A Facile Cascade Synthesis of 5,6-Diaryldibenzo[<i>a</i>,<i>e</i>]cyclooctenes from (<i>Z</i>,<i>Z</i>)-1-Aryl-3,5-octadiene-1,7-diynes<sup>†</sup>

Sequential treatment of (<i>Z</i>)-3-methyl-2-penten-4-ynal (<b>10</b>) with the allenylborane <b>2</b> and 2-aminoethanol furnished <b>11</b>. The use of <b>11</b> for cross-coupling with aryl iodides followed by the KH-induced syn elimination of the coupled adducts <b>13</b> provided easy access to a variety of dienediynes <b>14</b> for subsequent conversions to dibenzo[<i>a</i>,<i>e</i>]cyclooctenes (<i>sym</i>-dibenzocyclooctatetraenes) <b>17</b>. By cross-coupling with 1,2- and 1,4-diiodobenzene, it was possible to obtain <b>19</b> and <b>25</b> having two dienediynyl moieties. It was anticipated that the oligomers <b>21</b> and <b>26</b> containing multiple dibenzo[<i>a</i>,<i>e</i>]cyclooctenyl units could thus be synthesized. The <sup>1</sup>H NMR spectrum of <b>32</b> having three dibenzo[<i>a</i>,<i>e</i>]cyclooctenyl units indicates the presence of three diastereomers <b>32a</b>−<b>c</b> in a random statistical distribution of 2:1:1. Similarly, the <sup>1</sup>H NMR spectrum of <b>33</b> having two dibenzo[<i>a</i>,<i>e</i>]cyclooctenyl units exhibits signals that support the presence of two diastereomers <b>33a</b> and <b>33b</b> in a 1:1 ratio.