Preparation of halogen analogs of picloram
Methods for preparing 5-fluoro-6-(bromo or chloro)picloram analogs, or derivatives thereof, from picloram acid, picloram ester, or the nitrile analog of picloram are provided. The methods include chemical process steps that: (1) introduce a phthaloyl group onto the 4-amino substituent of picloram acid, picloram ester, or the nitrile analog of picloram, (2) add 2 fluorine atoms at the 5,6-positions of the pyridine ring using halex fluorination chemistry, (3) remove the phthaloyl group, hydrolyze the ester or nitrile substituent, and add chlorine or bromine to the 6-position by treatment with an acid and water, and finally, (4) esterify the 5-fluoro-6-(bromo or chloro)picloram acid produced in step (3) to a 5-fluoro-6-(bromo or chloro)picloram ester.
1. A compound of the formula:
wherein Z is COOR or CN, and R is a C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, or H; and each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4.
2. A method for preparing a compound of Formula II, or an HCl or HBr salt thereof:
wherein X is Cl or Br, Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN;
comprising the steps of:
a) combining a compound of Formula III with a phthaloyl halide of Formula IIIa or a phthalic anhydride of Formula IIIb, and, optionally a base,
wherein Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C1-C 3 alkyl substituted with CN, and wherein each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4; and W is Cl or Br;
b) isolating a compound of Formula IV from step a);
wherein Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN, and wherein each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4;
c) combining an isolated compound of Formula IV from step b) with a fluorinating compound or a fluorinating mixture of compounds;
d) isolating a compound of Formula V from step c);
wherein Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN, and wherein each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4;
e) combining an isolated compound of Formula V from step d) with HCl or HBr and water; and
f) isolating a compound of Formula II from step e).
3. The method of claim 2 wherein step a) is preceded by step a′) wherein step a′) comprises preparing a compound of Formula III, wherein Z is COOR and R is C 1 -C 12 alkyl, or C 6 -C 12 arylalkyl, by contacting a compound of Formula III wherein R is H with an alcohol ROH, and an acid or acid forming compound.
4. The method of claim 2 , wherein step a) further comprises a solvent selected from acetonitrile (ACN), toluene, dimethylformamide (DMF), propionitrile, benzonitrile, THF, 2-methyl-THF, dioxane, cyclopentyl methyl ether (CPME), monoethyleneglycol ethers, diethyleneglycol ethers, monopropyleneglycol ethers, dipropyleneglycol ethers, or methyl isobutyl ketone (MIBK), or mixtures thereof.
5. The method of claim 2 , wherein a base in step a) is a trialkylamine compound.
6. The method of claim 2 , wherein the combination of step a) is maintained at a temperature from about 25° C. to about 100° C.
7. The method of claim 2 wherein a fluorinating compound or a fluorinating mixture of compounds in step c) is potassium fluoride, cesium fluoride, tetramethylammonium fluoride, potassium fluoride/tetramethylammonium chloride, cesium fluoride/tetramethylammonium chloride, or mixtures thereof.
8. The method of claim 2 , wherein step c) further comprises an aprotic solvent, preferably an aprotic solvent selected from acetonitrile (ACN), propionitrile (PCN), benzonitrile (BCN), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), sulfolane, dimethylacetamide (DMA), 1,1-dimethyl-2-imidizolidinone (DMI), N,N′-dimethylpropyleneurea (DMPU), N-methylpyrrolidinone (NW), tetrahydrofuran (THF), 2-methyl-THF, dioxane, monoethyleneglycol ethers, diethyleneglycol ethers, monopropyleneglycol ethers, or dipropyleneglycol ethers, or mixtures thereof.
9. The method of claim 2 , wherein the combination of step c) is maintained at a temperature from about 15° C. to about 150° C.
10. The method of claim 2 , wherein the combination of step e) further comprises acetic acid.
11. The method of claim 2 , wherein step b) comprises isolating a compound of Formula IV by filtration or centrifugation, and step d) comprises isolating a compound of Formula V by filtration or centrifugation, and step f) comprises isolating a compound of Formula II by filtration or centrifugation.
12. A method for preparing a compound of Formula II, or an HCl or HBr salt thereof:
wherein X is Cl or Br, Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN;
comprising the steps of:
a) combining a compound of Formula III with a phthaloyl halide of Formula IIIa or a phthalic anhydride of Formula IIIb, and, optionally a base,
wherein Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN, and wherein each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4; and W is Cl or Br;
b) optionally isolating a compound of Formula IV from step a);
wherein Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN, and wherein each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4;
c) combining a compound of Formula IV from the previous step with a fluorinating compound or a fluorinating mixture of compounds;
d) optionally isolating a compound of Formula V from step c);
wherein Z is COOR or CN, and R is H, C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN, and wherein each Y substituent is independently selected from H, F, Cl, Br, I, C 1 -C 4 alkyl, C 1 -C 4 alkoxy, C 1 -C 4 haloalkyl, C 1 -C 4 haloalkoxy, or nitro, wherein n is 1, 2, 3, or 4;
e) combining a compound of Formula V from the previous step with HCl or HBr and water; and
f) isolating a compound of Formula II from step e).
13. The method of claim 12 , further comprising esterifying a compound of Formula II wherein Z═COOH by combining a compound of Formula II wherein Z═COOH, from step f) with an alcohol and an acid, or with an alkylating agent and a base, to provide a compound of Formula VI,
wherein X═Cl or Br, and R 1 is C 1 -C 12 alkyl, C 6 -C 12 arylalkyl, C 3 -C 12 alkynyl, or C 1 -C 3 alkyl substituted with CN.