Access to 1‐Phospha‐2‐azanorbornenes by Phospha‐aza‐Diels–Alder Reactions

: The unprecedented phospha-aza-Diels-Alder reaction between an activated electron-poor imine and 2H-phospholes yields 1-phospha-2-azanorbornenes in a highly chemoselective and moderately diastereoselective reaction. The intermediate 2H-phospholes, which act as dienes, are formed in situ from the corresponding 1H-phospholes. Theoretical calculations confirm that the phospha-aza-Diels-Alder reaction is of normal electron demand. The reactive P-N bond in 1-phospha-2-azanorbornenes can be cleaved by nucleophiles leading to the formation of 2,3-dihydrophospholes.