Electrocatalytic transformation of malononitrile and cycloalkylidenemalononitriles into spirobicyclic and spirotricyclic compounds containing 1,1,2,2-tetracyanocyclopropane fragment

Article abstract of DOI:10.1023/B:RUCB.0000011884.08799.a7

Electrolysis of malononitrile and cycloalkylidenemalononitriles in EtOH in an undivided cell in the presence of NaBr affords spirobicyclic compounds containing a 1,1,2,2-tetracyanocyclopropane fragment in 50-88% yields.

Full text of DOI:10.1023/B:RUCB.0000011884.08799.a7

Russian Chemical Bulletin, International Edition, Vol. 52, No. 10, pp. 2235—2240, October, 2003
2235
Electrocatalytic transformation of malononitrile
and cycloalkylidenemalononitriles into spirobicyclic and spirotricyclic
compounds containing 1,1,2,2ꢀtetracyanocyclopropane fragment
M. N. Elinson,ꢀ S. K. Fedukovich, A. N. Vereshchagin, A. S. Dorofeev, D. E. Dmitriev, and G. I. Nikishin
N. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (095) 135 5328. Eꢀmail: elinson@ioc.ac.ru
Electrolysis of malononitrile and cycloalkylidenemalononitriles in EtOH in an undivided
cell in the presence of NaBr affords spirobicyclic compounds containing a 1,1,2,2ꢀtetraꢀ
cyanocyclopropane fragment in 50—88% yields.
Key words: electrolysis, electrocatalytic transformation, malononitrile, cycloalkylꢀ
idenemalononitriles, mediators, spirobicyclic compounds.
Malononitrile is a commonly known and widely used
reagent in the synthesis of pharmaceuticals, pesticides,
fungicides, solvatochromic dyes, and organic semiconꢀ
ductors.1
electrooxidation of organic compounds. Among numerꢀ
ous mediators, the halide anion—halogen redox system
is one of the most promising for the use in organic synꢀ
thesis.
The unique reactivity of malononitrile promotes more
extensive and diverse applications of this reagent in orꢀ
ganic chemistry even compared to the use of other known
CHꢀacids such as malonic and cyanoacetic esters.
Nevertheless, little is known about the electrochemiꢀ
cal transformations of malononitrile. Although electroꢀ
oxidation of the malonic ester anion was performed back
in the 19th century,2 no studies devoted to electroꢀ
oxidation, electroreduction, or any other electrochemical
transformation of malononitrile is mentioned in the
monographs or reviews on electroorganic chemistry3,4 or
reviews on the use of malononitrile in organic chemꢀ
istry.5,6
Previously, in our studies dealing with electroꢀ
catalytic oxidation of organic compounds in the presence
of alkali metal halides as mediators, we performed elecꢀ
trochemical transformations of aldehydes and malonoꢀ
nitrile14 or cyanoacetic acid15 to functionally substiꢀ
tuted cyclopropanes and the transformation of ketones
and malononitrile to 3,3ꢀdisubstituted tetracyanocycloꢀ
propanes.16,17
The lastꢀmentioned reaction is an electrochemical
analog of the Wideqvist reaction, i.e., the reaction of
bromomalononitrile with ketones in the presence of stoꢀ
ichiometric amounts of sodium iodide.18 In the electroꢀ
chemical version, bromomalononitrile is replaced by
malononitrile and catalytic amounts of sodium bromide,
which is fully regenerated during the process. However,
to prepare large amounts of tetracyanocyclopropanes in
the electrochemical Wideqvist reaction, one should emꢀ
ploy a threeꢀ to fourꢀfold excess of the ketone. In addiꢀ
tion, it was found unexpectedly that in the case of cycloꢀ
hexanone, this electrochemical process cannot be stopped
after the formation of tetracyanocyclopropane; coꢀelecꢀ
trolysis of cyclohexanone and malononitrile under these
conditions furnishes 2ꢀaminoꢀ1,5ꢀdicyanoꢀ4,4ꢀdiethoxyꢀ
6,6ꢀpentamethyleneꢀ3ꢀazabicyclo[3.1.0]hexꢀ2ꢀene (1)17
in 62% yield (Scheme 1).
