Stereoselective Substitution of Configurationally Labile α-Bromo Aryl­acetates with Amines and Az­lactones byL-Threonine-Mediated Crystallization-Induced Dynamic Resolution

Configurationally labile α-bromoacid derivatives for asymmetric preparation of heterocycles

α-Bromoacid derivatives are configurationally labile under various conditions, and the dynamic resolution of them has been recognized as an effective strategy in asymmetric synthesis. This article is a concise review of our efforts on the heteroannulation of α-bromoacid derivatives through nucleophilic substitution and subsequent ring formation with diverse carbon, nitrogen, oxygen, and sulfur nucleophiles. Chiral auxiliary (Xc)-bound α-bromoacid derivatives serve as versatile chiral building blocks for the direct incorporation of a two-carbon unit in cyclization reactions. Eight readily available chiral auxiliaries are investigated and identified to be suitable for the dynamic resolution of α-bromoacid derivatives. We have presented selected results about three distinct dynamic resolutions such as dynamic kinetic resolution (DKR), dynamic thermodynamic resolution (DTR) and crystallization induced dynamic resolution (CIDR) that have been successfully employed in the asymmetric synthesis of fourteen different scaffolds of six- or five-membered heterocycles.

An access to highly enantioenriched cis-3,5-disubstituted γ-lactones from α-bromoacetate and silyl enol ether

A novel synthetic strategy for highly enantioenriched cis-3,5-disubstituted γ-lactones has been developed by the AgOTf-promoted nucleophilic substitution of α-bromoacetates with silyl enol ethers and subsequent reductive lactonization. The utility of this synthetic method was further demonstrated through the concise stereodivergent synthesis of cis- and trans-2,4-disubstituted tetrahydrofurans.

Synthesis of chiral piperazin-2-ones through palladium-catalyzed asymmetric hydrogenation of pyrazin-2-ols

A palladium-catalyzed asymmetric hydrogenation of pyrazines containing a tautomeric hydroxyl group was developed, providing a facile access to chiral disubstituted piperazin-2-ones with excellent diastereoselectivities and enantioselectivities.

Friedel-Crafts alkylation with α-bromoarylacetates for the preparation of enantioenriched 2,2-diarylethanols

Highly enantioenriched 2,2-diarylethanols can be efficiently synthesized through the Friedel-Crafts alkylation of (hetero)arenes with configurationally labile α-bromoarylacetates. The substitution of highly diastereoenriched α-bromoarylacetates occurs in the presence of AgOTf, and the subsequent reduction affords diverse 2,2-diarylethanols with high yields and enantioselectivities up to 99 : 1 er. In addition, the application of this asymmetric synthetic methodology to the preparation of highly enantioenriched dihydrobenzofuran and indoline derivatives is demonstrated.

Enantioselective synthesis of trifluoromethylated dihydroquinoxalinones via palladium-catalyzed hydrogenation

A highly enantioselective palladium-catalyzed asymmetric hydrogenation of 3-(trifluoromethyl)quinoxalinones has been successfully developed, providing a general and facile access to chiral 3-(trifluoromethyl)-3,4-dihydroquinoxalinones with up to 99% ee.

A Brønsted base-promoted diastereoselective dimerization of azlactones

A novel Brønsted base system for the diastereoselective dimerization of azlactones using trichloroacetate salts and acetonitrile has been developed. Desired products were obtained in good yields (60-93%) and with up to >19:1 dr after one hour of reaction. Additionally, the relative stereochemistry of the major dimer was assigned as being trans, by X-ray crystallographic analysis. The kinetic reaction profile was determined by using ¹H NMR reaction monitoring and revealed a second order overall kinetic profile. Furthermore, by employing this methodology, a diastereoselective total synthesis of a functionalized analogue of streptopyrrolidine was accomplished in 65% overall yield.

Enantioselective Organocatalytic Synthesis of 2-Oxopiperazines from Aldehydes: Identification of the Elusive Epoxy Lactone Intermediate

An organocatalytic linchpin catalysis approach was envisaged to convert simple aldehydes into enantioenriched 2-oxopiperazines. A four-step reaction sequence (chlorination, oxidation, substitution, and cyclization) was developed and led to different substitution patterns in high yields and selectivities. The reaction mechanism was studied, and the previously elusive epoxy lactone intermediate was identified by HRMS.