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

An approach to spiropyrazole derivatives containing iminolactone and/or cyclic imide moiety starting from 1 H ‐pyrazole‐4‐acetic acid derivative is described. Hydrolysis of C ‐cyanomethylated 1 H ‐pyrazole‐4‐acetic acid methyl ester ( 1 ), which was easily prepared from 1 H ‐pyrazole‐4‐acetic acid derivative by a C ‐cyanomethylation, led to the C ‐cyanomethylated 1 H ‐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 ).