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Electrochemical Oxidation of Croconate Salts; Evidence of the Chemical Equivalence of the Carbonyl Oxygen Atom and the Dicyanomethylene Group.

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[Cu(CH3CN)CI2l2S2N2
can be isolated, which likewise contains neutral S2N2groups as bridging ligands[6bJ.
Received: December 18, 1980 [Z 150b IE]
revised: October 19, 1981
German version: Angew. Chem. 94 (1982) 646
[ I ] M. M. Labes, P. Love, L. F. Nichols, Chem. Rev. 79 (1979) 1.
121 a) R. L. Patton, W. L. Jolly, Inorg. Chem. 8 (1969) 1389; b) R. L. Patton,
K. N. Raymond, ibid. 8 (1969) 2426; c) R. L. Patton, W.L. Jolly, ibid. 8
(1969) 1392.
(31 One of the other products characterized by X-ray structure analysis is
S2N"AIChe.
[4] C. H. Chan, F. P. Olsen, Inorg. Chem. I1 (1972) 2836.
[S] Crystallographic data: P2,/n with 2 = 2 ; lattice constants: a = 8.964(4),
b=9.636(7), c=7.309(4) A,fl= 110.45(3)". Measurement with MoKa radiation, h=0.71069 A;structure refined to R=0.042 using all 1030 reflections obtained for 8525"; unit weights.
16) a) M. J. Cohen, A. F. Garito, A. J. Heeger, A. G. MacDiarmid, C. M. MiI
Am.
. Chem. Soc. 98 (1976) 3844; b)
kulski, M. S . Saran, J. Kleppinger, .
U. Thewalt, B. Miiller, 2. Anorg. Allg. Chem. 462 (1980) 214.
Electrochemical Oxidation of Croconate Salts ;
Evidence of the Chemical Equivalence of the
Carbonyl Oxygen Atom
and the Dicyanomethylene Group**
By Lawrence M. Doane and Alexander J. Fatiadi*
We have found that dicyanomethylene derivatives of
croconates [pseudooxocarbon compounds of general formula C,O,[C(CN),]',r,]~'l
are excellent models for testing
the concept of Wallenfeld2'on the chemical equivalence of
carbonyl oxygen and the dicyanomethylene group. Several
electrochemical studies have been carried out on aromatic
ox~carbon[~"'
and pseudooxocarbon compounds[3b1,but,
as yet, no reversible electron transfer reactions have been
reported for croconates. We report here: (i) on some cyclovoltammetric and ESR investigations of salts of the oxocarbon dianion, croconate 1, and the pseudooxocarbon
dianions[", 3-(dicyanomethylene)croconate 2, 3,5-bis(dicyanomethy1ene)croconate [croconate violet] 3, and 3,4,5tris(dicyanomethy1ene)croconate [croconate blue] 4 ;(ii) on
the first supporting electrochemical evidence for the postulated chemical equivalence of =O and =C(CN)2.
These results suggest a reversible one-electron oxidation of
the dianion to a stable radical anion followed by a reversible one-electron oxidation of the radical anion to the neutral molecule. At scan rates less than 20 mV/s, the more
positive cathodic wave of the dianion of 4 is very small, indicating a fast chemical reaction following the electron
transfer.
Thin-layer cyclic voltammetry provides further evidence
of the electrochemical reversibility and the stability of the
components of the redox couple[51.If scan reversal occurs
immediately after the first oxidation wave, essentially
equal anodic peak and reversal cathodic peak currents are
obtained for all dianions. The stability of the radical anion
is therefore no less than several minutes. Equal anodic and
cathodic peak currents are obtained at the second redox
couple of the dianion of 1. However, for dianions of 3 and
4, scan reversal after the second oxidation wave gives no
cathodic wave where reversible reduction of the neutral
species and the radical anion should each occur. For the
dianion of 2, three cathodic waves appear on reversal after
the second oxidation wave. Despite the results of cyclic
voltammetry this indicates that the neutral species [except
in the case of 11 undergo chemical transformations that
alter their cathodic waves.
E vs SCE
E vs SCE
1 2 . 5 pA
E''= 0.45
E Q =0.87
c
E''= 0.91
Fig. 1. Cyclovoltammograms of the dianions 1-4. For conditions see Table
1.
Table 1. Cyclovoltammometric data for the oxidation of croconates in DMF
us. SCE.-In the case of 1-4 two reduction steps were observed in
[a]. E
[Vl us. SCE): 1: -0.78, -1.21; 2 : -0.68, -0.88; 3:
each case (Epc,,Epc2
- 1.48, - 1.73; 4 : - 1.05, - 1.40. Except in the case of 4, the reductions were
reversible.
