Oximes synthetic utility

However, the stereochemistry of the oxime cannot be easily controlled and this may be a drawback for the synthetic utility of the Beckmann rearrangement. When a mixture of oximes is obtained from the ketone and when the isomerization of the oxime cannot be prevented during the rearrangement reaction, a mixture of amides is obtained. In other less favourable cases, the intended oxime cannot be obtained and the wrong amide will result from the rearrangement reaction. 

Amidation of W-BOC-tetrahydro-l,2-oxazine-6-carboxylic acid 47 with free oxanipecotic acid afforded amide 48 <2003TL3447>. The 3-methyl-substituted 1,2-oxazine Woxide 280 can be selectively transformed into 2-silyloxy-1,2-oxazines 281, upon treatment with silylating reagents (ClSiMe3). Now, the synthetic utility of 2-silyloxy-l,2-oxazine 281 is extended and it can be rearranged into 3-silyloxymethyl-l,2-oxazine 282 and can further react with morpholine to produce 3-morpholinomethyl-l,2-oxazine 283 which exists in a tautomeric equilibrium with the corresponding open-chain oxime <2003JOC9477>. 

All three compounds (WF6 and MoF6 are best) will bring about a reaction (not a fluorination) that may have synthetic utility at 0CC in l,l,2-trichloro-l,2,2-trifluoroethane (Freon 113) or chloroform they will cleave N,TV-dimethyl- and N-tosylhydrazones and oximes back to the parent carbonyl compounds12,14 (UF6 converts any first-formed aldehydes into acid fluorides1213). All three hexafluorides will convert1215 tertiary amines into carbonyl compounds and carboxylic acids into acid fluorides.16 They also dope polyacetylene to the metallic regime.17... 

Finally, as examples of similar types of reactions, photolytic treatment of O-acyl ester (D) of benzophenone oxime, A-acyloxy-phthalimide (E), and O-acyl ester (F) of A-hydroxy-2-pyridone with a mercury lamp generates the corresponding alkyl radicals via decarboxylation. However, these reactions can be used only for the alkylation of aromatics (solvents such as benzene) and reduction [86-89], so their synthetic utility is extremely limited. 

Although imidoyl iodides are chemically labile, their in situ generation from oxime derivatives with trimethylsilyl iodide or diethylaluminum iodide has been ascertained spectroscopically (equation 14). The synthetic utility of these reactive species has been demonstrated by further reacting them with external nucleophiles such as thiolates or Grignard reagents. For example, the imidoyl iodide (28), generated from acetophenone oxime carbonate with trimethylsilyl iodide, is further transformed to ethylthioimidate (29) and a-alkylated amine (30), respectively (Scheme 1 and equation 15). 

The resurgent interest in the synthetic utility of 1-nitro-alkenes is evidenced by the variety of recent reports concerning their preparation. " Thus, the dehydration of 2-nitro-alcohols with sodium hydride or dicyclohexylcarbo-di-imide, the dehydrohalogenation of a-halogeno-oximes, and the nitro-selenylation of alkenes followed by oxidative deselenylation all provide 1-nitro-alkenes in moderate to excellent yield. In particular, these methods are all applicable to the synthesis of conjugated cyclic nitro-alkenes and complement those procedures previously reported for the preparation of both cyclic and acyclic nitro-alkenes (Vol. 3, p. 175 Vol. 4, p. 183 Vol. 5, p. 196 Vol. 6, p. 208). 

Methylation of the thio-oxime gave the salt (83), and the structure of dehydromethionine was confirmed by. -ray analysis to be azasulphonium betaine (84). " The synthetic utility of iV-substituted sulphimides has been the subject of increasing attention. Photolysis of (85)" and thermolysis of (85)," (86)," and (87) afforded various types of heterocycles, as indicated in Scheme 4. Reactions of sulphimides (88) " " and (89)" " with 1,3-dipoles or activated multiple bonds provided novel routes to the indicated heterocycles. 

Since the discovery of the reaction, extensive investigations have disclosed that the photorearrangement is very general in acyclic l-aza-l,4-dienes (Scheme 34). The reaction was recently extended to P,y-oximes. Thus, the scope of this reaction for the synthetic utility has been considerably expanded. 

The 1-ADPM rearrangement and the alternative reaction modes of 1-substituted-1,4-dienes via radical-cation intermediates described above have an obvious mechanistic interest. However, the yield of products in these reactions is considerably lower than in the triplet-sensitized photoreactions of these compounds, with the exception of oxime ethers 39e and 40c therefore, the synthetic utility of these reactions is limited. However, this inconvenience can be overcome using alternative electron-acceptor sensitizers. Recent results show that replacing DCA by dicyanodurene (DCD) as an electron-acceptor sensitizer and biphenyl as a co-sensitizer, results in a considerable increase in the yields of 1-ADPM photoproducts.Thus, for example, DCA-sensitized irradiation of 39c, for 2.5 h, affords cyclopropane 41c in 15% yield, whereas using DCD as the sensitizer, this compound is obtained in 60% yield after... 

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>. 

Functionalization of the carbon radical resulting from cyclization of an aminium radical is an important step for synthetic chemists in order to obtain the desired product directly or to provide a handle for further transformations. Radical reactions of A-chloroalkenylamines (Section III,B) lead to /3-chloro pyrrolidines, which are prone to rearrangement to give piperidines. Reactions of N-nitroso alkenylamines lead to 8-nitroso pyrrolidines and, if an a-hydrogen is present, ultimately to oximes of aldehydes or ketones. Advantages of the latter transformation are the formation of stable substituted pyrrolidines and the utility of the oxime moiety in regard to further transformations. 

Nitro compounds are versatile synthetic intermediates which have found widespread utility in industrial applications. Aromatic nitro compounds are the usual starting materials for commercial applications, but aliphatic compounds exhibit a greater diversity of chemical behavior under reducing conditions. " Nitroso compounds, hydroxylamines, oximes, amines, nitrones, ketones and silyl nitronates are frequently encountered during the reduction of nitro compounds. Several specialized reviews have appeared which highlight the versatility of the nitro group in organic chemistry. ... 

Synthetic methods which utilize the addition of nucleophiles to a-halo oximes and similar compounds (the Hoch-Campbell reaction) have been reviewed. ... 

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