Nov. 20, 1962
COMMUNICATIONS TO THE EDITOR
,4359
arrangement involved intramolecular proton trans- (96% sulfuric acid)? Xmax 268 (sh), 274 (4310), fer from C-2 to C-4. The possibility exists that 280 mp. A n d . Calcd. for C7H8Br2: C7H7+, some of the 0.46 atom of deuterium was incorpo- 36.17; Br, 63.42. Found: C7H7+, 35.9; Br, rated in cis-V after it was formed. These obser- 63.45, 63.21. Both salts dissolve instantly in water to give colorless solutions which neutralize vations indicate that in scheme (41, kc k d , and that if any deuterium was incorporated into czs-V two moles of base per mole of salt; qualitative during the rearrangement (as distinct from after), ultraviolet spectra of such solutions showed the presence of tropenium ion (Amax 273, 280 (sh) then k f > > keand k c > > k-@. Although in recent years a number of intra- mp)4 and no covalent species. Infrared spectraS molecular rearrangements involving carbonium ion- confirm the presence of tropenium ion in these anion ion pairs have been reported, t o the author's salts. The hydrogen dichloride does not show a knowledge this is the first example of an intra- discrete melting point, but decomposes slowly molecular carbanionic process. This phenomenon over 100'; the decomposition temperature is a may be rather general, and the scope and intimate function of rate and temperature of initial heating. mechanistic details are under active i n ~ e s t i g a t i o n . ~The hydrogen dibromide is converted to the brilliant yellow bromide on warming to 100'. (4) This research was sponsored by t h e U. S. Army Research Office (Durham). Both compounds are reasonably hygroscopic and DEPARTMENT OF CHEMISTRY were handled in the glove box a t all times. The DONALD J. CRAM stability of these compounds is demonstrated by UNIVERSITY OF CALIFORNIA ROYT. UYEDA AT Los ANGELES storage i n ~tacuounder continuous pumping a t 1 Los ANGELES24, CALIF. mm. for 18 hours which gave a 1% increase in RECEIVED SEPTEMBER 5, 1962 tropenium ion concentration in the hydrogen dichloride and a 4Yc increase in the case of the diCARBONIUM ION SALTS. VI. TROPENIUM HYDROGEN DIHALIDES AND AN IMPROVED ROUTE bromide. The vapor pressure of hydrogen halide over primary and secondary ammonium hydrogen TO TROPENIUM CHLORIDE' dihalides is quite high3" and cesium hydrogen diSir : Recent theoretical studies of the hydrogen di- chloride is reported to be unstable a t temperatures chloride anion2 indicate considerable interest in greater than 0°.3d Even tetramethylammonium this novel type of hydrogen-bonded species. We hydrogen dichloridezchas a vapor pressure of 2 mm. wish to report the preparation of tropenium hydro- a t room temperature, which suggests that this gen dichloride and hydrogen dibromide whose ease salt would be destroyed under these conditions. of preparation and marked stability may render Addition of hydrogen chloride gas to the brilliant them more amenable to physical chemical studies yellow solution of tropenium chloride in methylene than previously reported3 salts of these anions, chloride gives a colorless solution in which the and to describe a synthesis of tropenium chloride broad tailing of the tropenium peak from chloride which in yield and quality of product is superior charge-transferg is lost and a new C-T band (Xmax to any yet reported. 314 nip ( 1 i 0 0 ) ) appears. IX'hen hydrogen bromide Tropenyl methyl ether4was added to a saturated is passed into the deep orange solution of tropenium solution of hydrogen chloride in ether under a bromide in methylene chloride the color becomes stream of dry hydrogen chloride gas5; an immediate light yellow and the bromide C-T band (hxnax precipitate formed which when dried in vacuo gave 40% mp (1380))gis replaced by a new band (Amax 86.1% tropenium hydrogen dichloride as white 356 mp (1300)). This apparent shift in the C-T microcrystals, ultraviolet spectrum (96% sulfuric spectral" to shorter wave lengths shows the presence acid)' Xmax 268 (sh), 274 (4350), 280 mp. A n a l . of anions with higher ionization potentials than the Calcd. for C7H8C12: C7H7+, 55.89; C1, 43.49. corresponding halidesll as would be expected if Found: C7H7+, 55.8; C1, 43.23, 43.32. Use of the hydrogen dihalides were formed. hydrogen