U.S. patent application number 15/243996 was filed with the patent office on 2016-12-08 for process for the preparation of 4-amino-5-fluoro-3-chloro-6-(substituted)picolinates.
This patent application is currently assigned to Dow AgroSciences LLC. The applicant listed for this patent is Dow AgroSciences LLC. Invention is credited to Natalie C. Giampietro, James M. Renga.
Application Number | 20160355468 15/243996 |
Document ID | / |
Family ID | 50931648 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160355468 |
Kind Code |
A1 |
Giampietro; Natalie C. ; et
al. |
December 8, 2016 |
PROCESS FOR THE PREPARATION OF
4-AMINO-5-FLUORO-3-CHLORO-6-(SUBSTITUTED)PICOLINATES
Abstract
4-Amino-5-fluoro-3-chloro-6-(substituted)picolinates are
prepared from trifluoroacetic acid, p-methoxyaniline, a
C.sub.1-C.sub.4 alkyl propiolate and a substituted methylene amine
by a series of steps.
Inventors: |
Giampietro; Natalie C.;
(Carmel, IN) ; Renga; James M.; (Spokane,
WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow AgroSciences LLC |
Indianapolis |
IN |
US |
|
|
Assignee: |
Dow AgroSciences LLC
Indianapolis
IN
|
Family ID: |
50931648 |
Appl. No.: |
15/243996 |
Filed: |
August 23, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15040577 |
Feb 10, 2016 |
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15243996 |
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14104127 |
Dec 12, 2013 |
9260392 |
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15040577 |
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61736841 |
Dec 13, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C07D 213/79 20130101;
C07D 213/803 20130101; C07C 251/12 20130101 |
International
Class: |
C07C 251/12 20060101
C07C251/12 |
Claims
1. A compound of Formula C ##STR00025## wherein R.sup.2 represents
C.sub.1-C.sub.4 alkyl.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. patent Ser. No.
15/040,577, filed on Feb. 10, 2016, U.S. Pat. No. 14/104,127, filed
on Dec. 12, 2013, and claims the benefit of U.S. Provisional Patent
Application Ser. No. 61/736,841 filed Dec. 13, 2012, the disclosure
of which is expressly incorporated herein by reference.
FIELD
[0002] Provided herein are processes for the preparation of
4-amino-5-fluoro-3-chloro-6-(substituted)picolinates. More
particularly, provided herein are processes for the preparation of
4-amino-5-fluoro-3-chloro-6-(substituted)picolinates from a
non-pyridine source.
BACKGROUND
[0003] U.S. Pat. Nos. 6,784,137 B2 and 7,314,849 B2 describe inter
alia certain 4-amino-5-fluoro-3-chloro-6-(aryl)picolinate compounds
and their use as herbicides. U.S. Pat. No. 7,432,227 B2 describes
inter alia certain 4-amino-5-fluoro-3-chloro-6-(alkyl)picolinate
compounds and their use as herbicides. Each of these patents
describes the manufacture of 4-amino-5-fluoro-3-chloropicolinate
starting materials by fluorination of the corresponding
5-unsubstituted pyridines with
1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane
bis(tetrafluoroborate). Each of these patents also describes the
manufacture of 6-(aryl)-4-aminopicolinates from coupling reactions
involving picolines having either a facile leaving group or a metal
derivative in the 6-position of the picoline ring. It would be
advantageous to produce
4-amino-5-fluoro-3-chloro-6-(substituted)picolinates without having
to rely on metal assisted couplings. It would be advantageous to
produce 4-amino-5-fluoro-3-chloro-6-(substituted)picolinates
efficiently and in high yield from a non-pyridine source. It would
also be advantageous to produce
4-amino-5-fluoro-3-chloro-6-(substituted)picolinates without having
to rely on direct fluorination of the 5-position of the pyridine
ring with an expensive fluorinating agent like
1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane
bis(tetrafluoroborate).
