Mechanistic rationale for the NaBH4 reduction of α-keto esters

Article abstract of DOI:10.1016/S0040-4039(99)01006-0

An intramolecular hydride delivery process largely contributes during the double reduction of α-keto esters into diols by NaBH₄. In the case of enolic α-keto esters, the first step of the process, the reduction of the keto group, occurred exclusively through an 1,2-hydride addition despite the predominance of the tautomeric enolic form. The clear-cut difference of reaction rate between enolic and non enolic substrate 4 for reaction carried out in methanol is interpreted in terms of competitive hydride consumption due to the extremely favorable reaction between this solvent and NaBH₄.