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9-Azabicyclo[3.3.1]nonane N-Oxyl, ABNO

9-Azabicyclo[3.3.1]nonane N-Oxyl (ABNO) is a less hindered nitroxyl radical, that exhibits an enhanced reactivity compared with TEMPO.

Recent Literature

Cu/TEMPO catalyst systems show reduced reactivity in aerobic oxidation of aliphatic and secondary alcohols. A catalyst system consisting of (MeObpy)CuOTf and ABNO mediates aerobic oxidation of primary, secondary allylic, benzylic, and aliphatic alcohols with nearly equal efficiency. The catalyst exhibits broad functional group compatibility, and most reactions are complete within 1 h at room temperature using ambient air as oxidant.
J. E. Steves, S. S. Stahl, J. Am. Chem. Soc., 2013, 135, 15742-15745.

The combination of Fe(NO3)39H2O and 9-azabicyclo[3.3.1]nonan-N-oxyl enables an efficient aerobic oxidation of a broad range of primary and secondary alcohols to the corresponding aldehydes and ketones at room temperature with ambient air as the oxidant.
L. Wang, S. Shang, G. Li, L. Ren, Y. Lv, S. Gao, J. Org. Chem., 2016, 81, 2189-2193.

A modular Cu/ABNO catalyst system enables efficient aerobic oxidative coupling of alcohols and amines to amides. All four permutations of benzylic/aliphatic alcohols and primary/secondary amines are viable in this reaction, enabling broad access to secondary and tertiary amides with excellent functional group compatibility within short reaction time at rt.
S. L. Zultanski, J. Zhao, S. S. Stahl, J. Am. Chem. Soc., 2016, 138, 6416-6419.

Cu/nitroxyl catalysts promote a highly efficient and selective aerobic oxidative lactonization of diols under mild reaction conditions using ambient air as the oxidant. A Cu/ABNO catalyst system shows excellent reactivity with symmetrical diols and hindered unsymmetrical diols, whereas a Cu/TEMPO catalyst system displays excellent chemo- and regioselectivity for the oxidation of less hindered unsymmetrical diols.
X. Xie, S. S. Stahl, J. Am. Chem. Soc., 2015, 137, 3767-3770.