Microwave-Assisted\nSelective Nucleopalladation-Triggered\nCascade Process: Synthesis of Highly Functionalized 3‑Chloro‑1<i>H</i>‑indenes

A nucleopalladation-triggered\ncascade transformation\nof internal\nalkynes bearing an amino nucleophile and an electrophilic enone was\ninvestigated under unconventional microwave-assisted conditions. Among\nthe three possible pathways, the chloropalladation-triggered domino\nprocess proceeded selectively to furnish 3-chloro-1<i>H</i>-indenes in good to excellent yields. The reactions under microwave\nirradiation were completed in 30 min, and the conventional heating\nrequired 3–5 h for completion. The yields obtained under nonclassical\nheating using microwave irradiation are marginally higher (71–97%)\nthan those of the conventional heating conditions (67–96%).\nThe mechanism of this domino process involves chloropalladation of\nalkynes to deliver σ-vinylpalladium intermediates, intramolecular\ncarbopalladation via Heck-type olefin insertion, and protodepalladation\nsteps. The other two competitive intramolecular aminopalladation-initiated\ncascades via 7-<i>endo-dig</i> or 6-<i>exo-dig</i> cyclizations leading to oxazepine or benzoxazine scaffolds were\nnot observed.