Patent ID: 8716487

Claim:
A process for preparing 4-hydroxypyridines of formula I wherein R 1 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, aryl or hetaryl, where the two last-mentioned radicals are unsubstituted or substituted by 1, 2, 3 or 4 substituents which are selected from the group consisting of halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, C 1 -C 4 -alkoxy, and C 1 -C 4 haloalkoxy; R 2 , R 3 and R 4 independently are hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, NR 5 R 6 or aryl, where the aryl is unsubstituted or substituted by 1, 2, 3 or 4 substituents which are selected from the group consisting of halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, C 1 -C 4 -alkoxy and C 1 -C 4 -haloalkoxy; or the radicals R 3 and R 4 , together with the carbon atoms to which they are bound, form a 3-, 4-, 5-, 6- or 7-membered saturated, partly unsaturated or maximum unsaturated carbocyclic ring or a 3-, 4-, 5-, 6- or 7-membered saturated, partly unsaturated or fully unsaturated heterocyclic ring containing 1, 2, or 3 heteroatoms selected from the group consisting of O, S and N as ring members, where the carbocyclic or heterocyclic ring is unsubstituted or substituted by 1, 2, 3 or 4 substituents selected from the group consisting of halogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkoxy and C 1 -C 4 -haloalkoxy; R 5 is hydrogen, C 1 -C 4 -alkyl or C 1 -C 4 -haloalkyl; R 6 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, phenyl, or phenyl-C 1 -C 4 -alkyl; or R 5 and R 6 together form a linear C 4 - or C 5 -alkylene bridge or a group —CH 2 CH 2 OCH 2 CH 2 —or —CH 2 CH 2 NR 7 CH 2 CH 2 —; and R 7 is hydrogen or C 1 -C 4 -alkyl; the process comprising: a) mixing a compound of formula II wherein R 1 is as defined above; X is halogen or C 1 -C 4 -alkoxy; with a compound of formula IIIa wherein R 2 , R 3 , R 4 are as defined above; Y independently is halogen or C 1 -C 4 -alkoxy; or the two radicals Y in a compound of formula IIIa together form a group —O—(CH 2 ) n —O—, wherein the alkandiyl moiety —(CH 2 ) n —is unsubstituted or substituted with 1, 2 or 3 substitutents selected from the group consisting of halogen and C 1 -C 4 -alkyl; and n is 2, 3 or 4; and at least one base selected from alkali metal methylates and alkali metal ethylates to form a reaction mixture; b) after a first reaction period, the reaction mixture is treated with at least one acid; and c) after a second reaction period, the reaction mixture is treated with at least one ammonia source.