Condensation reactions of indole with acetophenones affording mixtures of 3,3-(1-phenylethane-1,1-diyl)bis(1<i>H</i>-indoles) and 1,2,3,4-tetrahydro-3-(1<i>H</i>-indol-3-yl)-1-methyl-1,3-diphenylcyclopent[<i>b</i>]indoles

<p>Condensation of indole <b>1a</b> with eight acetophenones <b>8a–h</b> in ethanolic HCl afforded the corresponding mixtures of condensation products: 3,3-(1-phenylethane-1,1-diyl)bis(1<i>H</i>-indoles) <b>11a–h</b> (2:1 condensation of indole:acetophenone, –H₂O) and diastereomers of substituted 1,2,3,4-tetrahydro-3-(1<i>H</i>-indol-3-yl)-1-methyl-1,3-diphenylcyclopent[<i>b</i>]indoles <b>12a–h</b> and <b>13a–h</b> (2:2 condensation of indole:acetophenone, –2H₂O). Each mixture was analyzed by ¹H NMR. The use of substituted electron-withdrawing acetophenones favored formation of 2:1 condensation products, whereas the use of substituted electron-donating acetophenones favored formation of 2:2 condensation products. Increased reaction temperature gave higher 2:2 condensation yields, but temperatures above 40 °C were unfavorable, giving complex, tarry mixtures.</p