May20, 1962
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days. The product was washed several times with petroleum ether. It could not be recrystallized because of decomposition in the usual solvents. Anal. Calcd. for C12H&12NiN2: Ni, 18.58; C1, 22.45. Found: Ni, 18.70; C1, 24.17.
I
I1
CHEMISTRY AND RADIATION LABORATORIES Ozonization of I1 and treatment with hydrogen UNIVERSITY O F NOTREDAME S R . M. DESNIS GLONEK 2-methylXOTREDAME,IXDIANA COLUMBA CURRAN peroxide gave 2-isopropyl-5-oxocaproic, FLORIDA STATEUNIVERSITY glutaric, and levulinic acids (isolated as methyl TALLAHASSEE, FLORIDA JAMES 1'. QUACLIANO esters by gas-liquid chromatography, silicone, RECEIVED MARCH 21, 1962 110'). These three acids account for all twenty
carbon atoms of the cembrene molecule. Since all are bifunctional, and since cembrene possesses but one ring, the dihydro derivative and therefore Sir: cembrene must contain a fourteen carbon ring. Cembrene (I) is a crystalline diterpene hydro- There are eight possible structures for the lithiumcarbon (CZOH32, mol. wt. 272 (mass spectrum'), liquid ammonia produced dihydrocembrene (11) 238' (c 1.13, chf.) ) first which could yield these three degradation products. m.p. 59-60', [cL]'~D isolated by Haagen-Smit, Wang and M i r ~ v , ~ Ozonization of cembrene and treatment with from the oleoresin of Pinus albicaulis and subse- hydrogen peroxide gave acetic, malonic, 2-isoquently found to occur in exudate of many other propyl-5-oxocaproic, and levulinic acids (isolated pine tree^.^'^ Cembrene,6 upon catalytic hydro- as methyl esters by gas-liquid chromatography, genation over Pd/C in ethyl acetate, yielded a silicone, 110'). When the ozonide was treated liquid saturated octahydro derivative (CZOHIO, with sodium iodide, then p-nitrophenylhydrazine, mol. wt. 280 (mass spectrum2) ), establishing the the p-nitrophenylosazone of pyruvaldehyde was presence of four double bonds and one ring in the isolated. The absence of 2-methylglutaric acid starting material (I). The ultraviolet and infrared and the appearance of malonic and pyruvic acid spectra of cembrene, X",tH 245 mp ( E 17,000), moieties permits placement of the olefinic bond vzYx 1660 (w), 1640 (w), 967 (s), 840 (m), 811 (m) which was reduced to form dihydrocembrene I1 cm.-', indicated the presence of a conjugated diene and suggests eight related structures for cembrene. Catalytic hydrogenation of cembrene over 57, as well as trans-disubstituted and trisubstituted double bonds. From the n.m.r. spectrum' (quan- Pd/C in ethyl acetate gave a mixture of three titative) of cembrene, it was determined that dihydrocembrenes (gas-liquid chromatography, silithere was an isopropyl group attached to a satu- cone, 200'). The major component I11 (no maxirated carbon (two doublets centered at 9.09 and mum in the ultraviolet; n.m.r., 3 vinyl protons; 9.20 p.p.m., G protons), two methyl groups on no 970 cm.-' band) was different from dihydrodouble bonds (8.47 and 8.38 p.p.m.), and one cembrene I1 and was formed by the hydrogenation methyl group on a conjugated diene (8.20 p.p.m.). of the trans-disubstituted double bond of the The presence of five vinyl protons was established conjugated diene. by a broad absorption band between 3.80 and 5.30 p.p.m. containing a sharp doublet a t 3.80 and 4.07 p.p.m. equal to one proton. The low field position of this doublet characteristic of a proton on a trans-disubstituted double bond further indicated I11 IV that the bond was part of the conjugated diene Ozonization of I11 and treatment with hydrogen system. Reduction of the conjugated diene system of I peroxide gave rise to approximately equal amounts with lithium in liquid ammonia gave a mixture of of neutral and acidic materials. The major comdihydrocembrenes,8 whose ultraviolet spectrum ponents of the latter were levulinic and malonic possessed no maximum above 205 mp, and which acids. The eight possible structures of cembrene may be consisted of two compounds in the ratio of 85:15 (g.l.c., silicone, 215'). The infrared absorption reduced to four by elimination of all structures not a t 973 cm.