Unravelling a New Class of Chiral Organocatalyst for Asymmetric Ring-Opening Reaction of Meso Epoxides with Anilines

Synthesis of Functionalized Five-Membered Heterocycles from Epoxides: A Hydrogen-Bond Donor Catalytic Approach

The synthesis of highly functionalized five-membered oxa- and aza-heterocycles has been reported utilizing hydrogen-bond donor (HBD) catalysis. In this method, an epoxide was taken as a substrate and reacted with functionalized arylidene/alkylidene malononitrile derivatives in the presence of a newly designed HBD catalyst. In all the cases, the products 2,5-disubstituted tetrahydrofurans (2,5-THFs) were obtained in good to excellent yields (up to 86%) with high diastereoselectivity (dr up to 99:1) as a single regioisomer. The stereochemistry at the 2- and 5-positions of the five-membered ring has been confirmed by single-crystal X-ray analysis, and cis is found to be the major product. The same strategy has been further utilized to obtain substituted oxazolidines whenever the epoxide has been reacted with isocyanate as an electrophile. In order to induce enantioselectivity, a chiral epoxide has been reacted with both the electrophiles in the presence of the same catalyst system to afford the single stereoisomer of the final products. This synthetic methodology involves a low catalyst loading and ambient reaction condition and has been generalized with various substituents present in the starting electrophiles to produce the resultant products in acceptable yields and stereoselectivity.

Catalytic Efficiency of Primary α-Amino Amides as Multifunctional Organocatalysts in Recent Asymmetric Organic Transformations

Chiral primary α-amino amides, consisting of an adjacent enamine bonding site (Bronsted base site), a hydrogen bonding site (Bronsted acid site), and flexible bulky substituent groups to modify the steric factor, are proving to be extremely valuable bifunctional organocatalysts for a wide range of asymmetric organic transformations. Primary α-amino amides are less expensive alternatives to other primary amino organocatalysts, such as chiral diamines and cinchona-alkaloid-derived primary amines, as they are easy to synthesize, air-stable, and allow for the incorporation of a variety of functional groups. In recent years, we have demonstrated the catalytic use of simple primary α-amino amides and their derivatives as organocatalysts for the aldol reaction, Strecker reaction, Michael tandem reaction, allylation of aldehydes, reduction of N-Aryl mines, opening of epoxides, hydrosilylation, asymmetric hydrogen transfer, and N-specific nitrosobenzene reaction with aldehydes.

Asymmetric ring opening of racemic epoxides for enantioselective synthesis of (S)-β-amino alcohols by a cofactor self-sufficient cascade biocatalysis system

Asymmetric ring opening of racemic epoxides to enantiopure β-amino alcohols via a cascade biocatalysis system.

γ-, Diastereo-, and Enantioselective Addition of MEMO-Substituted Allylboron Compounds to Aldimines Catalyzed by Organoboron-Ammonium Complexes

The first catalytic, broadly applicable, efficient, γ-, diastereo-, and enantioselective method for addition of O-substituted allyl-B(pin) compounds to phosphinoylimines (MEM=methoxyethoxymethyl, pin=pinacolato) is presented. The identity of the most effective catalyst and the optimal protecting group for the organoboron reagent were determined by consideration of the steric and electronic requirements at different stages of the catalytic cycle, namely, the generation of the chiral allylboronate, the subsequent 1,3-borotropic shift, and the addition step. Aryl-, heteroaryl-, alkenyl- and alkyl-substituted vicinal phosphinoylamido MEM-ethers were thus accessed in 57-92 % yield, 89:11 to >98:2 γ:α selectivity, 76:24-97:3 diastereomeric ratio, and 90:10-99:1 enantiomeric ratio. The method is scalable, and the phosphinoyl and MEM groups may be removed selectively or simultaneously. Utility is highlighted by enantioselective synthesis of an NK-1 receptor antagonist.

Chiral Pentacarboxycyclopentadiene-Based Brønsted Acid-Catalyzed Enantioselective Desymmetrization of Meso-Epoxides by 2-Mercaptobenzothiazoles

Enantioselective desymmetrization of meso-epoxides by 2-mercaptobenzothiazoles was realized by using the pentacarboxycyclopentadiene-based chiral Brønsted acid in combination of N-isopropylaniline as amine additive to give up to 90.5:9.5 er of the ring opening products.

Nucleophilic ring opening of trans-2,3-disubstituted epoxides to β-amino alcohols with catalyst-controlled regioselectivity

We report the nucleophilic ring opening of unsymmetrical trans-epoxides to β-amino alcohols with catalyst-controlled regioselectivity.

Asymmetric ring-opening reaction of meso-epoxides with aromatic amines using homochiral metal–organic frameworks as recyclable heterogeneous catalysts

Asymmetric ring-opening reactions of meso-epoxides by aromatic amines were achieved by using some chiral metal–organic frameworks. The corresponding β-amino alcohols were obtained with good yields and enantioselectivities (up to 97% ee).

The mechanism of an asymmetric ring-opening reaction of epoxide with amine catalyzed by a metal–organic framework: insights from combined quantum mechanics and molecular mechanics calculations

QM/MM computations suggest that the asymmetric ring-opening reaction of epoxide with amine is controlled by CH–π interactions between aniline and a naphthol moiety.

Efficient Routes to a Diverse Array of Amino Alcohol-Derived Chiral Fragments

Efficient syntheses of chiral fragments derived from chiral amino alcohols are described. Several unique scaffolds were readily accessed in 1-5 synthetic steps leading to 45 chiral fragments, including oxazolidinones, morpholinones, lactams, and sultams. These fragments have molecular weights ranging from 100 to 255 Da and are soluble in water (0.085 to >15 mM).

Cascade reaction for the construction of CF3 containing tetrasubstituted furan ring

Activated olefins are well known nucleophiles, but proton abstraction from the substituted α-methyl group in nitroolefin is rare.

Enantioselective syntheses of β-amino alcohols catalyzed by recyclable chiral Fe(iii) metal complex

An efficient asymmetric desymmetrization of meso-epoxides with anilines catalyzed by a series of simple and environmentally benign in situ generated Fe(iii) complexes based on chiral tridentate ligands L1–L7 was carried out at rt.

Chirality sensing and size recognition of N-Boc-amino acids by cage-type dimeric lanthanide complexes: chirality detection of N-Boc-aspartate anions via luminescence colour change

A mixture of chiral luminescent macrotricyclic-cyclen-Tb–Eu complexes enabled naked-eye discrimination of N-Boc-d- and l-aspartates via luminescence colour change.

Kinetic resolution of 2,3-epoxy 3-aryl ketones via catalytic asymmetric ring-opening with pyrazole derivatives

A highly efficient catalytic kinetic resolution of 2,3-epoxy 3-aryl ketones via asymmetric ring-opening with pyrazole derivatives has been achieved by using a chiral N,N′-dioxide–Sc(iii) complex as the catalyst.

Catalytic enantioselective synthesis of α-nitroepoxides via aminolytic kinetic resolution

The first enantioselective synthesis of β-aryl-substituted α-nitroepoxides, exploiting an organocatalyzed aminolytic kinetic resolution (AKR), has been developed.