Parent Carbonyl Compounds Research Articles

Oxidative removal of 1,3-dithiane protecting groups by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ)

A number of 1,3-dithianes have been efficiently converted into the parent carbonyl compounds in good yields by treatment with 1.5 equiv. of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in MeCN–H2O (9:1). The reactions of 2-aryl-substituted 1,3-dithianes bearing electron-donating groups on the benzene ring with DDQ afforded thioesters along with aldehydes. 1,3-Dithiolanes derived from aromatic aldehydes were transformed to thioesters, whereas 1,3-dithiolanes derived from aliphatic and aromatic ketones were stable under these reaction conditions. Diphenyl dithioacetals were stable except for 4-methoxy- and 3,4-dimethoxy-benzaldehyde diphenyl dithioacetals which gave the corresponding aldehydes. Selective cleavage reactions of 1,3-dithiane in the presence of 1,3-dithiolane or diphenyl dithioacetal have been investigated.

Cleavage of Acetals Promoted by Copper (II) Sulphate Adsorbed on Silica Gel

Abstract Copper sulphate supported on silica gel promotes the easy removal of cyclic acetals and tetrahydropyranyl ethers to give the respective parent carbonyl and hydroxyl compounds.

Characterization of 1,3‐dioxolanes upon positive‐ion chemical ionization

AbstractPositive‐ion chemical ionization (CI) mass fragmentations were studied in the case of different 1,3‐dioxolanes. The formation in methane CI mass spectra of interesting fragment ions allowing the characterization of their parent carbonyl compounds and diols is discussed and some mechanisms (supported by D2O CI analyses) are proposed in order to explain these fragmentations.

Deoximation of Oximes, Sodium Oximates, and O-Benzoyloximes with Copper (II) Chloride Dihydrate

Abstract Oximes, O-benzoyloximes and sodium salt of aldoximes and ketoximes were deoximated to their parent carbonyl compounds with copper (II) chloride dihydrate in acetonitrile as well as water. This method works well with both aldoximes and ketoximes without any risk of overoxidation in the former case. In addition, sensitive groups like ester, acetamido, isolated as well as conjugated carbon-carbon double bond and phenolic and ether linkages could survive the reaction conditions. The yields and reaction rates were increased in case of aromatic oximes when the reaction was carried out in aqueous acetonitrile. A novel deoximation procedure using sodium oximate which showed considerable rate enhancement over that of oximes, and tolerance to hydrolytically labile ester and amide groups is also described.

A new entry for the deprotection of monothioacetals and dithioacetals: Silver nitrite - iodine system

A new reagent system (silver nitrite-iodine) was developed for demonothioacetalization and dedithioacetalization reactions. The reaction using this reagent afforded the parent carbonyl compound in excellent yield under mild conditions.

Efficient hydrolysis of dithioacetals by the N-fluoro-2,4,6-trimethylpyridinium triflate-water system

Dithioacetals including 1,3-dithianes and 1,3-dithiolanes are efficiently cleaved by the title reagent system to the parent carbonyl compounds. The cleavage of diprotected symmetrical α-diketones and p-phenylenediketones gives monoketones in good yields. Amide, 1,3-dioxolane, disulfide, ester, ether, hydroxy, nitrile, nitro, and sulfide functions are relatively stable under the cleavage conditions but thiols are oxidized to disulfides.

Synthesis of functionalized nitroalkanes by oxidation of oximes with urea-hydrogen peroxide complex and trifluoroacetic anhydride

Reaction of urea-hydrogen peroxide complex with trifluoroacetic anhydride in acetonitrile at 0°C affords in a safe and easy fashion anhydrous solutions of peroxytrifluoroacetic acid. These can be used to oxidize aldoximes to nitroalkanes in good yields. Ketoximes fail to react in these conditions and are cleaved to the parent carbonyl compounds.

Co(salen) catalyzed oxidation of oximes with t-butyl hydroperoxide

Co(salen) catalyzed the oxidation of oximes with t-butyl hydroperoxide to give the parent carbonyl compounds, providing a new convenient route to deoximation reaction. A plausible mechanism involves a substrate radical intermediate.

Gallium Chloride-Mediated Hydrolysis of Dithioacetals

Abstract Acyclic dithioacetals of ketones are easily hydrolyzed with the action of gallium chloride in the presence of A) water or B) methanol with bubbling oxygen to give the parent carbonyl compounds in high yields.

Formation and hydrolysis of acetals catalysed by acid Faujasites

Dimethyl and cyclic ethylene acetals can be obtained in the presence of HY zeolites by treatment of the corresponding carbonyl compound with trimethyl orthoformate at room temperature or with ethylene glycol using a Dean-Stark system, respectively. The relationship between the percentage of Na + exchange of the zeolite and the initial reaction rates shows that only strong acid sites are active in the dimethyl acetal formation. Similarly, regeneration of the parent carbonyl compound was accomplished by simply heating suspensions of the appropriate acetal in carbon tetrachloride with HY catalysts. Evidence supporting the implication in the hydrolysis of the adsorbed water remaining on the zeolite after thermal activation was drawn from the results obtained using a dried solvent and a highly dealuminated zeolite. The possibility of using hydrolytic cleavage of acetals as a chemical activation procedure for zeolites was tested.

