Aromatic aldehydes and ketones

Palladium is usually the prefeired metal of choice for aromatic aldehyde hydrogenation in neutral non-polar solvents such as hexane, DMF, or ethyl acetate (5-100 °C and 1-10 bar) although ruthenium, which is less active, can be considered and run in aqueous alcohol at similar temperatures and pressures. If higher pressures are accessible ruthenium may be preferable because of its lower (historical) cost. Its use has recently been reviewed [4]. Although platinum and rhodium could 

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SchifT s bases A -Arylimides, Ar-N = CR2, prepared by reaction of aromatic amines with aliphatic or aromatic aldehydes and ketones. They are crystalline, weakly basic compounds which give hydrochlorides in non-aqueous solvents. With dilute aqueous acids the parent amine and carbonyl compounds are regenerated. Reduction with sodium and alcohol gives... 

Hydrazinopyridazines are easily formylated with formic acid or ethyl formate and acety-lated with acetic anhydride. A-Pyridazinylthiosemicarbazides are obtained from thiocyanates or alkyl- and aryl-isothiocyanates. Hydrazinopyridazines condense with aliphatic and aromatic aldehydes and ketones to give hydrazones. 

The method can be used to prepare a number of a-aminonitriles from aliphatic or aromatic aldehydes and ketones and secondary aliphatic amines.4... 

Allylmagnesium bromide, 41, 49 reaction with acrolein, 41, 49 5-Allyl-l,2,3,4,5-pentachlorocyclopen-tadiene, 43, 92 Allyltriphenyltin, 41, 31 reaction with phenyllithium, 41, 30 Aluminum chloride, as catalyst, for isomerization, 42, 9 for nuclear bromination and chlorination of aromatic aldehydes and ketones, 40, 9 as Friedel-Crafts catalyst, 41, 1 Amidation, of aniline with maleic anhydride, 41, 93... 

Aromatic aldehydes and ketones can be alkylated and reduced in one reaction vessel by treatment with an alkyl- or aryllithium, followed by lithium and ammonia and then by ammonium chloride." ... 

Another SBU with open metal sites is the tri-p-oxo carboxylate cluster (see Section 4.2.2 and Figure 4.2). The tri-p-oxo Fe " clusters in MIL-100 are able to catalyze Friedel-Crafts benzylation reactions [44]. The tri-p-oxo Cr " clusters of MIL-101 are active for the cyanosilylation of benzaldehyde. This reaction is a popular test reaction in the MOF Hterature as a probe for catalytic activity an example has already been given above for [Cu3(BTC)2] [15]. In fact, the very first demonstration of the catalytic potential of MOFs had aheady been given in 1994 for a two-dimensional Cd bipyridine lattice that catalyzes the cyanosilylation of aldehydes [56]. A continuation of this work in 2004 for reactions with imines showed that the hydrophobic surroundings of the framework enhance the reaction in comparison with homogeneous Cd(pyridine) complexes [57]. The activity of MIL-lOl(Cr) is much higher than that of the Cd lattices, but in subsequent reaction rans the activity decreases [58]. A MOF with two different types of open Mn sites with pores of 7 and 10 A catalyzes the cyanosilylation of aromatic aldehydes and ketones with a remarkable reactant shape selectivity. This MOF also catalyzes the more demanding Mukaiyama-aldol reaction [59]. 

Figure 1 present kci versus koH values for families of compoimds where both rate constants were found in the literature for n-alcohols, n-alkanes, n-ethers, chloroethenes, 1-chIoroalkanes, aromatics, aldehydes, and ketones. This graph demonstrates that ... 

Aromatic aldehydes and ketones are reduced to alkylaromatics under similar conditions through reactions involving benzylic cations.176... 

The most general procedures are based on low-valent titanium. Good yields of diols are obtained from aromatic aldehydes and ketones by adding catechol to the TiCl3-Mg reagent prior to coupling.250... 

Cp2ZnCl2 similarly catalyzes the coupling reaction of aromatic aldehydes and ketones [36]. Another ternary-component system consists of a catalytic... 

Hydrogenation of a C=0 double bond followed by catalytic hydrogenolysis of the resulting OH group is an alternative method for the conversion of aromatic aldehydes and ketones to alkanes. Pd/C and Pt02 are the most often used catalysts.49-51 In this way, dimethyltetralone was hydrogenated-hydrogenolyzed under 60 psi H2 for 5 hours in MeOH-HCl with 10% Pd/C (Scheme 4.22).52... 

Examples of the use of heterodienophiles under the action of microwave irradiation are not common. Soufiaoui [84] and Garrigues [37] used carbonyl compounds as die-nophiles. The first example employed solvent-free conditions the second is an example of the use of graphite as a susceptor. Cycloaddition of a carbonyl compound provided a 5,6-dihydro-2H-pyran derivative. These types of reaction proceed poorly with aliphatic and aromatic aldehydes and ketones unless highly reactive dienes and/or Lewis acid catalysts are used. Reaction of 2,3-dimethyl-l,3-butadiene (31) with ethyl glyoxylate (112) occurred in 75% yield in 20 min under the action of microwave irradiation. When conventional heating is used it is necessary to heat the mixture at 150 °C for 4 h in a sealed tube to obtain a satisfactory yield (Scheme 9.33). 

