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DOI: 10.1039/A709291A (Paper) Reference Section for: J. Chem. Soc., Perkin Trans. 1, 1998, 1705-1714

Polyhalogenated heterocyclic compounds. Part 42.1 Fluorinated nitrogen heterocycles with unusual substitution patterns

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Richard D. Chambers, Christopher W. Hall, John Hutchinson and Ross W. Millar

Abstract

Reductive replacement of fluorine in 3,5-dichloro-2,4,6-trifluoropyridine 2a and pentafluoropyridine 2 using DIBAL and LAH leads to useful syntheses of fluoro and chlorofluoro pyridine derivatives. Replacement of fluorine by bromine using a mixture of HBr and AlBr3 is extremely efficient, giving excellent routes to 2,4,6-tribromo-3,5-difluoropyridine 3. Bromofluoro-pyrimidine and -quinoxaline derivatives have also been efficiently synthesised from perfluorinated precursors. Catalytic hydrogenation of bromofluoro heterocycles gives high yields of the corresponding fluorinated heterocycles.

Reactions of nucleophiles with 3 gives surprising results. Soft nucleophiles, e.g. PhSNa displace bromine whereas hard nucleophiles, e.g. MeONa, displace fluorine.

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