Total Asymmetric Syntheses of β-Hydroxy-δ-lactones via Umpolung with Sulfur Dioxide

Cyclic stereotriads and stereotetrads of the β-hydroxy-δ-lactone type, e.g. prelactones B and E, common in polyketides and polypropionates, are prepared via SO2-induced oxyallylations of enoxysilanes with (1E,3Z)-1-(1-phenylethoxy)penta-1,3-dien-3-yl carboxylates. Using (Z)- or (E)-enoxysilanes both 4,5-cis- or 4,5-trans-δ-lactones are obtained. Depending on the reduction method applied to the obtained aldol intermediates 5,6-trans or 5,6-cis-derivatives are formed. The δ-lactones can be prepared in both their enantiomeric forms depending on the (1R)- or (1S)-configuration of the starting 1-(1-phenylethoxy)penta-1,3-dienes.

β-羟基-δ-内酯类环状立体三联体和立体四联体，例如预内酯B和E，常见于聚酮和聚丙酸酯中，通过二氧化硫诱导的氧代乙酰化法，利用(1E,3Z)-1-(1-苯基乙氧基)戊-1,3-二烯-3-基羧酸盐与烯氧硅烷进行制备。使用(Z)-或(E)-烯氧硅烷，可以同时获得4,5-顺式或4,5-反式δ-内酯。根据对获得的醛醇中间体5,6-转位或5,6-顺式衍生物所采用的还原方法，可以形成5,6-转位或5,6-顺式衍生物。δ-内酯可以根据起始1-(1-苯基乙氧基)戊-1,3-二烯的(1R)-或(1S)-构型，制备为其对映异构体形式。