Y+q -q - ACS Publications

give 1-ethoxycarbonylindane (IV), whose identity was established by hydrolysis to the known crystalline acid, 1-carboxyindane (V). '1 toluene. Y+q -q...
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March 5 , 1964



T h e n.m.r. spectrum showed a doublet (ca. 1 c . P . s . ) ~a ~t 8.31 (allylic methyl, 6 protons), a multiplet centered a t 7.70 r (allylic methylenes, 8 protons), and a multiplet centered at 4.64 r ( 2 olefinic protons). Ozonolysis of 111 and subsequent oxidative work-up afforded 2,5-hexanedione [bis-(2,4-dinitrophenylhydrazone), m.p. and mixture m.p. 256"S5] and succinic acid ( m . p . and mixture m.p. 184'36). The unidentified minor products had retention times on a number of V.P.C.columns which did not correspond to those of a n y of the known thermal dimers14,lsor photodimers" of isoprene. Kinetic Determinations.-For each kinetic run the following compounds were pipetted into a 10-ml. flask equipped with a micro reflux condenser, a thermometer inlet, and a septumcovered outlet arm: I (1.00 cc.), n-nonane (1.00 cc., internal standard), and o-dichlorobenzene (5.00 cc., solvent). T h e reaction flask was then partially submerged in a n oil bath (550 in.3) which had been preheated to constant temperature. Temperature control was maintained by a Jumo thermometer connected t o resistance heating coils and a mercury relay which served as a thermostat (H-B Instrument Co.). Control of f 0 . 2 ' was thus maintained. 7

(34) For similar examples of -CH=C(CH8)coupling, see E. I. Snyder, and J . D . Roberts, J . A m . Chem. SOC.,8 4 , 1582 (1962); G . S. Reddy, R . T . Hobgood, Jr , and J H . Goldstein, ibid.,84,336 (1962); " S M R Spectra Catalog," Varian Associates, National Press, Palo Alto, Calif., 1962, pp. 272-273. (35) F . Serdel, E. Henkel, R.Kayser, and G . Kannelbley, J prakl. Chem , 43, 153 (1956).



Microliter samples, withdrawn periodically and quenched, were analyzed b y v.p.cS3l Disappearance of I was determined by comparison t o the internal standard. Previous V.P.C. analyses of I and n-nonane in varying ratios established the relationship between peak areas and molar amounts. T h e constancy of the internal standard throughout a run was demonstrated by independent experiment^.^' T h e disappearance of I over the temperature range 101-128' proved t o be cleanly first order u p t o high conversions. The kinetic d a t a obtained are compiled in Table 11. Effect of Additives.-Three thick-walled glass tubes were charged with identical solutions of compound I (2.0 9 . ) in chlorobenzene (10.0 ml.). The solutions were outgassed three times by conventional techniques and saturated with oxygen, nitric oxide, and nitrogen (control), respectively, b y repeated additions of the gases to the evacuated systems. T h e tubes were then sealed and heated simultaneously in a n oil bath for 1 hr. After cooling, the tubes were opened and analyzed by v . P . c . ~ ~In each case reaction had proceeded t o 87 f 2% conversion.

Acknowledgments.-The authors are grateful t o Prof. P. R. Schleyer (Princeton) and Prof. H. H. Wasserman (Yale) for helpful suggestions. (36) M . T . LeMer and R . Adams, J . A m . Chem. SOC.,68, 1553 (1936). (37) The importance of precise temperature control and internal standard constancy was illustrated by earlier runs in which erroneously low values were obtained for a number of the specific rate constants.


The Thermal Rearrangement of 9-Ethoxycarbonylbicyclo[6.1.O]nona-2,4,6-triene BY KARLF. BANGERT AND V. BOEKELHEIDE RECEIVEDAUGUST19, 1963

9-Ethoxycarbonylbicyclo[6.1.0)nona-2,4,6-triene ( I ) undergoes rearrangement at 150" giving t h e 9,lO-dihydroindene derivative I1 a s t h e main product. T h e structure and stereochemistry of I1 have been established through degradation and aromatization studies.

