Oximes with diazonium salts

Other classical synthetic approaches to 2-furanamine have failed, including the Curtius method and Beckmann rearrangement of 2-benzoylfuran oxime. However, hydrazinolysis of AT-(2-furyl)phthalimide, obtained from phthalimide and 2,5-dimethoxy-2,5-dihy-drofuran, gives 2-furanamine which was not isolated but detected by GLC-MS and H NMR spectroscopy. The latter reveals the absence of imino tautomers (75AP713). The chemistry of 2-dialkylamino-5-phenylfurans is typical of enamines protonation occurs on carbon to produce iminium salts. They are stable to base but afford 5-phenylfuran-2(3//)-one on hydrolysis with dilute acid. 2-Morpholino-5-phenylfuran couples with diazonium salts and affords Diels-Alder adducts with maleic anhydride and IV-phenylmaleimide (73JCS(P1)2523). 

There is only one previous comprehensive review of the electrophilic animation of carbanions 2 shorter reviews3 9 and reviews limited to particular reagents, substrates, or products have appeared animation with haloamines,10 sulfonylhydroxylamines,11 oxaziridines,12 oximes,13 diazonium salts,14,15 diazo compounds,16 activated azo compounds,17 azides,18-23 and nitridomanganese(V) reagents 24,25 animation of enolates 26-30 and the preparation of a-amino acids by electrophilic animation.31-34... 

Elimination of the hydroxyaminomethyl moiety from nitro oxime 15 by treatment with a diazonium salt gave hydrazone 43 (75LA1029) (Scheme 15). The same product was obtained by coupling the diazonium salt with the compound 16. On heating in aniline, oxime 15 was transformed into Schiff base 42. Acylation of the oxime 15 with benzoyl chloride in pyridine led to a mixture of furazan 44 and dinitrile 45. 

Diazonium salts react with oximes to give aryl oximes, which are easily hydrolyzed to aldehydes (R = H) or ketones." A copper sulfate-sodium sulfite catalyst is essential. In most cases higher yields (40-60%) are obtained when the reaction is used for aldehydes than for ketones. In another method for achieving the conversion ArNj —> ArCOR, diazonium salts are treated with R4Sn and CO with palladium acetate as catalyst. In a different kind of reaction, silyl enol ethers of aryl ketones, Ar C(OSiMe3)=CHR, react with sohd diazonium fluoroborates, ArNj BF4, to give ketones, ArCHRCOAr. " This is, in effect, an arylation of the aryl ketone. 

Reaction of diazonium salts with oximes, followed by hydrolysis... 

The cyclization of a-hydrazono oximes (635) with orthocarboxylates is an excellent way of preparing 1,2,4-triazine 4-oxides (636) (73TL1429,7lLA(750)12,77LA1713). Using aldehydes or ketones instead of orthoesters provides 2,3-dihydro derivatives (637 Scheme 22) (75S794). Cyclization of a-hydrazonocarboxamides (638) with carbonic acid derivatives such as ethyl chloroformate affords l,2,4-triazine-3,5-diones (639) (68M1808). The a-hydrazonocarboxamides (638) can be prepared by the reaction of diazonium salts with a-activated acetamides such as cyanoacetamide as shown. 

The nitro group is converted to versatile functionalities. A carbon-carbon double bond can be produced from nitroalkane by elimination of a nitro group with vicinal hydrogen as nitrous acid. The Nef reaction is also often used for transformation from nitroalkanes to ketones. The most useful chemical modification of a nitro group is the reduction furnishing oximes and amines, and further chemical conversion to various functionalities can be performed via diazonium salts. 

Coupling of aromatic diazonium salts with methazonic acid gives the oxime-hydrazones 79, which can be dehydrated by acid anhydride or acid chloride in alkali to 4-nitro-2/f-1,2,3-triazoles (80) (Scheme 18).70,71... 

Indoles have been prepared from reactions of o-aminophenylketones with reactive , or stable " arsonium ylides. Oxo-stabilized ylides reacted with 2-chloro-oximes to give trans-5-acyl-A -isoxazolines, and isoxazoles have been obtained from reactive arsonium ylides and a-isonitrosoketones, and from triphenylarsonium methylide and nitrile oxides The latter ylide reacts similarly with nitrile imines to give pyrazoles. With triphenylarsonium benzylides and benzoylylides,benzene diazonium salts give 1,3,4,6-substituted 1,4-dihydro-1,2,4,5-tetrazines in a reaction in which initial coupling of the reagents is followed by a dimerisation. ... 

The reagent reacts with a diazonium salt to form an oxime which on acid hydrolysis affords an aryl methyl ketone. ... 

As part of their study aimed at the synthesis of veratramine (XXVI) Johnson and collaborators have synthesized alcohol XLIV and ketone XLV. The latter was synthesized by the same procedure as its dihydro derivative XXXI. XLIV was prepared by the following route. The oxime XXXV was first converted into the acetyl derivative XLVI which was transformed, by Beckman rearrangement with phosphorus oxychloride in pyridine, into the acetamido compound XLVII. Alkaline hydrolysis of the latter afforded the amino alcohol XLVIII which was converted by reduction of the diazonium salt with zinc and ethanol into the alcohol XLIV 28, 34). 

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