Regeneration of carbonyl compounds

The regeneration of carbonyl compounds from 1,3-dithianes can be achieved using potassium hydrogen persulfate, Oxone , supported on wet alumina <96SL767> and by periodic acid under non-aqueous conditions <96TL4331>. The deprotection of benzyl substituted 1,3-dithianes can be achieved using the one electron oxidant [Fe(phen)3](PF6)3 <96SL315>. 

The regeneration of carbonyl compounds from dithioacetals and dithiolanes is often done with reagents that oxidize or otherwise activate the sulfur as a leaving... 

The quest for a solvent-free deprotection procedure has led to the use of relatively benign reagent, ammonium persulfate on silica, for regeneration of carbonyl compounds (Scheme 6.10) [48]. Neat oximes are simply mixed with solid supported reagent and the contents are irradiated in a MW oven to regenerate free aldehydes or ketones in a process that is applicable to both, aldoximes and ketoximes. The critical role of surface needs to be emphasized since the same reagent supported on clay surface delivers predominantly the Beckmann rearrangement products, the amides [49]. 

Regeneration of carbonyl compounds from the hydrazones (75-98%) [53] and from semicarbazones (55-90 %) [54] has also been achieved with bismuth trichloride. 

Regeneration of carbonyl compounds from 5-(2-pyridyl)-l,3-dioxanes [75] can be effected by A-methylation and treatment with a mild base. The picolyl carbon is a donor site, and the loss of a proton from that position is facile. 

Regeneration of carbonyl compounds from certain derivatives. Ketones can be recovered in satisfactory yield from the phenylhydrazones, p-nitrophenyl-hydrazones, tosylhydrazoncs, oximes, and semicarhazones by reaction with 1 equivalent of (C6H,Se0)20. 2,4-Dinilrophenylhydrazones and N,N-dimethyl-hydrazones arc inert under even rather vigorous conditions. The reagent can also be used to regenerate aldehydes from oximes or tosylhydrazones. 

A catalytic amount of hydrobromic acid with an excess of hydrogen peroxide is found to be an effective reagent for the facile regeneration of carbonyl compounds from their 1,3-dithiane and 1,3-dithiolane derivatives.136 Bromide-assisted oxidation of substituted phenols with hydrogen peroxide, catalysed by heterogenous WO42-ions, resulted in the formation of p-quinols and their ethers in almost quantitative yields.137... 

Corsaro, U. Chiacchio, V Pistara, Regeneration of Carbonyl Compounds from the Corresponding Oximes, Synthesis 2001, 1903-1931. 

Microwave-promoted selective regeneration of carbonyl compounds from oximes has been carried out using... 

Zinc dichromate tiihydrate, ZnCr207<3H20, is obtained as an orange-red solid by adding zinc carbonate to a cold solution of chromium trioxide in dilute sulfuric acid [660]. The applications are oxidations of acetylenes lo a-diketones, of aromatic hydrocarbons to quinones, of alcohols to aldehydes, and of ethers to esters and the oxidative regeneration of carbonyl compounds from their oximes [660]. 

Deoximation. Regeneration of carbonyl compounds by oxidation with the supported reagent is aided by microwave irradiation. 

The regeneration of carbonyl compounds from 4-benzenesulfonyl-methyl- 1,3-dioxolanes requires treatment with DBU in dichloromethane at room temperature only. Thus, the mild conditions are favorable to the use of such protecting device. 

Deoximation. Regeneration of carbonyl compounds from oximes by refluxing with Mn(OAc)j in benzene is quite efficient (11 examples, 86-96%). ... 

Regeneration of carbonyl compounds from tosylhydrazones. The rapid hydrolysis is carried out in methanol at room temperature (9 examples, 75-93%). 

Table 1 Reagents for Regeneration of Carbonyl Compounds from Ketone and Aldehyde Hydrazones...

Still another powerful method for the regeneration of carbonyl compounds from dialkylhydrazones is copper-catalyzed hydrolysis. The reagents that have been tested for this purpose are 2% aqueous cop-per(II) acetate solution at pH 4, copper(II) chloride in 0.05M phosphate buffer and 75% tetrahydrofu-ran/water, and copper(II) sulfate pentahydrate . Under the conditions of the hydrolysis, no reaction is observed in the absence of the copper(II) ion. Typical yields are 85-100%. Other functional groups like a-dicarbonyl, a-tricarbonyl, acetal and aldehydic formyl groups were not affected by this hydrolysis procedure. Nitrile formation in the case of aldehyde dimethylhydrazones was not a significant side reaction. However, reaction times ranged from 1 to 15 h. The reaction is believed to be nonoxidative in nature rather, the copper is believed to activate the C=N bond and catalyze hydrolysis. The dimethylhydrazine produced during hydrolysis also complexes irreversibly with the copper(II) ion to drive the reaction to completion. 