In the course of an investigation directed toward the preparation of the cyclononatetraene anion, we have examined 9-ethoxycarbonylbicyclo [e.1.O]nona-2,4,6-triene (I) as a possible precursor. Its preparation has been previously described by Akiyoshi and Matsuda' and by Phillips,2 who utilized the reaction of cyclooctatetraece and ethyl diazoacetate for its preparation. Although the structure of I seemed secure from the earlier work, we were interested in having material of high purity and so subjected I to vapor phase chromatography. Two products were observed, neither of which corresponded t o the starting ester I. Further, when compound I was subjected to careful distillation using an efficient spinning-band column, the main product was not I but was instead an isomer. Subsequently, i t was shown that I undergoes a rearrangement a t temperatures above 150" giving I1 as the main product and another product I11 in minor amounts.

O C H C O , E t I





(1) S. Akiyoshi and T . Matsuda, J . A m . Chem. Sac., 7 7 , 2476 (1955). (2) D. D . Phillips, ibid., 77, 5179 (1955). (3) E. Vogel and H . Kiefer, Angew. Chem., 73, 548 (1961). (4) We are grateful t o Professor Vogel for making the details of this spectrum available t o us. Through this correspondence we learned that he has also observed this same rearrangement and we are indebted to him for re-

but in sharp contrast to the starting ester I [A,,, 244 mp (log e 3.56)]. In the infrared the ester carbonyl of I1 showed a normal absorption ( V C = O 1736 cm.-l) and the absence of conjugation was confirmed when hydrogenation of I1 did not affect the frequency of the carbonyl absorption. For the n.m.r. studies, the corresponding hydrazide of I1 proved t o be most suitable and its spectrum showed clearly that the ratio of olefinic to aliphatic protons was 6 : 3. Since the spectral data were nicely compatible with a structure such as 11, chemical studies were undertaken t o test this hypothesis. In accord with the proposed cis-conjugated diene grouping, I1 readily underwent a Diels-Alder addition with N-phenylmaleimide. Further, as expected for an 8,g-dihydroindene, I1 was easily aromatized on heating with a 10% palladium-on-charcoal catalyst in toluene t o give 1-ethoxycarbonylindane (IV), whose identity was established by hydrolysis t o the known crystalline acid, 1-carboxyindane (V). 1 '

Y+q -q





peited, bgth I1 and its hydrazide when subjected to hydrogenation over a palladium catalyst in ethanol absorbed 3 moles of hydrogen rapidly and cleanly. porting his work t o us prior t o publication (61. E. Vogel, W. Wiedemann, H.Kiefer, and W. F. Harrison, Tetrahedron Lellers, 11, 673 (1963))



VOl. 86

Conversion of the saturated ester VI to the correspond(8.68 T) is essentially the same as t h a t observed in ing amide VI1 occurred smoothly in the usual manner their case. via the acid and acid chloride. Hofmann degradation of the amide yielded the saturated amine VIII, whose benzoyl derivative I X melted a t 130-131'. I t has been shown previously by Hiickel and his collaborators that reduction of cis-hydrindan-1-one oxime gives a X mixture of the epimeric 1-amino-cis-hydrindane~.~ In studies on the thermal rearrangement of bicycloThese, after separation, give benzoyl derivatives [ 6.1.01nona-2,4,6-triene and its 9,g-dihalogen derivamelting a t 180 and 131', respectively. When this tives, Vogel has considered both X I and XI1 as probresult is combined with the fact that the hydrindane-lable intermediate^.^,^ I n the case of the 9,9-dichloro carboxylic acid obtained as an intermediate in our derivatives, which yield XI11 as the final product of sequence is definitely different from the presumably the rearrangement, a reaction path involving XI1 all cis-hydrindane- 1-carboxylic acid prepared by has been favored. However, such a reaction path Knowles, Kuck, and Elderfield,G it can be concluded seems unlikely for our 9-ethoxycarbonyl derivative that the stereochemistry of our l-benzoylamino-cissince it would predict 2-etho~ycarbonyl-8~9-dihydrohydrindane is correctly represented by I X . I n turn, indene as the final product rather than structure I1 the full assignment of stereochemistry to I1 can be as observed. made as shown. As a final detail, the amine VI11 was subjected t o the Hofmann exhaustive methylation procedure and the olefin so obtained was hydrogenated. The resulting saturated hydrocarbon was shown by infrared spectral comparison to be cis-hydrindane.




