Vol. 82
COMMUNICATIONS TO THE EDITOR
2644
TABLE I ISOTOPEDISTRIBUTIONIN SUCCINYL CoA DERIVEDFROX 2-c'"METHYLMALONYL COA Carbon
Cpm./patom
COSCoA 0 CHz 14 CHI 54 4 COOH 0 Ten ml. of reaction mixture containing 0.4 pniole of 2C14-methylmalonyl CoA (1.9 X 106 cpm.), 0.035 pmole of dimethylbenzimidazole-cobamide-coenzyme (supplied by H. A. Barker), 2.6 units of avidin,'* 200 pmoles ot histidineHCl buffer (PH 6.2), and an isomerase preparation from P . shermanii (700 pg. protein) were incubated a t 25' for 10 minutes. The mixture was then treated with concentrated NHnOH t o convert the acyl CoA compounds t o their acid amide derivatives. This and three similar reaction mixtures containing a total of 1.8 pmoles of 2-c14 D,L-niethplmalonyl CoA (7.3 X lo5 cpm.) were pooled and the succinic acid amide was isolated and degraded as described in the text. 1 2 3
established that isomerization involves rearrangement of the thiolester group. Although the data do not eliminate the possibility that isomerization occurs by an intermolecular transfer of the thiolester group, a much more reasonable mechanism is suggested by analogy to the intramolecular rearrangement of phenylneopentyl radical discovered by Urry and Kharasch.I3 In the proposed mechanism (Fig. 1) fOOH HC-CH?
THE SYNTHESIS OF THE DIPROPYLCY CLOPROPENIUM ION
Sir: Although the properties of the triphenylcyclopropenium ion1 strongly support the idea that the cyclopropenyl cation is a fundamental aromatic system, i t seemed desirable to prepare a derivative free of phenyl groups. The properties of the diphenylcyclopropenyl c a t i ~ n ~ suggested .~ that a simple alkylated cation might well be stable, and we wish to report that this is indeed the case. Reaction of dipropylcyclopropene carboxylic acid ( I ) 4 with acetyl perchlorate in acetic anhydride,3-5and then ether precipitation, led to dipropylcyclopropenium perchlorate (11),m.p. 4 3 0 ' (dec.), which was recrystallized from ethyl acetate and ether. Found: C, 48.7; H, 6.6. The compound is insoluble in ether, hexane, or other nonpolar solvents, but is soluble in acetone and other polar organic solvents and in 1 N HC1. It gives a positive perchlorate test with potassium nitrate, and the infrared spectrum also reveals the presence of perchlorate ion. I n strong acid the compound has only end absorption in the ultraviolet. CH3CHzCH2 Tr_7-C'lI~CHd2HHj
H
f00 H HS-CH,
xCOZH Y
c104
H I1
The n.rn.r. spectrum, in SOY0 aqueous sulfuric acid, is as expected, with a sharp band a t -4.15 p.p.m., shifted to very low field for the proton on a positive carbon, and the characteristic pattern of two I equivalent propyl groups also strongly shifted, with SCoA SCoA a 4 proton triplet centered a t +3.12, a four proton Fig. 1 sextuplet a t +4.43, and a six proton triplet a t the role of the cobamide coenzyme is to produce a +5.30 p.p.m. relative to a benzene capillary; radical by the one electron oxidation of methyl- the absence of any i u r t l a : i"!-b ~ d was s estabmalonyl-CoA. The radical then could isomerize lished by dilution of the solvent, with consequent by the mechanism of Urry and Kharasch and the shift of its absorption. succinic acid derivative could be stabilized by Although the cation is soluble and stable in 1 N acid, its solution in 0.1 N acid or water becomes interaction with reduced cobamide coenzyme. In view of the fact that the cobalt in cobamide turbid. This reaction of the carbonium ion with coenzyme has a valence of +3 i t is of further sig- water gives a complex mixture of products, but nificance for the proposed mechanism, that COf 3 a t least some of the components are cyclopropene is known to produce radicals by reaction with derivatives, as evidenced by their characteristic a variety of organic compounds.14 double-bond stretching absorption in the infrared M AX-PLANCK-INSTITUT H. EGCERER a t 5 . 3 ~ . From this it can be estimated that the FOR ZELLCHEMIE P. OVERATH p K a of the cation is greater than 0 and probably is F. LYNEN less than 1. For comparison, the diphenylcycloMUNCHEN,GERMANY NATIONAL HEARTINSTITUTE BETHESDA, MARYLAND E. R. STADTMAN propenyl cation has a p K a of 0.3.* That these two are so close is certainly a chance coincidence, RECEIVED APRIL6, 1960 for randomization of the carbon atoms was obtained by showing that, under otherwise identical conditions, the isomerization of unlabeled rnetbylmalonyl CoA in the presence of added trace amounts of 1,4-C"succinate led to the formation of C14-succinyl CoA n,hich was isolated as the succinic amide derivative. (12) Avidin was added to prevent the decarboxylation of rnethylmalonyl CoA to propionyl CoA ('4). (13) W. H. Urry and M . S Kharasch, THIS J O U R N A L , 66, 1438
(1944).
