Issue Date: March 17, 2008
Revised Amination Skips Olefin Tether
Last year, M. Christina White's group at the University of Illinois, Urbana-Champaign, developed the first catalytic amination method for transforming an allylic C–H bond to a C–N bond, bypassing an oxygenation step formerly needed for such conversions (C&EN, June 4, 2007, page 7). The researchers overcame the low reactivity of the reaction's carbamate nucleophile by tethering it to the olefin being converted, restricting the method to intramolecular reactions. Now, in work that could speed small-molecule synthesis, White and graduate student Sean A. Reed have gone a step further and avoided the tether by developing an intermolecular version of the reaction (J. Am. Chem. Soc. 2008, 130, 3316). The amination (shown) directly converts a broad range of α-olefins to linear allylic amines with good yields and high regio- and stereoselectivities. The reaction uses two catalysts: a palladium sulfoxide complex for C–H cleavage and a chromium salen complex for amine functionalization. To demonstrate the reaction's advantages, White and Reed synthesized a conformationally restricted analog of the antibiotic deoxynegamycin. In that synthesis a nitrogen group was installed in just two steps from a commercial precursor. In contrast, the previous best method required oxygenation and took seven steps.
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