Synthesis of Cyclopentenols and Cyclopentenones via Nickel-Catalyzed Reductive Cycloaddition.

While the “normal” cycloaddition between dienes and alkynes leads to formation of six-membered Diels—Alder or hetero-Diels—Alder ring products, the reductive cycloaddition using BEt3 as the active reducing agent and MeOH as the proton donor allows the synthesis of either cyclopentenols (from enals and alkynes) or cyclopentenones (from enoates and alkynes).