Vicinal Chiral Centers Research Articles

Simultaneous Stereoinvertive and Stereoselective C(sp3)-C(sp3) Cross-Coupling of Boronic Esters and Allylic Carbonates.

With increasing interest in constructing more three-dimensional entities, there has been growing interest in cross-coupling reactions that forge C(sp3)-C(sp3) bonds, which leads to additional challenges as it is not just a more difficult bond to construct but issues of stereocontrol also arise. Herein, we report the stereocontrolled cross-coupling of enantioenriched boronic esters with racemic allylic carbonates enabled by iridium catalysis, leading to the formation of C(sp3)-C(sp3) bonds with single or vicinal stereogenic centers. The method shows broad substrate scope, enabling primary, secondary, and even tertiary boronic esters to be employed, and can be used to prepare any of the four possible stereoisomers of a coupled product with vicinal chiral centers. The new method, which combines the simultaneous enantiospecific reaction of a chiral nucleophile with the enantioselective reaction of a chiral electrophile in a single process, offers a solution for stereodivergent cross-coupling of two C(sp3) fragments.

Stereodivergent Synthesis of All Stereoisomers of 2,3-Disubstituted δ-Lactam Derivatives via Organocatalytic Cascade Reactions and Base-Induced Epimerization.

A protocol was developed to achieve stereodivergent synthesis of stereoisomers of δ-lactam bearing vicinal chiral centers. Organocatalytic cascade reactions were employed to produce the target products as the kinetic products, which exhibited remarkable enantioselectivities. In the presence of DBU, the kinetic product underwent epimerization to form a thermodynamically more stable diastereomer without loss in enantioselectivity. By simply switching the chiral organocatalyst and its enantiomer, we can efficiently obtain four stereoisomers with high enantioselectivities.

Asymmetric α-Allylation for the Synthesis of α,α-Disubstituted Amino Acids with Vicinal Chiral Centers

Asymmetric α-Allylation for the Synthesis of α,α-Disubstituted Amino Acids with Vicinal Chiral Centers

Enantioselective Construction of Consecutive Tetrasubstituted Stereogenic Centers by Reaction of α-Substituted β-Nitroacrylates with Oxazol-5-(4H)-ones Catalyzed by Cinchona Alkaloid Sulfonamide Catalysts.

The enantioselective reaction of α-substituted β-nitroacrylates with oxazol-5-(4H)-ones (oxazolones) to construct consecutive tetrasubstituted stereogenic centers was accomplished. A cinchona alkaloid sulfonamide catalyst afforded products bearing vicinal chiral centers with excellent enantio- and diastereoselectivities. The obtained products were successively converted into various chiral compounds without loss of their enantiopurity. Furthermore, density functional theory (DFT) calculations were performed to elucidate the mechanism and origin of the observed stereoselectivity of the reaction.

Nickel-Catalyzed Asymmetric Friedel-Crafts Propargylation of 3-Substituted Indoles with Propargylic Carbonates Bearing an Internal Alkyne Group.

The nickel-catalyzed highly enantioselective Friedel-Crafts propargylation of 3-substituted indoles with propargylic carbonates bearing an internal alkyne group was developed. A wide array of the propargylic carbonates as well as 3-substituted indoles can be applicable to the asymmetric nickel catalysis, providing the corresponding chiral C-3 propargylated indolenine derivatives bearing two vicinal chiral centers in up to 89% yield with up to >99% ee and 94:6 dr (24 examples).

Asymmetric Multicomponent Reactions for Efficient Construction of Homopropargyl Amine Carboxylic Esters.

Developing an efficient and highly enantioselective protocol to access homopropargyl amines is of high interest to the synthetic community and also remains a formidable challenge for organic chemists. Here, we present integrated Rh2(OAc)4- and BINOL-derived chiral phosphoric acid cooperatively catalyzed three-component reactions of alkynyldiazoacetates, imines with various nucleophiles including alcohols, indoles, and N,N-disubstituted anilines, affording the corresponding homopropargyl amines containing two vicinal chiral centers in satisfactory yields with high to excellent diastereo- and enantioselectivities.

Enantioselective Cascade Reaction for Synthesis of Quinolinones through Synergistic Catalysis Using Cu-Pybox and Chiral Benzotetramisole as Catalysts.

In contrast to the well-studied asymmetric catalyzed synthesis of tetrahydroquinolines, the asymmetric methodologies toward 3,4-dihydroquinolin-2-ones are quite rare. Herein, the first asymmetric cascade reaction is reported between ethynyl benzoxazinanones and mixed-anhydrides generated from aryl acetic acids and pivaloyl chloride, based on synergistic catalysis. This allowed the formation of attractive 3,4-dihydroquinolin-2-ones bearing two vicinal chiral centers at C3 and C4 in high yields with excellent diastereo- and enantioselectivities. A plausible chiral induction model for this reaction was proposed. The utility of this methodology was exemplified by further elaboration of the cyclization products by removal of the N-protecting groups.

Enantioselective Multicomponent Reaction for Rapid Construction of 1,2,5-Triol Derivatives with Vicinal Chiral Centers.

