Cobalt, the catalyst of choice: The diastereoselective cobalt-catalyzed cross-coupling of 1-bromo glycosides and aryl or vinyl Grignard reagents is described. A convenient and inexpensive catalyst, [Co(acac)(3)]/tmeda (acac = acetylacetonate, tmeda = N,N'-tetramethylethylenediamine), gives full α selectivity in the mannose and galactose series, and an α selectivity in the glucose series with α/β ratios of 1.3:1-3:1.
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