Chiral Calcium Phosphate Catalyzed Enantioselective Amination of 3-Aryl-2-benzofuranones

Development and mechanistic studies of calcium-BINOL phosphate-catalyzed hydrocyanation of hydrazones

Asymmetric hydrocyanation of hydrazones, catalyzed by a calcium-BINOL phosphate complex, has been studied for the first time both experimentally and computationally with DFT methods. A full catalytic cycle for the enantioselective synthesis of α-hydrazinonitriles is proposed based on insights gained from DFT calculations. Trimethylsilyl cyanide (TMSCN) has been used as a sacrificial cyanide source. We found that isocyanide (rather than cyanide) is a preferred coordination to calcium during the catalytic cycle, while the active catalyst prefers a side-on coordination of cyanide. The configuration-determining step is a hydrocyanation via a calcium isocyanide complex, whereas the rate-limiting step is that which recovers the calcium catalyst and replaces the TMS-bound product from the catalyst. While our experimental data demonstrate enantioselectivity values as high as 89% under certain conditions, the overall enantioselectivity achieved with the calcium catalyst remains modest, mainly due to competing pathways for the Z- and E-hydrazone isomers leading to opposite enantiomers. The experimental results confirm these computational proposals.

Enantioselective Amination of 3-Substituted-2-benzofuranones via Non-covalent N-Heterocyclic Carbene Catalysis

Herein, an efficient method for asymmetric α-amination of 2-benzofuranones with N-heterocyclic carbene (NHC) catalysis is reported. The process is based on non-covalent interaction of NHC with substrate, facilitating the formation of a chiral ion-pair that encompasses enolate and azolium salt. The activated enolate adds to an electrophilic amine source with sufficient facial control to furnish an enantioenriched product having an amine substituted quaternary stereocenter. The process displays a broad substrate scope. A preparative scale synthesis has been achieved. Preliminary mechanistic investigations based on experimental and DFT studies suggest a reaction pathway that involves non-covalent substrate/NHC interactions and essentially implicate the role of π-π interaction in diastereomeric transition states for stereo-chemical discrimination.

Recent Advancement in H8-BINOL Catalyzed Asymmetric Methodologies

H₈-BINOL, a partially reduced form of BINOL, is widely employed in a broad array of organocatalyzed asymmetric methodologies. Over the last 25 years, asymmetric organocatalysis has witnessed an incredible improvement, and an advancement still continues to get a single enantio-enriched product. The broad-spectrum applications of H₈-BINOL organocatalyst in C-C bond formation, C-heteroatom bond construction, name reactions, pericyclic reactions, and one pot and multicomponent reaction are attracting the attention of researchers. A diversified unique H₈-BINOL-based catalyst has been synthesized and screened for catalytic activity. In this Review we frame out the H₈-BINOL catalyzed novel discoveries from the last two decades.

Chiral π-Cu(II) Catalysts for the Enantioselective α-Amination of N-Acyl-3,5-dimethylpyrazoles

We report the highly enantioselective α-amination of N-acyl-3,5-dimethylpyrazoles with dialkyl azodicarboxylates, catalyzed by in situ generated π-Cu(II) complexes that consist of Cu(OTf)₂ and N-(5H-dibenzo[a,d][7]annulen-5-yl)-l-alanine-derived amides, to give the corresponding products as d-α-amino acid derivatives (up to >99% yield and 99% ee). The site-selectivity and enantioselectivity can be satisfactorily explained by the coordination of dialkyl azodicarboxylate with π-Cu(II) complex. The synthetic potential of this one-pot transformation to the α-amino ester is also described.

Chiral Calcium Phosphate-Catalyzed Enantioselective Amination of 3-Aryl-2-oxindoles with Dibenzyl Azodicarboxylate

A chiral calcium phosphate-catalyzed enantioselective amination of 2-oxindoles with dibenzyl azodicarboxylate has been developed, affording the products in consistently high yields and excellent enantioselectivity. This synthetic method features low catalyst loading and a high catalytic efficiency. Moreover, the practical value of this process is well demonstrated by a scale-up experiment and a trial of catalyst recovery and reuse.

Enantioselective Peroxidation of C-Alkynyl Imines Enabled by Chiral BINOL Calcium Phosphate

Herein, we reported a catalytic enantioselective addition of C-alkynyl imines with hydroperoxides catalyzd by chiral BINOL calcium phosphate, affording a broad range of enantioenriched α-peroxy propargylamines in good yields (80-99%)...