A-hydroxy ketoximes

The Hoch-Campbell reaction of a-hydroxy ketoximes do not alter the course of the reaction although deprotonation probably took place concurrently for both the alcohol and the oxime. Treatment of oxime 40 afforded aziridine 42 in 30%, presumably via the intermediacy of azirine 41. a-Keto ketoximes would behave similarly to the a-hydroxy ketoximes in the Hoch-Campbell reaction after addition of the first equivalent of the Grignard reagent to the ketone. Therefore, the reaction between a-keto ketoxime 43 and phenylmagnesium bromide gave aziridine 45 in 41% yield, presumably via the intermediacy of azirine 44. 

Aldoximes are normally dehydrated by reaction with dichlorocarbene, produced under soliddiquid two-phase conditions, to yield nitriles in high yield [41, 42], whereas a-hydroxy ketoximes are cleaved with the simultaneous formation of a nitrile and either an aldehyde or ketone (Scheme 7.33). Yields are generally >70% and, in the case of cyclic hydroxy ketoximes, the products are acyclic oxo nitriles [43],... 

Further details of phase-transfer addition of dibromocarbene to a,(3-unsaturated esters and ketones [e.g. (18)] and subsequent reductive monode-bromination with tributyltin hydride (Vol. 7, p. 34) have been publishedJulia reports the use of solid NaOH-Et3NCH2Ph CP for the solid-liquid phase-transfer catalytic generation of dichlorocarbene (addition to a-pinene and limonene). Dichlorocarbene also provides a mild and efficient method for the Beckmann fragmentation of anh-a-hydroxy-ketoximes into aldehydes (or ketones) and nitriles [e.g. 2-exo-hydroxy-3-hydroxyiminobornane into (24 X = CHO, Y = CN)]. Trimethylsilylcyclopropanes are synthesized by adding the... 

Oximes and Related Derivatives.—Beckmann fragmentation of a-hydroxy-ketoximes occurred with dichlorocarbene. For example, a chloroform-ethyl acetate solution of the 5a-hydroxy-6-oximinocholestane (134) gave the keto-nitrile (135) with acqueous NaOH in the presence of benzyltriethylammonium chloride. Improved reduction of nitrimines to nitramines with NaBH4 and acetic acid has been reported and is exemplified by the conversion of the nitrimino-cholestane (136) into the 6 8-nitramino-compound (137). ... 

Cleavage of a-hydroxy ketoximes. a-Hydroxy ketoximes when treated with phosphonitrilic chloride (1) and pyridine undergo fragmentation to aldehydes or ketones and nitriles in high yield ... 

Certain ketoximes can be converted to nitriles by the action of proton or Lewis acids. Among these are oximes of a-diketones (illustrated above), a-keto acids, a-dialkylamino ketones, a-hydroxy ketones, p-keto ethers, and similar compounds. These are fragmentation reactions, analogous to 17-25 and 17-26. For example, ot-dialkylamino ketoximes also give amines and aldehydes or ketones besides nitriles. 

Aqueous NaOH (40%, 50 ml) and TEB A-Cl (0.50 g, 2.2 mmol) are added to the hydroxy ketoxime in CHCl, (l 00 ml) and EtOAc (100 ml). The precipitate, which forms immediately, slowly dissolves as the mixture is heated under reflux for 30 min. When the reaction is complete, as shown by TLC analysis, the organic phase is separated, washed with HCl (2M, 5 ml) and H20 (10 ml), dried (Na2S04), and evaporated to yield the cleavage products (70-80%), which can be purified by chromatography. 

Oxygenation of the dianion of a ketoxime by MoOPH (c/. Section 2.3.2.1.2) provides a-hydroxy ketones after hydrolysis, albeit in relatively low yield. The equivalent process for hydrazones was unsuc-essful, although it appears that this was a problem associated with manipulation of the products rather than an intrinsic failure of reaction. Indeed subsequent work with hydrazone anions has shown that the process is viable. 

CycHc ketones with functional groups at the a-position of the carbonyl moiety are easily cleaved into the corresponding dicarbonyl compounds. The most commonly used substrates are a-hydroxy ketones [283], a-diketones [284], a-halo [285], and a-ni-tro ketones [286]. 1,3-Diketones are oxidized to dicarboxyUc acids, and in this case loss of one carbon atom has been observed [287]. Ketone derivatives are also cleaved. For example, ketoximes afford unsaturated nitrile derivatives by Beckmann fragmentation (see Beckmann reaction, under Section 9.3.2.2). 

Nitroedianeundergoes base-catrilyzed addidon to to give3-hydroxy-l,3-dihydrofu]leryl ketoxime by way of a unique intramolecidar redox process, which is not observed in normal electron deficient alkenes fEq. S.77. " FSee Secdon 4.3 Michael addidon of nitroalkanes. ... 

In 1994, the scope of this p-hydroxy sulfoximine ligand was extended to the borane reduction of ketimine derivatives by these workers. The corresponding chiral amines were formed with enantioselectivities of up to 72% ee, as shown in Scheme 10.57. It was found that the A -substituent of the ketimine had a major influence on the asymmetric induction, with a ketoxime thioether (SPh) being the most successful substrate. 

Conversion of the keto ketoxime 1 to the exo-exo-amino alcohol 2 has been accomplished by hydrogenation over Adams catalyst and by reduction with lithium aluminum hydride. Amino alcohol 2 has also been prepared from 1 by a two-stage process in which selective reduction of the ketone is carried out with sodium borohydride, and the resultant hydroxy oxime is reduced with lithium aluminum hydride or by hydrogenation over Adams catalyst. ... 

Despite the isolation of O-vinyloximes from the products of reaction of ketoximes with acetylene, and the demonstration of their conversion to pyrroles by superbase KOH/DMSO (see Section IV.A), the suggested (81MI4) intermediate stages of this rearrangement long remained unproved. The intermediate 4//-2-hydroxy-2,3-dihydropyrroles (94) (Scheme 45) were first isolated by Trofimov et al. (83KGS276). 

The UV spectrum of the dihydropyrrole 94a contains two strong bands [A.max log(e)] 202 (4.37), 241 (4.0). Similar spectral characteristics are displayed by 4//-4-isopropyl-2-hydroxy-5-phenyl-2,3-dihydropyrrole (94b) obtained from isobutyl phenyl ketoxime (m.p., 133-134°C, yield 26%). When stored or heated, the dihydropyrrole 94b converts into 3-isopropyl-2-phenylpyrrole (95) with elimination of water. 

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