Reinvestigation of the Mechanism of gem‐Diacylation: Chemoselective Conversion of Aldehydes to Various gem‐Diacylates and Their Cleavage under Acidic and Basic Conditions

Abstract

The mechanism of gem-diacylate formation has been studied extensively using tetrabutylammonium tribromide (TBATB) as the catalyst. The reaction proceeds by a nucleophilic attack of an anhydride on an aldehydic carbonyl group, nucleophilic attack of the hemiacylate intermediate on a second molecule of the anhydride, followed by an intermolecular attack of a second acetate group to regenerate the anhydride. gem-Diacylates of various aliphatic and aromatic aldehydes were obtained directly from the reaction of a variety of aliphatic and aromatic acid anhydrides in the presence of a catalytic quantity of tetrabutylammonium tribromide (TBATB) under solvent-free conditions. A significant electronic effect was observed during its formation as well as deprotection to the corresponding aldehyde. Chemoselective gem-diacylation of the aromatic aldehyde containing an electrondonating group has been achieved in the presence of an aldehyde containing an electron-withdrawing group. Depro-

Tetrabutylammonium tribromide (TBATB): a mild and efficient catalyst for O-isopropylidenation of carbohydrates

“…27 A wide variety of organic transformations have also been developed by others involving tetrabutylammonium tribromide (TBATB). [28][29][30][31][32][33] Knowing the unique behavior, properties, and stabilities of these reagents, we conceived the idea that tetrabutylammonium tribromide (TBATB) 0008-6215/$ -see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carres.2010.12.018 might be a useful catalyst for the preparation of various O-isopropylidene derivatives from sugars.…”

Silica supported perchloric acid (HClO4-SiO2): A highly efficient and reusable catalyst for geminal diacylation of aldehydes under solvent-free conditions

“…[9], LiBF 4 [10], NBS [11], I 2 [12], TMSCl-NaI [13], FeCl 3 [14], CoCl 2 [17] and tetrabutylammonium tribromide (TBATB) [18]. Some metal triflates, e.g.…”

Reactions of Aldehydes and Ketones and their Derivatives

“…de R 3 = Ph and Me) and, when the reactions are carried out in THF, they show some diastereoselectivity. The rearrangement of 5-hydroxycycloctanone (3) to its hemiacetal (4) has been studied computationally. 2 A concerted intramolecular nucleophilic addition process is demonstrated.…”

“…4 Deprotection can be achieved with the same catalyst on addition of methanol. The reaction proceeds via protonation of aldehyde, nucleophilic attack of the anhydride, and further nucleophilic attack on the hemiacylate intermediate, followed by regeneration of anhydride.…”

“…212 Evidence for ethoxide attack at silicon, to give a hypervalent silicate intermediate, which then coordinates with the carbonyl (or imine), is presented. 29 Si NMR is particularly informative: when R 1 = OEt, the alkyne silicon shows up at −72 ppm [similar to (EtO) 4 Si at −80 ppm], but a new peak is seen very far upfield at −126 ppm, beyond a similar known silicate, (EtO) 4 SiPhK at −117 ppm, and indeed close to (EtO) 5 Si − , at −130 ppm.…”