Abstract
The efficiency of the deprotocupration–aroylation of 2-chloropyridine using lithiocuprates prepared from CuX (X=Cl, Br) and LiTMP (TMP=2,2,6,6-tetramethylpiperidido, 2 equiv) was investigated. CuCl was identified as a more suitable copper source than CuBr for this purpose. Different diaryl ketones bearing a halogen at the 2 position of one of the aryl groups were synthesized in this way from azines and thiophenes. These were then involved in palladium-catalyzed ring closure: substrates underwent expected CH-activation-type arylation to afford fluorenone-type compounds, and were also subjected to cyclization reactions leading to xanthones, notably in the presence of oxygen-containing substituents or reagents.
Highlights
Due to the biological interest of azafluorenones, for example, in relation to their antifungal,[1] antimicrobial,[2] antimalarial,2b,3 and cytotoxic2b,4 properties, or else for their role in the treatment of neurodegenerative disorders,[5] many studies have been devoted to their synthesis
Applied to the synthesis of 2-chloro diaryl ketones, this method could be combined with direct arylation through CeH bond activation by intramolecular transition metal-catalysis,[11] to afford azafluorenones and related compounds
We have recently demonstrated the feasibility of this two-step access to such tricyclic heterocycles;[12] the details of our investigations, including the testing of a large range of substrates, and the unexpected outcomes observed for the cyclization reactions are described
Summary
Due to the biological interest of azafluorenones, for example, in relation to their antifungal,[1] antimicrobial,[2] antimalarial,2b,3 and cytotoxic2b,4 properties, or else for their role in the treatment of neurodegenerative disorders,[5] many studies have been devoted to their synthesis. Tetramethylpiperidido (LiTMP) bases for the deprotonative metallation of aromatic compounds,[9] we have developed the use of the lithiocuprates prepared in situ from CuCl and LiTMP (2 equiv).[10]. Applied to the synthesis of 2-chloro diaryl ketones, this method could be combined with direct arylation through CeH bond activation by intramolecular transition metal-catalysis,[11] to afford azafluorenones and related compounds. We have recently demonstrated the feasibility of this two-step access to such tricyclic heterocycles;[12] the details of our investigations, including the testing of a large range of substrates, and the unexpected outcomes observed for the cyclization reactions are described
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