l-Proline catalyzed efficient one-pot three-component aza-Diels-Alder reactions on nitrostyrylisoxazoles: a facile synthesis of new isoxazolyl tetrahydroquinolines and isoxazolo[2,3-a]pyrimidines

l-Proline acts as an efficient organo catalyst and found to promote one-pot three-component aza-Diels-Alder reaction of aryl or isoxazole imines formed in situ from aromatic or isoxazole amines and aromatic aldehydes with nitrostyrylisoxazoles to afford the isoxazolyl tetrahydroquinolines or isoxazolo[2,3-a]pyrimidines, respectively, in excellent yields at ambient temperature under neutral conditions.