FACE SELECTION IN THE CAPTURE OF ANIONIC CARBON

Several reactions of 2-(5-phenyladamantyl) derivatives have been examined with the objective of determining the stereochemistry of addition of electrophiles to a trigonal center Ct carrying a full or partial negative charge. These reactions included the carbonation and bromination of the 2-lithioadamantane(s) attack at the zu face was found to be predominant. Methylation of 5-phenyl-2-adamantanone with either methyllithium or lithium dimethylcuprate gave mixtures of the methyl alcohols in which the E-isomer is the main product. Attempts to study the reactions of the enolate anion derived from the (E)- and (Z)-phenyl 2-(5-phenyladamantyl) ketones 7-Ph were not successful: bromination could not be forced at all, and methylation and protonation occur at oxygen. The enol ether and enol were studied also; brominations of these neutral species occur at the zu face. It is concluded that even the imposition of negative charge upon the trigonal center does not engender the type of hyperconjugation envisioned by Anh in the capture of electrophiles. Protonation of the enol ether led to an equilibrium mixture of ketones 7-Ph; protonation of the enol itself gave an excess of the E-isomer. Possible reasons for this unexpected outcome are discussed.