Aliphatic Ketones and Aldehydes

Reagent A is particularly useful for the treatment of the lower aliphatic aldehydes and ketones which are soluble in water cf. acetaldehyde, p. 342 acetone, p. 346). The Recent is a very dilute solution of the dinitrophenylhydrazine, and therefore is used more to detect the presence of a carbonyl group in a compound than to isolate sufficient of the hydrazone for effective recrystallisation and melting-point determination. 

A-Substituted pyrroles, furans and dialkylthiophenes undergo photosensitized [2 + 2] cycloaddition reactions with carbonyl compounds to give oxetanes. This is illustrated by the addition of furan and benzophenone to give the oxetane (138). The photochemical reaction of pyrroles with aliphatic aldehydes and ketones results in the regiospecific formation of 3-(l-hydroxyalkyl)pyrroles (e.g. 139). The intermediate oxetane undergoes rearrangement under the reaction conditions (79JOC2949). 

Two substituents on two N atoms increase the number of diaziridine structures as compared with oxaziridines, while some limitations as to the nature of substituents on N and C decrease it. Favored starting materials are formaldehyde, aliphatic aldehydes and ketones, together with ammonia and simple aliphatic amines. Aromatic amines do not react. Suitable aminating agents are chloramine, N-chloroalkylamines, hydroxylamine-O-sulfonic acid and their simple alkyl derivatives, but also oxaziridines unsubstituted at nitrogen. Combination of a carbonyl compound, an amine and an aminating agent leads to the standard procedures of diaziridine synthesis. 

Paal-Knorr synthesis, 4, 118, 329 Pariser-Parr-Pople approach, 4, 157 PE spectroscopy, 4, 24, 188-189 photoaddition reactions with aliphatic aldehydes and ketones, 4, 232 photochemical reactions, 4, 67, 201-205 with aliphatic carbonyl compounds, 4, 268 with dimethyl acetylenedicarboxylate, 4, 268 Piloty synthesis, 4, 345 Piloty-Robinson synthesis, 4, 110-111 polymers, 273-274, 295, 301, 302 applications, 4, 376 polymethylation, 4, 224 N-protected, 4, 238 palladation, 4, 83 protonation, 4, 46, 47, 206 pyridazine synthesis from, 3, 52 pyridine complexes NMR, 4, 165... 

Claisen reaction is the condensation of benzaldehyde with aliphatic aldehydes and ketones containing a-hydrogen C6H5CHO -r CH3CHO C6H5CH=CH CHO -r HjO... 

A range of electron-withdrawing groups on the nitrogen - N-P(0)Ph2, N-tosyl, and N-SES, for example - were tolerated. Imines derived from aromatic, heteroaromatic, unsaturated, and even aliphatic aldehydes and ketones were employed... 

Aliphatic aldehydes and ketones can be converted to gem-dichlorides by treatment with PCI5. The reaction fails for perhalo ketones. " If the aldehyde or ketone has an a hydrogen, elimination of HCl may follow and a vinylic chloride is a frequent side product ... 

In a related process, a-halo ethers can be prepared by treatment of aldehydes and ketones with an alcohol and HX. The reaction is applicable to aliphatic aldehydes and ketones and to primary and secondary alcohols. The addition of HX to an aldehyde or ketone gives tx-halo alcohols, which are usually unstable, though exceptions are known, especially with perfluoro and perchloro species. °... 

The addition of KCN to triisopropylbenzenesulfonyl hydrazones (53) provides an indirect method for achieving the conversion RR CO RR CHCN. " The reaction is successful for hydrazones of aliphatic aldehydes and ketones. 

Nitrilimines react with hydrazones of aliphatic aldehydes and ketones to yield addition products 9 which cyclise when treated with palladium charcoal at room temperature to give 1,6-dihydro-j-tetrazines 10 <96JCR(S)174>. 

The phenylacetaldehyde reductase involved in the degradation of styrene is also able to accept long-chain aliphatic aldehydes and ketones, and halogenated acetophenones (Itoh et al. 1997). 

An unusual reaction was been observed in the reaction of old yellow enzyme with a,(3-unsat-urated ketones. A dismutation took place under aerobic or anaerobic conditions, with the formation from cyclohex-l-keto-2-ene of the corresponding phenol and cyclohexanone, and an analogous reaction from representative cyclodec-3-keto-4-enes—putatively by hydride-ion transfer (Vaz et al. 1995). Reduction of the double bond in a,p-unsaturated ketones has been observed, and the enone reductases from Saccharomyces cerevisiae have been purified and characterized. They are able to carry out reduction of the C=C bonds in aliphatic aldehydes and ketones, and ring double bonds in cyclohexenones (Wanner and Tressel 1998). Reductions of steroid l,4-diene-3-ones can be mediated by the related old yellow enzyme and pentaerythritol tetranitrate reductase, for example, androsta-A -3,17-dione to androsta-A -3,17-dione (Vaz etal. 1995) and prednisone to pregna-A -17a, 20-diol-3,ll,20-trione (Barna et al. 2001) respectively. 

