- Multi-substituted heterocycles
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Pentafluoropyridine was used as the starting material for the preparation of a range of pyridine derivatives that bear five different substituents. In this context, syntheses of penta-functional pyridine systems by sequences of nucleophilic aromatic substitution, palladium catalysed coupling and bromo-lithiation processes are described.
- Benmansour,Chambers,Hoskin,Sandford
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p. 133 - 137
(2007/10/03)
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- Polyhalogenated heterocyclic compounds. Part 42. Fluorinated nitrogen heterocycles with unusual substitution patterns
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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. British Crown Copyright 1998, Defence Evaluation and Research Agency. Published by the Royal Society of Chemistry with the permission of the controller of Her Britannic Majesty's Stationery Office.
- Chambers, Richard D.,Hall, Christopher W.,Hutchinson, John,Millar, Ross W.
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p. 1705 - 1713
(2007/10/03)
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