Radical Cyclization in Heterocycle Synthesis. 12.¹⁾ Sulfanyl Radical Addition-Addition-Cyclization (SRAAC) of Unbranched Diynes and Its Application to the Synthesis of A-Ring Fragment of 1α, 25-Dihydroxyvitamin D₃

Abstract

Sulfanyl radical addition-addition-cyclization (SRAAC) of unbranched diynes proceeded smoothly to give cyclized exo-olefins, while the sulfanyl radical addition-cyclization-addition (SRACA) of diynes having a quaternary carbon gave cyclized endo-olefins. This method was successfully applied to the synthesis of A-ring fragment of 1α, 25-dihydroxyvitamin D₃.