A,p>-unsaturated aldehydes, ketones

The alkoxy radicals so formed are the precursors of a, P-unsaturated ketones, aldehydes, carboxylic acids and alcohols. Saturation reactions, Nor-rish type I reactions of ketonic compounds and oxidation of aldehydic species occur under irradiation. This finally leads to the formation of saturated carboxylic acids as the main oxidation products accompanied by esters, y-lactones, peresters, anhydrides, alcohols and ether bridges. 

Combination of LiAlH4 and catalytic amounts of Cul in HMPA/THF (1 4) is useful for 1,4-reduction of a,p-unsaturated ketones, aldehydes and esters. Reactions carried out at -78 °C for 1 h resulted pre-... 

The binuclear hydride NaHFe2(CO)s, is also useful for clean conjugate reductions. This reagent is capable of selective 1,4-reduction of a,p-unsaturated ketones, aldehydes, esters, nitriles, amides and lactones in good yields (Scheme 54). Reductions are generally performed at -50 °C in a THF solution of NaHFe2(CO)g and HOAc. Usually, 2 or more equiv. of the reagent are required for the reduction of 1 equiv. of substrate. 

Conversion of silyl enol ethers of ketones to a,p-unsaturated ketones or coupling to 1,4-diketones by means of Ag20 or Pd(ll) for a one pot conversion of ketones, aldehydes or alcohols to a,p-unsaturated ketones (aldehydes) with iodoxybenzoic acid see Nicolaou. 

Keywords Nitroalkanes, a,p-unsaturated ketones, aldehydes, CTAOH, solvent-free, room temperature, Michael reaction, Henry reaction, p-nitroalcohols... 

By catalytic reduction of a p-unsaturated ketones, prepared from aldehydes by the Claisen - Schmidt reaction (see under Aromatic Aldehydes), for example ... 

Hydroxyalkyl Alkyl Peroxides and Hydroxyalkyl Peroxyesters. The same stmctural restrictions discussed for the hydroxyhydroperoxides apply for the hydroxyalkyl alkyl peroxides, and those that exist are derived from aldehydes and certain ketones having electron-withdrawing groups, eg, polyfluorinated a,P-unsaturated ketones (136). 

When the a,P-unsaturated ketone is hydrogenated to the alcohol, a product with an intense sandalwood odor is produced (162). Many other examples of useful products have been made by condensation of campholenic aldehyde with ketones such as cyclopentanone and cyclohexanone. 

Regioselective coniugale reduction and reductive silylation of a,p-unsaturated ketones, esters, and aldehydes using a stable copper (I) hydride cluster (Ph3P)CuH 6... 

An interesting application of the Paal thiophene synthesis was documented for the synthesis of a polystyrene-oligothiophene-polystyrene copolymer. In the Stetter reaction of aldehyde 13 and P-dimethylaminoketone 14, in situ generation of the a,p-unsaturated ketone preceded nucleophilic 1,4-conjugate addition by the acyl anion... 

The imines are prepared by 16-12. The enamine salt method has also been used to give good yields of mono a alkylation of a,P-unsaturated ketones. Enamines prepared from aldehydes and butylisobutylamine can be alkylated by simple primary alkyl halides in good yields. N-alkylation in this case is presumably prevented by steric hindrance. 

Cyclic a,p-unsaturated ketones can be cleaved by treatment with base of their epoxy tosylhydrazone derivatives to give acetylenic ketones. The reaction can be applied to the formation of acetylenic aldehydes (R=H) by using the corresponding, 2,4-dinitrotosylhydrazone derivatives.Hydrazones (e.g., 47) prepared from... 

The base-catalyzed Michael addition of 2-chlorocyanoacetate to a,p-unsaturated ketones or aldehydes affords 5-oxopentenenitrile derivatives. In the presence of anhydrous HCl, these compounds cyclize to yield 2-chloro-3-pyridinecarboxylates. The process is highly regiospecific and usefiil in the synthesis of 2,Xdisubstituted pyridines <95T(51)13177>. 

Both aliphatic and aromatic terminal alkynes reacted with aliphatic aldehydes giving exclusively a mixture of ( ,Z)-1,5-dihalo-1,4-dienes and disubstituted ( )-a,p-unsaturated ketones, the former being the major products in all cases. When nonterminal aromatic acetylenes were used, the trisubstituted ( )-a,p-unsat-urated ketones were the exclusive compounds obtained. The procedure was not valid for ahphatic and unsaturated alkymes. However, the catalytic system was found to be compatible with alcohols and their corresponding acetates although limited yields were obtained. 

