Zinc-mediated carboxylations of allylic and propargylic halides in flow: synthesis of β-lactones via subsequent bromolactonization

Zinc-mediated carboxylation of allylic halides under flow conditions delivered β,γ-unsaturated carboxylic acids and subsequent bromolactonization provides a streamlined process for the synthesis of γ-bromo-β-lactones. The described process further demonstrates the utility of organozinc reagents prepared by passage of allylic halides through a metallic zinc column integrated into a flow process. Use of a tube-in-tube reactor for efficient CO₂ introduction led to improvements in conversion compared to a batch process and improved overall yields of β-lactones. The described flow process was also applied to propargylic bromides for the synthesis of allenic and propargylic acids.