bromide in the above reaction gave a Tropeiiium chloride is a difficult compound; white precipitate containing excess hydrogen it is implacably hygroscopic, and we find---once bromide which upon adiabatic removal of solvent having overcome the moisture problem enough to in vacuo gave 78.0% tropenium hydrogen dibromide tell-that it is also extremely sensitive to light. as small light yellow needles, ultraviolet spectrum Diffuse sunlight rapidly darkens the chloride through Pyrex glass, and a sunlamp destroys it (1) Supported b y t h e Petroleum Research Fund and t h e National Science Foundation. completely in minutes to give several as yet un-
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(2) (a) T. C. Waddington, J . Chem. Soc., 1708 (1958); (b) D. W. A . Sharp, ibid., 2538 (1958); (c) S. Chang a n d E. F . \\'estrum, Jr., J . Chem. P h y s . , S6, 2671 (1962). (3) (a) F. Kauffler and E. Kunz, Ber., 43, 38.5, 2482 (1909); (b) R . West, J . A m Chem SOL..79, 4568 (1967); (c) H. F . Herbrandson. R. T. Dickerson, Jr., and 1. Weinstein, ibid., 76, 4046 (1954); (d) R . E. ValleC and D. H. McDaniel, ibid., 84, 3412 (1962). (4) W. von E. Doering and L. H Knox, ibid., 76, 3203 (1934). ( 5 ) This method was suggested by our observation t h a t when tropenium chloride is prepared by passing hydrogen chloride over a n ethereal solution of tropenyl methyl e t h e 6 a a excess of hydrogen chloride gives products with low tropenium ion content. (6) Method suggested by H. J. Dauben, Jr., and L. R. Honnen, private communication, ( 7 ) H. J. Dauben, J r . , F. A. Gadecki, K . M. Harmon and D. L. Pearson, J . A m . Chem. Soc., 79, 4557 (1957), report Amax 268 (sh), 273.5 (4350), 280 mr for tropenium ion in this solvent.
(8) We wish t o thank Ilennis J. Dieitler who determined t h e infrared spectra of t h e salts by t h e potassium bromide disk technique ( 8 ) K . M. Harmon, F. E. Cummings, I ) . .4.I,a\,isand I ) . J. Iliestler, J . A m . Chem. Soc., 84, 120, 3 x 4 9 (1962). (10) Our placement of the chloride C-T hand a t 299 mgQis hased o n t h e assumption t h a t subtraction of t h e spectrum of tropenium fluoroborate from t h a t of trnpenium chloride of equivalent concentration would give a measure of the chloride C-T absorption, t h e fact t h a t t h e chloride t o hydrogen dichloride shift produces a peak a t 311 mr a n d also a loss of color makes os question t h e validity uf this subtraction. Although a value of 299 mg (33,500 an.-') gives a reasonably straight line when t h e energies of t h e tropenium halide C-T bands are plotted against halide ion ionization potentials. a true straight plot calls for a value of 31,200 ern.-', which lies t o longer wave lengths t h a n t h e hydrogen dichloride C-T band. (11) S. P . McGlynn, Chem. Re%, 68, 1113 (1958).
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COMMUNICATIONS TO THE EDITOR
identified compounds. No route yet rep0rted4~~. l2 has given tropenium chloride of high quality in good yield with consistency. The hygroscopic nature of the compound renders recrystallization difficult, and since the chloride is thermally unstable sublimation results in extensive decomposition. These difficulties are obviated by use of tropenium hydrogen dichloride as starting material. A sublimer is charged with the hydrogen dichloride in the glove box, wrapped in foil, and sublimation carried out a t 70" and 0.1 mm. for three to five hours to yield 100% tropenium chloride as colorless, hard, free-flowing prisms, ultraviolet spectrum (96(ro sulfuric acid)' Xmax 268 (sh), 274 (4340), 280 mp. A n a l . Calcd. for CiH7Cl: GH;+, 71.99. Found: C7Hr+, 71.9. The chloride is handled a t all times in the glove box where it is stable to the atmosphere for about 24 hours; complete liquidation occurs in 30 seconds on removal to the room. A11 operations are carried out in a darkened room under red-orange light. Trituration of the hydrogen dichloride with ether gave slightly darkened, less stable tropenium chloride (71.2% tropenium ion) which melted a t 101-102' ( r e p ~ r t e d 101') ,~ ; however, the sublimed prisms do not show any change under 115' and slowly decompose over 125'. Studies on carbonium ion hydrogen diiodides are in progress.
