Cyclisierungsreaktionen β,γ‐ungesättigter Kohlensäurederivate. IX. Regiochemie der elektrophilen Cyclofunktionalisierung β,γ‐ungesättigter Carbamidsäureester mit Brom – Synthese von Oxazolidin‐2‐onen und Tetrahydro‐2H‐1,3‐oxazin‐2‐onen

Abstract

Cyclization Reactions of β,γ‐Unsaturated Derivatives of Carbonic Acid. IX. Regiochemistry of Electrophilic Cyclofunctionalization of β,γ‐Unsaturated Carbamic Acid Esters with Bromine – Synthesis of Oxazolidine‐2‐ones and Tetrahydro‐2H‐1,3‐oxazine‐2‐onesN,N‐Disubstituted β,γ‐unsaturated urethanes (1) and bromine react in methylene chloride at room temperature. The crotyl urethanes (1a–1c and 1e) and bromine give mixtures of corresponding saturated urethanes (dibromine adducts) (2a–2c and 2e), the oxazolidine‐2‐ones (3a–3c and 3e), and the tetrahydro‐2H‐1,3‐oxazine‐2‐ones (4a–4c and 4e). The reaction of γ,γ‐dimethylallyl urethanes (1f–1h) with bromine gives similar results. A useful synthetic route to N‐substituted tetrahydro‐2H‐1,3‐oxazine‐2‐ones (4l–4q) is demonstrated by the reaction of cinnamyl urethanes (1l–1q) with bromine.