h u g . 20, 1964
3271
O P T I C i l L L Y A C T I V E a-r\;APHTHYLPHENYLXETHYLSILANES
ORGANIC A N D BIOLOGICAL CHEMISTRY [CONTRIBUTIOS F R O M
THE
DEPARTMEXT O F CHEMISTRY, THEP E S N S Y L V A S I A STATE VXIVERSITY, USIVERSITY
PARK,
PA.]
Stereochemistry of Asymmetric Silicon. I. Relative and Absolute Configurations of Optically Active a-Naphthylphenylme t hylsilanes' BY L. H. SOMIER, C. L. FRYE, G. A.PARKER, ASD K. LV. ~ I I C H A E L RECEIVED OCTOBER7 , 1963 Correlations of configuration for seven key conipounds containing the a-naphtti~-lplienyl~nethylsilyl group, RaSi*-, are reported. I n turn these lead to elucidation of the stereochemistry of some fourteen reactions of optically active I13Si*X compounds. Absolute configurations, based on X-ray results, are also reported.
It is clear t h a t stereochemical studies of'organic reactions have contributed greatly to our knowledge of the mechanisms of substitution of carbon compounds. However, prior to 1958, it was not even known whether substitution reactions a t silicon atoms are stereospecific. Resolutions of three organosilicon compounds, only two of which contained relatively unreactive functional groups bonded to silicon, had been carried out by the pioneer of organosilicon chemistry, F. S.Kipping, b u t the routes to these optically active compounds were tedious and lengthy, the amounts obtained were small, and the optical rotations were feeble. Furthermore, these substances had the serious disadvantage of sulfonic acid groups bonded to carbon.2 For the purpose of carrying out stereochemical studies of asymmetric silicon in organosilicon molecules, it was desirable to have optically active compounds which do not contain reactive functional groups bonded to carbon because of probable reactions between the functional groups on carbon and silicon.3 T h e condition t h a t organosilicon structures suitable for stereochemical studies should have no reactive functional groups bonded to carbon imposed the requirement t h a t resolution be effected by separation of diastereoisomers in which the silicon atom is directly linked to an optically active group provided b y the resolving agent. This requirement was met by separation of the diastereomeric a-naphthylphenylrnethyl( - ) menthoxysilanes, R&*( -)Ohfen, which were prepared as
+ ( - ) menthol
( f)R8SiOCH3
KOWB) __f
( - )RaSi*( -)OMen
+ ( +)RsSi*(
- )OMen
The sirupy mixture of diastereoisomers was dissolved in pentane and cooled to -78'. The higher-melting less soluble diastereoisomer was obtained in good yield and had m.p. 82-84', [ a ] D -53.9' (cyclohexane). This diastereoisomer is designated (-)R3Si*( -)OMen, (-)a-naphthylphenylmethyl-( - )-menthoxysilane. The lower-melting more soluble diastereoisomer was purified by repeated recrystallization from ethyl alcohol and (1) F o r preliminary publications dealing with optically active a - n a p h thylphenylmethylsilanes. see' L. H. Sommer a n d C. L. Frye, J . A m . Chem. S~JC 81, . , 1013 (1959); L . H . Sommer a n d C. I,. F r y e . ibid., 82, 3796 (1960); L. H . Sommer and C. L. F r y e , i b i d . , 82, 1118 (1960), L. H. Sommer, C. L. F r y e , M. C. S l u s o l f , G. A P a r k e r , P. G. Rodewald, K. W Michael, Y . O k a y a , and R . Pepinsky, i b i d . , 83, 2210 (19611, L. H . S o m m e r , Angew. Chem. I u ' e y n , E d . Engl. 143 11992). ( 2 ) F S Kipping a n d co-workers, J . Chem. Soc., 20Cl ( 1 9 1 7 ) ; 2090 (1908); 705 (1910). (3) Preparation of a n optically active organosilicon compound n o t havin a reactive functional group on silicon, p-carboxyphenylmethylethylsilane, has been reported more recently: C. E a b o r n a n d C. P i t t , Chem. I n d . (Lond o n ) , 830 (1958).
had m.p. 5G.5-5g0, [ a ] D -47' (cyclohexane). This diastereoisomer is designated (+)R3Si*( -)Ohfen, (+)a-naphthylphenylmethyl- ( - ) -menthoxysilane. Lithium aluminum hydride reduction of the separated diastereoisomers proceeded (-)I
