June 5, 1954
CI7Hz0 HYDROCARBONS OBTAINED BY DEHYDROGENATION OF ACATHICACID
gave 1.1 g. (29%) of a pale yellow oily acid which could not be crystallized. The amide was prepared by the procedure given for the amide of the acid obtained from the diolefin. A 0.250-g. sample of the acid gave 0.140 g. of impure amide of m.p. 87-92’. On two recrystallizations from aqueous ethanol the silky needles melted a t 97-98’. Analysis was correct for ~-(2,3-dimethoxyphenyl)-caprylamide. Anal. Calcd. for CleHzsOaN:-C, 68.78; H, 9.01. Found: C, 68.71; H,8.94. Ultraviolet Absorption Spectra.-The ultraviolet spectra of the saturated, diolefinic and triolefinic components of di-
[CONTRIBUTION FROM THE
Terpenes.
DEPARTMENT OF
2963
methyl “urushiol” were determined using a Cary recording photoelectric spectrophotometer with 0.00010 M solutions in 95% ethanol. Very similar spectra for the corresponding components of methylcardanol have been presented elsewhere .la
Acknowledgment.-The authors are indebted t o the Lederle Laboratories Division of the American Cyanamid Company for a grant to Columbia University for support of this investigation. NEWYORK,N. Y.
CHEMISTRY,
MASSACHUSETTS INSTITUTE
OF TECHNOLOGY]
I. Structure and Synthesis of the CI7H2,Hydrocarbon Obtained by Dehydrogenation of Agathic Acid BY G. BUCHIAND JAMES J. PAPPAS RECEIVED OCTOBER17, 1953
1.1.4.7-Tetramethvl~henalan has been synthesized and shown t o be identical with the hydrocarbon C17H20 obtained b y dehydrogenation of agathic acid.
The structure of agathic acid (I) has been established through the researches of Ruzicka and his co-workers.’ The carbon skeleton of this compound was determined from the structures of the aromatic hydrocarbons formed in the dehydrogenation of agathic acid. The detailed structure was deduced from resulk obtained in a study of oxidative degradation. The trans-locking of the two rings was demonstrated by conversion of agathic acid (I) to a degradation product of manooI2 which in turn had been related to abietic acid,3 the structure of which is known in all detail^.^ Dehydrogenation of agathic acid with either sulfur or selenium gave agathalene (1,2,5-trimethylnaphthalene) (11), pimanthrene (1,7-dimethyIphenanthrene) (111) and a hydrocarbon C17H20 (IV).l” When tetrahydroagathic acid was dehydrogenated, agathalene and the C17H20 hydrocarbon (IV) were isolated but pimanthrene (111) could not be detected. The hydrocarbon C17H20 (IV) was resistant to further dehydrogenation and readily absorbed two equivalents of hydrogen when hydrogenated over Adams platinum catalyst. Exhaustive oxidation of IV with potassium ferricyanide in aqueous potassium hydroxide solution gave a ketodicarboxylic acid C16H1205(V). The ultraviolet absorption spectrum of IV was similar to the spectrum of naphthalene and Ruzicka and Rey5 assumed that IV was 3,6-dimethyl-l-isopropylacenaphthene (VI). When they synthesized VI they found i t to be different from the hydrocarbon obtained from agathic (1) (a) L.Ruzicka and J. R . Hosking, A n n . , 469, 147 (1929); Helu. Chim. A d a , 18, 1402 (1930); i b i d . , 14, 203 (1931); (b) L. Ruzicka, R. Steiger a n d H. Schinz, ibid., 9, 962 (1326); (c) L. Ruzicka and H. Jacobs, Rec. Iraw. chim., 67, 509 (1938); (d) L. Ruzicka, E. Bernold and A. Tallichet, Helu. Chim. A d a , 24, 223 (1941); (e) L.Ruzicka and E. Bernold, i b i d . , 9 4 , 931 (1941); i b i d . , 94, 1167 (1941). (2) L.Ruzicka, R. Zwicky and 0. Jeger, i b i d . , 31, 2143 (1948). (3) 0.Jeger, 0.Diirst and G. Biichi, i b i d . , 30, 1853 (1347). (4) CJ’, J. Simonsen and D. H. R . Barton, “ T h e Terpenes,” Vol. 111, Cambridge University Press, Cambridge, 1952; L. F. Fieser and M. Fieser, “Natural Products Related to Phenanthrene,” Reinhold P s b l . Corp., New York, N. Y.,1940. (5) I,. Ruzicka and E. Rey. HeEv. Chitit. Ails, 26, 2136 (1943).
