Highly Efficient Darzens Reactions Mediated by Phosphazene Bases under Mild Conditions

The highly basic and poorly nucleophilic phosphazene base P(1)‐t‐Bu promotes the Darzens condensation of α‐halo esters with aromatic aldehydes affording α,β‐epoxy esters in nearly quantitative yields under mild conditions and in short reaction times. The more basic P(4)‐t‐Bu phosphazene was found useful with low reactivity aldehydes. These reactions can be performed in aprotic organic solvents of low polarity, thus minimizing the hydrolysis of α,β‐epoxy esters which often accompanies the base‐promoted Darzens condensations.