Total Synthesis of 8,14-Dihydromorphinandienone Alkaloids

A collective
synthesis of 8,14-dihydronorsalutaridine, 8,14-dihydrosalutaridine,
norisosinomenine, and isosinomenine is reported. The strategy provides
direct access to the correct oxidation level of the products. The
combination of an organocatalyst guanidine superbase, a tertiary amine
base, and a dehydrating agent was necessary for the successful Henry–Michael–dehydration
cascade to form the phenanthrene motif. The required selective aliphatic
nitro reduction could only be achieved under heterogeneous transfer–hydrogenation
conditions.