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DOI: 10.1055/s-2008-1078626
Pd-Catalyzed ortho Halogenation of C-H Bonds
Contributor(s):Paul Knochel, Andreas J. WagnerThe Scripps Research Institute, La Jolla and Brandeis University, Waltham, USA
PdII-Catalyzed Monoselective ortho Halogenation of C-H Bonds Assisted by Counter Cations: A Complementary Method to Directed ortho Lithiation
Angew. Chem. Int. Ed. 2008, 47: 5215-5219
Publication History
Publication Date:
22 August 2008 (online)
Key words
C-H activation - chemoselectivity - counter cations - ortho halogenation - palladium
Significance
The study shows a new catalytic method for the ortho halogenation of arylcarboxylic acids without the need for a nitrogen-containing directing group. Tetraalkylammonium cations as well as organic and inorganic bases such as DBU or DABCO are effective in promoting the C-H activation and enhance the monoselectivity of the halogenation.
Comment
Both dihalogenation as well as selective monohalogenation of carboxylic acid salts are enabled by this protocol. The scope and site selectivity of the reaction are complementary to those of the widely used directed ortho metalation (DoM). The large tetraalkylammonium cations appear to prevent dihalogenation by assisting in the displacement of the monohalogenated product from the Pd center.