Aluminum r-butoxide

Elimination of methanol from the dimethoxydihydropyran (166) on reaction with aluminum r-butoxide occurred at 155 °C and gave 2-methoxy-4//-pyran (55JA5601). 

Reductive cleavage of cyclic ethers This complex is effective for reductive cleavage of cyclic ethers. The order of reactivity is epoxide > oxetane > tetrahydrofurane>tetrahydropyrane>oxepane. It is less effective for cleavage of acyclic ethers, except for methyl ethers. The reaction involves formation of a complex of the ethereal oxygen with aluminum r-butoxide followed by Sn2 displacement with lithium triethylborohydride. Steric and electronic Victors are involved, but yields are >90% in favorable cases. 

Eastham and Teranishi compare their procedure with that described earlier by Oppenauer using aluminum r-butoxide which. fee), acetone, and benzene with the comment The present modification is less Itiborious than the earlier method," but we question this conclusion. Eight hours of unattended refluxing (Oppenauer) seems significantly less laborious than the lengthy distillation and steam distillaliun cited above. 

Oppenauer Aluminum r-butoxide. Aluminum isopropoxide. 1,4-Benzoquinone. Cyclohexanone. Potassium r-butoxide. 

Aluminum amalgam, 255, 459 Aluminum bromide, 19-21, 125 Aluminum r-butoxide, 21 Aluminum chloride, 21-23, 86, 124, 125, 423, 425, 464 Aluminum hydride, 23-24 Aluminum phosphide, 329 Amberlite IR-20, 227... 

The reverse reaction, the so-called Oppenauer oxidation, is carried out by treating a substrate alcohol with aluminum tri-r-butoxide in the presence of acetone. By using an excess of acetone, the equilibrium can be shifted to the right, yielding the ketone 1 and isopropanol ... 

The Oppenauer Oxidation. When a ketone in the presence of base is used as the oxidizing agent (it is reduced to a secondary alcohol), the reaction is known as the Oppenauer oxidation. This is the reverse of the Meerwein-Ponndorf-Verley reaction (16-23), and the mechanism is also the reverse. The ketones most commonly used are acetone, butanone, and cyclohexanone. The most common base is aluminum r r/-butoxide. The chief advantage of the method is its high selectivity. Although the method is most often used for the... 

The elimination of methanol, ethanol, or acetic acid is useful for the preparation of 4f/-pyrans, provided that the products exhibit sufficient stability. Thus the thermolyses of 2-ethoxy- and 2-acetoxy-2, 3-dihydro-4//-pyrans 265 undoubtedly led to unsubstituted 4//-pyran (5),18,293 but only when R = Ac was it possible to separate the unstable product 5 from reaction mixtures by GLC in 15 to 30% yields.18 Analogously, 25% of air-sensitive 2-methoxy-2//-pyran (267) was obtained on heating 266 with aluminum tri-butoxide under a nitrogen atmosphere at 155°C.33 A general technique for the preparation of condensed 4//-pyrans from their 2-ethoxy-2,3-dihydro derivatives is based on the elimination of ethanol in the presence of p-toluenesulfonic acid or polyphosphoric acid at decreased pressures293 to give... 

Pal and Kapoor74 have studied the reactions of isopropoxides of aluminum, titanium and zirconium with benzo- and phenylaceto-hydroxamic adds in anhydrous benzene. Solid products of the types Al(OPr )3 L and M(OPri)4 L (where M = Ti or Zr and L is the hydroxamic acid) have been isolated all the aluminum and zirconium products are white in colour whereas titanium ones are yellow. The mixed isopropoxide hydroxamates interchange their isopropoxy group with r-but-oxy groups, yielding r-butoxide products. 

Sodium aluminum chloride, 435 Sodium amalgam, 310, 416-417 Sodium amide-Sodium r-butoxide, 417-418 Sodium azide-Triphenylphosphine, 418 Sodium bis(2-methoxyethoxy)aluminum hydride, 166,418-420 Sodium borohydiidc, 323,420-421 Sodium borohydride-Alumina, 421 Sodium borohydride-Bis(2,4-pentane-dionato)copper(ll), 421 Sodium borohydride-Cerium(Ill) chloride,... 