Vol. 84
1
cyclic isoxazolidines I1 and 111 (70-80(r0 yield), in the ratio (determined by gas chromatography) of approximately 2 : 3, respectively. These isomers were separated by careful fractionation. The bornane derivative I1 (R = CH3)6had b.p. 97' (10 mm.), n Z 5 1.4858, ~ picrate m.p. 198-199' dec., methiodide m.p. 149-150' dec. The structure of 11 was supported by the n.m.r. spectrum which showed (60 mc., CC14, TMS) bands a t 6 = 0.87 and 0.93 (gem-diMe), 1.14 (Cs-Me), 2.64 (NMe), 2.95 broad doublet, J = 8 C.P.S.Cs-H) and 3.95 p.p.m. (broad doublet, J = 7.4 c.P.s., C1-H). Hydrogenolysis of the isoxazolidine gave an amino alcohol, m.p. 58-59'. The lower boiling camphene compound I11 (R = CHs) had b.p. 96' (10 mm.), n2'D 1.4830, picrate m.p. 216-218' dec., methiodide m.p. 169-170' dec. Hydrogenolysis of the isoxazolidine gave an amino alcohol melting a t 78.579'. The n.m.r. spectrum of I11 was very similar to that of 11, except that the methyl peaks were slightly shifted and no low field hydrogen resonance (H-C-0) was observed. When 4-cycloheptenecarboxaldehyde (IV) was (12) D. Bryce-Smith and N. A. Perkins, J . Ckem. Soc., 1339 (1962). condensed with N-methylhydroxylamine, a single (13) National Science Foundation and Petroleum Research Fund product V was obtained in 6OY0 yield. The triScholar, 1962. cyclic isoxazolidine structure V (b.p. 118-120' a t DEPARTMENT OF CHEMISTRY MUDDCOLLEGE KENNETHM. HARMON 25 mm., n " ~1.5002, methiodide m.p. 190.0-190.5" HARVEY CLAREMONT, CALIFORNIA SHARON DAVIS13 dec.) was consistent with infrared and n.m.r. RECEIVED AUGUST24, 1962 spectral data, and hydrogenolysis could be effected. RING CLOSURE TO BRIDGED BICYCLIC SYSTEMS BY T H E INTRAMOLECULAR NITRONE-OLEFIN CONDENSATION
Sir:
R I /N.
In the course of our investigations of the scope and utility of the intramolecular addition of nitrones to olefins,'t2 we have observed recently an apparent qualitative relationship between the Several groups have reported the lack of doubleformation of cyclic products obtained in the condensations of N-alkylhydroxylamines with a 3- bond participation and the failure to isolate bicyclopentenylacetaldehyde or 4-cycloheptenylcar- cyclic products from the solvolyses of 3-cycloboxaldehyde and the reported anchimerically as- hexenylcarbinyl ester^.^^^,^ When 3-cyclohexene sisted solvolysis of five and seven-membered cyclo- carboxaldehyde (VI) reacted with N-ethylhydroxylalkenyl esters to give bridged bicyclic p r o d ~ c t s . ~ amine, , ~ ~ ~ only the corresponding nitrone (VII) was Although these reactions seem to be of widely difC,H, ferent nature, we feel that this relationship has (yCHo C,H,NHOH A 08 some bearing on the mechanism of the intramolecular nitrone-olefin and, perhaps, other 1,3dipolar additions. VI VI I Acetolysis of esters of p-( A3-cyclopentenyl)0 ethanol gave high yields of exo-norbornyl acetate.4,5 The condensation of campholenic aldehyde (I) with N-methyl or N-isopropylhydroxylamines afforded, after distillation, a mixture of the tri(1) N. A. LeBel and J. J. Whang, J. A m . Chcm. Soc., 81, 6334 (1939). (2) N. A. LeBel and J. J. Whang, to be submitted. (3) G . LeNy, Compf. rend., 261, 1526 (1960). (4) R. Lawton, J . Am. Ckcm. SOL, 83, 2399 (1961). ( 5 ) P. 1). Bartlett snd S. Bank, ibid., SS, 2691 (1961).
(6) Satisfactory analyses have been obtained for all new compounds described herein. (7) R. S. Bly, Jr., and H. L. Dryden, Jr., Ckem. and I d . , 1287 (1959). (8) C. F. Wilcox, Jr., and S. S . Chibber, J. Ore. Chctn.. 27, 2332 (1962).