[v
~~~
D ia nion
1. Peak [b]
2. Peak [b]
1, R 1 = R 2 = R 3 = 0
2, R'=R'=O, R2=C(CN)2
of
Epa
E,
AE,
Em
Epc
3, R'=O, R'=R3=C(CN)2
4, R' = R2= R3=C(CN)2
1
0.26
0.36
0.48
0.58
0.20
0.06
0.06
0.07
0.07
0.51
0.72
0.90
1.00
0.44
0.66
0.83
0.94 [c]
2
Figure 1 shows cyclic voltammograms of the salts of 1-4
in N,N-dimethylformamide (DMF) containing 0.5 mol/L
tetraethylammonium perchlorate (TEAP); the peak potentials are given in Table 1. The general behavior of dianions of 1-4 is similar and is characterized by essentially
equal anodic and reversal cathodic peak currents and a
V.
peak potential separation (Ep,-Epc) of 0.06-0.07
[*I Dr. A. J. Fatiadi, Dr. L. M. Doane
[*'I
Organic Analytical Research Division, National Bureau of Standards
Washington, DC 20234 (USA)
We thank Dr. Ts-Tse Chang for assistance with the ESR experiments.
Angew. Chem. Inr. Ed. Engl. 21 (1982) NO. 8
3
4
0.30
0.41
0.51
0.07
0.06
0.07
0.06
[a] Concentration of TEAP 0.5 mol/L. Working electrode: gold disk with surface area of 0.079 cm' (in the case of 3: 0.051 cm'), sweep rate 0.05 V/s. [b]
E , and Epc are the anodic and cathodic peak potentials, respectively. [c]
Weak current on scan reversal.
Evidence of radical anion formation was obtained from
ESR spectra of dianion solutions electrooxidized in
DMSO at a potential approximately 100 mV more positive
than the peak potential of the first oxidation wave. The
ESR spectrum of the electrooxidized solution of the salt 3
shows a 9-line pattern, which possibly indicates interac-
0 Verlag Chemie GmbH, 6940 Weinheim. 1982
0570-0833/82/0808-0635 $02.50/0
635
tion of the unpaired electron with four magnetically equivalent nitrogen atoms (a" = 5.2 G). The half-life of the radical anion is ca. 100 minutes. Russell and Osuch@l have
shown that the ESR spectrum of the 1,2-cyclopentanesemidione radical is a symmetrical pentet; the unpaired electron is delocalized over the semidione group. The 9-line
pattern of the radical anion of 3 indicates that the unpaired electron is delocalized over the dicyanomethylene
group and the oxygen atoms.
Wallenfels[21 has proposed that the dicyanomethylene
group and the oxygen atom are chemically analogous and
that substitution of one group for the other merely reflects
a change in electronegativity. The potential of the first oxidation wave increases linearly by ca. 100 mV on addition
of each dicyanomethylene group [see 1-4 in Table 1 and
Fig. 11; i. e. the electrochemical oxidation becomes increasingly difficult in the series 1-4. This linearity and the delocalization in the radical anions indicate that the inductive
effect of each dicyanomethylene group is independent of
the other and independent of the position in the ring.
Clearly a linear change in electronegativity of the substituting dicyanomethylene group supports Wallenfels' concept of chemical equivalency of =O and =C(CN)*.
Received: October 30, 1981 [Z 167 IE]
German version: Angew. Chem. 94 (1982)649
CAS Registry numbers:
1, 66888-97-9;2, 82457-05-4;3, 82457-06-5;4,82457-07-6.
[ I ] A. J. Fatiadi in R. West: Oxocarbons, Academic Press, New York 1980,
Chap. 4, p. 59ff.
[2] K. Wallenfels, Chimia 20 (1966) 303; K. Wallenfels, K.Friedrich, J. Rieser, W. Ertel, H. K. Thieme, Angew. Chem. 88 (1976)31 l; Angew. Chem.
Inr. Ed. Engl. I5 (1976) 261.
131 a) M. Fleury, P. Souchay, M. Gouzerh, Bull. Soc. Chim. Fr. 1968, 2562;F.
Arcamone, C. Prevost, P.Souchay, ibid. 1953, 891 ;b) S. Hiinig, H. Piitter,
Chem. Ber. 110 (1977)2524, 2532; G. Seitz, Nachr. Chem. Tech. Lab. 28
(1980) 804.
[4]A. J. Fatiadi, J. A m . Chem. Soc. 100 (1978)2586;J. Org. Chem. 45 (1979)
1338.
[5] For the method see A. T. Hubbard, F. C. Anson, Anal. Chem. 38 (1961)
58.
161 G.A. Russell, C. E. Osuch, J . Org. Chem. 45 (1980) 1242.
methyl-3-methylene-5-oxobicyclo[2.2.2]octane-2-carboxyIate 513)(Route b).
