Aliphatic and cyclic ketone

By changing from the simplest to larger aliphatic and cyclic ketones, structural factors may be introduced which favor alternative unimolecular primary photoprocesses or provide pathways to products not available to the simple model compound. In addition, both the increase in molecular size and irradiation in solution facilitate rapid vibrational relaxation of the electronically excited reactant as well as the primary products to thermally equilibrated species. In this way the course of primary and secondary reactions will also become increasingly structure-selective. In a,a -unsym-metrically substituted ketones, the more substituted bond undergoes a-cleavage preferentially. 

Attack by eCN is slow (rate-limiting), while proton transfer from HCN or a protic solvent, e.g. HzO, is rapid. The effect of the structure of the carbonyl compound on the position of equilibrium in cyanohydrin formation has already been referred to (p. 206) it is a preparative proposition with aldehydes, and with simple aliphatic and cyclic ketones, but is poor for ArCOR, and does not take place at all with ArCOAr. With ArCHO the benzoin reaction (p. 231) may compete with cyanohydrin formation with C=C—C=0, 1,4-addition may compete (cf. p. 200). 

Acetophenones, aliphatic and cyclic ketones were a-acetoxylated by DIB in acetic acid-acetic anhydride, in the presence of sulphuric acid, in moderate yield some / -diketones were similarly acetoxylated at the methylene carbon. The more reactive trimethylsilyl ethers reacted at room temperature without acid catalysis, with retention of their silyl group the products came either from substitution of the vinylic hydrogen or from bis acetoxylation of the double bond. 

Reaction of 201 with 1,3-dicarbonyl compounds, or with aliphatic and cyclic ketones 203 in the presence of dilute sulfuric acid, gave the 3//-l,2,3-triazolo[4,5-6]pyridines 204 (79CPB2861). The mechanism of transformation involves ring fission to 202, followed by reaction with 203 to give 204, a type of Friedlaender synthesis (see Scheme 42). 

The choice of sublimed potassium t-butoxide free of -butyl alcohol in peroxide-free tetrahydrofuran (THF) was found to be a suitable base for the nitration of aliphatic and cyclic ketones, nitriles ( ) and N-disubstituted amides ( 7). As the nitrating agent, primary alkyl nitrates such as ethyl nitrate were chosen, after it was established that they were not affected by the base, t-butoxide below -10 . 

The Bredereck-type synthesis, which is well known as a conventional preparation of pyrimidine derivatives, generally requires a reaction temperature of more than 160 °C, and the product yield is moderate. A simple, high-yielding synthesis of pyrimidines from ketones in the presence of HMDS and formamide is reported. Under microwave irradiation, heteroaromatic, aryl, aliphatic, and cyclic ketones cyclized to give pyrimidines in good yields. 

The structure activity relationship developed for these dihydropyridines showed that optimal activity was derived from BTF, using anilines containing a halogen, cyano or CFj group in the para position and small aliphatic and cyclic ketones and acetophenones. 

Aldehydes and ketones, both aromatic and aliphatic (including cyclic ketones), can be converted in high yields to dimeric alkenes by treatment with TiCl3 and a zinc-... 

Recently, it has been demonstrated that coordination vacancies on the surface metal cations are relevant to the unique redox reactivity of oxide surfaces]2]. Oxidation of fonnaldehyde and methyl formate to adsorbed formate intermediates on ZnO(OOOl) and reductive C-C coupling of aliphatic and aromatic aldehydes and cyclic ketones on 1102(001) surfaces reduced by Ar bombardment are observed in temperature-prognunmed desorption(TPD). The thermally reduced 1102(110) surface which is a less heavily damaged surface than that obtained by bombardment and contains Ti cations in the -t-3 and +4 states, still shows activity for the reductive coupling of formaldehyde to form ethene]13]. Interestingly, the catalytic cyclotrimerization of alkynes on TiO2(100) is also traced in UHV conditions, where cation coordination and oxidation states appear to be closely linked to activity and selectivity. The nonpolar Cu20( 111) surface shows a... 

Organic-Base Catalyzed. Asymmetric direct aldol reactions have received considerable attention recently (Eq. 8.98).251 Direct asymmetric catalytic aldol reactions have been successfully performed using aldehydes and unmodified ketones together with chiral cyclic secondary amines as catalysts.252 L-proline and 5,5-dimethylthiazolidinium-4-carboxylate (DMTC) were found to be the most powerful amino acid catalysts for the reaction of both acyclic and cyclic ketones as aldol donors with aromatic and aliphatic aldehydes to afford the corresponding... 

All reducing agents used for reductions of aliphatic and aromatic ketones can be used for reduction of cyclic ketones to secondary alcohob (pp. 107 and 109). In fact, reduction of cyclic ketones is sometimes easier than that of both the above mentioned categories [262]. What is of additional importance in the reductions of cyclic ketones is stereoselectivity of the reduction and stereochemistry of the products. 

