Reagents for oxidation

In a biotechnology-based approach, Japanese workers have reported on the microbial conversion of 2-methylnaphthalene to both 2-methyl-1-naphthol and menadione by Jiodococcus (64). The intermediate 2-methyl-1-naphthol can readily be converted to menadione by a variety of oxidizing agents such as heteropoly acids (65) and copper chloride (66). A review of reagents for oxidizing 2-methylnaphthalene and naphthol is available (67). 

The most widely used reagent for oxidation of alkenes to glycols is osmium tetroxide. Osmium tetroxide is a highly selective oxidant that gives glycols by a stereospecific syn addition.39 The reaction occurs through a cyclic osmate ester that is formed by a [3 + 2] cycloaddition.40... 

V-Sulfonyloxaziridines are useful reagents for oxidation of enolates to a-hydroxyketones.251 The best results are frequently achieved by using KHMDS to form the enolate. The hydroxylation occurs preferentially from the less hindered enolate face. 

Pd2+ salts are useful reagents for oxidation reactions of olefins. Formation of acetaldehyde from ethylene is the typical example. Another reaction is the formation of vinyl acetate by the reaction of ethylene with acetic acid (16, 17). The reaction of acetic acid with butadiene in the presence of PdCl2 and disodium hydrogen phosphate to give butadienyl acetate was briefly reported by Stem and Spector (110). However, 1-acetoxy-2-butene (49) and 3-acetoxy-l-butene (50) were obtained by Ishii and co-workers (111) by simple 1,2- and 1,4-additions using PdCl2/CuCl2 in acetic acid-water (9 1). 

Potassium persulfate, reagent for oxidation of o-iodobenzoic acid, 46, 107... 

OxidationThe rate of oxidation of alcohols with 1 can be markedly increased by addition of pyridine. In fact 1 in combination with pyridine is an excellent reagent for oxidation of 1,4-hydroquinones to the quinones. When used in the absence of pyridine, 1 can effect selective oxidation of benzylic alcohols in the presence of a secondary alcohol. 

A better reagent for oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HCl. 

Table 2 Reagents for Oxidative Cleavage of S-Protecting Groups 45-48 66 67 72 89 90 93-96 ...

TPAP is a standard reagent for oxidizing alcohols to aldehydes. It can be introduced either stoichiometrically or. as here, in catalytic amounts in combination with a cooxidant (NMO see Chapter 16). 

Imines and iminiums salts are oxidized by peracids into oxazidines and oxaziridinium ions, which are good reagents for oxidation of sulfides. The imine or iminium salt can, in principle,... 

Alkaline silver oxide is the most satisfactory reagent for oxidation of the aldehyde 3 to the acid 4.2 This reagent has been recommended for oxidation of aryl aldehydes (1,1012-1013), but only moderate yields have been reported for oxidation of a,/ -enals with Ag20.3 Apparently, the successful results in the oxidation of 3 are the result of the activating effect of the keto group. 

Oxidation of n-allylpalladiam chloride complexes. Snatzke s reagent is superior lo other chromium(VI) reagents for oxidation of steroidal tt-allylpalladium chloride complexes to a,/l-enones.1 Examples ... 

Oxidation of a,p-enals. Sodium chlorite is superior to other reagents for oxidation of oc,/l-unsaturated aldehydes to the corresponding carboxylic acid, particularly of aldehydes containing an ct-methylene group. In addition, the oxidation is stereospecific. 2-Methyl-2-butene2 was used as the chlorine scavenger. 

Bis(acetoxy)iodo]benzene (7, BAIB) can be used in combination with various reagents for oxidative additions to C,C-double bonds. Recent publications in this area are focused on C-N, C-O, C-S, C-Se, and C-X bond formation with emphasis on the co-introduction of non-equivalent heteroatom groups. The role of BAIB in such reactions is diverse, ranging from addition of the iodane to the double bond to the generation of iodine(III) and non-iodine(III) species that react with the olefinic substrates. 

