Rh(III)-Catalyzed Reaction of 4‑Diazoisochroman-3-imines with (2-Formylaryl)boronic Acids To Access a Straightforward Construction of 5H‑Isochromeno[3,4‑c]isoquinolines

An Rh­(III)-catalyzed one-pot synthesis of 5H-isochromeno­[3,4-c]­isoquinolines from readily available 4-diazoisochroman-3-imines and (2-formylphenyl)­boronic acids is reported. The cascade annulation involves a Rh­(III)-catalyzed cross-coupling and an intramolecular nucleophilic addition–elimination process. A series of biologically important 5H-isochromeno­[3,4-c]­isoquinolines were obtained in good to excellent yields. The method can be extended to synthesize 7H-isochromeno­[3,4-b]­thieno­[3,2-d]­pyridines and 7H-isochromeno­[3,4-b]­thieno­[2,3-d]­pyridines from the corresponding heteroaryl boronic acids.