Synthesis of 12- and 13-Membered Sulfur-Containing Lactones by Homolytic Macrocyclization of Mercaptoacetic Esters with Alkynes

Starting from mercaptoacetic acid esters of 1,2- or 1,3-diols and substituted acetylenes 12- and 13-membered sulfur-containing lactones as 1:1 adducts were synthesized in yields up to 48%. The mechanism of this homolytic reaction, which is initiated by the tripropylborane/oxygen system, includes generation of thiyl radicals and their addition to the triple bond of alkynes.