Stereoselective synthesis of polyether antibiotics, lasalocid A and isolasalocid A, via a chelation-controlled formation of tetrahydrofuran rings under thermodynamic conditions
of lasalocid A (6) and isolasalocid A (7) were stereoselectively constructed from the corresponding p-methoxyphenylallyl alcohols (13a, 13b) by treatment with ZnBr2 to give C13-C24 fragments (14a, 14b) via a new chelation-controlled cyclization under thermodynamic conditions. After their conversion into lasalocid ketone (19) and BOM-isolasalocid ketone (20), coupling with the C1-C11 aldehyde (22) completed