A new strategy for the stereoselective synthesis of alkaloids with perhydro-9b-azaphenalene skeleton has been developed. The starting material is the substituted glutarimide derivative 1, readily available in either enantiomeric form through the palladium-catalyzed asymmetric allylic alkylation of glutarimide. The strategy relies on an iterative methodology encompassing two nucleophilic allylations and two ring closing metathesis processes. The approach has been used in the first synthesis of (−)-9a-epi-hippocasine.

Azaphenalene alkaloids are biosynthesised and segregated by diverse insects of the Coccinellidae family (ladybirds) and are believed to play an important role in the defensive mechanism against their natural predators. The particular unique framework of these alkaloids, along with their potential in the field of biological pest control, has led to several research groups developing synthetic sequences to prepare these compounds. The main purpose of the present review is to provide an update of the more recent synthetic progress towards these alkaloids, including the pioneering enantioselective approaches to chiral congeners.

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