(14) A. F. Trotman-Dickenson, "Free Radicals," John Wiley and Sons, New York, N. Y.,1959,p. 10.
(1) R.Breslow and C. Yuan, THISJ O U R N A L , 6 0 , 5991 (1958). (2) T h e diphenylcyclopropenyl cation has been prepared by Dr. Joyce Lockhart, unpublished work, by the reaction of phenylrhlorocarbene with phenylacetylene. (3) Prepared independently by Dr. Donald Farnum by the use of acetyl perchlorate on the appropriate acid. We wish to thank Dr. Farnum for making his results available prior to publication. ( 4 ) I. A. Dyakonov, cl al., Zhrrr. Obshchei Khitn., 29,3848 (1959). (5) A similar reaction with acetyl Euoroborate, to form the tropylium ion, has been reported by M. Dewar and C. Ganellin, J . Ciiem. Soc.,
2438 (1958).
May 20, 1960
COMMUNICSTIONS TO
THE
2645
EDITOR
The formation of methyl ethers in these cases is inconsistent with radial attack on solvent (which should produce hydrocarbon by hydrogen atom abstractioni), but suggestive of cationic intermediates. Further, the particular ethers produced correspond exactly to the products obtained via bridged ions V I P and VIII' in solvolysis. Anodic oxidation of cyclobutanecarboxylic acid in water (20 volts, 100') afforded mainly cyclobutanol and cyclopropylcarbinol (ratio 1.1to 1) and a small amount of allylcarbinol, a mixture identical with that resulting from deamination of cyclobutylamine.8 (6) Cf J D Roberts and S L hlanatt, J Org Chem , 24, 1336 Electrolysis of cholesteryl-3~-carboxylic acidg (1959) in methanol (150 volts) produced G&methoxy-3,5DEPARTMEN r OF CHEMISTRY COLUMBIA UYIVERSITY RONALD BRESLOW cyclocholestane, the characteristic methanolysis NEW YORK27, NEW YORK HERMANN HOVER product of cholesteryl tosylate,'" and a mixture of RECEIVED MARCH30, 1960 6~-methoxy-A4-cholesteneand 4p-methoxy-A6-cholestene, previously obtained from methanolysis of epicholesteryl tosylate.1° GENERATION OF CATIONIC CARBON BY ANODIC Electrolysis of 7-benzyl-7-hydroxyvaleric acid OXIDATION OF CARBOXYLIC ACIDS (IX) (methanol, 100 volts) gave two products Sir: resulting from double 1,2-migrationj X and XI The sequence involved in the Kolbe synthesis of (ratio 1 to 2.5), whose formation is most readily hydrocarbons from carboxylate ions, RCOO--. explicable on the basis of cation intervention. In RCOO+R. can be extended by another stage of addition, methyl benzyl ketone (XII) and ethylene electron transfer to the generation of species which OH 0 behave like carbonium ions. The anodic synthesis I1 of such ionic species becomes more important with C ~ H ~ C HI Z ~ C H I C H Z C O + OHCGH~CH~CCHCH~ increasing voltage and seems to be especially favorI I CH3 CH3 able with those structures which give rise to IS X relatively stable carbonium ions. In fact, the cases in which the Kolbe coupling reaction has 0 I1 been reported to fail usually are such instances.' f C ~ H ~ C H Z C C HCH2 ~ ==: CH2 Anodic oxidation2 of exo- or endo-norbornane- CBH~CH~CHCOCH, I 