March 20, 1960
COMMUNICATIONS TO THE EDITOR
1511
We report here such a reaction and its utility in organic syntheses. The donor properties of triphenylphosphine are well known, and we have found that the preparation of halocarbenes from halomethanes, either by the alkoxide method2 or by the alkyllithium m e t h ~ d when , ~ carried out in the presence of triphenylphosphine, gives triphenylphosphinehalomethylene reagents6, e.g. CHCla 4- n-BuLi f (CsHs)aP ---f
in 1: 1.15 ratio; no assignment of structure was attempted. Triphenylphosphinechloromethylene may also be prepared by treatment of the triphenylchloromethylphosphonium bromide described above with phenyllithium in ether. The reagent prepared in this manner reacted with acetophenone to give 1-chloro-2-phenyl-1-propene in yields of SO-SO%. The lower yield of the chloroolefin obtained when (CeH6)3P=CHCl was used in the solution in which (CeHjhP=CHCI LiCl CaHlo it was generated by trapping of chloromethylene may be due to the presence of unreacted triphenylAddition of hydrogen bromide to the yellow solu- phosphine which interferes in isolation of the chlorotion of triphenylphosphinechloromethylene,pre- olefin by distillation. pared by adding 0.1 mole of n-butyllithium in ether Some of the other conversions carried out into 0.11 mole of triphenylphosphine and 0.13 mole clude : cyclohexanone to chloromethylenecycloof methylene chloride in ether a t - 30°, precipitated hexane; methyl isobutyl ketone to l-chloro-2,4a mixture of [(C6H5)3PH]Brand [ ( C ~ H ~ ) ~ P C Hdimethyl-1-pentene; Zdiethyl ketone to l-chloro-2ClIBr. The precipitated solids were dissolved in ethyl-1-butene and acetophenone to 1,l-dibromo-2water, causing quantitative decomposition of tri- phenyl-1-propene (via CBr2 generated using potasphenylphosphonium bromide to HBr and triphenyl- sium tert-butoxide) . phosphine. Filtration of the latter was followed Extension of this reaction to the preparation of by precipitation of [ ( C ~ H L ) ~ P C H [B(CeH5)4], ~C~] other phosphinemethylene reagents and the apm.p. 189-192” (dec.) (Calcd. for C43H37ClPB: C, plication of these reagents in organometallic syn81.84; H I 5.91; C1, 5.62. Found: C, 82.03; H, theses such as those we have reported recentlyg is 6.17; C1, 5.37) by addition of aqueous sodium in progress. tetraphenylborate to the filtrate. It was deterWe are grateful to the National Science Foundamined in this manner that triphenylphosphine- dation for a predoctoral fellowship awarded to chloromethylene had been formed in about 65% one of us (S.O.G.) and to the Quartermaster Reyield. A separate experiment using [ (C6H5)s- search and Engineering Command for support of PCH2C1]Br, purified by recrystallization from this work. 2-propanol-ether (m.p. 209-211’. Calcd. for (219(9) S. 0. Grim and D. Seyferth, C h e m . a n d I n d . (London), 849 H17C1BrP: C, 58.26; H, 4.38; C1, 9.05; Br, (1959). 20.40. Found: C, 58.47; H, 4.31; C1, 8.6; Br, DEPARTMENT OF CHEMISTRY 20.3. Picrate, m.p. 192-194’. Calcd. for C25- MASSACHUSETTS IXSTITUTE DIETMAR SEYFERTH SAMUEL 0. GRIM H1907N3C1P:C, 55.61; H, 3.55; C1, 6.56. Found: OF TECHSOLOGY 39, MASSACHUSETTS TERENCE 0. READ C, 55.60; H, 3.76; C1, 6.32) in aqueous solution a t CAMBRIDGE RECEIVED JANUARY 22, 1960 comparable pH showed that the [ (CGHC,)~PCHZC~]+ ion is precipitated quantitatively by sodium tetraphenylborate. When phenyllithium was used as CONDITIONS FOR STEREOSPECIFIC OLEFINthe base in the chlorocarbene