Aromatic erythrinan alkaloids synthesis

Scheme 3. Strategies for the synthesis of aromatic erythrinane alkaloids (5.2.1.) Generation of one alicyclic ring in the final step...

Concerning the non-aromatic erythrinane alkaloids, only one single total synthesis has been achieved until now. Thus, the synthesis of ( )-cocculolidine (15, Fig. 2) has been completed in 0.42% overall yield through 21 steps (54). Furthermore, several synthesis approaches to ring D oxaerythrinane frameworks are known (79). 

Tsuda Y, Sano T (1989) Synthesis of Erythrina Alkaloids. In Atta-ur-Rahman (ed) Studies in Natural Products Chemistry Vol. 3, Stereoselective Synthesis (Part B) Elsevier, Amsterdam, p 455 (Erythrinane and Homoerythrinane alkaloids, approaches to non-aromatic Erythrina 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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