Condition-controlled selective synthesis of spiroisoquinolinones or spiroisoindolinones via CHA–initiated spiroannulation, ring opening and ring contraction

Abstract

Presented herein is a condition-controlled selective synthesis of isoindole spiroisoquinolinone or isoindole spiroisoindolinone derivatives based on the cascade reactions of 3-phenylisoxazolone with diazo homophthalimide. When the reaction was carried out in the presence of Rh(III) and NaOAc under argon for 1 h, the former was obtained via C–H activation-initiated formal [4 + 1] spiroannulation and isoxazolone ring opening. When the reaction was carried out in the presence of Rh(III) and KOAc under air for 12 h, the latter was obtained via [4 + 1] spiroannulation, isoxazolone ring opening and isoquinolinone ring contraction. With this method, concise and effective synthesis of two classes of valuable spirocyclic products from the same starting materials was achieved by simply tuning the reaction conditions. In general, this protocol features easily controllable selectivity, oxidizing and transformable directing group, redox-neutral conditions, unique reaction pathway and good functional group compatibility. The methodology is readily scalable and the structure of the product thus obtained could be diversely decorated.