G. Wickham, W. Kitching
1983
Citations
0
Influential Citations
13
Citations
Journal
Organometallics
Abstract
The stereochemistry of the 3,4-bis(trimethylsilyl)cyclohexene resulting from disilylation of 1,3-cyclohexadiene is concluded to be cis on the basis of 1H and 13C nuclear magnetic resonance spectra and hydrogenation to Cis-1,2-bis(trimethylsilyl)cyclohexane. The higher boiling cis- and trans-3,6-bis(trimethylsilyl)cyclohexenes could be separated from the above 3,4-isomer but not from each other by careful spinning band distillation. However, the cis,trans compositions of various fractions were established by 13C NMR spectra and chromatographic characteristics. Trifluoroacetolysis (CF3COOD in chloroform) of the cis 3,4-isomer proceeds to yield cyclohexene-d2 as the final product, and analysis of 2H NMR spectra and intermediates demonstrates the importance of a facile 1,2-trimethylsilyl shift in the presumed intermediate ion. Trifluoroacetolysis of the mixtures of the 3,6-disilyl isomers proceeds regiospecifically to yield cyclohex-3-enyltrimethylsilane. A preferred anti mode of attack by the electrophile is indicated for the cis isomer, but syn and anti modes are about equally preferred in the trans isomer. This is attributed to steric congestion by the trimethylsilyl group in the γ-carbon region, hindering anti approach by the electrophile.