FACE SELECTION IN THE CAPTURE OF ANIONIC CARBON

Several reactions of 2-(5-phenyladamantyl) derivatives have been exami ned with the objective of determining the stereochemistry of addition of electrophiles to a trigonal center Ct carrying a full or partial ne gative charge. These reactions included the carbonation and brominatio n of the 2-lithioadamantane(s) attack at the zu face was found to be p redominant. Methylation of 5-phenyl-2-adamantanone with either methyll ithium or lithium dimethylcuprate gave mixtures of the methyl alcohols in which the E-isomer is the main product. Attempts to study the reac tions of the enolate anion derived from the (E)- and (Z)-phenyl 2-(5-p henyladamantyl) ketones 7-Ph were not successful: bromination could no t be forced at all, and methylation and protonation occur at oxygen. T he enol ether and enol were studied also; brominations of these neutra l species occur at the zu face. It is concluded that even the impositi on of negative charge upon the trigonal center does not engender the t ype of hyperconjugation envisioned by Anh in the capture of electrophi les. Protonation of the enol ether led to an equilibrium mixture of ke tones 7-Ph; protonation of the enol itself gave an excess of the E-iso mer. Possible reasons for this unexpected outcome are discussed.