Pyridine compounds or salts thereof and herbicides containing the same

A pyridine compound represented by formula (Ia):

• wherein R1 represents hydrogen or alkyl which may be substituted;
• R2 represents alkyl which may be substituted, alkenyl which may be substituted, alkynyl which may be substituted, cycloalkyl which may be substituted, alkoxy which may be substituted, alkylthio which may be substituted, mono- or di-alkylamino which may be substituted, phenylamino which may be substituted, or cyclic alkylamino which may be substituted;
• R3 represents alkyl which may be substituted, cycloalkyl which may be substituted, aryl which may be substituted, or heteroaryl which may be substituted;
• R4 represents alkyl, haloalkyl, —OR8, or —SR8;
• R5, R6 and R7 each represents hydrogen, halogen, or alkyl;
• R8 represents alkyl which may be substituted, alkenyl which may be substituted, alkynyl which may be substituted, or cycloalkyl which may be substituted;
• and Xa represents oxygen or sulfur, and wherein R4 is not chlorodifluoromethyl, bromodifluoromethyl, nor iododifluoromethyl, or
• a salt thereof

A process for producing a pyridine compound represented by formula (I):

• wherein R1 represents hydrogen or alkyl which may be substituted;
• R2 represents alkyl which may be substituted, alkenyl which may be substituted, alkynyl which may be substituted, cycloalkyl which may be substituted, cycloalkenyl which may be substituted, alkoxy which may be substituted, alkylthio which may be substituted, mono- or di-alkylamino which may be substituted, phenylamino which may be substituted, cyclic alkylamino which may be substituted, aryl which may be substituted, or a cyclic ether group which may be substituted;
• R3 represents alkyl which may be substituted, cycloalkyl which may be substituted, aryl which may be substituted, or heteroaryl which may be substituted;
• R4 represents hydrogen, alkyl, haloalkyl, halogen, —OR8 or —SR8;
• R5, R6 and R7 each represents hydrogen, halogen, or alkyl;
• R8 represents alkyl which may be substituted, alkenyl which may be substituted, alkynyl which may be substituted, or cycloalkyl which may be substituted;
• and X represents CO, CS, or SO2, and wherein R4 is not chlorodifluoromethyl, bromodifluoromethyl, nor iododifluoromethyl, or a salt thereof,
• which comprises:
• (1) reacting an amine derivative represented by formula (II):
• wherein R1, R3, R4, R5, R6 and R7 have the same meanings as described above,
• with a carboxylic acid derivative represented by formula (III-1):
• R2—COY1 (III-1)
• wherein R2 has the same meaning as described above;
• and Y1 represents OH, chlorine, or R2COO,
• (2) reacting the amine derivative represented by formula (II) described above with a sulfonic acid derivative represented by formula (III-2):
• R2—SO2Y2 (III-2)
• wherein R2 has the same meaning as described above;
• and Y2 represents chlorine or R2SO2O,
• (3) reacting a pyridine compound represented by formula (I-1):
• wherein R1, R2, R3, R4, R5, R6 and R7 have the same meanings as described above,
• with a sulfurizing agent,
• (4) reacting an amine derivative represented by formula (II-1):
• wherein R3, R4, R5, R6 and R7 have the same meanings as described above,
• with a compound represented by the formula:
• R2—X—Y1
• wherein Y1 represents OH, chlorine, or bromine;
• and R2 and X have the same meanings as described above,
• (5) reacting a pyridine compound represented by formula (I-5):
• wherein R2, R3, R4, R5, R6 and R7 have the same meanings as described above,
• with a compound represented by the formula:
• R1a—Y4
• wherein R1a represents alkyl which may be substituted;
• Y4 represents chlorine, bromine, iodine, —OSO2R9, or —OSO3R9;
• and R9 represents C1-C6 alkyl or phenyl which may be substituted with C1-C6 alkyl, or
• (6) reacting a pyridine compound represented by formula (I-6):
• wherein R2, R3, R4, R5, R6 and R7 have the same meanings as described above,
• with a compound represented by the formula:
• R1a—Y4
• wherein R1a and Y4 have the same meanings as described above.