Conversions carbonyl compounds alkenes

Phosphate groups can also be removed by dissolving-metal reduction. Reductive removal of vinyl phosphate groups is one method for conversion of a carbonyl compound to an alkene.224 (See Section 5.7.2 for other methods.) The required vinyl phosphate esters are obtained by phosphorylation of the enolate with diethyl phospho-rochloridate or /V A /V -tetramethyldiamidophosphorochloridate.225... 

Both unsymmetrical alkenes and diols can be prepared by applying these methods to mixtures of two different carbonyl compounds. An excess of one component can be used to achieve a high conversion of the more valuable reactant. A mixed reductive... 

Insertion of carbon monoxide into Csp2—Zr bonds occurs readily at ambient temperatures or below to produce a,(5-unsaturated, reactive acyl zirconocene derivatives [27—29]. Early work by Schwartz demonstrated the potential of such intermediates in synthesis [5d], as they are highly susceptible to further conversions to a variety of carbonyl compounds depending upon manipulation. More recently, Huang has shown that HC1 converts 16 to an enal, that addition of a diaryl diselenide leads to selenoesters, and that exposure to a sulfenyl chloride gives thioesters (Scheme 4.11) [27,28]. All are obtained with (F)-stereochemistry, indicative of CO insertion with the expected retention of alkene geometry. 

The perruthenate oxidation of alcohols has been incorporated into a one-pot conversion of alkenes into carbonyl compounds via their initial hydroboration [44], Overall yields can be as high as 98%. Where the initial alkene also contains carbonyl groups these are reduced in the first step and are reoxidized by the perruthenate. 

Interestingly, sulfonium ylides generated from electrophilic carbene complexes and sulfides can react with carbonyl compounds, imines, or acceptor-substituted alkenes to yield oxiranes [1320-1325], aziridines [1321,1326,1327] or cyclopropanes [1328,1329], respectively. In all these transformations the thioether used to form the sulfonium ylide is regenerated and so, catalytic amounts of thioether can be sufficient for complete conversion of a given carbene precursor into the... 

A convenient method for the conversion of aldehydes (RCHO) to alkenes (RCH = CHj), knovm as methylenation, involves the reaction of a zinc/copper couple with diiodomethane in the presence of the carbonyl compound dissolved in tetrahy-drofuran. The reaction first generates an organometallic intermediate (ICH2ZnI) which then reacts with the carbonyl compound. The conversion of benzaldehyde to styrene using this conventional methodology required a reaction time of 6 h at 40 °C. When the reaction was sonicated however comparable yields of around 70%... 

Aside from the relatively trivial conversions of nitronates to the corresponding oxime and carbonyl compounds (10,11), the chemistry of nitronates remained relatively unexplored for much of the early 1900s. However, in 1964, Tartakovskii et al. (12) demonstrated that alkyl nitronate esters were competent partners in the newly discovered class of dipolar cycloadditions with alkenes (Scheme 2.1). Both cyclic and acyclic nitronates participated, thus providing a new functional group were the nitrogen atom existed at the center of an acetal (13). These compounds were subsequently referred to as nitroso acetals (14) or nitrosals (15). 

Toyota, Ihara, and coworkers demonstrated that silyl enol ethers undergo Pd -promoted intramolecular nucleophilic attack on alkenes [18]. Allhough early examples required stoichiometric Pd [167], they have also shown that Pd(OAc)2 in DMSO is an effective catalyst in the presence of an aerobic atmosphere (Eq. 38) [168-170]. The reaction is proposed to proceed through an oxo-jt-allyl intermediate that can undergo competitive alkene insertion or P-hydride elimination (Scheme 11). The latter reaction is the basis for the synthetically useful conversion of silyl enol ethers to a,P-unsaturated carbonyl compounds (see below). Efforts to use BQ as an oxidant were not described. 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

Substrates suitable for oxidative conversion into carbonyl compounds are alkenes, primary or secondary alcohols, and benzyl halides. Polystyrene-bound alkenes have been converted into aldehydes (with the loss of one carbon atom) by ozonolysis followed by reductive cleavage of the intermediate ozonide (Entry 1, Table 12.3). 

The conversion of carbonyl compounds to their enol triflates provides a very simple way to couple the carbonyl carbon to an alkene. In general, however, aryl... 

In addition to being useful reagents for the reductions of carbonyl compounds, boron-based reagents can also be used for the conversion of an alkene to a wide variety of functionalized alkanes. Because the majority of these reagents carry a terpene substituent, they are discussed under these chiral pool materials (Chapter 5). 

The oxidation of primary and secondary trialkylboranes with pyridinium chlorochromate (PGG) provided aldehydes or ketones.504-507 An oxidative conversion of alkenes into a carbonyl compound was conducted by tandem hydroboration and oxidation with excess A-methylmorpholine-A-oxide (NMO) in the presence of Pr4NRu04 (TPAP) (Equation (105)).508... 

On the other hand, hydrogenations under mild conditions, in particular those at ordinary temperature and pressure, are advantageous for monitoring the extent of conversion of substrate exactly and thus achieving selective hydrogenation successfully, as in selective hydrogenation of alkynes to alkenes and in selective hydrogenation of the carbon-carbon double bond of unsaturated carbonyl compounds. 

The deoxygenation of epoxides is not of great preparative value since it involves some loss of stereochemical integrity and the alkenes produced are more readily approached in other ways. Reductive cleavage of ozonides, for example, using triphenylphosphine, commonly forms part of the ozonolysis procedure for conversion of alkenes into carbonyl compounds. If a carbonyl compound is treated with an appropriate P(III) reagent then the reverse process may occur—reductive coupling to form a new C=C double bond. This has found a particularly important... 