This protocol complements Akiyama s method which provides P-amino carbonyl compounds as i yn-diastereomers [14], It tolerated aromatic, heteroaromatic, and aliphatic aldehydes. Cyclic ketones, acetone, as well as acetophenone derivatives could be employed. The use of aromatic ketones as Mannich donors was up to that time unprecedented in asymmetric organocatalysis. Rueping et al. independently expanded the scope of the asymmetric Brpnsted acid-catalyzed Mannich reaction of acetophenone [45]. 

Conversion of Various Aliphatic, Aromatic and Cyclic Ketones. 83... 

The first suitable representative of this class of substances, 6-methyl-5-heptene-2-one, was investigated by Neuberg and Lewite. This ketone, which is a natural constituent of ethereal oils, can also be obtained by degradation of various aliphatic and cyclic terpenes. By means of fermenting yeast it is converted to 6-methyl-5-heptene-2-ol,... 

Ketones, in contrast to aldehydes, occur frequently in plants. A phytochemical reduction of the keto group has been shown in aliphatic, aromatic s and cyclic ketones although it takes longer and is less complete than in the case of aldehydes. (For the theory of this transformation see Neuberg and Gorr. )... 

R) -specific ADH from L. kefir was used for the reduction of various ketones to the corresponding secondary alcohols. Aliphatic, aromatic, and cyclic ketones as well as keto esters were accepted as substrates. The activities achieved with several substrates were compared with the activity obtained with the standard substrate of ADH, acetophenone (Fig. 2.2.4.4). As the figure shows, recombinant LK-ADH has a very broad substrate spectrum, including many types of ketones. 

An analogous non-electrochemical Ni(0)-catalysed process, exploited in a Mannich/ Reformatsky multicomponent process58, will be discussed in Section III (equation 41). In the third study, the a-bromoester Id is simply electrolysed in the presence of a carbonyl compound in DMF/THF in a 1 2 ratio using both indium and zinc rods as sacrificial anodes. While aldehydes afford the expected 3-hydroxyesters in high yield, aliphatic, aromatic and cyclic ketones, with the exception of acetone, directly afford /3-lactones,... 

The NADP-dependent TBADH was used for the laboratory-scale preparation of several chiral aliphatic and cyclic hydroxy compounds by reduction of the corresponding ketones. For the regeneration of NADPH, this reduction reaction can be coupled with the TBADH catalyzed oxidation of isopropanol. For the reduction of some ketones it was observed that the reaction rate was increased in the presence of the regenerating substrate isopropanol, for instance in the presence of 0.2 v/v isopropanol, the reduction rate of butanone or pentanone was increased 3-4-fold [57], In some cases, the enantiomeric excess of the reduction reaction is not very high, especially when small molecules are converted, but also for compounds such as acetophenone [138]. 

The synthesis of 3-substituted isoquinolinones and fused isoquinolinones can be performed by the photoinduced SRN1 reactions in DMSO of o-iodobenzamide with the enolates of acyclic aromatic and aliphatic ketones and cyclic ketones, respectively. These reactions proceed from moderate to good yields (Schemes 10.47 and 10.48) [65],... 

Aliphatic and cyclic polyfluorinated alkencs are readily oxidized by potassium permanganate. Polylluoroalkenes whose C = C bonds are deficient in electrons are readily attacked by the permanganate anion. Depending on the substitution of the C = ( bond, the resulting products are acids or ketones. 

The structural variety of carbonyl compounds appears to be almost unlimited since aliphatic, aromatic, and cyclic ketones are good substrates for the bioreduction. Also, organometallic carbonyl compounds such as Cr(CO)3-complexed aromatic aldehydes (eq 2) or ketones (eq 3) are enantioselectively reduced by BY. 

The conversion of ketones into a-hydroxy ketones can be achieved by the oxidation of enolates or enol ethers. A special reagent for enolates is the oxodiperoxy molybdenum complex with pyridine and hexamethylphos-phoramide. The reaction is applied to aromatic aliphatic ketones and cyclic ketones and furnishes 34-81% yields of a-hydroxy ketones with up to 26% of a-diketones (equation 401) [531]. 

The direct selenoacetalization of carbonyl compounds by selenols is by far the shortest and most convenient route to selenoacetals. The reaction is usually carried out at 20 C with zinc chloride (0.5 equiv. versus the carbonyl con x>und) and delivers rapidly (<3 h) and in reasonably good yields methyl and phenyl selenoacetals derived from aliphatic aldehydes and ketones and cyclic ketones (Scheme 69). Selenoacetalization is more difficult to achieve with hindered ketones, such as adamantanone and diisopropyl ketone, and with hindered aromatic carbtmyl compounds. In these cases the reaction is best achieved with titanium tetrachloride instead of zinc chloride and is often limited to the methylseleno derivatives (Scheme 78). Tris(methylseleno)borane offers the advantage of not requiring an acid catalyst and is particularly useful for the selenoacetalization of acid labQe aldehydes such as citronellal (Scheme 70, e). 

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