1512
1701. 82
COMMUNICATIONS TO THE EDITOR
STEREOCHEMISTRY OF THE LITHIUM-AMMONIA isomerization, the products are the same mixture of erythro- and threo-3-deuterio-2-methylthiobutane REDUCTION OF a,@-UNSATURATED KETONES starting with either olefin. Rationalization of these Sir: observations requires an open chain radical which I t has been proposed that the reduction of an u,Pisomerizes more rapidly than the transfer of a deu- unsaturated ketone with lithium in ammonia leads terium atom from CH3SD. to the more stable epimer at the &carbon atom.' Results in this Laboratory have led us to reexamine these conclusions. We will illustrate the argument by reference to the reduction of octalones such as I. The transition state for protonation of the intermediate anion I1 must have considerable \-/ CH,ST) tetrahedral character at the P-carbon atom (CIO) and : if the P-carbon atom were still trigonal in the transition state for protonation (cf. 11) approach of the proton source would be a t least as easy to give a cis as a trans product and considerable quantities of cis decalones would be expected. This is contrary to experience. Even though the transiI n the liquid phase a t -7S0, product analyses tion state has considerable tetrahedral character for the reaction of HBr, CH3SH and cis-2-butene a t C ~ Othe , developing orbital a t that carbon will be (1:2 :1) yielded an apparent relative rate of hydro- expected to overlap continually with the double gen atom transfer to CH3-CHX-CH-CH3 of K H B ~ / bond, i.e., must remain perpendicular to it (cf. 111 k c H s S H = 1.94. Thus it was deemed advisable to and IV). This leads to introduction of the Clo hyexamine the stereospecificity of CH3SD additions drogen axially to ring A . It is in the recognition of in the presence of DBr. Under these conditions the necessity of continual overlap of the 0-orbital the formation of the 3-deuterio-2-bromobutanes is with the enolate double bond that the picture difstereospecific, as it is in the absence of methyl mer- fers from that previously suggested.' captan.a The 3-deuterio-Zmethylthiobutanes are Nre are thus led to the following rule: I n realso producrd by stereospecific trans additions, cis- duction of an octalone system with lithium in amand trans-2-butenes yielding threo (I) and erythro monia the product will be the more stable of the (11) products, respectively. Evidence for struc- two isomers (cis or trans) having the newZy introduced ture and purity was obtained through syntheses hydrozen axial to the ketone ring. The conforof the thioethers by reactions of CH3SNa with pure mation of the cis form of a B-decalone which is not erythro- and threo-3-deuterio-2-bromobutanes, in- permitted in the transition state (cf. V) is in many versions a t C-2 being assumed. Examination of infrared spectra provides no evidence of isomer intercontamination for the radical additions. lo These results require that (1) DBr be the sole transfer agent with radicals CH3-CHX-CH-CH3, and (2) equilibration Rr. CH3SD + DRr C H S be more rapid than additions of Rr. and CH& t o these olefins. Steric control of mercaptan addition is achieved by the rapid reaction of the diastereomerically related 3-methylthio-%butyl radicals with hydrogen bromide, a reaction which is more rapid than the isomerizations of the radicals. MO' ___t
+
+
Il
t
-
~iila-2-butene ('HIS
(R'.)- UBr C & - M / \
CH,
,C511J
iII
€1
A
Hr
H
DEPARTMEKT OF CHEMISTRY PHILIP S.SKELL~' cases more stable than the conformation of the THEPENNSYLVANIA STATE UNIVERSITY UNIVERSITY PARK, PA. RICHARD G. ALLEN trans isomer, whereas the permitted cis form is in RECEIVED JANUARY 5, 1960 general less stable than the trans. The product of (10) Throughout, vapor phase chromatography homogeneous samples were examined neat. Less than 570 intercontamination might have escaped detection. (11) This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command, under contract No. AF 49(638)457.
the reduction of an octalone such as I will thus often be exclusively the trans-0-decalone even when the cis-decalone would be expected to be the more stable isomer. (1) D. H. R . Barton and C. H. Robinson, J . Chcm. Soc., 3046 (1954).
March 20, 1960
COMMUNICATIONS TO THE EDITOR
For example, reduction of the octalone I2 (R = CHI, R.’ = OCH3, R”, I
