Isoanhydroberberilate

In contrast to the reaction of the betaine 58 in wet diethylether, wet THF, in which the betaine is better soluble, gives the methyl isoanhydroberberilate 64 in 71% yield. The mechanism seemingly involves an unusual carbon to nitrogen acyl migration as shown in Scheme 23. Hydration and air oxidation of the betaine to the peroxide leads to the formation of an aziridine intermediate and loss of a hydroxide anion (77TL3787). 

The methoxyberberine betaine (83) will undergo acyl migration in aqueous THF to give the imide methyl isoanhydroberberilate (94). That acyl migration had indeed occurred was shown by the conversion of the betaine (83) into the acetoxy-enamine (95) by acetic anhydride and pyridine, followed by hydrolysis of this by methanolic potassium hydroxide to the known methyl anhydroberberilate (97). The two isomeric compounds (94) and (97) react differently when treated with sodium borohydride in ethanol, the former suffering only solvolysis to noroxy-hydrastinine (98) and the diester (99) and the latter reduction to the ortho-ester (96). This ortho-ester, on A -methylation and further reduction with sodium borohydride, yields hydrohydrastinine and i -meconine. ... 

The Further Chemistry of Berberinephenolbetaine, 8-Methoxyberberine-phenolbetaine, and 8J3 Dioxo-14-hydroxycanadine. Hydration of 8-methoxy-berberinephenolbetaine in wet tetrahydrofuran, a solvent in which it is appreciably soluble, generates methyl isoanhydroberberilate in 807 yield by the... 

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