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Synthesis of Functionalized Pyridazin-3(2H)-ones via Bromine−Magnesium Exchange on Bromopyridazin-3(2H)-ones

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posted on 18.12.2009, 00:00 by Oxana Ryabtsova, Tom Verhelst, Mattijs Baeten, Christophe M. L. Vande Velde, Bert U. W. Maes
The potential of halogen−magnesium exchange reactions, followed by quenching with electrophiles, for the functionalization of the pyridazin-3(2H)-one core was investigated. 2-Benzyl-4-bromo-5-methoxy- (1), 2-benzyl-5-bromo-4-methoxy- (4), and 2-benzyl-4,5-dibromopyridazin-3(2H)-one (10) were selected as readily available model substrates. While 1 and 10 gave exclusively C-4 metalation, a tandem reaction involving nucleophilic substitution via addition elimination and bromine−magnesium exchange was observed with 4.