Cyclopenta[b]annulation of Heteroarenes by Organocatalytic γ′[C(sp3)−H] Functionalization of Ynones

A new approach for the cyclopenta[b]annulation of heteroarenes through metal‐free and directing‐group‐free γ′[C(sp3)−H] functionalization and intramolecular hydroalkylation of ynones has been developed. In an unprecedented event, nucleophilic addition of an organophosphine to the designed ynones triggers γ′[C(sp3)−H] functionalization, leading to the formation of heteroaryl‐based ortho‐quinodimethane (oQDM) intermediates that undergo carbocyclization to provide cyclopentannulated heteroarenes in good yields and excellent stereoselectivities. Deuterium‐labeling experiments substantiated the proposed reaction mechanism as well as the speculated epimerization. Redox by an organophosphine! Organocatalytic intramolecular hydroalkylation of ynones has been achieved. Nucleophilic addition of an organophosphine to the designed ynones generate heteroaryl‐based ortho‐quinodimethanes (oQDMs) through γ′[C(sp3)−H] functionalization, which undergo annulative hydroalkylation leading to the formation of a diverse set of cyclopentannulated heteroarenes (see scheme).