1,2-Addition of Allyl and 2-Oxo-2<i>H</i>-pyran-6-ylcarbonyl Groups to Cyclic C=N Double Bonds by Means of Organotin Reagent for Alkaloids Synthesis; A Facile Synthesis of 8-Oxoprotoberberine and Norketoyobirine (Demethoxycarbonyloxogambirtannine)

Abstract

Abstract 1,2-Introduction of allyl and 2-oxo-2H-pyran-6-ylcarbonyl groups into isoquinoline system can be effectively accomplished by reaction of allyltributyltin with 3,4-dihydroisoquinoline activated by 2-oxo-2H-pyran-6-ylcarbonyl chloride. Allyltributyltin reacts similarly with 3,4-dihydro-β-carboline activated by 2-oxo-2H-pyran-6-ylcarbonyl chloride to gave the corresponding 1,2-adduct. Intramolecular Diels–Alder reactions of the 1,2-adducts followed by DDQ oxidations afford 8-oxoprotoberberine and norketoyobirine.