Transition metal-catalyzed intramolecular (4 + 2) cycloadditions: a novel method for the assembly of nitrogen heterocycles and its application to yohimbian alkaloid synthesis

Nickel(0)-catalyzed intramolecular (4 + 2) cycloadditions of nitrogen-containing dienynes have been evaluated as method for the synthesis of hydroisoindole and hydroisquinoline derivatives. The results showed that the reactions can tolerate amide, sulfonamide and carbamate functionalities. The method has been applied to the expedient synthesis of (+/-)-19.20-didehydroyohimbane, the pentacyclic framework of the medicinally active Rauwolfia alkaloids.