Diastereoselective Synthesis of Dispirobarbiturates through Et3N-Catalyzed [3 + 2] Cycloaddition of Barbiturate-Based Olefins with 3-Isothiocyanato Oxindoles

Under catalysis of 10 mol % of Et3N, the [3 + 2] cycloaddition of barbiturate-based olefins with 3-isothiocyanato oxindoles underwent smoothly and afforded the desired dispirobarbiturates in up to 99% yield with up to 99:1 dr. The relative configuration of the dispirobarbiturates was unambiguously determined by X-ray single-crystal structure analysis. The reaction mechanism was proposed to shed light on the diastereoselective formation of the dispirobarbiturates.