Iridium‐Catalyzed Enantioselective Allylic Substitution of Aliphatic Esters with Silyl Ketene Acetals as the Ester Enolates

Abstract

Enantioselective allylic substitutions with enolates derived from aliphatic esters under mild conditions remain challenging. Herein we report iridium-catalyzed enantioselective allylations of silyl ketene acetals, the silicon enolates of esters, to form products containing a quaternary carbon at the nucleophile moiety and a tertiary carbon at the electrophile moiety. Under relatively neutral conditions, the allylated aliphatic esters were obtained with excellent regioselectivity and enantioselectivity. These products were readily converted to primary alcohols, carboxylic acids, amides, isocyanates, and carbamates, as well as tetrahydrofuran (THF) and γ-butyrolactone derivatives, without erosion of enantiomeric purity.

Trimethyl Orthoacetate and Ethylene Glycol Mono‐Vinyl Ether as Enolate Surrogates in Enantioselective Iridium‐Catalyzed Allylation

“…However, for compounds with attenuated C−H acidity, such as esters and ketones, masked enolate equivalents are necessary. The use of silyl enol ethers and silyl ketene acetals in enantioselective iridium‐catalyzed allylic substitution reactions has been reported primarily by Hartwig . Additionally, their use in allylic substitution has been well‐documented using palladium and ruthenium .…”

Trimethyl Orthoacetate and Ethylene Glycol Mono‐Vinyl Ether as Enolate Surrogates in Enantioselective Iridium‐Catalyzed Allylation

“…[4] However,f or compounds with attenuated CÀHa cidity,s uch as esters and ketones,m asked enolate equivalents are necessary.The use of silyl enol ethers and silyl ketene acetals in enantioselective iridium-catalyzed allylic substitution reactions has been reported primarily by Hartwig. [5,6] Additionally,t heir use in allylic substitution has been well-documented using palladium [7] and ruthenium. [8] Interestingly,the use of the parent silyl ketene acetals derived from acetic acid esters in iridium-catalyzed allylation has not been reported.…”

Reactions of Bis(trimethylsilyl)ketene Acetals with Several Activated Organic Substrates

“…Additionally, Jiang and Hartwig used iridium complex 27 to catalyze enantioselective allylic substitution of the aliphatic ether 26 to give a product that contained the quaternary carbon atom at the nucleophile moiety and the tertiary carbon atom at the electrophile moiety 28 , Scheme …”