One-Pot Synthesis of Tetrahydroquinolines by an Imino-Diels-Alder Reaction

Significance

Reported is a synthesis of 1,2,3,4-tetrahydroquinolines by the Diels-Alder reaction of alkenes with iminium salts formed in situ from N-methylaniline and different sources of formaldehyde. The influence of the source of formaldehyde, Lewis acid and alkene structure on yield and stereochemistry of the products obtained was moderately investigated. The formation of both syn and anti products suggests the competition of pericyclic [4+2] cycloaddition with a stepwise mechanism involving cationic species.