2340
COMMUNICATIONS TO THE EDITOR
VOl. 85
It is quite clear that the reduction process has to involve phenylmercuric cation and not the phenyl cation, and therefore a hydride abstraction by phenyl carbonium ion from toluene t o yield benzene and benzyl carbonium ion is ruled out. As regards the difference in the yield of benzene between toluenesulfonate and perchlorate, it perhaps reflects the extent of ionization of the salts. Acknowledgment.-We wish to thank Dr. P. L. Levins for helpful discussion and technical assistance and the Research Committee of Arthur D. Little, Inc., for financial support.
phenyl group in each moiety of I1 a t position-5 of the numbered four-carbon system is located in the resulting ketone I11 at carbon-2, the other end of this same fourcarbon system. Empirically, therefore, a phenyl group migration has occurred. Pyrolysis and photolysis of samples of I1 CL4-labeled, respectively, in the gem-diphenyl groups (*) and at the %carbon atom (#) traced the migration and limited mechanistic po~sibilities.~I n the first case (*) the resulting sample of unsaturated ketone III* upon permanganate oxidation gave benzophenone V* and benzoic acid IV* each containing half of the CI4 acARTHUR D. LITTLE,INC. CHI-HUAWANC CAMBRIDGE tivity. Except for the possibility of total scrambling of 40, MASSACHUSETTS RECEIVED MAY8, 1963 the locations of the four phenyl groups which would have led to the same result, this showed that carbon4 of 11* had lost one of its two labeled phenyl groups, that A Novel Phenyl Group Migration during Pyrolysis carbon-2 had gained one, and that the migration must and Photolysis of Bis- (2,3,5,5-tetraphenyl-2have been transannular or cis-1,4. The mechanistically dihydrofurany1)-hydrazine improbable migration of a 5-phenyl group of 11* in Sir: successive steps around the ring to the 2-position is excluded because it would have led to a 2-gem-diphenyl This rearrangement was discovered during reinvestigation of the cyclic hemiketal, 2,3,5,5-tetraphenyldihy- group in the unsaturated ketone I11 with one-third or less of the C1*activity,5bdepending on the order and redrofuranol-2 (Ia) and its conversion supposedly through versibility of the steps. That total scrambling of the the acyclic cis hydroxy ketone form into a "hydrazone" locations of the *Cl4-1abeled phenyl groups had not ocfor which the sym,bis cyclic hydrazine structure I1 is now curred was rigorously proved in the case of dimethylsuggested on the basis of the following data. The comformamide pyrolysis by addition of phenyllithium to pound gave the correct C, H, and N analyses and molecthe unsaturated ketone III* and oxidation of the reular weight; it was converted under acid catalysis into sulting pentaphenylbutenol VI* to benzophenone VII* the cyclic ketal I b and dehydratively rearranged to tecontaining all of the *C14 and benzoic acid VI11 contraphenylfuranIb; i t showed Amax 253.5 mp, ( E 28,400) taining none (scrambling would have led to *C14 concorresponding to two styryl groups, two infrared N H tents of 75 and 25%, respectivelysb). peaks,2a narrow one a t 3560 cm.-', and a broad one at The pyrolysis and photolysis reactions can be ex3440 cm. persisting on dilution and suggestive of intrapressed stoichiometrically as intramolecular oxidation molecular hydrogen bonding, and no absorption in the of the hydrazo group t o molecular nitrogen and reduc1600 cm.-l range corresponding to NH:, or C=N groups tion of the two ring moieties by hydrogen transfer from of gem,bis hydrazine or acyclic azine structures.2 the hydrazo group.5b The drive for furanization existing before this reactim is absent afterward because of the lower oxidation stage of the nitrogen-free products (e,g,, 111, IX-XI). Initial formation of a carbene-like transition is suggested, e.g., IX, followed by 5-2 migration of a phenyl group6 and formation of the unsaturated ketone 111, either through its diene-ol or through the cyclobutenol X.5b.7
HLO'
VI
VI1
