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Aluminium compounds carbonylation

The reactivity of organometals increases in the order Li < Na < K alkali metal organometals are more efficient than magnesium and aluminium compounds and the reaction of aryllithium organometals with ketones is more rapid than that of alkyllithium compounds [202], Wittig and Bub [204, 205] postulated the formation of transition complexes with simultaneous nucleophilic attack on the carbonyl and electrophilic attack on the oxygen by the metal. [Pg.120]

Instead of using a complex metal hydride as the source of the hydride anion, the hydride anion may be donated from a carbon atom. In such a case, the reaction is called the Meerwein-Ponndorf-Verley reduction, or MPV reduction. In contrast to the reduction by a complex metal hydride, the MPV reduction is reversible. It is performed by heating aluminium isoproproxide with an excess of propan-2-ol. Two different routes compete one involves one molecule of the aluminium isoproproxide for each molecule containing a carbonyl group to be reduced, while the other route uses two. Suggest the mechanism that involves only one molecule of the aluminium compound. [Pg.336]

The stereochemistry of alkylation was next investigated. 2-Methylcyclohexanone (43) was treated with MeLi to afford predominantly the trans methylated product 45. However, when the aluminium compounds MAD or MAT were present, they coordinate to the carbonyl group and cause the configuration to be reversed (14). Very complex cases using other sophisticated alkylating reagents are not reported. When 2-methyl-l-propenyl magnesium bromide was reacted with the ketone 27, the isomer of natural product 46 was the... [Pg.621]

The above reversible equation indicates that one mol of aluminium iso-propoxlde will reduce directly three mols of the carbonyl compound. It is generally desirable to use excess of the reductant except for aromatic aldehydes for the latter side reactions (e.g., 2RCHO-----> RCOOCH R Tischenko re-... [Pg.882]

The following mechanism of the reaction has been suggested it includes the coordination of the carbonyl compound with the aluminium atom in aluminium sopropoxide and the transfer of a hydride Ion ... [Pg.882]

Meerwein-Pondorff reduction is the synthesis of alcohols by heating carbonyl compounds with aluminium isopropoxide in isopropanol and distilling off acetone by-product... [Pg.256]

The tosylhydrazone is prepared from the carbonyl compound and then reduced with lithium aluminium hydride, sodium borohydride or potassium borohydride. In this way D-glucose tosylhydrazone was converted into crystalline 1-deoxyglucitol by reduction with potassium borohydride... [Pg.152]

The particle size depends on the chain length of the aluminium-alkyl group and the concentration of the tri-alkylaluminium compound applied. If mixtures of, e.g., Fe- and Co-carbonyl compounds are used, Fe/Co alloy particles are formed. When the magnetic particles... [Pg.35]

Sodium borohydride is a much milder reducing agent than lithium aluminium hydride and like the latter is used for the reduction of carbonyl compounds like aldehydes and ketones. However, under normal conditions it does not readily reduce epoxides, esters, lactones, acids, nitriles or nitro groups. [Pg.289]

Solid lithium aluminium hydride can be solublized in non-polar organic solvents with benzyltriethylammonium chloride. Initially, the catalytic effect of the lithium cation in the reduction of carbonyl compounds was emphasized [l-3], but this has since been refuted. A more recent evaluation of the use of quaternary ammonium aluminium hydrides shows that the purity of the lithium aluminium hydride and the dryness of the solvent are critical, but it has also been noted that trace amounts of water in the solid liquid system are beneficial to the reaction [4]. The quaternary ammonium aluminium hydrides have greater hydrolytic stability than the lithium salt the tetramethylammonium aluminium hydride is hydrolysed slowly in dilute aqueous acid and more lipophilic ammonium salts are more stable [4, 5]. [Pg.476]

The asymmetric reduction of prochiral ketones to their corresponding enantiomerically enriched alcohols is one of the most important molecular transformations in synthetic chemistry (20,21). The products are versatile intermediates for the synthesis of pharmaceuticals, biologically active compounds and fine chemicals (22,23). The racemic reversible reduction of carbonyls to carbinols with superstoichiometric amounts of aluminium alkoxides in alcohols was independently discovered by Meerwein, Ponndorf and Verley (MPV) in 1925 (21—26). Only in the early 1990s, first successful versions of catalytic... [Pg.43]

A number of complex metal hydrides such as lithium aluminium hydride (LiAlH4, abbreviated to LAH) and sodium borohydride (NaBHj) are able to deliver hydride in such a manner that it appears to act as a nucleophile. We shall look at the nature of these reagents later under the reactions of carbonyl compounds (see Section 7.5), where we shall see that the complex metal hydride never actually produces hydride as a nucleophile, but the aluminium hydride anion has the ability to effect transfer of hydride. Hydride itself, e.g. from sodium hydride, never acts as a nucleophile owing to its small size and high charge density it always acts as a base. Nevertheless, for the purposes of understanding the transformations. [Pg.205]