-l of the major component (11) indicated containing a trans-disubstituted double bond as part the continued presence of the trans-disubstituted of the conjugated system. Two of the remaining double bond and the n.m.r. spectrum showed the four structures also may be eliminated, since the product from their dihydrogenation would not presence of four vinyl protons. yield levulinic and malonic acids upon ozonization. (1) This work was supported in part by Grant No. 14526, National The two remaining structures are isoprenoid I Science Foundation. and the non-isoprenoid IV. ( 2 ) We are indebted t o Dr. D. P . Stevenson of Shell Development Cumpany for all t h e mass spectral d a t a quoted in this work, Hydroboration of 111, then oxidation, gave a (3) A. J. Haagen-Smit, T . H . Wang, and K. T. Mirov, J. A m . triol mixture V, whose n.m.r. spectrum showed a P h a r m . A s s n . , Sci. E d . , 40, 557 (1951). broad peak a t 6.28 p.p.m. corresponding to three ( 4 ) N. T. hlirov, "Composition of G u m Turpentines of Pines," Technical Bulletin S o . 1239, U. S. Department of Agriculture, June, protons attached to carbon atoms bearing hydroxyl 1961. groups. Acetylation of V with acetic anhydride ( 3 W. G. Dauben and C. Ashcraft, unpublished observations. and sodium acetate a t 145' gave the triacetate VI ( 6 ) We are indebted t o Dr S . T.Mirov for t h e supply of oleoresin whose n.m.r. spectrum showed a broad band a t ( 7 ) All chemical shifts are quoted in reference t o t h e r scale. ( 8 ) Satisfactory analyses were obtninad for all new compoundr. 6.20 p , p m corresponding to three protons atCEMBRENE, A 14-MEMBERED RING DITERPENE HYDROCARBON'
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VOl. 84
cycles) a t 6.85 7 (60 mc., benzene capillary reference, 2.73 used to relate benzene to tetramethylsilane). This is in striking contrast to the n.m.r. spectrum of IIa (CC14solution), which consists of a complex multiplet from 5.9-9.4 7 and a complex multiplet from 9.5-9.8T with areas in the approximate ratio of 13. This reduction of the complex cyclopropyl n.m.r. pattern to a single band is also found in protonated dicyclopropyl ketone, which exhibits a band (with poorly resolved fine structure) a t 7.06 7 in 96% H2SOa, These observations both support the identification of Ia and show the close relation between carbonium ions and protonated ketones. I I a was recovered in 63% yield from solutions of I a in 96% H2S04. The b.p. and both n.m.r. and infrared spectra are identical with those of the original IIa used to form Ia. Addition of a solution of I a in 9Syo DzS04 to ice-lOyo NaOH yielded a CCl4 extract. The n.m.r. spectrum of this ex(9) L. M . Jackman, "Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry," Pergamon Press, London, 1959, tract was virtually identical with that of the original p. 55. IIa demonstrating that no rapid H-D exchange had (10) J. B. Hendrickson, Tetrahedron, 9, 82 (1959). occurred and that IIa was the only water insoluble (11) M. D. Sutherland and 0. J. Waters, A u s f . J . Chem., 1 4 , 596 (1961). product derived from drowning Ia. Even slow (12) National Science Foundation Predoctoral Fellow, 1957-1959 H-D exchanges are absent because the n.m.r. WILLIAMG. DAUBEN spectrum of I a in 96Y0 D2SO4was essentially unDEPARTMENT OF CHEMISTRY WILLIAME. THIESSEN'~ UNIVERSITY OF CALIFORNIA PAULR. RESNICK changed after one hour. This eliminates an olefin 4, CALIFORNIA BERKELEY as a component of the equilibrium and reflects the RECEIVED MARCH16, 1962 high energy of cyclopropylidene derivatives. The initial i-factor of I I a in HzS04 was 4.1 in PHYSICAL PROPERTIES OF THE accord with the equation ROH 2HzS04 = R+ TRICYCLOPROPYLMETHYL CATION' H30+ 2HS04-. The infrared spectrum of Ia Sir: exhibits bands a t 837, 1279, and 1445 ( ~ m . - ' ) . ~I n Recently the physical properties of a simple the ultraviolet, Xmax for Ia (270 mp, t 22,000)5bears aliphatic alkenyl cation were reported. We now a relation to alkenyl cations (310-335 mp) that is report the physical properties of the tricyclopropyl- comparable to the relation between protonated methyl cation, an aliphatic carbonium ion contain- cyclopropyl ketones (dicyclopropyl ketone.H+ ing no formal double bonds. 