I 2"

IX VI11 on the reaction product of In the previous cyclooctatetraene and ethyl diazoacetate, no definite assignment of stereochemistry was given to I. However, Phillips suggested that there was an interaction between the triene system and the ester carbonyl in order to explain the fact that the ultraviolet absorption maximum (A 245 m,u) is abnormally low. Our examination of the n.m.r. spectra of I and its derivatives, especially the acid X , is not in agreement with this interpretation but favors instead the stereochemistry shown for X. Thus, the lone proton in the cyclopropane ring gives a triplet signal centered a t 8.68 T with a coupling constant of 4.7 C.P.S. The remaining two protons of the cyclopropane ring appear as a doublet centered a t 7.88 7 and again with a coupling constant of 4.7 C.P.S. Since the work of Graham and Rogers7 indicates that the coupling constant for trans-protons of a cyclopropane ring should be about 5.68 C.P.S. whereas that of cis-protons should be around 8 . 2 c.P.s., the trans assignment as shown by X is clearly indicated. With regard to an explanation for the abnormal absorption in the ultraviolet, we would suggest that this is probably due to an interaction between the triene system and the cyclopropane ring rather than the ester carbonyl. Recently, Sauer and SonnetR have obtained n.m.r. evidence supporting a transannular effect between an olefinic double bond and the proton of a similarly-substituted cyclopropane ring. I t is of interest that the chemical shift of our lone proton (a) W. Huckel, M. Sachs, J Yantschulerwitsch, and F. Nerdrl, A n n , 618, 155 (1935) ( 6 ) W S Knowles, J A . K u c k , and R C. Elderfield. J Org C h e r n . . 7 , 371 (1942). (7) J I). Graham and M. T . Rogers, J . A m . Chem Soc , 8 4 , 2249 (1962) (8) R . R . Sauer and P. E Sonnet, Chem. I n d . (London), 786 (1963).

XI11 Thus, a reasonable postulate for the rearrangement would be that I undergoes rupture of the cyclopropane ring to give the cyclononatetraene derivative XIV which then, by ring closure as indicated by the dotted line, would lead to the product 11. I t was because of this, in part, that we have been concerned with the stereochemistry of I and 11. An examination of models would suggest that, if the transition from I to 11, as envisioned with XIV as an intermediate, is essentially a rapid and efficient reorganization of bonding, then a molecule having the stereochemistry deduced for I should lead cleanly to a product having the stereochemistry deduced for 11. At least the experimental data are consistent with postulating a simple thermal reorganization of bonding. COZEt






XIV The minor product I11 from the rearrangement is a colorless, air-sensitive oil. The separation and purification of I1 and I11 by vapor phase chromatography indicates that the two products are formed in the ratio of 4 : 1. The ultraviolet absorption spectrum of I11 shows maxima a t 307 (log E 3.45)) 295.5 (log E 3.54), 282.5 (log e 3 . 5 8 ) , 271 (log E 3.60), 262 (log e 3.54), and 252 r n w (log E 3.41). Also, it readily forms an adduct with tetracyanoethylene, suggesting the presence of a &-conjugated diene. However, the sensitivity of 111 has prevented obtaining sufficient material of satisfactory purity to determine its structure.

