Dec. 20, 1960
COMMUNICATIONS TO THE EDITOR
C-X bond. The first term decreases along the series R-H, R-CI, R-Br, R-I as expected on the basis of decreasing D(R-X). On the other hand, the second term seems to be negligible for X-H (no repulsion between p electron of a radical and a positive H), but i t probably is considerable for X =halogen. This accounts for the reported facts. Moreover, presence of electron withdrawing groups should decredse this repulsion and increase, therefore, the reactivity. For example, although D(CH3-I) is approximately equal to D(CF3-I),4the reactivity of CF31 is greatly larger than that of CHJ, pointing to the change in the repulsion energy. The same is found when reactivities of PhCH2Br and CCLBr are compared, since again D(PhCH2-Br) D(CC13-Br).4 The effect of repulsion energy in determining the rate of halogen abstraction reactions seems therefore to be indisputable. We wish to thank Dr. John Meyer for his help in counting the radioactive samples.
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of racemization and exchange that had occurred after a short reaction period. The types of systems examined, the experimental conditions, and the results are recorded in Table I. CH3
I
X-C*-H(D)
I Y
CHy
I +- ROD(H) -+ S-C-D(H) I Base
Y
Clearly 2-octyl phenyl sulfone undergoes electrophilic substitution2 with high retention of configuration (85 to >97%) irrespective of the dissociating power of the solvent, the concentration of proton or deuteron donors, or the nature of the cation of the basic catalyst (runs 1-7). In contrast, the steric course of reaction of 2-phenylbutane and 1-phenylmethoxyethane depends markedly on these factors (runs 8, 9 and ref. 1). A third type of behavior is exhibited by 2-methyl-3-phenylpropionitrile, N,N-diethyl-2-phenylpropionamide and tert(4) A. H. Sehon and M. Szwarc, Proc. Roy. SOC.(London), A209, butyl 2-phenylpropionate. I n these systems, 110 (1951). substitution occurs with complete racemization, DEPARTMENT OF CHEMISTRY F. W. EVANS irrespective of solvent character. STATEUNIVERSITY COLLEGE OF FORESTRY Although a detailed explanation requires further AT SYRACUSE UNIVERSITY R. J. Fox SYRACUSE 10, SEW YORK M. SZWARCwork, general patterns are visible in these results. I n the first type of system exemplified by the sulRECEIVED h-OVEMBER 4, 1960 fone, the carbanion formed as intermediate is probably asymmetric, and the stereospecificity of the reEFFECT O F STRUCTURE OF CARBANIONaction is not entirely dependent on maintaining an STABILIZING SUBSTITUENTS ON asymmetric solvent envelope. The carbanion might STEREOCHEMICAL COURSE OF HYDROGENexist either as a d-orbital stabilized sp3hybrid with DEUTERIUM EXCHANGE REACTIONS A T SATURATED CARBON exchange occurring faster than inversion, or as a reSir: hybridized but still asymmetric species in which carBase-catalyzed hydrogen-deuterium exchange bon is "doubly bonded" to sulfur by p-d orbital overreactions a t benzyl carbon of optically pure 2- lap. In the latter case, formation and disposal of the phenylbutane and 1-phenylmethoxyethane previ- carbanion might occur preferentially from the same ously were reported to occur with high retention side due to steric and (or) dipoledipole interactions. of configuration in tert-butyl alcohol, and with Under such circumstances substitution could occur complete racemization in dimethyl sulfoxide. with retention of configuration.
-
TABLE I ,-----Starting Run 1 2 3 4 5 B
7 8 9 10 11 12 13
material"-
X Y n-CsHia CsHsSOl n-CaHn CsHaSOa n-CsH~a CeHaSOt n-CaHlr CsHaSOa CaHaSOr n-CsHlr n-CaHla CsHsSOs n-CeHia CsHsSO2 CZHK CsHa CsHs OCHa C B H ~ C H BCN C6HaCHa C N CON(CzHs)z CsHa COzC(CHa)a CsHs
LD
Conm..
