Stereoselective Radical Cyclopropanation by Co(II)-Based Metalloradical Catalysis

Abstract

Chapter 1. Stereoselective Cyclopropanation of Alkenes with Alkynyl- and Vinyl-Substituted Diazo Compounds Alkynyl- and vinyl-substituted cyclopropanes are ubiquitous structural motifs in drug molecules and bioactive compounds. In addition, alkynyl- and vinyl-substituted cyclopropanes may serve as useful intermediates for stereoselective organic synthesis. Metal-catalyzed cyclopropanation of alkenes with alkynyl- and vinyl-substituted diazo compounds offers a potentially general approach for stereoselective construction of these valuable three-membered ring structures. This chapter summarizes the development of stereoselective olefin cyclopropanation with alkynyl- and vinyl-substituted diazo compounds. Chapter 2. Metalloradical Activation of In Situ-Generated α-Alkynyldiazomethanes for Asymmetric Radical Cyclopropanation of Alkenes We have developed a Co(II)-based metalloradical system that is highly effective for asymmetric radical cyclopropanation of alkenes with in situ-generated α-alkynyldiazomethanes. Through fine-tuning the cavity-like environments of D₂-symmetric chiral amidoporphyrins as the supporting ligand, the optimized Co(II)-based metalloradical system is broadly applicable to different alkynyldiazomethanes for asymmetric cyclopropanation of a broad range of alkenes, providing general access to valuable chiral alkynyl cyclopropanes in high yields with excellent diastereoselectivities and enantioselectivities. Chapter 3. Asymmetric Radical Process for Cyclopropanation of Alkenes with In Situ-Generated α-Vinyldiazomethanes We have demonstrated the feasibility of using vinyl aldehyde-derived sulfonylhydrazones as new metalloradicophiles for the generation of allylic radicals. Through fine-tuning the cavity-like environments of D₂-symmetric chiral amidoporphyrins as supporting ligands, the key α-Co(III)-allylic radical intermediates are exclusively engaged in the highly asymmetric cyclopropanation with wide-ranging alkenes in the optimized Co(II)-based metalloradical system, as shown broadly applicable to activate different α-vinyldiazomethanes. Chapter 4. Asymmetric Synthesis of Vinyl-Substituted Cyclopropanes by Radical C-H Alkylation from Alkynes and In Situ-Generated Alkyldiazomethanes via Co(II)-Based Metalloradical Catalysis We have successfully expanded the application of Co(II)-based MRC by applying in-situ generated alkyldiazomethanes as new radical precursors for stereoselective synthesis of vinyl-substituted cyclopropanes by radical cascade C-H alkylation of alkynes. Through fine-tuning of D₂-symmetric chiral amidoporphyrins as the supporting ligands, the Co(II)-catalyzed radical cascade process, which proceeds in a single operation under mild conditions, enables asymmetric construction of vinyl-substituted cyclopropanes in high yields with excellent diastereoselectivities and good enantioselectivities.