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DOI: 10.1055/sos-SD-020-00673

Yan, L.; Lin, S.; Liu, P.Science of Synthesis, (200720743.

The Tishchenko reaction, discovered in the early 1900s,[‌52‌] and its subsequent variations are widely used in organic synthesis.[‌53‌,‌54‌] The classic reaction involves the dimerization of both enolizable and non-enolizable aldehydes to afford the corresponding symmetric esters via a redox process in the presence of a catalyst of sufficient Lewis acidity. Aluminum triisopropoxide is commonly employed for this purpose, reacting with an aldehyde to form a hemiacetal 53 via the transfer of an isopropoxide group from the metal to the carbonyl function (Scheme 19).[‌55‌,‌56‌] The hemiacetal then reacts with another equivalent of the aldehyde to generate a mixed aluminum alkoxide 54 via the transfer of a hydride ion from aluminum to the aldehyde with concomitant release of an isopropyl ester. An acetal 55 is formed by a reaction between the mixed aluminum alkoxide 54 and a third equivalent of the starting aldehyde. Finally, hydride transfer yields the desired ester 56, and the aluminum alkoxide 54 is regenerated ready to re-enter the catalytic cycle. The final hydride transfer (to form the isopropyl ester) is regarded as the rate-limiting step.

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