Complementary Tandem Reaction Manifolds and "Switch Mechanisms" in the Reaction of Epoxides with Selectfluor.

Tandem reactions are highly sought after transformations in organic synthesis as they accomplish multiple steps at once and can serve as golden keys unlocking mechanistic complexities. Reactions that operate through different mechanisms depending on the conditions ("switch mechanisms") are of intense interest to organic chemists as fonts of new reactivity. We report that Selectfluor can catalyze the rearrangement of 1,1-disubstituted epoxides, providing a new approach to benzylic fluorination.

Photoactivated Pyridine Directed Fluorination through Hydrogen Atom Transfer.

We have established hydrogen atom transfer (HAT) as the key player in a directed, photopromoted fluorination of pyridylic groups. The Lewis basic pyridyl nitrogen directs amine radical dication propagated HAT and Selectfluor fluorination of various ortho substituents in a highly regioselective manner with little to no side product formation. A variety of pyridines and quinolines were employed to showcase the directing capability of the nitrogen atom.

C-C Bond Activation and Demethylenation of Epoxides by Amine Radical Dications.

In this note, we explore a unique reactivity pattern that involves a rare radical-based C-C bond scission of epoxides followed by demethylenation. The reaction is accomplished by Selecfluor and its radical dication working in tandem; a mechanism supported by experiment and DFT calculations is proposed that involves the generation and identification of a key reactive intermediate. The reaction seems to be fairly general for 1,1-disubstituted epoxides.

C-F Bonds as "Frozen" Nucleophiles: Unconsummated S2 Reactions.

In this note, we present a series of rigid molecules that show close enforced interactions between Ar-F moieties and -CHX groups in a "tetrel bond" configuration similar to a nascent S2 attack. We explore the spectroscopic, crystallographic, and chemical reactivity consequences of these unusual interactions, including significant through-space spin-spin couplings, short C-F···CHX distances, and differential S1 and S2 reaction pathways. We also reveal experimental evidence of carbon-based tetrel bonds influencing chemical reactivity in solution.

Solvent Effects on the Intramolecular Charge Transfer Character of ,-Diaryl Dihydrophenazine Catalysts for Organocatalyzed Atom Transfer Radical Polymerization.

The nature of intramolecular charge transfer of ,-diaryl dihydrophenazine photocatalysts (PCs) in different solvents is explored in context of their performance in organocatalyzed atom transfer radical polymerization (O-ATRP). PCs having a computationally predicted lowest energy excited state exhibiting charge transfer (CT) character can operate a highly controlled O-ATRP in a wide range of solvent polarities, from non-polar hexanes to highly polar ,-dimethylacetamide. For PCs having a computationally predicted lowest energy excited state not possessing CT character, their ability to operate a controlled O-ATRP is decreased.