Palladium-catalyzed cross-coupling reactions of pyridylboronic acids with heteroaryl halides bearing a primary amine group: synthesis of highly substituted bipyridines and pyrazinopyridines.
Amy E Thompson, Gregory Hughes, Andrei S Batsanov, Martin R Bryce, Paul R Parry, Brian Tarbit
Index: J. Org. Chem. 70 , 388, (2005)
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Abstract
A range of halogenated aromatics and heteroaromatics bearing a primary amine group are shown to be suitable substrates for Suzuki cross-coupling reactions with arylboronic acids and pyridylboronic acids under standard conditions, without the need for protection/deprotection steps. New amino-substituted arylpyridines, bipyridines, and pyrazinopyridines have thereby been obtained. Conditions for the efficient syntheses of 2-methoxy-5-pyridylboronic acid 1 and 2-methoxy-3-pyridylboronic acid 2 in ca. 75 g batches have been defined. A 2-fold reaction of 2-amino-5-bromopyrazine with 2,5-dimethoxy-1,4-benzenediboronic acid affords 1,4-dimethoxy-2,5-bis[2-(5-aminopyrazyl)]benzene 31. The X-ray crystal structures of 1 and 31.DMF are reported.