Stereoselective Synthesis of<i>trans</i>-2,5-Disubstituted Tetrahydrofurans<i>via</i>the Lewis Acid Mediated Reduction of Cyclic Hemiketals with Triphenylsilane
An efficient method for the synthesis of trans-2,5-disubstituted tetrahydrofuran derivatives has been developed. Dithioacetal-functionalized cyclic hemiketals are reduced by triphenylsilane (Ph3SiH) in the presence of TiCl4 to afford the corresponding trans-2,5-disubstituted tetrahydrofuran derivatives in good yield and high stereoselectivity. Asymmetrical synthesis of (2S,5S) disubstituted tetrahydrofuran
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