The first asymmetric synthesis of protoberberine alkaloids based
upon the (-)-sparteine-mediated lateral metalation of o-toluamides and subsequent addition-cyclisation
with 3,4-dihydroisoquinolines is described (up to 77% ee).
anion addition - (-)-sparteine - 3,4-dihydroisoquinoline - asymmetric synthesis - protoberberine