A Divergent Synthesis of Spiropyrazole Derivatives Containing Iminolactone and/or Cyclic Imide Moiety

Abstract

An approach to spiropyrazole derivatives containing iminolactone and/or cyclic imide moiety starting from 1H‐pyrazole‐4‐acetic acid derivative is described. Hydrolysis of C‐cyanomethylated 1H‐pyrazole‐4‐acetic acid methyl ester (1), which was easily prepared from 1H‐pyrazole‐4‐acetic acid derivative by a C‐cyanomethylation, led to the C‐cyanomethylated 1H‐pyrazole‐4‐acetic acid (2). Compound 2 was reacted with ethanol in the presence of tin(IV) chloride in refluxing chloroform to give the key intermediate ethyl imidate (3). Sodium hydride‐assisted lactonization of 3 in N,N‐dimethylformamide afforded the spiropyrazole derivative containing iminolactone moiety (4). On the other hand, thermal treatment of 3 with sodium acetate in the absence of solvent caused another intramolecular cyclization to yield the spiropyrazole derivative containing cyclic imide moiety (6).