[-] · C6H4KNO6S · Potassium o-Nitrobenzeneperoxysulfonate · (MW 257.28)
Solubility: sol MeCN, DMF.
Form Supplied in: not commercially available.
Preparative Methods: reactive intermediate (1) is generated in situ according to eq 1. Many experiments suggest that the reactive intermediate formed by mixing (3) and (4) is a radical;6 however, the existence of the anion (2) cannot be ruled out.
Handling, Storage, and Precautions: intermediate (1) cannot be stored, but is generated and reacted in situ. Reactions are carried out under dry argon atmosphere.
Alkenes are epoxidized under mild conditions in high yields by the peroxy intermediate (1); for example, see the preparation of epoxide (6) from (-)-carvone (5) (eq 2).
A solution of sulfonyl chloride (3) (0.22 g, 1.0 mmol) and (-)-carvone (5) (0.09 g, 0.6 mmol; MeCN, 2.0 mL) is added to a heterogeneous solution of KO2 (0.222 g; 3.0 mmol, MeCN, 1.0 mL) at -35 °C under dry argon atmosphere. After stirring at -35 °C for 4 h, the reaction mixture is concentrated and then extracted with CHCl3. The residue obtained after removal of solvent is purified by preparative TLC to furnish (6) in 83% yield.1
Epoxidation of cis-stilbene (7) by reaction with the intermediate (1) furnishes a 70:30 mixture of oxides (8) and (9); this reaction suggests that the reactive intermediate is a radical.2
Metal peroxides have low solubility in organic solvents and are usually used in the presence of crown ethers. KO2 is soluble enough in aprotic solvents such as MeCN and DMF; hence there is no need to use crown ether for preparing the intermediate according to eq 1.2
Certain arenes (acenaphthylene, phenanthrene, and pyrene) are readily oxidized to the corresponding arene oxides by the peroxy intermediate (1) generated from sulfonyl chloride (3) in polar aprotic solvents such as MeCN and DMF. Superoxide (4) is a strong base and reactions with (1) take place under mild and basic conditions. Acenaphthylene oxide (10) is unstable under acidic conditions but is more stable under basic conditions. Oxide (10) was obtained in 95% yield.2
The peroxy intermediate (1) generated from sulfonyl chloride (3) oxidized compounds containing benzylic methylene groups to ketones under mild conditions (-35 °C) (eq 3).3
Thiocarbonyl compounds such as substituted thioureas, thioamides, and thiocarbamates undergo oxidative desulfurization in high yields when reacted with the peroxy intermediate (1) under mild conditions (eq 4).4
Dialkyl, alkyl aryl, and diaryl sulfoxides are readily oxidized to sulfones in excellent yields under mild conditions (-30 °C) in MeCN by the peroxy intermediate (1). Oxidation of the unsaturated sulfoxide (11) was chemoselective; it furnished the sulfone (12) in 70% yield when reacted with (1) for 5 h. The double bond was not epoxidized.5 Similar chemoselective epoxidation has been carried out with only one other reagent (potassium hydrogen persulfate).7
The peroxy intermediate (1) is an excellent reagent for the synthesis of acid-sensitive benzylic epoxides from alkenes, the oxidation of benzylic CH2 to C=O, and the chemoselective oxidation of alkene sulfoxides to alkene sulfones. It is noteworthy that the reactions are carried out under mild conditions (-35 °C).
A. Somasekar Rao & H. Rama Mohan
Indian Institute of Chemical Technology, Hyderabad, India