ALDEHYDE - KETONE REARRANGEMENT

This is sufficiently reactive to attack the C—H bond forming the five-coordinate car-bocation 16 to give protonated pivalaldehyde (Scheme 7.2). The latter undergoes the aldehyde-ketone rearrangement to yield the corresponding branched ketone. 

Propose a mechanism for the reaction in Equation 10, an example of the aldehyde-ketone rearrangement. 

Nucleophilic aromatic substitution Protection of aldehydes, ketones. Rearrangements ch37... 

A summary of some typical processes for which borosilicates are of interest was provided by Holderich in 1986 (56). Advantages in their use were reported for double bond migrations in carbonyl containing compounds (aldehyde - ketone rearrangement), for the dehydration of aldehydes, for aldol... 

A recent review (Collins, 1960) of the pinacol rearrangement covers nearly all of the pertinent isotopic experiments that have been performed. One example of the use of two carbon-14 labels to relate the aldehyde-ketone and pinacol rearrangements will be discussed in detail here. The anomaly of the apparent reversal, in the aldehyde-ketone rearrangement, of the usual order of migratory aptitudes has been mentioned by Wheland (1949) and by Ingold (1953), and relates to the fiict that, for example, 2-methyl-2-phenylpropionaldehyde (67), in concentrated sul-... 

Rearrangements. The epoxide to aldehyde/ketone rearrangement is a classic reaction mediated by BF3-Et20. Recent... 

An example of skeletal isomerization is the aldehyde/ketone rearrangement over zeolites (equation 3). Thereby the effects of variable acidity of isomorphous substituted zeolites and of shape selectivity on the course of the reaction are clearly evident [20]. 

An alternate method of producing the 21-hydroxy-20-ketone consists in lithium aluminum hydride reduction of the dimethyl acetal, hydrolysis to the 20-hydroxy-21-aldehyde and rearrangement, preferably via the bisulfite addition product... 

Treatment with alkaline H2O2 oxidizes trialkylboranes to esters of boric acid. This reaction does not affect double or triple bonds, aldehydes, ketones, halides, or nitriles. The R group does not rearrange, and this reaction is a step in the hydro-boration method of converting alkenes to alcohols (15-16). The mechanism has been formulated as involving a rearrangement from boron to oxygenr ... 

Dithiophosphoric acids, (RO)2PS2H, have been used for the thionation of carbonyl groups in certain aldehydes, ketones, amides, esters, thio-carboxylates and other organics.163 The mechanism for this reaction proceeds via a reversible nucleophilic attack of the thioacid on the carbonyl compound, which can then rearrange by way of a four-membered PSCO cyclic intermediate into the desired C=S containing molecule and thiophosphoric acid (Equation 81).163... 

During the first month of this experiment, it was realized that this reaction is extremely variable. Thus, diverse amines (ammonia, primary and secondary amines, hydrazine derivatives, hydroxylamines) 13, carbonyl compounds (aldehydes, ketones) 14, acid components 15 or their anions (H2O, Na2S203, H2Se, R2NH, RHN-CN, HN3, HNCO, HNCS, RCO2H, RCOSH, ROCO2H, etc.), and the isocyanides could form the a-adducts 16 that rearrange into their products 17 (Scheme 1.5). 

The rearrangements of 3-methylbut-l-ene oxides" and l,2-epoxybut-3-ene on lithium phosphate have been studied, and a detailed theoretical study of the rearrangement of allene oxide (342) to cyclopropanone (344), which shows that the transformation proceeds via an intermediate oxyallyl (343), has been presented. It has been shown that aldehydes, ketones, and cyclic ethers are all produced... 

Another important reaction in synthetic chemistry leading to C-C bond formation is the Michael addition. The reaction typically involves a conjugate or nucleophilic 1,4-addition of carbanions to a,/l-unsaturated aldehydes, ketones, esters, nitriles, or sulfones 157) (Scheme 21). A base is used to form the carbanion by abstracting a proton from an activated methylene precursor (donor), which attacks the alkene (acceptor). Strong bases are usually used in this reaction, leading to the formation of byproducts arising from side reactions such as condensations, dimerizations, or rearrangements. 

Reaction LV. Intramolecular condensation of Phenylhydrazones of Aldehydes, Ketones and Ketonic Adds by heating with Hydrochloric Acid or Zinc Chloride (Fischer). (B., 19, 1563 26, R., 14 E.P., 385605.)— This is an important method of preparation for the alkylindols. The reactions occurring are somewhat complicated, since both a rearrangement and the elimination of ammonia take place. 

The group of rearrangements brought about by treatment of aldehydes, ketones, or carboxylic acids with hydrogen azide are known as Schmidt rearrangements. All are acid-catalyzed and all involve addition of HN3 to the carbonyl group followed by dehydration. They are shown in Equations 6.58-6.60. 

Reaction of (284) with an aldehyde, ketone, or enol ether in the presence of acid results in an electrophilic substitution that produces a -ferrocenylalkyl carbocations that may be trapped by nucleophiles (azides, amines, thiols). This chemistry may be used to prepare enantiomerically pure ferrocene derivatives in a maimer that avoids resolution procedures (Scheme 86)." For example, the enol ether from (-)-menthone affords a kinetic carbocation (302) that may be trapped or allowed to rearrange to the more thermodynamically stable cation (303) and then trapped, thus offering a means of controlling the configuration of the stereocenter adjacent to the ferrocene unit. Use of an enantiomerically pure aldehyde derived from Q -pinene (304) affords a 1 1 carbocationic mixture that similarly isomerizes to a single cation. 

The McLafferty rearrangements is the mass spectrometric analog of the Norrish type II photochemical cleavage of ketones. The relationship between these two processes is easily the most extensively studied of aU mass spectral photochemical correlations. In addition to the well known reaction of aldehydes, ketones, and esters, Eq. (62), many analogous y-hydrogen... 

Oxidation of olefins Olefins are oxidized rapidly by thallium(lll) nitrate in methanol at room temperature to aldehydes or ketones. Rearrangement is the exclusive or predominant pathway with olefins in which at least one of the substituted groups has a high migratory aptitude. 

The Beckmann rearrangement of ketoximes to the corresponding amides (31), the Fischer indole cyclization, isomerization of epoxides to the corresponding aldehydes, ketones, or alcohols, hydration and ammo-nolysis of epoxides, oxygen-sulfur interchange, formation of diaryl-ureas and -thioureas from condensation of aniline and carbonyl sulfide, and olefin carbonylation occur over zeolite catalysts (62). The oxo reaction over rhodium and cobalt containing zeolites recently has been claimed (22). 

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