Strem is pleased to provide further advancement in Buchwald Palladacycle technology by offering a 4th generation as “N-methyl” analogues of the catalysts’ 2-aminobiphenyl moiety. Whereas the 2nd and 3rd generation Buchwald precatalysts fostered significant advances in organic syntheses and produced high yields with a wide variety of substrates, they were based on the 2-aminobiphenyl ligand. However, the primary amino group in the ligand can lead to synthetic limitations, especially in a pharmaceutical environment.
Upon activation of the catalyst, the 2-aminobiphenyl converts mainly into carbazole, a secondary amine that itself can serve as a substrate in the coupling reactions of amines with aryl halides. This side reaction can consume valuable starting material and lead to complications in purification. Buchwald 4th generation precatalysts based on N-methyl biphenyl will produce N-methylcarbazole upon activation, which cannot act as substrate in these types of reactions. Another drawback from 3rd generation precatalyst is remaining traces of 2-aminobiphenyl in the product. Aminobiphenyls have been associated with carcinogenicity (4-aminobiphenyl is a known carcinogen); therefore, its absence is desirable, especially in pharmaceutical syntheses.
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