Abstract
Asymmetric hydroalkoxylation of alkenes constitutes a redox-neutral and 100% atom-economical strategy toward enantioenriched oxygenated building blocks from readily available starting materials. Despite their great potential, catalytic enantioselective additions of alcohols across a C–C multiple bond are particularly underdeveloped, especially compared to other hydrofunctionalization methods such as hydroamination. However, driven by some recent innovations, e.g., asymmetric MHAT methods, asymmetric photocatalytic methods, and the development of extremely strong chiral Brønsted acids, there has been a gratifying surge of reports in this burgeoning field. The goal of this review is to survey the growing landscape of asymmetric hydroalkoxylation by highlighting exciting new advances, deconstructing mechanistic underpinnings, and drawing insight from related asymmetric hydroacyloxylation and hydration. A deep appreciation of the underlying principles informs an understanding of the various selectivity parameters and activation modes in the realm of asymmetric alkene hydrofunctionalization while simultaneously evoking the outstanding challenges to the field moving forward. Overall, we aim to lay a foundation for cross-fertilization among various catalytic fields and spur further innovation in asymmetric hydroalkoxylations of C–C multiple bonds.
Highlights
100% atom-economical strategy toward enantioenriched oxygenated building blocks from readily available starting materials
We conclude this review by highlighting some outstanding challenges and identifying potential areas of improvement that could provide an inspiration for future studies
Similar to discussion in section 2.2.2, for gold-catalyzed reactions proceeding through asymmetric counteranion directed catalysis (ACDC), there exists a continuum of noncovalent interactions that dictate stereoselectivity, i.e., ion pairing and/or hydrogen bonding
Summary
Owing to the versatile reactivity of metal π complexes, transition-metal catalysis has provided innumerable platforms for hydrofunctionalization reactions of C−C multiple bonds, including hydroamination, hydroformylation, and hydroboration reactions, among others.[1−5,26] In recent years, considerable attention has been devoted to the employment of chiral ligand scaffolds and/or chiral anions to effect asymmetric variants of such processes. In a hydroalkoxylation reaction of dicyclopentadiene using Cu(OTf)[2], the [Cu] species suppresses polymerization of the nucleophilic partner (2-hydroxyethyl methacrylate), and the control experiment with pure TfOH resulted in gelation of the reaction mixture and poor overall yields of the desired product.[32] the authors provide strong evidence that TfOH is the catalytically active species, underscoring the importance of well-designed control experiments To this end, protocols developed by Hintermann that deliberately generate hidden acids are encouraged as benchmark control experiments in reactions involving metal triflates.[27] one of the strongest arguments that a transition-metal complex is responsible for catalytic reactivity is the induction of high levels of enantioselectivity when employing a chiral ligand scaffold. We recognize the everevolving nature of mechanistic postulation and have organized these methods based on current proposals
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