Face selectivity in the reactions of 2,4-disubstituted adamantanes and their modification by inclusion in β-cyclodextrin solutions

Sodium borohydride reduction reactions on 4-X-adamantan-2-ones (where X=ethyleneketal , ethylenethioketal , and methylene ) were studied, which gave Z-alcohols and (from en-face attack) as the predominant products for ketones and , but gave 1:1 mixture of Z- and alcohols for ketone . The en/zu face selectivity of in sodium borohydride reduction was enhanced to 32/68 in β-CD solution. Both 1,3-dipolar addition and dichlorocarbene addition reactions on 4-ethyleneketal-2-methyleneadamantane underwent again predominant en-face attack to give products in an E/Z ratio of >99:1 and 92:8, respectively. The exceptional high zu-face selectivity on the dichlorocarbene addition reaction of may be explained by a temporal complexation between the carbene and the C4-oxo group. In the epoxidation reaction of and the zu-face attack products were favored despite their steric congestions suggesting that hydrogen bonding interaction between the peroxide reagent and the C4-oxo or 4-ethyleneketal is involved.