Diastereoselective Synthesis of Arylglycine Derivatives by Cationic Palladium(II)-Catalyzed Addition of Arylboronic Acids to N-tert-Butanesulfinyl Imino Esters

Enantioselective Synthesis of Arylglycines via Pd-Catalyzed Coupling of Schöllkopf Bis-Lactim Ethers with Aryl Chlorides

Arylglycines are important pharmacophores present in several top-selling drugs. This compound class has now been made accessible from abundant aryl chlorides by a Pd-catalyzed Schöllkopf-type amino acid synthesis. In the presence of the catalyst methylnaphthyl(XPhos)-palladium bromide, the base lithium 2,2,6,6-tetramethylpyrrolidide and the additive ZnCl2 , tert-leucine-derived bis-lactim ethers were efficiently arylated at room temperature, reaching yields of 95 % and diastereoselectivities of 98 : 2. Hydrolysis gave the corresponding arylglycines in high enantiomeric excess.

Nickel-Catalyzed Enantioselective Reductive Arylation and Heteroarylation of Aldimines via an Elementary 1,4-Addition

Nickel catalysts of chiral pyrox ligands promoted enantioselective reductive arylation and heteroarylation of aldimines, using directly (hetero)aryl halides and sulfonates. The catalytic arylation can also be conducted with crude aldimines generated from condensation of aldehydes and azaaryl amines. Mechanistically, density functional theory (DFT) calculations and experiments pointed to an elementary step of 1,4-addition of aryl nickel(I) complexes to N-azaaryl aldimines.

Palladium-catalyzed asymmetric three-component reaction between glyoxylic acid, sulfonamides and arylboronic acids for the synthesis of α-arylglycine derivatives

A palladium-catalyzed asymmetric three-component synthesis of α-arylglycine derivatives starting from glyoxylic acid, sulfonamides and arylboronic acids is reported. This novel, operationally simple method offers access to the α-arylglycine scaffold in good yields and enantioselectivities. The utilization of α tailored catalyst system enables the enantioselective synthesis of the desired α-arylglycines despite a fast racemic background reaction. The obtained products can be directly employed as building blocks in peptide synthesis.

Rh-Catalyzed diastereoselective addition of arylboronic acids to α-keto N-tert-butanesulfinyl aldimines: synthesis of α-amino ketones

Herein we present a diastereoselective addition of arylboronic acids to α-keto N-tert-butanesulfinyl aldimines catalyzed by a Rh(i) catalyst.

Palladium-catalyzed oxidative cross-coupling for the synthesis of α-amino ketones

A novel oxidative cross-coupling reaction for the synthesis of α-aryl α-amino ketones in the presence of palladium catalysts using T⁺BF₄⁻ as an oxidant has been developed. This transformation was achieved by direct C–H oxidation of α-aminocarbonyl compounds and arylation. The mild reaction has a broad reaction scope and gives desired α-aryl α-amino ketones in moderate to excellent yields.

A novel oxidative cross-coupling reaction for the synthesis of α-aryl α-amino ketones in the presence of palladium catalysts using T⁺BF₄⁻ as an oxidant has been developed.

Synthesis of chiral seven-membered cyclic sulfonamides through palladium-catalyzed arylation of cyclic imines

An enantioselective palladium-catalyzed addition of arylboronic acids to seven-membered cyclic N-sulfonyl aldimines and ketimines has been developed, giving the chiral cyclic sulfonamides with excellent yields and up to 99% ee.

Synthesis of paracyclophanes with planar and central chirality: kinetic resolution of [2.2]paracyclophane aldimines via palladium-catalyzed addition of arylboronic acids

Kinetic resolution of [2.2]paracyclophane aldimines was achieved through a palladium-catalyzed enantioselective arylation, providing access to chiral paracyclophanes with planar and central chirality as well as the recovered chiral aldimines.

Diastereoselective Synthesis of Unnatural Amino Acids by Alkylation of α- tert-Butanesulfinamide Auxiliary-Bound Enolates

A new chiral auxiliary for the diastereoselective alkylation of amino ester enolates that takes advantage of chiral information stored on the enolate side of the amino ester substrate has been developed. Chiral α-sulfinamido esters were alkylated under basic conditions in good yields (up to 90%) and good to high diastereoselectivities (generally >6:1) to provide unnatural mono- and α,α-disubstituted amino acid derivatives. This auxiliary allowed for the ready conversion of ester functionality without the need for esoteric reagents. Furthermore, the auxiliary is easily removed to provide enantiopure amino acids. Computational studies revealed that a chelated transition state governs electrophile addition from the convex face of a transient bicyclic intermediate. This method allows ready access to enantioenriched natural and unnatural amino acids.

