The development of a new process to the 6-aryl-5-fluoropicolinate broadleaf herbicide, DAS-534, is reported. The discovery route, developed by Dow AgroSciences, employs an electrophilic fluorination of Aminopyralid using F-TEDA, followed by regioselective Suzuki coupling. Strategies which introduced the 5-fluoro substituent of DAS-534 via the Halex reaction (nucleophilic aromatic substitution of Ar-Cl by fluoride ion) were investigated to reduce manufacturing costs. The Halex reaction of 3,4,5,6-tetrachloropicolinonitrile with CsF was examined in detail to understand the regioselectivity of fluoride substitution. A G3MP2B3 ab initio computational study indicated Halex regioselectivity was under kinetic control. The desired intermediate, 3-chloro-4,5,6-trifluoropicolinonitrile, was kinetically favored over other isomers. The purity of the trifluorinated fraction was further increased by preferential conversion of the undesired isomers to tetra-fluoropicolinonitrile. This tetra-fluoro by-product was recycled to usable chlorofluoropicolinonitrile intermediates using novel reverse-Halex and halopyridine metathesis strategies. These findings will be discussed in this presentation.

Process research for DAS-534:  New routes to 6-arylpicolinate herbicides

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.