Oxidation of oximes

Conversion of carbonyl to nitro groups fretro Nef Reacdoni is tin importiint method for the preparadon of nitro compounds. Such conversion is generally effected vii oximes using strong oxidiints such as CF-vCOaH. 

Various convenient methods for the oxidadon of oximes to nitro compounds have beo) developed in recent years. Olah has reported a convenient oxidadon of oximes to nitro compounds v/ith soditun perborate in glaciid acedc acid fEq. 2.60.  

OxiddQon of oximes to rutro compounds with w-CPBA has been applied to the synthesis of dialkyl l-nitroalkanephosphonates fEq 2 63, which are useful reagents for d carbonyl compounds to nitroalkenes 

Tsible 2.6 PnpiirACian of palycydic niua campaunck Cram out 

Energedcdlly rich polynitro compounds hjve been prepared from polycyclic kelones by the nitro compounds, as shown In Table 2.6. 

Anhydrous peroxytrifluoroacetic acid is not easy to handle, but the procedure has recently been revised.121 Namely, reaction of urea-hydrogen peroxide complex (UHP) with tri-fluoroacetic anhydride in acetonitrile at 0 °C gives solutions of peroxytrifluoroacetic acid, which oxidize aldoximes to nitroalkanes in good yields (Eqs. 2.58 and 2.59). Ketoximes fail to react under these conditions, the parent ketone being recovered. 

The conversion of oximes to nitroalkanes has been achieved by employing an Mo(IV) oxodiperoxo complex as oxidant in acetonitrile. Both aldoximes and ketoximes are converted into the corresponding nitroalkanes (Eqs. 2.61 and 2.62),123 representing a complementary synthetic route to the use of the UHP method. 

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Oxidation of oximes or semicarbazones of saturated and a,/9-unsaturated aldehydes and ketones with DMSO/MesSiCl 14 results in high recoveries of the car-... 

Oxidation of oxime 422 with aqueous sodium hypochlorite has been used to synthesize the central piperidine ring of the tricyclic system 423 in moderate yield, which presumably proceeds via an intramolecular 1,3-diploar cycloaddition of the intermediate nitrile oxide (Equation 114) <2000EJ0645>. 

The oxidation of oxime 291 by MnC>2 gave two isomers 292 and 293 in approximately equal amounts with their ratio changing with time toward isomer 293 (Equation 58) <2001RCB874>. 

The nitrile oxide generated in situ by oxidation of oxime 325 gives the dimer 326 in 15% yield (Equation 72) <2001J(P1)415>. 

Direct oxidation of oximes is prospective promising procedure for the generation of nitrile oxides. Mercury(II) acetate (54), dimethyldioxirane (55), ceric... 

Synthesis of energetic polynitropolycycloalkanes via the oxidation of oximes with peroxytrifluoroacetic acid... 

Nitrile oxides, which are formed by dehydration of nitroalkanes or by oxidation of oximes with hypochlorite,87 88 are also useful 1,3-dipoles. They are highly reactive and must be generated in situ.ss They react with both alkenes and alkynes. Entry 5 in Scheme 6.5 is an example in which the cycloaddition product (an isoxazole) was eventually converted to a prostaglandin derivative. 

A more recent procedure recommends the careful exclusion of light during the oxidation of oximes with dry chlorine [52a, b]. 

The oxidation of oximes of oj//-perfluoroaldehydes with fuming nitric acid gives furoxane derivatives, e.g. the preparation of 3,4-bis(8//-hexadecafluoro)-l,2,5-oxadiazole (V-oxide (9).128 The conversion of ketone oximes to nitro compounds is of practical importance. Hexa-fluoroacetone oxime is transformed into l,l,l,3,3,3-hexafluoro-2-nitropropane (10) using dinitrogen pentoxide liberated in situ.249... 

Active manganese dioxide was used by Canonica in 19472 for the oxidation of oximes into nitrocompounds before the seminal publication of Ball et al. on the oxidation of vitamin A (76). Canonica prepared active manganese dioxide by reacting MnCb with KMn04. In fact the oxidation power of precipitated manganese dioxide is known since the 1870 s.3... 

The oxidation of oximes offers an attractively simple route to nitroalkanes from carbonyl compounds. The most effective reagent is pertrifluoroacetic acid in acetonitrile in the presence of sodium hydrogen carbonate as a buffer. Yields are improved by the addition of small quantities of urea to remove oxides of nitrogen. The reaction is illustrated by the conversion of dipropyl ketoxime into 4-nitroheptane (Expt 5.190). 

Oxidation of Oximes A different type of N-oxidation reaction involves the direct oxidation of oximes to nitro compounds. Although a variety of oxidizing agents have been described for this reaction, the use of non-heme iron-based systems is rather limited. In this context, the oxidation of the oxime group in tetrahydro-4H-pyrido[ 1,2-a]pyrimidines was carried out at room temperature in the presence of 50 mol% of Clayfen [K10 montmorillonite-supported iron(III) nitrate] (Scheme 3.45) [147]. Under these conditions the corresponding nitro derivatives were obtained in 32-35% yield. 1SN mass studies revealed that the reaction involved the direct oxidation of the hydroxyimino group. 

Kinetics and activation parameters for the oxidation of phenol with tetrakis(pyridine) cobalt(II) chromate have been determined.16 The oxidation of oximes of cyclopen-tanone, cyclohexanone, and cycloheptanone with pyridinium fluorochromate is first order each in the oxidant and oxime. The observed reactivity sequence has been rationalized on the basis of I-strain.17... 

A convenient method for the selective oxidation of oximes to carbonyl compounds using A-bromo-A-benzoyl-4-toluenesulfonamide is reported.172 A convenient method for the preparation of 2-phenylthio-3-bromopropene by bromination of allyl phenyl sulfide is shown to proceed via the formation of a l,3-dibromo-2-(phenylthio)propane intermediate.173... 

Oxidation of oxime 4.41 produces nitrile oxide 4.46 which cyclises to isoxazole 4.47. 

A nitro group may also be introduced by the oxidation of oximes. For this, salts of hypobromous acid are generally used. This method is sometimes applied for the preparation of aliphatic nitro compounds. The reaction proceeds in the following way (Forster [206], Cherkasova and Mehrikov [207], Iffland et al. [208]) ... 

The A(-oxidation of oximes leads to the formation of nd-nitro compounds. In a polar organic solvent such as acetonitrile these compounds are isomerized to nitro compounds (Scheme 26) and are thus protected from further oxidation. The reagent of choice is trifluoroperacetic acid. The oxidation of oximes derived from a-epoxy ketones results in the formation of a nitroalkene with opening of the epoxide, as illustrated in Scheme 27. ... 

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