Issue Date: August 12, 2013
Hooking Up With Heterocycles
Nitrogen-rich heterocyclic groups are often key components of drugs and other biologically active molecules. But because of their free N–H groups, appending these substituents usually requires tedious protection and deprotection steps. Now, researchers at MIT have gotten around those extra steps by developing a Suzuki-Miyaura cross-coupling of aryl boronic acids with unprotected, nitrogen-rich heterocyclic halides (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja4064469). Stephen L. Buchwald, M. Alexander Düfert, and Kelvin L. Billingsley came up with the transformation, which makes use of a palladium precatalyst to coax the hetereocyclic halide to react. The reaction (example shown) provides easy access to compounds containing indazole, benzimidazole, pyrazole, indole, oxindole, and azaindole groups. The MIT team used the cross-coupling in a two-step synthesis of a kinase inhibitor containing an indazole group. The researchers also investigated the mechanism of the reaction, concluding that transmetalation is the rate-determining step. Knowing this, the researchers note, should help chemists pick optimal conditions and reagent combinations.
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