DONALD D. PHILLIPS AND EARLJ. MCWHORTER
3856
[CONTRIBUTION FROM THE BAKERLABORATORY
Polynuclear Aromatic Hydrocarbons. B Y DONALD D.
OF
111.
P H I L L I P S AND
VOl. 77
CHEMISTRY, CORNELL UNIVERSITY]
The Synthesis of 4-Methylpicene
EARLJ.
nICWHORTER2
RECEIVED FEBRUARY 24, 1955 The synthesis of picene froin 9,10-dihydrophenanthrenehas been extended to the preparation of 4-methylpicene followiiig the reaction sequence outlined in Chart I. Cyclization of acid 117, an important intermediate in the scheme, produced R larger ratio of the octahydropicene derivative (Lr) (one of four possible isomers) than was obtained from the acid having unbranched side chains. Although i t was very similar to picene in physical properties, 4-methylpicene (VI) differed signific m t l y in its infrared and ultraviolet absorption spectra.
I n a recent communication1 it has been shown that ester I can be prepared conveniently by the Friedel-Crafts condensation of 9,lO-dihydrophenanthrene and ethyl allylacetate. We now wish to record the synthesis of 4-methylgicene (VI) from this important intermediate. CHARTI
~
7H2C02CH3
CHzCOC1
\VV I I
'I I
LA'
COlCzH,
1, Pti/C, 270' 2, KOH
AICh
+
picene was the principal hydrocarbon obtained oil dehydrogenation. The synthesis of VI, a new compound in ihc monomethylpicene series, was accomplished by the scheme outlined in Chart I. Ester I was succinoylated by the previously reported3 method and thc oily ketoester I1 was re duced t o 111 by Horning and Reisner's procedure. The latter compound then was aromatized and saponified in the usual fashion to give the dibasic acid IV. Polyphosphoric acid cyclization5 of IV gave a mixture I of diketones and the pre\/COZCH~ 11 dominant isomer was reI duced, dehydrated and dehydrogenated t o 4-methylpicene (VI), m p 372-374" dlthough similar in physical properties i o picene, polyphosphoric the infrared sDectrum of L-I was A acid quite different'. (FLg1.) I t was somewhat unexpected that 4-methylpiccne would havc an rn.p. slightly higher than the seemingly more synimetrical parent compound, since substitution by methyl generally lowers the m.p. of a polynuclear aromatic hydrocarbon. However, l-methylchrysene, the analogous compound in the chrysene system, has approximately the same m.p. as chrysene6and other exaingles i r o n the 1,2-benzanthracene series7 indicate that there are several exceptions to the generalization so that the behavior in the picene series is not unique.
ExperimentalK The reaction sequence (Chart I) was based on our original3 synthesis of the picene skeleton. One of the purposes of the investigation was t o study the effect of a branched side chain on the cyclization of acid I V , which theoretically could produce four isomeric diketones. If the cyclization favored the formation of a reduced picene skeleton as in V, our original scheme3 then could be adapted safely to the synthesis of substituted picenes which we require for comparison with certain dehydrogenation products of a-amyrin. Although the mixture of diketones was not separated carefully, the predominant isomer must have been V,since 4-methyl(1) Paper 11, D. D. Phillips and E.5. AIclX'horter, T H I SJ W R X A L , 7 6 , 49-28 (1954). 12) Shell Felloiv i n Chemistry, 1953-1954. This material is a b stracted from t h e P h . D . thesis of E . J . McWhorter, Fehruary, 1:):; !:
