Directed Electrophilic Cyclizations: Efficient Methodology for the Synthesis of Fused Polycyclic Aromatics.

A versatile method for the synthesis of complex, fused, polycyclic, arom. systems in high chem. yield is described. Construction is achieved using a general two-step synthetic sequence. Pd-catalyzed Suzuki and Negishi type cross-coupling chemistries allow for the prepn. of non-fused skeletal ring systems in yields consistently >80%. The crit. ring-forming step, which generally proceeds in very high to quant. yield, utilizes (4-alkoxyphenyl)ethynyl groups and is induced by strong electrophiles such as trifluoroacetic acid and iodonium tetrafluoroborate. The reaction in essence produces phenanthrene moieties which are integrated into extended polycyclic arom. structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepd. by this methodol. The scope of the described cross-coupling/cyclization chem. including mechanistic insights and problematic side reactions are described. [on SciFinder(R)]