As far as we know, apart from the studies performed by
our research group, only one relevant publication can be
mentioned, namely, one dealing with electrochemical
anodic arylation of malononitrile.7
The use of alkylidenemalononitriles, which contain
an activated double bond together with the reactive CN
group (see reviews8,9), is also quite common in orꢀ
ganic synthesis. These reagents are usually prepared
from malononitrile and carbonyl compounds by the
Knoevenagel reaction.10 Known reactions in the electroꢀ
chemistry of alkylidenemalononitriles include cathodic
hydrogenation11 and cyclodimerization of arylideneꢀ
malononitriles,12 and cathodic addition of alkylideneꢀ
malononitriles to acrylonitrile and methyl acrylate.13
In recent decades, mediators and mediator systems
have been successfully used for electroreduction and
Recently, we proposed a new approach to the syntheꢀ
sis of functionally substituted cyclopropanes, namely,
coꢀelectrolysis of CHꢀacids with activated olefins19,20
(Scheme 2).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2117—2121, October, 2003.
1066ꢀ5285/03/5210ꢀ2235 $25.00 © 2003 Plenum Publishing Corporation

2236
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 10, October, 2003
Elinson et al.
Scheme 1
In this study, we used this approach to prepare
tetracyanoꢀsubstituted spirobicyclic and spirotricyclic
compounds containing a cyclopropane fragment from
cycloalkylidenemalononitriles 2a—d, 3a—c, and 4a,b and
malononitrile. Compounds of this type are also promising
for the synthesis of natural biologically active products22,23
and upꢀtoꢀdate drugs24 (Scheme 4).
Scheme 4
i. Electrolysis, NaBr, EtOH.
n = 1 (a), 2 (b), 3 (c), 8 (d)
Scheme 2
R = Me (a), Ph (b), But (c)
Z = COOMe, CN
i. Electrolysis, NaHal, MeOH; Hal = Br, I.
The coꢀelectrolysis of alkylidenecyanoacetic and maꢀ
lonic esters carried out within the framework of this apꢀ
proach resulted in stereoselective synthesis of (E)ꢀisoꢀ
mers of trialkyl 3ꢀsubstitutedꢀ2ꢀcyanocyclopropaneꢀ1,1,2ꢀ
tricarboxylates21 (Scheme 3).
Scheme 3
n = 1 (a), 2 (b)
i. Electrolysis, NaBr, EtOH.
The first phase included development of a method for
the preparation of 3,3ꢀpentamethyleneꢀ1,1,2,2ꢀtetraꢀ
cyanocyclopropane 5b from cyclohexylidenemalononitrile
2b and malononitrile (Table 1). It is noteworthy that elecꢀ
trolysis of malononitrile in the presence of excess cycloꢀ
hexanone yielded tricyclic compound 1 as the only
product.17
i. Electrolysis, NaBr, R2OH.

Spirobicyclics with cyclopropane fragment
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 10, October, 2003
2237
Table 1. Coꢀelectrolysis of malononitrile and cyclohexylꢀ
idenemalononitrilea
Table 2. Coꢀelectrolysis of malononitrile and cycloalkylideneꢀ
malononitriles
Run
Qb
/F mol–1
T/°С
2b/malononitrile,
Cycloꢀ
propane 5b,
yield (%)c
Cycloalkylideneꢀ
malononitrile
n
R
Qa
/F mol–1
Cyclopropane,
yield (%)b
mol/mol
2a
2b
2c
2d
1
2
3
8
—
—
—
—
3
3
3
3
5a, 65
5b, 82
5c, 87
5d, 69
1
2
3
4 d
5 d
6 d
2.0
2.0
2.5
2.2
2.5
3.0
5
1 : 1
1 : 1
1 : 1
2 : 3
2 : 3
2 : 3
51
65
48
69
84
93 (82)e
20
20
20
20
20
3a
—
Me
3
6a, 63
3b
3c
4a c
4b c
—
—
1
Ph
But
—
3
3
4
4
6b, 61
6c, 88
7a, 57
7b, 51
Note: a 10 mmol of malononitrile, 10 mmol of 2b, 5 mmol of
2
—
NaBr, 20 mL of EtOH, Fe cathode, C anode, current density
100 mA cm–2
.
Note: a Quantity of electricity.
b Quantity of electricity.
b The yield is related to the isolated cyclopropane.
c According to H NMR data.