Experimental lo 9-Ethoxycarbonylbicyclo[6.l .O]nona-2,4,6-triene (I) was prepared following the procedure described by Phillips* in 627, yield based on the ethyl diazoacetate employed. T h e n.m.r. spectrum of I shows the vinyl hydrogens of I a s a split peak a t 4.25 (4-protons) and 4.30 T ( 2 protons). This split peak absorption in t h e vinyl region is typical of all the bicvclo[6.1.0]nona-2,4,6-triene derivatives we have examined. For characterization, t h e Diels-Alder adduct of I with dimethyl acetylenedicarboxylate was formed by heating I in a fivefold excess of dimethyl acetylenedicarboxylate overnight a t 128'. After removal o f the excess dimethyl acetylenedicarboxylate and ~~


(9) E T'ogel, Angrw Chem , 74, 829 (1962). (10) Analyses by F Pascher and Microtech Laboratories The n m.r. spectra were determined w i n g a Varian A-60 spectrometer, the infrared using a Beckman IR-5, and the ultraviolet using a C a r y Model 11.

hlarch 3 , 1964


recrystallization of the solid from methanol, white crystals, m.p. 123-124', were obtained. A n a l . Calcd. for ClsH2oOa: C , 65.04; H, 6.07. Found: C , 64.74; H , 6.04. The corresponding acid X was obtained by alkaline hydrolysis, as described by Akiyoshi and Matsuda,' and melted a t 162-163". I t s n . m . r . spectrum showed the split vinyl peak at 4.20 and 4.25 T . For further characterization the acid was converted t o the corresponding acid chloride using thionyl chloride; this, in turn, was converted t o the corresponding amide and methyl ester. Bicyclo [6.1.O]nona-Z ,4,6-trien-9-carboxamide was obtained after recrystallization from methanol-water as white crystals, m.p. 194-195', in 80% yield. Anni. Calcd. for C l r r H l l S O : C , 74.51; H , 6.88; h', 8.69. Found: C , 71.82; H,6.95; N,8.82. 9-Methoxycarbonylbicyclo [6.1.O]nona-2,4,6-triene was obtained in 857, yield as an oil, b.p. 78-87' a t 0.8 mm., which solidified on standing. Recrystallization of the solid from pentane gave white crystals, m . p . 42-43', A,, 242 mG (log e 3.63). Passage of the methyl ester over a Carbowax column in the vapor phase chromatograph a t 200' effected isomerization in t h e same manner as with the ethyl ester I. Anni. Calcd. for CllH1202: C , 74.97; H, 6.86. Found: C , 74.66; H , 6.99. Thermal Rearrangement of 9-Ethoxycarbonylbicyclo [6.1 .O]nona-2,4,6-triene ( I ) to Give I1 and 111.-.A 20.0-g. sample of I was placed in a distilling flask attached t o an efficient spinningband distillation column and heated a t a bath temperature of 160-180° for about 10 niin. under partially reduced pressure. The pressure was then reduced t o 14 mm. and the material was slowly and carefully distilled. This required about 1.5 hr. and the boiling point range was 120-130". T h e crude product (15.0 g.) was then subjected to preparative vapor phase chromatography using a Carbowax column. Analytical vapor phase chromatography had indicated the presence of one main component and two minor ones. From the