scheme4

Scheme 4. Substrate scope of the reaction between benzoxazines 1 and 2-methylene-3-oxoalkanoates 4. A mixture of 1 (0.1 mmol), 4 (0.2 mmol), and C5 (10 mol%) in CH₂Cl₂ (0.1 mL) was stirred at 35 °C for 96 h. All dr > 20:1, determined by ¹H NMR. Products 5 were obtained in isolated yield. The enantiomeric excess (ee) was determined by chiral-HPLC analysis.