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

The asymmetric hydroboration of 1-cyclopentenol derivatives, such as ethers , acetate, silyl ether and borinate, was investigated using diisopinocamphe ylborane, (d)Ipc(2)BH. The product trialkylboranes were treated with excess df acetaldehyde to give the corresponding diethyl boronate esters. These b oronate esters on oxidation using alkaline hydrogen peroxide gave optically active trans-cyclopentane-1,2-diol derivatives in 50-85% enantiomeric exce ss and up to 95% overall yield. Some of the optically active trans-2-alkoxy cyclopentanols were converted by ether cleavage to optically active trans-( 1R,2R)-cyclopentane-1,2-diol. The asymmetric hydroboration-oxidation of 3-m ethoxy-2,5-dihydrofuran gave trans-(3R,4R)-4-methoxytetrahydrofuran-3-ol of 75% ee in 70% overall yield. (C) 1999 Elsevier Science S.A. All rights res erved.