Pd(II)-Catalyzed Aminofluorination of Alkenes in Total Synthesis 6-(R)-Fluoroswainsonine and 5-(R)-Fluorofebrifugine

Intermolecular Sulfenoamination of Alkenes with Free-Thiols and NIS to Access β-Succinimide Sulfides

A convenient and practical multicomponent strategy for the sulfenoamination of alkenes was realized, which using free-thiols as the sulfur-reagent, NIS both as radical initiator and an N-nucleophile. This protocol excellent in terms of transition-metal-free, good functional group tolerance, easily available substrates and facile scale-up. And provided a direct- and general way to synthesize various β-succinimide sulfides with high regioselectivity.

The emergence of the C-H functionalization strategy in medicinal chemistry and drug discovery

Owing to the market competitiveness and urgent societal need, an optimum speed of drug discovery is an important criterion for successful implementation. Despite the rapid ascent of artificial intelligence and computational and bioanalytical techniques to accelerate drug discovery in big pharma, organic synthesis of privileged scaffolds predicted in silico for in vitro and in vivo studies is still considered as the rate-limiting step. C-H activation is the latest technology added into an organic chemist's toolbox for the rapid construction and late-stage modification of functional molecules to achieve the desired chemical and physical properties. Particularly, elimination of prefunctionalization steps, exceptional functional group tolerance, complexity-to-diversity oriented synthesis, and late-stage functionalization of privileged medicinal scaffolds expand the chemical space. It has immense potential for the rapid synthesis of a library of molecules, structural modification to achieve the required pharmacological properties such as absorption, distribution, metabolism, excretion, toxicology (ADMET) and attachment of chemical reporters for proteome profiling, metabolite synthesis, etc. for preclinical studies. Although heterocycle synthesis, late-stage drug modification, ¹⁸F labelling, methylation, etc. via C-H functionalization have been reviewed from the synthetic standpoint, a general overview of these protocols from medicinal and drug discovery aspects has not been reviewed. In this feature article, we will discuss the recent trends of C-H activation methodologies such as synthesis of medicinal scaffolds through C-H activation/annulation cascade; C-H arylation for sp²-sp² and sp²-sp³ cross-coupling; C-H borylation/silylation to introduce a functional linchpin for further manipulation; C-H amination for N-heterocycles and hydrogen bond acceptors; C-H fluorination/fluoroalkylation to tune polarity and lipophilicity; C-H methylation: methyl magic in drug discovery; peptide modification and macrocyclization for therapeutics and biologics; fluorescent labelling and radiolabelling for bioimaging; bioconjugation for chemical biology studies; drug-metabolite synthesis for biodistribution and excretion studies; late-stage diversification of drug-molecules to increase efficacy and safety; cutting-edge DNA encoded library synthesis and improved synthesis of drug molecules via C-H activation in medicinal chemistry and drug discovery.

Stereocontrolled Synthesis of Functionalized Azaheterocycles from Carbocycles through Oxidative Ring Opening/Reductive Ring Closing Protocols

Fluorine-containing organic scaffolds are of significant interest in medicinal chemistry. The incorporation of fluorine into biomolecules can lead to remarkable changes in their physical, chemical, and biological properties. There are already many drugs on the market, which contain at least one fluorine atom. Saturated functionalized azaheterocycles as bioactive substances have gained increasing attention in pharmaceutical chemistry. Due to the high biorelevance of organofluorine molecules and the importance of N-heterocyclic compounds, selective stereocontrolled procedures to the access of new fluorine-containing saturated N-heterocycles are considered to be a hot research topic. This account summarizes the synthesis of functionalized and fluorine-containing saturated azaheterocycles starting from functionalized cycloalkenes and based on oxidative ring cleavage of diol intermediates followed by ring expansion with reductive amination.

