On the mechanism of Lewis acid mediated nucleophilic substitution reactions of acetals

摘要: Lewis acid mediated nucleophilic substitution of acetals can occur by direct displacement (S N 2) or oxocarbenium ion 1) mechanisms. With acyclic acetals, stereoselectivity increases with increasing steric bulk the alkoxy group and polarity reaction medium. The enhanced observed secondary tertiary alcohols is explained perturbation approach trajectory alkene as it attacks ion. Highest seen in 2-(1-phenylethyl)-4,4,5,5-etramethyl-1,3-dioxolane enol silane; only one diastereomeric product obtained