CERIUM(IV) OXIDATIONS OF BETA-AMINOKETONES .8. SYNTHESIS OF 1,2,3,4-TETRAHYDROISOQUINOLINES WITH DIFFERENTLY SUBSTITUTED PIPERIDINE PARTS

1- and 3-Alkyl- and/or aryl substituted tetrahydroisoquinolines are ob tained by oxidative cyclisation of N-benzyl-beta-aminoketones with cer ium(IV) sulphate. In nearly all cases formation of mixtures of diaster eomeres is observed. If the ketone function is replaced with COOR-, CN -, CHO and NO2-groups no cyclisation occurs under standard reaction co nditions. The products of hydrolysis, N-benzyl-N-methylaminopropionic acid, and of oxidation in benzylic position, benzaldehyde and benzoic acid, are mainly formed during the reaction. The oxidation of the N-be nzylaminopropional-dehydacetal 1k yields the isoquinolinedione 4k.