Regioselective alkylation of phenol with cyclopentanol over montmorillonite K10: An efficient synthesis of 1-(2-cyclopentylphenoxy)-3-[(1,1-dimethylethyl)amino]propan-2-ol {(S)-penbutolol}

Regioselective alkylation of phenol with cyclopentanol is achieved over Mon tmorillonite K10 clay, producing 2-cyclopentylphenol, the key intermediate. The synthesis of optically active (S)-penbutolol 1, an important antihyper tensive drug, is realized in 5 steps from 2-cyclopentylphenol by employing Sharpless asymmetric dihydroxylation.