Ketoximes, deoximation

Scheme 6.11 Deoximation of ketoximes with silica-supported periodate.

A facile deoximation procedure with sodium periodate impregnated on moist silica (Scheme 6.11) has also been introduced that is applicable exclusively to ketoximes [50], Aldehydes have been regenerated from the corresponding bisulfites (85-98%) on KSF clay surface [51]. 

Oxidative deoximation/ Ketoximes revert to ketones by reaction with H,0, in an alkaline medium (75 95° yield, five examples). 

Ketoximes from some aromatic ketones (benzophenone and substituted acetophenones) underwent deoximation, at room temperature, in 65-80% yield [56]. 

The Cj p3-O bond of 2-tert-butoxy-furan and -thiophene is cleaved catalytically by BiCl3 or Bi(OTf)3 to produce 2(5H)-furanone and -thiophenone, respectively [254]. The selective hydrolysis of aryl esters is catalyzed by bismufh(III) mandelate in DMSO [255]. In the presence of 50 mol% Bi(NO3)3-5H2O, 10 mol% Cu(OAc)2, and Montmorillonite KIO ketoximes undergo facile deoximation in acetone-H2O [256]. Under microwave irradiation the BiCls-promoted hydrolytic cleavage of the C=N bond of dimethylhydrazines, tosylhydrazines, semicarbazones, and oximes proceeds in wet THF (Scheme 14.120) [257-259]. 

Conversion of ketoximes into ketones. Corey and Richman1 have reported a new procedure for regeneration of ketones from their oximes. The oxime is first converted into the O-acetate by treatment with acetic anhydride at 20° this derivative is then reductively deoximated by treatment with > 2 molar equivalents of chromous acetate in 9 1 THF-water at 25-65°. The reaction presumably involves reductive fission of the oxime N—O linkage to give an imine which is then rapidly hydrolyzed. Yields are in the range 75-85%. It is noteworthy that the reaction occurs more readily with acetoximes of conjugated ketones than with those of nonconjugated ketones and that the reaction occurs readily with acetoximes of hindered ketones such as camphor. 

Some polyfunctional isoxazolines of generic structure 44 were obtained in 78-91% yields by treatment of aryl aldoximes 42 with Baylis-Hillman adducts 43 in the presence of diacetoxy iodobenzene (DIB). The reaction is completely diastereoselective and involves the formation of nitrile oxides from aldoximes followed by 1,3-DC with the activated alkenes. Under the same conditions, ketoximes afforded only deoximation products <04TL7347>. 

This reductive dehydroxylation may be involved in deoximation by Fe(CO)s (2, 229-230). Thus treatment of methyl mesityl ketoxime (3) under the conditions used above gives the imine (4). In this case steric hindrance probably inhibits ready hydrolysis to the ketone. 

A variety of ketoximes 291, easily prepared from the corresponding ketones, undergo the Beckmann rearrangement upon treatment with 2,4,6-trichloro[l,3,5]triazine in A,A-dimethylformamide at room temperature in excellent yields (Equation 47). This method can be applied successfully on a large scale and no deoximation of the oximes to carbonyl compounds occurs. This procedure can be applied also to aldoximes for the preparation of the corresponding nitriles <2002JOC6272>. 

Ketoximes generally react with HTIB to afford the corresponding ketones as deoximation products [481]. However, the treatment of oximes of o-allyloxyacetophenones 396 with HTIB gives tricyclic products 397... 

An interesting stoichiometric oxidative cleavage reaction of an oxime with a palladium dioxygen complex has been observed [160]. The palladium dioxygen complex, [Pd(PPh3)2(02)] has been shown to rapidly deoximate a variety of ketoximes in benzene at 25 °C. The yield of ketone formed was 98%. A l -dipolar cycloaddition of the dioxygen complex to the ketoxime was proposed, equation (119). 

Decrease in the reaction temperature to 100 C and lower leads to deceleration of pyrrolization in comparison with rates of side processes, the most probable of which are prototropic isomerization of the bond in the initial ketoxime and partial deoximation. At 100°C (5 h), along with oxime of A -chloesten-3-one (isomer of A -cholesten-3-one), only traces of N-vinylpyrrolocholestene are detected in the reaction mixture OH NMR). When the temperature is raised above 120°C, a considerable amount of resin is formed that complicates isolation of the target pyrroles. 

Varma et al. (1999) reported that the role of the surface is critical since the same reagent supported on a clay surface delivers predominantly the Beckmann rearrangement products. They also observed a facile deoximation protocol with sodium periodate impregnated moist silica that is applicable exclusively to ketoximes (Varma et al., 1997). 

---