Synthesis of azafluorenones and related compounds using deprotocupration–aroylation followed by intramolecular direct arylation
摘要:
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. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
4-Chloropyridine and 4,6-dïchloropyrimidine react regioselectively with lithium diisopropylamide to give 4-chloro-3-lithiopyridine and 4,6-dichloro-5-lithiopyrimidine, respectively. These intermediates react with benzaldehydes to give (4-chloro-3-pyridinyl) and 4,6-dichloro-5-pyrimidinyl)-arylmethanols which are oxidized to the corresponding ketones by chromium(VI) oxide in acetone. These compounds ran be nucleophilically substituted with ammonia or primary amines to give 4-amino-3-aroylpyridines or amino-5-aroylpyridines. The 3 aroyl-4-chloropyridines can also be easily converted into 3-aroyl-4(1H)-pyridinones.