Asymmetric Synthesis Using the Bis(2,4-dimethyl-3-pentyl)-(L)-tartrate Esters of Substituted Allylboronic Acids. Synthesis of α,β-Disubstituted Tetrahydropyrans and Tetrahydrofurans.

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Abstract
A highly useful application of allylboration for the synthesis of optically pure α,β-disubstituted tetrahydropyrans and tetrahydrofurans is described. The allylboronate esters 4, easily prepared by esterification of allylboronic acids 3 with bis(2,4-dimethyl-3-pentyl)-(L)-tartrate, readily undergo smooth reaction with representative aldehydes at -100 °C to afford the corresponding halohydrins 5. These are readily cyclized with sodium hydride in the presence of dimethyl sulfoxide to give the cyclic ethers 6 in good yields (70-80%) and in excellent enantiomeric excesses (83-98%).

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