Erythroidine alkaloids synthesis

The efficient approach to erythravine paved the way for a second erythrina alkaloid [(- -)-/l-erythroidine (56)] synthesis by Hatakeyarna et al. This alkaloid was found in several species of the Erythrina genus and was synthesized in 26 linear steps as depicted in Scheme 2.12. Starting from 54, tandem ene-yne RCM of the isomeric mixture 55 underwent cyclization with [Ru]-I catalyst (10mol%) to... 

In the course of investigating Erythrina alkaloids, treatment of / -erythroidine (186) with phosphoric acid gave a rearranged demethoxy derivative, apo-/J-erythroidine (77), which was isomerized on alumina to give isoapo-/ -erythroidine (187) (50JA2062). Compound 77 is of interest because of its own physiological activity. A synthesis is described in Section IV,A,2. 

The above syntheses of the parent spiroamine system establish the skeleton of the aromatic alkaloids. A synthesis of a derivative of jS-erythroidine (III) with the intact spiro skeleton, achieved in Boekel-heide s laboratory (15), provides similar confirmation for the lactonic alkaloids. 

These results led to the postulation of the spirocyclic erythrinane skeleton and this was confirmed by synthesis of the parent nucleus by Belleau (1953). The structures of the two lactonic alkaloids (3) were also elucidated by Boekelheide (1960) and coworkers, who recognised their close structural identity to the other aromatic erythrina alkaloids (1) the lactonic alkaloids also underwent an apo -type rearrangement under drastic acidic conditions. Subsequently the structures of both the aromatic and lactonic alkaloids were confirmed by X-ray crystallography of erythra-line hydrobromide (Nowacki and Bonsma 1958) and of the erythroidines (Hanson 1963). The spiro centre was shown to have the same configuration in all the erythrina alkaloids by use of optical rotatory measurements (Weiss and Ziffer 1963, Beecham 1971). 

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