Renaissance of pyridine-oxazolines as chiral ligands for asymmetric catalysis

Oxazoline-containing ligands have been widely employed in numerous asymmetric catalytic reactions. Pyridine-oxazoline-type ligands, a class of hybrid ligands, were designed earlier than bisoxazoline and phosphine-oxazoline ligands; however, their unique properties have only been discovered recently. Pyridine-oxazoline-type chiral ligands are rapidly becoming popular for use in asymmetric catalysis, especially for several new and efficient asymmetric methodologies. Several types of challenging asymmetric reactions have been discovered recently using pyridine-oxazoline-type ligands showing their special properties and potential for future application in a wide range of new catalytic methodologies. This review provides an overview of this field, with the aim of highlighting both ligand design and synthetic methodology development.

Pd(ii), Ni(ii) and Co(ii)-catalyzed enantioselective additions of organoboron reagents to ketimines

This feature article highlights the development of Pd(ii), Ni(ii), and Co(ii)-catalyzed asymmetric additions of organoboron reagents to ketimines.

Ru-Catalyzed highly diastereoselective hydrogenation of N-tert-butylsulfinyl ketimines for the synthesis of aryl glycine derivatives

A Ru-Pincer catalyst enables the diastereoselective hydrogenation of N-tert-butylsulfinyl ketimino esters, affording a promising method for the synthesis of aryl glycine derivatives.

Chiral Bidentate NHC Ligands Based on the 1,1'-Binaphthyl Scaffold: Synthesis and Application in Transition-Metal-Catalyzed Asymmetric Reactions

The use of the chiral 1,1'-binaphthyl scaffold to construct chiral ligands can be traced back for a long time. However, the development of bidentate NHC ligands based on the same backbone has only appeared recently. In this account, we describe the design and synthesis of a new family of chiral NHC ligands based on the 1,1'-binaphthyl scaffold and demonstrate the applications of these chiral NHC-metal complexes in the catalyzed oxidative kinetic resolution of secondary alcohols, asymmetric carbon-carbon bond formations, hydrosilylations, and cyclizations of 1,6-enynes. The chiral NHC ligands containing the 1,1'-binaphthyl backbone can be synthesized in good yields from enantiomerically pure 1,1'-binaphthyl-2,2'-diamine. These transition metals coordinated with chiral bidentate NHC ligands exhibit high catalytic activities and good enantioselectivities for a wide range of metal-catalyzed asymmetric reactions.

Enantioselective synthesis of quaternary α-aminophosphonates by Pd-catalyzed arylation of cyclic α-ketiminophosphonates with arylboronic acids

A highly enantioselective addition of arylboronic acids to cyclic α-ketiminophosphonates is reported using a chiral palladium phosphinooxazoline catalyst, providing an efficient and facile route to quaternary α-aminophosphonates in high yields and up to 99.9% enantioselectivity.

Palladium-Catalyzed Enantioselective Three-Component Synthesis of α-Arylglycines

A general Pd-catalyzed, enantioselective three-component synthesis of α-arylglycines starting from sulfonamides, glyoxylic acid derivatives, and boronic acids was developed. This operationally straightforward procedure enables the preparation of a wide variety of α-arylglycines in high yields and excellent levels of enantioselectivity from a simple set of readily available starting materials. Incorporation of Pbf-amides gives a racemization-free access to N-unprotected α-arylglycines.

Preparation of Enantiomerically Pure Perfluorobutanesulfinamide and Its Application to the Asymmetric Synthesis of α-Amino Acids

A high yielding and practical two-step synthesis of enantiomerically pure perfluorobutanesulfinamide from Senanayake's 2-aminoindanol-derived sulfinyl transfer reagent was developed and carried out on a multigram scale. Straightforward condensation of this sulfinamide with ethyl glyoxylate provided the N-perfluorobutanesulfinyl imino ester. The utility of this activated N-sulfinyl imino ester was demonstrated for reactions that gave either no product or very low yields with the corresponding less electrophilic N-tert-butanesulfinyl derivative. Specifically, the Rh(III)-catalyzed C-H bond addition of aromatic compounds to the N-perfluorobutanesulfinyl imino ester provided arylglycines with very high diastereoselectivities for a range of directing groups including pyrrolidine amide, azo, sulfoximine, 1-pyrazole, and 1,2,3-triazole functionalities. Thermal asymmetric aza-Diels-Alder reactions also proceeded in good yields and with high selectivity, including for the substituted dienes (E)-1,3-pentadiene and (2E,4E)-2,4-hexadiene.