generation, triMERCAPTAN RADICAL ADDITIONS phenylphosphinechloromethylene resulted in yields Sir: of ca. 40%. Dibromo- and dichlorocarbene could Non-stereospecificity in radical-olefin addition also be trapped in this manner to give triphenyl- reactions is the generally accepted pattern, cerphosphinedihalomethylene reagents. tain additions involving hydrogen bromide being Triphenylphosphinehalomethylenes undergo the the only established exceptions.1~2~3~4.5 Although Wittig reactionI7 thus providing a new general mercaptans add to alkenes with high specific reacsynthesis of substituted vinyl chlorides and vinyli- tion velocities6 (lo6 1. mole-1 sec.-l), there have dene chlorides and bromides. Treatment of solu- been a number of reports on non-stereospecificity tions of triphenylphosphinechloromethylene with for olefin-mercaptan addition^.^^^^^ We confirm aldehydes and ketones using standard Wittig reacthis pattern for the reaction of C H S D with the tion conditions resulted in the expected substituted cisand trans-2-butenes a t - 70’. Under reaction vinyl chlorides. A mixture of the cis and trans conditions producing only minor amounts of olefin isomers was obtained when an aldehyde or un(1) For reviews of the earlier literature, C. Walling, “Free Radicals symmetrical ketone was used. As an example Solution,” John Wiley and Sons, Inc., New York, pi. Y., 1957; and may be given the preparation of 1-chloro-2-phenyl- in P. S. Skell, R . C. Woodworth and J. H. Mch’amara, THISJ O U R N A L , 1-propene*in 46% yield, based on methylene chlo- 79, 1253 (1957). ride, by the reaction of (CsH5).P=CHCl with aceto(2) P. S. S e l l and R. G. Allen, ibid., 80,5997 (1958). (3) P. S. Skell and R. G. Allen, ibid., 81, 5383 (1959). phenone. Gas chromatographic analysis showed (4) H. L. Goering and D. W. Larsen, ibid., 81, 5937 (1959). that both possible geometrical isomers were present ( 5 ) N. A. Le Bel (Abstracts Boston Meeting 1959, 4-0) described
+
+
( 5 ) G. L. Closs and L. E. Closs, THISJOURNAL, 81, 4996 (1959); W. T. Miller, Jr., and C. S. Y. Kim, ibid., 81, 5008 (1959). (6) G. Wittig and W. Haag, Chem. Ber., 88, 1654 (1955), with this end in mind, added diazomethane to triphenylphosphine in ether solution, but stable (CaHa)sP=N-N=CHt was formed instead of (C6Hs)aP=CHz. (7) G. Wittig and U. Schollkopf, Chem. Ber., 87, 1318 (1954); see also U. Schollkopf, Angezu. Chem., 71, 260 (1959). (8) B.p. 102-105° a t 14 mm. Calcd. for CpHsC1: C, 70.82; H , 5.94. Found: C, 70.81; H , 5.95.
non-stereospecific reaction of HBr with norbornene. Also, private communication from Prof. P. I. Abell indicates t h a t in the 1-bromo-1cycloalkenes (C4,C6,C7). additions of hydrogen bromide are not stereospecific. (6) C. Sivertz, J . Phys. Chem., 63, 34 (1959). (7) F. G. Bordwell and W. A. Hewett, THIS J O U R N A L , 79, 3493 (1957). (8) H. L. Goering, D. I. Relyea and D. W. Larsen, ibid., 78, 348 (1956). (9) S. J. Cristol and R. P. Arganbright, ibid., 79, 6039 (1957).
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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) and tetrahedral character at the P-carbon atom (CIO) : 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 transiIn 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: In 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, CH3SD + DRr and (2) equilibration Rr. C H S be more rapid than additions of Rr. and CH& to 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).
