Yb(OTf)3-Catalyzed Asymmetric [3+3] Cycloaddition of N-Vinyl Nitrones with Activated Cyclopropanes to Prepare 1,2-Oxazines

We described a Yb(OTf)₃ combined with Pybox ligand catalyzed asymmetric [3+3] cycloaddition of N-vinyl cinnamaldehyde nitrones with activated cyclopropanes to prepare various functionalized 1,2-oxazines in 24%—95% yields and 22%—96% ee. Experimental results revealed that the reaction underwent a domino [3+3] cycloaddition, dealkenylation, and aza-1,4-addition in three steps. The chiral 1,2-oxazine could be obtained in gram scales and easily converted into various 1,2-oxazine scaffolds. The present method features broad substrate scope, good functional group compatibility, three-component domino reaction, and asymmetric [3+3] cycloaddition of N-vinyl nitrones with activated cyclopropanes.