反应详情

In step a of Scheme 1, 3-hydrazinopyridine dihydrochloride is reacted with methyl acrylate in the presence of a base such as sodium methoxide or sodium ethoxide to yield 1-(pyridin-3-yl)pyrazolidin-3-one followed by chlorination of 1-(pyridine-3-yl)pyrazolidin-3-one with phosphoryl chloride (POCl3) in a two-step process to yield dihydropyrazole chloride (5a). The first step may be conducted in a polar protic solvent such as, methanol (MeOH) or ethanol (EtOH), at a temperature from about 40° C. to about 80° C. The second step may be conducted neat in phosphoryl chloride at a temperature from about 40° C. to about 80° C. When the crude product from the first step was neutralized, the second step can also be conducted in a solvent like acetonitrile (MeCN) at a temperature from about 40° C. to about 80° C.