Telescoped Synthesis of γ-Bromo-β-Lactones from Allylic Bromides Employing Carbon Dioxide

A direct synthesis of the title compounds involving a stepwise Zn-mediated carboxylation of allylic bromides with CO₂ delivering β, γ-unsaturated carboxylic acids and a subsequent bromolactonization is reported. The described method demonstrates the use of readily prepared allylzinc bromides by the method of Knochel for fixation of CO₂ employing commodity chemicals and zinc dust. This process was then optimized into a two-stage, telescoped process for the direct synthesis of γ-bromo-β-lactones from allyl bromides. The described strategy delivers functionalized β-lactones with dual reactivity as acylating and alkylating agents, which have utility as synthetic intermediates and are attracting growing interest as proteomic tools for activity-based protein profiling.