preparative column the ratio of the tnain product I1 t o the minor product 111 was about 4 : 1. The minor product 111 is discussed later and the second minor component was not isolated in useful amounts. Distillation of the main product I1 from the preparative column gave a colorless oil, b.p. 78' a t 0.5 m m . A n a l . Calcd. for C I ~ H I ~ O C ? ,: 75.23; H, 7.42. Found: C, 74.77; H , 7.34. The N-phenylmaleimide adduct of I1 was prepared in boiling chloroform a n d , after recrystallization from ethanol, was obtained as white crystals, n1.p. 166.5-167". Anal. Calcd. for C22H2,NOa: C , 72.71; H, 5.82; S , 3.85. Found: C , 72.45; H , 5 . 6 1 ; N , 3 . 5 5 . T h e hydrazide of I1 was prepared by heating a solution of 500 mg. of I1 and 500 mg. of hydrazine in 10 nil. of ethanol containing 0.5 ml. of water under reflux for 2 hr. The volatile solvents were removed under reduced pressure and the solid residue was recrystallized from water t o give white crystals, n1.p. 124-125', A,, 262 (log e 3.41) and 270 11111 (log e 3.38). A n a l . Calcd. for ClaH12N20: C, 68.16; H, 6.86; N, 15.90. Found: C,67.66; H , 6 . 8 1 ; S ,15.79. Hydrolysis of I1 t o the corresponding acid was carried out b y dissolving 3.0 g. (Jf I1 in 20 nil. of a 55; rnetlianolic potassium hydroxide solution and allowing the solution t o stand overnight, After removal of the methanol, the residue was acidified and the resulting oily acid was extracted with methylene chloride. The methylene chloride extract was concentrated and the residual oil distilled ( b . p . 108-115" a t 0 . 5 turn). Since the acid could not be induced t o crystallize, it was taken up in chlorof~rrma n d treated w i t h maleic :inliydride t o obtain a crystalline derivative for characterization. T h e maleic anhydride adduct of l-carboxy-8,9-dihydroindene, thus prepared, was :i solid which, after recrystallization from etlih-l acetate, gave white needles, m . p . 204.5-206.5". :1nal. Calcd. for C,,H,,O,: C , 64.61; H , 4.65. Found: C, 64.11; H , 1.83. Separation of I11 by Vapor Phase Chromatography.-This separation !vas effected using ii 5-ft. column filled with Carbowax a n d held a t ~ 0 with ~ :I~ helium " pressure of 40 p.s.i. The retention time ( i f the main product I1 WLS 17.8 rnin. Tlie retention time of tlie iniiior product I r I was 19.5 t r i i n . Traces of another prciduct \vue eluted a t 22.0 niin., but this c(iultl never be isolated in useful aniounts. Because of tlie instability of 111, it was used directly froin the preparative colunin for spectral cleterrniti:itions arid for characteriziti!iti. Tlie iliain features of its ultraviolet spectrum :ire given i n tlie Discussion. The tetracyanoethylene adduct of I11 was prepared in ethyl acetate. After retnrival of solvent, the resulting solid \vas recr>-stallizedfrom ~ n e t h a i i t~o~give l white crystals, 1i1.p. 169-170". A n d . Calcd. for C~EHI,S%OP: C , 67.91; H , 4.43; S , 17.60. Found: C , 67.80; H , 4.70; N , 17.70.