1
c The cycloalkylidenemalononitrile/malononitrile ratio = 1 : 2.
d 15 mmol of malononitrile.
e Relative to isolated 5b.
pounds containing a 1,1,2,2ꢀtetracyanocyclopropane
fragment.
It follows from the data of Table 1 that a decrease in
the temperature to 5 °C entails some decrease in the
yield of compound 5b. With the use of an equimolar
2b/malononitrile ratio, passing a quantity of electricity
exceeding the theoretical value (2 F/mol) results in a
decrease in the yield of compound 5b (see Table 1, run 3);
in addition, tricyclic pyrroline 1 is formed (yield 17%)
together with 5b. As shown by NMR analysis of the reacꢀ
tion mixtures obtained in runs 2 and 3 (see Table 1), at
the instant of full conversion of malononitrile, the degree
of conversion of 2b is only 60—65%. Therefore, the subꢀ
sequent experiments (see Table 1, runs 4—6) were carried
out with a 1.5ꢀfold excess of malononitrile. Under the
optimal conditions, tetracyanocyclopropane 5b was obꢀ
tained in 93% yield at full conversion of 2b and 95%
conversion of malononitrile.
The reactions that take place at the electrodes during
the joint electrochemical transformation of malononitrile
and cycloalkylidenemalononitriles are the usual reactions
for the mediator system involved (bromide anion—moꢀ
lecular bromine), which include the formation of broꢀ
mine at the anode and hydrogen evolution at the cathode
with generation of ethoxide ions
anode: 2 Br– – 2e
Br2,
2 EtO– + H2.
cathode: 2 EtOH + 2e
The ethoxide ion reacts with malononitrile in the soꢀ
lution to give the malononitrile anion:
–
CH2(CN)2 + EtO–
CH(CN)2 + EtOH.
Under the conditions of choice for the preparation of
tetracyanocyclopropane 5b from malononitrile and 2b (see
Table 1, run 6), we carried out coꢀelectrolysis of cycloꢀ
alkylidenemalononitriles 2a—d, 3a—c, 4a,b, and malonoꢀ
nitrile (Table 2).
The reaction of the malononitrile anion with bromine
results in bromomalononitrile:
–
CH(CN)2 + Br2
CH(Br)(CN)2 + Br–.
It follows from the data of Table 2 that the electrolysis
conditions optimal for 2b are also applicable to cycloꢀ
alkylidenemalononitriles 2a,c,d with various ring size and
to substituted cyclohexylidenemalononitriles 3a—c.
In the case of compounds 4a,b containing a fused
benzene ring, for obtaining cyclopropanes 7a,b in a subꢀ
stantial yield, the amount of malononitrile needs to be
increased to a twoꢀfold excess and the quantity of elecꢀ
The subsequent processes that take place in the soluꢀ
tion were considered in relation to the coꢀelectrolysis of
malononitrile and cyclohexylidenemalononitrile 2b.
The bromomalononitrile anion generated under the
action of the ethoxide ion adds to the double bond of
nitrile 2b to give cyclopropane 5b (pathway A, Scheme 5):
Cyclopropane 5b can also be produced via a different
reaction pathway B, namely, the Michael addition of the
malononitrile anion to 2b and the subsequent brominaꢀ
tion and cyclization (Scheme 6).
tricity, to 4 F mol–1
.
Relying on the above results (and the data on the
mechanism of the electrochemical version of the Wideqvist
reaction15,17), we propose a mechanism for the electroꢀ
chemical transformation of malononitrile and cycloalkylꢀ
idenemalononitriles into spirobicyclic and ꢀtricyclic comꢀ
Reaction pathway B is embodied in the coꢀelectrolysis
of malonic and alkylidenemalonic esters19 or malonic and
alkylidenecyanoacetic esters.21 When the quantity of elecꢀ
tricity passed was insufficient for completion of the proꢀ

2238
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 10, October, 2003
Elinson et al.
Scheme 5
tion of ethoxide ions. As a consequence, unlike the
electrocatalytic version of the Wideqvist reaction,17 in
the case of coꢀelectrolysis of malononitrile and comꢀ
pound 2b, cyclopropane 5b was prepared in a yield of
more than 90%.
