Characterization of (Z)-cyclooct-2-enylstannanes

Article abstract of DOI:10.1021/om00051a022

(Z)-Cyclooct-2-enyltrimethylstannanes and -triphenylstannanes have been synthesized and characterized by ¹H and ¹³C NMR spectra, which indicate a predominating unsymmetrical chair-boat arrangement. A mixture of the cis and trans isomers of both the (4-methylcyclooct-2-enyl)- and (8-methylcyclooct-2-enyl)trimethylstannanes (allylic stannanes) results from a sequence commencing with methylcyanocuprate opening of the monoepoxide of 1,3-cyclooctadiene, which is considered to afford regio- and stereoselectively trans-4-methylcyclooct-2-enol. Chlorination of this alcohol with both thionyl chloride and N-chlorosuccinimide/dimethyl sulfide has been conducted and the structures of the chlorides established by NMR methods and use of [1-²H₁]-4-methylcyclooct-2-enol. Trimethylstannylation of the chloride mixtures provides the four possible allylic stannanes, with one of the rearranged 8-methyl isomers slightly predominating. NMR spectra of various fractions from preparative gas chromatography have been obtained, and full assignment of the ¹³C NMR spectra of the isomers is reported. Acidolysis of these fractions (with CF₃COOD) proceeds rapidly to yield mixtures of ²H-substituted 3- and 4-methylcyclooctenes, but only one diastereomer of each system appears to be formed, on the basis of the ¹³C NMR spectra. This implies that electrophile approach to the π-face at the γ-carbon is not influenced by the orientation of the C-Sn bond but is probably dictated by the predominant molecular conformation.