Ring-Opening Reactions of N-Aryl-1,2,3,4-tetrahydroisoquinolines: Synthesis of Novel Isoquino[2,1-a][3,1]benzoxazine Derivatives

The aldehydes 7e and 7h were prepared by treatment of the 1,2,3,4-tetrahydroisoquinolines 5e and 5h,, respectively, with N-bromosuccinimide (NBS). Basic hydrolysis of compounds 7e and 7h gave the 4bH,6H-isoquino[2,1-a][3,1]benzoxazine derivatives 9 (R=H, OMe). Heterocycle 10 was obtained from the reaction of compound 5c with NBS and isolated as the ethyl derivative 11.