Dec. 5 . 1935
REARRANGEMENT I N 3,4-DIMETHYL-4-PHENYL-%HEX.4NOLSYSTEM
[COsTRIBUTIOS FROM THE
DEPARTMENT OF CHEMISTRY OF THE UNIVERSITY OF CALIFORNIA,
5839
AT LOS ANGELES]
Studies in Stereochemistry. XII. Molecular Rearrangements in the 3,4-Dimethyl-4phenyl-3-hexanol System BY DONALD J. CRAMAND JACK D. KNIGHT RECEIVED MARCH 12, 1952 T w o optically pure diastereomerically related isomers of 3,4-dirnethyl-4-phenyl-3-hexyl-p-brotnobenzoates were solvolyzed in dry acetic and formic acids. The results suggest the following conclusions. ( 1 ) I n the quaternary-tertiary system repreintramolecular rearrangements take place involving mainly the phenyl and sented by 3,4-dimethyl-4-phenyl-3-hexanol, methyl groups as migrating species, with the ethyl group becoming involved to only a minor extent. ( 2 ) The phenyl group migrates a t least twelve times as frequently as the methyl group in acetic acid. (3) The phenyl group migrates by two mechanisms, one stereospecific, the other non-stereospecific in character. (4)A simple elimination reaction accompanies the molecular rearrangements, and this reaction is also partially stereospecific and partially non-stereospecific in nature when conducted in acetic acid. ( 5 ) In formic acid, multi-stage reactions occur in which the products of the initial reaction undergo further reaction to produce conjugated olefin (products of methyl and ethyl migrations). The methyl group migrates roughly thirty-five times as frequently as the ethyl group. The mechanisms of these reactions are discussed.
The occurrence of phenonium ions (A) as discrete intermediates in the IVagner-hIeerwein rearrangement has been demonstrated in the following systems (11: R1 = R3 = CH3, R2 = R4 = H and R1 = R< = CH3, Rz = R3 = Hla,lb; R1 = CH3, R3 = G H j , Rz = J& = 1-1 and R1 = CH3, R4 = CzH5,
C2H6,evythro isomer) would reveal substantial differences in the course of the substitution, rearrangement and elimination reactions in this $quaternary-a-tertiary system (11) as compared to the p-tertiary-a-secondary systems (I) studied previously. Paper XI of this series reports the synthesis and tentative assignment of relative configuration to the four stereoisomers of 11,2whereas this paper reports the results of the solvolyses of the threo- and erythro-p-bromobenzoates of I1 in formic and acetic acids.
I (S= OTos or OBros.)
Results
Rz = R3 = HLc,l';R1 = CzHs, R j = CH3, Rz = R.4 = H and RI = C&, R4 = CH3 and Rz= RB= H. The widely recognized electronic and steric differences in reactivity at secondary, tertiary and quaternary carbon atoms suggested that a study of the reactions of the 3,4-dimethyl-4-phenyl-
Preliminary experiments indicated that a t 25' in pure glacial acetic acid the p-bromobenzoate of threo-I12was soluble, but that no detectable reaction occurred in 60 hours. Therefore the solvolyses experiments (runs 1 and 2 ) were conducted a t 73' in this solvent, conditions under which only olefinic
CH,
I1 (OBb. = 0 - C1 - O -- B r j
R
=
Ii or CHI
0
I
CH3-CH=C--C-CzHr
I
CsHj CH,
I?;
3-hexanol s!atem (11, R1 = R3 = CH3, RZ = Rh GHs, flireu isomer; Ri = Rh = CH3, RZ = R3
= =
( 1 ) (a) D.J. Cram, THISJ O ~ R S A L . 71, 3863 (1949); (b) 74, 2129 (1952); (r) 71. 3875 (1949): ( d ) 74, 2159 (1952).
products were produced. Although in formic acid a t 3.5' the esters of I appeared to react readily (runs and 4),the rate Of consumption Of starting Illate(2) D. J. Cramand J. D. Knight, ibid.,74, 5835 (1952).
5840
DONALD
I
I
200
220
I
I 240
I
I
I
I
280
280
,
n.EIXICHT
J. CRAM AXD JACK
I
VOl. 74
lb
t
320
300
3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.(111.0 IVave length in p . Fig. 1.-Ultraviolet absorption spectra of ketones in cycloFig. 2.--Infrared absorption spectra of ketones: liquid hexane, Cary Spectrophotometer, Model 11PMS: - ..-, acetophenone; ----,l-phenyl-2-methyl-2-ethyl-l-butanone;films 0.03 mm. thickness, YaC1 prism, Beckman spectro. . . , l-phenyl-2,2-dimethyl-l-butanone;-, 4-methyl-4- photometer (model I.R.2T): A, 3-inethyl-3-phenyl-2-pent~tnone; B, 4-methyl-4-phenyl-3-hexanone; C , l-phenyl-2,23-methy1-3-phenyl-Z-pentanone. phenyl-3-hexanone; dimethyl-1-butanone; D, l-pheriyl-2-inethyl-2-ethyl-l-butarial was severely limited by the low solubility of the none. -1-,
esters in formic acid. again only olefinic products were obtained. The nature of these products was ascertained by submitting the olefinic mixtures to ozonolysis. The aldehydic components of the resulting mixtures were removed through the use of silver oxide, and the ketonic products were submitted to polarimetric and spectral analyses. The diagram sketches the structural relationships between the starting esters and the final ketonic products. Ketone V could arise only as a product of a methyl migration, and ketone VI as a product of an ethyl migration from the p- to the a-carbon atom. The optically pure (t)and (-)-isomers of IT1 and ketones V and IV were reported and V i were prepared by the action of the agpropriate Grignard reagent on benzonitrile as shown below. In each case the ketones were purified through their crystalline oxime derivatives. Figure 1 records the ultraviolet absorption spectra of ketones 111, IV, V, VI arid a~etophenone,~ and Fig. 2, the infracrI,
KZ
R 1 = CHs, Rz = CaH; or Ri = Rz = C P H L
c, 113
1 , ether
-c
c-I
