Reactions of Azides with Electrophiles: New Methods for the Generation of Cationic 2‐Azabutadienes. Synthesis of 1,2, 3,4‐Tetrahydroquinolines and 1,2‐Dihydroquinolines via a Hetero Diels–Alder Reaction

Two methods for the generation of iminium ions of the type ArN+(X)=CHR (X = H or alkyl, R = H or alkyl) are reported: (1) the Bronsted‐acid‐promoted rearrangement of benzylic azides and (2) the intermolecular Schmidt reactions of azides XN3 (X = aliphatic) with benzylic carbocations derived from benzylic alcohols ArCH(R)OH. The iminium ions ArN+(X)=CHR behave as cationic 2‐azabutadienes in the presence of alkenes and alkynes, producing 1,2, 3,4‐tetrahydroquinolines and 1,2‐dihydroquinolines by a hetero Diels–Alder reaction.