Substituted ketones

Androst-4-ene-3,17-dione (83) is converted into the enol ether (84) by reaction with triethyl orthoformate. Treatment of the enol ether (84) with DDQ in aqueous acetone gives the title dienone (85). This method is particularly suitable for A" -3-ketones substituted at the 6-position. 

A reaction related to the Michael addition reactions of enamines to unsaturated esters, which leads to S-ketoesters, is the reaction with 1-carb-ethoxy-l-cyanocyclopropane (318). This gives access to ketones substituted with the next higher homologous acid chain. 

Asymmetric syntheses of warfarin <96TL8321> and the axially chiral bicoumarin, isokotanin A <96TL3015> have been reported. The former is based on a Rh-catalysed asymmetric hydrogenation of a 3-(a,P-unsaturated ketone) substituted coumarin, whilst the key steps of the latter are an asymmetric Ullmann coupling and a selective demethylation. The stereochemistry of the fused dihydrocoumarin resulting from Li/NHs reduction of... 

P-keto acid X = alkyl or aryl = ketone substituted malonic acid X=OH = substituted acetic acid... 

In the hydrogenation of cyclic / -keto esters (ketones substituted with an al-koxycarbonyl moiety), Ru(II)-binap reduced a racemic substrate in DCM with high anti-diastereoselectivity to give a 99 1 mixture of the trans-hydroxy ester (92% ee) and the ds-hydroxy ester (92% ee), quantitatively [Eq. (18)] [119, 120]. 

Another series of experiments has been performed using simple ketones substituted by fluoroalkyl groups. In this way it is clearly shown that the presence of a perfluorine group adjacent to the carbonyl to be hydrogenated is essential in order to provide both excellent activities and enantioselectivities (Table 33.9). 

Asymmetric hydrogenation of prochiral ketones,s Ketones substituted in the a- or (3-position by diverse polar groups, particularly OH,OR,NR2,COOR, can undergo highly enantioselective hydrogenation catalyzed by BINAP-Ru complexes. A key factor of asymmetric induction is undoubtedly chelation of the carbonyl group and the hetero atom to the Ru atom. 

E)-Enol silyl ethers.1 A new highly stereoselective route to (E)-enol silyl ethers involves addition of CH,Li to silyl ketones substituted at the a -position by a SC6H5 group such as 1. The adduct (a) undergoes a Brook rearrangement and... 

Figure 2). -Diketones 35 and j5-ketoesters 36-38 are commonly used as CH-acidic ketones 24. Cyanoketones 39 and 40, nitroketones 41, as weU as ketones substituted with beteroaromatic 42, sulfur-containing 43, and phosphorus-containing groups 44 and 45 are also favored (Figure 2). Syntheses... 

Dialkylation of enones. 6 The reaction of a lithium dialkyl cuprate (excess) with an 2,/3-unsaturated ketone substituted by a heteroatom at the / -position (I) results in two successive conjugate additions to introduce an alkyl group at both the ft- and / -position. 

Various benzophenones and aryl alkyl ketones substituted with a fluorine atom on the ortho position were effectively converted into the corresponding alcohols with high to excellent enantioselectivities in the presence of the optically active ketoim- inatocobalt(II) complexes (14). The combination of o-F substituent and a modified lithium borohydride reagent contributed to the high yield and high enantioselectivity (88-96% ee).316... 

The stabilization of ketone-substituted ketone enols that has just been presented suggests that all ketone enols that are acceptor-substituted should have an enhanced enol content. All car-... 

The a-silyl-/J-X-alkoxidcs were generated in the reactions of acylsilanes with a-X-substituted nucleophiles190,191,193,195 and in the reactions of silyllithiums with ketones substituted by a-X groups193,200. 

D. / -Cleavage. Ketones substituted with heteroatoms on an a-carbon, including a-halo, a-tosyl and a-aminoketones, undergo photoinduced loss of that substituent either as a radical or as an anion 17>. 

As in the malonic ester synthesis, you should identify the structural fragments of the target compound. The acetoacetic ester synthesis converts an alkyl halide to a methyl ketone ("substituted acetone"). The methyl ketone component comes from acetoacetic ester the other component comes from a halide. 

Addition to ketones. Potassium cyanide in combination with 18-crown-6 is generally superior to Znij as the catalyst for additii n of cyanotrimethylsilane to ketones substituted at the a-position with an electron-withdrawing group. 

C yclopropyl ketones. Substituted cyclopropyl ketones can be obtained by base-induced isomerization of y, -epoxy ketones. Thus treatment of the epoxide (2) of... 

Benzisoselenazoles and their heterofused analogues can be obtained in a similar way as isoselenazoles from aromatic or heteroaromatic aldehydes or ketones substituted at the 2-position with a bromoseleno group (Schemes 34 and 46). 

The question of halogen substitution has not arisen here. The earlier investigators attempted the isolation of halogenated sugars as possible intermediates in the oxidation reactions. None were found. In the case of some simpler alcohols and hydroxy aldehydes and ketones, substitution has been found to occur and the products have been hydrolyzed to oxidation products. Since most of these halogenated compounds have been formed in non-aqueous systems, it seems doubtful that substitution would occur readily in the presence of water without decomposition of the halogenated products. 

Scheme (5), like (3), predicts the formation of the enol form, thus, all the evidence put forward in support of mechanism (3) may also be regarded as evidence in favour of mechanism (5). According to Wagner and Hammond the biradical mechanism is supported by the relative reactivities of the excited states of the ketones substituted to various extents. 

Hexafluoroacetone imine has been prepared by the reaction of hexafluoroacetone with triphenylphosphine imine, by the pyrolysis of N-phenyl-2,2-diaminohexafluoropropane, by the reaction of hexafluorothioacetone with hydrazoic acid, and by the reaction of ammonia and phosphorus oxychloride with hexafluoroacetone. The latter method, which is described here, is the most convenient for it does not require preparation of several intermediates or use of pressure equipment. This method has also been used to prepare the imines of other Huoroketones, including the imines of chloropentafluoroacetone, dichlorotetrafluoroacetone, and perfluorodiethyl ketone. Substitution of methylamine for ammonia in this procedure gives the N-methyl imine. ... 

The location of the absorption bands due to chromophores depends markedly on environmental factors. By studying the displacements of the Amax of the chromophores by the introduction of other groups, one can understand the nature of substituent effects. The interpretation of the spectra of organic molecules often becomes difficult because of the presence of more than one chromophore. Typical examples of such complex chromophores would be dienes, ajS-unsaturated ketones, substituted benzenes etc. However, by a study of the electronic spectra of a large number of different types of molecules, it has generally been possible to correlate the spectroscopic data with the structure of molecules. 

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