Of keto oximes

The furo- and pyranobenzopyranones 114 and 115 are prepared by the reaction of 0-enolate of i(-keto lactone 113[132], The isoxazolc 117 is obtained by the oxidation of the oxime 116 of a, /3- or, d, 7-unsaturated ketones with PdCh and Na2C03 in dichloromethane[l 33], but the pyridine 118 is formed with PdCl2(Ph3P)2 and sodium phenoxide[134]. 

This transformation can also be carried out under solvent-free conditions in a domestic oven using acidic alumina and ammoniiun acetate, with or without a primary amine, to give 2,4,5-trisubstituted or 1,2,4,5-tetrasubstituted imidazoles, respectively (Scheme 15A) [69]. The automated microwave-assisted synthesis of a library of 2,4,5-triarylimidazoles from the corresponding keto-oxime has been carried out by irradiation at 200 ° C in acetic acid in the presence of ammonium acetate (Scheme 15B) [70]. Under these conditions, thermally induced in situ N - O reduction occurs upon microwave irradiation, to give a diverse set of trisubstituted imidazoles in moderate yield. Parallel synthesis of a 24-membered library of substituted 4(5)-sulfanyl-lff-imidazoles 40 has been achieved by adding an alkyl bromide and base to the reaction of a 2-oxo-thioacetamide, aldehyde and ammonium acetate (Scheme 15C) [71]. Under microwave-assisted conditions, library generation time was dramatically re-... 

Indium-mediated allylation reactions of a-keto imides derived from Oppolzer s sultam proceeded in aqueous THF in good yields and excellent diastereoselectivity (Eq. 11.43).74 The indium-mediated allylation of the Oppolzer camphorsultam derivatives of glyoxylic oxime ether... 

The scope and efficiency of [4+2] cycloaddition reactions used for the synthesis of pyridines continue to improve. Recently, the collection of dienes participating in aza-Diels Alder reactions has expanded to include 3-phosphinyl-l-aza-l,3-butadienes, 3-azatrienes, and l,3-bis(trimethylsiloxy)buta-l, 3-dienes (1,3-bis silyl enol ethers), which form phosphorylated, vinyl-substituted, and 2-(arylsulfonyl)-4-hydroxypyridines, respectively <06T1095 06T7661 06S2551>. In addition, efforts to improve the synthetic efficiency have been notable, as illustrated with the use of microwave technology. As shown below, a synthesis of highly functionalized pyridine 14 from 3-siloxy-l-aza-1,3-butadiene 15 (conveniently prepared from p-keto oxime 16) and electron-deficient acetylenes utilizes microwave irradiation to reduce reaction times and improve yields <06T5454>. 

A closely related protocol for the synthesis of imidazoles was independently investigated by Sparks and Combs (Scheme 6.199) [362]. Here, the authors employed readily available unsymmetrical keto-oximes as building blocks, initially leading to N-hydroxyimidazoles. Diaryl keto-oximes were condensed with various aldehydes (1.1 equivalents) in the presence of 4 equivalents of ammonium acetate under microwave conditions at 160 °C. In this way, the N-hydroxyimidazoles were formed... 

Scheme 6.199 Preparation of imidazoles from keto-oximes.

Reduction of oximino esters, i.e. oximes of keto esters, is very useful for the preparation of amino esters. Reductions are very selective since the oximes are easily reduced by catalytic hydrogenation over 10% palladium on carbon in ethanol (yield 78-82%) I094, by aluminum amalgam in ether (yields 52-87%) [750, 70P5], or by zinc dust in acetic acid (yield 77-78%). None of these reagents attacks the ester group. The last mentioned reaction gives an N-acetyl derivative [1096. ... 

Selective reduction of the nitrile group in 87% yield without the reduction of the carbonyl was achieved by stannous chloride [1153]. Oximes of keto nitriles are reduced preferentially at the oximino group by catalytic hydrogenation in acetic anhydride over 5% platinum on carbon (yield 85%)... 

