Description General description 4-Pentynoic acid undergoes copper-catalyzed intramolecular cyclizations to form enol lactones. It also reacts with 1-bromo-1-alkynes in the presence of a Pd catalyst to yield biologically active ynenol lactones. Application 4-Pentynoic acid was used: • as building block for the synthesis of library of eight sequence-defined model oligomers • in one-pot synthesis of the complex polycyclic heterocycles benzo[4,5]imidazo[1,2-c]pyrrolo[1,2-a]quinazolinone derivatives • in the synthesis of various allenenols lactones [5(E)-(2-allenylidene)-tetrahydro-2-furanones] • in the synthesis of a cyctotoxic macrolide by ring-closing metathesis of a bis acetylene Packaging 1, 5 g in glass bottle