Enantioselective C-H Olefination of α-Hydroxy and α-Amino Phenylacetic Acids by Kinetic Resolution

Significant progress has been made in the past decade regarding the development of enantioselective C-H activation reactions by desymmetrization. However, the requirement for the presence of two chemically identical prochiral C-H bonds represents an inherent limitation in scope. Reported is the first example of kinetic resolution by a palladium(II)-catalyzed enantioselective C-H activation and C-C bond formation, thus significantly expanding the scope of enantioselective C-H activation reactions.

Enantioselective palladium-catalyzed arylation of N-tosylarylimines with arylboronic acids using a chiral 2,2′-bipyridine ligand

An enantioselective palladium-catalyzed arylation of N-tosylarylimines with arylboronic acids was developed by using an axially chiral 2,2′-bipyridine ligand C3-ACBP, affording chiral diarylmethamines with up to 94% ee under exogenous-base-free conditions.

Enantioselective synthesis of arylglycine derivatives by direct C–H oxidative cross-coupling

A new method for the synthesis of chiral α-amino acid derivatives by enantioselective C–H arylation of N-aryl glycine esters with aryl boric acids by direct C–H oxidative cross-coupling has been performed. This work successfully integrates the direct C–H oxidation with asymmetric arylation and exhibits excellent enantioselectivity.

Regulation of diastereoselectivity in the carbocyclization of allenyl (S)-N-tert-butylsulfinimines through a three-component assembly

Allenyl sulfinimines can be stereoselectively cyclized with hexamethylditin under palladium catalysis conditions followed by a selection of additives for an activated transmetalation. Reactivity and diastereoselectivity for the cyclization strongly depend on the characteristics of additives. A highly diastereoselective synthesis of five-membered rings is achieved from the reaction of the corresponding allenyl (S)-N-tert-butylsulfinimies through the following sequence. After the distannylation of the allenyl group with hexamethylditin catalyzed by the Pd complex, stereochemical routes are additive dependent: addition of SnCl4 affords a cis ring exclusively, whereas a trans ring is formed predominantly by the introduction of B-bromocatecholborane. Extension of the methodology to the synthesis of six-membered cis rings is achieved by using B-bromocatecholborane. Stereochemical relationships of products were unambiguously deduced by X-ray crystallography.

A Lewis acid palladium(II)-catalyzed three-component synthesis of α-substituted amides

A Lewis acid palladium-catalyzed reaction of amides, aryl aldehydes, and arylboronic acids is described. This new method allows for a practical and general synthesis of α-substituted amides from simple, readily available building blocks.

Asymmetric synthesis of amines using tert-butanesulfinamide

Chiral amines are prevalent in many bioactive molecules, including amino acids and pharmaceutical agents. tert-Butanesulfinamide (tBS) is a chiral amine reagent that has enabled the reliable asymmetric synthesis of a very broad range of different amine structures from simple, readily available starting materials. Three steps are commonly applied to the asymmetric synthesis of amines: (i) condensation of tBS with a carbonyl compound, (ii) nucleophile addition and (iii) tert-butanesulfinyl group cleavage. Here we demonstrate these steps with the preparation of a propargylic tertiary carbinamine, one of a class of amines that have been used for many different biological purposes, including click chemistry applications, diversity-oriented synthesis, the preparation of peptide isosteres and the development of protease inhibitors as drug candidates and imaging agents. The process described here can be performed in 3-4 d.

The Synthesis of a Cubane-Substituted Dipeptide

Amino acids and peptides bearing cyclic hydrocarbon side-chains are of interest in the development of a wide range of bioactive molecules. The preparation of an amino acid and a dipeptide derivative bearing an unfunctionalised cubane substituent is described. Attempts to prepare a cubylalanine derivative via the corresponding dehydroalanine were unsuccessful due to the high sensitivity of this vinyl cubane compound. Conversely, the addition of cubyllithium to a (RS)-glyoxylate sulfinimine led to an effective synthesis of a cubylglycine derivative and a cubane-substituted dipeptide in diastereomerically pure form.