Chemo- and Diastereoselective Synthesis of Spirooxindole-pyrazolines and Pyrazolones via P(NMe2)3-Mediated Substrate-Controlled Annulations of Azoalkenes with α-Dicarbonyl Compounds

P(NMe2)3-mediated substrate-controlled annulations of azoalkenes with α-dicarbonyl compounds are reported, where the azoalkenes serve as either four or five-atom synthons chemoselectively. The azoalkene participates in annulation with isatins as a four-atom synthon to furnish the spirooxindole-pyrazolines, whereas it functions as a novel five-atom synthon in annulation with aroylformates, thereby leading to chemo- and stereoselective formation of pyrazolones. The synthetic utilities of the annulations have been demonstrated, and a novel TEMPO-mediated decarbonylation reaction is unveiled.