Aromization of I1 over Palladium.--A mixture of 1 . 0 g. of I I and 200 mg. of a 5c0palladium-on-charcoal catalystLL i n 10 1111. of toluene was boiled under reflux overnight. Xfter reinoval of the catalyst and solvent, the residue remained oily and could not be induced t o crystallize. Therefore, it was hydrolyzed directly by dissolving it in 10 ml. of a lOY0 methanolic potassiutn hydroxide solution and allowing the mixture t o stand at room teiiipera ture overnight. After concentration of the solution the residue was dissolved in water and acidified. This gave a solid which, when recryst:illized from methanol, yielded white crystals, i n . p . 59-60' (lit.6 12 gives 59-60' as the melting point of I-carbox>.indane( \')), 1-Ethoxycarbonyl-cis-hydrindane( V I ) .-.I mixture ( J f 24.0 g. of I1 and 250 mg. of Adams catalyst i l l 200 nil. of ethanol was subjected t o hydrogenation a t room temperature and atmospheric pressure. .Absorption of 3 moles of hydrogen was complete in 4.5 h r . Xfter removal of the catalyst, the solution was cuncentrated and the residual oil distilled t o give 22.5 g. (9474) of a colorless oil, b.p. 97-99' a t 2.3 m m . Anal. Calcd. for Ci2H2oOa: C, 73.43; H , 10.27. Found: C , 73.30; H,10.41. The hydrazide of VI was prepared by heating a solution of \'I in ethanol with hydrazine as described before for the hydrazide of 11. The resulting solid was recrystallized several tiines from water to give white crystals, m . p . l l O - l l l o . When the hydrazide of I1 was subjected t o hydrogenation, as described above for the preparation of \.I, there was a rapid uptake of 3 moles of hydrogen and the resulting product, after recrystallization from water, melted a t 110-1 11O , utidepressed by admixture of the previously prepared sample of the hydrazide of \'I. Also, the infrared spectra of the two samples of the hydrazide of VI were superimposable. Anal. Calcd. for C1~Hi8X20:C , 65.89; H , 9.96; N , 15.37. Found: C,65.79; H , 9 . 5 3 ; S , 14.99. cis-Hydrindane-1-carboxamide (VII).-A solution of 22.0 g. of \'I in 100 ml. of a 15% methanolic potassium hydroxide solution was allowed to stand at room temperature overnight. After concentration under reduced pressure, the residue was dissolved in water and acidified with 570 sulfuric acid. The oily acid, which separated, was extracted with methylene chloride arid then dried by azeotropic distillation of the iiiethylene chloride. Despite many attempts, this oil could nut be induced t o crystallize. Therefore, it was used directly by treating it with 60 1111. of thionyl chloride. The mixture was boiled under reflux ftrr 2 hr. The solution was then allowed to stand a t rooiii temperature overnight before concentrating under reduced pressure. Distillation of the residual oil gave 18.5 g. (8Yc;~,) of the acid chloride as a colorless oil, b . p . 108-118' zit 0.1 nitn. This was disst~lvedin ether and carefully mixed with concentrated aininoniurn hydroxide. The solid which separated \vas c(>llectedand washed carefully with water. I t was then recrystallized froin tiietlianol to give 10.5 g. (64%) (if white crystals, I I I . ~157-158'. . Tliis amide is clearly different froui the ris-liytlrindarie-l-carb(Jx~iItiiide de,cribed by Elderficld.fi Anal. Calcd. for CloHliSO: C, 71.81; H , 10.25; S, 8.38. Found: C , 72.07; H , 10.15; S,8.40. Hofmann Degradation of VI1.-To a solution I J f 2.0 g. of 1'11 in 30 nil. of a lUyGaqueous sodium hydroxide sulution there was added 1 nil. of bromine with stirring. N'hen the solution was stirred overnight a t room temperature, a cr!xt;illine solid sepnrated. The mixture was then warined t o 75' c:iusing tlie s(ilitl to redissolve, and an oil separated. T h e oil was extracted with methylene chloride, dried, and concentrated. Distillation of the residue gave 150 mg. of the ainine \'I11 a s :I coIorIcss oil, b . p . 120-150° a t 12 tniii. This w:i$ taken up in etlier; aqueous 10(,, sodium hydroxide and tlieii benzoyl cliloride were ;iddctl. After the mixture was slt:ikcii vigoroubly, crybtals hegnii to separate from the ether layer. 'The ether was retii(,vetl by evapor:ition arid the solid was collected. Kecryst~cllizatioii of the snlid from methanol gave white crhxtals, m . p . l30-13lo (Hiickcl, et u l . , 3 give 131" for the one stereoisomer of l - h e n z ~ i } l ~ i t n i iis-hydriiii~~-~ dane; for the epimeric l-beiizoyl~irtiiiic,-cis-liy~lriii~~iiic, they give 180' as the melting point.) Conversion of VI11 to cis-Hydrindane.-Tlie preparati(m of the crude amine \.I1 I was carried out i ~ sdewribetl before starting with 2.0 g . !if the amide \'I[. Tlie :imine \.[I1 \ v a s dissolved in 3 ml.of 909; formic acid, 4.0 ml. of formalin (37°C) \viis adtletl, and the mixture was boiled under reflux for 12 hr. 'Then, 1 i n I . of concentrated hydrochloric acid was added and tlie mixture was concentrated under reduced pressure. The solid residue was dissolved in a small amount of water, made basic with sotliu~ii hydroxide, and extracted with cliloroforiii. Concentration of the chloroforin gave an oily residue wliich w i s treated direct1 y (11) K . Xlozingo, Procedure C , "Organic Syntheses," Cull Yo1 1 1 1 . John Wiley and Son-, I n c . , S e w Yclrk. S Y , YI,; p 686 (12) M. Tiffeneati and A Orehhoff, Bid1 soc ~ i ~ r i i l:rai?(e t (41 '27, 7 8 2 (1Y20)



