Development of a Divergent Synthetic Route to the Erythrina Alkaloids: Asymmetric Syntheses of 8-Oxo-erythrinine, Crystamidine, 8-Oxo-erythraline, and Erythraline
A general synthetic methodology toward the erythrina alkaloids has been developed. Inspired by a proposed biosynthetic mechanism, the medium-sized chiral biaryl lactam was asymmetrically transformed into the common core A-D rings by a stereospecific singlet oxygen oxidation of the phenol moiety, followed by a transannular aza-Michael reaction to the dienone functionality. The late-stage manipulation of the oxidation and oxygenation states of the functional groups on the peripheral moieties enabled the flexible syntheses of the erythrina alkaloids. Then there were four: The fixed atropisomeric stereochemistry of a medium-sized biaryl intermediate was fully transferred to the central point chirality of a helical intermediate as a result of singlet oxygen oxidation and transannulation. This finding enabled the asymmetric synthesis of a common intermediate, which is amenable to a variety of oxidation-reduction transformations, thus giving rise to the first asymmetric syntheses of four erythrina alkaloids.
Synthesis of Erythrina and related alkaloids. XVI. Diels-Alder approach: Total synthesis of dl-erysotrine, dl-erythraline, dl-erysotramidine, dl-8-oxoerythraline and their 3-epimers
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Sano,Toda,Kashiwaba,et al.
p. 479 - 500
(2007/10/02)
SYNTHESES OF ERYTHRINA AND RELATED ALKALOIDS (6) TOTAL SYNTHESIS OF ERYSOTRINE AND ERYTHRALINE
An efficiently stereocontrolled synthesis of the erythrina alkaloids, erysotrine and erythraline was described.