Enantioselective Hydrocarbamoylation of Alkenes

The asymmetric hydroaminocarbonylation of olefins represents a straightforward approach for the synthesis of enantioenriched amides, but is hampered by the necessity to employ CO gas, often at elevated pressures. We herein describe, as an alternative, an enantioselective hydrocarbamoylation of alkenes leveraging dual copper hydride and palladium catalysis to enable the use of readily available carbamoyl chlorides as a practical carbamoylating reagent. The protocol is applicable to various types of olefins, including alkenyl arenes, terminal alkenes, and 1,1-disubstituted alkenes. Substrates containing a diverse range of functional groups as well as heterocyclic substructures undergo functionalization to provide α- and β-chiral amides in good yields and with excellent enantioselectivities.

Synergistic Peptide and Gold Catalysis: Enantioselective Addition of Branched Aldehydes to Allenamides

The combination of a peptide catalyst and a gold catalyst is presented for enantioselective addition reactions between branched aldehydes and allenamides. The two catalysts act in concert to provide γ,δ-enamide aldehydes bearing a fully substituted, benzylic stereogenic center - a structural motif common in many natural products and therapeutically active compounds - with good yields and enantioselectivities. The reaction tolerates a variety of alkyl and alkoxy substituted aldehydes and the products can be elaborated into several chiral building blocks bearing either 1,4- or 1,5- functional group relationships. Mechanistic studies showed that the conformational features of the peptide are important for both the catalytic efficiency and stereochemistry, while a balance of acid/base additives is key for ensuring formation of the desired product over undesired side reactions.

Development of Dipolarophiles for Catalytic Asymmetric Cycloadditions through Pd-π-Allyl Zwitterions

The development of new and efficient methodology for the construction of optically active molecules is of great interest in both synthetic organic and medicinal chemistry fields. To this end, the personal account summarizes our studies on the development of electron-deficient alkenes, allenes, and alkynes containing single activator as new dipolarophiles for Pd-catalyzed asymmetric cycloaddition reactions. These new dipolarophiles can participate in Pd-catalyzed asymmetric [3+2] and [4+2] cycloadditions through Pd-π-allyl 1,3- and 1,4-zwitterions in-situ generated by the reaction of Pd(0) catalyst with vinyl aziridines, vinyl epoxides, vinyl cyclopropanes, 4-vinyl-1,3-dioxan-2-ones, and vinyl benzoxazinanones. These [3+2] and [4+2] cycloadditions provide efficient approaches to a wide range of enantiomerically enriched five- and six-membered ring compounds containing contiguous chiral centers with high to excellent chemo-, diastereo-, and enantioselectivities. The utilities of these protocols are demonstrated by transformation of the cycloadducts into other useful chiral building blocks. DFT calculations reveal the dissimilar reactivity of different electron deficient alkenes and rationalize the mechanism and stereo-control of the reaction. A Pd-catalyzed inverse [3+2] cycloaddition is disclosed.

Stereoconvergent 1,4-Addition Reaction of 5H-Oxazol-4-ones with E,Z Isomeric Mixture of Alkylidene β-Ketoesters Catalyzed by Chiral Guanidines

A 1,4-addition reaction of 5H-oxazol-4-ones to alkylidene β-ketoesters, which was catalyzed by using chiral guanidines via a dynamic kinetic resolution process that involved geometric isomerization of the alkylidene β-ketoesters, was developed. This method allowed using E,Z isomeric mixture of various acyclic alkylidene β-ketoesters to obtain the products stereoselectively. The relation between the geometry and the stereoselectivity of products was investigated, and the derivatization of the products to the corresponding α-acyl-γ-lactone was performed.

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

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

Non-stabilized enolates – versatile nucleophiles in transition metal-catalysed allylic alkylations

This review covers new developments in the transition metal-catalyzed allylic alkylations of non-stabilized enolates, preferentially generated from ketone, esters or amides.

Palladium-catalyzed allylic alkylation of carboxylic acid derivatives: N-acyloxazolinones as ester enolate equivalents

A general asymmetric allylic alkylation of ester enolate equivalents at the carboxylic acid oxidation state is reported. N -Acylbenzoxazolinone-derived enol carbonates are synthesized in good yield and employed in the palladium-catalyzed alkylation reaction. Good yields (up to 99%) and enantioselectivities (up to 99% ee) are obtained and the imide products are readily converted to a series of carboxylic acid derivatives without loss of enantiopurity. High enantioselectivity in the reaction is achieved by a new strategy for ligand design involving variation of the steric properties of the diarylphosphine moiety.

Enantioselective decarboxylative alkylation reactions: catalyst development, substrate scope, and mechanistic studies

α-Quaternary ketones are accessed through novel enantioselective alkylations of allyl and propargyl electrophiles by unstabilized prochiral enolate nucleophiles in the presence of palladium complexes with various phosphinooxazoline (PHOX) ligands. Excellent yields and high enantiomeric excesses are obtained from three classes of enolate precursor: enol carbonates, enol silanes, and racemic β-ketoesters. Each of these substrate classes functions with nearly identical efficiency in terms of yield and enantioselectivity. Catalyst discovery and development, the optimization of reaction conditions, the exploration of reaction scope, and applications in target-directed synthesis are reported. Experimental observations suggest that these alkylation reactions occur through an unusual inner-sphere mechanism involving binding of the prochiral enolate nucleophile directly to the palladium center.

Enantioselective and diastereoselective Tsuji-Trost allylic alkylation of lactones: an experimental and computational study

The Tsuji-Trost protocol has been successfully employed for the allylic alkylation of preformed lactone enolates. It has been demonstrated that this Pd-catalyzed reaction can be carried out in an enantio- and diastereoselective manner. The use of additives, such as LiCl, was found to be crucial for reaching high levels of product selectivity. For one particular pair of reactants, density functional theory was used to investigate the mechanism of the nucleophilic addition. Among the five pathways considered, the reaction between an (allyl)Pd(BINAP) complex and a LiCl-lithium enolate adduct is predicted to be the most likely route for C-C bond formation. LiCl plays a key role as the connecting link between the noble metal and the enolate in the kinetically favored transition state. The computed diastereoselectivity ratio is in good agreement with the experimentally observed value.