Copper-Catalyzed Formal [4+2] Cycloaddition of Ethynylethylene Carbonates for the Construction of 3,4-Dihydro-2H-benzo[b][1,4]oxazines

A formal [4+2] cycloaddition reaction of ethynylethylene carbonates and 2-aminophenols has been developed for the synthesis of 3,4-dihydro-2H-benzo[b][1,4]oxazines bearing quaternary carbon atoms. The reaction features mild reaction conditions, good functional group compatibility and good yields. Furthermore, when using chiral PyBox ligand, this strategy could also achieve the asymmetric synthesis of 3,4-dihydro-2H-benzo[b][1,4]oxazines. Application studies indicated that the hydroxymethyl group of final products was an excellent functional group that can be further modified easily.