Abstract
Pyraflufen-ethyl [ethyl 2-chloro-5- (4-chloro-5-difluoromethoxy-l-methylpyrazol-3-yl) -4-fluo-rophenoxyacetate] is a potent Protox inhibiting cereal herbicide. It was discovered by Nihon Nohyaku Co. Ltd. through a series of synthetic research on biologically active compounds, the lead compound of which was synthesized by utilization of ketene dithioacetal chemistry extended by Nihon Nohyaku. Pyraflufen-ethyl controls troublesome broad-leaved weeds including Galium aparine at a rate of 6-12 g a.i./ha in post-emergence application. It was introduced into the mar-ket in 1999, and is now utilized as the active ingredient for a cereal herbicide and for a total vege-tation control herbicide in combination with another active ingredient in Japan and will be launched worldwide in near future.
This paper describes the characteristics of this herbicide and the background of discovery including lead generation and lead optimization, as well as the process chemistry of this unique herbicide. It is noted that the manufacturing process was dramatically improved by the application of the Heck reaction and the Friedel-Crafts reaction to the process chemistry.
