Rapid and Easy Access to (E)-1,3-Enynes, 1,3-Diynes and Allenes Starting from Propargylic Acetals, Exploiting the Different Reactivity of Lithium and Mixed Lithium-Potassium Organometallic Reagents

The treatment of propargylic acetals with various lithium and mixed lithium–potassium Schlosser reagents, has allowed a one-pot synthesis of (E)-1,3-enynes, 1,3-diynes and allenes, depending on the reaction conditions and the selected base. Various reaction conditions were investigated in order to control the selectivity of the reactions and to obtain pure products. The metallation–elimination sequence in the presence of a suitable electrophile has provided a linear route to functionalized (E)-conjugated enynes, diynes and allenes.