Organogermanium compounds. Part VIII. The preparation of optically active asymmetric germanium compounds

Abstract

Recrystallisation of ethyl-1-naphthalyphenylgermyl (–)-menthoxide from pentane at –70° gave a diastereoisomer which, on reduction with lithium aluminium hydride in ether, gave the (+)-hydride, Et(1-C₁₀H₇)PhGeH, m. p. 31–32·5°, [α]_D²⁵+ 23·6°(c 5·5 in benzene). Crystallisation of ethyl-1-naphthylphenylgermyl (–)-1-phenylethoxide at ca.–15° gave crystals from which the optically impure (–)hydride, [α]_D²⁰–10·9°(c 13 in benzene) was obtained on reduction. The (+)-hydride was converted into the (–)-chloride by treatment with chlorine in carbon tetrachloride, and reduction of the chloride with lithium aluminium hydride gave the (–)-hydride. Only 7% of racemisation occurred in this Walden cycle, the existence of which shows that substitution at germanium can proceed by at least two distinct mechanisms, one involving predominant inversion and the other predominant retention of configuration. An unsuccessful attempt was made to repeat the work described in an earlier claim for resolution of a germanium compound, and that claim is critically considered.