Diastereoselective Substitution Reactions of Acyclic β-Alkoxy Acetals via Electrostatically Stabilized Oxocarbenium Ion Intermediates

Substitution reactions of acyclic β-alkoxy acetals proceeded with generally high diastereoselectivities (>90:10) to form the anti product. Mechanistic experiments supplemented with computational studies suggest that, upon activation of the acetal, the resulting oxocarbenium ion is electrostatically stabilized by the β-alkoxy group. This stabilization defines the conformation of the reactive intermediate, which can be attacked preferentially from the more exposed face, leading to the observed products.