Divergent Synthesis of ()- and ()-Alkenones via Photoredox C(sp)-H Alkenylation-Dehydrogenation of -Iodoarylalkanols with Alkynes.

A photoredox C(sp)-H alkenylation-dehydrogenation of -iodoarylalkanols with terminal alkynes for the synthesis of ()- and ()-quaternary carbon center-containing pent-4-en-1-ones is described. The stereoselectivity depends on the utilization of alkynes and photocatalysts. While using an organic photocatalyst like 4-DPAIPN manipulates the C(sp)-H alkenylation-dehydrogenation of -iodoarylalkanols with arylalkynes to assemble ()-pent-4-en-1-ones, in the case of an Ir potocatalyst such as Ir(ppy)(dtbbpy)PF the reaction with arylalkynes delivers ()-pent-4-en-1-ones. For alkylalkynes, the reaction furnishes ()-pent-4-en-1-ones exclusively in the presence of 4-DPAIPN or Ir(ppy)(dtbbpy)PF.