Organocatalytic dynamic kinetic resolution of N-arylindole lactams: atroposelective construction of axially chiral amino acids bearing a C-N chiral axis

Nickel-Catalyzed Chemoselective Carbomagnesiation for Atroposelective Ring-Opening Difunctionalization

There is a pressing need for methods that can connect enantioenriched organic compounds with readily accessible building blocks via asymmetric functionalization of unreactive chemical bonds in organic synthesis and medicinal chemistry. Herein, the asymmetric chemoselective cleavage of two unactivated C(Ar)-O bonds in the same molecule is disclosed for the first time through an unusual nickel-catalyzed carbomagnesiation. This reaction facilitates the evolution of a novel atroposelective ring-opening difunctionalization. Utilizing readily available dibenzo bicyclic substrates, diverse valuable axially chiral biaryls are furnished with high efficiencies. Synthetic elaborations showcase the application potential of this method. The features of this method include good atom-economy, multiple roles of the nucleophile, and a simple catalytic system that enables the precise magnesiation of an α-C(Ar)-O bond and arylation of a β-C(Ar)-O bond.

Catalytic Asymmetric Synthesis of Unnatural Axially Chiral Biaryl δ-Amino Acid Derivatives via a Chiral Phenanthroline-Potassium Catalyst-Enabled Dynamic Kinetic Resolution

Axially chiral biaryl δ-amino acids possess significantly different conformational properties and chiral environment from centrally chiral amino acids, therefore, have drawn considerable attention in the fields of synthetic and medicinal chemistry. Herein, a novel chiral phenanthroline-potassium catalyst has been developed by constructing a well-organized axially chiral ligand composed of one 1,10-phenanthroline unit and two axially chiral 1,1'-bi-2-naphthol (BINOL) units. In the presence of this catalyst, good to excellent yields and enantioselectivities (up to 99 % yield, 98 : 2 er) have been achieved in the ring-opening alcoholytic dynamic kinetic resolution of a variety of biaryl lactams, thereby providing an efficient protocol for catalytic asymmetric synthesis of unnatural axially chiral biaryl δ-amino acid derivatives.

Chiral Phosphoric Acid Catalyzed Asymmetric Hydrolysis of Biaryl Oxazepines for the Synthesis of Axially Chiral Biaryl Amino Phenol Derivatives

The development of catalytic asymmetric reaction with water as the reactant is challenging due to the reactivity- and stereoselectivity-control issues resulted from the low nucleophilicity and the small size of water. We disclose herein a chiral phosphoric acid (CPA) catalyzed atroposelective ring-opening reaction of biaryl oxazepines with water. A series of biaryl oxazepines undergo the CPA catalyzed asymmetric hydrolysis in a highly enantioselective manner. The key for the success of this reaction is the use of a new SPINOL-derived CPA catalyst and the high reactivity of biaryl oxazepine substrates towards water under acidic conditions. Density functional theory calculations suggest that the reaction proceeds via a dynamic kinetic resolution pathway and the CPA catalyzed addition of water to the imine group is both enantio- and rate-determining.

Stereodynamic Strategies to Induce and Enrich Chirality of Atropisomers at a Late Stage

Enantiomers, where chirality arises from restricted rotation around a single bond, are atropisomers. Due to the unique nature of the origins of their chirality, synthetic strategies to access these compounds in an enantioselective manner differ from those used to prepare enantioenriched compounds containing point chirality arising from an unsymmetrically substituted carbon center. In particular stereodynamic transformations, such as dynamic kinetic resolutions, thermodynamic dynamic resolutions, and deracemizations, which rely on the ability to racemize or interconvert enantiomers, are a promising set of transformations to prepare optically pure compounds in the late stage of a synthetic sequence. Translation of these synthetic approaches from compounds with point chirality to atropisomers requires an expanded toolbox for epimerization/racemization and provides an opportunity to develop a new conceptual framework for the enantioselective synthesis of these compounds.

Asymmetric synthesis of chiral pyrazolo[3,4-b]pyridin-6-ones under carbene catalysis

A structurally diverse set of chiral pyrazolo[3,4-b]pyridin-6-ones was efficiently prepared in excellent yields with excellent enantioselectivities via N-heterocyclic carbene-catalyzed oxidative [3 + 3] annulation of enals with pyrazol-5-amines. The reaction features mild reaction conditions, a broad substrate scope, and easy scale-up.

Atroposelective Amination of Indoles via Chiral Center Induced Chiral Axis Formation

The construction of an N-C chiral axis for N-aryl indole derivatives is meaningful as they widely exist in functionalized molecules. This work provides a novel method for this purpose via amination of amino acid derivatives at the C2 position of the indole and chiral center induced chiral axis formation. The protocol of this transformation is easily accessible, not requiring metal or an organic chiral catalyst, endowing this method with great potential in the construction of axis chiral N-aryl indoles.

Catalytically atroposelective ring-opening of configurationally labile compounds to access axially chiral biaryls

In this minireview, we evaluate and summarize the construction of axially chiral biaryls, and briefly state our personal perspectives on the future advancement of this direction.