Z-Selective Intramolecular Horner−Wadsworth−Emmons Reaction for the Synthesis of Macrocyclic Lactones

When the substrates (ArO)(2)P(O)CH(2)CO(2)---CHO (Ar = Ph, o-t-BuPh) were added to a THF solution containing 3 equiv of NaH at 0 degrees C or NaI-DBU at rt over 1-10 h, the intramolecular Horner-Wadsworth-Emmons reaction proceeded efficiently to give the 12-18-membered-ring lactones in 69-93% yields with 89-100% Z selectivity. On the other hand, (EtO)(2)P(O)CH(2)CO(2)---CHO gave the 13-18-membered-ring lactones in 52-82% yields with 89-99% E selectivity using LiCl-DBU in MeCN or THF.