Directed Electrophilic Cyclizations: Efficient Methodology for the Synthesis of Fused Polycyclic Aromatics
摘要:
A versatile method for the synthesis of complex, fused polycyclic aromatic systems in high chemical 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 preparation of nonfused skeletal ring systems in yields consistently > 80%. The critical ring-forming step, which generally proceeds in very high to quantitative yield, utilizes 4-alkoxyphenylethynyl 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 aromatic structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepared utilizing this methodology. The scope of the described cross-coupling/cyclization chemistry including mechanistic insights and problematic side reactions are described.
Synthesis of Ethynyl-Substituted Quinquephenyls and Conversion to Extended Fused-Ring Structures
作者:Marc B. Goldfinger、Khushrav B. Crawford、Timothy M. Swager
DOI:10.1021/jo9721251
日期:1998.3.1
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.