Iodine(V) reagents such as Dess-Martin periodinane (DMP) and o-iodoxyben-zoic acid (IBX) are known as general reagents for oxidation of alcohols and have been utilized widely for natural product syntheses. Besides their general use for alcoholic oxidation, recently, the active studies on novel utilization of iodine( V) reagents such as DMP and IBX have been pursued mainly by Nicolaou and coworkers [26]. In particular, the versatile reactivities of anilides (62) with IBX or DMP are interesting and involve unprecedented features as follows. o-Imido-quinones (63) are prepared from 62 by the action of DMP and water. This reaction has been investigated extensively and was found to lead to p-quinones (64)... 

Oxidation of aldoses by hypoiodite can also be used for preparative purposes.7 Other types of halogen oxidants, especially A-halo compounds, are useful. For example, A -bromocarbamide was recommended by Kiss8 as a selective and convenient reagent for oxidizing benzylated sugars to their corresponding aldonolactones in yields exceeding 90%. Another example is the use of A-iodosuccinimide and tetrabutylammonium iodide.9... 

The oxidation to the enone was realized with catalytic amounts of tetra-n-propylammonium perruthenate (TPAP)21 (46), which is a mild oxidant for conversion of multifunctionalized alcohols to aldehydes or ketones. Catalytic TPAP oxidations are carried out in the presence of stoichiometric or excess A-methylmorpholine-A-oxide (NMO)22 (47) as cooxidant. Other common reagents for oxidation of alcohols are e.g. DMS0/C202C1223, Dess-Martin periodinane24, PCC25, PDC26 or the Jones reagent27. 

Problem 1 emphasizes reagents for oxidation and reduction. Problems 2-4, stress the selectivity of oxidations and reductions in reaction sequences. Syntheses of Problem 5 TMs require choosing specific reagents to achieve chemo-, stereo-, or enantioselective oxidations or reductions. 

Corey, E. J. and W. Suggs (1975) Pyridinium chlorochromate. An efficient reagent for oxidation of primary and secondary alcohols to carbonyl compounds. Tetrahedron Letters 16,2647-2650. 

Tab. 17.5 Standard Reagents for Oxidations in the Series Alcohol —> Aldehyde —> Carboxylic Acid and Alcohol —> Ketone...

P. Langer, Tetra-n-propyl Ammonium Perruthenate (TPAP) - An Efficient and Selective Reagent for Oxidation Reactions in Solution and on the Solid Phase, J. Prakt. Chem. 2000, 342, 728-730. 

A better reagent for the limited oxidation of primary alcohols to aldehydes is pyridinium chlorochromate (PCC), a complex of chromium trioxide with pyridine and HC1. PCC oxidizes most primary alcohols to aldehydes in excellent yields. Unlike most other oxidants, PCC is soluble in nonpolar solvents such as dichloromethane (CH2C12), which is an excellent solvent for most organic compounds. PCC can also serve as a mild reagent for oxidizing secondary alcohols to ketones. 

In the presence of 18-crown-6, potassium permanganate dissolves in benzene to give purple benzene, a useful reagent for oxidizing alkenes in an aprotic environment. Use a drawing of the complex to show why KMn04 dissolves in benzene and why the reactivity of the permanganate ion is enhanced. 

Sodium dichromate in sulfuric acid ( chromic acid, H2Cr04) is the traditional laboratory reagent for oxidizing secondary alcohols to ketones. Bleach (NaOCl) is an inexpensive, chromium-free alternative that also oxidizes secondary alcohols to ketones. Primary alcohols are usually over-oxidized to carboxylic acids under these conditions. 

Fig. 2-24. Preparation of D-glucuronic acid from D-glucose. The primary hydroxyl group at C-6 is selectively oxidized after protection of the anomeric center (see Fig. 2-17). The most useful reagent for oxidation is oxygen in the presence of platinum metal but potassium permanganate and dinitrogen tetroxide can also be applied.

TabU 21-1 Reagents for Oxidative Addition Reactions to Metal Complexes ... 

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