Although there are now several catalysts useful for hydrogenation of saturated carbonyl compounds to alcohols (see Section XII), an alternative approach has involved initial hydrosilylation (Chapter 9 in this volume) followed by acid hydrolysis [Eq. (41)]. The area first developed using principally the RhCl(PPh3)3 catalyst (207-210), and has since proved particularly useful in asymmetric syntheses (see Section III,A,4). Besides simple aliphatic and aromatic aldehydes and ketones, the ter-pene-ketones camphor and menthone were stereoselectively reduced to mainly the less stable alcohols e.g., camphor gave 9 (209). 

Metalated cyclic aldo-nitrones are characterized by high reactivity toward electrophilic reagents. Reactions with aldehydes and ketones afford satisfactory yields of a-hydroxymethyl substituted derivatives of nitrones (551). The reactions were also carried out with a number of aliphatic, aromatic, and hetero-aromatic aldehydes and ketones (Schemes 2.124 and 2.125). 

In 2001, the preparation of allylytterbium bromide and the synthesis of homoallylic alcohols using allylytterbium bromide were reported.39 393 Ytterbium metal was found to be activated by a catalytic amount of Mel at 0 °C in THF to produce allylytterbium bromide 66 (Equation (11)). The allylation reaction of a wide range of aromatic aldehydes and ketones proceeded at ambient temperature or less in good to high yields (Table 2). Imines also reacted with allylytterbium bromide to afford homoallyl amines (Table 3). 

The effect of cryptands on the reduction of ketones and aldehydes by metal hydrides has also been studied by Loupy et al. (1976). Their results showed that, whereas cryptating the lithium cation in LiAlH4 completely inhibited the reduction of isobutyraldehyde, it merely reduced the rate of reduction of aromatic aldehydes and ketones. The authors rationalized the difference between the results obtained with aliphatic and aromatic compounds in terms of frontier orbital theory, which gave the following reactivity sequence Li+-co-ordinated aliphatic C=0 x Li+-co-ordinated aromatic C=0 > non-co-ordinated aromatic C=0 > non-co-ordinated aliphatic C=0. By increasing the reaction time, Loupy and Seyden-Penne (1978) showed that cyclohexenone [197] was reduced by LiAlH4 and LiBH4, even in the presence of [2.1.1]-cryptand, albeit much more slowly. In diethyl ether in the absence of... 

Many aromatic aldehydes and ketones (e.g. benzophenone, anthrone, 1- and 2-naphthaldehyde) have a low-lying n-n excited state and thus exhibit low fluorescence quantum yields, as explained above. The dominant de-excitation pathway is intersystem crossing (whose efficiency has been found to be close to 1 for benzophenone). 

Thus, Mukaiyama [30] introduced the TiCU-Zn couple, which gives good results with aromatic aldehydes and ketones, but not with the corresponding aliphatic derivatives ... 

The reduction of the preformed tosylhydrazones with sodium borohydride may be effected in aprotic solvents, such as tetrahydrofuran or dioxane. The use of lithium aluminium hydride in nonhydroxylic solvents permits the reduction of aromatic aldehydes and ketones. 

Physical organic experiments have shown that simple organolithinm reagents exist as aggregates in solution and react with aromatic aldehydes and ketones as a monomer. In most cases, the reactions are initiated by ET, as in Grignard reactions, althongh... 

In 1999, Hajipour reported that silica gel, without any base, could be a useful catalyst for the preparation of oximes in dry media coupled with microwave irradiation. Hydroxylamine hydrochlorides were reacted with several aliphatic and aromatic aldehydes and ketones affording the desired oximes. 

The reaction is stereospecific for at least some aliphatic ketones but not for aromatic carbonyl compounds.130 This result suggests that the reactive excited state is a singlet for aliphatics and a triplet for aromatics. With aromatic aldehydes and ketones, the regio-selecitivity of addition can usually be predicted on the basis of formation of the more stable of the two possible diradical intermediates by bond formation between oxygen and the alkene. 

Phenylthiosemicarbazones (198) of aromatic aldehydes and ketones give 1,2,4-dithiazolidines (199) with the same reagent, whereas those of aliphatic ketones produce 1,2,4-triazolines only (Equation (20)) <91JHC1957>. Aromatic and heteroaromatic thiodihydrazones (200) in the same reaction conditions afford 1,2,4-dithiazolidines (201) (Equation (21)) <91JHC1957>. 

Aminocarbazoles are typical aromatic amines 3-aminocarbazoles, which are the most studied, form Schiff bases with aromatic aldehydes, and ketones. Use was made of such a benzaldehyde imine by methyla-tion with dimethyl sulfate and then by hydrolysis with acid to produce the mono-N-methylated amine. The dimethylated material was obtained via the trimethylammonium iodide, which gave 3-dimethylaminocarbazole on... 

For A-(trimethylsilylmethyl)-5-methylisothioureas 262, cycloaddition with carbonyl compounds results in 2-aminooxazolines 263. ° Aliphatic and aromatic aldehydes and ketones can be employed successfully. However, reaction with ketones appears to be poor. Ylide generation with CsF is the method of choice although TBAF and KF have also been used but with lower yields. A polar solvent such as MeCN, DMF, or hexamethylphosphoric triamide (HMPA) is required for a succesful reaction (Scheme 8.73). 

Hydrogen and a catalyst.2 0 The most common catalysts are platinum and ruthenium, but homogeneous catalysts have also been used.281 Before the discovery of the metal hydrides this was one of the most common ways of effecting this reduction, but it suffers from the fact that C=C, CssC, C=N and C=N bonds are more susceptible to attack than C=0 bonds.282 For aromatic aldehydes and ketones, reduction to the hydrocarbon (9-37) is a side reaction, stemming from hydrogenolysis of the alcohol initially produced (0-78). 

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