Synthesis of 3,6-Dihydro-2H-1,2-oxazines via Dimethylsulfoxoniurn Methylide Addition to α,β-Unsaturated Nitrones

A unique and efficient formation of 3,6-dihydro-2H-1,2-oxazines starting from alpha,beta-unsaturated nitrones has been achieved. The nucleophilic addition of dimethylsulfoxonium methylide to the C=N bond of an alpha,beta-unsaturated nitrone to form an aziridine N-oxide followed by the Meisenheimer rearrangement affords 3,6-dihydro-2H-1,2-oxazine in up to 70% yield. Methylene was confirmed to be incorporated at the C-3 position of the ring. A wide range of beta-aryl-substituted alpha,beta-unsaturated nitrones were applicable to this reaction.