The symbols * and # indicate the respective locations of the C L 4label in the two tracer experiments. The 2-5 numbering is used throughout to trace the four ring carbons of I and 11. Pyrolysis of 11 a t its melting point ( 2 2 0 ' ) , in refluxing decalin ( 1 goo),and in dirnethylformamide (133"), and photolysis i n benzene, caused evolution of nitrogen (identified i n one case, v.p.c.) and formation of the p, y-unsaturated ketone 1114 ( 5 0 - 6 0 ~ G ) . The gem-di( I ) ( a i S Salkind and V T e t e r i n , J . p r n k t . C h r m , 133, 19.5 ( 1 9 3 2 ) , ( h i R E I.utz. C I, Dickerson,and K' J U'elstead, Jr , J 0i.n C h i i n , 2 7 , 3062 (l!if32), ( c ) further studies in these areas a r e in progress (2) Determined in CCli ( P e r k i n - E l m e r 421 grating spectrophotometer) and interpreted hy \V I, T r u e t t , d u P n n t C i i , Waynesburo, Va (3) IIaiiovia 45O-watt high pressure mercury arc l a m p , Pyrex filter. 14) Rrrimeoudy formulated ( a ) as a hutenn1"and ( b ) a s a cyclic enol ether
'CsHs
X Preliminary study of the dihydrofuran, presumably XI, which has been made by lithium aluminum hydride reduction of Ia to a glycol and subsequent cyclodehydration [m.p. 94-95'; analyzed; Amax 254 mp, ( E [K Scholtis, A n n , 6 6 7 , 82 (1945)l. For s t r u c t u r e proof see (c) R E . 1,utr a n d C. 1. Dickerson, J Ovg Chem , 1 7 , 2040 (1962) ( 5 ) (a) Samples of CLd-labeled 11, and d , were prepared from samples of Ia made f r o m acetophenvne labeled, respectively, in t h e phenyl group a n d a t t h e carbonyl carbon T o be certain t h a t there had been n o rearrangement in going f r o m l a t o 11, Clb-labeled 11* was converted i n t o I b , which upon (b) chrnmic acid oxidation gave benzophenone carrying all of t h e C'd, details a n d mechanistic discussion will appear in t h e forthcoming paper ( 6 ) Cr' (a) l,: phenyl shift in photolysis nf cis-dibenzoylethylenr [G W Griffin and E J O ' C o n nell, ;hid , 84, 4 1 4 8 (1962) I . cf references cited in a-c. ( 7 ) Cf.(a) P. A . 1,eerrnakers and G. F Vesley, J . 01.8 Chem , 18, 1160 (1963), cf ( b ) R E 1-utz, I. T Slade, and P . A . Zoretic. ihid , 18, 1358 (1963) work in this field is under further investigation. and t h e reactions are subject t o possible reinterpretation in t e r m s vf carbene intermediates [cf. (c) G I,, Closs and 1. E Closs, J . A m C h e m . Soc , 8 6 , 98, (1963)l.
*
~
Aug. 5 , 1963
COMMUNICATIONS TO THE EDITOR
18,200) (styryl); n.m.r., T ca. 2.7, 3.10, 3.65 p.p.m. (intensities ca. 20 : 1 : 1)1, indicates that this compound is not an intermediate (through cyclization of I X ) because it behaves differently under reaction conditions.5b A mechanism involving intermediate ring contracisomer of the tion t o a 2-hydroxy-2,3,5,5-tetraphenyl cyclobutenol X8 bej'ore phenyl group migration. was excluded by the second group oi tracer experiments designed to test this point, starting from 11# Cl4-1abeled a t carbon-5. Oxidation of the resulting samples of unsaturated ketone I I I # gave benzophenone V carrying none of the #CI4 activity and benzoic acid IV# containing all of i t ; and oxidation of the pentaphenylbutenol VI# obtained by adding phenyllithium to these samples of the ketone III# gave benzophenone VII# containing all of the #C14 and benzoic acid VI11 containing none. This showed that all of the CI4 of the ketone III# had been located a t position4 as demanded by the mechanism 11 + I X or X --t III.5b The drive for the rearrangement seems to be furnished by the extraordinary coincidence of steric pressure a t the quaternary carbon4 and strain release by ring cleavage with formation of the acyclic ketone 111. The reaction bears some analogy to the pinacol rearrangemen t . Studies of these a.nd related reactions are in progress to gain more detailed understanding of the scope, byproducts and mechanisms. ( 8 ) Cf.Also N. C Yang, A. Morduchowitz, and D - D . H. Yang, i b i d . , 8S, 1017 (1963); cf. also r e f . 7b. (9) Cf. ( a ) G . W. Griffin a n d R. B Hager, J . Org. C h e m . , 28, 599 (1963); cf. Also t h e pinacol-like rearrangements of (b) 1,2-di-(benzhydryl)cyclopropane t o an acyclic unsaturated ketone [R.A. D a r b y a n d R . E . Lutz. ibid., 22, 1353 (1957)1 and of (c) Irans-(CsHs)pC(OH)CH=CHC(CaHa)?OH t o C B H ~ C O C H ( C ~ H ~ ) C H = C ( Ca ~ nH isomer ~ ) ~ , of 111 [R.E. Lutz and R . G . Bass, unpublished results (see Dissertation, University of Virginia, 1961). (IO) ( a ) W o r k supported in p a r t b y a National Science Foundation Research G r a n t ; (b) Shell Co. Fellow, 1961-1962; (c) Shell Co. Fellow 1962-1963. ( d ) P h . D . Dissertation, University of Virginia, October, 1962.
