Twelve dibenzo- and naphtho- fluoranthenes were synthesized via a Pd-catalyzed arene-triflate intramolecular ring closing reaction. Our strategy involves the targeted coupling of naphtyl boronic acids with anthracenyl and phenanthrenyl bromides. Ring closings bridging the 9 and 1 positions of anthracene and phenanthrene proceed with complete regioselectivity and high yields, while those at the 1-4 positions rearranged via a single or double palladium migration pathway. All rearrangement products were positively identified and, where possible, the synthetic method was strategically modified to minimize the occurrence of undesired compounds. One instance of a double palladium migration was found to yield high regioselectivity as opposed to alternate methods which resulted in high amount of rearranged side product. All compounds were characterized via UV-Vis, fluorescence, cyclic voltammetry, and complete proton-carbon structural assignments with 2-dimensional NMR techniques, which show that small structural variations yield vast differences in physical properties between each structural isomer. This work provides a methodology for the synthesis of large fluoranthene PAHS by mix and matching strategically chosen smaller building units, as well as valuable insight into the rearrangement mechanisms inherent to the Pd-catalyzed arene triflate ring closing methodology.

Synthetic strategies relative to rearrangments featured in the palladium catalyzed arene-triflate ring closing reaction

255th National Meeting (2018)

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