Synthesis of aryl allylic fluorides by direct electrophilic fluorination of alkenes

Bioorthogonal labeling and profiling of N6-isopentenyladenosine (i6A) modified RNA

Chemical modifications in RNAs play crucial roles in diversifying their structures and regulating numerous biochemical processes. Since the 1990s, several hydrophobic prenyl-modifications have been discovered in various RNAs. Prenyl groups serve as precursors for terpenes and many other biological molecules. The processes of prenylation in different macromolecules have been extensively studied. We introduce here a novel chemical biology toolkit that not only labels i6A, a prenyl-modified RNA residue, by leveraging the unique reactivity of the prenyl group, but also provides a general strategy to incorporate fluorescence functionalities into RNAs for molecular tracking purposes. Our findings revealed that iodine-mediated cyclization reactions of the prenyl group occur rapidly, transforming i6A from a hydrogen-bond acceptor to a donor. Based on this reactivity, we developed an Iodine-Mediated Cyclization and Reverse Transcription (IMCRT) tRNA-seq method, which can profile all nine endogenous tRNAs containing i6A residues in Saccharomyces cerevisiae with single-base resolution. Furthermore, under stress conditions, we observed a decline in i6A levels in budding yeast, accompanied by significant decrease of mutation rate at A37 position. Thus, the IMCRT tRNA-seq method not only permits semi-quantification of i6A levels in tRNAs but also holds potential for transcriptome-wide detection and analysis of various RNA species containing i6A modifications.

Fluorofunctionalization of C═C Bonds with Selectfluor: Synthesis of β-Fluoropiperazines through a Substrate-Guided Reactivity Switch

The halofunctionalization of alkene substrates remains an essential tool for synthetic chemists. Herein, we report regioselective ammoniofluorination of unactivated alkenes through photochemical means. A one-pot transformation of the ammonium fluoride products into pharmaceutically relevant β-fluoropiperazines is highlighted. Furthermore, a substrate-guided reactivity switch is observed: certain alkenes are shown to react with the same fluorinating reagent to instead give the less-substituted fluoride. We hope that the ammoniofluorination reaction will be of utility in the area of medicinal chemistry, where nitrogen and fluorine are among the most important heteroatoms.

Amidyl Radicals by Oxidation of α-Amido-oxy Acids: Transition-Metal-Free Amidofluorination of Unactivated Alkenes

A three-component transition-metal-free amidofluorination of unactivated alkenes and styrenes is presented. α-Amido-oxy acids are introduced as efficient and easily accessible amidyl radical precursors that are oxidized by a photoexcited organic sensitizer (Mes-Acr-Me) to the corresponding carboxyl radical. Sequential CO₂ and aldehyde/ketone fragmentation leads to an N-centered radical that adds to an alkene. Commercial Selectfluor is used to trap the adduct radical through fluorine-atom transfer. The transformation features by high functional-group tolerance, broad substrate scope, and practical mild conditions. Mechanistic studies support the radical nature of the cascade.

Transition-Metal-Free Fluoroarylation of Diazoacetamides: A Complementary Approach to 3-Fluorooxindoles

An efficient transition-metal-free fluoroarylation reaction of N-aryl diazoacetamides with NFSI (N-fluorobenzenesulfonimide) is described. This reaction directly provides 3-fluorooxindole derivatives in yields of 67-93% with high selectivity via a carbene-free process under mild reaction conditions.

Copper-catalyzed oxidative esterification of unactivated C(sp3)–H bonds with carboxylic acids via cross dehydrogenative coupling

An effective copper-catalyzed esterification of unactivated (non-benzylic and allylic) C(sp³)–H bonds of hydrocarbons with Selectfluor as an oxidant has been developed.

A combination of directing groups and chiral anion phase-transfer catalysis for enantioselective fluorination of alkenes

We report a catalytic enantioselective electrophilic fluorination of alkenes to form tertiary and quaternary C(sp3)-F bonds and generate β-amino- and β-aryl-allylic fluorides. The reaction takes advantage of the ability of chiral phosphate anions to serve as solid-liquid phase transfer catalysts and hydrogen bond with directing groups on the substrate. A variety of heterocyclic, carbocyclic, and acyclic alkenes react with good to excellent yields and high enantioselectivities. Further, we demonstrate a one-pot, tandem dihalogenation-cyclization reaction, using the same catalytic system twice in series, with an analogous electrophilic brominating reagent in the second step.