Highly Enantio- and Diastereoselective [4 + 2] Cycloaddition of 5H‑oxazol-4-ones with N‑Maleimides

An organocatalytic asymmetric reaction between 5H-oxazol-4-ones and N-substituted maleimides is disclosed. Employing Takemoto’s chiral tertiary amine–thiourea as the catalyst, [4 + 2] annulation reactions were performed with high chemoselectivity, leading to a series of biologically important chiral oxo-bridged piperidone-fused succinimides in good to excellent enantioselectivities (up to >99% ee) and >19:1 dr.