Ketones, potassium tert-butoxide

The ketones 1 and 3, or compounds with a similar structure, have been used for the preparation of methoxy derivatives of 1-benzoxepin. In the standard procedure for methylation, the 1-benzoxepinone is deprotonated by potassium tert-butoxide and subsequently reacted with methyl fluorosulfonate at low temperature.16 173 - 175 The yields are generally high. 

Trialkylboranes react rapidly and in high yields with a-halo ketones,a-halo esters, a-halo nitriles, and a-halo sulfonyl derivatives (sulfones, sulfonic esters, sulfonamides) in the presence of a base to give, respectively, alkylated ketones, esters, nitriles, and sulfonyl derivatives. Potassium tert-butoxide is often a suitable base, but potassium 2,6-di-tert-butylphenoxide at 0°C in THF gives better results in most cases, possibly because the large bulk of the two tert-buXy groups prevents the base from coordinating with the R3B. The trialkylboranes are prepared by treatment of 3 mol of an alkene with 1 mol of BH3 (15-16). With appropriate boranes, the R group transferred to a-halo ketones, nitriles, and esters can be vinylic, or (for a-halo ketones and esters) aryl. " °... 

The propargylic alcohol 102, prepared by condensation between 100 and the lithium acetylide 101, was efficiently reduced to the hydrocarbon 103, which on treatment with potassium tert-butoxide was isomerized to the benzannulated enyne-allene 104 (Scheme 20.22) [62], At room temperature, the formation of 104 was detected. In refluxing toluene, the Schmittel cyclization occurs readily to generate the biradical 105, which then undergoes intramolecular radical-radical coupling to give 106 and, after a prototropic rearrangement, the llJ-f-benzo[fo]fluorene 107. Several other HJ-f-benzo[fo]fluorenes were likewise synthesized from cyclic aromatic ketones. 

The classical procedure for the Wolff-Kishner reduction—i.e. the decomposition of the hydrazone in an autoclave at 200 °C— has been replaced almost completely by the modified procedure after Huang-Minion The isolation of the intermediate is not necessary with this variant instead the aldehyde or ketone is heated with excess hydrazine hydrate in diethyleneglycol as solvent and in the presence of alkali hydroxide for several hours under reflux. A further improvement of the reaction conditions is the use of potassium tert-butoxide as base and dimethyl sulfoxide (DMSO) as solvent the reaction can then proceed already at room temperature. ... 

This reaction involves the condensation of an aldehyde or ketone with an a-halo ester in the presence of a basic condensing agent (sodium ethoxide, sodamide, finely divided sodium or potassium tert.-butoxide) to give a glycidio (or ap-epoxy) ester. Thus acetophenone and ethyl chloroacetate yield phenyl-methylglycidic ester (I) ... 

The condensation of aldehydes and ketones with succinic esters in the presence of sodium ethoxide is known as the Stobbe condensation. The reaction with sodium ethoxide is comparatively slow and a little reduction of the ketonic compound to the carbinol usually occurs a shorter reaction time and a better yield is generally obtained with the more powerful condensing agent potassium ieri.-butoxide or with sodium hydride. Thus benzophenone condenses with diethyl sucoinate in the presence of potassium tert.-butoxide to give a 94 per cent, yield of (3-carbethoxy-YY-diphenylvinylacetic acid (I) is the potassium salt ... 

Experimental conditions leading to good yields of olefins comprise heating the hydrazone or semicarbazone of the ketone with potassium tert-butoxide in anhydrous toluene/7]. The reason for the product difference is not known, but may be associated with preferential protonation at C(S) arising from the particular charge distribution and geometrical relationship in a specifically solvated ion-pair of the type (9), which would be favoured by the non-polar solvent. 

Woodward, Barton, and co-workers [159] in 1954, and the reaction has received considerable attention since, that date [160]. The process is very efficient, apart from a tendency to give additional methyiation at C(g) under vigorous conditions, but attempts to stop the methyiation halfway as a route to 4-methyl-A -3-ketones (4 have been only moderately successful. The reason behind the preference for rapid di-methylation becomes apparent from consideration of the mechanism. If the initial step is the abstraction of a proton by base (usually potassium tert-butoxide or tert-amyloxide) to give the A -dienoIate ion (2), an electrophihc reagent... 

