Alternative Approaches to Enolate Chemistry

Abstract

This article highlights recently developed methods for the in-situ generation of enolates from non-carbonyl precursors. Suitable enolate precursors include allylic alcohols, vinyl borates and alkynes.

Oxidation and β‐Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N‐Heterocyclic Carbene Ligands

“…Enolate species are key building blocks in synthetic organic chemistry for the formation of new carbonÀcarbon and carbonÀheteroatom bonds. [34] Nowadays, the chemistry and reaction mechanisms involvinge nolates have been established, especially those focused on CÀCb ond-formation reactions, such as aldol condensations. [35] The cross-aldol condensation is driven by the nucleophilic attack of the enolate, generated under basic conditions, to the electrophile aldehyde to form a b-hidroxyketone (Scheme 6).…”

Catalytic Asymmetric β,γ Activation of α,β‐Unsaturated γ‐Butyrolactams: Direct Approach to β,γ‐Functionalized Dihydropyranopyrrolidin‐2‐ones

“…Inspired by the utilization of in situ generation of enolates,7 we postulated that the selective β,γ activation of α,β‐unsaturated γ‐butyrolactams through the in situ formation of a 1,4‐unsaturated enolate so as to raise the energy of the HOMO would be more feasible. In light of our recent studies on dual HOMO dienophile /LUMO diene ‐controlled asymmetric Diels–Alder (DA) reactions,8 we rationalized that such activated 1,4‐unsaturated enolates might serve as electron‐rich dienophiles with a properly designed electron‐deficient diene to undergo a β,γ‐selective inverse‐electron‐demand DA [4+2] annulation, while avoiding the direct γ‐selective vinylogous addition reaction as outlined in Scheme .…”

Rh‐Catalyzed AldehydeAldehyde Cross‐Aldol Reaction under Base‐Free Conditions: In Situ Aldehyde‐Derived Enolate Formation through Orthogonal Activation

“…Therefore, a method for the generation of an aldehyde‐derived enolate from a non‐carbonyl precursor through an orthogonal activation mode10 should provide an alternative and complementary approach to chemoselective aldehydealdehyde cross‐aldol products. Herein, we report a Rh‐catalyzed one‐pot isomerization/cross‐aldol sequence by using primary allylic, homoallylic, and bishomoallylic alcohols with their related allyloxy‐ and homoallyloxyboranes as donor precursors (Scheme ) 11.…”