Dendrobatid alkaloids enantioselective

First Enantioselective Synthesis of Dendrobatid Alkaloids Indolizidine 2091 and 223J 53... 

The utility of stereospecific nucleophile-induced iminium ion-alkyne cyclizations that proceed in the exocyclic mode was recently demonstrated by Overman and coworkers in efficient enantioselective total syntheses of the Dendrobatid alkaloids (+)-pumiliotoxin A and (+)-allopumiliotoxin 323B. 78,79 The piperidine ring and 6-alkylidene side chain of these alkaloids were stereospecifically generated in good... 

Oppolzer, W. FrostI, W. Weber, H. P. "The Total Synthesis of d/-Pumiliotoxin-C" Helv. Chim. Acta 1975, 58, 593. Oppolzer, W. Flaskamp, E. "An Enantioselective Synthesis and the Absolute Configuration of Natural Pumiliotoxin-C" Helv. CNm. Acta 1977, 60, 204. Oppolzer, W. Flaskamp. E. Bieber. L. W. "Efficient Asymmetric Synthesis of Pumilbtoxin C via Intramolecluar [4+2] Cycloaddition" Helv. Chim. Acta 2001, 84,141-145. Eor a related approach to pumiliotoxin-C and other Dendrobatid alkaloids see Banner, E. J. Stevens, E. D. Trudell, M. L. Tetrahedron Lett. 2004,45,4411-4414. 

The Dendrobatid poison arrow frogs of Central and South America exude a potent mixture of alkaloids from their skins. It was originally thought that the frogs biosynthesized these alkaloids, but it has since been shown that they are of dietary origin. The skin exudate of the Colombian frog Minyobates bombetes causes severe locomotor difficulties, muscle spasms and convulsions upon injection in mice. The major component of the alkaloid mixture is 251F3. Jeff Aube of the University of Kansas recently described (J. Am. Chem. Soc. 2004,126,5475) the enantioselective total synthesis of 3. The key step in the synthesis was the cyclization of the keto azide 2. 

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