Rhodium‐Catalyzed (3+3) Cascade Cyclization of Diazobarbiturates with 2H‐Azirines for the Diastereoselective Construction of Spirooxazinopyrimidinediones

Under the catalysis of Rh2(esp)2 (10 mol%) and BINAP (20 mol%) in 1,2‐dichloroethane at 80 °C, a (3+3) cascade cyclization between diazobarbiturates and 2H‐azirines proceeds smoothly, yielding spirooxazinopyrimidinediones in 24–92% yield with >20:1 diastereoselectivity. The chemical structure of one compound has been confirmed by X‐ray diffraction analysis, and the others are suggested by inference.