SUMMARY
[0004] Provided herein are processes for the preparation of
4-amino-5-fluoro-3-chloro-6-(substituted)picolinates from a
non-pyridine source without a metal assisted coupling and without
fluorination with an expensive fluorinating agent like
1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane
bis(tetrafluoroborate). More particularly, provided herein are
processes for the preparation of a
4-amino-5-fluoro-3-chloro-6-(substituted)picolinate of the Formula
I
##STR00001## [0005] wherein [0006] R.sup.1 represents
C.sub.1-C.sub.4 alkyl, cyclopropyl, C.sub.2-C.sub.4 alkenyl or
phenyl substituted with from 1 to 4 substituents independently
selected from halogen, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4
haloalkyl, C.sub.1-C.sub.4 alkoxy or C.sub.1-C.sub.4 haloalkoxy,
and [0007] R.sup.2 represents C.sub.1-C.sub.4 alkyl, which
comprises the following steps:
[0008] a) contacting trifluoroacetic acid with p-methoxyaniline in
the presence of a triarylphosphine and a trialkylamine base in
carbon tetrachloride solvent to produce an acetimidoyl chloride of
Formula A
##STR00002##
[0009] b) contacting the acetimidoyl chloride of Formula A with a
C.sub.1-C.sub.4 alkyl propiolate (Formula B)
##STR00003## [0010] wherein R.sup.2 is as previously defined, in
the presence of copper (I) iodide, an alkali metal iodide and an
alkali metal phosphate in a polar aprotic solvent to produce an
(imino)pent-2-ynoate of Formula C
##STR00004##
[0011] c) cyclizing the (imino)pent-2-ynoate of Formula C with an
amine of Formula D
##STR00005## [0012] wherein R.sup.1 is as previously defined, in
the presence of an inorganic alkali metal base in a polar aprotic
solvent at temperature from about ambient to about 100.degree. C.
to produce an alkyl 4-amino-5-fluoro-6-(substituted)-picolinate of
Formula E
[0012] ##STR00006## [0013] wherein R.sup.1 and R.sup.2 are as
previously defined; and
[0014] d) halogenating and deprotecting the alkyl
4-amino-5-fluoro-6-(substituted)picolinate of Formula E with
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione (Formula F)
##STR00007##
in the presence of a mineral acid in a polar solvent to produce the
4-amino-5-fluoro-3-chloro-6-(substituted)picolinate of the Formula
I.
[0015] Provided herein are also processes for the preparation of a
4-amino-5-fluoro-3-chloro-6-(substituted)picolinate of the Formula
I
##STR00008## [0016] wherein [0017] R.sup.1 represents
C.sub.1-C.sub.4 alkyl, cyclopropyl, C.sub.2-C.sub.4 alkenyl or
phenyl substituted with from 1 to 4 substituents independently
selected from halogen, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4
haloalkyl, C.sub.1-C.sub.4 alkoxy or C.sub.1-C.sub.4 haloalkoxy,
and [0018] R.sup.2 represents C.sub.1-C.sub.4 alkyl, which
comprises halogenating and deprotecting an alkyl
4-amino-5-fluoro-6-(substituted)-picolinate of Formula E
[0018] ##STR00009## [0019] wherein R.sup.1 and R.sup.2 are as
previously defined, with
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione (Formula F)
##STR00010##
[0019] in the presence of a mineral acid in a polar solvent to
produce the 4-amino-5-fluoro-3-chloro-6-(substituted)picolinate of
the Formula I.
[0020] Another embodiment is a compound of Formula E
##STR00011##
[0021] wherein [0022] R.sup.1 represents C.sub.1-C.sub.4 alkyl,
cyclopropyl, C.sub.2-C.sub.4 alkenyl or phenyl substituted with
from 1 to 4 substituents independently selected from halogen,
C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 haloalkyl, C.sub.1-C.sub.4
alkoxy or C.sub.1-C.sub.4 haloalkoxy, and [0023] R.sup.2 represents
C.sub.1-C.sub.4 alkyl.
[0024] Another embodiment is a compound of Formula C
##STR00012##
[0025] wherein [0026] R.sup.2 represents C.sub.1-C.sub.4 alkyl.
[0027] Another embodiment is a compound of Formula G
##STR00013##
[0028] wherein [0029] R.sup.1 represents C.sub.1-C.sub.4 alkyl,
cyclopropyl, C.sub.2-C.sub.4 alkenyl or phenyl substituted with
from 1 to 4 substituents independently selected from halogen,
C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 haloalkyl, C.sub.1-C.sub.4
alkoxy or C.sub.1-C.sub.4 haloalkoxy, and [0030] R.sup.2 represents
C.sub.1-C.sub.4 alkyl.
