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Synthesis of Dibenzo[g,p]chrysenes from Bis(biaryl)acetylenes via Sequential ICl-Induced Cyclization and Mizoroki−Heck Coupling

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posted on 23.11.2007, 00:00 by Chia-Wen Li, Cheng-I Wang, Hsin-Yi Liao, Rupsha Chaudhuri, Rai-Shung Liu
We report a facile synthesis of functionalized dibenzo[g,p]chrysenes via initial ICl-promoted cyclization of bis(biaryl)acetylenes, followed by the Mizoroki−Heck coupling reaction. This new approach works well for various bis(biaryl)acetylenes to afford dibenzo[g,p]chrysenes bearing various functionalities. With substrates of one special type including 4‘-methoxy-2-ethynylbiphenyls, we found that the ICl treatment led to ipso cyclization to give bicyclic spirocyclohexadienones. In the presence of MeOH/H2SO4, these spiroketone products undergo rearrangement to give 9-iodophenanthrenes through a selective 1,2-alkenyl migration. We prepared various 4‘-methoxy-2-ethynylbiphenyl compounds to show the generalization of such an ipso cyclization and 1,2-alkenyl shift. This ipso-cyclization approach can be extended to the preparation of dibenzo[g,p]chrysenes.