Tischtschenko reaction hydride transfer

Normally, Oppenauer oxidations are performed employing Al3+ cations as catalyst because aluminium alkoxides possess a good balance of a desired high hydride transfer capability versus a low propensity to promote undesired base-induced reactions, like aldol condensations and Tischtschenko reactions. In the reaction, as originally described by Oppenauer, aluminium t-butoxide is used as catalyst,4 because its high basicity allows a very favourable equilibrium towards the formation of the aluminium alkoxide of the alcohol whose oxidation is desired. However,... 

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). ... 

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