Boron trifluoride-catalyzed Diels–Alder reaction of α,β-unsaturated iminoindoles for the construction of 2-imino-3-spiroindoles

The BF ₃ -catalyzed Diels–Alder reaction of α,β-unsaturated iminoindoles with less reactive substituted dienes affords 2-imino-3-spiroindoles, a diverse class of 3-spiroindole derivatives, with high stereoselectivity.