Studies on tetrahydroisoquinolines. Part 15. Lead tetra-acetate oxidation of four hydroxytetrahydroprotoberberines, (±)-govanine, (±)-discretine, (±)-corytencine, and (±)-10-hydroxy-2,3,11-trimethoxytetrahydroprotoberberine

Abstract

Lead tetra-acetate oxidation of (±)-2-(1) and (±)-10-(2) hydroxytetrahydroprotoberberines afforded the p-quinol acetates (5) and (6), which on treatment with acetic anhydride-concentrated sulphuric acid gave (±)-2,5β(35), and (±)-10,13α-(40) and (±)-10,13β-(41) diacetoxytetrahydroprotoberberines respectively. Alkaline hydrolysis of the diacetate (35) produced the (±)-5α-(38) and (±)-5β-(39) methoxy-compounds, whereas similar treatment of the diacetates (40) and (41) produced the same (±)-13α-methoxy-derivative (42). While oxidation of (±)-3-hydroxytetrahydroprotoberberine (3) gave directly the (±)-5α-(7) and (±)-5β-(8) acetoxy-derivatives, oxidation of the (±)-11-hydroxy-congener (4) produced the unexpected rearranged product, the (±)-12-acetoxy-9-hydroxy-derivative (18), together with a small amount of (±)-13β-acetoxytetrahydroprotoberberine (17). A discussion of the stereochemistry of the reactions is presented.