An efficient and highly regioselective synthesis of isomeric 3-[1-substituted pyrazol-3(5)-yl]indoles has been developed by the acid-mediated regioselective cyclocondensation reaction of β-ethyltho-β-indolyl-α,β-unsaturated ketones and monosubstituted hydrazines. In the presence of 1 equivalent of AcOH in refluxing EtOH, the cyclocondensation reaction of β-ethyltho-β- indolyl-α,β-unsaturated ketones with monosubstituted hydrazines yielded 3-(1-substituted pyrazol-5-yl)indoles in excellent yields, while 3-(1-substituted pyrazol-3-yl)indoles were obtained in good yields when the cyclocondensation reaction was carried out in refluxing AcOH.
