Rapid Construction of the ABCE Tetracyclic Tertiary Amine Skeleton in Daphenylline Enabled by an Amine-Borane Complexation Strategy.

A synthetically challenging tetracyclic tertiary amine framework in the Daphniphyllum alkaloid daphenylline was established in a six-step sequence featuring an intermolecular Diels-Alder cycloaddition/oxidative aromatization sequence. The utilization of an amine-borane complexation strategy is the key to successful transformations on our tertiary amine substrates.