Total Syntheses of (±)-β-Erythroidine and (±)-8-oxo-β-Erythroidine by an Intramolecular Diels−Alder Cycloaddition of a 2-Amidoacrolein

[reaction: see text] The total syntheses of (+/-)-beta-erythroidine and (+/-)-8-oxo-beta-erythroidine are described. The tetracyclic ring system of the natural products was quickly assembled by a strategy that features a retrocycloaddition/cycloaddition reaction of an amidodioxin, an intramolecular Heck reaction, and a 6pi-electrocyclic ring closure of a dienoic acid.