Wieland reaction, on the other hand, proceeds successfully with toluene, benzene, chlorobenzene and cthylbenzoate.
product proportions are controlled by the difference in free energy between the transition states derived from IV and V.3 That from ITis the more DEPARTMENT OF CHEMISTRI ROBERT A. BEXKESER stable, since in it, the compression of the groups PURDUEUXIVERSITY REX B. GOSXELL attached to the keto carbonyl as the latter begins INDIAS.4 1511~1 IAX SCHROEDER LAFAYETTE, to become tetrahedral is against H, whereas in that from IV, this compression is against the large RECEIVED MARCH18, 19.57 group R. When the effective bulk of R increases (I -+ 11), the stereoselectivity increases. -1 ASYMMETRIC INDUCTION AND ABSOLUTE number of alternative interpretations ascribing CONFIGURATION IN THE BIPHENYL SERIES special stability to other conformations because of Sir: chelate complexing, appear less probable. In Methylmagnesium iodide converts the phenyl- particular, the conformation in which each carglyoxylates of phenyldihydrothebaine (I) and its bonyl group is complexed with a ring niethoxyl, derivatives (IIa-c) (absolute configurations1 as and the plane of the phenylglyoxylate residue is shown) to atrolactic esters. Saponification and perpendicular to ring Ai and parallel to ring B, isolation vithout optical fractionation give ( - ) - m-ould also lead to 111. However, in order to esatrolactic acid (111) (absolute configuration? as plain on this basis the fact that the stereoselectivshown) in optical yields of i 0 7 0 from I and 91, S9, ities with the phenylglyoxylates of IIa-c are 3.5 and 93%, respectively, from Ira-c. These are the t o 3.5 times greater than with that of I it is neceshighest optical yields known in the reactions of sary to assume that the degree of complexing is less a-ketoesters with Grignard reagents. in the latter case. There is no obvious reason why this should be so and, a t present, this alternative, while not rigorously excluded, appears unlikely. I n elegant studies, McKenzie, Prelog, Turner and their respective co-workers have examined a large number of reactions of the general type RICOCOzRa RzMgX --t --t RlRzC(OH)COzH. In eighteen such cases, complete resolution data are available on the product hydroxyacid and, using these, we have now calculated optical yields4 the optical For a fixed asymmetric group (Rd), yield is quite insensitive to the size of the incoming The forniation of I11 is most reasonably ex- group (Rz),but becomes larger as the size of the plained on the consideration that most of the prod- group (R1)already attached to the keto group inuct is derived from the two most stable ground creases. This phenomenon requires modification state conformations IV and V, in which repulsive of the previously proposed6 shielding effect theory of asymmetric induction in cr-ketoesters. I t is OCHj I most readily encompassed by the hypothesis that the relative contribution to the total product made by conformation 1'1 diminishes with increasing siie of R1 because of compression effects of the type discussed above.
+
Ho%
CH30
IV
v
interactions are minimized by disposition of the two keto groups coplanar-transoid and the plane of the phenylglyoxylate chain as far away as possible from the ring A methoxyl and ring B, i.e., perpendicular to ring A and a t a dihedral angle of 60" with respect to ring B. Approach to the keto carbonyl group in IV and V by the attacking methyl must occur from the direction of ring A, since the underside of the keto group is shielded by ring B. If the rotational barrier between IV and V is high, the major proportion of the product is derived from V, which is more stable than IV because the phenylglyoxylate chain interferes with H instead of R. If the rotational barrier is low compared to the energy of activation for chemical reaction, the (1) J. A. Berson, THISJOURNAL, 78, 4170 (1956). (2) Cf.J. H. Brewater, i b i d , , 7 8 , 4061 ( I Q R G )
S-.. Ll d
0
c
& , \n
M
, ,
"
R 4 '
'
L
0 \I
We are indebted to the National Science Foundadation for financial support. (3) Cf. D . Y. Curtin, Rec. Chem. Pvogress, 1 5 , 111 (1954); D . T Curtin and ?VI.C. Crew, THISJOURK.AL, 77, 354 (1954). (4) Complete literature references will be given in a forthcoming publication. ( 5 ) V. Prelog, Bull. SOC. chim., 987 (l956), and references r i t a l therein.
DEPARTMENT OF CHEMISTRY UNIVERSITY O F SOUTHERX CALIFORNIA JEROME .I.BERSOS Los ANGELES 7 , CALIFORNIA MICHAEL-4. GREESBAUM RECEIVED FEBRUARY 9, 1857 CYANOCARBON CHEMISTRY-SYNTHESIS AND CHEMISTRY O F TETRACYANOETHYLENE
Sir: Investigation of cyanocarbons, compounds co11taining only ---C=S groups attsched t o carbon,
