Synthesis of Sulfur-Containing Macrocyclic Lactones. The lactonization of 3a was carried out in dichloromethane in the presence of potassium carbonate as a base under reflux conditions to give sulfur-containing 17-membered lactone 13a and diolide 14a (R= H) in 19% and 31% yields, respectively. On the other hand, under high-dilution conditions in acetone, the desired lactone 13a was obtained in good yield (86%) and the formation of
