Alkali Metal tert‐Butoxides, Hydrides and Bis(trimethylsilyl)amides as Efficient Homogeneous Catalysts for Claisen–Tishchenko Reaction

Abstract

AbstractShelf‐available alkali metal tert‐butoxides, hydrides and bis(trimethylsilyl)amides were shown to be highly efficient homogeneous precatalysts for the disproportionation of aldehydes to the corresponding carboxylic esters. Potassium compounds in combination with 18‐crown‐6 ether could drastically increase the rate of reaction in a few cases. Alternatively, efficient aldol condensations were found for aldehydes possessing an enolizable methylene group at the α‐position to the aldehyde functionality. The active species involved in this esterification using any of these alkali metal catalysts is expected to be the metal alkoxide. Potassium compounds were found to be much more efficient when compared to analogous sodium compounds and kinetic studies revealed the rate‐determining step to be a second order concerted hydride transfer from a potassium hemiacetal species to another molecule of aldehyde.