DETAILED DESCRIPTION
[0031] The term alkyl and derivative terms such as alkoxy, as used
herein refer to straight chain or branched chain groups. Typical
alkyl groups are methyl, ethyl, propyl, 1-methyl-ethyl, butyl,
1,1-dimethylethyl and 1-methylpropyl. Methyl and ethyl are often
preferred.
[0032] Unless specifically limited otherwise, the term "halogen,"
as well as derivative terms such as "halo," refers to fluorine,
chlorine, bromine and iodine.
[0033] The phenyl groups substituted with from 1 to 4 substituents
independently selected from halogen, C.sub.1-C.sub.4 alkyl,
C.sub.1-C.sub.4 haloalkyl, C.sub.1-C.sub.4 alkoxy or
C.sub.1-C.sub.4 haloalkoxy may be of any orientation, but
4-substituted phenyl, 2,4-disubstituted phenyl,
2,3,4-trisubstituted phenyl, 2,4,5-trisubstituted phenyl, and
2,3,4,6-tetrasubstituted phenyl isomers are preferred.
[0034] Alkyl 4-amino-5-fluoro-3-chloro-6-(substituted)picolinates
are prepared from trifluoroacetic acid, p-methoxyaniline, a
C.sub.1-C.sub.4 alkyl propiolate and a substituted methylene amine
by a series of steps.
##STR00014## ##STR00015##
[0035] In the initial step, trifluoroacetic acid is reacted with
p-methoxyaniline and carbon tetrachloride in the presence of a
triarylphosphine and a trialkylamine base to produce
2,2,2-trifluoro-N-(4-methoxyphenyl)acetimidoyl chloride. While one
equivalent of p-methoxyaniline is required for each equivalent of
trifluoroacetic acid, it is often convenient to use an excess of
the aniline, typically a 10 to 20% excess. A similar excess of
trialkylamine base is also preferred. It is often convenient to use
a much larger excess of triarylphosphine, typically in the range of
a 2 to 4 fold excess. Carbon tetrachloride, while serving as a
reactant, is also conveniently used as a solvent for the initial
reaction. The reaction is exothermic and it is convenient to
control the exotherm by external cooling and the controlled
addition of a carbon tetrachloride solution of p-methoxyaniline to
a mixture of trifluoroacetic acid, trialkylamine and
triarylphosphine in carbon tetrachloride. After the initial
exotherm subsides, the reaction mixture is generally heated to
reflux until the conversion is complete.
[0036] In a typical reaction, a mixture of about 3 equivalents of
triphenylphosphine and trifluoroacetic acid in carbon tetrachloride
is cooled to about 0.degree. C. in an ice bath and a 20% excess of
triethylamine is added. With continued cooling, about a 20% excess
of p-methoxyaniline in carbon tetrachloride is slowly added. After
completion of the addition, the mixture is heated to about
70.degree. C. for several hours. After cooling, the reaction
mixture is extracted with hexane and the solvent is evaporated to
provide crude 2,2,2-trifluoro-N-(4-methoxyphenyl)acetimidoyl
chloride.
[0037] In the second step, the
2,2,2-trifluoro-N-(4-methoxyphenyl)acetimidoyl chloride is coupled
with a C.sub.1-C.sub.4 alkyl propiolate in the presence of copper
(I) iodide, an alkali metal iodide and an alkali metal phosphate in
a polar aprotic solvent to produce a C.sub.1-C.sub.4 alkyl
5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate. While one
equivalent of C.sub.1-C.sub.4 alkyl propiolate is required for each
equivalent of acetimidoyl chloride, it is often convenient to use
an excess of the propiolate, typically a 10 to 20% excess.
