Preparation of 8-methylberberines and aza analogues: Synthesis of (±)-alamaridine

Abstract

Methyllithium reacted with oxyberberine, affording on alkaline work-up a compound with an exomethylene group at C-8 that was transformed in acidic media into an 8-methylberberinium salt. The iminium salt was reduced to a mixture of racemic α- and β-8-methylcanadine. 5,6-Dihydro-8H-isoquino[2,1-b][2,7]naphthyridin-8-ones were similarly transformed into 8-exo-methylene and 8-methyl derivatives, which were subjected to further reduction. These reactions have been employed in a synthesis of the Alangium alkaloid, (±)-alamaridine.