Cobalt-Catalyzed Diastereo- and Enantioselective Reductive Allyl Additions to Aldehydes with Allylic Alcohol Derivatives via Allyl Radical Intermediates

Abstract

Catalytic generation of ambiphilic π-allyl−metal complexes and their utility in enantioselective transformations constitutes a powerful approach for introduction of allyl groups to a molecule. Herein an unprecedented cobaltcatalyzed highly site-, diastereo-, and enantioselective protocol for stereoselective formation of nucleophilic allyl−Co(II) complexes followed by addition to aldehydes is presented. The reaction features diastereo-and enantioconvergent conversion of easily accessible allylic alcohol derivatives to diversified enantioenriched homoallylic alcohols with a remarkably broad scope of allyl groups that can be introduced. Mechanistic studies indicated that allyl radical intermediates were involved in this process. These new discoveries establish a new strategy for development of enantioselective transformations through capture of radicals by chiral Co complexes, pushing forward the frontier of Co complexes for enantioselective catalysis.

Divergent Reactivity of α,α-Disubstituted Alkenyl Hydrazones: Bench Stable Cyclopropylcarbinyl Equivalents

“…The synthesis of 3-functionalized 1,4-dienes (skipped dienes) is a challenge that has received considerable attention in the past decade due in part to the prevalence of this structural motif in natural compounds arising from fatty acid biosynthetic pathways (e.g., insect pheromones) . State-of-the-art catalytic methods for synthesis of skipped dienes rely heavily on allylic substitution reactions using vinyl organometallic nucleophiles, − and few catalytic methods deviate from this regime (Figure A). − Strategically, these reactions append a vinyl group onto electrophiles to construct the skipped diene group. These methods are constrained by the regioselective outcomes of alkyne hydrometalation reactions or the stereoselectivity in the synthesis of vinylboronic acid derivatives.…”

Enantioselective Cobalt-Catalyzed Reductive Cross-Coupling for the Synthesis of Axially Chiral Phosphine–Olefin Ligands

“…The above observations provided support for this transformation possibly being involved in the catalytic cycle of the Co I to Co III pathway (for details see the Supporting Information). On the basis of the above experiments and literature reports, 14,25 we proposed a tentative pathway for this transformation (Scheme 4). First, the activated catalytic species Co I -A was generated from CoBr 2 through singleelectron reduction by Mn powder and combined with chiral ligand L 5 .…”

“…On the basis of the above experiments and literature reports, , we proposed a tentative pathway for this transformation (Scheme ). First, the activated catalytic species Co I -A was generated from CoBr 2 through single-electron reduction by Mn powder and combined with chiral ligand L 5 .…”

Dual Cobalt/Organophotoredox Catalysis for Diastereo- and Regioselective 1,2-Difunctionalization of 1,3-Diene Surrogates Creating Quaternary Carbon Centers

“…Metallaphotoredox catalysis has recently emerged as a powerful approach, enabling carbon–carbon bond formation under mild conditions, though cobalt-catalyzed protocols remain relatively unmapped . In this realm, the allylation of aldehydes enabled by a nucleophilic allyl-Co II species has recently been studied by various groups, and we showed that 1,3-diols featuring quaternary carbon centers can be prepared from VCCs under high diastereocontrol…”