Regiospecific and Stereoselective Syntheses of (±) Morphine, Codeine, and Thebaine via a Highly Stereocontrolled Intramolecular 4 + 2 Cycloaddition Leading to a Phenanthrofuran System

Total syntheses of the morphine alkaloids are described that use a direct stereoselective formation of the phenanthrofuran system via an intramolecular 4 + 2 cycloaddition of a diene tethered to the 4-position of a 7-methoxybenzofuran-3-carboxylic acid ester.