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

The paper describes the first total synthesis of toddaquinoline, an alkaloi d 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 halo gen bond then acting as a Lewis acid to promote cyclisation to C-6. Other a pproaches examined are also outlined. These include a photocyclisation of a n azastilbene; a cyclisation induced by halogen to metal exchange and a tin mediated radical cyclisation. (C) 2001 Elsevier Science Ltd. All rights re served.