Numerous acid amides derived from aliphatic and aromatic amines have hitherto been synthesized and tested on their herbicidal activity, but they include little or no acid amide derived from isoxazolidine which is a unique heterocyclic amine.
A class of herbicidally active compounds, 2-[4-(4-trifluoromethyl)phenoxy]phenoxypropionic acid and its salts, esters, amides and other derivatives, is disclosed in Japanese patent application unexamined prepublication KOKAI Sho 52-83618, which are represented by the formula: ##STR2## wherein R.sub.1 is a hydrogen atom or a halogen atom; R.sub.2 is a hydroxy, (C.sub.1-4)alkoxy, cyclohexyloxy, phenyloxy, phenylthio, hydrazino, amino, (C.sub.1-4)alkylamino, di(C.sub.1-4)alkylamino, phenylamino optionally substituted by a halogen or trifluoromethyl on the phenyl nucleus or --Okat group where Kat is a cation of an inorganic or organic base. These compounds have an asymmetric carbon atom adjacent to the carbonyl group, so that they have a pair of optical antiposes, i.e. d- and l-isomers. The d-isomer of these compounds is known to have a high herbicidal activity as disclosed in Japanese patent application KOKAI Sho 54-112828.
It is also known as disclosed in Japanese Patent Publication No. 8727/79 that 2-(substituted phenoxy or substituted phenylthio)aliphatic acids and their salts, esters, amides and other derivatives have a herbicidal activity, which are represented by the formula: ##STR3## wherein R which may be the same with each other or different from each other is selected from the group consisting of a halogen atom, alkyl having 1 to 4 carbon atoms, alkoxy and alkylthio both having 1 to 4 carbon atoms; R.sup.1 is selected from the group consisting of a hydrogen atom, a halogen atom and an alkyl having 1 to 4 carbon atoms; X and Y each is an oxygen atom; n is an integer of 1 to 3; R.sup.2 is a halogen atom, an alkyl having 1 to 10 carbon atoms or an alkoxyalkyl containing 2 to 6 carbon atoms; R.sub.3 is a hydrogen atom; and R.sup.4 is a hydroxy, alkoxy having 1 to 10 carbon atoms, trichloroethyloxy, alkylthio having 1 to 6 carbon atoms, alkenyloxy having 2 to 4 carbon atoms, cyclohexyloxy, methylcyclohexyloxy, phenoxy substituted by one or two halogen atoms, phenylthio optionally substituted by one or two halogen atoms, alkylamino having 1 to 4 carbon atoms, dialkylamino having 1 to 4 carbon atoms in each alkyl group, di-substituted amino having the formula: ##STR4## phenylamino substituted by a halogen, --CF.sub.3, --OCF.sub.2 CF.sub.2 H or --COOCH.sub.3 or --O--Kat group where Kat is a cation of an inorganic or organic base. These compounds have an asymmetric carbon atom adjacent to the carbonyl group, so that they have a pair of optial antiposes, i.e. d- and l-isomers. The d-isomer of these compounds is known to have a high herbicidal activity as described in Japanese patent application KOKAI Sho 54-112828.
Japanese patent application KOKAI Sho 52-125626 discloses another class of herbicidally active compounds, 2-[4-(3,5-dichloro-2-pyridyloxy)phenoxy]propionic acid amide derivatives which are represented by the formula: ##STR5## wherein R.sup.1 is a hydroxyalkyl, lower alkoxy, lower alkenyloxy, acyl, amino, aralkyl, chloro-substituted aralkyl, --R.sup.3 COOR.sup.4 where R.sup.3 is a lower alkylene and R.sup.4 is a hydrogen, lower alkyl or salt-forming atom or group, or ##STR6## where R.sup.5 and R.sup.6 each are a hydrogen, lower alkyl or lower alkoxy; and R.sup.2 is a hydrogen, lower alkyl, lower alkoxy, hydroxyalkyl, phenyl or chloro-substituted phenyl; or ##STR7## may form a cyclic group ##STR8## where X is a methylene group or oxygen atom. These compounds have an asymmetric carbon atom adjacent to the carbonyl group, so that they have a pair of optical antipodes, i.e. d- and l-isomers. The d-isomer of these compounds has a high herbicidal activity as described in Japanese patent application KOKAI Sho 54-112828.
Japanese patent application KOKAI Sho 54-122728 discloses a different class of herbicidally active compounds, 4-(5-fluoromethyl-2-pyridyloxy)phenoxyalkane carboxylic acids and their derivatives of the formula: ##STR9## wherein X is a chlorine or fluorine atom; Y is a hydrogen or chlorine atom; R is a hydrogen atom, methyl or ethyl; n is 0 or 2; and Z' is a hydroxyl, lower alkoxy optionally substituted by a halogen atom, lower alkoxyalkoxy, lower alkenyloxy, lower alkynyloxy, cycloalkoxy optionally substituted by a lower alkyl, lower alkoxycarbonylalkoxy, phenoxy optionally substituted by a halogen atom or by lower alkyl, benzyloxy, glycidyloxy, lower alkylthio, lower alkenylthio, phenylthio optionally substituted by a halogen atom or by lower alkyl, amino, lower alkylamino, lower alkoxycarbonylmethylamino, hydroxycarbonylmethylamino, anilino optionally substituted by a halogen atom, 2-pyridylamino, --O--cation or halogen atom.
We have had a great interest in investigating the usability as herbicide of isoxazolidine derivatives and synthesized and tested a variety of isoxazolidine derivatives on their herbicidal activity. As a result, we have now found that new 2-(substituted-phenoxy)propionic acid derivatives having general formula (I) undermentioned exhibit a high herbicidal activity. ##STR10## and R.sub.2 is a hydrogen atom or a lower alkyl group.