Keto aldehydes acids

These reversible reactions are cataly2ed by bases or acids, such as 2iac chloride and aluminum isopropoxide, or by anion-exchange resias. Ultrasonic vibrations improve the reaction rate and yield. Reaction of aromatic aldehydes or ketones with nitroparaffins yields either the nitro alcohol or the nitro olefin, depending on the catalyst. Conjugated unsaturated aldehydes or ketones and nitroparaffins (Michael addition) yield nitro-substituted carbonyl compounds rather than nitro alcohols. Condensation with keto esters gives the substituted nitro alcohols (37) keto aldehydes react preferentially at the aldehyde function. 

The most important routes to B-norsteroids involve oxidative fission of 5,6-double bonds to keto acids or keto aldehydes which are then closed to five-membered rings by condensation reactions. Three of the best oxidation methods are exemplified in the following examples chosen from the cholestane, androstane, and pregnane series. 

Carboxylic esters can be treated with ketones to give p-diketones in a reaction that is essentially the same as 10-118. The reaction is so similar that it is sometimes also called the Claisen condensation, though this usage is unfortunate. A fairly strong base, such as sodium amide or sodium hydride, is required. Yields can be increased by the catalytic addition of crown ethers. Esters of formic acid (R H) give P-keto aldehydes. Ethyl carbonate gives P-keto esters. 

The acid (VII) formed in the Jones oxidation is readily separated from the nonacidic organic material by extraction of the ether layer with NaHC03 solution. The material not extracted by NaHC03 (neutral organics) was shown by NMR spectroscopy to consist of primarily the keto aldehyde VI. 

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... 

Possible racemisation of imines, derivatives of amino acids and R(—)-myrtenal, has been examined by Dufrasne et al.1 After 72 h, no significant effect on chiral purity was observed. For imines being derivatives of chiral primary amines and the a-substituted 8-keto-aldehydes, no evidence of epimerisation has been indicated by the NMR measurements.3 For a series of imines, being derivatives of amino acids or amino acid esters and (R)-BINOL reagents, Chin et al.5 have tested the possibility of epimerization under experiment conditions. It was shown that R S ratio has changed only slightly, and after 24 h, the difference was lower than 10%. 

Biochemical reactions include several types of decarboxylation reactions as shown in Eqs. (1)-(5), because the final product of aerobic metabolism is carbon dioxide. Amino acids result in amines, pyruvic acid and other a-keto acids form the corresponding aldehydes and carboxylic acids, depending on the cooperating coenzymes. Malonyl-CoA and its derivatives are decarboxylated to acyl-CoA. -Keto carboxylic acids, and their precursors (for example, the corresponding hydroxy acids) also liberate carbon dioxide under mild reaction conditions. 

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. 

Phytochemical Reduction of Keto Acids and Keto Aldehydes. 85... 

The well-known Robinson-Schbpf reaction has been applied to the synthesis of JZ-adaline (107) from ketoglutaric acid (457), ammonium chloride, and keto-aldehyde (458) (Scheme 58) 338). The second synthesis of starts with nitrone 459 462). Reaction of 459 with pentylmagnesium bromide gave a hydroxylamine (460) which was oxidized to yield a mixture of nitrones 461 and 462. Without separation of the nitrones (461 and 462), successive treatments with allylmagnesium bromide and then mercuric oxide gave a mixture of desired nitrones 466 and 467 and by-product 468. Nitrones 466 and 467 are capable of 1,3-dipolar cycloaddition and, on heating in chloroform, 466 and 467... 

More recently, the same group achieved a simple, highly stereocontrolled total synthesis of (+)-hirsutic acid (Scheme LXXIX) ". This chirally directed effort developed subsequent to reaction of dl-728 with (+)-di-3-pinanylborane, alkaline hydrogen peroxide oxidation, chromatography, PCC oxidation, and hydrogenolysis. The dextrorotatory hydroxy ketone 729 was nicely crafted into keto aldehyde 730 from which 720 was readily obtained. Once again, the Wacker oxidation played an instrumental role in annulation of the third five-membered ring. The remainder of the asymmetric synthesis was completed as before. 

The second synthetic approach to oidiolactone C (61) is summarized in Scheme 20. This route also commences with the ozonolysis of trans-communic acid 180. Now, when this compound was exposed to ozone in excess, keto aldehyde 187 was obtained in 76% yield. The key step in this approach was the y-lactone closure via chemoselective reduction of the lactone moiety on compound 189 through a SN2 mechanism. Compound 189 could be prepared by saponification of the corresponding methyl ester with sodium propanethiolate. Once the primary alcohol is oxidized, the completion of the synthesis of key lactone 103 only requires the allylic oxidation of the C-17 methyl with concomitant closure of the 8-lactone. This conversion was achieved with Se02 in refluxing acetic acid to give 103 in 51% yield. 

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