I
1’
09 I
I11
vI
I1
65 I
IV
VI1
acid. Fieser and Fieser4 suggested 2,2,S-trimethyl1,2,3,4-tetrahydrophenanthrene (VII) as an expression for the C17HZO hydrocarbon. However, this structure can be ruled out because it would not give a ketodicarboxylic acid (C16H1206)an oxidation with potassium ferricyanide, and in addition VI1 should give pimanthrene on further dehydrogenation. It is worthy of note that the structure of this important product of dehydrogenation, in which more carbon atoms of agathic acid are retained than in any other one, was, until the present investigation, still unknown. The knowledge of its structure would certainly have facilitated the efforts to arrive at a structural expression for agathic acid (I). I n this paper we report work on the structure and a synthesis of the hydrocarbon Cli”20 (Iv). We turn first to a discussion of a possible mecha-
G. BUCHIAND JAMES J. PAPPAS
2964
nism of ring closure during the dehydrogenation of agathic acid. The formation of pimanthrene involves the synthesis of a new carbocyclic ring, which must precede the aromatization of the bicyclic system. This change may go through the following stages: (a) decarboxylation of agathic acid to an intermediate VIII; (b) cyclization of VI11 to a tricyclic species IX, a reaction which is probably catalyzed by either hydrogen selenide or hydrogen sulfide depending on the dehydrogenating agent used ; and (c) dehydrogenation of IX to pimanthrene (111). This mechanism explains the absence of
Vol. 76
a-diketone could undergo a benzilic acid rearrange ment and the a-hydroxy acid X I 1 would be oxidized further to C16H1206 (V) which would be resistant to further oxidation because i t does not contain any activated hydrogen atoms. Consequently we were convinced that the C1?H2ohydrocarbon has structure IV and decided to synthesize this compound.
$I+ XI11
VI11
4
.1
IX f-
I
pyooc*I15
COOH XVI
COOH XV
.1
0J?l ,
I
IV
-~-~:cooH
b+WH
I
$;coo*
--+ XVII
p C O O E I
I
COOH
COOH
V
XI1
pimanthrene (111) in the products of the dchydrogenation of tetrahydroagathic acid.‘” If the dehydrogenation precedes the formation of the third ring the production of a phenanthrene hydrocarbon becomes impossible, but instead substitution on the acarbon atom of the naphthalene nucleus can occur in the intermediate X and the resulting product is 1,1,4,7-tetramethylphenaIan (C17HZo) IV. The formula IV explains all of the reported reactions of the hydrocarbon C17H20 thus: (a) phenalan and its homologs are resistant to further dehydrogenatione; (b) two out of the five double bonds present in such compounds can be hydrogenated over Adams platinum catalyst; (c) the ultraviolet spectrum is similar to the spectrum of naphthalene; and (d) the oxidation of IV with potassium ferricyanide in basic solution leads to a ketodicarboxylic acid V. Oxidation to carboxyl and ketone functions, respectively, would occur a t the activated methyl and methylene groups to give intermediate XI. This ( G ) (a) L. C. Craig, W.A. Jacobs and G. I. Lavin. J. Bioi. Chern., 139, 277 (1041); (h) K. Fleischer a n d E . Retze. BcY.,66, 3280 (1922).
IV
’
OH XVIII
Ioiiene (XIII) was oxidized with chroiniunl trioxide in acetic acid solution,’ and the neutral fraction separated into ketonic and nun-ketonic fractions by extraction with Girard reagent “T.”A ketone whose ultraviolet spectrum was similar to that of tetraloneBwas obtained in approximately 25% yield. The compound was iaentical- with 4,4,7-trimethyl-3,4- dihydro - 1(2H) - naphthalenone (XIV) which had previously been synthesized by another route.9 The Stobbe condensation between diethyl succinate and XIV proceeded in excellent yield when potassium t-butoxideln was used as a condensing agent. The ultraviolet absorption spectrum indicated that the ester is P-carbethoxy6 - (4,4,7-trimethyl-3,4-dihydro-1-naphthyl) - propionic acid (XV) rather than the corresponding a$unsaturated ester. The hydrogenation of XV to 6 - carbethoxy-P-(4,4,7-trirnethyl1,2,3,4- tetrahydro-1-naphthyl)-propionicacid (XVI) was fastest in the presence of a mixed catalyst consisting of palladium on charcoal and Adams platinum catalyst. Conversion of XVI to XVII could not be brought about by anhydrous hydrogen fluoride. Cycliza(7) T h e oxidation of ionene was reported previously by F. Tiemann a n d P. Kriiger ( B e y . , 116, 2694 (1893)) but they did not investigate the neutral compounds formed in this reaction. (8) Mme. P. Ramart-Lucas and M. J . Hoch, BzLII.SOL. chim.. 6, 848 (1938). (9) R. A . Barnes and C. K. Bucliwalter. THISJ O U R N A L , 73, 3858 (1051). ( 1 0 ) \V. S, JU~IIISOII, 11, C. li. J o h ~ ~ s ,&i1