Similarly, a 10 to 20% molar excess of alkali metal iodide and
alkali metal phosphate are generally preferred. While the reaction
is catalytic in copper (I) iodide, usually about 0.1 to about 0.3
equivalents are employed. The coupling reaction is conducted in a
polar aprotic solvent at a temperature from about 40.degree. C. to
about 100.degree. C. Preferred polar aprotic solvents include
ethers like tetrahydrofuran, esters like ethyl acetate, nitriles
like acetonitrile, amides like N,N-dimethylformamide and N-methyl
pyrrolidinone and sulfoxides like dimethyl sulfoxide. Anhydrous
solvents are preferred with anhydrous acetonitrile being especially
preferred.
[0038] In a typical reaction,
2,2,2-trifluoro-N-(4-methoxyphenyl)acetimidoyl chloride and a
slight excess of methyl propiolate are mixed with about 0.3
equivalents of copper (I) iodide and slight excesses of potassium
phosphate and potassium iodide in anhydrous acetonitrile. The
mixture is heated at about 60.degree. C. under a nitrogen
atmosphere until the reaction is complete. After cooling, an
extraction solvent like a halogenated hydrocarbon is added to the
mixture along with water. The organic layer is recovered, washed
with brine and dried. The solvent is evaporated to provide crude
methyl 5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate.
[0039] In the cyclization reaction, the
5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate is reacted
with a methylene amine substituted with an alkyl, cyclopropyl,
alkenyl or (substituted)phenyl group in the presence of an
inorganic alkali metal base in a polar aprotic solvent to produce
an alkyl
4-(4-methoxyphenylamino)-5-fluoro-6-(substituted)picolinate. While
one equivalent of substituted methylene amine is required for each
equivalent of
5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate, it is
often convenient to use an excess of the methylene amine, typically
a 2 to 4 fold excess. Suitable inorganic alkali metal bases include
the lithium, sodium, potassium and cesium salts of hydroxides,
carbonates and phosphates. Cesium carbonate is particularly
preferred. In general, it is convenient to use a 2 to 4 fold excess
of the inorganic alkali metal base. Preferred polar aprotic
solvents include ethers like tetrahydrofuran, esters like ethyl
acetate, nitriles like acetonitrile, amides like
N,N-dimethylformamide and N-methylpyrrolidinone and sulfoxides like
dimethyl sulfoxide. Anhydrous solvents are preferred with anhydrous
tetrahydrofuran and dimethyl sulfoxide being especially preferred.
The reaction is typically conducted at a temperature from about
ambient to about 100.degree. C.
[0040] In a typical reaction, methyl
5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate is mixed
with about a 2.5 to 3 fold excess of 4-chlorobenzyl amine and about
a 2.5 to 3 fold excess of cesium carbonate in anhydrous
terahydrofuran. The mixture is heated at about 80.degree. C. until
the reaction is complete. After cooling, an extraction solvent like
a halogenated hydrocarbon is added to the mixture along with water.
The organic layer is recovered, washed with brine and dried. The
solvent is evaporated to provide crude methyl
4-(4-methoxyphenylamino)-5-fluoro-6-(4-chlorophenyl)picolinate.
[0041] The final step involves both the chlorination and the
deprotection of the amino group by removal of the 4-methoxyphenyl
substituent. An alkyl
4-(4-methoxyphenylamino)-5-fluoro-6-(substituted)picolinate is
reacted with 1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione in
the presence of a mineral acid in a polar solvent at a temperature
from about ambient to about 100.degree. C. to produce an alkyl
4-amino-5-fluoro-3-chloro-6-(substituted)picolinate. While one
equivalent of 1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione is
required for each equivalent of alkyl
4-(4-methoxyphenylamino)-5-fluoro-6-(4-chlorophenyl)picolinate, it
is often convenient to use an excess of the
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione, typically a 2 to
4 fold excess. Suitable mineral acids include sulfuric and
phosphoric acids with sulfuric acid being preferred. The mineral
acids are usually used as aqueous solutions. Approximately one
equivalent of mineral acid is required but a 10 to 30% excess is
preferred. The chlorination/deprotection is conveniently performed
in a mixture of a polar solvent such as acetonitrile with
water.
[0042] If the chlorination/deprotection reaction is performed in
the absence of the mineral acid, an alkyl
4-((4-oxocyclohexa-2,5-dien-1-ylidene)amino)-5-fluoro-6-(substituted)-pic-
olinate (Formula G) is obtained without chlorination of the
3-position on the pyridine ring.
