Urea nitrate catalyzed imino Diels-Alder reactions: Synthesis of cyclopentaquinolines, pyranoquinolines, and furoquinoline derivatives

Urea nitrate is found to be an efficient catalyst for the imino Diels-Alder reaction of aldimines with cyclopentadiene, 3,4-dihydropyran and dihydrofuran is reported for the first time. One pot synthesis of cyclopentaquinolines from benzaldehyde, aromatic amines with cyclopentadiene catalyzed by urea nitrate is also reported.