Novel anionic polycyclisation cascade. Highly stereocontrolled assembly of functionalised tetracycles akin to the middle core of the manzamines

Substituted gramines, in the presence of tBuOK, react with acrolein and β-keto-phosphonates, via a novel sequence involving a multicomponent condensation followed by an anionic polycyclisation cascade, to afford in excellent overall yields, highly functionalised tetracyclic structures akin to the middle core of the manzamines. In this unique process, up to eight elementary transformations take place with remarkably high chemo- and stereocontrol.