Unexpected oxidation of a nitroxide alcohol with m-chloroperbenzoic acid

Abstract

Oxidation of 2,2,6,6-tetramethylpiperidin-4-01 forcing conditions, (2) becomes the principal product of the (la) with m-chloroperbenzoic acid in methylene chloride produces, in addition to the expected nitroxide (lb), varying amounts of 4-OXO-2, 2,6,6-tetramethylpiperidin-reaction (see Table ).

Synthesis and Reduction Kinetics of Sterically Shielded Pyrrolidine Nitroxides

“…15 However, we found that the major product was alcohol 8 , 16 which could be obtained in about 50% yield using a larger excess of Raney Ni. We expected that, under similar conditions for preparation of Tempone ( 16 ), 17 oxidation of 8 using m -CPBA would provide 10 . Instead, we obtained 9 , 16 which was then oxidized further with Dess–Martin periodinane (DMP) to give ketone-nitroxide 10 .…”

TEMPO-Catalyzed Oxidations of Alcohols Using m-CPBA: The Role of Halide Ions

“…Desirable characteristics of these oxidations include the use of 1 mol % or less of the catalyst and only 1 equiv of the bulk oxidant and good selectivity for primary alcohols. Many different bulk oxidants have been used in this reaction including m -CPBA, , sodium hypochlorite, N -chlorosuccinimide, sodium bromite, [bis(acetoxy)iodo]benzene, high-valent metal salts, and electrooxidation. , The TEMPO-bleach oxidation developed by Anelli is the most useful for large-scale oxidations, although it does not work well with unsaturated alcohols. Our interest was drawn to the TEMPO-catalyzed m -CPBA oxidations 2,3 when we observed an unprecedented racemization of a chiral nitroxyl radical under similar conditions .…”

“…The development of nitroxyl radical catalyzed peracid oxidations arose from Cella's report of an unexpected alcohol oxidation 2c. Cella found that the reaction was catalyzed by HCl and developed a convenient oxidation procedure using m -CPBA and 2,2,6,6-tetramethylpiperidinium hydrochloride (TMP·HCl) as the catalyst precursor 2a.…”

“…The development of nitroxyl radical catalyzed peracid oxidations arose from Cella's report of an unexpected alcohol oxidation 2c. Cella found that the reaction was catalyzed by HCl and developed a convenient oxidation procedure using m -CPBA and 2,2,6,6-tetramethylpiperidinium hydrochloride (TMP·HCl) as the catalyst precursor 2a. The HCl was reported to act as a general acid catalyst to facilitate the oxidation of the nitroxyl radical to an N -oxo ammonium salt, the ultimate oxidant in the catalytic cycle .…”

Nitroxide synthesis using the methyltrioxorhenium/hydrogen peroxide system

“…[22] bp 95ЊC/20 mm Hg. [23,24] 3-Carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl. The general procedure was followed using 0.173 g (1 mmol) of 4-oxo-2,2,6,6-tetramethylpiperidine.…”