A FACILE CASCADE SYNTHESIS OF 5,6-DIARYLDIBENZO[A,E]CYCLOOCTENES FROM(Z,Z)-1-ARYL-3,5-OCTADIENE-1,7-DIYNES

Sequential treatment of (Z)-3-methyI-2-penten-4-ynal (10) with the all enylborane 2 and 8-aminoethanol furnished II. The use of II for cross- coupling with aryl iodides followed by the KH-induced syn elimination of the coupled adducts 13 provided easy access to a variety of dienedi ynes 14 for subsequent conversions to dibenzo[a,e]cyclooctenes (sym-di benzocyclooctatetraenes) 17. By cross-coupling with 1,2- and 1,4-diiod obenzene, it was possible to obtain 19 and 25 having two dienediynyl m oieties. It was anticipated that the oligomers 21 and 26 containing mu ltiple dibenzo[a,e]cyclooctenyl units could thus be synthesized. The H -1 NMR spectrum of 32 having three dibenzo[a,e]cyclooctenyl units indi cates the presence of three diastereomers 32a-c in a random statistica l distribution of 2:1:1. Similarly, the H-1 NMR spectrum of 33 having two dibenzo[a,e]cyclooctenyl units exhibits signals that support the p resence of two diastereomers 33a and 33b ina 1:1 ratio.