235 mp, tricyclanone.H+ 250 mp)6 and protonated Hart and Sandri3 showed from solvolysis studies unsaturated ketones (4-methyl-3-penten-2-one." that cyclopropyl groups stabilize carbonium ions. 284 mp)? The p-nitrobenzoates of IIb, IIc, and IId solvolyzed Solutions of Ia in 96% H2S04 show little change with relative rates of 23,500:246:1, indicating that in n.m.r. or ultraviolet spectra after one hour althe effect of cyclopropyl groups was nearly addi- though decomposition is progressing. The ion beti~e.~ comes increasingly unstable (chemically) as the % H&O4 is reduced from 85 to 52%. At 25*, the half-life is 700 seconds in 71y0 acid and 30 seconds in .%yoacid. Extrapolations of the first order rate plots suggest that I I a is completely converted to I a even in 52y0 acid. The mode of decomposition appears to be nucleophilic attack on the -CHzI I1 I11 tached to carbons bearing acetoxyl groups. The downfield shift of 1.08 p.p.m. is characteristic of an acetate of a secondary alcoh01.~ These data agree with structure VI, a structure derived from dihydrocenibrene 11 and cembrene I and would not agree with a similar group of structures derived from IV. Thus, I represents the structure of cembrene. Although no information is available with regard to the stereochemistry of the trisubstituted double bonds, from a study of models the structure written containing one cis bond appears to be more favored than an all trans structure. This diterpene hydrocarbon, the first naturally-occurring fourteen carbon ring compound, is specially significant from the biogenetic standpoint, since i t is the monocyclic diterpene derived from geranylgeraniol in a manner analogous to the formation of the sesquiterpene humulene from farnesol.lol.l1
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a, R1 b, R1 Rs c, R1 R2 d, R1 e , R1
R2 = Rs = cyclopropyl R2 = cyclopropyl isopropyl cyclopropyl Rs = isopropyl = RZ = Rs = isopropyl = R2 = cyclopropyl RI = -CH2CHzCHtOH2+ = = = = =
Ad( ition of I I a t o 96% produces the tricyclopropylmethyl cation (Ia). This ion has a most remarkable n.m.r. spectrum consisting of a single sharp band (width a t half-height about 3.5 (I) Grateful acknowledgment is made of partial support of this Research b y grants from t h e Petroleum Research Fund of the American Chemical Society, and t h e National Science Foundation. ,2) N. C. Deno, 11. C. Richey, Jr., J D. Hodge, and hl. J. Wisotsky, J . A m . Chem. Soc., 84, 1498 (1462). (3) H . H a r t and J. M. Sandri, ibid., 81, 320 (1959).
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(4) T h e H2S04 solution was held in plastic films between N a C l prisms. B y taking two spectra, one with high clarity polyethylene and one with high clarity F E P fluorocarbon polymer (kindly supplied by the d u Pout Company), t h e complete 2-15 1.1 reaion can be measured. T h e HBO, has a strong background absorption throughout this region, but t h e intense bands pierce through this background. (5) I I a Solvolyzes a t a moderate r a t e in acetic acid (and probably also methanol and ethanol) so t h a t it was necessary t o introduce IIa directly into 96% H B O , and dilute the resulting solutions. (6) Simple protonated ketones d o not abqorb above 220 mp (H. J. Campbell and J. T. Edward, Can. J . Chem., 38,2100 (1960)). ( 7 ) 4-Methyl-3-penten-2-one. H + has a strong absorption hand a t 1540 cm. -1 in close agreement with t h e value 1533 cm. -1 found in a n alkenyl cation (ref. 2). This is ascribed t o a stretching mode of the C-C-C system and suggests that the hydroxyalkyl cation form makes the dominant contribution t o t h e structuie of this protonated ketone. A second intense band at 1595 cm.-1 m a y be t h e second stretchinp band of t h e allylic system though a band a t 1590-1610 bas been found in several simple protoiiateri kttones including acetone. H
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