236
JAMES
I%-.WHEELER,JR.,
AND
cis-3,5-Dimethylcycloheptanone (VIb) .-The ring expansion of Vb was carried out in a n identical manner to t h a t described for the expansion of T'a. From 15.0 g. of Vb the following fractions were obtained a t 12 mm.: (1) 3.33 g., 11.p. 66.5-70.5:; (2) 1.30 g., b.p. 70.583.5'; ( 3 ) 8 . i 5 g., 11.p. 83.5-86.0'; (4) 0.97 g., b.p. 85-94'. Fraction 3 was the desired ketone YIb, @D 1.4524, d25 0.9115 g.,/ml. The semicarhazone, prepared in the usual way and recrystallized illice, had m.p. 165.7-166.6', reported" m.p. 166.5'. Equilibration Studies.--.L 100-ing. sample of the ketone t o he equilibrated w a i placed in ;t stnall sexled t u h e Iyitli 25
RICHARD H. EASTXAS
Vol. 51
ing. of palladium-on-carbon. The tube, placed in an iron pipe, was heated in a furnace a t the desired temperature which was maintained f 3 ' . The pipe was then removed from the furnace and cooled rapidly by wrapping with a wet towel. The sealed tube was opened to the atmosphere arid the catalyst was settled by centrifuging. The liquid \vab drawn off with a dropper and weighed into a vial and the proper amount of chloroform was weighed in to givc t h r solution for the infrared analysis. The analysis was made in the usual ~ - a ? - , ' ~a n d the results are summarized in Table I. D E I K O I T~,I I C M .
! C O N T K I B L T I O S F R O M T H E L ) E P A R T M E N T OF C H E M I S T R Y A X D CHEMICAL E S G I N E E R I S G , S T A S F O R D r S I V E R S I T l ]
The Photolysis and Pyrolysis of Umbellulone l 131' J A M E S
n-. M'HEELER,
JR., AND KICI~ARD H. EASTNAX RECEIVED AL~GUST 26, 1958
,.
Ihe pliotolysis of umbellulone produces t h q mol in easentially quantitative duces, in addition t o thymol, E-lOyo of sym-thymol and traces of p-cymene It has recently been ivund that the cyclohexadienone systems of prednisone acetate and santonin undergo isomerization to the bicyclo [3.1.O] hexeiione system found in umbellulone (I) upon ultraviolet irradiation, prednisone acetate yielding I1 : m l santonin (III).*
J
ield,
\I
hile the p~ rolysis o f u~ribelluloi~e pn-
only thymol (IV) but also sym-thymol (VI) to the extent of 5-10y0. and traces of p-cymene. Separation of sym-thymol from thymol proved difficult, but was achieved by fractional crystallization of the pyrolysate followed by liquid-vapor partition chromatography of the mother liquors. The identity of the sym-thymol (rn.p. 49.5-50.0') from the pyrolysis was established by comparison with an authentic sample (m.p. 49.5-50.0') prepared following the method of Knoevenagel.6 No depression was observed in a mixed melting point determination, and the two samples had identical infrared absorption spectra. n'hile the appearance of sym-thymol as a pyrolysis product was somewhat surprising,' it can be rationalked on the basis of a ring-enlargement in the >pecies as
11-e have noted that samples of umbellulone (I) which have been exposed t o light invariably contain traces of thymol (11-j ; and in view of the appareiit stability of the umbellulone systems of 11 and 111. it became of interest to determine thc course of the photolysis of umbellulone itself. The photolysis of umbellulone using a variet!. cri sources of radiation (cf. Experimental) produces thymol i i i quantitative yield. In view of the clear-cut iiature v i the pliotolysis, we undertook a reinvestigation of the therinal isonicrization of uinbellulotic, first reported by ,9~111111l d to yield thyiiiol, aiid a vital link in his proof Oi the structure of uiiibelluluiie.4 Since his obser\-atioii. the thermal isomerization of umbelluloiie has continued to be of interest." Contrary to a recent I t is iioteworthy that the pyrolysis and photolywe have fvund that the crude pyrolysate sis of umbellulone apparently proceed by different froin carefully-purified umbellulone contains not pathways. The results suggest an ionic course for the pyrolysis and a free radical course for the pho[ I ) ' l h e material of this article is taken irum t h e thebib fur the b1.S. ilcjiirc of James \Y. Wheeler, Jr., a t Stanford Uni\-ersity. tolysis. 12) U . Arigoni. 13. Bosshard, H. Bruderer. G. Buchi, 0. Jeger and The failure of the umbellulone systems in I1 and I.. Icrebaum, Heln. Chim. A c t a , 40, 1733 (1957); D . H. R. Barton I11 to undergo facile aromatization on irradiation . t i i d \\', C. Taylor, THISJOCKSAI., 8 0 , 244 (19S8); D. H. R . Barton, P. ( I C S l a y o and 51. Shafiq, Prvc. Chevi. Soc.. 205 (1957); J . Chein. S O L . , in analogy to umbellulone may be related to the 141) ,l!i>S) structural situations in I1 and I11 that require the 4 1 F. Semmler, Bev., 40, 5019 (1907); 41, 3992 (1908). scission of two carbon-carbon bonds for the proI 1 T h e recent synthesis of a n isomer of umbellulone [H. E. Smith duction of an aromatic system. .ind I
