Design, Preparation, and Implementation of Axially Chiral Benzotetramisoles as Lewis Base Catalysts for Asymmetric Cycloadditions

Developing novel catalysts with potent activity is of great importance in organocatalysis. In this study, we designed and prepared a new class of benzotetramisole Lewis base catalysts (AxBTM) that have both central and axial chirality. This unique feature of these catalysts results in a three-dimensional microenvironment with multi-layers of chirality. The performance of the developed catalysts was tested in a series of cycloaddition reactions. These included the AxBTM-catalyzed (2+2) cycloaddition between α-fluoro-α-aryl anhydride with imines or oxindoles, and the sequential gold/AxBTM-catalyzed (4+2) cycloaddition of enynamides with pentafluorophenyl esters. The interplay between axial and central chirality had a collaborative effect in regulating the stereochemistry in these cycloadditions, leading to high levels of stereoselectivity that would otherwise be challenging to achieve using conventional BTM catalysts. However, the (2+2) and (4+2) cycloadditions have different predilections for axial and central chirality combinations.

Photoredox-catalyzed 1,2-oxo-alkylation of vinyl arenes with 1,3-diketones: an approach to 1,4-dicarbonyls via C-C activation

A mild and inexpensive approach to synthesising a series of 1,4-diketones in moderate to excellent yields via 1,2-oxo alkylation has been developed using fluorescein as a photocatalyst and air as an oxidant. The key features include (i) varied substrate scope (39 examples); (ii) good functional group tolerance; (iii) unsymmetrical 1,4-dicarbonyls; (iv) late-stage functionalization of thymol and ibuprofen derivatives; and (v) the synthetic expansion to 5- and 6-membered N-, O- and S-containing heterocycles.

Expanding the Promiscuity of a Copper-Dependent Oxidase for Enantioselective Cross-Coupling of Indoles

Herein, we disclose the highly enantioselective oxidative cross-coupling of 3-hydroxyindole esters with various nucleophilic partners as catalyzed by copper efflux oxidase. The biocatalytic transformation delivers functionalized 2,2-disubstituted indolin-3-ones with excellent optical purity (90-99 % ee), which exhibited anticancer activity against MCF-7 cell lines, as shown by preliminary biological evaluation. Mechanistic studies and molecular docking results suggest the formation of a phenoxyl radical and enantiocontrol facilitated by a suited enzyme chiral pocket. This study is significant with regard to expanding the catalytic repertoire of natural multicopper oxidases as well as enlarging the synthetic toolbox for sustainable asymmetric oxidative coupling.