Metal-free Reductive Cyclization and Isomerization of Sulfanyl-1,6-diynes Using Sodium Borohydride

Abstract

Abstract In this study, we demonstrated the metal-free reductive cyclization of sulfanyl-1,6-diynes with sodium borohydride in ethanol in the presence of diazabicyclo[5.4.0]undec-7-ene. 1,6-Diynes 1 and 5a–5h bearing hydrogen or phenyl as the R2 group afforded pyrroles 2 and 6a–6e in high yields without any side reaction products such as enynyl sulfides. 1,6-Diyne (R2 = Et) produced both pyrrole and enynyl sulfides; however, the use of cesium fluoride succeeded in the selective formation of pyrrole 6f.