Iterative enolate Claisen rearrangements: versatile route to optically pure 2,7-nonadiene-5-carboxylic acids
作者:John C. McKew、Mark J. Kurth
DOI:10.1021/jo00069a019
日期:1993.8
A short, versatile, and diastereoselective method of preparing 2,7-nonadiene-5-carboxylic acids by an iterative enolate Claisen rearrangement procedure has been developed. Homochiral (E)- and (Z) secondary allylic alcohols 1-4, prepared from (S)-(-)-ethyl lactate, were esterified with acetic acid and enolized, and the resulting silyl ketene acetals were warmed to room temperature to effect [3,3]-sigmatropic rearrangement to 4-hexenoic acids 5-8. Esterification of these acids with alcohols 1-4 followed by a second enolate Claisen rearrangement delivered the targeted 2,7-nonadiene-5-carboxylic acids with high diastereoselectivity. This second [3,3]-sigmatropic rearrangement provides well-placed and potentially synthetically useful functionality and stereochemistry.