14-hydroxy vincadifformine

Hydroxy vincadifformine indolenine (285) can also be rearranged to a mixture of vincamine (286) and 16-epivincamine by pyrolysis or flow thermolysis at 580°C (795). 

The vincadifformine-tabersonine group of alkaloids provide a rich field for the study of oxidative rearrangements. New work reported recently101" includes a study of the oxidation of 3-oxovincadifformine (189) with m-chloroper oxy benzoic acid (Scheme 27). The products were 3-oxovincamine (190), 3-oxo-16-ep/-vincamine (191), and a dilactam (192), which is simply the result of oxidative fission of the 2,16 bond. Under carefully controlled conditions, the hydroxy-indolenine (193) was isolated, and it was subsequently shown to be an intermediate (as expected) in the formation of (190)—(192). Photochemical oxidative rearrangement gave similar results. 

Comparison,in a straightforward way, of the chemical shifts for the carbons of the new Aspidosperrm alkaloids vandrikidine, vandrikine, and hazuntinine with those of tabersonine and vincadifformine and the application of the aromatic methoxyl shift rules (see p. 190) lead inevitably to the structures 19-hydroxy-11-methoxytabersonine, 15,18-epoxy-11-methoxy vincadifformine, and 14,15-epoxy-10,11-dimethoxyvincadifformine respectively. Thus for example, compare the data on (32), hazuntinine, with those for (31) (p. 189). 

The iboga alkaloids behave differently from the vincadifformine group on photochemical oxidation iboxyphylline is rapidly oxidised at C-16 to give a hydroxy-indolenine, but only in the presence of oxygen and in the absence of cyanide. 

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