Ring transformation of spirocyclopropanepyrazoles into pyrano[2,3‐<i>c</i>]pyrazoles

Abstract

Abstract magnified image An approach to pyrano[2,3‐ c ]pyrazoles starting from spirocyclopropanepyrazoles via a ring‐opening/cyanomethylation and intramolecular cyclization is described. Reactions of spirocyclopropanepyrazoles 1a , 1b , 1c , 1d with chloroacetonitrile in the presence of sodium hydride gave the corresponding cyanomethoxypyrazoles 4a , 4b , 4c , 4d . Treatment of 4a , 4b , 4c , 4d with sodium hydride at room temperature caused intramolecular Michael addition reaction to afford the corresponding pyrano[2,3‐ c ]pyrazoles 5a , 5b , 5c , 5d . J. Heterocyclic Chem., (2009).