Esters, reaction with aluminum borohydride

The importance of reactions with complex, metal hydrides in carbohydrate chemistry is well documented by a vast number of publications that deal mainly with reduction of carbonyl groups, N- and O-acyl functions, lactones, azides, and epoxides, as well as with reactions of sulfonic esters. With rare exceptions, lithium aluminum hydride and lithium, sodium, or potassium borohydride are the... 

Polystyrene-bound carboxylic esters have been reduced with diisobutylaluminum hydride or lithium aluminum hydride. Use of the latter reagent can, however, lead to the formation of insoluble precipitates, which could readily cause problems if reactions are performed in fritted reactors. An alternative procedure for reducing carboxylic esters to alcohols involves saponification, followed by activation (e.g. as the mixed anhydride) and reduction with sodium borohydride (Entries 10 and 11, Table... 

CHROMIC ACID, DI-fert-BUTYL ESTER (1189-85-1) A strong oxidizer. Violent reaction with reducing agents, alcohols, combustible materials, ethers, fluorine, hydrazine, powdered metals, including aluminum, magnesium, zirconium, potassium iodide, sodium tetraborate, sodium tetraborate decahydrate, sodium borohydride. Incompatible with water, steam. 

This was exercised with ester 266. The magnesium complex formed in the Grignard reaction was stereoselectively reduced with lithium borohydride while the aldehyde-aluminum complex formed in the low temperature DIBAL reduction is also stereoselectively attacked by the Grignard reagent [102]. 

Hydride reagents (lithium aluminum hydride, LiAlHt, and sodium borohy-dride, NaBHt) are a source of the nucleophilic hydride species Hr. Reaction of hydride with a suitable carbon electrophile results in a reduction of that carbon (by increasing the number of C-H bonds). Reactions of carbonyl compounds with lithium aluminum hydride (LAH) generally give an alcohol product (after workup), with the exception of amides, which give amine products. Sodium borohydride is less reactive than LAH. It does not react with esters, amides, or carboxylic acids, so it is described as being selective for aldehydes and ketones. Sodium borohydride also fails to reduce nitroalkanes or alkyl halides, so LAH must be used in those reactions. 

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