Dicarbonyl products

A Michael reaction involves the conjugate addition of a stable enolate ion donor to an o,/3-unsaturated carbonyl acceptor, yielding a 1,5-dicarbonyl product. Usually, the stable enolate ion is derived from a /3-diketone, jS-keto ester, malonic ester, or similar compound. The C—C bond made in the conjugate addition step is the one between the a carbon of the acidic donor and the (3 carbon of the unsaturated acceptor. 

Stork reaction (Section 23.11) A carbonyl condensation between an enamine and an a,/3-unsaturated acceptor in a Michael-like reaction to yield a 1.5-dicarbonyl product. 

The bis[l,2]dithiolo[5,4- ][5, 4 -< ][l,4]thiazine ring systems of Rees and co-workers easily extrude sulfur from the thiazine ring and undergo contraction to the fused pyrrole derivatives <1997CC879>. These tricycles generally have a nonplanar, scorpion-like solid-state structure <1998JOC2189> however, the dicarbonyl product of... 

Dialkoxycarbonylation has been reported using a Pd-catalyst/oxidant system on propynols or butynols furnishing respectively /3- or y-lactone derivatives with a-(alkoxycarbonyl)ethylene chains (Scheme 24) [83,137, 138]. This reaction occurs in a stereospecific way leading exclusively to cis-dicarbonylated products in fair to excellent yields (25-97%). Noteworthy, a butynol bearing an alkyl or an aryl substituent instead of a TMS one undergoes a different course of reaction under the same conditions here frans-alkoxycarbonylation takes place selectively (Scheme 25). 

Both aldol and Claisen reactions are equilibria, and product formation is a result of disturbing these equilibria. This would be dehydration in aldol reactions and ionization in Claisen reactions. Ionization would be the more immediate determinant. On that basis, it is obvious that the 1,3-dicarbonyl products from Claisen reactions are going to be more acidic than the aldol products, which possess just one carbonyl group. 

The aldehydes 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, methional, and phenylacetaldehyde are so-called Strecker aldehydes, formed as a result of a reaction between dicarbonyl products of the Amadori pathway and amino acids, having one less carbon atom than the amino acid (i). 

To understand how to control process conditions to give methyl, 4-pentadienoate, the reaction mechanism must be examined. (See Equation 2.). -palladium hydride elimination from 4 gives rise to trans and cis-methyl penta-, 4-dienoate which is the desired monocarbonylation intermediate for sebacic acid. The desired mono-carbonylation reaction is promoted by low carbon monoxide pressure ( 1000 psig) while high pressure (1800 psig) gives excellent 1,4-dicarbonylation product yield. The mono-carbonylation reaction is also facilitated by using a Lewis Acid as a co-catalyst and iodide as the preferred palladium counter-ion (Table III.). Chloride is the preferred palladium counter-ion for 1,4-dicarbonylation. 

Grosjean et al. (1994c) propose that the hydroperoxide channel may also be responsible for the formation of hydroxycarbonyl and/or dicarbonyl products ... 

Reaction (44a) is analogous to the 02-reaction of the vinyl radical leading to HCO and HCHO as reported by Gutman and co-workers [118,119], Evidence for the occurrence of reaction (44b) was based on the observation of a-dicarbonyl products in the absence of NO. Schmidt et al. [120] have recently observed the regeneration of HO from the HO + C2H2 reaction by means of a laser fluorescence technique. The branching ratios for the two unimolecular dissociation channels typified by reactions (44a) and (44b) were estimated to be 0.4 0.1 and 0.7 + 0.3 (acetylene), 0.12 + 0.02 and 0.53 0.03 (propyne), and 0.12 + 0.87 0.07 (2-butyne), respectively. In any case, the formation of acidic products as well as the a-dicarbonyl products from these reactions is of potential importance in the atmosphere. 

Oxidation by PCC or by Jones reagent would lead to the dicarbonyl product ... 

The sequence of cyclohexene cleavage and aldol reaction on the dicarbonyl product gives ring-contracted cyclopentenes. This proved particularly valuable when Iwata6 wanted to make subergorgic acid 41 that has three five-membered rings awkwardly joined around a quaternary carbon atom. So crowded are these compounds that they are difficult to draw clearly. Ozono-lysis of the synthetic cyclohexene 38 gave the unstable dialdehyde 39 that cyclised by an aldol condensation to 40 and hence could be oxidised to 41. 

Claisen condensations usually give 1,3-dicarbonyl products, with one I saturated carbon between two carbonyl groups. Michael additions commonly give 1,5-dicarbonyl products, with three saturated I carbons between two carbonyl I groups. When you need a compound with three carbons between two carbonyl groups,... 

Intramolecular addition of more elaborated diazoacetates and diazoketones to a pendant furan moiety are more complex <1997TL5623>. 2-Substituted substrates uniformly provided the 2,4-diene-1,6-dicarbonyl products. Products of 3-substituted substrates depended on the structure of the diazocarbonyl and the rhodium catalyst used. For example. 

Only one equivalent of base is required for the trifluoroacetylation step apparently the chelated tetrahedral intermediate is stable at -78°C and the ft-dicarbonyl product is not generated until workup. Crucial to the success of the trifluoroacetylation reaction in some cases is the selection of lithium hexamethyldisilazide (LiHMDS) for the generation of the ketone enolate under otherwise identical conditions diazo transfer to several aryl ketones proceeds in dramatically reduced yield when lithium diisopropylamide is employed as base. 

Oxidative cleavage reactions occur in cells as well. Recent research has shown that ozone generated in vivo oxidatively cleaves the double bond in cholesterol to form a dicarbonyl product. This oxidation product is thought to contribute to arterial deposits, which are observed in coronary artery disease. 

Butyl hydroperoxides have been identified from the oxidation of each of the butanes, especially at 7 <520K [177,178], but there seems to be no unequivocal experimental evidence that diperoxyalkyl species are formed, such as would be obtained from the identification of dicarbonyl products. Many of the products identified by Minetti et al. [22] could be derived from a diperoxyalkyl oxidation route, as described in their paper, but since alternative mechanisms based on butylperoxy radical isomerization and decomposition are feasible, this evidence is not conclusive. 

The earliest mechanistic proposal related to the formation of diperoxyal-kyl species appears to be that made in 1951 by Neu et al. [188]. It was based on the formation of dicarbonyl products, detected by absorption spectroscopy, during the slow oxidation of pentane and that of other organic compounds. 

Formation of these products can be understood by assuming that the carbonylation of propargyl alcohol under high pressure involves two different reaction pathways. One is the Pd(0)-catalyzed carbonylation and the other is the Pd(II)-catalyzed oxidative carbonylation 2,3-Butadienoate (80) is a primary product of the Pd(0)-catalyzed carbonylation, but further attack by carbon monoxide at the central sp carbon of 80 under high carbon monoxide pressure yields itaconate (81) as the dicarbonylation product. Formation of aconitate (83) is explained by the oxidative dicarbonylation of a triple bond with Pd(II) species, followed by Pd(0)-catalyzed allylic carbonylation. As a supporting evidence, methyl aconitate (83) was... 

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