Cleavage of Carbon-Carbon Bonds with High Stereochemical Control. 7. Chiral α-Silyl Benzoylcycloalkanes Undergo Base-Catalysed Cleavage with Retention of Configuration When Not Sterically Congested

Article abstract of DOI:10.1021/jo00267a032

The cyclic phenyl ketone (-)-1 has been prepared in a manner that allows definition of its absolute configuration.On being heated with sodium and potassium amide in benzene, (-)-1 undergoes C-C bond cleavage with outstanding (96-98percent) levels of configurational retention.This conclusion required interconversion of (-)-1-(trimethylsilyl)-3-isopropylidenecyclopentane (2) with (S)-(-)-3-(trimethylsilyl)cyclopentene (3).The racemic ketones 21, 22, 36, and 37 have also been synthesized and subjected to the Haller-Bauer process.In each case, the resultant cyclic silanes were demonstrated to arise by virtually exclusive stereochemical retention.In the case of 28, an example where the benzoyl carbonyl group is sterically shielded, desilylation was the kinetically dominant reaction with these bases.These results are interpreted on the basis of initial α-silyl carbanion formation within a solvent shell that also encases benzamide.The benefits derived from these special solvational features are predicted not to be useful for extending stereocontrol to targets requiring the operation of intermediate energy-demanding steps.