Photocatalytic Reductive Olefin Hydrodifluoroalkylation Enabled by Tertiary Amine Reductants Compatible with Complex Systems

Flavin-Catalyzed, Photochemical Conversion of Dehydroalanine into 4,5-Dihydroxynorvaline

The chemical synthesis of unnatural amino acids (UAA) is a key strategy for preparing designed peptides, including pharmaceutically active compounds. Alterations of existing amino acid residues such as dehydroalanine (Dha) are particularly important since selected positions can be addressed without the necessity of a complete de novo synthesis. The intriguing UAA 4,5-dihydroxynorvaline (Dnv) is found in a variety of naturally occurring peptides and biologically active compounds. However, no method is currently available to modify an existing peptide with this residue. We report the use of flavin catalysts and visible light irradiation for this challenge, which serves as a versatile strategy for converting Dha into Dnv. Our study shows that excited flavins are competent hydrogen atom abstraction catalysts for ethers and acetals, which allows masked 1,2-dihydroxyethylene functionalization from 2,2-dimethyl-1,3-dioxolane. The masked diol was successfully coupled to Dha residues, and a series of Dnv-containing products is reported. A mild and orthogonal protocol for deprotection of the acetal group was also identified, allowing free Dnv-modified peptides to be obtained. This method provides a straightforward strategy for Dnv functionalization, which is envisioned to be crucial for accessing natural products and synthetic analogues with pharmaceutical activity.

A solution to the anti-Bredt olefin synthesis problem

The π-bonds in unsaturated organic molecules are typically associated with having well-defined geometries that are conserved across diverse structural contexts. Nonetheless, these geometries can be distorted, leading to heightened reactivity of the π-bond. Although π-bond-containing compounds with bent geometries are well utilized in synthetic chemistry, the corresponding leveraging of π-bond-containing compounds that display twisting or pyramidalization remains underdeveloped. We report a study of perhaps the most notorious class of geometrically distorted molecules that contain π-bonds: anti-Bredt olefins (ABOs). ABOs have been known since 1924, and conventional wisdom maintains that ABOs are difficult or impossible to access. We provide a solution to this long-standing problem. Our study also highlights the strategic manipulation of compounds that display considerable distortion arising from the presence of geometrically constrained π-bonds.

Simplified Modular Access to Enantiopure 1,2-Aminoalcohols via Ni-Electrocatalytic Decarboxylative Arylation

Chiral aminoalcohols are omnipresent in bioactive compounds. Conventional strategies to access this motif involve multiple-step reactions to install the requisite functionalities stereoselectively using conventional polar bond analysis. This study reveals that a simple chiral oxazolidine-based carboxylic acid can be readily transformed to substituted chiral aminoalcohols with high stereochemical control by Ni-electrocatalytic decarboxylative arylation. This general, robust, and scalable coupling can be used to synthesize a variety of medicinally important compounds, avoiding protecting and functional group manipulations, thereby dramatically simplifying their preparation.

Visible Light Induced C-H/N-H and C-X Bonds Reactions

Herein, we report efficient visible light-induced photoredox reactions of C–H/N–H and C–X Bonds. These methods have provided access to varied portfolio of synthetically important γ-ketoesters, azaspirocyclic cyclohexadienones spirocyclohexadienones, multisubstituted benzimidazole derivatives, substituted N,2-diarylacetamide, 2-arylpyridines and 2-arylquinolines in good yields and under mild conditions. Moreover, we have successfully discussed the construction through visible light-induction by an intermolecular radical addition, dearomative cyclization, aryl migration and desulfonylation. Similarly, we also spotlight the visible light-catalyzed aerobic C–N bond activation from well-known building blocks through cyclization, elimination and aromatization. The potential use of a wide portfolio of simple ketones and available primary amines has made this transformation very attractive.

Radical-Based Route to Functionalized Tetralin: Formal Total Synthesis of (±)-Hamigeran B

A formal synthetic route to hamigeran B, an antiviral marine natural product with a unique tricyclic molecular architecture, has been developed. The key chemical transformations in the present route include a novel zinc(II)porphyrin-catalyzed photoredox radical cascade cyclization to access a functionalized tetralin, a catalyst-free benzylic radical bromination with NBS by visible-light irradiation, and a samarium(II)-induced cyclization of brominated tetralone possibly via an orthoquinodimethane-like intermediate.