Stereocontrolled 1,4-Asymmetric Reduction of Cyclic Hemiketals. Synthesis of Both<i>anti</i>and<i>syn</i>-1,4-Diols, and Their Transformations into<i>trans</i>-and<i>cis</i>-2,5-Disubstituted Tetrahydrofurans
Reduction of dithioacetal-functionalized cyclic hemiketals with LiAlH4 in THF and NaBH4 in ethanol gave the corresponding anti- and syn-1,4-diols with excellent Stereoselectivity, respectively. The anti- and syn-1,4-diols were easily transformed into trans- and cis-2,5-disubstituted tetrahydrofurans with complete stereospecificity by the one-step cyclodehydration with p-TsCl in pyridine, respectively