| Abstract: | 2-(Trimethylsilyl)ethyl Esters as Carboxyl Protecting Group; Application in the Synthesis of (?)-(S)-Curvularin The mould metabolite curvularin (VIII) has been synthesized with the help of a new carboxyl protecting group that can be removed selectively with fluoride ions. 2-(Trimethylsilyl)ethyl 7-hydroxy-octanoate (III) was acylated with 3,5-dibenzyloxy-phenacetyl chloride (IV) to form V with two different ester groups. Tetrabutyl-ammonium fluoride in tetrahydrofuran cleaved the 2-(trimethylsilyl)ethyl ester in V selectively to form the carboxylate anion of VI together with ethylene and trimethylsilyl fluoride. Curvularin dibenzyl ether (VII) was formed by intramolecular acylation of VI. Removal of the benzyl ether groups in VII by hydrogenolysis led to (±)-curvularin (VIII). The naturally occurring (?)-enantiomer was formed when (+)-(S)-III served as starting material. |
