Spirocyclopropanes from Intramolecular Cyclopropanation of Pyranopyrazoles and Pyranopyrimidine-diones and Lewis Acid Mediated (3 + 2) Cycloadditions of Spirocyclopropylpyrazolones

A robust
intramolecular cyclopropanation reaction was first performed
on pyranopyrazole and pyranopyrimidine-dione derivatives to obtain
spirocyclopropylpyrazolones and barbiturates, using iodosylbenzene
(PhIO) or the combination of iodobenzene diacetate (PIDA)/molecular
iodine (I2), under mild reaction conditions. Syntheses of functionally and
stereochemically diversified, novel spiropyrazolone fused 2-iminothiophene
and spiropyrazolone fused pyrroline scaffolds were also demonstrated
via Lewis acid catalyzed highly diastereoselective (3 + 2) cycloaddition
reactions of the synthesized spiro-cyclopropyl pyrazolones with phenyl
isothiocyanate and benzonitrile, respectively.