Decarboxylative Ipso Halogenation of Mercury(II) Pyridinecarboxylates. Facile Formation of 3-Iodo- and 3-Bromopyridines

Article abstract of DOI:10.1021/jo00167a027

Treatment of mercury(II) nicotinate with iodine and bromine in nitrobenzene at 180-185 deg C for 2 h afforded 3-iodo- and 3-bromopyridines in 44percent and 27percent yields, respectively, without any regioisomers and dihalopyridines.From mercury(II) picolinate only 2-3percent of 2-bromopyridine was obtained under similar reaction conditions, while the reaction using mercury(II) isonicotinate did not give any products.When a mixture of nicotinic acid and HgO was used in place of mercury(II) nicotinate, the halodecarboxylation occurred with similar ease.An ionic pathway involving the initial attack of electrophilic Hg(II) species on the ring-C bearing carboxyl group to afford a 3-pyridylmercury(II) compound and the subsequent replacement of the Hg(II) moiety by electrophilic iodine and bromine was proposed for this reaction.