Some properties of reserpine partial formulae

The chemistry of the yohimbines forms an excellent example of the value of studying related alkaloids together and Chart 5.4 which illustrates this and its obvious conclusions, can be checked against Table 5.1. The absolute stereochemistry of the yohimbines has been looked at by most of the optical comparative methods. A purely chemical proof depends on the conversion of yohimbine into a seco base which in turn has been related to cinchonine infra). 

Historically it was a total stereospecific synthesis (p. 25) of 3-epja//oyohimbane in 1954 that put all the conclusions up to that time on a solid basis. It also confirmed the opinion that the platinum catalysed hydrogenation of sempervirine was an all cis addition. Sempervirine (a constituent of yellow jasmine, Gel-semium sempervirens) had previously been synthesized thus. 

C-3 Stereochemistry. The methods which are valid for these tetrahydro-/3-carboline alkaloids depend for the most part on the 

Chemistry of yohimbine and ns close relatives (partial formulae) 

Chemical methods depend on acid catalysed equilibrium studies and hydrogenation of the derived tetradehydro and/or J -com-pound to get with say, sodium borohydride predominantly the thermodynamically more stable (usually 3a isomer) or with zinc and perchloric acid the less stable usually the 3j8 isomer. As has been stated before with alio systems care must be taken in the interpretation of any single experiment. 

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