with excess methyl iodide. An exothermic reaction occurred giving a semicrystalline mass. This was dissolved in water, the aqueous solution was extracted with ether, and then a n aqueous solution of sodium perchlorate and perchloric acid was added. T h e crystals t h a t separated from the aqueous solution were collected and recrystallized from water t o give 1.4 g. of N,N,N-trimethyl-cis-hydrindane-1-ammoniumperchlorate a s white crystals, m.p. 218-220'. Anal. Calcd. for C12HdOaCI: C , 51.14; H, 8.58; iX,4.9T. Found: C, 50.49; H, 8.29; N, 4.89. ,4solution of 1.2 g . of the perchlorate in 20 ml. of a 207, aqueous potassium hydroxide solution was heated a t 120" for 2 hr. T h e cold solution was extracted with ether and the ether extract was carefully concentrated. T h e residual oil was dissolved in ethanol, 100 mg. of a 57, palladium-on-charcoal catalyst" was added, and t h e mixture was subjected t o hydrogenation a t room temperature and atmospheric pressure. There was a rapid up-



Vol. 86

take of 61 ml. of hydrogen indicating the presence of 320 mg. (617,) of olefin. After removal of the catalyst, the solution was carefully concentrated. Vapor phase charomatography of the residue using a Carbowax column was carried out and t h e main component was collected and examined in t h e infrared using carbon tetrachloride as solvent. T h e infrared spectrum thus obtained agreed very closely with t h a t given for ~ i s - h y d r i n d a n e ' ~ and was different from t h a t of trans-hydrindane.14

Acknowledgment.-We are indebted t o the National Science Foundation for support of this work. Also, we wish to thank the Badische Anilin and Soda Fabrik A. G., Ludwigshaven A. Rhein, for a generous supply of cyclooctatetraene. (13) American Petroleum I n s t i t u t e Tables of Infrared Spectra, No 1647 (14) American Petroleum I n s t i t u t e Tables of Infrared Spectra, No 1648


Conjugation Effects in Phenylcyclopropanes BY ALANL. GOODMAN' A N D RICHARD H. EASTMAN RECEIVED JULY22, 1963 T h e ultraviolet absorption spectrum of phenylcyclopropane has previously been interpreted as evidence t h a t the cyclopropane ring electrons interact with those of t h e benzene ring t o form a conjugated system. It has now been shown, using rigid model compounds, t h a t t h e steric relationship between the cyclopropane and benzene rings is of little consequence spectroscopically.

