3-Selective Halogenation of Pyridines via Zincke Imine Intermediates

06 July 2022, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Pyridine halogenation reactions are crucial for obtaining the vast array of derivatives required for drug and agrochemical development. Yet, despite more than a century of synthetic endeavors, there are no broadly applicable 3-selective halogenation processes that function directly from pyridine C–H precursors. We have developed a ring-opening, halogenation, ring-closing sequence that temporarily transforms pyridines into a reactive series of alkenes. These Zincke imine intermediates undergo highly regioselective halogenation reactions under mild conditions. Experimental and computational mechanistic studies indicate that the selectivity-determining step changes based on the halogen electrophile. Using this method, we formed a diverse set of 3-halopyridines and demonstrated late-stage halogenation of complex pharmaceuticals and agrochemicals.

Keywords

Pyridines
halogenation
regioselective
late-stage functionalization
Zincke
Ring-opening

Supplementary materials

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