Reactions of Vincadifformine and Tabersonine

The electrochemical (anodic) oxidation of tabersonine or 3-oxotaberson-ine gives dimeric products 335a and 335b, respectively (232). In the oxidation of 3-oxotabersonine the dimer 335b was the sole product, but in the oxidation of tabersonine itself some of the symmetrical 10,10 -dimer (5%) was also obtained, together with a trimer (2%) and several other, unidentified, products. 

Reaction of 3-oxotabersonine (107) with nitrosonium tetrafluoroborate in dichloromethane at 0°C gives a mixture of lO-nitro-3-oxotabersonine, the 16-nitroindolenine derivative 336, and the dimeric species 335b (234). The configuration at C-16 in 336 has not been proved unequivocally, but is based on the known selectivity of reactions at this position in the parent alkaloid. 

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