The Reduction of Esters with Sodium Borohydride¹

Abstract

anol (6 ml.) added to dissolve the aniline. The yield of amine was 1.35 g. (91%). Benzamide had m.p. 62-65°, lit.13 63-65°.N-Benzylaniline.-The method was similar to the previous with aniline and benzaldehyde (5 ml.), and ethanol (20 ml.).The yield was 1.67 g" (83%), m.p. 36-37.2°, lit.14 37-38°.N-Ethylpiperidine.-The method was similar to the previous with piperidine, 1.0 ml. (10.1 mmoles), and acetaldehyde (10 ml.). The borohydride was added over 30 min.; half of the acetaldehyde was added at the beginning, and the remainder after 15 min. The product was crystallized as the hydrochloride. The yield was 0.81 g. (53%) m.p. (evacuated capillary, uncor.) 225-227°, lit.16 225°. The picrate was also prepared, m.p. 165-167.5°, lit.16 167-168°. Corresponding synthetic attempts with acetone and cyclohexanone in place of acetaldehyde gave no detectable tertiary amine.

High specific activity tritium labeling of anti-tumor agent CEP-2563

“…Although not common, such a reduction of esters by sodium borohydride does have precedent. 5 In our hands the transformation of 6 to 7 went very smoothly and in good yield (Scheme 1).…”

Systematic investigations on the reduction of 4-aryl-4-oxoesters to 1-aryl-1,4-butanediols with methanolic sodium borohydride

“…esters, nitro, nitriles, etc., remain unaffected [1–10]. Although it has been reported that some aliphatic and aromatic esters have been reduced with a large excess of sodium or other metal borohydrides [11–12], often in higher boiling solvents [13] and in combination with various additives [14–15] including at a cationic micellar surface [16], selective reduction of the keto group in oxoesters has been accomplished using potassium borohydride in refluxing ethanol [17] where the product distribution critically depends on the relative proportions of substrate and reagent. Despite the occurrence of several recent reports of borohydride-mediated reduction of the ester moiety in α-oxo- [18–19] and β-oxoesters [20], sodium borohydride in various alcoholic solvents, often in the presence of additives [21], has been judiciously utilized [22] for the chemoselective reduction of the oxo-group, occasionally with subsequent transesterification and the formation of the alkoxy-modified β-hydroxyesters.…”

Simple reduction of ethyl, isopropyl and benzyl aromatic esters to alcohols using sodium borohydride-methanol system

“…2,3 Although this reducing agent has been constantly used for reduction of aldehydes, ketones and other important functional groups, it is not common to use NaBH 4 itself for reduction of esters. [4][5][6] Due to this low reactivity towards esters, additives which enhance the activity of NaBH 4 have been reported. 7 For example, addition of iodine to NaBH 4 in THF provides H 3 B-THF, which is useful for hydroborations, reduction of esters and various others functional groups.…”