Divergent Synthesis of (<i>E</i>)- and (<i>Z</i>)-Alkenones via Photoredox C(sp³)–H Alkenylation–Dehydrogenation of <i>o</i>-Iodoarylalkanols with Alkynes

A photoredox C(sp³)-H alkenylation-dehydrogenation of <i>o</i>-iodoarylalkanols with terminal alkynes for the synthesis of (<i>E</i>)- and (<i>Z</i>)-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(sp³)-H alkenylation-dehydrogenation of <i>o</i>-iodoarylalkanols with arylalkynes to assemble (<i>E</i>)-pent-4-en-1-ones, in the case of an Ir potocatalyst such as Ir(ppy)₂(dtbbpy)PF₆ the reaction with arylalkynes delivers (<i>Z</i>)-pent-4-en-1-ones. For alkylalkynes, the reaction furnishes (<i>E</i>)-pent-4-en-1-ones exclusively in the presence of 4-DPAIPN or Ir(ppy)₂(dtbbpy)PF₆.