COMMUNICATIONS TO THE EDITOR
Aug. 5 , 1963
there is complete correspondence with respect to configuration between germanium and silicon enantiomers with the same sign of rotation. I n addition, Brewster's rules of atomic asymmetry, which in the case of methyl a-naphthylphenylsilyl compounds correctly predict the configurations of the H , C1, Br, OH, OMe, and other derivatives,fipredict the same configuration, viz. P a-iXp- -Me
Ph
for (-)G*eH, (+)G*eCOOH, (-)G*eOMe, (+)geCl, and their silicon analogs. Hence, i t follows that retention of configuration is involved in each of the reactions so specified in Scheme I, and that in all similar cases studied to date (except bromination2), the stereochemistry of displacements a t asymmetric germanium is the same as that of displacements at silicon. The stereochemistry described above is in accord with other known reactions. Studies on vinyl metall i c ~ and , ~ other organometallic systems8 indicate that metalation, or halogen-metal exchange, carbonation, and addition to a carbonyl group each occur with retention of configuration. Thermal rearrangements of silane- and germanecarboxylates to ethers have been shown t o be intramolecular p r o c e s ~ e s ,and ~ would be expected to involve "flank" attack, leading to retention of configuration. Similar results were found in the intramolecular rearrangements of a-hydroxysilanes t o silyl ethers.6,6 The most significant result of this study is the remarkable optical stability of methyl-a-naphthylphenylgermyllithium, which through the carbonation cycle, is shown to have essentially complete optical stability in ether at room temperature over 30 min. While organometallics such as sec-butyllithium'O have considerable optical stabilities in hexane a t low temperatures, the presence of diethyl ether leads to rapid racemization. Further studies are in progress. Configurational relationships were established by weighing known quantities of silicon and germanium enantiomers, dissolving them in ether or pentane and immediately pumping off the solvent. Compounds of like configuration had narrow mixed melting point ranges, whereas compounds of unlike configuration had melting point ranges of from 10 to 25". Analyses and infrared spectra were in accord with the assigned structures of all compounds. Acknowledgment.-This research was sponsored in part by the National Research Council of Canada. (6) A. G Brook a n d W. M . L i m b u r g , J A m . Chem. Soc., 85, 832 (1963). (7) D.Y C u r t i n a n d J. W. Crump, ibid., 80, 1922 (1958). (8) H . M.Walborsky a n d F. J . I m p a s t a t o , i b i d . , 81, 5835 (1959); H.M. Walborsky a n d A . E. Young, ibid., 83, 2593 (1961). (9) A . G . Brook, ibid., 77, 4827 (1955); A. G.Brook a n d R. J . M a u r i s , i b i d . , 79, 971 (1957) (10) D . Y . C u r t i n a n d W. J . Koehl, ibid.,84, 1967 (1962). (11) Cities Service Corporation Fellow, 1962-1963.
DEPARTMENT OF CHEMISTRY A. G. BROOK UXIVERSITY OF TOROXTO, G. J . D. PEDDLE^' TORONTO, CAXADA RECEIVED JUNE 5 , 1963
2339
r e a c t i o q p 4 the most probable and simplest one as outlined by Jensen and Ouellette' involves the ionization of alkylmercuric salt followed by dissociation of carbon mercury linkage to yield carbonium ion and mercury.
+
RHg+ +R + HgO R + --+ Products
Robson and Wright4pointed out that phenylmercuric acetate does not undergo heterolysis in methanol with boron trifluoride. Jensen and Ouellette in their elegant work also emphasized that the reaction has been found to be general for all alkyl groups, and the ionic mechanism is beyond doubt; however, the fate of solvolysis of phenylmercuric salts was not mentioned. I n our Laboratories we have found that phenylmercuric acetate. preferably perchlorate or tosylate, undergoes solvolysis in acetic acid or even toluene in the presence of a reducing agent. For example, with ferrocene, the reaction furnishes the phenyl radical with concomitant oxidation of ferrocene to ferroceniurn ion. Phenylmercuric acetate (Eastman Kodak White Label, m.p. 148-150') in acetic acid reacts with ferrocene very slowly, as indicated by the gradual appearance of the characteristic blue color of ferrocenium ion. Addition of a catalytic amount of perchloric acid to the mixture led to almost instantaneous formation of the characteristic f errocenium ion color. Csing acrylonitrile as solvent, phenylmercuric acetate and ferrocene initiated polymerization of the monomer and the polymerization process was inhibited by both free radical scavengers such as p-hydroquinone and ions such as NaCl, NaN02, etc. When the reaction was carried out in toluene with an equimolar (0.1 mmole) amount of phenylmercuric acetate, perchloric acid, and ferrocene, the appearance of ferrocenium ion color was instantaneous and the yield of benzene was practically quantitative. With toluenesulfonic acid, the yield of benzene was 25%. The previous failure t o observe the cleavage of phenyl-mercury bond4 is perhaps indicative of the unfavorable energetics for such heterolysis and may be attributed a t least partially to the stabilization of phenylmercuric cation by dissipating the positive charge to the aromatic ring.