Fluoride ion catalyzed 1,3-dipolar cycloaddition of bromo nitrile oxide, obtained in situ from dibromoformaldehyde oxime 184, to nonactivated alkynes provides a new approach to the synthesis of neuroactive isoxazoles. However, the regioselectivity of cycloaddition in this case is not high—products 185 and 186 are obtained in a 1 1 to 1 1.4 ratio (equation 80). Cycloaddition reaction of hydroximoyl chlorides and acetylene was snc-cessfully carried out also in the presence of NaHCOs as a base. For instance, a-keto oximes 187 were reacted with acetylene and NaHCOs to give isoxazoles 188 in good yields (equation 81). 

Oxadiazole to furazan transformations are not limited to the oximes of keto substituents amidoximes and hydrazidoximes <92KGS969> also rearrange readily. For example, Z)-N,N,-6is-ubstituted amidoximes of l,2,4-oxadiazole-3-carboxylic acids on treatment with acid isomerize even at room temperature to the thermodynamically more stable (F)-isomers, which then rearrange to diaminofurazans <91KGS822>. 

One attractive possibility is the use of the a-keto-oxime chromophore. It has a strong absorption at 220 nm whose tail, which extends to 240-250 nm, would improve the absorption characteristics of PMMA. Also, the esters possess a N-O bond which is photochemically labile yet sufficiently thermally stable so as to be compatible with the various processing steps. The solution degradation of a-keto oximino methacrylate esters upon irradiation with light of X365 nm has been reported by Delz-enne (2), and we proceeded to investigate the solid state photodegradation of similar copolymers and their possible utility as deep UV photoresists. 

In an effort to improve PMMA s photosensitivity further, methyl methacrylate has been copolymerized with higher percentages of the a-keto-oxime methacrylate and terpolymerized with varying amounts of methacrylonitrile. The resulting effects on resist properties, e.g., sensitivity, contrast and resolution, and plasma resistance, are reported here. The terpolymers are up to 85 times more sensitive than PMMA, and retain its high resolution characteristics. 

A representative sample of terpolymers was exposed to a variety of etchants for polysilicon and silicon dioxide, and the results are given in Table V. The ratio of the etch rate of the substrate to the etch rate of the resist must be at least 2 1 for the resist to be a viable etch mask. Inspection of Table V, shows that the materials examined are unacceptable for only the QFj — CF3CI (4 1) plasma. The etch rates are comparable to those for PMMA the a-keto-oxime exhibits essentially no effect on that rate and the nitrile affords a slight decrease in the plasma etch rate. The etch rates of some commercially available materials are shown for comparison. 

Reaction of DAMN with x-Keto Aldehydes, a-Keto Oximes, and x-Diketones... 

Hydroxydihydro-l,2-oxazines (20) are in equilibrium with the corresponding open-chain keto oximes (21) (70T1315), and a related tautomerism is exhibited by certain TV-oxides (22), the seco forms (23) of which are nitronic acids (78TL2339). 

The kinetics of oxidative deoximation of aldo- and keto-oximes by 2,2/-bipyridinium chlorochromate (back to the parent carbonyl compounds) have been studied in DMSO, where the reaction is found to be first order in both oxime and oxidant.89 The aldoximes proved more reactive, and rates correlated well with the Pavelich-Taft dual substituent equation. Following extension of the study to hindered cases, and to 18 other solvents (analysed by Taft and Swain multi-parametrics), a cyclic intermediate is proposed for the rate-determining step. The same reaction order behaviour is found using the pyridinium version, and again electronic, steric, and solvent effects were examined.90... 

Activation of the Beckmann rearrangement of the enantiopure spirocyclic keto oximes (—)-(12) and (—)-(13) has been initiated with four acidic promoters.17 In two cases (PPE and PPSE), concerted [1,2]-shift of the anti carbon operates exclusively. This is not the case with PPA or Eaton s reagent, although optical activity is fully maintained in these ring expansions. 

Benzoin 23 could be used instead of benzil 22, provided that the microwave-assisted cyclocondensation is performed on inorganic support (silica gel or alumina) under solvent-free conditions [40]. A related diversity-oriented approach towards imidazoles utilized the cyclocondensation of unsymmetrical keto-oximes with aldehydes in the presence of NH4OAc [41] (Scheme 16). Hydroxyimidazoles 24 were formed in the cyclization step and... 

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