Experimental determination of carbon vs. oxygen regioselectivity in reactions of gas‐phase enolate ions

AbstractA gas‐phase experimental investigation of the competition between carbon and oxygen alkylation of a series of cyclic and acyclic enolate ions is described. Perfluoropropylene is shown to react in a characteristic way with oxyanions and carbanions to produce distinctive ionic products. The relative yields of these products formed in reactions with ambident enolate ions provides a measure of their intrinsic carbon vs. oxygen regioselectivity. The results for a series of enolates derived from aldehydes, ketones, esters, amides and related compounds show a wide range of reactivity which is a function of the nature of the central substituent. Most aldehyde and ketone enolates react mainly through oxygen, while enolates with σ‐acceptor of π‐donor type central substituents react mainly thorugh carbon. Ring‐size in cyclic ketone enolates also influences C vs. O regioselectivity, i.e. small‐ring enolates react mainly through carbon, while larger ring enolates (C7–C9) react preferentially through oxygen. The enolate reactivity patterns can be generally accounted for by the keto–enol energy differences for the parent carbonyl compounds, although some exceptions are evident. The origins of the highly variable, kinetically determined regioselectivities are discussed.

ChemInform Abstract: A Convenient Method for the Hydrolysis of Diethylthioacetals Catalyzed by Trityl Perchlorate.

AbstractThe diethylthioacetals (I) are transformed into the parent carbonyl compounds (II), using trityl perchlorate as a catalyst.

Reductive Dehalogenation of α-Haloketones by Sodium Borohydride and Tin(II) Chloride in Tetrahydrofuran

Abstract α-H aloketones and α-halocarbonyl compounds are effectively reduced to dehalogenation to their corresponding parent ketones or carbonyl compounds in good yield by sodium borohydride and tin(II) chloride in tetrahydrofuran.

A Convenient Method for the Hydrolysis of Diethylthioacetals Catalyzed by Trityl Perchlorate

Abstract Treatment of diethylthioacetals with two equivalents of trityl methyl ether in the presence of a catalytic amount of trityl perchlorate, and successive quenching with aqueous sodium hydrogencarbonate gave parent carbonyl compounds, hydrolyzed products, in high yields under mild conditions. According to this method, it is also possible to hydrolyze diethylthioacetals selectively even when another thioacetal, such as 1,3-dithiane, coexisted in the same molecule.

ChemInform Abstract: THE DIRECTED ALDOL REACTION

The aldol reaction, usually carried out in protic solvents with base or acid as the catalyst, is one of the most versatile methods in organic synthesis. By application of this reaction a great number of aldols and related compounds have been prepared from various carbonyl compounds. However, because of difficulty in directing the coupling, the conventional method has serious synthetic limitations. This is particularly notable when two different carbonyl compounds are used in a cross-coupling; the reaction is often accompanied by undesirable side reactions such as self-condensation and polycondensation. The synthetic limitation arises because the reaction is reversible and cannot be driven to completion if the aldol is less stable than the parent carbonyl compounds. In addition, the reverse reaction, in the presence of acid or base, generates regioisomeric enols or enolates, which in turn attack the carbonyl compounds to yield a mixture of aldols. Furthermore, the aldols are often dehydrated and the resulting unsaturated carbonyl compounds may undergo a Michael addition between enolate anions to give a complex reaction mixture. During the last decade new methods have been developed for the directed coupling of two different carbonyl compounds (or carbonyl equivalents) to give specific carboncarbon bond formation between the α-carbon atom of one carbonyl compound and the other carbonyl component to produce a desired crossed aldol. These methods provide regiospecific reactions for forming carboncarbon bonds and allow the synthesis of a wide variety of aldols by directed self- or cross-coupling. The success of the reaction depends on effective interception of the aldol-type adduct by formation of a stable six-membered chelate. This interception can usually be achieved by reaction of a carbonyl compound with a suitably reactive metal enolate or enol ether that is derived regioselectively from the other carbonyl compound. Reaction of a carbonyl compound with lithium enolates or preformed lithio derivatives of imines is a typical method used for preparation of crossed aldols, even though the reaction is carried out under strongly basic conditions. Use of magnesium, aluminum, or zinc enolates permits rather milder reaction conditions. A clean aldol reaction has been achieved using vinyloxyboranes in a process that is carried out under neutral conditions to produce various crossed aldols in excellent yields. The titanium tetrachloride–promoted coupling of silyl enol ethers, enol ethers, or enol esters with carbonyl compounds, acetals, or ketals is another particularly useful method for the preparation of aldols. The powerful electrophilic activation of the carbonyl acceptor by titanium tetrachloride provides the driving force for this reaction. The acidic reaction medium makes the method useful for compounds that have base-sensitive functional groups. These directed aldol reactions provide efficient methods for the regiospecific formation of new carboncarbon bonds and can be used for the preparation of key intermediates in the synthesis of important natural products. This chapter includes examples where the coupling reactions are of aldehydes, ketones, or their equivalents. Keywords: directed aldol reaction; stereochemsitry; lithium enolates; fluoride ion catalyst; trimethylsilyl enol ether; lithiated schiff base; lithiated hydrazones; lithiated oximes; magnesium enolates; zinc enolates; aluminum enolates; vinyoxyboranes; vinylaminoboranes; Lewis acid promoted aldol reactions; aldehydes; ketones; ketals; acetals; enol esters; enol ethers; trimethylsilyl enol ethers

