Method for the preparation of pyridine-2,3-dicarboxylic acids

Claim 1

A method for the preparation of unsubstituted and substituted pyridine-2,3-dicarboxylic acids of formula I wherein R₁, R₂ and R₃ are each hydrogen, C₁-C₆ alkyl, hydroxy-­C₁-C₆ alkyl, C₁-C₆ alkoxy, phenoxy, C₁-C₄ halo­alkyl, nitro, hydroxy, amino, C₁-C₄ alkylamino, diloweralkylamino or C₁-C₄ alkylamino, dilower­alkylamino or C₁-C₄ alkylsulfonyl group, carboxy, acyl, amido; or phenyl optionally substituted with one C₁-C₄ alkyl, C₁-C₄ alkoxy or halogen; difluoro­methoxy, trifluoromethoxy, 1,1,2,2-tetrafluoro­ethoxy, C₃-C₈ straight or branched alkenyloxy optionally substituted with one to three halogens, or C₃-C₈ straight or branched alkynyloxy optionally substituted with one to three halogens; and when taken together, R₂ and R₃ may form a ring which may optionally be substituted, in which YZ are represented by -(CH₂)₂-Q- or -(CH)₂-Q-, wherein Q is oxygen, sulfur, or nitrogen, with the proviso that R₁ is hydrogen; comprising oxidizing a substituted quinoline of formula II wherein R₁, R₂ and R₃ are as described for formula I above; X₁, X₂, X₃, X₄ are each hydroxy, hydrogen, SO₃H, SO₂Cl, SH Cl, F, Br, I, CO₂H, NO₂, NH₂; or NHR, NR₂, CONR₂ or COR wherein R is C₁-C₄ alkyl; with the proviso that one of X₁, X₂, X₃ or X₄ is other than hydrogen; or the N-oxide thereof; or an acid addition salt therof; in aqueous base with hydrogen peroxide.

Claim 2

A method for the preparation of unsubstituted and substituted pyridine-2,3-dicarboxylic acids of formula I wherein R₁, R₂ and R₃ are each hydrogen, C₁-C₆ alkyl, hydroxy-­C₁-C₆ alkyl, C₁-C₆ alkoxy, phenoxy, C₁-C₄ halo­alkyl, nitro, hydroxy, amino, C₁-C₄ alkylamino, diloweralkylamino or C₁-C₄ alkylamino, dilower­alkylamino or C₁-C₄ alkylsulfonyl group, carboxy, acyl, amido; or phenyl optionally substituted with one C₁-C₄ alkyl, C₁-C₄ alkoxy or halogen; difluoro­methoxy, trifluoromethoxy, 1,1,2,2-tetrafluoro­ethoxy, C₃-C₈ straight or branched alkenyloxy optionally substituted with one to three halogens, or C₃-C₈ straight or branched alkynyloxy optionally substituted with one to three halogens; and when taken together, R₂ and R₃ may form a ring which may optionally be substituted, in which YZ are represented by -(CH₂)₂-Q- or -(CH)₂-Q-, wherein Q is oxygen, sulfur, or nitrogen, with the proviso that R₁ is hydrogen; comprising oxidizing a substituted quinoline of formula II wherein R₁, R₂ and R₃ are as described for formula I above; X₁, X₂, X₃, X₄ are each hydroxy, hydrogen, SO₃H, SO₂Cl, SH Cl, F, Br, I, CO₂H, NO₂, NH₂; or NHR, NR₂, CONR₂ or COR wherein R is C₁-C₄ alkyl; with the proviso that one of X₁, X₂, X₃ or X₄ is other than hydrogen; or the N-oxide thereof; or an acid addition salt therof; in aqueous base with hydrogen peroxide.