##STR00016##
The alkyl 4-((4-oxocyclohexa-2,5-dien-1
-ylidene)amino)-5-fluoro-6-(substituted)picolinate can be
subsequently reacted with a mineral acid to deprotect the amino
group and provide an alkyl
4-amino-5-fluoro-6-(substituted)picolinate (Formula H).
##STR00017##
[0043] In a typical reaction accomplishing both chlorination and
deprotection, methyl
4-(4-methoxyphenylamino)-5-fluoro-6-(4-chlorophenyl)picolinate is
reacted with about two equivalents of
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione in the presence of
a 1 M (molar) solution of sulfuric acid in a mixture of
acetonitrile/water. The mixture is heated at reflux until the
reaction is complete. The mixture is added to methylene chloride
and the organic layer is separated, washed with brine and dried.
The solvent is evaporated to provide crude methyl
4-amino-5-fluoro-3-chloro-6-(4-chlorophenyl)picolinate.
[0044] The products obtained by any of these processes, can be
recovered by conventional means, such as evaporation or extraction,
and can be purified by standard procedures, such as by
distillation, crystallization or chromatography.
[0045] The described embodiments and following examples are for
illustrative purposes and are not intended to limit the scope of
the claims. Other modifications, uses, or combinations with respect
to the compositions described herein will be apparent to a person
of ordinary skill in the art without departing from the spirit and
scope of the claimed subject matter.
EXAMPLES
Example 1
2,2,2-Trifluoro-N-(4-methoxyphenyl)acetimidoyl chloride
##STR00018##
[0047] A mixture of triphenylphosphine (34.6 grams (g), 132.0
millimoles (mmol)), 2,2,2-trifluoroacetic acid (3.37 milliliters
(mL), 44 mmol), triethylamine (7.38 mL, 53.0 mmol) and carbon
tetrachloride (21.3 mL, 220.0 mmol) was magnetically stirred while
cooled with an ice bath. After 10 minutes (min), p-methoxyaniline
(6.53 g, 53.0 mmol) dissolved in carbon tetrachloride (21 mL, 220.0
mmol) was added slowly (exothermic). The ice bath was removed, and
the reaction mixture was stirred at reflux for 4 hours (h). Upon
cooling to room temperature, the reaction mixture was washed with
hexane (3.times.100 mL). Solvent was removed using a rotary
evaporator to give 9.8 g of an orange oil. Distillation gave
2,2,2-trifluoro-N-(4-methoxyphenyl)acetimidoyl chloride (9.31 g,
39.2 mmol, 89% yield) as a light yellow liquid: by 75-77.degree.
C./0.3 mmHg; .sup.1H NMR (400 MHz, CDCl.sub.3) .delta. 7.31 (m,
2H), 6.96 (m, 2H), 3.84 (s, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3)
.delta. 159.56 (s), 135.45 (s), 127.98 (q), 124.35 (s), 117.05 (q),
114.25 (s), 55.50 (s).
Example 2
Methyl 5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate
##STR00019##
[0049] To a magnetically stirred solution of
2,2,2-trifluoro-N-(4-methoxyphenyl)-acetimidoyl chloride (2.376 g,
10.00 mmol) and methyl propiolate (1.009 g, 12.00 mmol) in
anhydrous acetonitrile (CH.sub.3CN; 20 mL) was added a ground-up
mixture of copper(I) iodide (0.571 g, 3.00 mmol), potassium
phosphate (2.55 g, 12.00 mmol) and potassium iodide (1.660 g, 10.00
mmol). After heating for 4 h at 60.degree. C. under nitrogen, the
reaction mixture was added to dichloromethane (CH.sub.2Cl.sub.2;
100 mL) and water (H.sub.2O; 50 mL). The organic layer was washed
with a saturated solution of sodium chloride (NaCl) and dried
(magnesium sulfate (MgSO.sub.4)), and the solvent was removed
leaving 3.4 g of a dark brown oil. The material was passed through
a plug of silica gel eluting with 5% ethyl acetate (EtOAc)/hexane
to give methyl
5,5,5-trifluoro-4-((4-methoxyphenyl)imino)pent-2-ynoate (2.11 g,
7.40 mmol, 74.0% yield) as an orange oil: .sup.1H NMR (400 MHz,
CDCl.sub.3) .delta. 7.54 (m, 2H), 6.97 (m, 2H), 3.86 (s, 3H), 3.85
(s, 3H); .sup.13C NMR (101 MHz, CDCl.sub.3) .delta. 161.11 (s),
152.43 (s), 138.87 (s), 131.88 (q), 125.46 (s), 118.70 (q), 114.33
(s), 86.82 (s), 73.95 (s), 55.59 (s), 53.50 (s); HRMS-ESI (m/z)
[M+H].sup.+ calcd for C.sub.17H.sub.11ClF.sub.3NO, 285.0613; found
285.0611.
