New Approach for the Construction of the Coumarin Frame and Application in the Total Synthesis of Natural Products.

A new synthesis of naturally occurring coumarins, e.g. scopoletin (IV), herniarin (VII) or citroptene (Xa), is described, involving the formation of enaminones, e.g. (III), from the corresponding acetates and Brederecks reagent followed by ZnCl2-mediated cyclization.