Methyl tert-butyl ketone reactions

Heating 2,3-dimethyl-2,3-diol, pinacol (24), at 80°C in the presence of Nafion-H gave a 92% yield of pinacolone (methyl-tert-butyl ketone) (25) (Eqn. 22.18). Similar yields were obtained with other ditertiary vicinal diols. Reaction of pinacol with either La-HY or H-ZSM-5 or aluminum exchanged montmorillonite 2 gave both pinacolone (25) and 2,3-dimethylbutadiene (26), resulting from the dehydration of the diol, in nearly equal quantities. Only a small amount of dehydration was observed when the rearrangement was run over... 

In another type of application, water-immiscible ILs can form biphasic systems, where the enzyme and the cofactor dissolved in the aqueous phase is physically separated from the substrates and products mainly in the IL phase. The first report of enzymatic ketone reduction in an IL-buffer biphasic system described the IfoADH-catalyzed enantioselective reduction of 2-octanone in a biphasic system containing buffer and [BMIM][Tf2N], which showed higher reaction rates than that in buffer-methyl tert-butyl ether biphasic system [53]. 

The typical CBS reduction sees use of between 2-10 mol% of the oxaza-borolidine catalyst, with BHg THF, BH3 DMS or less commonly DEANB as reducing agent, the reactions being run in solvents such as THF, methyl tert-butyl ether (MTBE) or toluene at temperatures usually between 0-25 °C. The ketone is usually added in a slow, dropwise fashion to a preformed mixture of the oxazaborolidine catalyst and borane (addition usually complete within 1-1.5 h). However, it is also possible to simultaneously add the borane and ketone together this sometimes results in improvements to the enantios-electivily of the reaction. 

The ketones are also present in readily detectable amounts, with acetone concentrations usually dominating those of the other ketones. Several alcohols have been observed in urban atmospheres methanol and ethanol are present at the highest concentrations. Methyl tert-butyl ether (MTBE) is observed in urban atmospheres where this compound is used as a gasoline additive. Esters are observed in urban atmospheres, especially near sources of solvent manufacture or heavy use. The smaller organic acids are usually observed in urban areas. Although their sources are not strong, their removal rates by reaction are small, as loss occurs largely by deposition on terrestrial or water surfaces, or by accumulation in aerosols. A number of dicarboxylic acids (C2-C12)... 

If, on the other hand, unsymmetrically substituted carbonyl compounds such as monosubstituted benzophenones (X = OCH3, CH3, Cl), tert-butyl methyl ketone, acetophenone, acetaldehyde, or benzaldehyde are used for trapping 39a, diastere-omeric mixtures are formed in each case they could all be resolved except for the products obtained with p-methoxybenzophenone and acetophenone 33>. An X-ray structure analysis has been performed for the E-isomer 57g 36) which, in conjunction with H-NMR studies, permitted structural assignment in cases 56 and 57e, g and h35>. Additional chemical evidence for the structure of the six-membered heterocycles is provided by the thermolysis of 56 a considered in another context (see Sect. 3.1). In general the reaction 39a- 56 or 57 is accompanied by formation of phosphene dimers, presumably via [4 + 4]- and via [4 + 2]-cycloaddition 35). 

Tetrahydrobenzo[6]thiophen-4-one (103) may be prepared from y-(2-thienyl)butyric acid by cyclization with phosphoric acid854 or by Friedel-Crafts cyclization of the corresponding acid chloride.194, 355.358 j s 5-methyl,357 2-ethyl,194 2-isopropyl,358 2- and 3-tert-butyl,359 2,3-dimethyl,360 2-ethyl-3-methyl,360 and 2-bromo 354 derivatives and diethyl 4,5,6,7-tetrahydrobenzo[6]thiophene-4,5-di-carboxylate861 may be prepared similarly. 4,5,6,7-Tetrahydrobenzo-[6]thiophen-7-one (104)357 362,863 and its 5- and 6-methyl 357 and 2-chloro 362 derivatives are obtained from the appropriately substituted y-(3-thienyl)butyric acid, A recent patent 364 describes the vapor phase cyclization of y-(2-thienyl)butyric acid to 103. Ketones (103 and 104) are useful intermediates for the synthesis of 4- and 7-substituted benzo[6]thiophenes, respectively their reactions are discussed in Section VI, B, 4. 

There are some known unsuccessful attempts to carry out alkylation (Mel, Me2S04), halogenation (tert-butyl hypochloride) and nitration of aromatic dihydrobenzodiazepines [7, 105]. Such attempts only resulted in the destruction of the seven-membered heterocycle. As a rule, these destructive processes are typical of dihydrodiazepine systems and often manifest themselves during the synthesis and study of these compounds. Therefore, the results of the destruction of a seven-membered heterocycle are most widespread and include its decomposition into ortho-diamine and carbonyl compounds (Scheme 4.43, reactions A and B) [105, 106] and benzimidazole rearrangement accompanied by splitting out of a methyl aryl ketone molecule (Scheme 4.43, reaction C) [117]. 

The first example of a catalytic asymmetric Horner-Wadsworth-Emmons reaction was recently reported by Arai et al. [78]. It is based on the use of a chiral quaternary ammonium salt as a phase-transfer catalyst, 78, derived from cinchonine. Catalytic amounts (20 mol%) of organocatalyst 78 were initially used in the Homer-Wadsworth-Emmons reaction of ketone 75a with a variety of phospho-nates as a model reaction. The condensation products of type 77 were obtained in widely varying yields (from 15 to 89%) and the enantioselectivity of the product was low to moderate (< 43%). Although yields were usually low for methyl and ethyl phosphonates the best enantioselectivity was observed for these substrates (43 and 38% ee, respectively). In contrast higher yields were obtained with phosphonates with sterically more demanding ester groups, e.g. tert-butyl, but ee values were much lower. An overview of this reaction and the effect of the ester functionality is given in Scheme 13.40. 

Other peroxides—2,6-dichlorobenzoyl peroxide lauroyl peroxide, tert-butyl hydroperoxide, and methyl ethyl ketone peroxide—are also highly effective for the free radical reaction at low temperatures. On the other hand, azobisisobutyronitrile (AIBN) is ineffective. Hence, the mechanism cannot be simple, free radical formation which then initiates polymerization. 

The number of publications describing new ligands that allow the transfer hydrogenation of aromatic ketones with over 90 % ee has grown in leaps and bounds since 1996 [15]. In these reactions the use of ruthenium [15a-f] and iridium [15g] as the catalytically active metals has recently been augmented by the use of phosphorus-free ligands such as chiral diamines, amino alcohols, and bisthioureas such as 7 [15a,e-g]. A ruthenium-catalyzed transfer hydrogenation with 92 % ee has even been reported for the aliphatic ketone pinacolone (tert-butyl methyl ketone) [16]. 

Treatment of a-iodo ketone and aldehyde with an equimolar amount of Et3B yielded the Reformatsky type adduct in the absence of PhaSnH (Scheme 21), unlike ot-bromo ketone as shown in Scheme 15 [22], Ethyl radical abstracts iodine to pro-duee carbonylmethyl radical, which would be trapped by EtsB to give the corresponding boron enolate and regenerate an ethyl radical. The boron enolate reacts with aldehyde to afford the adduct. The three-component coupling reaction of tert-butyl iodide, methyl vinyl ketone and benzaldehyde proceeded to give the corresponding adduct 38, with contamination by the ethyl radical addition product 39. The order of stability of carbon-centered radical is carbonylmethyl radical > Bu > Pr > Ef > Me . 

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