Triphenylphosphine-Catalyzed [3+2] Cycloaddition of Allenoate and Active Olefins: Syntheses of Spirooxindole Derivatives - Guo, Shanyan; Wang, Rendong; Li, Jian; Li, Chunju; Deng, Hongmei; Jia, Xueshun (Synlett, 2011)