Thus, coꢀelectrolysis of malononitrile and cyclic
alkylidenemalononitriles carried out in an undivided cell
in the presence of a mediator provided a oneꢀstep syntheꢀ
sis of spirobicyclic and spirotricyclic compounds containꢀ
ing a 1,1,2,2ꢀtetracyanocyclopropane fragment. Using
techniques of classical organic chemistry, this transforꢀ
mation could be accomplished only as a twoꢀstep process
comprising (i) halogenation of malononitrile and (ii) adꢀ
dition of halomalononitrile to the double bond of cyclic
alkylidenemalononitrile followed by cyclization.25
The only electrochemical analog of this process is elecꢀ
trochemical transformation of ketones and malononitrile
into substituted tetracyanocyclopropanes.17 However, this
requires a considerable excess of ketone, which is a sigꢀ
nificant drawback, especially in those cases where the
ketone is a more expensive chemical than malononitrile.
In addition, in some cases, electrolysis performed in an
excess of a ketone cannot be stopped after the formation
of tetracyanocyclopropane.
Scheme 6
The electrocatalytic transformation of malononitrile
and cyclic alkylidenemalononitriles into spirobicyclic and
spirotricyclic compounds containing a 1,1,2,2ꢀtetraꢀ
cyanocyclopropane fragment was accomplished within the
framework of development of a new approach to the synꢀ
thesis of functionally substituted cyclopropanes by coꢀ
electrolysis of CHꢀacids and activated olefins.19—21
The electrochemical route we developed for the transꢀ
formation of malononitrile and cyclic alkylidenemalonoꢀ
nitriles into spirobicyclic and spirotricyclic compounds
containing a 1,1,2,2ꢀtetracyanocyclopropane fragment is
convenient and economic. The use of common and readily
available reagents, inexpensive equipment, and undivided
cells are advantages of this method. The procedures of
electrolysis and product isolation are facile and conveꢀ
nient when implemented both in the laboratory and on a
pilot scale.
cess, the reaction mixtures were found to contain the
corresponding Michael adducts.
When coꢀelectrolysis of malononitrile and unsaturꢀ
ated nitrile 2b was carried out under conditions of run 6
(see Table 1) with 0.5, 1.0, and 2.0 F mol–1 of electricity,
the corresponding Michael adduct, namely, 2ꢀ(1ꢀdicyanoꢀ
methylcyclohexyl)malononitrile, was not detected in
the electrolysis products. Only the starting compounds
and cyclopropane 5b were found in the reaction mixture
in 21, 35, and 68% yields, respectively. These results sugꢀ
gest that occurrence of the reaction by pathway B is unꢀ
likely.
Experimental
1
H NMR spectra were recorded on Bruker WMꢀ250 and
Bruker AMꢀ300 instruments operating at 250 and 300 MHz,
respectively, for solutions in CDCl3. The NMR chemical shifts
are given in the δ scale and referred to Me4Si. The malononitrile
used was a commercial preparation (Aldrich).
Cyclohexylidenemalononitriles were prepared by
Knoevenagel condensation of appropriate ketones (commercial
preparations, Merck and Aldrich) with malononitrile.26
Cyclopentylidenemalononitrile (2a),25 yield 78%, b.p.
142—145 °C (16 Torr).
It should be emphasized that excess malononitrile in
the reaction mixture prevents the subsequent electroꢀ
catalytic transformation of cyclopropane 5b into biꢀ
cyclic pyrroline 1 by decreasing the current concentraꢀ

Spirobicyclics with cyclopropane fragment
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 10, October, 2003
2239
Cyclohexylidenemalononitrile (2b),25 yield 86%, b.p.
160—162 °C (18 Torr).
Calculated (%): C, 72.15; H, 6.81; N, 21.04. 1H NMR
(DMSOꢀd6), δ: 0.89 (s, 9 H, Me); 1.21 (m, 2 H); 1.25 (m, 1 H);
1.66, 1.97, 2.24 (all m, each 2 H). 13C NMR (DMSOꢀd6), δ:
24.2 (CH2); 25.9 (C); 27.3 (CH3); 28.1 (C); 29.5 (CH2); 32.1
(C); 45.7 (CH); 109.7, 109.9 (CN).
1,1,2,2ꢀTetracyanoꢀ4,5ꢀbenzospiro[2.4]heptane (7a), m.p.