Example 3
Methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-methoxyphenyl)amino)picolinate
##STR00020##
[0051] A magnetically stirred solution of methyl
5,5,5-trifluoro-4-(4-methoxyphenyl-imino)pent-2-ynoate (0.570 g,
2.0 mmol), p-chlorobenzylamine (0.850 g, 6.00 mmol) and cesium
carbonate (1.629 g, 5.00 mmol) in anhydrous terahydrofuran (THF; 10
mL) was heated to 80.degree. C. in a Discover CEM microwave for 4
h. Upon cobbling to room temperature, the reaction mixture was
added to CH.sub.2Cl.sub.2 (50 mL) and H.sub.2O (50 mL). The organic
layer was washed with a saturated solution of NaCl and dried
(MgSO.sub.4), and the solvent was removed leaving 1.3 g of a dark
orange/brown oil. Preparative thin layer chromatography (TLC) on
silica eluting with 20% EtOAc/hexane gave methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-methoxyphenyeamino)picolinate
(0.31 g, 0.801 mmol, 40.1% yield) as an orange/yellow solid.
Trituration with ether gave a white solid (0.145 g): mp
162-164.degree. C.; .sup.1H NMR (400 MHz, CDCl.sub.3) .delta. 7.91
(dd, J=8.5, 1.5 Hz, 2H), 7.61 (d, J=6.0 Hz, 1H), 7.52-7.39 (m, 2H),
7.25-7.13 (m, 2H), 7.07-6.91 (m, 2H), 6.30 (d, J=3.6 Hz, 1H), 3.92
(s, 3H), 3.85 (s, 3H); .sup.19F NMR (376 MHz, CDCl.sub.3) .delta.
-133.26; HRMS-ESI (m/z) [M+H].sup.+ calcd for
C.sub.20H.sub.16ClFN.sub.2O.sub.3, 386.0833; found 386.0834.
Example 4
Methyl 4-amino-3-chloro-6-(4-chlorophenyl)-5-fluoropicolinate
##STR00021##
[0053] To a mixture of methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-methoxyphenyl)amino)-picolinate
(0.146 g, 0.377 mmol) and
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione (0.149 g, 0.755
mmol) in 1:1 CH.sub.3CN/H.sub.2O (5 mL) was added 1 M sulfuric acid
(H.sub.2SO.sub.4, 0.4 mL). After heating to reflux for 1 h,
analysis by liquid chromatography/mass spectrometry (LC/MS) showed
that the reaction was complete. The reaction mixture was added to
CH.sub.2Cl.sub.2 (20 mL). The organic layer was washed with a
saturated solution of NaCl and dried (MgSO.sub.4), and the solvent
was removed leaving 0.242 g of an orange oil. Preparative TLC on
silica gel eluting with 20% EtOAc/hexane gave methyl
4-amino-3-chloro-6-(4-chlorophenyl)-5-fluoropicolinate (47 mg,
0.142 mmol, 38% yield) as a yellow oil: .sup.1H NMR (400 MHz,
CDCl.sub.3) .delta. 7.87 (m, 2H), 7.43 (m, 2H), 4.94 (br s, 2H),
3.99 (s, 3H); .sup.19F NMR (376 MHz, CDCl.sub.3) .delta. -140.86;
ESIMS m/z 315.607 ([M]).
