Commzlnz'cations obtained by adding cyclopentadiene directly to the cold reaction mixture. The continuous removal of 2 as it was formed prevented its subsequent thermal decomposition. Such a technique was employed previously by US.^ S u m m a r y : Controlled current electroreduction of 1Compound 3 showed IH nmr signals a t 7 3.82 (s, 2 H ) , bromo-4-chlorobicyclo[2.2.0]hexane(1) in dimethylformamide a t -20" on a mercury cathode gave ~ l ~ . ~ - b i c y c l o -7.46 (s, 2 H), and 7.55-8.75 (m, 10 H), in excellent agreement with the values reported previously.2 The mass spec[2.2.0]hexene (2) as the only organic product, identified as trum (re1 intensity) m / e 146 (M+, lo%), 131 (CloHI1+, the Diels--Alder adduct (3) with cyclopentadiene. 22%), 117 (CgHg+, 26%), 91 (CyHy+, 100?/0), 90 (C;He+, Sir: The theoretically interesting A1,4-bicyclo[2.2.0]hexene 42%), 77 (CeHj+, 32%), 66 (CjHg', 35%), 61 (CjHj+, 23%), (2) represents one of the most highly strained olefins consupports earlier structural assignment. With a direct convenient synthesis of this unusual olefin now available, work ceivable. Examination of its physical and chemical properis in progress directed toward the isolation and study of the ties would constitute a valuable contribution to a study of physical properties of the pure olefin. the bonding properties of strained molecules. Convincing evidence has been presented2 for the presence of 2 during Acknowledgment is made to the donors of the Petrolethe thermolysis of tosylhydrazone salt 4. The Diels-Alder um Research Fund, administered by the American Chemiadduct (3) of olefin 2 was isolated and characterized by cal Society, for support of this work. Wiberg and coworkers, who also reported the low temperature IH nmr spectrum of the olefin itself. Subsequently the References and Notes
Electroorganic Chemistry. IV.' A1*4-Bicyclo[2.2.0]hexene
Br
cb-on I c1
Q 3
2
1
same research group has reported3 that 2 can be isolated as the bis(tripheny1phosphine)ethylene)platinum T complex ( 5 ) from which it could be freed by treatment with carbon disulfide.
5
6
We wish to report that, when bromochloride l 4 [E112 -2.50 V us. saturated calomel electrode in dimethylformamide (DMF)] was electroreduced a t -20' in a compartmented cell similar to one described elsewherel>jand the reaction product treated with excess cyclopentadiene, the only volatile organic product (excepting dicyclopentadiene) was adduct 3. The yield was nearly quantitative, and the crude reaction mixture was free from the Diels-Alder adduct of 1,2-dimethylenecyclobutane(6) and olefin 2 , an adduct reported to be formed during the thermolysis of 4.* That the primary product of the reaction was olefin 2 could be demonstrated in two ways. Controlled current electroreduction was conducted a t a stirred mercury cathode a t 200 mA and -20' using DMF as solvent and tetraethylammonium fluoborate6 as supporting electrolyte. Following the passage of 2.0 F, excess cyclopentadiene was added to the cold catholyte. The catholyte was worked up in the usual way1 after it has stood overnight a t room temperature. Compound 3 was separated from dicyclopentadiene by preparative glpc. Alternatively, if the reduction was carried out a t -20' under 0.6-Torr pressure in a very gentle stream of dry nitrogen and the volatiles were collected directly on the vacuum line in a trap a t -200' which contained excess cyclopentadiene, the same result was obtained after the trap was allowed to warm to room temperature as had been
(1) Paper 111: J. Casanova and H. R. Rogers, J. Amer. Chem. SOC.,96, 1942 (1974). Paper ii: J. Casanova and H. R . Rogers, J. Org. Chem., 39,2408 (1974). (2) K. Wiberg, G. J. Burgmeier, and P. Warner, J, Amer. Chem. SOC., 93, 246 (1971). (3) M. E. Jason, J. A. McGinnety, and K. B. Wiberg, J. Amer. Chem. SOC., 96,XXXX (1974). (4) K. V. Scherer and T. J. Meyers, Abstract of Papers, 155th National Meeting of the American Chemical Society, San Francisco, Calif., March 31April 5, 1968, Section P-180. K. Katsumoto, Ph.D. Thesis, University of California at Berkeley, 1968: Diss. Abstr., 29, 32628 (1968-1969). K. V. Scherer, Jr., Tetrahedron Lett., 5585 (1966). The authors are deeply indebted to Professor Scherer, Department of Chemistry, University of Southern California, for a generous gift of compound 1. (5) (a) Paper 11; (b) H. R. Rogers and J. Casanova, Inorg. Syn.. in press. (6) Electrometric Grade, Southwestern Analytical Chemicals, Inc., Austin, Texas. (7) J. P. Dirlam, L. Eberson, and J. Casanova, J. Amer. Chem. SOC.,94,240 (1972).
