Synthesis of ethynyl-substituted quinquephenyls and conversion to extended fused-ring structures

An organometallic coupling, electrophile-induced cyclization strategy for the synthesis of p-terphenyl compounds has been extended to the synthesis of p-quinquephenyl systems. In this work we report the synthesis of various polycyclic aromatic systems containing nine annelated rings including the synthesis of functionalized polycyclic aromatic systems. An interesting side reaction which leads to an indenyl spiro ring system is also described. This side reaction can be suppressed by changing the electrophile (from H+ to I+) or by modification of the cyclization precursor. The UV-vis and fluorescence spectra of several of these polycyclic aromatics and the p-quinquephenyl precursors are also reported.