r .,018
Vol. 77
N. J. LEONARD, ,4. J. KRESGEAND MICHINORI OK1 [CONTRIBUTION FROM
THE
?*TOYES CHEMICAL LABORATORY, USIVERSITY OF
ILLINOIS^
The Influence of Steric Configuration on the Ultraviolet Absorption of ‘Fixed” Benzils1*2 B Y NELSON
J. LEONARD, -4. JERRY
K R E S G E 3 AR‘D MICHINOR1 O K 1
RECEIVED APRIL 13, 1955 5-lvfethyldibenzo[a,d]cyclohepta[ 1,4]diene-lO,ll-dione (IXb) and 11,12-dihydrocycloocta[u,e]dibenzene-5,~-dione (IXc) have been synthesized by efficient yet lengthy procedures starting with 2-(a-phenylethy1)-benzoic acid and 2-(P-phenylethyl)-benzoic acid, respectively. Structure establishment of the diketones was based upon their chemical conversions and upon the infrared absorption spectra of their intermediates. Isomers IXb and e , which can be regarded as “fixed” analogs of benzil with the geometry of the molecule determined by the size of the central ring, have ultraviolet absorption spectra markedly different from each other and from that of the open model, o-tolil. The position of the long wave length maximum is dependent primarily upon the magnitude of the inter-carbonyl angle in these diketones. The possibility of isoinerizatioii of IXa and IXb t o substituted tropolones also has been investigated.
I t has been established previously, using a series of alicyclic l,a-diketones, that the position of the long wave length ultraviolet absorption band is dependent upon the angle between the planes of the carbonyl groups; thus, the band moves toward shorter wave length as the angle increases from 0 to 90” and shifts back again toward longer wave length as the angle increases beyond I t also has been shown, in a study of sterically hindered benzils, that the dicarbonyl absorption maximum is shifted to longer wave length with increasing hindrance a t the o-carbons of benzil, corresponding to increasing tendency to coplanarity of the two carbonyl groups (probably 90 + 1SOo).6 The information that was still lacking was the location of the dicarbonyl absorption maxima for compounds of the benzil type in which the two carbonyl groups approached cis coplanarity rather than trans coplanarity. We felt that this information might be provided by a study of “fixed” benzils in which the steric configuration of the carbonyl groups was somewhat restricted by linking the o-carbons of the two rings through an alkylene group of varying size
(IX).6 When less conventional methods failed to produce the desired diketones IX, we resorted to a straight-forward reaction sequence, illustrated in the accompanying diagram (I 4 IX). 2-(y-Phenylpropyl)-benzoic acid (Id) was obtained by treatment of o-phthalaldehydic acid with 0-phenylethylmagnesium bromide, followed by reduction of the 3-(8phenylethyl) -phthalide. The esters prepared from this acid and from 2-benzylbenzoic acid (Ia),j 2-(aphenylethyl) -benzoic acid (Ib),8 and 2-(P-phenylethyl)-benzoic acid (1c)Y were reduced with lithium aluminum hydride to the correspondingly substituted a-toluols (111). These were converted in good yields through the a-tolyl bromides (IV) and a-tolunitriles (V) to the acids : 2-benzyl-a-toluic acid (VIa), 2-( a’-phenylethy1)-a-toluic acid (VIb) (1) Presented a t the 127th National Meeting of t h e American Chemical Society, Cincinnati, Ohio, M a r c h 30, 19.55; see Abstracts of Papers, p. 13p\-. ( 2 ) T h i s work mas supported in p a r t b y a grant from E . I . d t i Pont de S e m o u r s a n d Co , Inc. ( 3 ) Eli Lilly and Co. Fellow, 1952-1933. ( 4 ) N . J . Leonard a n d P. 3 [ . Slader, THTSJ O I J R N A I . , 1 2 , 3 8 8 :1950). ( 5 ) IJ. Leonard . and E . R . Blout. ibid., 72, 484 (1950). 16) This project mas initiated b y P. 11. S I a d e r ; see P h . D . T h e i i i , Univerqity of Illinois, 195C. (7) E. d e B. B a r n e t t , J. W. Cook a n d I. G. K i x o n , J . Chein. .So?-A(
+
I
(1) H. 0. House, THISJOURNAL, 77, 3070 (1955). (2) D.Y.Curtin and E. K . Meislich, i b i d . , 74, 5905 (1952). (3) F. Bergmann and A. Kalmus, ibid., 76, 4137 ('954). (4) I t seems probable that similar generalizations apply to 1,2-disubstituted ethylene oxides where one of both of the substituents are vinyl groups rather than aryl groups. The following references report cases where the treatment of such epoxides with magnesium bromide
Compt. rend., 307, 920 (1938); 311,441 (1940). (h) M. Tiffeneau and P. K. Kuriaki, i b i d . , 309, 465 (1939). ( 5 ) Only one of the enantiomorphic structures of the racemate em-
ployed has been pictured. (6) F. H. Norton and H. B . Hass, THIS JOURNAL, 58, 2147 (1936). (7) M. Tiffeneau and B. Tchoubar, Compl. r e n d . , 207, 918 (1938). T h e stereochemistry of the 2,3-epoxypentane was not stated.