"p
R
The high endo-selectivity of the addition is noteworthy
also in this example. However, although acrylic acid esters
react with both cyclohexadienolates of type 3 as well as
with the corresponding trimethylsiloxycyclohexadienes 2
to give 5-oxobicyclo[2.2.2]octane-2-carboxylicacid esters,
allenecarboxylic acid esters such as 4 form the bicycles 5
only on reaction with 3 ; with trimethylsiloxy-activated
dienes such as 2 they undergo polar [2 + 21-cycloaddition
to give mainly cyclobutylideneacetic acid esters (e. g. 6)L41.
Both 5 as well as analogous bicyclo[2.2.2]octanes are suitable e d ~ c t s [for
~ ] the synthesis of tricyclic sesquiterpenes
such as seychellene 7.
Received: July 29, 1981 (2166 1Ej
revised: June 14, 1982
German version: Angew. Chem. 94 (1982)639
Bicyclol2.2.2loctanes from Allenecarboxylic Acid
Esters and Cyclohexadienolates
By Dietrich Spitzner*
Cyclohexenones such as 1 can be selectively deprotonated in a kinetically controlled reaction with lithiated
bases such as lithium diisopropylamide (LDA) to give lithium cyclohexadienolates of type 3. Compounds 3 react
with acrylic acid esters in what may be formulated as a
Diels-Alder cycloaddition or Michael cascade reaction to
give 5-oxobicyclo[2.2.2]octane-2-carboxylicacid esters, exclusively in the endo-form['al.
Allenecarboxylic acid esters are capable of undergoing
[2 21- as well as [4 21-cycloadditions; Lewis acids accelerate both reactions, but decisively improve the endo selectivity only in the case of the [2+2]-~ycloaddition['~~.
We
have now reacted the allenecarboxylic acid ester ethyl 2methyl-2,3-butadienoate 4IZ1
with 3 in amine-free medium
and obtained isomer-free (capillary-GC/MS) ethyl 1,2-di-
+
+
[*I Dr. D. Spitzner
Institut fur Chemie der Universitat Hohenheim
Garbenstr. 30, D-7000 Stuttgart 70 (Germany)
636
0 Verlag Chemie GmbH, 6940 Weinheim, 1982
CAS Registry numbers:
2, 54781-27-0;3, 78070-27-6;4, 5717-41-9;5, 82432-15-3
[I] a) R. A. Lee, Tetrahedron Lett. 1973, 3333; b) H. M. R. Hoffmann, 2. M.
Ismail, A. Weber, ibid. 22 (1981) 1953; B. B. Snider, D. K. Spindell, J.
Org. Chem. 44 (1980) 5017.
121 H.J. Bestmann, H. Hartung, Chem. Ber. 99 (1966) 1198.
[3] 5: A solution of 3 (prepared from 2, R=CH,, and a 5% solution of methyllithium in ether at -60 "C under argon) in tetrahydrofuran-ether (ca.
4:1) is treated dropwise within 10 min at -60°C with 1.1 equivalents of
4. The reaction mixture, which is initially yellow and later turns orangered, is kept at this temperature for 3 h and then warmed to - 20°C. After
12 hours' stirring at -20°C the mixture is worked up (acidification with
1 M HCI, ether extraction, drying of the organic phase over MgSO,) and
distilled in a Kugelrohr (100- 1 1OoC/0.O1 torr). 5 is obtained as a colorless oil (yield 75%), which crystallizes on cooling in a refrigerator (m.p.
65°C). ELMS: m / z 236 ( M + ,18%); 250 MHz 'H-NMR (CDCI,):
6=5.05, 4.82 (s, 2 olefin-H), 4.18-4.06 (4.J = 7 Hz, on AB, J A B =I 1 Hz,
diastereotopic ester-CH2, 2 H), 2.99 (t, J=3 Hz, 1 bridgehead-H), 2.86,
2.79 (d, J=3 Hz, on A part of an AB, JAB= 19 Hz, 1 H), 2.05, 1.97(B part,
JAB=19 Hz, 1 H), 1.95-1.85 (m. 3H), 1.47 (5, CHI), 1.43-1.31 (m,1 H),
1.22 (t, J=7 Hz, ester-CH,), 0.99 (s, bridgehead-CH,); 62.9 MHz "CNMR (CDC13):6=210.8 (s, ketone-C), 173.9 (s, ester-C), 149.2(s), 111.4
0570-0833/82/0808-0636 $02.50/0
Angew. Chem. In(. Ed. Engl. 21 (1982) No. 8
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salt, equivalence, oxidation, carbonyl, chemical, dicyanomethylene, group, evidence, atom, croconate, electrochemically, oxygen
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