Reduction of a range of allyl and benzyl chlorides at a stainless steel cathode in dimethylformamide in the presence of carbonyl compounds and using a sacrificial anode of aluminium or zinc, leads to a Reformatsky-type reaction in 40-80 % yields. Allyl halide give products by reaction at both the a- and y-positions. Tetra-chioromethane and bromotrifluoromethane take part in similar reactions provided a... [Pg.134]

Reformatsky reactions between allyl chloride and carbonyl cortqiounds are also effected in protic solvents using aluminium and a catalytic amount of tin chloride. Finely divided tin is formed and organotin reagents are involved as intermediates. These react with the carbonyl compound releasing tin ions, which are recycled by the dissolving aluminium [189],... [Pg.136]

Electrocatalytic hydrogenation is also achieved by reaction of carbonyl compounds with aluminium and nickel(ll) chloride in tetrahydrofuran. Nickel(li) is reduced to finely divided nickel(o) which is deposited on the aluminium.This se-tsup corrosion cells where aluminium dissolves, liberating electrons which are transferred to the nickel. Protons are then reduced to hydrogen at the nickel surface. Hydrogenation of benzaldehydes to the alcohol has been effected under these conditions [206]. [Pg.364]

The competition between insertion and hydrogen transfer is also crucial to the selectivity of the reaction of aluminium alkyls with carbonyl compounds. Aluminium alkyls, like organolithium compounds and Grignard reagents, can add to aldehydes and ketones to form secondary or tertiary alcohols, respectively. If the aluminium alkyl has a j -hydrogen, however, reduction of the carbonyl compound is a common side reaction, and can even become the main reaction [16]. Most authors seem to accept that reduction involves direct j5-hydrogen transfer to ketone. [Pg.143]

Since aluminium alkyls are easily available from inexpensive starting materials, their addition to carbonyl compounds could constitute a cheap alternative to the more expensive Grignard reagents or alkyllithium compounds. Unfortunately, this addition is only clean for aluminium alkyls without /1-hydrogens [16, 19], which are precisely those not accessible via the convenient... [Pg.154]

Unlike olefin insertion, the reaction of aluminium alkyls with carbonyl compounds has not been studied theoretically before. The calculated barriers for addition and j -hydrogen transfer in the system Me2AlEt -I- CH2=0 are very similar (15.4 and 14.3 kcal/mol, respectively see Table 1), in accord with the close competition between the two reaction types observed experimentally. [Pg.156]

Meerwein-Pondorf-Verley reduction, discovered in the 1920s, is the transfer hydrogenation of carbonyl compounds by alcohols, catalyzed by basic metal compounds (e.g., alkoxides) [56-58]. The same reaction viewed as oxidation of alcohols [59] is called Oppenauer oxidation. Suitable catalysts include homogeneous as well as heterogeneous systems, containing a wide variety of metals like Li, Mg, Ca, Al, Ti, 2r and lanthanides. The subject has been reviewed recently [22]. In this review we will concentrate on homogeneous catalysis by aluminium. Most aluminium alkoxides will catalyze MPV reduction. [Pg.158]

Maruoka reported the use of the didentate catalyst 8 for double electrophilic activation of carbonyl compounds [70], but since no comparison with monofunctional phenolates was given it is not clear whether having two aluminium centres in the same catalyst offers any special advantages. They used this catalyst to effect transfer hydrogenation between remote aldehyde and alcohol groups in the same molecule [71], but again it is not clear whether the transfer is truly intramolecular or in any way different from that of reduction by an external alcohol using 8 or a monuclear aluminium catalyst. [Pg.158]

Organomagnesium compounds usually insert carbonyl compounds, rather than reducing them. This is borne out by calculations, which show that barriers for both processes are lower than for aluminium, but the one for insertion is lowered most. Gallium, on the other hand, has significantly higher... [Pg.162]

Carbazole will react with 1 or 2 mol of ferrocene in hot decalin in the presence of aluminium-aluminium chloride producing crystalline derivatives in which either one or both" of the benzene rings is linked to iron, 25 and 26, respectively. The sandwich compound 25 was deprotonated to 27 with sodamide in liquid ammonia. A chromium carbonyl complex 28... [Pg.94]


See other pages where Aluminium compounds carbonylation is mentioned: [Pg.79]    [Pg.38]    [Pg.191]    [Pg.437]    [Pg.696]    [Pg.289]    [Pg.882]    [Pg.105]    [Pg.119]    [Pg.192]    [Pg.882]    [Pg.194]    [Pg.475]    [Pg.102]    [Pg.107]    [Pg.110]    [Pg.134]    [Pg.134]    [Pg.141]    [Pg.157]    [Pg.158]    [Pg.450]    [Pg.49]    [Pg.49]   
See also in sourсe #XX -- [ Pg.90 ]




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Aluminium compounds

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