Aluminium isopropoxide reductions with

Estradiol may be prepared conveniently by the reduction of estrone either with aluminium isopropoxide or with lithium-aluminium-hydride. 

The reduction of thiazole carboxaldehydes with isopropanol and aluminium isopropoxide gives the corresponding alcohols (37, 107, 108). 

Reduction with aluminium isopropoxide by the Meerwein-Pondorf procedure yields the alcohol (56, 57, 112). 

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

Dining distillation of 2-propanol recovered from the reduction of crotonaldehyde with isopropanol/aluminium isopropoxide, a violent explosion occurred. This was attributed to peroxidised diisopropyl ether (a possible by-product) or to peroxidised crotonaldehyde. An alternative or additional possibility is that the isopropanol may have contained traces of a higher secondary alcohol (e.g. 2-butanol) which would be oxidised during the Meerwein-Ponndorf reduction procedure to 2-butanone. The latter would then effectively sensitise the isopropanol or other peroxidisable species to peroxidation. 

High yields and enantiopurity have been realized by a highly diastereoselective MPV reduction of protected a-amino aromatic ketones using catalytic amounts of aluminium isopropoxide. The high anti selectivity resulted from the chelation of the (g) nitrogen anion to the aluminium. In contrast, high syn selectivity was obtained with a-alkoxy ketones and other compounds via Felkin-Ahn control.354... 

The secondary alcohols are oxidized to ketones by refluxing with aluminium isopropoxide, A1[0CH(CH3)2]3 [or Al(0-iPr)3], or potassium t-butoxide, KOC(CH3)3 [or KO-t-Bu]. A ketone such as acetone used in the reaction as refluxing agent is reduced to alcohol, 2-propanol. The reaction is known as the Oppenauer oxidation. The reverse reaction known as the Meerwein-Ponndorf-Verly reduction is the reduction of ketones to alcohols in the presence of alcohol such as 2-propanol. Potassium fert-butoxide can be used for the oxidation of primary alcohols. Aluminium isopropoxide in acetone is particularly used for... 

Reduction of 2,2-dimethyl-1-phenylphosphorinan-4-one 1--sulphide with lithium tetrahydridoaluminate, sodium tetra-hydridoborate, aluminium isopropoxide, or sodium in ethanol gives a mixture of two stereoisomers (1) and (2) of 2,2--dimethyl-1-phenylphosphorinan-4-ol 1-sulphide (Z.A. Abramova, Yu. G. Bosyakov, and K.B. Erzhanov, Izv. Akad. Nauk Kaz. SSR, Ser. Khim., 1978, 28, 33). 

The most likely mechanism of the reaction is shown in Figure 2.1. It involves two half-reactions , with the formation of a 4-keto sugar intermediate. In the first half-reaction this is precisely reversed, except that the direction of addition of hydrogen is such as to reverse configuration at C-4. Each half-reaction shows some formal resemblance to the Meerwein-Ponndorf reduction of ketones to secondary alcohols, in that the second halfreaction is in the same direction as the Meerwein-Ponndorf reaction, while the first is its reverse. In the Meerwein-Ponndorf reaction the hydride ion is the reducing species and is derived from aluminium isopropoxide in 4-epimerase reactions effective H is derived from NADH, which becomes NAD. ... 

Reduction with aluminium isopropoxide in toluene represents a convenient way of reducing (543) to the epimers represented by (544). ... 

It is noteworthy that in some cases reduction with metal alkoxides, including aluminium isopropoxide, involves free-radical intermediates (single electron transfer (SET) mechanism). ... 

Fig. 8.36. As the asymmetric center of citronellal is unaffected by the reactions, all of the isopulegol and menthol isomers formed have the correct stereochemistry at Cl of the /i-menthane skeleton. There are therefore two strategies for recycling unwanted isomers. The first is to purify the ( )-isopulegol (172) by crystallization and recycle (178-180) back to citronellal by pyrolysis [221, 223, 224]. The second is to hydrogenate the mixture, separate the (—)-menthol by crystallization and treat the remainder with aluminium isopropoxide, which converts all of them, by Oppenauer oxidation, enoliza-tion, reketonization and Meerwein-Ponndorf-Verley reduction, to (—)-menthol, which is the thermodynamically most stable isomer (225).

This alcohol can be obtained from methyl angolensate by borohydride reduction (75) or by rapid reduction with aluminium isopro-poxide. Prolonged reduction with isopropoxide leads to equilibration to the equatorial 3P-isomer (76). 

Isothiazolanthrone (125) reacts with dimethylaniline, anisole, or thiophen in the presence of phosphorus oxychloride to yield 6-arylisothiazol-anthrenium salts [e.g. perchlorates, (128)]. The unsubstituted isothiazolan-threnium perchlorate (127), forming a brown solid, is obtainable by reduction of isothiazolanthrone (125) by aluminium isopropoxide, and dehydrogenation of the resulting isothiazolanthrene (126) with trityl perchlorate. Addition of dimethyl sulphate to the isothiazolanthrene (126) yields the quaternary salts (129). U.v. spectral data were provided. ... 

Rehydrated Mg/Al-OH catalysts have been found to be inactive in the MPV reduction of 4-ferf-butylcyclohexanone by isopropanol, whereas the bifunctional character of the Mg(Al)0 mixed oxides made them highly active in this reaction. The aluminium alkoxidc intermediate of the MPV reaction indeed involves a cooperation between basic and acidic sites. On mixed oxides, the abstraction of a proton from isopropanol on O2 sites gives isopropoxide anions, which are then stabilized on Al3+ and form intermediates with the aldehyde. The high activity of mixed oxide comes from the synergetic effect of strong Lewis basicity and mild acidity. 

The main drawback of the historic aluminium tri-isopropoxide-based catalytic systems is their low reactivity, the reduction of the carbonyl proceeding slowly even with an excess of catalyst . As mentioned in the introduction, many aluminium alkoxides are known to form aggregates and the observed low reactivity is in many cases correlated to the stability of the... 

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