A prototype example is the famous McMurry coupling of carbonyl compounds to alkenes (Scheme 1) [4]. The very high stability of the accumulating titanium oxides constitutes the thermodynamic sink which drives the conversion but demands the use of stoichiometric or excess amounts of the low-valent titanium reagent [Ti]. Only recently has it been possible to elaborate a procedure that for the first time enables us to perform intramolecular carbonyl coupling reactions catalyzed by titanium species [5]. 

Positive halogen complexes with pyridine bases are known as versatile halogenating reagents. Bis(sym-collidine)iodine(I) tetrafluoroborate (59) in dimethyl sulfoxide is a potential reagent for the direct conversion of alkenes to a-iodo carbonyl compounds (Scheme 6). The oxidation involves the... 

The oxidative rearrangement of allylic alcohols to a -unsaturated kelmies or alddiydes is one of the most widely used synthetic reactions in this group, and forms part of a 1,3-carbonyl tran sition sequence. Scheme 7 shows this reaction and the related conversion of the allylic alcdiol to an a,p-epoxy carbonyl compound. Chromate reagents induce some allylic alcohol substrates to undergo a directed qmxidation of the alkene without rearrangement, but this reaction is beyond the scope of the present discussion. 

A method for the conversion of alkenes to a-phenylseleno carbonyl compounds involves the use of benzeneselenenic anhydride. This reagent, which has a relatively short lifetime, is prepared in situ from diphenyl diselenide and r-butyl hydroperoxide. The alkene is converted to a phenylseleniranium ion... 

A procedure for the large-scale conversion of alkenes to unsaturated carbonyl compounds using singlet oxygen has been published, whereby the conversion of cyclopentene to cyclopentenone can be carried out on a molar scale in 60% yield. 

Lithiation of vinylic sulfones. Phenyl vinyl sulfones (1), prepared as indicated, react with methyllithium regiospecifically at — 95° at the a-vinyl position to give the lithium derivatives 2. As expected, 2 can be alkylated to give 3. The reaction of 2 with enolizable carbonyl compounds proceeds more satisfactorily by prior conversion to the vinylic Grignard reagent a. This sequence constitutes a route to disubstituted alkenes, since a sulfone group is reductively cleaved by sodium amalgam (7, 326). ... 

Direct transition from level 2 to level 0 can be achieved by way of the Wolff-Kishner reaction (treatment of the respective hydrazones with alkali), a classical pathway for the reduction of carbonyl compounds. At the same time, a direct conversion of aldehydes and ketones into alkenes is also feasible via reductive cleavage of their tosylhydrazones under the action of MeLi, the Shapiro reaction (Scheme 2.63). "... 

Thiolate ions react with a-(alkylthio)carbonyl compounds to afford disulfides and the corresponding reduced ketone (equation 26). The reaction apparently involves direct nucleophilic attack by thiolate on the sulfur atom of the alkylthio group. Other soft bases, such as cyanide ion, thiourea and tertiary phosphines, also effect this conversion. Raney nickel of course readily desulfurizes a-alkylthiocarbonyl compounds. The reaction is quite selective for example, the ester, ketone and alkenic moieties of (43) are unaffected by the Raney nickel treatment (equation 27). Raney nickel reduction of (44) is reported to proceed with retention of configuration in ethanol and with inversion in acetone. Telluride salts also desulfurize a-alkylthio ketones. ... 

In the Wittig reaction an aldehyde or ketone is treated with a phosphorus ylid (also spelled ylide and called a phosphorane) to give an alkene. The conversion of a carbonyl compound to an alkene with a phosphorus ylid is called the Wittig reaction. Phosphorus ylids are usually prepared by treatment of a phosphonium salt with a base, and phosphonium salts are usually prepared from a triaryl phosphine and an alkyl halide (10-31) ... 

Selenium dioxide, Se02 (mp 315 °C, sublimes), and selenious acid, H2Se03, which is obtained by the evaporation of an aqueous solution of Se02 [507, 50S], are very selective oxidants. They are capable of mild dehydrogenation to form double bonds [375] and can oxidize alkenes and acetylenes to vicinal dicarbonyl compounds [509, 510] and allylic ethers to aldehydes [511]. The most important applications are conversions of alkenes into allylic alcohols [5i2] of benzylic, methyl, or methylene groups into carbonyl groups [513, 514, 5i5] and of carbonyl compounds into a-... 

Sodium permanganate monohydrate, NaMn04 H20, which is commercially available, is used for the oxidation of alkenes to carboxylic acids [834] and of alcohols to carbonyl compounds [SJ5], the conversion of sul-finic acids into sulfonic acids [836], and the selective oxidation of sulfoxides to sulfones (sulfides are not oxidized with sodium permanganate in dioxane solutions) 837. ... 

Primary alcohols are oxidized to aldehydes or acids, and secondary alcohols are oxidized to ketones. Tertiary alcohols resist oxidation, unless they are dehydrated in acidic media to alkenes, which are subsequently oxidized. The conversion of alcohols into carbonyl compounds can be achieved by catalytic dehydrogenation or by chemical oxidation. Catalytic dehydrogenation is especially of advantage with primary alcohols, because it prevents overoxidation to carboxylic acids. Examples are tabulated in equations 223-227 and 265-268. 

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