Highly stereoselective construction of spiro[cyclopropane-1,4′-pyrazolin-5′-one]with 4-arylidene-3-methyl-1-phenyl-pyrazolin-5-one and arsonium ylide

A highly stereoselective synthesis of exo-spiro[cyclopropane-1,4'-pyrazolin-5'-one] from 4-arylidene-3-methyl-1-phenyl-pyrazolin-5-one and arsonium bromide in the presence of base has been achieved. The triphenylarsine-catalyzed cyclopropanation of 4-arylidene-3-methyl-1-phenyl-pyrazolin-5-one with bromide in the presence of NaHCO3 has also been studied. Both exo and endo isomers were formed in this reaction. The structures of the products were characterized by IR, MS, H-1 NMR, elemental analysis, and X-ray diffraction analysis.