Dendrobatid toxin synthesis

A stereoselective total synthesis of dendrobatide toxin 251 D was developed by Overman et al.237) involving an epoxidation of the (S)-proline derivative (237) to furnish the oxirane (238) as major product. In their approach towards the total synthesis of the same natural product Thomas et al.238) investigated the stereoselectivity of the epoxide formation from (S)-5-acetylpyrrolidin-2-one and dimethyloxosulfonium methylide. A diastereoselectivity of d.s. 50-60% was achieved 238. ... 

Dendrobatid toxins. The first step in a synthesis of ( )-perhydrogephyrotoxin (S, a poison-frog alkaloid) involves a Diels-Alder reaction of 1 and a suitable a.ft-unsulurated aldehyde, which proceeds selectively to give the erafo-adduct 2. Another key step is the selective reduction of a bicyclic imine (3) with LiAlH4 in about 9 1 ratio from the sterically more hindered a-face.2... 

An elegant application of vinylsilane chemistry reported this year is the clean and stereospecific iminium ion-vinylsilane cyclization to dendrobatid toxin 25 ID shown in Scheme and a spiroannulation synthesis has been described in which the final stage is Lewis-acid-catalysed cyclization of (111) to (112)/ °... 

An iminium ion-vinylsilane cyclization (Scheme 6) provides the basis for a very short synthesis of dendrobatid toxin 25 ID (85) as reported by Overman and Bell. A related iminium ion cyclization [(86) (87)] is a key step in a... 

Overman, L. E., and K. L. Bell Enantiospecific total synthesis of dendrobatid toxin 25ID. A short chiral entry to the cardiac-active pumiliotoxin A alkaloids via stereospecific iminium ion — vinylsilane cyclizations. J. Amer. Chem. Soc. 103, 1851— 1852 (1981). 

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