Synthesis of δ-lactones from 2-alkynyl epoxides and 4-alkynyl-1,3-dioxolan-2-ones by palladium catalysed carbonylation and conjugate nucleophilic addition

Palladium catalysed carbonylation of both 4-alkynyl-1,3-dioxolan-2-ones and alkynyl epoxides occurs under mild conditions to give methyl 5-hydroxy-2,3-dienoates which are converted to gamma,delta-unsaturated delta-lactones by tandem conjugate addition-cyclisation with lithium dimethylcuprate or to methyl (E)-5-hydroxypent-3-enoates by stereoselective reduction with sodium borohydride.