M
He 0.4 Df .4 Df .4 Df .4 HC .4 Df .4 .4 Df .ig D< D k .12 .14 H' HI .23 H"' .12 H" .15
B -asConcn., Temp., Time, Solvent TYDe M OC. hr. .. 0,396 25 0.05 (CHa)sCOK (CHdrCODd 25 0.70 (CHa)aCOK ,224 (CHa)aCOH 25 0.80 .048 (CHa)rN +OH (CHdaCOH 75 165 HOCHZCHIOK .5 HOCHZCHIOH DOCHzCHzODg DOCHzCHzOR .5 100 2.25 7.0 .5 100 CHaOK CHaOH 1.0 ,200 25 (CHa)&O-CHsOHh CHaOK 140 260 ( H O C H ~ C H ~ O ) ~ H(HOCH~CH~O),K .36 420 .40 260 (HOCHzCH2O)aK (HOCHzCHz0)aH 1.3 ,013 25 (CHaIaCOK (CHdaCODd 19 .14 84 DOCHzCHzONa DOCHzCHzODg 1.5 .17 70 (CHI)sCOK (CHs)aCOD 0.25 .0051 25 (CHdrCOK (CHdaCOD
-
% % Net steric Rac. Exch.8 course 4.5 62 93% Ret. 8.0 96 92%Ret. 6 40 85% Ret. 2.2 69 97%Ret. 4.5 53 91%Ret. 100 HighRet. 48 98 90%Ret. 9.8 13 51% 1nv.i 20 4 Rac.orinv. 6.6 19 100% Rac. 20 52 100% Rac. 52 51 -100% Rac. 54 23 -100% Rac. 25
M.p., 47.5-48.0" [ a I 2 % 1 8 -13.3" (c, 5.37, Optically pure unless otherwise specified. b Leaving group, H or D. CHC13). Analyzed by combustion and falling drop method t o be 99% 0-D. 6 Analyzed by combustion and falling ~ ~ ~ (C, 5.06, CHCl,), 97% C-D by combustion and falling drop method. drop method. f M.p. 47.5-48.0°,[ C I I S ~-14.0 92% (CH3)2SO, 8% CH3O.H by weight. 87% 0 Analyzed by combustion and falling drop method to be 99% (0-D)z. optically pure 81y0m-D, by infrared analysis (see ref. 1). j Corrected for lack of optical purity and incomplete deuteratm a*2~ +37.4" ( I , 1 dm., neat), almost optically of starting material. b 97% a-D, by combustion and falling drop method. a 4 6118.Io ~ (l, 1 dm., neat). n C I * ~ D$35.6" (1, 1 dni., neat). pure.
'
We have now found that the steric course of the reaction varies widely with the structure of the carbanion-stabilizing group attached to the seat of substitution. The steric course in each case was through Of the amount (1) D. J. Cram, C. A Kingsbury and B. Rickborn, THISJOURNAL, 81, 5835 (1959).
The second type of system, exemplified by 2 phenylbutane, probably forms a carbanion which is essentially flat, due to delocalization of charge (2) Hydrogen or deuterium are only two of a number of possible leaving groups in this general reaction [see D. J. Cram, A. Langemann, J. Allinger and K. R. Kopecky, {bid.. 81,5740 (1959)l and subsequent papers of the series.
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6416
into the benzene ring. The stereochemical fate of such an intermediate would depend entirely on the symmetry properties of its environment, and would be expected to vary as the character of the solvent and of the basic catalyst were changed. I n the third type of system, exemplified by the nitrile, ester and amide of Table I, a flat carbanion is also envisioned as intern~ediate.~These intermediate anions are ambident, and probably protonate largely on the more electronegative element (oxygen or nitrogen) and produce symmetrical tautomers which in a second stage go to the more stable nitrile, ester or amide forms of the molecule. Such a sequence would invariably involve substitution with racemization as the steric course. The effects of other carbanion-stabilizing groups on the stereochemistry of hydrogen-deuterium reactions, as well as the detailed kinetics of these reactions, are under active investigation.
Vol. 82
strongly solvate I11 and/or the cation associated with it, and also can raise the dielectric constant of the medium, should reduce or eliminate the attractive interaction. The suggestion has been tested by running the reaction in dimethylformamide and various mixtures of benzene and hexamethy1phosphoramide.j The experimental conditions are those using sodium hydride described previously1a,2with only minor modifications. I n both systems 100 ml. of solvent were used with 0.1 mole of chloride, 11; the dimethylformamide reaction mixtures were filtered to remove sodium chloride and then distilled; the hexamethylphosDhoramide mixtures required thoiough washing to remove the amide completely from the benzene solution. Some results are summarized in Tables I and 11; the results of some previously reported runs are included for comparison.
(3) S. K . Hsu, C. K . Ingold and C. L. Wilson [ J . Chein. Soc., 78 (1938) I observed that the rates of hydrogen-deuterium exchanged and of racemization of 1-phenyl-2-methyl-1-butanone in dioxane-deuterium oxide were equal to one another.
TABLE I RATIOSO FOR THE VARIATIONOF YIELDS AND ISOMER SEVERALDIFUNCTIONAL CYCLOPROPANES PREPARED IN VARIOUS SOLVENTS DONALD J. CRAM
DEPARTMEXT OF CHEMISTRY OF CALIFORSIA AT UNIVERSITY Los ANGELES W. DAVIDNIELSEN Los ANGELES24, CALIFORNIA BRUCERICKBORN RECEIVED NOVEMBER 9, 1960 THREE MEMBERED RINGS. 11. THE STEREOSELECTIVE FORMATION O F DIFUNCTIONAL CYCLOPROPANES
Compound
CsHa or CrHab
Dimethylformamideb
5O'%sHs: hexamethylphosphoramideb
71 ( 7 ) c
62 (66)
60 (64)"
59 (25)c
55 (66)
"COOCH3
Sir:
,4 general method for the preparation of polyfunctional cyclopropanes recently has been described.l It generally has been observed that
