Carreiras retrosynthetic analysis of -zaragozic acid

Metallation of alkyne, nucleophilic addition x to aldehyde (9), oxidation 

In order to side-step potential problems with hydroxyl-directed hydro-metallation of the alkyne, ester 14 was reduced with sodium borohydride in methanol. This also led to a small amount of alkyne desilylation (5%-10%). Fortunately, however, this was the next step of the synthesis. After selective protection of diol 15 to obtain 8, the stabilised acetylenic anion 

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