Synthesis of 1H-Isochromenes and 1,2-Dihydroisoquinolines by Indium(III)-Catalyzed Cycloisomerization of ortho-(Alkynyl)benzyl Derivatives

Fabio Seoane-Carabel, Lorena Alonso-Marañón, Luis A. Sarandeses, José Pérez Sestelo


Synthesis 2023, 55,  1714-1723 (10.1055/s-0042-1751383)

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1H-Isochromenes and 1,2-dihydroisoquinolines are synthesized
by regioselective indium(III)-catalyzed intramolecular hydrofunctionalization
of o-(alkynyl)benzyl derivatives. The reaction with o-
(alkynyl)benzyl alcohols and amines proceeds using indium triiodide
(5–10 mol%) in toluene at 80–100 °C via regioselective 6-endo-dig intramolecular
alkyne hydroalkoxylation or hydroamination in good yields.
Alternatively, the cycloisomerization reaction of o-(alkynyl)benzaldehydes
and imine derivatives using InI3 (5 mol%) and the Hantzsch ester
(120 mol%) takes place, under milder reaction conditions, to give a variety
of functionalized 1H-isochromenes and 1,2-dihydroisoquinolines
through a domino cycloisomerization/reduction approach.