Regeneration of carbonyl compounds from the corresponding oximes 01S1903. 

Regeneration of Carbonyl Compounds from Oximes, Hydrazones, Semicarbazones, Acetals, 1,1-Diacetates, 1,3-Dithiolanes, 1,3-Dithianes, and 1,3-Oxathiolanes ... 

Regeneration of carbonyl compounds from oximes is accomplished by heating with iodine in MeCN, and a mild workup of the products from reduction of amides with bo-rane involves treatment with iodine. ... 

Chlorination. Amides and carbamates undergo iV-chlorination by NaCl-Oxone. Under the same conditions, oximes afford a-chloro nitroalkanes. - When the chlorine source is absent, regeneration of carbonyl compounds from oximes and hydrazones occurs. ... 

Regeneration of carbonyl compounds from p-toluenesulfonylhydrazones. Aldehydes and ketones can be regenerated from the p-toluenesulfonylhydrazones by treatment in acetone-methanol with excess NBS at 0-5°. Nitrogen is evolved rapidly sodium hydrogen sulfite is then added to suppress bromination. The dimethyl ketal is an intermediate. Yields are generally in the range 75-90% ... 

Regeneration of carbonyl compounds. Oximes, tosylhydrazones, and dithio-... 

Hydrolysis of dimethylhydrazones. The regeneration of carbonyl compounds is promoted by Pd(OAc),-SnCL. 

Thioacetals and ketals are important protecting groups used in organic manipulations. The regeneration of carbonyl compounds by cleavage of acid and base-stable thioacetals and thioketals is a challenging task. Cleavage of thioacetals normally requires use of toxic heavy metals such as Ti +, Hg, Ag, Tl +, or uncom-... 

Carbonyl compounds are also rapidly regenerated from the corresponding semi-carbazone and phenylhydrazone derivatives by use of montmorillonite KIO clay impregnated with ammonium persulfate (Scheme 8.16) [59]. Interestingly, the microwave or ultrasound irradiation techniques can be used in these solvent-free procedures. Microwave exposure achieves deprotection in minutes whereas ultrasound-promoted reactions require 1-3 h for regeneration of carbonyl compounds [59]. 

Altamura, A. Curci, R. Edwards, J.O. Facile regeneration of carbonyl compounds by oxidative cleavage of hydrazones using dioxiranes. J. Org. Chem. 1993, 58, 7289. 

The search for a solvent-free deprotection procedure has led to the use of the relatively benign reagent ammonium persulfate on silica, for regeneration of carbonyl compounds (Scheme 2.2-29) [93]. Neat oximes are simply admixed with the so-... 

Miscellaneous Reactions. In addition to the key reactions above, DDQ has been used for the oxidative removal of chromium, iron, and manganese from their complexes with arenes and for the oxidative formation of imidazoles and thiadia-zoles from acyclic precursors. Catal)ftic amounts of DDQ also offer a mild method for the oxidative regeneration of carbonyl compounds from acetals, which contrasts with their formation from diazo compounds on treatment with DDQ and methanol in nonpolar solvents. DDQ also provides effective catalysis for the tetrahydropyranylation of alcohols. Furthermore, the oxidation of chiral esters or amides of arylacetic acid by DDQ in acetic acid provides a mild procedure for the synthesis of chiral a-acetoxy derivatives, although the diastereoselectivity achieved so far is only 65-67%. ... 

AiT-Bromosuccinimide is the reagent of choice for the regeneration of carbonyl compounds from tosylhydrazones when preservation of stereochemical integrity at the a-position is important. 

Oximes, semicarbazones and carboxylic acid hydrazides are oxidatively cleaved in a synthetically useful method for the regeneration of carbonyl compounds and carboxylic acids (75). 

The regeneration of carbonyl compounds from dithioacetals and ketals is done best with reagents that oxidize or otherwise activate the sulfur as a leaving group and facilitate hydrolysis. Among the reagents that have been found effective are nitrous acid, -butyl hypochlorite, PhI(02CCF3)2, DDQ, SbCls, and cupric salts,... 

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