Abstract Pyrazole, 1-methylpyrazole and 3-methylpyrazole are chlorinated by the enzyme chloroperoxidase from Caldariomyces fumago, in the presence of potassium chloride and hydrogen peroxide at pH 2.7, yielding the corresponding 4-chloro derivatives in good yields. A 4H-pyrazole is proposed as an intermediate in this reaction. 2-Aminopyridine was converted regiospecifically by the same enzyme into 2-amino-3-chloropyridine, and 8- ...
