Synthesis of Degradation and Rearrangement Products

A key reaction in the structure elucidation was the rearrangement leading to apo derivatives, which occurs when the alkaloids are heated with strong acid. The reaction was formulated as shown in Fig, 1, The 

During the course of attempts to synthesize unsaturated derivatives of erythrinane Mondon and Menz (2) found an unexpected ring closure of VIII to form a seven-membered ring. The product (IX) could readily be converted to apoerysopine as shown in Fig. 2. Several of the intermediates in the conversion of VIII to IX could be isolated using milder conditions. 

The primary evidence for the structure of a-erythroidine had come from Hofmann degradation of the reduction product XV. With one 

These syntheses of Hofmann degradation products established the structure of XV but left two possibilities for a-erythroidine itself, II or XIX. The correctness of II was demonstrated by showing that a- and j8-erythroidines could be interconverted by warming in aqueous alkali. 

The equilibrium favors -erythroidine (III), in which the double bond is unconjugated but more highly substituted, consistent with earlier studies on unsaturated acids (5). 

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