Monoalcoholates of 1,3-diols as effective catalysts in the Tishchenko esterification of 1,3-dioxan-4-ols

Alkali metal monoalcoholates of 1,3-diols can be used as very effective catalysts in the Tishchenko reaction of 4-hydroxy-1,3-dioxanes to the corresponding monoesters of 1,3-diols. These catalysts are extremely efficient and fast compared to metal hydroxides commonly used. Thus, monoalcoholate catalysts give fast transesterification with the product ester. The loss in yield due to ester interchange can be minimized by using a suitable 1,3-diol moiety in the catalyst. © 2001 Published by Elsevier Science Ltd. In the normal Tishchenko reaction two aldehydes are converted to a monofunctional simple ester in the presence of a Lewis acid catalyst, most commonly with aluminium alcoholates. The reaction has been carried out with a number of other catalysts such as ruthenium complexes, alkali earth metal oxides, boric acid, sodium alkoxides (with aryl aldehydes), alkali metals, zirconocenes, and lanthanide (amide) complexes. The mechanism of the Tishchenko reaction involves a hydride shift. Very recently a bidentate bisaluminum alcoholate has been reported to give an especially fast Tishchenko reaction with excellent yield. One special case of the Tishchenko reaction is the esterification of 1,3-dioxan-4-ols where an intramolecular hydride shift is activated in the presence of a base catalyst. These dioxanols are usually dimers of b-hydroxyaldehydes (aldol product) or similar hemiacetals formed between b-hydroxyaldehydes and another aldehyde. Merger et al. have reported the first mechanistic features of the esterification of such compounds (Scheme 1). Esterification of 1,3-dioxan-4-ols is usually carried out with basic catalysts such as alkali metal hydroxides instead of the aluminium alcoholates used in the traditional Tishchenko reaction.