Oxalates as Activating Groups for Tertiary Alcohols in Photoredox-Catalyzed gem-Difluoroallylation To Construct All-Carbon Quaternary Centers

Photocatalyzed 1,3-Bromodifluoroallylation of [1.1.1]Propellane with α-Trifluoromethylalkenes and KBr Salts

Herein we unveil a visible-light-driven transition-metal-free 1,3-bromodifluoroallylation of [1.1.1]propellane. This reactivity is harnessed through organophotocatalysis, providing practical synthetic pathways to 1-brominated-3-gem-difluoroallylic bicyclo[1.1.1]pentane derivatives, particularly derived from readily available α-trifluoromethylalkenes and inexpensive KBr salts utilized as precursors for bromine radicals. Mechanistic investigations reveal that bromide anions quench the excited state of the photocatalyst, leading to the formation of bromine radicals, which react in a strain-release radical addition process rather than hydrogen atom abstraction with [1.1.1]propellane.

Asymmetric synthesis of unnatural α-amino acids through photoredox-mediated C-O bond activation of aliphatic alcohols

Unnatural α-amino acids constitute a fundamental class of biologically relevant compounds. However, despite the interest in these motifs, synthetic strategies have traditionally employed polar retrosynthetic disconnections. These methods typically entail the use of stoichiometric amounts of toxic and highly sensitive reagents, thereby limiting the substrate scope and practicality for scale up. In this work, an efficient protocol for the asymmetric synthesis of unnatural α-amino acids is realized through photoredox-mediated C-O bond activation in oxalate esters of aliphatic alcohols as radical precursors. The developed system uses a chiral glyoxylate-derived N-sulfinyl imine as the radical acceptor and allows facile access to a range of functionalized unnatural α-amino acids through an atom-economical redox-neutral process with CO2 as the only stoichiometric byproduct.

Lewis Acid Promoted Vicinal Oxytrifluoromethylselenolation of Alkenes

Herein, we have developed a metal-free, Lewis acid promoted vicinal oxytrifluoromethylselenolation of alkenes using trifluoromethyl selenoxides as electrophilic trifluoromethylselenolation reagents and alcohols as nucleophiles. With less steric and good nucleophilic solvents (such as ethanol and methol), Tf₂O-catalyzed oxytrifluoromethylselenolation could be realized, while stoichiometric Tf₂O was required to promote full transformation with less nucleophilic and steric solvents (such as isopropanol and tert-butanol). The reaction featured good substrate scope, functional group compatibility, and diastereoselectivity. This method could be further applied to oxytrifluoromethylselenolation, aminotrifluoromethylselenolation with stoichiometric nucleophiles under modified conditions. A mechanism involving a seleniranium ion was proposed based on the preliminary results.

Visible-Light-Induced Monofluoroalkenylation and gem-Difluoroallylation of Inactivated C(sp3)-H Bonds via 1,5-Hydrogen Atom Transfer (HAT)

The direct monofluoroalkenylation of C(sp³)-H bonds is of great importance and quite challenging. Current methods have been restricted to the monofluoroalkenylation of activated C(sp³)-H bonds. Here, we reported the photocatalyzed C(sp³)-H monofluoroalkenylation of inactivated C(sp³)-H bonds with gem-difluoroalkenes via 1,5-hydrogen atom transfer. This process shows good functional group tolerance, such as halides (F, Cl), nitrile, sulfone, ester, and pyridine, and good γ-selectivity. Moreover, this method succeeds in the photocatalyzed gem-difluoroallylation of inactivated C(sp³)-H with α-trifluoromethyl alkenes.

Nickel-Catalyzed Unsymmetrical Bis-Allylation of Alkynes

The catalytic bis-allylation of alkynes is an important but challenging protocol to construct all-carbon tetra-substituted alkenes. Particularly, the catalytic unsymmetrical bis-allylation of alkynes remains as an underexplored task to date. We herein report an unprecedented unsymmetrical bis-allylation by simultaneously utilizing electrophilic trifluoromethyl alkene and nucleophilic allylboronate as the allylic reagents. With the aid of robust Ni⁰ /NHC catalysis, valuable skipped trienes can be obtained in high regio- and stereo-selectivities under mild conditions. Mechanistic studies indicate that the reaction may proceed through a β-fluorine elimination of a nickelacycle followed by a transmetalation step with allylboronate. The present method exhibits a good tolerance of various functional groups. Besides, the skipped triene products can undergo an array of elaborate transformations, which highlights the potential applications of this strategy.

Deaminative defluoroalkylation of α-trifluoromethylalkenes enabled by photoredox catalysis

Herein, we disclose a new photoredox-catalysed strategy to access gem-difluoroallylarenes from α-trifluoromethylalkenes with sterically hindered primary amines via C-N and C-F bond activation. This deaminative and defluorinative allylation is generally compatible with diverse functional groups and sterically hindered α-3° and 2° primary amines.

Alkyl Radical Generation via C–C Bond Cleavage in 2-Substituted Oxazolidines

There is an urgent need to develop uncharged radical precursors to be activated under mild photocatalyzed conditions. 2-Substituted-1,3-oxazolidines (E_ox < 1.3 V vs SCE, smoothly prepared from the corresponding aldehydes) have been herein employed for the successful release of tertiary, α-oxy, and α-amido radicals under photo-organo redox catalysis. The reaction relies on the unprecedented C–C cleavage occurring from the radical cation of these heterocyclic derivatives. Such a protocol is applied to the visible-light-driven conjugate radical addition onto Michael acceptors and vinyl (hetero)arenes under mild metal-free conditions.