Synthesis and herbicidal activity of the halo analogues of pyoluteorin.

The synthesis of some halo analogues of pyoluteorin [2,3-dichloro-5-(2',6'-dihydroxybenzoyl)-1H-pyrrole] through the use of a Friedel-Crafts aroylation of pyrrole with 2,6-dimethoxybenzoyl chloride, followed by halogenation and demethylation with boron tribromide, is described. Stepwise bromination of the intermediate 2-(2',6'-dimethoxybenzoyl)pyrrole yielded the di-, tri-, and tetrabromo derivatives. Similarly, chlorination gave the dichloro and the trichloro derivatives whereas iodination with even an excess of iodine gave only the monoiodo derivative. (...)