Dicarbonyl compounds Carbon dioxide

What is described as a domino Knoevenagel-hetero-Diels-Alder reaction , involving the reaction of the glucose-derived aldehyde 93 with a 1,3-dicarbonyl compound in presence of either proline or ethylenediammonium acetate, leads to the doubly annulated 5 6 6-fused compound 94 (Scheme 30) <2004S1150>. If the dicarbonyl compound is Meldmm s acid, however, the sequence is completed by spontaneous elimination of acetone and carbon dioxide from the Diels-Alder adduct, to give compound 95 <2005ASC1353>. 

Tributyltin hydride, 316 Tributyltinlithium, 319 Trichloroacetonitrile, 321 Other carbohydrates (Diethylamino)sulfur trifluoride, 110 Triethyloxonium tetrafluoroborate, 44 Carbonates (see also Enol carbonates) Carbon dioxide, 65 Di-/-butyl dicarbonate, 94 Carboxylic acids (see also Dicarbonyl compounds, Unsaturated carbonyl compounds)... 

XXXVII). The typical reaction74 of /3-dicarbonyl compounds, over-oxidation, will then give one mole of glyoxylic acid per mole, and thence one mole of carbon dioxide. 

This is a reaction of a-amino acids, in which they are oxidised to the corresponding aldehyde, giving off carbon dioxide, and ammonia is transferred to other components of the system, very little being liberated as such. The reaction is initiated by compounds, such as a-dicarbonyl compounds and their vinylogues, or compounds which can give rise to them readily, such as reductones by dehydrogenation or imino analogues by hydrolysis. The reaction may therefore be represented as follows ... 

The gaseous carbonyl difiuoridc (bp — 83 C) is used as a fluorinating agent for aldehydes and ketones. In a first reaction step, isolable fluoroformatcs are formed which are converted into the ew-difluorides 1 by loss of carbon dioxide. a-Dicarbonyl compounds yield cyclic 1,2-di-fluoroethene carbonates. ... 

Dimethylcyclohexane-l,3-dione (dimedone) and Ai,Ai-dimethylbarbituric acid are relatively acidic (3-dicarbonyl compounds 5.3 and 4.7, respectively). The deprotection reaction involves (Scheme 16) a prototropic equihbrium between the P-dicarbonyl compounds and the deprotected carbamate species (shifted further to right by the formation of carbon dioxide and the respective amine). 

Hydrolysis of the 4-amino group provided entry to the corresponding 4-oxo derivatives and, so, 157 was converted readily to the l//-pyrazino[2,3-H[l,2,6]thiadiazin-4(3//)-ones 158 (X = 0) by reaction with potassium carbonate in aqueous methanol. The parent system was prepared previously by reaction of 4,5-diamino-2//-l,2,6-thiadiazin-3(6//)-one 1,1-dioxide with 1,2-dicarbonyl compounds <1984JHC861>, but the starting diamine was difficult to prepare, so this is a more versatile method for preparation of the 4-oxo compounds. The 4-oxo compounds 158 (X = O) were converted to the corresponding 4-thioxo derivatives 158 (X = S) by reaction with phosphorus pentasulfide (Scheme 10) <2003HCA139>. 

These doubly stabilized anions are alkylated so well that it is common to carry out an alkylation between two carbonyl groups, only to remove one of them at a later stage. This is made possible by the fact that carboxylic acids with a 3-carbonyl group decarboxylate (lose carbon dioxide) on heating. The mechanism below shows how. After alkylation of the dicarbonyl compound the unwanted ester is first hydrolysed in base. Acidification and heating lead to... 

The amino acid is degraded to an aldehyde with one less carbon atom and carbon dioxide, while the nitrogen combines with the dicarbonyl compound. 

C-2 modification of the 1,3-dicarbonyl compound is possible by deprotonation in the 2-position followed by electrophilic capture (path A). Depending on the type of electrophile used, oxygen modification is also possible (path B). Nucleophilic attack on one of the Meldrum s adds carbonyl groups leads to a tetrahedral intermediate, which decomposes easily to generate carbon dioxide, acetone, and an enolate product, which is protonated either by addic leadion media or in a separate work-up step. This nucleophilic displacement reaction equals the use of Meldrum s acid as a —CH CCO) equivalent. Indeed, this is a very common application of Meldrum s acid in multicomponent syntheses (vide infra). 

We begin with reactions of polar organometallics with aldehydes, ketones, and v/c-dicarbonyl compounds (a-oxoaldehydes, 1,2-diketones, a-oxocarboxamides, and a-oxocarboxylic acids). Next we focus on carboxamides, lithium carboxylates, carboxylic acid esters, and acyl chlorides. Finally we turn to ketenes, (thio)isocyanates, and carbon dioxide, all featuring cumulated double bonds, and last but not least to carbon monoxide. 

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