We present the details of an organophosphinecatalyzed Morita−Baylis−Hillman-type reaction of activated alkynes. The outcome is an intramolecular hydroacylation of α,β-ynones leading to the formation of 1,3-cyclopenta-, cyclohepta-, and cyclooctadione-fused arenes and heteroarenes. In addition, during the course of the investigation, a phosphine-catalyzed intramolecular aldol reaction of ketoynones via δ′[C(sp 3 )-H]-functionalization was discovered, and a new annulation event comprising of a ω′[C(sp 3 )-H]functionalization of α,β-ynones was also uncovered. The mechanisms governing these processes have been thoroughly elucidated.

A new approach for the cyclopenta[b]annulation of heteroarenes through metal-free and directing-group-free γ'[C(sp )-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(sp )-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.

An efficient organocatalytic approach for the cyclopenta[b]annulation of benzothiophenes via γ′[C(sp3)–H] functionalization of ynones is described. Nucleophilic addition of an organophosphine to the designed ynones generates heteroaryl-based ortho-quinodimethanes (oQDMs), which undergo carbocyclization to provide a variety of cyclopenta-fused benzothiophenes. This approach also constitutes an unusual organophosphine-catalyzed intramolecular hydroalkylation of ynones.

Intramolecular Hydroalkylation Organocatalytic γ’[C(sp3)−H] functionalization of ynones has been achieved for the first time. Nucleophilic addition of an organophosphine to the designed ynones leads to the formation of heteroaryl‐based ortho‐quinodimethane (oQDM) intermediates, which undergo an unusual carbocyclization to provide functionalized cyclopenta‐fused heteroarenes. The present study can have potential implications on the development of new organocatalytic C(sp3)−H‐functionalization pathways. For more details, see the Communication by S. S. V. Ramasastry et al. on page 18316 ff.