Organocatalytic One‐Pot Synthesis of Pseudo‐Terpenoids

Abstract Structurally complex cedrane scaffolds were synthesized in very good yields with high chemo‐ and diastereoselectivities in a sequential one‐pot manner. A combination of intermolecular olefination, intramolecular Michael and Michael reactions or intermolecular olefination, intramolecular Michael and aldol reactions were used as the key steps from the readily available hydroxy‐ p ‐quinone butanals and phosphoranes with catalytic amounts of quinine at ambient temperatures for a few hours. This is a unique one‐pot combination of coupling and annulation routes for the green synthesis of a library of tricyclic pseudo‐terpenoids (cedrane scaffolds) with high selectivity and yields. Organocatalytic ring isomerization was highlighted through transforming one ring into another one by retro‐cyclization. We have discussed thoroughly mechanistic aspects of these tandem coupling/annulation and ring isomerization reactions based on control experiments and X‐ray crystal structure analysis.