D e p a r t m e n t of Chemistry California S t a t e University, Los Angeles Los Angeles, California 90032
3803
Joseph Casanova* Harold R. Rogers
Received August 28, 1974
A Convenient Synthesis of A1~4-Bicyclo[2.2.0]hexene1 S u m m a r y : The electrochemical dehalogenation of 1chloro-4-bromobicyclo[2.2.0]hexanegives an almost quantitative yield of A1,4-bicyclo[2.2.0]hexene. Sir; The synthetically and theoretically interesting hydro(I),has been prepared by carbon, A1,4-bicyclo[2.2.0]hexene the thermolysis of the anion derived from spiro[2.3]hexanone-4 tosylhydrazone.2 1,2-Dimethylenecyclobutane (11) was formed in similar amount, and, because of the rapid I
3804 J . Org. C h e m . Vol. 39, N o . 25, 1974 Diels-Alder reaction between I and I1 even a t -60°, it was not possible to isolate I in pure form. Subsequently, we have shown that I may be separated from I1 by reaction with bis(triphenylphosphine)(ethyle n e ) p l a t i n ~ m The . ~ complex, 111, on reaction with carbon disulfide, liberated I. Although this made it possible to obtain a pure sample of I, it cannot be considered a convenient preparative method.
Communications
c1
Br I'?
I
0 -
VI
The use of butane as the extracting solvent permits facile separation of I from the electrolysis mixture. Treatment of a butane solution of I with ozone a t - 7 8 O , followed by reductive work-up with dimethyl sulfide, afforded 1,4-cyclohexanedione. Isolation of I from the butane solution was I11 unsuccessful. One of the more interesting of the properties of I is its Dehalogenation of l-chloro-4-bromobicyclo[2.2.0]hexane thermal stability. A dilute solution of I was prepared by ex(IV)4using 8 molar equiv of sodium in liquid ammonia5 afit from the electrolysis mixture with heptane and tracting fords an almost quantitative yield of dimer, A3fj-tetracywashing the heptane layer several times with water. Triethclo[6.2.2.01~s.03~6]dodecene (V), identical in all respects ylamine was added, and the solution was sealed in several with the product of the Diels-Alder reaction between I and small ampoules. Kinetic points were taken by quenching IL2 A small amount of I (up to -18%) is produced by the the contents of an ampoule with cyclopentadiene and then dehalogenation of IV when less sodium is employed, as evianalyzing the decrease in Diels-Alder adduct VI and the denced by the isolation of the well-characterized Dielsincrease in Diels-Alder dimer V by glc. At 14.85", the conAlder adduct, VI, when the reaction mixture is treated with centration of I was found to decrease by a process second excess cyclopentadiene. A short reaction time (2-3 min, inorder in I, h14 850 = 2.2 X 1. mol-I sec-l. The amount complete reduction) does not improve the yield of L6 of V present did not increase. Thus, I is stable a t this temperature toward unimolecular isomerizations, but in solution readily undergoes a reaction with itself, possibly by an "ene" reaction as has been observed with cy~lopropene.~ References a n d Notes
i
Br IV
v
While this procedure offers a route to I, it is not attractive on a preparative scale. Therefore we have examined the electrochemical reduction of IV in dimethylformamide a t a platinum electrode with tetraethylammonium bromide as the supporting electrolyte. When a potential of -2.50 V us. a mercury pool a t -20" was used, the current dropped rapidly when 2 equiv of charge had been transferred. The DMF solution was added to a cold mixture of brine and pentane, and the pentane solution was washed with water. Addition of cyclopentadiene followed by removal of solvent gave a quantitative yield of the Diels-Alder adduct of I with cyclopentadiene (VI, mp 79.5-80'). None of the DielsAlder product derived from I and I1 was found, indicating that I1 was not a by-product in the reaction.
This investigation was supported by the National Science Foundation. K. B. Wiberg, G. J. Burgmaier, and P. Warner, J. Amer. Cbem. Soc., 93, 246 (1970). M. E. Jason, J. A. McGinnety, and K. B. Wiberg, J. Amer. Chem. Soc., 96, 6531 (1974). The bromochloride iV was prepared by converting 7,7-dimethoxy-l,2,3,4tetrachlorobicyclo[2.2.I]hept-2-ene to 4-chlorobicycio-[2.2.O]hexane1-carboxylic,acid by the procedure of W. G. Dauben, J. L. Chitwood, and K . V. Scherer, Jr., J. Amer. Chem. SOC.,90, 1014 (1968), followed by a modified Hunsdiecker reaction. Cf. K. V. Scherer, Jr., and T. J. Meyers, 155th National Meeting of the American Chemical Society, San Francisco, Calif., March 31-April, 1968, p 180; K. Katsumoto, Ph.D. Dissertation, University of California at Berkeley, 1968. E. L. Allred. B. R. Beck, and K. J. Voorhees, J. Org. Cbem., 39, 1426 (1974). Dehalogenation of i using activated zinc in ether [W. T. Brady, H. G. Cidell, and W. L. Vaughn, J. Org. Cbem., 31, 626 (1966)] has, in our hands, not been successful. P. Dowd and A. Gold, Tetrahedron Lett., 85 (1969).
D e p a r t m e n t of Chemistry Yale University N e w H a v e n , Connecticut 06520
Kenneth B. Wiberg* William F. Bailey M a r k E. J a s o n
Received S e p t e m b e r 23, 1974
