undergo the Prins reaction with aldehydes in situ to afford conjugated homoallylic alcohols. These sequential transformations enable the conversion of diastereomeric mixtures of 3-hydroxy-4-pentenoic acids, which are readily prepared from the simple crossed aldol reaction of esters and α,β-unsaturatedaldehydes, into 3,5-hexadienyl alcohols with high regio- and stereoselectivities in a single manipulation