6-DIKETONES FROM METHYL ALKYL

Diiron enneacarbonyl, 50, 2J Diketones, from diazoketones and organoboranes, 53/ 82 3-DIKETONES FROM METHYL ALKYL KETONES 3-n-BUTYL-2,4-PENTANEDIONE, 51, 90 2,6-Dimethoxybenzaldehyde, by reduction of 2,6-dime thoxy-benzonitrile with Raney nickel alloy in formic acid,... 

P-DIKETONES FROM METHYL ALKYL KETONES 3-w-BUTYL-2,4-PENTANEDIONE... 

DIKETONES from methyl alkyl KETONES 3-n-BUTYL-2,4-PENTANEDIONE, 51, 90... 

Enamines derived from /3-diketones can be alkylated only with difficulty, and the structure of the products varies.222 Thus, Kochetkov,203 on treatment of 4-dimethylamino-3-buten-2-one with methyl... 

A closely related methodology (route c) involves the dianion from a diketone (R = Me) with the anion of dimethyl malonate (R = Me) (ref.25). The bis-trimethylsilyl ether from methyl acetoacetate has been interacted with the ketalised acid chloride shown (R = CgH ) to furnish the methoxy carbonyl derivative of olivetol (route d) (ref.26). It was also found that pentane-2,4-dione with dimethyl malonate in the presence of sodium hydride afforded methyl orsellinate (ref.26). In a biomimetic approach (route e) a tetraketone has been enzymically cyclised to give the corresponding orsellinic acid (R=H, R = alkyl) (ref. 27). 

The Paal-Knorr reaction was used for the synthesis of the pyrrole 250 from methyl 4,4,4-trifluoroacetoacetate (248) in two steps [85]. Alkylation of 248 with 4-fluorophenacyl bromide gave the 1,4-diketone 249 in 25 % yield after decarboxylation. Its cyclization with 2-cyanoethylamine in acetic acid provided 250,... 

The ketone 73 was reduced chemo- and diastereoselectively and protected to provide the silyl ether 74. The ester function was then deprotonated to the corresponding ester enolate (75) that was alkylated with methyl iodide exclusively from the Re face of the enolate to afford the bicycle 76 (Scheme 11). The substrate for the retro-aldol reaction (77) was prepared by a sequence that consists of seven functional and protecting group transformations. The retro-aldol reaction converted the bicyclic yS-hydroxy ketone 77 into the 1,3-diketone 69 via the alkoxide (78) in very good yield. 

KETENE, feef-butylcyano-, 55, 32 37, 38 Ketene 1 1-dimethylpropylcyano-, 55, 38 7-KETOESTERS, 58, 79, 81, 82 7-KETOESTERS TO PREPARE CYCLIC DIKETONES, 58, 83 KETONE terf-butyl phenyl, 55, 122 Ketone, methyl ethyl- 55, 25 Ketone, methyl vinyl, 56, 36 KETONES, acetylenic, 55, 52 Ketones, alkylation of, 56, 52 KETONFS aromatic, aromatic hydrocarbons from 55, 7... 

Chiral 2,2-disubstituted cycloalkanones.1 The imine 2 prepared from racemic 2-methylcyclohexanone and (S)-( - )-l, reacts with methyl vinyl ketone to form an adduct that is hydrolyzed to the (R)-( + )-diketone 3 in 91% ee with recovery of 1 in almost quantitative yield. The reaction is described as a deracemizing alkylation. ... 

The reactivity profiles of the boronate complexes are also diverse.43 For example, the lithium methyl-trialkylboronates (75) are inert, but the more reactive copper(I) methyltrialkylboronates (76) afford conjugate adducts with acrylonitrile and ethyl acrylate (Scheme 16).44 In contrast, the lithium alkynylboronates (77) are alkylated by powerful acceptors, such as alkylideneacetoacetates, alkylidene-malonates and a-nitroethylene, to afford the intermediate vinylboranes (78) to (80), which on oxidation (peracids) or protonolysis yield the corresponding ketones or alkenes, respectively (Scheme 17).45a Similarly, titanium tetrachloride-catalyzed alkynylboronate (77) additions to methyl vinyl ketone afford 1,5-diketones (81).4Sb Mechanistically, the alkynylboronate additions proceed by initial 3-attack of the electrophile and simultaneous alkyl migration from boron to the a-carbon. 

With alkyl methyl ketones (R-CH2,CO,Me) the reaction is complicated by the presence of two alternative sites of oxidation in practice the methyl group appears to be oxidised in preference to the methylene group for reasons which have not been adequately clarified, but in any case the yields are usually poor. Unsubstituted, or symmetrically substituted cyclic ketones possessing of course an a-methylene group, are similarly converted into 1,2-diketones (e.g. the formation of cyclohexane-l,2-dione from cyclohexanone, Expt 5.99, cognate preparation) unsymmetrically substituted cyclic ketones would normally give rise to regioisomers. 

S-Diketones.1 /3-Diketones react readily with hydroxylamine to form isoxazoles and can be reformed by acid hydrolysis and thus can function as / -diketone synthons. For example, 3,5-dimethylisoxazole, readily obtained from acetylacetone, can be metallated by a variety of bases, and the anion so obtained can be alkylated at the C5-methyl group. A second alkylation occurs only at the C3-methyl group. Thus it is possible to prepare selectively 3,5-dialkylisoxazoles, from which the corresponding / -diketones are obtained in 70-95% yield by acid hydrolysis in ethanol. 

Found in processed truffles but absent in fresh truffles were two furans (compound 4 and 7) and a pyrazine (compound 24). Furans are well known to result from the thermal degradation of carbohydrates while alkyl pyrazines result from the reaction of amino acids and alpha-diketones. A number of methyl ketones were also observed in the canned product which were absent in the fresh product. Methyl ketones are known to result from the thermal decomposition of beta-keto acids (17-19) -... 

These have a partial common structure, i.e. enolyzed a-diketone and a-hydrogen to the enollzable carbonyl is substituted by a methyl group. For a characteristic sugary aroma, the presence of enol-hydrogen was essential, because the acetyl ester or methyl ether of sotolon showed no characteristic aroma. The extraordinarily low threshold value of sotolon may be due to its coexistence with hydrophilic and hydrophobic (alkyl-substituted lactone) partial structures in one molecule. The lower threshold value of the ethyl-substituted homolog (II) than that of sotolon may also be explained from the balance of these opposite physicochemical properties. 

Intramolecular versions of reactions other than aldols can also be considered as useful options to prepare five- or six-membered rings from their corresponding bifunctional precursors. Several examples to illustrate the diverse approaches to construct five-membered rings are given in Scheme 2.110. A high-yield method to prepare cyclopentenone 284 is given in the sequence (i) alkylation of formyl-anion equivalent 285 to give 286 (ii) Michael addition of the latter to methyl vinyl ketone (iii) removal of the carbonyl protection and (iv) intramolecular cyclization of the 1,4-diketone, 287. 

Subsequent work has shown that the presence of an alkyl substituent a to the ketone carbonyl is crucial for the intramolecular five-membered-ring cyclization to occur. Thus, jS-hydroxy cyclopentanones can be synthesized from ketones containing both methyl and cyclopropanol moieties a to the carbonyl by treatment with sodium hydride at 0-25 °C. In the case of phenyl ketone, further retro-aldol ring scission leads to the 1,4-diketone as the only product. A retro-aldol/re-aldol sequence occurs when the methyl substituent is replaced by a longer alkyl substituent, such as an allyl group. In this case, the allyl substituent is located 7 to the carbonyl of the final product. ... 

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