Since the solvolytic step is reversible, no appreciable demercuration of this cation is anticipated. I n the presence of a reducing agent such as ferrocene, the intermediate cation from solvolysis is reduced to phenylmercury (I), followed by demercuration and formation of phenyl radical. When the reaction is carried out in toluene, the phenyl radical abstracts hydrogen from toluene to form benzene and the more stable benzyl radical. O -H g + + Ferrocene
O ?
H
I
g
+ Ferrocenium ion
Generation of Phenyl Radical via Reduction of Phenylmercuric Cation
Sir : The solvolysis of alkylmercuric salts such as acetate (or more effectively perchlorate) has been well established t o be a general route to afford carbonium ions.' Among the many possible mechanisms proposed for this (1) F. R. Jensen a n d R . J. Ouellette, J . A m . Chem. Soc., 88, 4477, 4478 (1961); 86, 363 (1963).
W'LQ
+products
(2) K . Ichikawa a n d H . Ouchi, ibid., 81, 3876 (1960). (3) S . Winstein, e l a l . , ibid., 77, 3741 (1955); Chem. I n d . ( L o n d o n ) , 2 5 1 (1962). (4) J. H.Robson a n d G. F. Wright, Can. J. Chem., 88,21 (1960). ( 5 ) S. G.Cohen and C. H . Wang, J. A m . Chem. Soc., 77, 3628 (1955)
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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 ARTHUR D. LITTLE,INC. CHI-HUAWANC benzoic acid IV* each containing half of the CI4 acCAMBRIDGE 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 a n d 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, D i c k e r s o n , a n d K' J U'elstead, J r , J 0i.n C h i i n , 2 7 , 3062 (l!if32), ( c ) f u r t h e r s t u d i e s 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 s p e c t r o p h o t o m e t e r ) a n d i n t e r p r e t e d hy \V I, T r u e t t , d u P n n t C i i , W a y n e s b u r o , V a (3) IIaiiovia 45O-watt high pressure m e r c u r y a r c l a m p , P y r e x filter. 14) R r r i m e o u d y formulated ( a ) as a hutenn1"and ( b ) a s a cyclic enol e t h e r
'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 C h e m , 1 7 , 2040 (1962) ( 5 ) ( a ) S a m p l e s of CLd-labeled 11, a n d d , were p r e p a r e d from samples of Ia m a d e f r o m acetophenvne labeled, respectively, in t h e phenyl g r o u p a n d a t t h e carbonyl carbon T o be certain t h a t t h e r e h a d been n o r e a r r a n g e m e n t in going f r o m l a t o 11, Clb-labeled 11* was c o n v e r t e d i n t o I b , which u p o n chrnmic acid oxidation g a v e benzophenone carrying all of t h e C'd, (b) details a n d mechanistic discussion will a p p e a r in t h e forthcoming paper ( 6 ) Cr' (a) l , : < - h l e t h y l s h i f t [P Y a t e s a n d S Danishefsky, J A m Chpm Sec.. 84, 879 ( 1 9 6 2 ) l : l , : j . , 1.1-a n d 1,.5-phenyl shifts [ ( b ) h 4 . Stiles a n d A J I.ibbey, J r , J 0i.p r h e i n . , 11, 1213 (19.57). ( c i P T 1-ansbury a n d R I, 1,etsinger. J . A m i'hem SOC , 81, 940 (I959i1, ( d ) c.!' t,i.Ysl,.> phenyl s h i f t 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 a n d G. F Vesley, J . 01.8 C h e m , 18, 1160 (1963), cf ( b ) R E 1-utz, I. T S l a d e , a n d P . A . Zoretic. ihid , 18, 1358 (1963) work in this field is u n d e r f u r t h e r investigation. a n d t h e reactions a r e s u b j e c t t o possible r e i n t e r p r e t a t i o n in t e r m s vf carbene i n t e r m e d i a t e s [cf. (c) G I,, Closs a n d 1. E Closs, J . A m C h e m . Soc , 8 6 , 98, (1963)l.
*
~
