Brefeldin Gais synthesis

In the synthesis of brefeldin A 92) by Gais and Lied [54], seco acid 90 was lactonized to 91 with the push-pull acetylene 93 (Scheme 31) in 71% yield (Scheme 30). The mechanism is outlined in Scheme 31. 

Both the enol phosphate method, and the reduction of the keto sulfone to the p-hydroxy sulfone followed by reductive cleavage to produce ( )-alkenes, have been applied to the synthesis of brefeldin A. Gais and cowoikers added the sidfone (462) to the lactone (461), formed the enol phosphate and reduced with sodium and ammonia to the ( )-alkene (463), in a 65% overall yield (equation 107). ... 

Enzymatic degradation was the cornerstone of a synthesis of optically active 161 developed by Gais (Scheme 1.41). Construction of the acyclic portion of brefeldin A began with the addition of ethoxyethyl protected l-lithio-3-propanol... 

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