Synthesis of dibenzo[g,p]chrysenes from bis(biaryl)acetylenes via sequential ICl-induced cyclization and Mizoroki-Heck coupling

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.