1,2,5-Triol derivatives with vicinal chiral centers have been synthesized from simple starting materials by one-pot method in good yields and with an excellent enantioselectivity. This process was promoted by a chiral secondary amine and iridium(I) cocatalyzed three-component reaction of aryldiazoacetates and alcohols with enals as electrophiles followed by a reduction with NaBH4. Iridium(I)-associated oxonium ylide intermediates were efficiently generated and successfully trapped by the amine-activated enals via a selective 1,4-addition manner, generating enantioselective three-component coupling products.

Asymmetric Synthesis of Chiral α-Methyl-α,β-diamino Acid Derivatives via Group-Assisted Purification Chemistry Using N-Phosphonyl Imines and a Ni(II)-Complexed Alanine Schiff Base.

The Mannich reaction between chiral N-phosphonyl imines and a Ni(II)-complexed alanine Schiff base (Ala-Ni) is reported. With a chiral phosphonyl auxiliary, a single isomer of α-methyl-α,β-diamino acid derivative containing vicinal chiral centers, including a chiral quaternary carbon center, can be obtained simply by washing the crude mixture with cosolvents. The absolute stereochemistry of the enantiomerically pure product has been unambiguously determined by X-ray crystallographic analysis.

ChemInform Abstract: Highly Diastereo‐ and Enantioselective Copper‐Catalyzed Propargylic Alkylation of Acyclic Ketone Enamines for the Construction of Two Vicinal Stereocenters.

AbstractA highly diastereo‐/enantioselective construction of two vicinal chiral centers via the copper‐catalyzed propargylic alkylation of acyclic ketone enamines with propargylic esters by using a bulky and structurally rigid tridentate ketimine P,N,N‐ligand is developed.

Chiral Lewis Acid Catalyzed Asymmetric Cycloadditions of Disubstituted Ketenes for the Synthesis of β-Lactones and δ-Lactones

Highly diastereo- and enantioselective [2 + 2]- and [4 + 2]-cycloadditions of disubstituted ketenes were realized by chiral Lewis acid catalysis. A series of arylalkylketenes underwent the reaction smoothly with isatins and β,γ-unsaturated α-ketoesters, providing optically active β-lactones and δ-lactones with vicinal chiral centers in excellent yields (up to 99%) and enantioselectivities (up to 99% ee), as well as exclusively high diastereoselectivities under 0.2-2 mol % catalyst loading.

ChemInform Abstract: Synthesis of Unfunctionalized Carbonated Fragments Containing Two Vicinal Chiral Centers: Stereocontrolled Benzylation of Vinylsulfones Mediated by a Remote Sulfinyl Group.

ChemInform Abstract: Synthesis of Unfunctionalized Carbonated Fragments Containing Two Vicinal Chiral Centers: Stereocontrolled Benzylation of Vinylsulfones Mediated by a Remote Sulfinyl Group.

ChemInform Abstract: Most Efficient Routes for the Synthesis of α,β‐Diamino Acid Derived Compounds

AbstractReview: 55 refs.

Synthesis of Unfunctionalized Carbonated Fragments Containing Two Vicinal Chiral Centers: Stereocontrolled Benzylation of Vinylsulfones Mediated by a Remote Sulfinyl Group

Synthesis of Unfunctionalized Carbonated Fragments Containing Two Vicinal Chiral Centers: Stereocontrolled Benzylation of Vinylsulfones Mediated by a Remote Sulfinyl Group

Most Efficient Routes for the Synthesis of α,β-Diamino Acid-Derived Compounds

Alpha,beta-Diamino acids have attracted considerable attention recently due to their growing importance in pharmaceutical and biochemical research. For example, this special class of alpha,beta-diamino acids has become the components of enzyme inhibitors, and has been incorporated into peptides which are used to modulate secondary and tertiary structural conformations. Although their widely occurrence in nature, optically active diamino acids are hard to isolate and purify from available natural resources on large scale. Therefore, their asymmetric synthesis becomes a great interest for organic and medicinal chemists. However, there still exist great challenges for enantioselective synthesis of diamino acids, especially those with two vicinal chiral centers. This review highlights the recent promising methodologies for enantioselective synthesis of alpha,beta-diamino acids, with special emphasis on catalytic asymmetric reactions, as well as methods for natural chiral compound derivatization, and chiral auxiliaries.

Asymmetric Direct Vinylogous Michael Reaction of Activated Alkenes to Nitroolefins Catalyzed by Modified Cinchona Alkaloids

[reaction: see text] The first organocatalytic and asymmetric direct vinylogous Michael reaction that employs the electron-deficient vinyl malononitriles as the nucleophilic species has been reported. The novel transformations exhibit exclusive gamma-selectivity and high diastereo- and enantioselectivity in the addition to nitroolefins, which give the multifunctional products with two vicinal chiral centers.

Versatile route to 2,6-dideoxyamino sugars from non-sugar materials: Syntheses of vicenisamine and kedarosamine

A new strategy for the synthesis of 2,6-dideoxyamino sugars from non-sugar starting materials has been developed. The key reaction in this strategy is the acid-catalyzed intramolecular cyclization, by which a nitrogen functional group is introduced with simultaneous control of vicinal chiral centers. The synthesis of two kinds of 2,6-dideoxyamino sugars, D-vicenisamine and L-kedarosamine, by this strategy is described.

Asymmetric [2,3]-Wittig rearrangement as a general tool for asymmetric synthesis

Abstract