SYNTHESIS AND HERBICIDAL ACTIVITY OF THE HALO ANALOGS 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. A comparison of the herbicidal activity using a cress seedling assay indicated that some of the halo analogues were 2-40 times as active as the parent compound, pyoluterin, with the tribromo analogue being the most active. This activity range appears to be comparable to that seen with some of the commercially used herbicides tested in this assay. © 1990, American Chemical Society. All rights reserved.