Synthetic Applications of Oxone^®

Biographical Sketches

Wei He was born in Shaanxi, P. R. of China. She studied organic chemistry at Northwest University, Xi’an, P. R. of China, where she obtained her B.Sc. (1994) and M.Sc. (1999). She is currently pursuing her Ph.D. under the supervision of Prof. Sheng Yong Zhang at the School of Pharmacy, Fourth Military Medical University, Xi’an, P. R. of China. Her research interests include asymmetric catalysis, new synthetic methods for green chemistry and bioactive natural product synthesis.

Introduction

Oxone^® consists of 2KHSO₅ ^. KHSO₄ ^. K₂SO₄; its active component is potassium peroxymonosulfate (KHSO₅), a powerful oxidizing agent in synthetic organic chemistry which has proved to be a versatile reagent for various organic transformations. Oxone^® is commercially available and can be used immediately. Apart from its well-known applications as oxidizing agent in some transformations reviewed by Narsaiah, [1] it has found a number of other ­applications in synthetic chemistry in recent years, such as deprotection of functional groups, functional-group transformations, and cleavage of linker molecules from solid support. It has also shown wide potential in chiral ketone-catalysed asymmetric epoxidation of alkenes [2] leading to a variety of natural product skeletons, where its unique ­regioselective properties gave excellent results for the preparation of key intermediates.

Abstracts

(A) Oxidation of aldehydes to acids and esters: B. Borhan and coworkers [3] reported a highly efficient, mild and simple protocol for the oxidation of aldehydes to carboxylic acids using Oxone® as the sole oxidant. Direct conversion of aldehydes to their corresponding esters in alcoholic solvents was also reported, which was proved to be a valuable alternative to traditional metal-mediated oxidations.
(B) Oxidation of alkyl amines to nitroxides and hydroxylamines: Secondary amines were oxidized to the corresponding nitroxides with Oxone® in aqueous buffered solution at 0 °C and yields of 75-93% can be obtained for different substrates. [4] When Oxone® is supported on silica or alumina, primary and secondary amines can also be oxidized selectively to hydroxylamines in either the ­presence or absence of a solvent. [5]
(C) Oxidation of aromatic amines to nitro- or nitrosoarenes: Apart from oxidation to nitro compounds with Oxone® in 5-20% aqueous acetone and buffered sodium bicarbonate, [6] aromatic amines can also be oxidized to nitrosoarenes in CH2Cl2-H2O in good to excellent yields. [7]
(D) Oxidative cleavage of 1,3-dicarbonyls and alkynes to carboxylic acids: Using Oxone® as oxidizing agent, 1,3-dicarbonyls were transformed to carboxylic acids in good yield. [8] Also alkynes were transformed to carboxylic acids with ruthenium-catalyzed Oxone® oxidative cleavage. [9]
(E) Oxidation of unactivated C-H bonds: D. Yang and coworkers [10] have reported the intramolecular oxidation of unactivated C-H bonds by dioxiranes generated in situ. This method has been applied successfully for the construction of novel tetrahydropyran derivatives.
(F) Selective halogenation reaction: When using NaX combined with Oxone®, selective halogenation could be carried out effectively in some flavanones. [11]
(G) Deprotection of tert-butyldimethylsilyl ethers: G. Sabitha et al. [12] have reported an approach for the cleavage of tert-butyldimethylsilyl ethers by Oxone® in 50% aqueous methanol at room temperature. This method enables one to deprotect tert-butyldimethylsilyl ethers to yield primary alcohols in the ­presence of tert-butyldimethylsilyl ethers of secondary and tertiary alcohols and phenols, which could tolerate a wide variety of other functional groups. The silyl ethers of phenols were also deprotected after longer reaction times.
(H) Cleavage methodology for solid-phase synthesis: E. Petricci [13] et al. have developed an original and highly efficient Oxone® cleavage methodology for the solid-phase synthesis of substituted uracils.

References

• 1 Narsaiah AV. Synlett  2002,  1178 
• 2 Yang D. Acc. Chem. Res.  2004,  37:  497 
• 3 Travis BR. Sivakumar M. Hollist GO. Borhan B. Org. Lett.  2003,  5:  1031 
• 4 Brik ME. Tetrahedron Lett.  1995,  36:  5519 
• 5 Fields JD. Kropp PJ. J. Org. Chem.  2000,  65:  5937 
• 6 Webb KS. Seneviratne V. Tetrahedron Lett.  1995,  36:  2377 
• 7 Priewisch B. Ruck-Braun K. J. Org. Chem.  2005,  70:  2350 
• 8 Ashford SW. Grega KC. J. Org. Chem.  2001,  66:  1523 
• 9 Yang D. Chen F. Dong Z.-M. Zhang D.-W. J. Org. Chem.  2004,  69:  2221 
• 10 Wong M.-K. Chung N.-W. He L. Wang X.-C. Yan Z. Tang Y.-C. Yang D. J. Org. Chem.  2003,  68:  6321 
• 11 Bovicelli P. Bernini R. Antoniolettia R. Mincioneb E. Tetrahedron Lett.  2002,  43:  5563 
• 12 Sabitha G. Syamala M. Yadav JS. Org. Lett.  1999,  1:  1701 
• 13 Petricci E. Renzulli M. Radi M. Corelli F. Botta M. Tetrahedron Lett.  2002,  43:  9667