3-Methoxypyrazoles from 1,1-dimethoxyethene, few original results

Elise Salanouve (1) , Sandrine Guillou (1) , Marine Bizouarne (1) , Frédéric J. Bonhomme (1) , Yves Louis Janin (1)

1 CNRS - UMR3523 - Chimie organique

From the condensation between 1,1-dimethoxyethene and anhydrides, synthetically useful b,bedimethoxyea,b-unsaturated ketones were prepared. Upon addition of hydrazine, followed by iodination, 4-iodinated 3-methoxypyrazoles were obtained. The occurrence of a side compound also provided insights in the scope of this synthesis. In a second part, 1-(4-chlorophenyl)-3,3-dimethoxyprop- 2-en-1-one was obtained from 1,1-dimethoxyethene and 4-chlorobenzoylchloride. The subsequent addition of hydrazine or phenylhydrazine led to 5-(4-chlorophenyl)-3-methoxy-1H-pyrazole or 1-phenyl- 5-(4-chlorophenyl)-3-methoxypyrazole in unprecedented 64 or 54% overall yield. Unexpectedly, addition of 2-pyridylhydrazine led to the 2-([1,2,4]triazolo[4,3-a]pyridin-3-yl)-1-(4-chlorophenyl) ethanone. This led us to design original conditions, which led to the target 1-(2-pyridyl)-5-(4-chlorophenyl)-3- methoxypyrazole in a 39% overall yield. Additional examples are provided, starting from various carboxychlorides.

Domaines: Chimie organique

Elise Salanouve, Sandrine Guillou, Marine Bizouarne, Frédéric J. Bonhomme, Yves Louis Janin. 3-Methoxypyrazoles from 1,1-dimethoxyethene, few original results. Tetrahedron, 2012, 68, pp.3165. ⟨10.1016/j.tet.2012.02.057⟩. ⟨pasteur-00680094⟩