The general mechanistic features of the aldol addition and condensation reactions of aldehydes and ketones were discussed in Section 7.7 of Part A, where these general mechanisms can be reviewed. That mechanistic discussion pertains to reactions occurring in hydroxylic solvents and under thermodynamic control. These conditions are useful for the preparation of aldehyde dimers (aldols) and certain a,(3-unsaturated aldehydes and ketones. For example, the mixed condensation of aromatic aldehydes with aliphatic aldehydes and ketones is often done under these conditions. The conjugation in the (3-aryl enones provides a driving force for the elimination step. 

Samarium diiodide is another powerful one-electron reducing agent that can effect carbon-carbon bond formation under appropriate conditions.257 Aromatic aldehydes and aliphatic aldehydes and ketones undergo pinacol-type coupling with Sml2 or SmBr2. 

Although the sulfur trifluoride compounds are generally useful as selective agents for conversion of carbonyl and carboxyl groups to difluoromethylene and trifluoromethyl groups, variations in reaction conditions are often necessary.7 Thus the reaction of aromatic ketones requires heating at 150°. Since the reaction with aliphatic aldehydes and ketones is exothermic, it is advan-... 

In the 1970s, Brouwer and Kifflin reported the reactions of saturated hydrocarbons with aliphatic aldehydes and ketones in superacidic media. Analysis of the products from these reactions suggested that the protonated aldehydes and ketones (carboxonium ions) were reacting at the carbon-hydrogen o-bonds of the alkanes. This was a surprising observation because carboxonium... 

Condensation of [3- or "y-amino alcohols with aldehydes or ketones RR CO gives the product 27. In solution the position of the equilibrium varies with R and R, and with the solvent (73). When the carbonyl reactant is a substituted benzaldehyde, the solid is found (IR, KBr) to comprise molecules of the open-chain structure 27a, whereas aliphatic aldehydes and ketones give crystals of dihydro- 1,3-benzoxazines, 27b. An interesting case is that of the condensation product of o-hydroxybenzylamine with cyclopentanone, for which McDonagh and Smith (73) suggest that ring and chain tautomers coexist in the solid. 

The use of polymer-supported quaternary ammonium salts to catalyse the Wadsworth-Emmons reaction produces acceptable yields from both aromatic and aliphatic aldehydes and ketones [16]. 

Pinacolisation, cathodic, aliphatic aldehydes and ketones, 40 165-166 Pinene, 20 282... 

The effect of substituent groupings upon the first ionization potential of, at least, the aliphatic aldehydes and ketones does not seem to provide clear evidence for a choice between loss of a 7r-electron from the C=0 double bond or one of the oxygen lone-pair electrons. Concordant data for the homologous series of aliphatic ketones have been obtained by... 

The two established Hnls, those from L. usitatissimum and P. amygdalus, have found biocatalytic applications for the production of (i )-cyanohydrins. The former of these Hnls is the least widely applied, the natural substrates being acetone cyanohydrin or (i )-2-butanone cyanohydrin (Table 1) [28]. Although an improved procedure for the purification of this enzyme has been reported [27] it is still only available in limited quantities (from 100 g of seedlings approximately 350 U of enzyme are obtained). It was found that this enzyme transforms a range of aliphatic aldehyde and ketone substrates [27], the latter of which included five-membered cyclic (e.g. 2-methylcyclopentanone) and chlorinated ketone substrates. In contrast, attempts to transform substituted cyclohexanones and 3-methylcyclopentanone failed and it was even found that benzaldehyde deactivated the enzyme. 

Although most consumers appreciate the fieriness of chile, capsaicinoids are not perceived through odor or taste receptors but through the nociceptive pain receptors described earlier. The compounds in chile fruit that create the flavor and aroma are produced in the fruit wall. Buttery et al. [90] generated vacuum steam distilled oil from green bell pepper macerate, with well over 40 peaks on subsequent GC/MS analysis. Of these peaks, the major flavor compound associated with bell pepper aroma was 2-methoxy-3-isobutylpyrazine (Fig. 8.1). They also reported several monoterpenoids in abundance, limonene, trans- 3-ocimene, and linalool as well as other aliphatic aldehydes and ketones. The flavor composition of dried red bell pepper powder (sweet paprika) extracted with ether identified 44 key peaks by GC/MS [91]. In these dried samples the key compounds were P-ionone and several furanones. The post-harvest processing and the different fruit maturities as well as possible varietal differences are all causes for the different aromatic profiles. 

Control of Regiochemistry and Stereochemistry of Mixed Aldol Reactions of Aliphatic Aldehydes and Ketones... 

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