Optical isomerism in asymmetric-silicon compounds.

The previous work on the preparation and resolution of asymmetric-silicon compounds is reviewed. The asymmetric-silicon compound MeEtPhSiC6H4COOH-P was prepared, and was resolved by fractional crystallisation of its quinine salts from ethanol. The less-soluble salt yielded the pure (+) acid, [?] D25 = +2.75, (benzene). A laevorotatory sample, [?] D25 = -1.65, of the acid was obtained from the more-soluble fractions. This represents the first well authenticated resolution of a tetracovalent silicon compound, containing only one asymmetric-silicon atom, which may be obtained free from other asymmetric centres. The (+)acid was shown to be optically stable when maintained in the liquid state at 100 0 for six hours, and in solution with 5% aqueous methanolic potassium hydroxide at room temperature for eighteen hours. A preliminary investigation of the optical consequences of cleavage of the silicon-phenyl group of the (+) acid was made. The diastereoisomorphous organosilicon (-) menthoxides MeEtPhSiOR and MeBunPriSiOR (R = (-) menthyl), which it was hoped to resolve by fractional crystallisation, were prepared, but they could not be obtained as solids. The possibility of employing gas-liquid chromatography to separate the volatile diastereoisomers of an asymmetric- silicon compound was investigated, using the sec-Tjutoxy- derivatives of (j:)MeBu.;r.;SiGl. Inattempting to prepare the acids (+)MeRPSiGgH.;G00H-2 "by oxidation of the corresponding.;-tolyl-suhstituted organosilane with alkaline permanganate, it was shownthat oxidation of the 3i-R group occurred when R v/as ethyl, vinyl or iso-propyl. The acid ( + )MePr.;(OH)SiCgH2.;COOH~2 was synthesised, and its salts with anumber of optically- active bases were prepared, hut these salts could not be resolved by fractional crystallisation. The organosilicon-substituted q.uarte|.;ryammonium iodides, (+)MeR(OEt)SiC.;H.;NMe.;i and (+)MeR(OH)SiCgH.;lke.;i (R = Et,Pr.;), were synthesised. Diastereoisomorphous salts were prepared from thequarte.;nary ammonium iodides, by treatment with the silver salts of optically-activeacids, but these salts could not be resolved by fractional crystallisation.