A borane-mediated palladium-catalyzed reductive allylic alkylation of α,β-unsaturated carbonyl compounds

Abstract

A palladium-catalyzed allylation of ester-derived boron enolates, which is prepared through 1,4-reduction of α,β-unsaturated ester analogues.

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

“…Subsequently, the same group also reported the allylic alkylation of allyl acetate with enol boranes, prepared in situ from α,β-unsaturated carbonyl compounds via 1,4-hydroboration, albeit with low ee values (up to 35%). 397 …”

“…Subsequently, the same group also reported the allylic alkylation of allyl acetate with enol boranes, prepared in situ from α,β-unsaturated carbonyl compounds via 1,4-hydroboration, albeit with low ee values (up to 35%). 397 Enolates from esters and lactones have also been studied. An example was reported by Ooi and co-workers who developed a highly enantioselective allylation of benzofuranones with a range of linear allylic substrates using ion-paired chiral ligands consisting of a phosphinoaryl ammonium salt and a chiral biaryl phosphate (Scheme 121).…”

“…Moreover, the range of substrates was successfully expanded to rac -allenyl acetates, which reacted via a dynamic kinetic asymmetric transformation (DYKAT) with high enantio- and diastereoselectivities (Scheme ). Subsequently, the same group also reported the allylic alkylation of allyl acetate with enol boranes, prepared in situ from α,β-unsaturated carbonyl compounds via 1,4-hydroboration, albeit with low ee values (up to 35%) …”

Straightforward α-allylation of carbonyl compounds with alkenes via α-carbonyl radical intermediates

“…To circumvent this issue, metal-catalyzed methods for cross-coupling of allylic electrophiles with the pre-constructed enolate precursors have emerged as a complement to the Tsuji–Trost reaction. In this context, silyl/boron enol ethers 5 or enamines 6 have been successfully used as mild and efficient precursors of enolate nucleophiles to establish a valuable approach for the construction of α-allylated carbonyl compounds under strong-base free conditions (Scheme 1b).…”

Development of an Enantioselective Allylic Alkylation of Acyclic α‐Fluoro‐β‐ketoesters for Asymmetric Synthesis of 3‐Fluoropiperidines

“…Adapting a Pd‐catalyzed asymmetric allylation [10] strategy to our system raises several challenging issues that must be overcome to deliver an enantioselective route to 3‐fluoropiperidines: (1) our piperidine forming strategy requires the employment of acyclic α ‐fluoro‐ β ‐ketoesters, and so the potential for enantiodivergence in E/Z enolate mixtures must be overcome; (2) the enolate functions as the prochiral fragment making the efficient relay of stereochemistry from chiral catalyst to prochiral substrate difficult (assuming an outer sphere mechanism [11] ). [12] With these challenges in mind, we set out to investigate if the Pd‐catalyzed allylic alkylation of 1 was viable for the generation of 3‐fluoropiperidine derivatives with useful levels of enantiocontrol (Figure 2 ).…”