Enantioselective Allylic Alkylation with 4-Alkyl-1,4-dihydro-pyridines Enabled by Photoredox/Palladium Cocatalysis

Abstract

Highly regio- and enantioselective allylic alkylation has been achieved enabled by the merger of photoredox and palladium catalysis. In this dual catalytic process, alkyl radicals generated from 4-alkyl-1,4-dihydropyridines act as the coupling partners of the π-allyl palladium complexes. The generality of this method has been illustrated through the reaction of a variety of allyl esters with 4-alkyl-1,4-dihydropyridines. This mechanistically novel strategy expands the scope of the traditional Pd-catalyzed asymmetric allylic alkylation reaction and serves as its alternative and potential complement.

Synergistic Photoredox/Transition‐Metal Catalysis for Carbon–Carbon Bond Formation Reactions

“…These approaches have been recently enriched by an enantioselective version of the allylic alkylation via a combined photoredox and Pd‐catalysis method. In this work, Yu and co‐workers, capitalized on enantioselective allylation known under thermal conditions to explore a photoinduced method (Scheme ) . The screening of several chiral phosphorus ligands identified ( R )‐GarPhos (L*) to be the best ligand for the enantioselective induction.…”

Der “Persistent Radical Effect” in der organischen Chemie

“…[273,274] Beispielsweise präsentierte Yu eine enantioselektive Version durch die Verwendung chiraler Phosphinliganden mit Alkyl-1,4-dihydropyridin (Alk-DHP) als Radikalvorläufer.I n dieser radikalischen Allylierung wurden Allylacetate 149 in moderaten bis guten Ausbeuten und hohen Enantioselektivitäten in die Alkene 151 überführt (Abbildung 45). [275] Wie in einer klassischen Tsuji-Trost-Reaktion addiert dabei Pd 0 an 149,u md ie Allyl-Pd II -Spezies zu bilden, welche in der Lage ist die Alkyl-Radikale -a us der photokatalytischen Oxidation von Alk-DHP 150 -abzufangen. Reduktive Eliminierung führt zu 151 und einem Pd I -Komplex.…”

Metal-supported and -assisted stereoselective cooperative photoredox catalysis

“…By a combination of palladiumand photocatalysis using [Ir( ppy) 2 (dtbbpy)]PF 6 , Zhang and coworkers were able to achieve a highly regio-and enantioselective allylic alkylation with a range of such unstabilized alkyl nucleophiles (Scheme 35). 118 Alkyl radicals generated from dihydropyridines (DHP) 92 serve as the coupling partners for π-allyl palladium complexes, thereby complementing the scope of previous palladium catalyzed asymmetric allylic alkylation protocols.…”

“…(2.0 mol%), Pd-cat. (2.5 mol%), ligand (6.0 mol%), CH 3 CN, blue LED (45 W), 12 h. 118 The difunctionalization of alkynes 107 can be realized by direct cyclization as in the example above. Another useful method is atom transfer radical addition.…”