Synthetic transformations of higher terpenoids: XXII. Reactions of lambertianic acid derivatives with organozinc reagents obtained from ethyl bromoalkanoates

Reactions of 16-cyanomethyllambertianate with organozinc reagents obtained from ethyl esters of α-bromoacetic, α-bromopropionic, and α-bromobutyric acids gave the corresponding enaminoesters, β-ketoesters, and β-hydroxyesters of labdanoids whose yield depended on the reaction conditions and the structure of the α-bromoester. By Reformatsky reaction of 16-formylmethyllambertianate with α-bromoesters of carboxylic acids stereoisomeric β-hydroxyesters of labdanoids were synthesized.