198—200 °C. Found (%): C, 73.94; H, 3.43; N, 22.83. C15H8N4.
Calculated (%): C, 73.76; H, 3.30; N, 22.94. 1H NMR
(DMSOꢀd6), δ: 2.65 (t, 2 H, J = 7 Hz); 3.20 (t, 2 H, J = 7 Hz);
7.35—7.60 (m, 4 H, Ar). 13C NMR (DMSOꢀd6), δ: 27.5 (C);
29.1 (CH2); 31.9 (CH2); 52.1 (C); 109.4, 110.0 (CN); 122.8,
125.4, 125.6, 130.7, 131.6, 148.2 (all Ar).
1,1,2,2ꢀTetracyanoꢀ4,5ꢀbenzospiro[2.5]octane (7b), m.p.
173—175 °C (Ref. 25: m.p. 167—170 °C). 1H NMR (CDCl3), δ:
2.15, 2.42, 3.03 (all m, 2H each); 7.20—7.60 (m, 3 H); 7.85
(m, 1 H). 13C NMR (DMSOꢀd6), δ: 18.7 (CH2); 27.6 (C); 28.5,
30.2 (CH2); 45.5 (C); 109.9, 110.0 (CN); 124.8, 125.9, 126.9,
129.5, 129.9, 141.1 (all Ar).
Cycloheptylidenemalononitrile (2c),27 yield 75%, b.p.
169—172 °C (16 Torr).
Cyclododecylidenemalononitrile (2d),28 yield 76%, b.p.
218—219 °C (11 Torr).
4ꢀMethylcyclohexylidenemalononitrile (3a),29 yield 85%, b.p.
163—166 °C (18 Torr).
4ꢀPhenylcyclohexylidenemalononitrile (3b), yield 92%, m.p.
101—103 °C. Found (%): C, 79.84; H, 6.13, N, 12.38. C15H14N2.
Calculated (%): C, 81.05; H, 6.35; N, 12.60. 1H NMR (CDCl3),
δ: 1.78, 2.29, 2.55 (all m, each 2 H); 2.92 (m, 1 H); 3.21 (m, 2 H);
7.18—7.50 (m, 5 H, Ph).
4ꢀtertꢀButylcyclohexylidenemalononitrile (3c), yield 83%,
m.p. 84—85 °C (Ref. 30: m.p. 82—83 °C).
2,3ꢀDihydroꢀ1Hꢀindenꢀ1ꢀylidenemalononitrile (4a), yield
72%, m.p. 147—149 °C (Ref. 25: m.p. 147—150 °C).
3,4ꢀDihydroꢀ2Hꢀnaphthalenꢀ1ꢀylidenemalononitrile (4b), yield
65%, m.p. 107—108 °C (Ref. 25: m.p. 108—109 °C).
Electrolysis (general procedure). A solution of malononitrile
(10—20 mmol), cycloalkylidenemalononitrile (10 mmol), and
NaBr (5 mmol) in 20 mL of EtOH was subjected to electrolysis
in an undivided cell equipped with a C anode and a Fe cathode
(the electrode area was 5 cm2) at 20 °C and at a constant current
density equal to 100 mA cm–2; the quantities of electricity passed
are given in Tables 1 and 2. The tetracyanocyclopropane preꢀ
cipitate was filtered off and washed with cold EtOH. The filtrate
was concentrated and extracted with chloroform. Chloroform
was evaporated and the residue (Table 1, runs 1—6) was anaꢀ
lyzed by 1H NMR spectroscopy and crystallized from an acꢀ
etone—hexane mixture to isolate an additional amount of
tetracyanocyclopropane from the reaction mixture.
1,1,2,2ꢀTetracyanospiro[2.4]heptane (5a), m.p. 250—251 °C
(Ref. 17: m.p. 250—251 °C). 1H NMR (DMSOꢀd6), δ: 1.90,
2.05 (both m, 4 H).
This work was financially supported by the Russian
Foundation for Basic Research (Projects No. 03ꢀ03ꢀ32068
and No. 03ꢀ03ꢀ06084) and by the Foundation for Leadꢀ
ing Scientific Schools (Project No. 2121.2003.3).
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Received May 15, 2003:
in revised form June 21, 2003