A Modular Approach to the Asymmetric Synthesis of Cytisine

The asymmetric synthesis of (+)- and (-)-cytisine starts with Matteson homologations for the construction of a chiral C3-building block. Conversion of the C3-building block into a dihydropyridone is achieved by straightforward functional group interconversions and ring closing metathesis. After bromination, this central building block was diastereospecifically converted into cytisine in five steps.