Process for the preparation of 3-(3-chloro-1
3-(3-Chloro-1H-pyrazol-1-yl)pyridine is prepared by coupling 3-bromopyridine with commercially available 3-aminopyrazole, purifying the 3-(3-amino-1H-pyrazol-1-yl)pyridine by crystallization, and converting the amino group to a chloro group by a Sandmeyer reaction.
1. A process for preparing 3-(3-chloro-1H-pyrazol-1-yl)pyridine (5b)
which comprises
a) treating 3-bromopyridine
with 3-aminopyrazole in an excess of about 10 mole percent to about 50 mole percent
in a water-miscible polar aprotic organic solvent at a temperature of about 75° C. to about 155° C. in the presence of about 5 mole percent to about 30 mole percent of copper chloride and a base in an excess of about 1.5 fold to about 2 fold to provide 3-(3-amino-1H-pyrazol-1-yl)pyridine (8a)
b) crystallizing the 3-(3-amino-1H-pyrazol-1-yl)pyridine (8a) from water;
c) treating the 3-(3-amino-1H-pyrazol-1-yl)pyridine (8a) in excess aqueous hydrochloric acid with sodium nitrite in an excess of about 1.5 fold to about 2 fold at a temperature of about 0° C. to about 25° C. to provide the diazonium salt (8b)
and
d) treating the diazonium salt (8b) with about 5 mole percent to about 50 mole percent copper chloride at a temperature of about 0° C. to about 25° C.
2. The process of claim 1 , wherein the water-miscible polar aprotic organic solvent is acetonitrile, dimethyl sulfoxide, N-methylpyrrolidinone, N,N-dimethylformamide or N,N-dimethylacetamide.
3. The process of claim 2 , wherein the water-miscible polar aprotic organic solvent is N,N-dimethylacetamide.
4. The process of claim 1 , wherein a water immiscible organic solvent is added in step d) to suppress foaming.
5. The process of claim 1 , wherein the copper chloride is copper (I) chloride.
6. The process of claim 1 , wherein the copper chloride is copper (II) chloride.
7. The process of claim 1 , wherein the copper chloride in step (d) is in an amount of from about 15 mole percent to 30 mole percent.
8. The process of claim 4 , wherein the water immiscible organic solvent is toluene or chloroform.
9. A process for preparing 3-(3-chloro-1H-pyrazol-1-yl)pyridine (5b)
which comprises
a) treating 3-bromopyridine
with 3-aminopyrazole
in N,N-dimethylformamide at a temperature of about 110° C. in the presence of about 5 mole percent to about 30 mole percent of copper (I) chloride and an excess of potassium carbonate to provide 3-(3-amino-1H-pyrazol-1-yl)pyridine (8a)
b) crystallizing the 3-(3-amino-1H-pyrazol-1-yl)pyridine (8a) from water;
c) treating the 3-(3-amino-1H-pyrazol-1-yl)pyridine (8a) in excess aqueous hydrochloric acid with sodium nitrite in an excess of about 1.5 fold to about 2 fold at a temperature of about 0° C. to about 5° C. to provide the diazonium salt (8b)
and
d) treating the diazonium salt (8b) with copper (I) chloride at a temperature of about 0° C. to about 25° C.