A compound represented by formula (7): ##STR00001## or a salt thereof can be manufactured by the following steps: a step of allowing a compound represented by formula (1-S): ##STR00002## to react with a compound represented by formula (2):
R.sup.2SM.sup.2(2) to give a compound represented by formula (3-S): ##STR00003## a step of allowing the compound represented by formula (3-S) to react with hydrogen peroxide in the presence of a tungsten catalyst and an acid to give a compound represented by formula (6-S) or a salt thereof: ##STR00004##
and a step of reducing the compound represented by formula (6-S) or salt thereof in the presence of a base and a heterogeneous transition metal catalyst to give a compound represented by formula (7) or a salt thereof, wherein X, R.sup.1, R.sup.2, and M.sup.2 are defined in the specification.

A 3-(alkylsulfonyl)pyridine-2-carboxylic acid or a salt thereof can be manufactured by comprising: a step of allowing a compound represented by formula (1-N):

##STR00001## (wherein X represents a halogen atom) to react with a compound represented by formula (2):

R.sup.2SM.sup.2(2) (wherein R.sup.2 represents a C.sub.1-8 straight-chain alkyl group, and M.sup.2 represents a hydrogen atom or an alkali metal) to give a compound represented by formula (3-N):

##STR00002## (wherein R.sup.2 and X are as defined above); a step of allowing the compound represented by formula (3-N) to react with hydrogen peroxide in the presence of a tungsten catalyst and an acid to give a compound represented by formula (6-N):

##STR00003## (wherein R.sup.2 and X are as defined above); a step of reducing the compound represented by formula (6-N) in the presence of a base and a heterogeneous transition metal catalyst to give a compound represented by formula (8-N):

##STR00004## (wherein R.sup.2 is as defined above); and a step of hydrolyzing the compound represented by formula (8-N) in the presence of a base to give a compound represented by formula (7) or a salt thereof:

##STR00005## (wherein R.sup.2 is as defined above).

A compound represented by formula (7) or a salt thereof can be manufactured by the following steps: a step of allowing a compound represented by formula (1-S):

##STR00001## (wherein R.sup.1 represents a C.sub.1-8 straight-chain alkyl group, and X represents a halogen atom) to react with a compound represented by formula (2):

R.sup.2SM.sup.2(2) (wherein R.sup.2 represents a C.sub.1-8 straight-chain alkyl group, and M.sup.2 represents a hydrogen atom or an alkali metal) to give a compound represented by formula (3-S):

##STR00002## (wherein R.sup.1, R.sup.2, and X are as defined above); a step of allowing the compound represented by formula (3-S) to react with hydrogen peroxide in the presence of a tungsten catalyst and an acid to give a compound represented by formula (6-S) or a salt thereof:

##STR00003## (wherein X and R.sup.2 are as defined above); and a step of reducing the compound represented by formula (6-S) or salt thereof in the presence of a base and a heterogeneous transition metal catalyst to give a compound represented by formula (7) or a salt thereof:

##STR00004## (wherein R.sup.2 is as defined above).

A compound represented by formula (7) or a salt thereof can be manufactured by the following steps: a step of allowing a compound represented by formula (1-S):

##STR00001## (wherein R.sup.1 represents a C.sub.1-8 straight-chain alkyl group, and X represents a halogen atom) to react with a compound represented by formula (2):

R.sup.2SM.sup.2(2) (wherein R.sup.2 represents a C.sub.1-8 straight-chain alkyl group, and M.sup.2 represents a hydrogen atom or an alkali metal) to give a compound represented by formula (3-S):

##STR00002## (wherein R.sup.1, R.sup.2, and X are as defined above); a step of allowing the compound represented by formula (3-S) to react with hydrogen peroxide in the presence of a tungsten catalyst and an acid to give a compound represented by formula (6-S) or a salt thereof:

##STR00003## (wherein X and R.sup.2 are as defined above); and a step of reducing the compound represented by formula (6-S) or salt thereof in the presence of a base and a heterogeneous transition metal catalyst to give a compound represented by formula (7) or a salt thereof:

##STR00004## (wherein R.sup.2 is as defined above).

4-Amino-3-chloro-5-fluoro-6-(substituted)picolinates are conveniently prepared from 3,4,5,6-tetrachloropicolinonitrile by a series of steps involving fluorine exchange, amination, reaction with hydrazine, halogenation, hydrolysis and esterification, and transition metal assisted coupling.

4-Amino-3-chloro-5-fluoro-6-(substituted)picolinates are conveniently prepared from 3,4,5,6-tetrachloropicolinonitrile by a series of steps involving fluorine exchange, amination, reaction with hydrazine, halogenation, hydrolysis and esterification, and transition metal assisted coupling.