A-Keto aldehydes

A new, versatile and selective synthesis of 6- and 7-substituted pteridines was reported by Rosowsky (73JOC2073). /3-Keto sulfoxides, which can be viewed as latent a keto aldehydes, react with (251) to give 6-substituted pterins, and the use of a-keto aldehyde hemithioacetals leads in a regiospecific synthesis to the isomeric 7-substituted pterins (equation 85). 

Aldehyde enamines react with aromatic diazonium salts in two ways, depending on the degree of substitution at the enamine earbon (130). Thus the piperidine enamine of butyraldehyde (60) reacted with p-nitrophenyl-diazonium chloride to give the p-nitrophenylhydrazone of the a-keto aldehyde (190). 

In addition to the glycol, a compound, Cj H Oj, was formed, which Semmler and Hoffman regard as a keto aldehyde, or a diketone, of specific gravity 1-055. 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Si. rra(pentafluorophenyl)boron was found to be an efficient, air-stable, and water-tolerant Lewis-acid catalyst for the allylation reaction of allylsilanes with aldehydes.167 Sc(OTf)3-catalyzed allylations of hydrates of a-keto aldehydes, glyoxylates and activated aromatic aldehydes with allyltrimethylsilane in H2O-CH3CN were examined. a-Keto and a-ester homoallylic alcohols and aromatic homoallylic alcohols were obtained in good to excellent yields.168 Allylation reactions of carbonyl compounds such as aldehydes and reactive ketones using allyltrimethoxysilane in aqueous media proceeded smoothly in the presence of 5 mol% of a CdF2-terpyridine complex (Eq. 8.71).169... 

A keto thioester was also efficiently reduced to a keto aldehyde by the previously-mentioned Fukuyama hydrosilylation procedure using Lindlar s catalyst (Pd/CaC03/PbO) in acetone at room temperature.411... 

In this reaction the osone (or a-keto aldehyde (VI)) is allowed to react with hydrogen cyanide or preferably with potassium cyanide in aqueous... 

Second step. The elements of CH4O3 are eliminated. The most likely by-products are H20 and HCOOH. Make None. Break C4-C5, C6-O8, 010-011. The base can deprotonate the OH on C5, and the lone pair on O can then push down to form a n bond with C5, causing the C4-C5 bond to break. The electrons keep getting pushed around until they end up on O again and the 0-0 bond is broken, providing the driving force for the step. A keto-aldehyde and formate anion are obtained. Now C7 (deprotonated) is nucleophilic and C6 is electrophilic, so an aldol reaction followed by dehydration gives the observed product. 

Periodic acid oxidation will also act on a-hydroxy aldehydes and ketones, a-diketones, a-keto aldehydes, and glyoxal. If the two neighboring hydroxyl groups are on an aromatic ring, the carbon-carbon bond is not cleave but the reactant is still oxidized. Thus, catechol is oxidized to the corresponding quinone. 

DAMN reacts readily with a-keto aldehydes, a-keto oximes, and x-diketones to give mono- and disubstituted aryl/alkyl dicyanopyrazines (127) in good yield (Scheme 45). 

Chiral 4,4-dialkyl-l-cyclopentenones.1 The chiral bicyclic lactam 2, derived from levulinic acid and 1, on monoalkylation exhibits slight if any selectivity regardless of the electrophile. However, a second alkylation exhibits high endo-selectivity. This product (3), after reductive cleavage, furnishes a keto aldehyde that is cyclized by base to a chiral 4,4-disubstituted-2-cyclopentenone (4). Either antipode of 4 can be prepared by the sequence of alkylation. 

Several other carbonyl components have also been employed in this process, including a-keto-aldehydes which form directly the corresponding amino ketones 121 (Scheme 7.16) [62],... 

When amino alcohols are used as the amine components along with glyoxal or a-keto-aldehydes, this process generates 2-hydroxy-morpholines 128 (Scheme 7.17) [62, 63], According to Carboni [63], this reaction proceeds with variable diastereo-selectivities (e.g. 129-131), and we have found that certain chiral amino alcohols give modest asymmetric induction (e.g. 132) [62]. 

A model system demonstrating the nutritional destruction of lysine in bovine plasma albumin (BPA) by reaction with either a dialdehyde (MA) or a keto-aldehyde (MGA) was studied in relation to reaction rates as affected by pH, temperature, reaction time and carbonyl concentration. The BPA was Fraction V obtained from Schwartz/Mann and had a molecular weight of 69 x 103 with sixty lysine residules/mole, an assayed content of 11.4%. It was dissolved in 0.0200 M phosphate-citrate buffer adjusted to the desired pH. Malonaldehyde was prepared by acid hydrolysis of its bis-(dimethyl acetal). An aqueous solution of pyruvic aldehyde was diluted with distilled water and phosphate-citrate buffer to give an MGA solution of the desired pH (16). 

At the present time, various oxidizing and reducing agents can be used to carry out such conversions (with higher yields), so that today the Cannizzaro Reaction has limited synthetic utility except for the abovementioned conversion of a-keto aldehydes. 

Corey needed the spiro-enone 34 for his synthesis of gibberellic acid.4 The obvious enone disconnection reveals a keto-aldehyde 35 with a 1,4-relationship between the carbonyl groups and disconnection at the branchpoint suggests some enol(ate) equivalent of the aldehyde 36 and the bromoketone 37. 

Weber [61,62] has developed in the context of prebiotic chemistry an original pathway for a-aminothioester synthesis [180], which can start from hydroxyaldehydes 30 intermediates in the formose reaction (a likely prebiotic pathway to carbohydrates). Obviously, thioesters themselves are not observed as products because of their fast hydrolysis in the medium, but they could be converted into peptide bonds in the presence of amino acids or peptide free amino groups, and into mixed anhydride with phosphoric acid in the presence of inorganic phosphate. The reaction involves two key-steps the condensation of ammonia and of the mercaptan on a-keto aldehyde 31... 

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