As an extension of this work, the same authors explored such methodology for the synthesis of 2,6-disubstituted dihydropyrans using secondary homopropargylic alcohols (Scheme 10, route E). Surprisingly, the treatment of pent-4-yn-2-ol and 3-methylbutanal in the presence of FeCls led to unsaturated ( )-(3-hydroxyketone and ( )-a,p-unsaturated ketone in 2.5 1 ratio and 65% yield, without any trace of the expected Prins-type cyclic product (Scheme 22) [36]. To test the anion influence in this coupling, FeCE and FeBrs were used in a comparative study for the reaction of pent-4-yn-2-ol (R = R" = H, = Me) and several aldehydes. A range of aldehydes except for benzaldehyde was transformed into unsaturated (3-hydroxy-ketones in moderate to good yields. 

To support the 2,3-allenol as an intermediate in this reaction, 2,3-allenols were employed in test experiments as starting materials (Scheme 10, route F). The crossover aldol product was obtained as the sole product, when the reaction was run in the presence of the suitable aldehyde. In the absence of an aldehyde the corresponding ( )-a,p-unsaturated ketone was obtained (Scheme 24) [37]. 

An unusual reaction was been observed in the reaction of old yellow enzyme with a,(3-unsat-urated ketones. A dismutation took place under aerobic or anaerobic conditions, with the formation from cyclohex-l-keto-2-ene of the corresponding phenol and cyclohexanone, and an analogous reaction from representative cyclodec-3-keto-4-enes—putatively by hydride-ion transfer (Vaz et al. 1995). Reduction of the double bond in a,p-unsaturated ketones has been observed, and the enone reductases from Saccharomyces cerevisiae have been purified and characterized. They are able to carry out reduction of the C=C bonds in aliphatic aldehydes and ketones, and ring double bonds in cyclohexenones (Wanner and Tressel 1998). Reductions of steroid l,4-diene-3-ones can be mediated by the related old yellow enzyme and pentaerythritol tetranitrate reductase, for example, androsta-A -3,17-dione to androsta-A -3,17-dione (Vaz etal. 1995) and prednisone to pregna-A -17a, 20-diol-3,ll,20-trione (Barna et al. 2001) respectively. 

In contrast to kinetic models reported previously in the literature (18,19) where MO was assumed to adsorb at a single site, our preliminary data based on DRIFT results suggest that MO exists as a diadsorbed species with both the carbonyl and olefin groups being coordinated to the catalyst. This diadsorption mode for a-p unsaturated ketones and aldehydes on palladium have been previously suggested based on quantum chemical predictions (20). A two parameter empirical model (equation 4) where - rA refers to the rate of hydrogenation of MO, CA and PH refer to the concentration of MO and the hydrogen partial pressure respectively was developed. This rate expression will be incorporated in our rate-based three-phase non-equilibrium model to predict the yield and selectivity for the production of MIBK from acetone via CD. 

The cyclizations to obtain cyclic thioureas have been performed using thiocarbonyldiimidazole.232 Reaction of methyl acetoacetate, thiourea and an aliphatic aldehyde in the presence of the zinc iodide (Znl2) was studied. Under the normal pressure, reaction has not been occurred whereas at high pressure (300 MPa) conditions 3,4-dihydropyrimidine-2-thione was obtained only in 10% yield.233 The same one-pot three-component cyclocondensation reaction in the presence of iodide (I2) provides a variety of 3,4-dihydropyrimi-dine-2-thione in high yields.234 Condensation reaction of thioureas with a,p-unsaturated ketones in the presence of the sodium methoxide in methanol affords 3,4-dihydropyrimidine-2-thione derivatives.235,236 Acylation of N,N -disubstituted thioureas with methyl malonyl chloride followed by base-catalysed cyclization leads in the formation of l,3-disubstituted-2-thiobarbituric acids (Scheme 78).237... 

A possible mechanism for the P-alkylation of secondary alcohols with primary alcohols catalyzed by a 1/base system is illustrated in Scheme 5.28. The first step of the reaction involves oxidation of the primary and secondary alcohols to aldehydes and ketones, accompanied by the transitory generation of a hydrido iridium species. A base-mediated cross-aldol condensation then occurs to give an a,P-unsaturated ketone. Finally, successive transfer hydrogenation of the C=C and C=0 double bonds of the a,P-unsaturated ketone by the hydrido iridium species occurs to give the product. 

Dicarbonyl derivatives from aldehydes and a,P-unsaturated ketones. The thi-azolium catalyst serves as a safe surrogate for CN. Also known as the Mi-chael-Stetter reaction. Cf. Benzoin condensation. 

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