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ture with electron-rich alkenes t o form 1,2-bis-(trifluoromethyl)-1,2-dicyanocyclobutanes(111) with complete stereos6ecificity over a wide range of solvent polarity.
CH-X
C (CN)CFa It
+
C(CN)CFs
X
CH2 It
-*
(CN)CFs u(CN)
CF3
I, (cis and trans)
I1 I11 X = RO-, RS-, p-ROC&-
Reactions of trans-I with the alkenes I1 in the absence of solvent give exclusively the cyclobutane diastereomers I I I a and I I I b ; reactions of cis-I give a different set of diastereomers, I I I c and I I I d . Similar stereospecificity is observed in reactions of trans-I with cisand trans-propenyl n-propyl ether.
s CN
I
C F3
CN
IIIa
m f
c
C F3 CN
C F3
IIIb
CN
CN
IIIc
i
I
CN IIId
The cyclobutane structures for the products were confirmed by elemental and spectral analyses. Comparative fluorine n.m.r. spectroscopy was particularly useful for determining the number and kinds of diaCOBBCHEMICAL LABORATORY ROBERTE. LIJTZ~O' stereomers formed. For example, the cyclobutane UNIVERSITY JOHNI. DALE'O~,~ OF VIRGINIA diastereomer mixture I I I a I I I b resulting from the CHARLOTTESVILLE, VIRGINIA DAVIDW. BOYKIN,J R . ' " ~ reaction of trans-I and t-butyl vinyl sulfide (11, X = RECEIVED MAY3, 1963 SCMe3) exhibits a fluorine n.ni.r. spectrum consisting of four singlet resonances appearing as two pairs whose Stereochemistry of the Cycloaddition Reaction of components are of equal intensity. The fluorine n.m.r. 1,Z-Bis-(trifluoromethyl)- 1,Z-dicyanoethylene and Elecspectrum of diastereomer mixture I I I c IIId (X = tron-Rich Alkenes SCMea), prepared from cis-I and t-butyl vinyl sulfide, Sir: also exhibits two pairs of resonances whose components are of equal intensity, but the chemical shifts are difIt has been emphasized that few quantitative data ferent from those obtained from the mixture I I I a -t about the stereochemistry of additions to form cycloIIIb, and the resonances appear as quadruplets (due t o butanes are available.' We wish to report on the mutual splitting of the CF3 groups) rather than singlets. stereochemistry of a type of cycloaddition recently disA further verification of isomer composition was also covered,2in which strongly electrophilic olefins, such as obtained in certain cases by chromatographic separation tetracyanoethylene, undergo cyclization with electronof the diastereomers. rich alkenes, e.g., 11, under very mild conditions. The rate of cycloaddition of I t o t-butyl vinyl sulfide Such reactions involve a highly colored charge-transfer is strongly influenced by solvents. Qualitative measurecomplex and exhibit reaction rates t h a t are markedly ments based on observation of the disappearance of dependent on solvent polarity. For tetracyanoethylcolor of the charge-transfer complex gave reaction ene, the relative rates for cyclobutane formation vary times ranging from less than 1 min. in methanol t o by as much as 8 X lo4depending on solvent, with nitromethane being one of the fastest and cyclohexane one of 4320 min. in carbon tetrachloride for cis-I and 1.5 min. the s l ~ w e s t . ~ in methanol t o 17,280 min. in carbon tetrachloride for We have prepared 1,2-bis-(trifluoromethyl)-1,2-di- trans-I. The stereospecificity of the reaction was, cyanoethylene (I) by pyrolysis of l-cyano-2,2,2-trihowever, maintained throughout the whole range of : fluoroethyl chlorosulfite. Anal. Calcd. for C6F6NZ solvents tested. C, 33.66; F, 53.25; N , 13.09. Found: C, 33.91; F, These observations place some stringent require53.43; N , 12.81. The pure cis and trans isomers of ments on the mechanism of this type of cycloaddition this strongly electrophilic olefin react at room temperawhich will be discussed in detail in a forthcoming paper.
+
+
(1) J. D. Roberts a n d C . M . S h a r t s , "Cyclobutane Derivatives from Thermal Cycloaddition Reactions" in "Organic Reactions," Vol. 12, John Wiley and Sons, Inc., New York, N.Y . , 1962. (2) J. R . Williams, D. W Wiley, and B.C. McKusick, J . A m . C h e m . Soc., 84, 2210 (1962);A. T. Blornquist and Y . C. Meinwald, ibid., 79, 5316
(1957); 81,667 (1959). (3) D . W. Wiley, private communication.
CONTRIBUTION No. 871 STEPHEN PROSKOW E SIMMONS CENTRAL RESEARCH DEPARTMENT HOWARD EXPERIMENTAL STATION T. L CAIRNS E. I DU PONTDE SEMOURS A N D COMPANY WILMINGTON, DELAWARE RECEIVED MAY29, 1963
