Aluminum tri-r-butoxide

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 ... 

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). 

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... 

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