Reductive dehalogenation of α-halogenated carbonyl and cyano compounds with the hexamethyldisilane/tetrakis(triphenylphosphine)palladium system

Treatment of α-halogenated carbonyl or cyano compounds with hexamethyldisilane in the presence of catalytic amounts of tetrakis(triphenylphosphine)-palladium gives the corresponding parent carbonyl or cyano compounds in excellent yields via oxy-π-allyl(trimethylsilyl)palladium intermediates.

Hydrogen atom transfer oxidation of primary and secondary alcoholates into aldehydes and ketones by aromatic halides in liquid ammonia. A new electrochemically induceable reaction

It is possible to induce the oxidation of alcoholates into the corresponding carbonyl compounds by electrochemical reduction of aromatic halides in liquid ammonia, Le., to electrochemically trigger the reaction ArX + >CH-OArH + >C=O + X-. H-Atom transfer from the alcoholate to the aryl radical formed upon reduction of the aryl halide appears as the key step of the oxidation process. The ketyl anion radical thus formed can be oxidized into the parent carbonyl compound, remain electrochemically stable, or be reduced into the dianion depending upon the location of the two corresponding standard potentials toward the reduction potential of the aryl halide. Electricity consumption thus tends toward 0, 1, and 2 F/mol for the three cases, respectively. The reactions competing with H-atom transfer, thus lowering the efficiency of the electrochemical inducement of the oxidation process, are electron transfers to the aryl radical which occur at the electrode surface and/or in the solution. These will play the role of termination steps for the corresponding chain systems involving homogeneous initiation of the reaction. The kinetic analysis of the competition between H-atom transfer and homogeneous or heterogeneous electron transfer allows a detailed investigation of the reaction mechanism by electrochemical techniques such as cyclic voltammetry. This also leads to the determination of the rate constant of H-atom transfer of the alcoholate-aryl radical couple. Electrochemical inducement of a chemical reactionza is based upon the reactivity of the system being larger at a higher or a lower oxidation level than at the original one. A few examples of such processes have been described in organic or coordination chemistry? This reaction that has been the most extensively studied in this respect is SRNl aromatic nucleophilic s~bs t i t u t ion ,~ the electrochemical inducement”Sk of which is based on the following reaction sequence: ArX + l e 9 ArX-. ArX-. Ar. + XAr. + NuArNu-.

Uebergangsmetall—methylen-komplexe : XII. Zur reversiblen protonierung einer elektronenreichen metall—metall-bindung

The dinuclear cationic μ-hydridorhodium complex [(μ-CO)(μ-H) (η 5-C 5H 5)-Rh(CO) 2]BF 4 has been synthesized in quantitative yield by metal—metal bond protonation of the parent carbonyl compound (μ-CO)[(η 5-C 5H 5)Rh(CO)] 2 with HBF 4/diethyl ether, the complex is characterized by conductivity measurements and IR, 1H NMR and { 1H}- 13 C NMR spectroscopy, rapid deprotonation is effected by sodium methoxide. The C 3υ-isomer of (η 5-C 5H 5) 3Rh 3(CO) 3 is isolated in 92% yield from reaction of the parent compound with HBF 4/H 2O in tetrahydrofuran.

ChemInform Abstract: THE USE OF SODIUM DITHIONITE FOR THE REDUCTION OF IMINES AND THE CLEAVAGE OF OXIMES

Sodium dithionite reduces a variety of imines to secondary amines. Oximes are cleaved by the reagent to the parent carbonyl compound.

ChemInform Abstract: REGENERATION OF KETONES FROM HYDRAZONES, OXIMES, AND SEMICARBAZONES BY BENZENESELENINIC ANHYDRIDE

AbstractDie Steroid‐Ketone (I)‐(IV) werden durch Behandlung ihrer Hydrazone, Oxime und Semicarbazone mit dem Anhydrid (V) in Tetrahydrofuran bei 50‐60°C in guten Ausbeuten erhalten.