RESUMO
Direct C-H fluorination is an efficient strategy to construct aromatic C-F bonds, but the cleavage of specific C-H bonds in the presence of other functional groups and the high barrier of C-F bond formation make the transformation challenging. Progress for the electrophilic fluorination of arenes has been reported, but a similar transformation for electron-deficient azaarenes has remained elusive due to the high energy of the corresponding Wheland intermediates. Nucleophilic fluorination of electron-deficient azaarenes is difficult owing to the identity of the Meisenheimer intermediate after fluoride attack, from which fluoride elimination to regenerate the substrate is favored over hydride elimination to form the product. Herein, we report a new concept for C-H nucleophilic fluorination without the formation of azaarene Meisenheimer intermediates through a chain process with an asynchronous concerted F--e--H+ transfer. The concerted nucleophilic aromatic substitution strategy allows for the first successful nucleophilic oxidative fluorination of quinolines.
RESUMO
In this work, we developed an efficient method for the rapid construction of fluoranthene skeleton to access a variety of substituted hydroxyfluoranthenes. The 1-iodo-8-alkynylnaphthalene derivatives, which serve as substrates for the key fluoranthene-forming step, were prepared via selective monoalkynylative Sonogashira reactions of 1,8-diiodonaphthalene. The domino reaction sequence which involves a sequential Suzuki-Miyaura coupling, an intramolecular Diels-Alder reaction, and an aromatization-driven ring-opening isomerization has been shown to give substituted hydroxyfluoranthenes in up to 92% yield. This work demonstrates the utility of designing new domino reactions for rapid access to substituted polycyclic aromatic hydrocarbons (PAHs).
