Chiral synthesis via organoboranes. 45. Asymmetric hydroboration of 1-cyclopentenol derivatives using diisopinocampheylborane. Synthesis of optically active cyclopentane-1,2-diol derivatives of high optical purity

摘要

The asymmetric hydroboration of 1-cyclopentenol derivatives, such as ethers, acetate, silyl ether and borinate, was investigated using diisopinocampheylborane, ~dIpc_2BH. The product trialkylboranes were treated with excess of acetaldehyde to give the corresponding diethyl boronate esters. These boronate esters on oxidation using alkaline hydrogen peroxide gave optically active trans-cyclopentane-1,2-diol derivatives in 50-85% enantiomeric excess and up to 95% overall yield. Some of the optically active trans-2-alkoxycyclopentanols were converted by ether cleavage to optically active trans-(1R,2R)-cyclopentane-1,2-diol. The asymmetric hydroboration-oxidation of 3-methoxy-2,5-dihydrofuran gave trans-(3R,4R)-4-methoxytetrahydrofuran-3-ol of 75% ee in 70% overall yield.