Surface-mediated reactions. 9. Selective oxidation of primary and secondary amines to hydroxylamines

OXONE over silicagel or, in some cases, alumina has been found to oxidize t he primary and secondary amines 3 selectively to the corresponding hydroxyl amines 4, in either the presence or absence of a solvent. Treatment of Boc- protected L-lysine (6) under the latter conditions afforded hydroxylamine 7 in excellent yield. The trialkylamine la and pyridine (Ib), in which selec tivity is not an issue, were readily oxidized to the corresponding oxides 2 by OXONE over silica gel or alumina, as well as by (CH3)(3)COOH over silic a gel. Solvent-free oxidation assisted by microwave irradiation was more fo rcing, while still affording the hydroxylamines 4 selectively, and is the s ynthetic method of choice. The mechanistic aspects of these reactions are d iscussed.