The classical Meerwein-Ponndorf-Verley (MPV) process, named after the independent originators, can be illustrated by the reduction of crotonaldehyde (43) by aluminum isopropoxide (44) in isopropyl alcohol (equation 24). Aluminum isopropoxide transfers hydride reversibly to a carbonyl acceptor. Acetone is formed as a volatile side product, which can be removed during reaction. The reaction of equation (24) is forced even further to the right by the use of excess isopropyl alcohol. MPV reactions have been reviewed.In the Oppenauer variant of this reaction an alcohol is oxidized to a ketone, and acetone is used as hydride acceptor in the presence of a strong base like r-butoxide. This reaction was originally developed for the selective oxidation of sterols. The synthetic aspects of this procedure have also been reviewed. ... 

The byproduct R R CH-0" is a strong base that perpetuates the reaction so that only catalytic amounts of aluminum fert-butoxide are needed to initiate the oxidation. The reaction is reversible and leads to an equilibrium, which must be systematically destroyed by removal of the byproduct to drive the reaction to completion. Carbonyl compounds used as hydrogen acceptors are acetone, cyclohexanone, benzaldehyde, cinna-... 

Isomerization Aluminum bromide. Boron trifluoride-Hydrogen fluoride. Dimethyl sulfoxide. Formic acid. N-Lithioethylenediamine. Mercuric acetate. Perchloric acid. Potassium r-butoxide. Potassium hydride. Potassium hydroxide. Zinc dust. 

Hydride transfer is also involved in the Tischtschenko reaction, wherein an aliphatic aldehyde is dimerized under the influence of aluminum tri-r-butoxide to the corresponding ester (equation 15). Tischtschenko reaction products are sometimes observed as side products in aldol reactions. Under proper conditions, rather complex esters may be prepared in excellent yield (e.g. equations 16 and 17). ... 

Aldol condensations of monoketones can lead to trimeric products if the reaction is carried out under more vigorous conditions. The prototypical example of this behavior is acetone, which can give rise to mesityl ketone (7), phorone (8) and isophorone (9 equation 30). An example is seen in the treatment of acetone with aluminum tri-r-butoxide in toluene (equation 31). Isophorone is frequently obtained as a by-product in base treatment of acetone it may be formed from the phorone enolate by an electrocycli-zation mechanism (equation 32). 

Although the traditional Oppenauer conditions utilized aluminum catalysts, alternative metal alkoxides, for example, chloromagnesium alkoxides, are competent in the transformation.3 In 1945, Woodward devised a new system, which involved the use of potassium r-butoxide, and benzophenone for the oxidation of quinine (29) to quinone (30).13 This was termed the modified Oppenauer oxidation. The traditional aluminum catalytic system failed in this case due to the complexation of the Lewis-basic nitrogen to the aluminum centre. The synthetic flexibility of this procedure was extended by the use of more potent hydride acceptors.46... 

The alumina aerogel (490 m2.g-l, 1.3 cm. g-l micro-mesopore volume) was prepared from aluminum sec - butoxide dissolved in sec - butanol by hydrolysis with a stoichiometric amount of water. The alcogel was then dried in an autoclave under supercritical conditions with respect to sec - butanol [4]. Two conventional alumina xerogels ( Degussa 110 m2.g-l and R.P. 100 m2.g-i ) were also used as supports of Pd and Pt-Rli catalysts. 

Fragmentation of an epoxy mesylate. The key step in a synthesis of the sesquiterpene lactone saussurea lactone (4) involved fragmentation of the epoxy mesylate (I), obtained from -santonin by several steps. When treated with aluminum isopropoxide in boiling toluene (N2, 72 hours), 1 is converted mainly into 3. The minor product (2) is the only product when the fragmentation is quenched after 12 hours. Other bases such as potassium r-butoxide, LDA, and... 

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