A New Reduction of Some Carboxylic Esters with Sodium Borohydride and Zinc Chloride in the Presence of a Tertiary Amine

Abstract

In the presence of a tertiary amine, sodium borohydride (NaBH4) combined with zinc chloride (ZnCl2) showed powerful reducing properties and carboxylic esters were smoothly reduced to their corresponding alcohols which were not obtained by reduction with NaBH4 and ZnCl2 alone. Tetrahydrofuran (THF) was an efficient solvent, and the effective molar ratio of the reducing agents, NaBH4 : ZnCl2 : tertiary amine, was 2 : 1 : 1. In particular, aminobenzoates such as anthranilic esters, were reduced to aminobenzyl alcohols with high yields without the addition of a tertiary amine. Further, it was also found that this combination reduced nitro, cyano, and amido groups to their corresponding amino groups.

Sensitive NMR method for detecting carbohydrate influx into competing chemocatalytic pathways

“…Commercially available carbohydrate substrates and routine detection instruments can be used. The approach installs protons at the C1 position of methyl lactate through reduction with NaBH 4 [33][34][35] prior to the indirect detection of 13 C and 12 C sites in multiplets of the sensitive 2D 13 C directly bonded to either, both or none of the hydrogens. The experimentally observed signal is a weighted average of these four forms.…”

The Chemistry of Anthranilic Acid

“…104]. For reductions of esters of AAs to the corresponding alcohols, NaBH 4 [105] or NaBH 4 /ZnCl 2 [106] have been used successfully.…”

Stabilization of NaBH4 in Methanol Using a Catalytic Amount of NaOMe. Reduction of Esters and Lactones at Room Temperature without Solvent-Induced Loss of Hydride

“…Scheme summarizes the known methods for the reduction of esters with NaBH 4 in methanol. Addition of metal salts, such as LiCl, LiBr, MgCl 2 , CaCl 2 , ZnCl 2 , and AlCl 3 , to sodium borohydride increases its reduction capabilities (Scheme , entry 1). − There are also reports of the reduction of esters using NaBH 4 in the presence of Ce or Co catalyst (Scheme , entry 2) supported on cationic surfaces . Under reflux conditions, NaBH 4 has been reported to reduce esters in protic solvents (Scheme , entry 3). ,− Esters bearing substituents like hydroxyl/oxo/amino in the α- or β-positions have been reduced by NaBH 4 via intramolecular hydride transfer (Scheme , entry 4). − Unfortunately, alcohol solvents, such as methanol, are not compatible with NaBH 4 at elevated temperatures because decomposition of NaBH 4 becomes competitive with the reduction.…”