The first total synthesis of toddaquinoline, an alkaloid from Toddalia asiatica

The paper describes the first total synthesis of toddaquinoline, an alkaloid from the root bark of Formosan Toddalia asiatica. The key step is cobalt(I) mediated radial cyclisation to a pyridine. Cobalt appears to play a dual role in the reaction, firstly initialising homolysis of the carbon to halogen bond then acting as a Lewis acid to promote cyclisation to C-6. Other approaches examined are also outlined. These include a photocyclisation of an azastilbene; a cyclisation induced by halogen to metal exchange and a tin mediated radical cyclisation.