A Flexible Approach to (<i>S</i>)-5-Alkyl Tetramic Acid Derivatives:  Application to the Asymmetric Synthesis of (+)-Preussin and Protected (3<i>S</i>,4<i>S</i>)-AHPPA

A flexible asymmetric approach to 5-alkyl tetramic acid derivatives is described, which is based on the use of <b>9</b> as the first synthetic equivalent to chiral nonracemic tetramic acid 5-carbanionic synthon <b>9b</b>. The existence of the carbanion intermediate <b>9b</b> was proven by trapping with trimethylchlorosilane. Application of the present method to the synthesis of antifungal alkaloid (+)-preussin, as well as protected (3<i>S</i>,4<i>S</i>)-AHPPA <b>6</b>, is also described.