The ability of the cyclopropane ring to enter into conjugation with a neighboring unsaturated system has been the subject of a number of recent investigations.* However, few of these have been concerned with ascertaining the steric requirement necessary for such interaction to occur. Walsh3" predicted for interaction that the plane of the cyclopropane ring should be perpendicular to the plane of the unsaturated side chain ; his model was used by Music and h i a t ~ e nto~ predict ~ the ultraviolet absorption maximum of phenylcyclopropane from molecular orbital calculations. Experimental evidence was given by Cromwell* in the case of the cis and trans forms of arylaroylethylenimines and ethylene oxides to the effect t h a t a rather critical orientation of the three-ring atoms and the adjacent p-orbital bearing carbon atom must be met for appreciable conjugation to occur. Fuchs and Bloomfield.ja have provided kinetic evidence for a pronounced geometrical bias in the transmission of electronic effects by the cyclopropane ring, whereas the equilibrium studies of Trachtenberg and Odianjb showed the cyclopropane system to be inferior to a two-carbon saturated chain in such transmission. Kosower and Ito,6a in the cases of the two cyclopropyl ketones spiro [4.2]heptan-l-one and bicyclo[3.l.O]hexan-2-one,predicted and found the spiroketone to absorb a t longer wave lengths than the fused ring ketone. They interpreted their data as supporting the importance of the geometrical factor for which ( 1 ) This material is taken Iron t h e Ilissertation of Alan 1,. Goodman offered in partial fulfillment of the requirements f o r t h e degree of I)octur of Philosophy a t Stanford Cni\,ersity S a t i o n a l Science Foundation Predoctoral Fellow, 1Y.i!J-l960; I ) u Pont Fellow, 1961-1962 (2) For leading references see: M 'I' Rogers and J I). Roberts, J A m . C'hrm Soc , 68, 84X ( l W 6 1 , R H Bastman and S K Freeman. ibiii.. I T , 6642 (193.5), and earlier papers, R. S lIohrhacher and K . H Cromwell, ibid , 79, 401 (l!I.i71, G \V. C a n n o n , .A A Santilli, and P Shenian. zbid , 81, 1660 ( l Y Z Y ) , R Fuchs, C . A Kaplan, J . J Bloomfield. and I,. F H a t c h , J . O v n C h e m . . 2 1 , 7 3 3 (196'2). (:3) ( a ) A I ) Walsh. 7'i.ans. F a r a d a y S,.c , 45, 179 ( l Y 4 Y ) ; (b) J . F RIusic and F A RIatsen, J A m Chen: SOL , 1 2 , A236 (1950) ( 4 ) See N . H Cromwell. F H Schumacher, and J I. Adelfang, % b i d . . 83, 974 (19611, f o r a bibliography of the extensive work in this field ( 3 ) ( a ) R Fuchs and J J Bloomfield, J 0 i . k C'i:e?n.. 28, 9 1 0 (1963); !b) E S .Trachtenherg and G Odian, J A m Chuin. S O C . ,80, 1081 (1!158) 16) ( a ) €2 &I K o s o a e r and R I . I t o , Proc. Chum. Soc , 25 (1962), (h) G Buchi and H . J €3. Loewenthal, i b i d . , 280 (19621

evidence had earlier been reported by Cromwell. * , The ultraviolet spectra of compounds derived from natural products where the cyclopropyl ring is a ysubstituent on an a$-unsaturated ketone have also been interpreted to correspond t o changes in the overlapping of the electrons of the ring and the double bond in the excited state.6a,b Striking differences in the position of maximum absorption were observed in a series of substituted trans2-phenylcyclopropanecarboxamides by Per01d.~ According to Walsh's t h e ~ r y for , ~ maximum conjugative interaction the hydrogen atom o n that carbon atom of the cyclopropane ring which is bonded to the aromatic nucleus must lie in the plane of the benzene ring. If bulky groups such as methyl are substituted in the position ortho to the cyclopropyl substituent, the rings might be expected to twist out of conjugation. Perold7 reports t h a t 2-o-tolylcyclopropanecarboxamide possesses no measurable band near 220 mp, while the corresponding m- and p-tolyl compounds have absorption maxima a t 223 mp (log E 3.96) and 226 mp (log E 4.12). On the other hand, trans-1-methyl-2-phenylcyclopropanecarboxamide has its absorption maximum a t 220 mp (log E 4.0), and the corresponding trans-2-phenyl3,3-dimethyl compound has a maximum a t 218 mp (log E 4.01) The bathochromic shifts relative to the o-tolyl compound were taken by Perold7 to correspond to the appearance of a complete chain of conjugation from the phenyl group through the cyclopropane ring to the amide. I t seemed likely that it was the phenylcyclopropane chromophore that was being affected.* The relative ease of shifting the position of the absorption maximum in Perold's amide series suggested that a possibility existed for semiquantitative measure-





(7) G . W. Perold, J . S Africa>z Chem Znsl., 6 , 22 (lY3:3), 8 , 1 ( I Q X ) ; 10, 11 ( I Q Z 7 ) ; Chem. A b s i v . , 48, 43146 (l!lA4); 50, 6 3 2 6 d { l Y 5 6 ) , 52, 10741 (19.58) (8) M . T . Rogers, J . A m . Chem. Soc , 69, 2544 (1!447).