Triphenylphosphonium perchlorate as an efficient catalyst for mono- and bis-intramolecular imino Diels–Alder reactions: synthesis of tetrahydrochromanoquinolines

Triphenylphosphonium perchlorate (TPP) is found to be an efficient catalyst for the mono- and bis-intramolecular imino Diels–Alder (IMIDA) reaction of aldimines derived from aromatic amines and O-allyl derivatives of salicylaldehydes to afford the corresponding tetrahydrochromano[4,3-b]quinolines in excellent yields and short reaction times under mild conditions.