The following chemicals were purchased from Kanto Chemical Co. Inc. and used as received neopentyl glycol, p-toluenesulfonic acid, sodium, and n-BuLi. N,N,N, N -Tetramethylethylenediamine was purchased from Aldrich Chemical Company, Inc. and distilled before use. 1,3-Dichloroacetone was obtained from Wacker Chemicals East Asia and used as received. Reagent grade benzene, pentane, ether, THE, tert-butyl alcohol, acetonitrile, and toluene were purchased from Wako Chemicals Industries Ltd. Benzene, pentane, and tert-butyl alcohol were distilled from CaH ether and THF from sodium benzophenone ketyl immediately before use acetonitrile successively from PjOj and anhydrous KjCOj and toluene from LiAlH. Potassium tert-butoxide and 2-cyclopenten-1-one were purchased from Tokyo Kasei Kogyo Co. Ltd. the ketone was distilled before use. 

The hexahydrothianaphthoxazines 38 and 39 were synthesised from the commercially available ketone 58, which was readily converted into the tosyloxime 60 in two steps. Neber rearrangement of 60 with potassium tert-butoxide afforded the desired amino-ketone 61. The amino ketone 61 was readily acylated with chloroacetyl chloride. Reduction of the keto-chloroacetamide 62 with sodium borohydride gave only the trans isomer. The proton on Cl gave a doublet at 8 4.6 ppm with a coupling constant of 7.2 Hz indicating a di-axial coupling. The cis-compound would have a couplings constant of about 3.5 Hz. 

Any equilibrium will produce the thermodynamically most stable enolate. The most stable enolate will have the greatest charge delocalization. In the above example, the thermodynamically favored enolate is conjugated the kinetically favored enolate is not. Common conditions for thermodynamic control are to use average bases (like sodium ethoxide or potassium tert-butoxide, p abH 16 to 19) in alcohol solvents. Proton transfer equilibria rapidly occur among base, solvent, ketone, and enolate. Sodium hydride or potassium hydride in an ether solvent are also thermodynamic reaction conditions that allow equilibration between the ketone and the enolate. Enones have two possible enolates weaker bases give the thermodynamically more stable extended enolate, whereas kinetic conditions produce the cross-conjugated enolate. 

If extreme steric hindrance is present in the ot-halo ketone substrate, base treatment can, however, lead to the isolation of a bulky cyclopropanone. The classic example in this area is the 1,3-dehydrobromination of a-bromo(dineopentyl) ketone 4 with potassium tert-butoxide in tert-butyl alcohol or diethyl ether, or with potassium 4-chlorophenyldimethylcarbinolate, ° giving ra i-2,3-di-rert-butylcyclopropanone 5 in 30-75 and 20-40% yields, respectively. In this case, it is crucial to use slightly less than one equivalent of base (max 0.95 equiv) since even a small excess results in complete conversion into the Favorskii ester. ... 

When a mixture of a cyclopropyl phenyl selenone and a ketone or an aldehyde is treated with potassium tert-butoxide in tetrahydrofuran, metalation of the selenone takes place preferentially and the metalloselenone formed immediately reacts with the carbonyl compound. Oxaspiropentanes are produced almost quantitatively when ketones are used whereas a mixture of oxaspiropentanes and cyclopropyl ketones are obtained when the reaction is carried out with aldehydes, for example, formation of 5 and... 

Trimethylcyclopropanone (12) reacted with sodium methoxide to give a 4 1 mixture of isomeric carboxylic esters 14 and 15 while a-bromo ketone 16 rearranged with potassium tert-butoxide in fcrt-butyl alcohol to provide carboxylic acid 18. ... 

Decarbonylation of a /9-aldehyde 3 has been achieved at elevated temperatures using a catalytic amount of tris(triphenylphosphane)rhodium(I) chloride (Wilkinson s catalyst) and of a 1 -cy-clopropylalkyl phenyl ketone using potassium tert-butoxide. ... 

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