2-carboxylic acid (I or 11) in methanol (50 volts, CHa 10 ") produced exo-norbornyl methyl ether (111) XI XI1 in 35-40y0 yield and a very small amount of norwere formed (30435% yield depending on temperacamphor as the only volatile materials; no endo ture) by a cleavage process analogous to that obmethyl ether could be detected by vapor chromatography or infrared analysis. The methyl ether served earlier.'l The generation of cations by anodic decarboxyla111 obtained from optically active II was racemic, tion can be of value in synthesis, as illustrated by [ a ]2 5 0.00 ~ 0.09" ( [ a ]25D 5 10.6' for optically pure 111). Electrolysis of exo- or endo-5-norborn- its application to the ring expansion of cyclic ene-2-carboxylic acid (IV or V) gave 3-methoxy- ketones via the operations nortricyclene (VI) * (56%).
considering the many factors which are involved, but i t is of interest that the qualitative idea that phenyl groups should stabilize the cation more than alkyl groups do apparently is incorrect. This result is predicted by simple L.C.X.O. calculations,B which show that the AD.E. of ionization for our cation should be 26 compared to only 1.9p for the diphenyl cation, the explanation of this apparent anomaly being that the phenyl groups stabilize the covalent cyclopropene even more than they stabilize the cation. Our results furnish strong support for this striking prediction.
+
+
*
1 Reforrnatshl
( C H d ,,+p
/
3 oxldatlon
I
R2
1x2
1, R I = COOHlRz = H 11, RI = H, Rz = COOH 111, R I = OCHj, RI = H
&OCH3 VI
JV, RI = COOH, R I = H H, R2 = COOH V, RI
6-& .....
1711
_--
VI11
(1) See for example J. Walker and bI. Carmack, J. Chem. SOL,77, 374 (1900); R. P . Linstead. B. R . Shephard and B. C. L. Weedon, i b i d . , 2854 (1951); M. Finkelstein and R . C. Peterson, J. Org. Chem., 25, 136 (1960). (2) Smooth platinum electrodes were used throughout. Triethylamine was added to increase carboxylate ion concentration. (3) T. G. Traylor and A. W. Baker, Tetrahedmn Lefrers, 19, 1 4 (1950). (4) Shell eo., Technical Information Bulletin MD-101.
Electrolysis of 1-hydroxycyclohexylaceticacid in acetonitrile (175 volts, 10")afforded cycloheptanone (45-53%) ; 1-hydroxycyclopentylaceticacid yielded cyclohexanone (54-63%). Cyclooctanone and amethylcycloheptanone have been obtained similarly. (6) W.H. Urry, F. W. Stacey, E. S. Huyser and 0. 0. Juveland. THISJOURNAL, 76, 450 (1964). (6) S. Winstein and D. Trifan, i b i d . , 74, 1147, 1154 (1952). (7) J. D. Roberts, E. R. Trumbull, W. Bennett and R . Armstrong, ibid., 72, 3116 (1950). (8) R . H. Mazur, W. N. White, D. A. Semenov. C. C. Lee, M. S. Silver and J. D. Roberts, i b i d . , 81, 4390 (1959). (9) E. J. Corey and R . A. Sneen, i b i d . , 75, 6234 (1953). (10) D. D. Evans and C. W. Shoppee, J. C h o n . SOC.,510 (1053); E. M. Kosower and S. Winstein, THISJOURNAL, 78, 4354 (1956). (11) E. J. Corey and R. R. Sauers, ibid., 81, 1743 (1959).
