Alkoxy diketones

The formation of cM-3,4-dihydroxymethylenecyclopentanes by addition of a dinucleophilic species to an a-diketone acceptor, mediated by tin difluoride, can also be extended to chiral acceptors. Thus, addition to the a-alkoxy diketone 2-acetoxy-3,4-octanedione, in the presence of tin difluoride, affords two products in a 7.5 1 ratio. The major diastereomer is that resulting from Felkin-Anh addition followed by chelation-controlled cyclization14. 

Substitution of some of the alkoxy groups on the polytitanoxanes with glycols, P-diketones or P-ketoesters, fatty acids, diester phosphates or pyrophosphates, and sulfonic acids gives a group of products that are very effective surface-treating agents for carbon black, graphite, or fibers (32). 

Titanium chelates are formed from tetraalkyl titanates or haUdes and bi- or polydentate ligands. One of the functional groups is usually alcohoHc or enoHc hydroxyl, which interchanges with an alkoxy group, RO, on titanium to Hberate ROH. If the second function is hydroxyl or carboxyl, it may react similarly. Diols and polyols, a-hydroxycarboxyflc acids and oxaUc acid are all examples of this type. P-Keto esters, P-diketones, and alkanolamines are also excellent chelating ligands for titanium. 

The mercaptals obtained by the acid catalyzed reaction of J3-ketoesters, e.g., ethyl acetoacetate, with methyl thioglycolate (73) undergo the Dieckmann cyclization with alcoholic potassium hydroxide at lower temperatures to give ethyl 3-hydroxy-5-methyl-2-thiophenecarboxylate (74) in 75% yield. ° Besides ethyl acetoacetate, ethyl a-ethylacetoacetate, ethyl benzoyl acetate, and ethyl cyclopentanonecarboxylate were also used in this reaction/ It is claimed that /8-diketones, hydroxy- or alkoxy-methyleneketones, or /8-ketoaldehyde acetals also can be used in this reaction. From acetylacetone and thioglycolic acid, 3,5-dimethyl-2-thiophenecarboxyl-ic acid is obtained. ... 

Cyclopentenones. 1,3-Dicarbonyl compounds add to enol ethers or esters (terminal) in the presence of Mn30(OAc)7 (excess) to form l-alkoxy-l,2-dihydro-furans. These can be converted to a 1,4-diketone, which undergoes aldol cyclization to fused (or spiro) cyclopentenones.1... 

A similar type of acid-catalyzed condensation of aldehydes with 4-methylene-2-oxetanone (diketene), giving 4-oxo-6-methyl-l,3-dioxins, has been patented (73GEP2149650). However, other work has established that <5-hydroxy-/3-keto acids or unsaturated keto acids are formed as the principal products (equation 24) (78CPB3877, 78CL409). The latter reaction probably involves electrophilic attack of the protonated aldehyde on the nucleophilic exocyclic methylene carbon atom of the diketone. A closely related reaction of acetals with diketene, catalyzed by titanium tetrachloride, gives the corresponding <5-alkoxy-/3-keto esters (74CL1189). 

Application of this ring enlargement and oxidation procedure to 2-alkoxy-l-siloxycyclopropanes incorporated in a large ring provides macrocyclic diketones which act as potent chelating agents for metal cations [50]. 

Diketones can be converted to a-keto enol ethers by treatment with an alkoxy tri-methylsilane ROSiMe3.616... 

The reaction in alcoholic medium of a /3-diketone, a base and VOCl2 in 1 2 1 molar ratios leads to compounds [VO(alkoxy)(/8-diketonato)]2.553 This is an interesting result since [VO(/3-diketonato)2] form if the reaction with the same species is carried out in molar ratios of 2 2 1 or 1 1 1. Therefore, the stoichiometry in which the reagents are mixed will drive the reaction towards one product or the other. This behaviour was rationalized assuming Scheme 16 where an intermediate [VO(OH)L] (not isolated) forms and is irreversibly transformed to the corresponding [VO(OR)L] compound. 

Intramolecular condensation of either 2-formylpyrrole or 2-benzoylpyrrole with phenacyl bromide gave pyrrolizin-3-ones 52a39 and 52b,40 respectively. JV-Acylpyrroles presumably are intermediates. Similarly, 5-alkoxy-2-for-mylindoles (53) were converted to benzopyrrolizines (54) by treatment with methyl vinyl ketone in the presence of trimethylbenzylammonium hydroxide in dioxane 41 From diketone 55 a mixture of pyrrolizines [56a (25%) and 56b (11%)] was obtained.42... 

Contrary to the oxonium intermediate 115 (Section III,C,2), the intermediate 211 having the alkoxy leaving group readily opens its heterocyclic ring under these conditions. Diketones 205 (R3 is not H) thus formed are then cyclized into a-naphthols 204 (or /3-naphthols of type 209). If anhydro-bases 212 were formed, they would have to take part in the analogous conversions described previously. Obviously, the same mechanism may be applied to the scheme of formation of a-naphthols 204 from 2-benzopyrylium salts under the action of dimethylamine hydrochloride in ethanol (77KGS996) (cf. Section III,C,4,a,iv). 

Scheme 8.14 Michael reaction of p-diketones (X = alkyl) and p-oxo esters (X = alkoxy) with methyl vinyl ketone (41a, MVK).

Eine Katalyse ist bei Verwendung von Trichloracetaldehyd (Chloral) als Carbonyl-Kom-ponente398 nicht notwendig. 1,5-Diketone reagieren unter Basenkatalyse durch Ring-schluB zu 1-Alkoxy-2,6-dihydroxy-phosphorinan-l-oxiden399 ... 

The diastereoselective allylindium addition to norbornyl cr-diketones leads to acyloins. The diastereoselection in the case of monoallylation products greatly depends on the nature of 5-endo substituents. Non-chelating groups direct the addition from the sterically less congested exo-face, diagonal to the substituent, whereas chelating substituents, such as an alkoxy or acetoxy unit, induce a complete reversal in the selectivity (Equation (16)).169... 

Tertiary alcohol 293, when reacted with iodobenzene diacetate and iodine, underwent a formal alkoxy radical fragmentation and provided the nine-membered diketone 294 in 80% yield as a separable 1.2 1 mixture of epimers (Equation 40) <1999JOC4576>. 

Metal alkoxides react with hydroxylated compounds XOH such as carboxyhc acids or /3-diketones leading to the elimination of alkoxy groups, following equation (4). These complexing XOH species behave as bridging (acetate, AcO ) (4) or chelating (acetylacetonate, acac) (5) bidentate... 

As outlined in Scheme 9, compounds containing gronp 13 elements in the -1-2 oxidation state are generally synthesized either by the alkali metal reduction of suitable halogenated precursor R2MX or by metathesis reactions with available X2M-MX2 compounds that contain M. The ligands that have been introduced using this method include aryl, alkoxy, and diketonates, but the most extensively examined series of compounds bear either the bis(trimethylsilyl)methyl ( disyl ),... 

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