(3)-Amino-pyrazolo-pyrimidine derivs. - for use as herbicides

摘要

New pyrazolopyrimidine derivs. are of formula (I): In (1) R1 is H or opt. substd. alkyl, cycloalkyl, phenyl or heterocyclyl. R2 is H, halogen, OH, alkyl, haloalkyl, hydroxyalkyl, alkenyl, alkynyl, cycloalkyl, aryl, aralkyl, heterocyclyl or S(O)nR5; n = 0-2 and R5 is alkyl, aryl or aralkyl, or n=O and R5=H. R3 and R4 are H, alkyl, aryl, aralkyl, acyl, alkylsulphonyl, alkoxycarbonyl, carbamoyl or alkylcarbamoyl, or NR3R4 is a heterocyclic group or an N=CR8R9 group; R8 and R9 are H or opt. substd. alkyl, phenyl or heterocyclyl, or CR8R9 is cycloalkyl. A is CONR6 or C(OR7)=N, with the C atom bonded to the pyrazole ring; R6 is H, opt. substd. alkyl, alkenyl, alkynyl or cycloalkyl, NH2 or mono- or dialkylamino; R7 is H or opt. substd. alkyl. (I) and their salts are esp. useful for selective pre-emergence weed control in cereal, sugar beet, pea, bean, carrot, soya, maize, rice or potato crops. They are pref. used in combination with benzofuran, urea or triazine herbicides. A typical cpd. is 2-methyl-3-amino-6-t-butyl-2,5-dihydro-pyrazolo 3,4-d pyrimidin-4-one. In an example, this is prepd. starting from methylhydrazine and the K salt of tricyanomethane.