Structure and Stereochemistry of Vincatine

K02CN=NCOaK, MeOH, AcOH v, W-2 Raney nickel, DME, r.t. 

21-stereoisomers. The validity of the conclusions of Pakrashi and his co-workers 237,238) concerning the relative stereochemistry of (-)-vincatine was accepted, and the fact that their synthetic 75,20/ ,215 base and (-)-vincatine (340), prepared from (-)-vincadifformine, exhibited enantiomeric circular dichroism curves, proves unequivocally that (-)-vincatine has the absolute configuration 1R,1QS,2 R 236). It should be added that bases of the vincatine type (cf. the oxindole analogs of the heteroyohimbine alkaloids) can readily isomerize at positions 7 and 21 by a reversible Man-nich reaction, even in chloroform solution, and optical rotation values tend to be variable and unreliable. 

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