Example 5
Methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-oxocyclohexa-2,5-dien-1-ylidene)a-
mino)-picolinate
##STR00022##
[0055] A mixture of methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-methoxyphenyl)amino)-picolinate
(0.155 g, 0.400 mmol) and
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione (0.158 g, 0.800
mmol) in 1:1 CH.sub.3CN/H.sub.2O (5 mL) was stirred at room
temperature. After 30 min the suspension of the solid ester
dissolved giving a yellow/orange solution, then an orange solid
began to form. After stirring at room temperature for 2 h, the
reaction solution was decanted, and the orange solid was washed
with 1:1 CH.sub.3CN/H.sub.2O (10 mL). The solid was dissolved in
CH.sub.2Cl.sub.2 and dried (MgSO4), and the solvent was removed to
give methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-oxocyclohexa-2,5-dien-1-ylidene)amino)p-
icolinate (0.13 g, 0.316 mmol, 79% yield) as an orange solid: mp
154-156.degree. C.; .sup.1H NMR (400 MHz, CDCl.sub.3) .delta. 7.97
(d, J=7.3 Hz, 2H), 7.65 (d, J=5.4 Hz, 1H), 7.48 (d, J=8.6 Hz, 2H),
7.36 (dd, J=10.1, 2.6 Hz, 1H), 6.87 (d, J=10.3 Hz, 1H), 6.77 (dd,
J=10.1, 2.1 Hz, 1H), 6.61 (dd, J=10.2, 2.1 Hz, 1H), 4.02 (s, 3H);
.sup.19F NMR (376 MHz, CDCl.sub.3) .delta. -145.68.
Example 6
Methyl 4-amino-6-(4-chlorophenyl)-5-fluoropicolinate
##STR00023##
[0057] A mixture of methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-oxocyclohexa-2,5-dien-1-ylidene)amino)p-
icolinate (0.074 g, 0.20 mmol) and 0.1 M H.sub.2SO.sub.4 (0.2 mL)
in a 1:1 mixture of CH.sub.3CN/H.sub.2O (2 mL) was heated to
80.degree. C. for 1 h. After stirring at room temperature for 2 h,
the reaction mixture was added to CH.sub.2Cl.sub.2 (10 mL). The
organic layer was washed with a saturated solution of NaCl and
dried (MgSO.sub.4), and the solvent was removed. Preparative TLC on
silica gel eluting with 20% EtOAc/hexane gave methyl
4-amino-6-(4-chlorophenyl)-5-fluoropicolinate (0.050 g, 0.169 mmol,
85% yield) as a light yellow solid: .sup.1H NMR (400 MHz,
CDCl.sub.3) .delta. 7.83 (m, 2H), 7.45 (d, J=6.2 Hz, 1H), 7.37 (m,
2H), 4.40 (br s, 2H), 3.90 (s, 3H). ESIMS m/z 279.77 ([M-H].sup.-);
.sup.19F NMR (376 MHz, CDCl.sub.3) .delta. -145.11.
Example 7
Methyl 4-amino-3-chloro-6-(4-chlorophenyl)-5-fluoropicolinate
##STR00024##
[0059] A magnetically-stirred mixture of methyl
6-(4-chlorophenyl)-5-fluoro-4-((4-methoxyphenylamino)-picolinate
(112 mg, 0.4 mmol) and
1,3-dichloro-5,5-dimethylimidazolidine-2,4-dione (47.3 mg, 0.240
mmol) in CH.sub.3CN (5 mL) was heated to reflux for 1 h. Upon
cooling to room temperature the reaction mixture was added to
EtOAc/H.sub.2O (25 mL). The organic layer was washed with a
saturated solution of NaCl (25 mL) and dried (MgSO.sub.4), and the
solvent was removed to give 0.21 g of a light oil. Preparative TLC
on silica gel eluting with 40% EtOAc/hexane gave methyl
4-amino-3-chloro-6-(4-chlorophenyl)-5-fluoropicolinate (94 mg,
0.292 mmol, 73.1% yield) as an off-white solid: .sup.1H NMR (400
MHz, CDCl.sub.3) .delta. 7.88 (m, 2H), 7.44 (m, 2H), 4.92 (br s,
2H), 3.99 (s, 3H); .sup.19F NMR (376 MHz, CDCl.sub.3) .delta.
-140.86;. ESIMS m/z 315 ([M+H].sup.+).
* * * * *