Fe-BPsalan Complex-Catalyzed Asymmetric 1,3-Dipolar [3 + 2] Cycloaddition of Nitrones with α,β-Unsaturated Acyl Imidazoles

A highly efficient,
iron(III)-BPsalan complex-catalyzed
asymmetric
1,3-dipolar cycloaddition of nitrones and α,β-unsaturated
acyl imidazoles has been developed to afford isoxazolidine (31 examples)
and isoxazoline derivatives (13 examples) in moderate to excellent
yields (up to 99%) and excellent stereoselectivity (up to 99% ee and
>20:1 dr). The reaction proceeds readily in acetone under air conditions,
maintaining high efficiency and selectivity.