Research Article

Heterobiaryl synthesis by contractive C–C coupling via P(V) intermediates

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Science  16 Nov 2018:
Vol. 362, Issue 6416, pp. 799-804
DOI: 10.1126/science.aas8961

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Heterocycles meet and marry on phosphorus

Metals such as palladium are routinely used to link together carbon rings in pharmaceutical synthesis. However, the presence of nitrogen in both rings can trip up this process. Hilton et al. report a versatile alternative process in which phosphorus takes the place of the metal. The phosphorus binds successively to both rings at the sites opposite the nitrogen, and treatment with acidic ethanol then pushes them off, bound to each other. Theory implicates a five-coordinate phosphorus intermediate that kinetically favors coupling of the two nitrogen-bearing rings over reactions of the other all-carbon substituents.

Science, this issue p. 799

Abstract

Heterobiaryls composed of pyridine and diazine rings are key components of pharmaceuticals and are often central to pharmacological function. We present an alternative approach to metal-catalyzed cross-coupling to make heterobiaryls using contractive phosphorus C–C couplings, also termed phosphorus ligand coupling reactions. The process starts by regioselective phosphorus substitution of the C–H bonds para to nitrogen in two successive heterocycles; ligand coupling is then triggered via acidic alcohol solutions to form the heterobiaryl bond. Mechanistic studies imply that ligand coupling is an asynchronous process involving migration of one heterocycle to the ipso position of the other around a central pentacoordinate P(V) atom. The strategy can be applied to complex drug-like molecules containing multiple reactive sites and polar functional groups, and also enables convergent coupling of drug fragments and late-stage heteroarylation of pharmaceuticals.

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