Chiral Arylaminophosphonium Barfates as a New Class of Charged Brønsted Acid for the Enantioselective Activation of Nonionic Lewis Bases

A Selenourea-Thiourea Brønsted Acid Catalyst Facilitates Asymmetric Conjugate Additions of Amines to α,β-Unsaturated Esters

β-Amino esters are obtained with high levels of enantioselectivity via the conjugate addition of cyclic amines to unactivated α,β-unsaturated esters. A related strategy enables the kinetic resolution of racemic cyclic 2-arylamines, using benzyl acrylate as the resolving agent. Reactions are facilitated by an unprecedented selenourea-thiourea organocatalyst. As elucidated by DFT calculations and 13C kinetic isotope effect studies, the rate-limiting and enantiodetermining step of the reaction is the protonation of a zwitterionic intermediate by the catalyst. This represents a rare case in which a thiourea compound functions as an asymmetric Brønsted acid catalyst.

Atroposelective Synthesis of Biaryl Diamines and Amino Alcohols via Chiral Phosphoric Acid Catalyzed para-Aminations of Anilines and Phenols

A versatile method for atroposelective synthesis of chiral biaryl diamines and amino alcohols has been developed via para-amination of anilines and phenols with azodicarboxylates enabled by chiral phosphoric acid catalysis. Meanwhile, highly efficient kinetic resolution of the racemic biaryl anilines has also been realized through these reactions, giving selectivity factor up to 246. The gram-scale reaction and facile derivatizations of the chiral products well demonstrate the potential of these reactions in the development of novel chiral ligands and catalysts.

•

Versatile methods for asymmetric synthesis of biaryl diamines and amino alcohols

•

Atroposelective para-aminations of biaryl anilines and phenols

•

Kinetic resolution of racemic biaryl anilines

•

Facile transformations of chiral products

Highly Enantioselective Synthesis of Fused Tri- and Tetrasubstituted Aziridines: aza-Darzens Reaction of Cyclic Imines with α-Halogenated Ketones Catalyzed by Bifunctional Phosphonium Salt

The first enantioselective aza-Darzens reaction of cyclic imines with α-halogenated ketones was realized under mild reaction conditions by using amino-acid-derived bifunctional phosphonium salts as phase-transfer promoters. A variety of structurally dense tri- and tetrasubstituted aziridine derivatives, containing benzofused heterocycles as well as spiro-structures, were readily synthesized in high yields with excellent diastereo- and enantioselectivities (up to >20:1 d.r. and >99.9 % ee). The highly functionalized aziridine products could be easily transformed into different classes of biologically active compounds.

Mechanistic Studies on the Michael Addition of Amines and Hydrazines To Nitrostyrenes: Nitroalkane Elimination via a Retro-aza-Henry-Type Process

In this article we report on the mechanistic studies of the Michael addition of amines and hydrazines to nitrostyrenes. Under the present conditions, the corresponding N-alkyl/aryl substituted benzyl imines and N-methyl/phenyl substituted benzyl hydrazones were observed via a retro-aza-Henry-type process. By combining organic synthesis and characterization experiments with computational chemistry calculations, we reveal that this reaction proceeds via a protic solvent-mediated mechanism. Experiments in deuterated methanol CD₃OD reveal the synthesis and isolation of the corresponding deuterated intermediated Michael adduct, results that support the proposed slovent-mediated pathway. From the synthetic point of view, the reaction occurs under mild, noncatalytic conditions and can be used as a useful platform to yield the biologically important N-methyl pyrazoles in a one-pot manner, simple starting with the corresponding nitrostyrenes and the methylhydrazine.

Calcium(ii)-catalyzed enantioselective conjugate additions of amines

The direct enantioselective chiral calcium(ii)·phosphate complex (Ca[CPA]₂)-catalyzed conjugate addition of unprotected alkyl amines to maleimides was developed.

The direct enantioselective chiral calcium(ii)·phosphate complex (Ca[CPA]₂)-catalyzed conjugate addition of unprotected alkyl amines to maleimides was developed. This mild catalytic system represents a significant advance towards the general convergent asymmetric amination of α,β-unsaturated electrophiles, providing medicinally relevant chiral aminosuccinimide products in high yields and enantioselectivities. Furthermore, the catalyst can be reused directly from a previously chromatographed reaction and still maintain both high yield and selectivity.

Heterocycle-based bifunctional organocatalysts in asymmetric synthesis

Different chiral bifunctional organocatalysts derived from trans-cyclohexane-1,2-diamine bearing different types of guanidine units able to form-hydrogen bonding activation have been designed. Conformational rigid 2-aminobenzimidazoles bearing a tertiary amino group have been used in enantioselective Michael type reactions of activated methylene compounds to nitroalkenes. The C2 symmetric bis(2-aminobenzimidazole) derivatives the appropriate organocatalyst for the conjugate addition of 1,3-dicarbonyl compounds to maleimides as well as for the SN1 reaction of benzylic alcohols with carbon nucleophiles. 2-Aminobenzimidazoles bearing a primary amino group have shown excellent catalytic activity in the Michael reaction of aldehydes to maleimides and nitroalkenes. Diastereomeric 2-aminopyrimidines bearing a prolinamide unit have been incorporated in the trans-cyclohexane-1,2-diamine scaffold and have been used for the inter- and intra-molecular direct aldol reaction under solvent-free conditions. For the Michael reaction of aldehydes with maleimides the primary amine 2-aminopyrimidine has shown excellent efficiency as organocatalyst. The bifunctional character of these organocatalysts has been demonstrated by means of DFT calculations.

Chiral Phosphoric Acid Catalyzed Asymmetric Synthesis of 2-Substituted 2,3-Dihydro-4-quinolones by a Protecting-Group-Free Approach

Chiral 2-substituted 2,3-dihydro-4-quinolones were synthesized based on the chiral phosphoric acid catalyzed intramolecular aza-Michael addition reaction using N-unprotected 2-aminophenyl vinyl ketones as substrates in good yields with high enantioselectivities.

Catalytic asymmetric synthesis of 4-nitropyrazolidines: an access to optically active 1,2,3-triamines

The first catalytic enantio- and diastereoselective synthesis of 4-nitropyrazolidines is presented. Asymmetric hydrogen-bonding activation of nitro-olefins facilitated the 1,3-dipolar cycloaddition with hydrazones, affording optically active 4-nitropyrazolidines containing three continuous stereogenic centers as a single diastereomer in up to 99% ee. Furthermore, it is demonstrated that the optically active 4-nitropyrazolidines can be applied as precursors for the synthesis of highly interesting 1,2,3-triamines.