the chlorine atom transfer and
formation of 9ꢀchlorofluorene.
We also studied the decomposition of diazofluorene
5g under the same conditions in the presence of the copꢀ
per catalyst and CCl4. For this process, unlike hydrazone
transformations under similar conditions, fluorenone 1g
(60%) is the main product, and 9,9´ꢀbifluorenylidene 7g
(10%) additionally forms. Dichloroalkene 3g and
9ꢀchlorofluorene 6g are formed only in trace amounts.
These data agree completely with our proposal that
diazoalkanes are involved in the formation of the "anomaꢀ
lous" products and are evident for the effect of the kinetic
parameters of the reaction. An increase in the stability of
diazoalkanes 5 under these conditions and, as a conseꢀ
quence, a decrease in the rate of copperꢀcarbene complex
formation result in the escape of diazoalkane from the
catalytic cycle of COR and participation in side reactions,
which are both catalyzed by copper salts and noncatalyzed.
These data allow us to supplement the catalytic cycle
describing COR by another direction: transformation of
diazoalkanes into byꢀproducts (Scheme 4).
These results evidence that fluorenone exists at the
boundary of COR application in this series of carbonyl
compounds. This specific feature of fluorenone is very
useful for analysis of the effect of various factors on the
competition between COR and side reactions of intermeꢀ
diately formed diazofluorene. We assumed that the enꢀ
hancement of the reactivity of polyhaloalkane should reꢀ
sult in an increase in the rate of its reaction with the
Fluorenone 1g (45%) and fluorenol 8g (30%) are the
main reaction products of diazofluorene 5g transformaꢀ
tion (see Table 2). Benzophenone 1h (41%) was the only
product isolated in the case of diphenyldiazomethane 5h.
Table 2. Yields (%) of the products of decomposition of diazoꢀ
fluorene 5g
Reaction conditions
Reaction products
1g 7g 8g 3g and 6g
CCl4 (5 equiv.), without CuCl
CuCl (10 mol.%), without CCl4
45
0
0
21
30
0
—
—
CuCl (10 mol.%), CCl4 (5 equiv.) 60 10
0
Traces

496
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 2, February, 2003
Korotchenko et al.
Scheme 4
Experimental
Н NMR spectra were recorded on a Varian VXRꢀ400
1
spectrometer (working frequency 400 MHz) in СDCl3 using
Me4Si as internal standard. The reaction was studied by TLC on
Merck 60F254 plates. Column chromatography was carried out
on Merck silica gel (63—200 mesh). GLCꢀMS spectra were
obtained on an HP5890 instrument (EI, 70 eV) using a 5989xꢀG
detector.
Hydrazones 2a—с,5 2d—f,7,16 2g,17 and 2h 18 were syntheꢀ
sized from the corresponding carbonyl compounds according to
published procedures. Diazofluorene 5g 19 and diphenyldiazoꢀ
methane 5h 18 were prepared by oxidation of the corresponding
hydrazones.
Reactions of hydrazones 2a—h with CCl4 (general proceꢀ
dure). Aqueous ammonia (1.80 mL) and freshly purified CuCl 20
(50 mg, 0.5 mmol, 10 mol.%) and then one portion of CCl4
(2.41 mL, 25 mmol) were added to a solution of freshly syntheꢀ
sized hydrazone 2a—h (5 mmol) in DMSO (5 mL) at 20 °C. The
volume of the evolved gas was measured using a gas burette.
After the end of the reaction (TLC monitoring), the reaction
mixture was poured into water (500 mL). The reaction products
were extracted with CH2Cl2 (3×50 mL), the combined extracts
were dried with Na2SO4, the solvent was evaporated, and
the reaction products were isolated using column chromatoꢀ
graphy (SiO2).
The reaction of hydrazone 2g with CBr4 was performed
similarly using a solution of CBr4 (8.30 g, 25 mmol) in DMSO
(20 mL).
Decomposition of diazofluorene 5g. Freshly prepared diazoꢀ
fluorene (0.96 g, 5 mmol) was dissolved in DMSO (5 mL). The
resulting solution was added by concentrated (25%) aqueous
ammonia (1.80 mL). The further treatment was carried out
using one of the following methods.
copperꢀcarbene complex and, correspondingly, in the
competitive increase in the amount of the COR products
over that of byꢀproducts. It has previously7 been shown
that the reactivity of CBr4 is much higher than that of
CCl4 in the series of substrates of the same type under the
COR conditions. To check the hypothesis about the critiꢀ
cal role of the copperꢀcarbene complex in the reactions
with halohydrocarbons, we treated fluorenone hydrazone
2g with CBr4 under similar conditions. It turned out that
the yield of dihaloalkene increased almost 1.5ꢀfold.
9ꢀDibromomethylenefluorene 9 and bifluorenylidene 7g
are the main products of this reaction (Scheme 5), which
additionally confirms the advanced hypothesis.
Scheme 5
A. One portion of CCl4 (2.41 mL, 25 mmol) was added to
the resulting solution at 20 °C.
B. The solution was added by one portion of CuCl (50 mg,
0.5 mmol, 10 mol.%) at 20 °C.
C. The solution was added by one portion of CCl4 (2.41 mL,
25 mmol) and immediately by CuCl (50 mg, 0.5 mmol,
10 mol.%) at 20 °C.
After the end of nitrogen evolution, the reaction mixture
was treated as described for hydrazones.
Thus, the relation between the structure of the starting
carbonyl compound and its derivatives and the nature of
the reaction products was revealed from the experimental
data. The ratio of rates of formation and consumption of
diazoalkane 5 in the catalytic COR cycle and outside the
latter plays the determining role, and the competition of
these directions depends on the reactivity of diazoalkane.
In the case of formation of lowly stable diazoalkanes from
hydrazones of aromatic aldehydes and alkyl aryl ketones,
COR is the main process.4—10 Diazofluorene exhibits
the intermediate type of stability, due to which both
olefination and noncatalytic transformations of this
diazoalkane occur. In the case of diphenyldiazomethane,
the COR cycle does not occur. These data substantially
deepen our knowledge about the nature of the reaction
under study and suggest that COR can be applied to variꢀ
ous aromatic aldehydes and alkyl aryl ketones.
Freshly synthesized diphenyldiazomethane 5h (0.97 g,
5 mmol) was decomposed according to method A described for
diazofluorene 5g.
The spectroscopic and physical characteristics of syntheꢀ
sized compounds 1g,h,20 3a—c,5 3d—f,7 3g,21 4a—c,5 4d,22 4e,16
4f,7 6g,23 7g,24 8g,25 and 9 21 agree with the published values.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 00ꢀ03ꢀ
32760, 00ꢀ03ꢀ32763, and 03ꢀ03ꢀ32052a).
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62, 3305.
Received July 4, 2002;
in revised form October 18, 2002