Selective, Catalytic, and Dual C(sp3)-H Oxidation of Piperazines and Morpholines under Transition-Metal-Free Conditions.

By using cheap and innocuous reagents, such as NaClO2, NaOCl, and catalytic amounts of TEMPO, a new environmentally friendly protocol for the selective and catalytic TEMPO C(sp3)-H oxidation of piperazines and morpholines to 2,3-diketopiperazines (2,3-DKP) and 3-morpholinones (3-MPs), respectively, has been developed. This novel direct access to 2,3-DKP from piperazines provides significant advantages over the traditional N-monoacylation/intramolecular C-N cyclization procedure. Additionally, by modulating the amounts of TEMPO, 2-alkoxyamino-3-morpholinone can be prepared from morpholine derivatives, which would enable further functionalization at the C2 position of the morpholine skeleton.