Pd(II)-Catalyzed Intramolecular Acetoxylative (3 + 2) Annulation of Propargylic Alcohol and Alkene: Polycyclic Oxa-heterocycle Synthesis and Mechanistic Insight

A Pd(II)-catalyzed intramolecular and highly selective acetxoylative (3 + 2) annulation of propargylic alcohol and alkene is reported. Mechanistically, a hydroxy-guided regioselective alkyne acetoxypalladation is followed by 6-exo-trig alkene insertion to form an alkyl-Pd(II) intermediate. After oxidation, the resulting cyclometalated alkoxy-Pd(IV)-alkyl undergoes direct reductive elimination to afford a polycyclic oxa-heterocycle. When an additional coordinating site or ligand accessible by palladium is present, an S_N2-type C-C reductive elimination of alkyl-Pd(IV) instead occurs along with hydroxy acetylation, affording 3-bicyclo[4.1.0]heptan-5-one products.

Chemical synthesis of febrifugine and analogues

The quinazolinone-containing 2,3-disubstituted piperidines febrifugine and isofebrifugine have been the subject of significant research efforts since their occurrence in Dichroa febrifuga and their anti-malarial actions were first described in the late 1940s. Subsequently they have also been shown to be present in other plants belonging to the hydrangea family and various analogues of febrifugine have been prepared in attempts to tune biological properties. The most notable analogue is termed halofuginone and a substantial body of work now demonstrates that this compound possesses potent human disease relevant activities. This review focuses on the literature associated with efforts dedicated towards uncovering the structures of febrifugine and isofebrifugine, the development of practical methods for their synthesis and the syntheses of structural analogues.

Hypervalent iodine(iii) fluorinations of alkenes and diazo compounds: new opportunities in fluorination chemistry

The fluorination of organic molecules is a rapidly evolving and exciting field in synthesis, which still poses huge challenges despite the advances made in the past decades. Hypervalent iodine(iii) reagents, which have already proven their versatility as synthetic tools in organic chemistry, are currently on the rise in fluorination chemistry. With their ability to break new mechanistic grounds, they grant access to completely new reactivities and thus also to novel fluorinated structural scaffolds. This review aims to provide an overview of the achievements made in the iodine(iii) mediated fluorinations of aliphatic Csp²-carbon atoms with special focus on the opportunities provided by this exciting class of hypervalent substances.

Palladium(II)-Catalyzed Oxidative Difunctionalization of Alkenes: Bond Forming at a High-Valent Palladium Center

Difunctionalization of alkenes to incorporate two functional groups across a double bond has emerged as a powerful transformation to greatly increase molecular complexity in organic synthesis with improved efficiency. Historically, palladium-catalyzed difunctionalization of alkenes has suffered from difficulties with introducing a second functional group through reductive elimination of a Pd(II) intermediate and competing β-hydride elimination reactions. To overcome these challenges, one strategy involves utilizing a steric bulky ligand to promote the reductive elimination steps from the Pd(II) center and impeding the β-hydride elimination reactions, which are beyond the scope of this Account. Alternatively, strong oxidants have been utilized to generate high-valent palladium species, which are prone to undergo reductive elimination to form a second C-X bond. This new strategy has been extensively applied to explore the difunctionalization of alkenes with enriched functional group diversity over the past decade. In this Account, we discuss our exploration and application of a "high-valent palladium strategy" for the synthesis of fluorine-containing organic molecules that are typically inaccessible from other methods. These studies were focused on the difunctionalization of alkenes that was initiated by nucleopalladation to form the alkyl C-Pd(II) species in high exo/endo regioselectivity. In the presence of nucleophilic fluorine-containing reagents (e.g., AgF, TMSCF₃, and AgOCF₃) and strong oxidants (hypervalent iodine and electrophilic fluorinating reagents), the in situ generated fluorine-containing high-valent Pd(IV) intermediates undergo reductive elimination to provide the corresponding alkyl C-F, C-CF₃, and C-OCF₃ bonds. Using these methods, we synthesized a variety of heterocycles containing fluorine, trifluoromethyl, and trifluoromethoxyl moieties from alkene substrates under mild reaction conditions. Besides hypervalent iodine reagents and electrophilic fluorinating reagents, our group has demonstrated that hydrogen peroxide, which is an environmentally friendly oxidant, can oxidize alkyl C-Pd(II) species to form high-valent alkyl C-Pd intermediates, and based on this observation, several catalytic difunctionalizations of alkenes, such as aminochlorination, aminoacetoxylation, and aminohydroxylation reactions, have been successfully developed. In addition, water was the only waste derived from the oxidant. All of these studies provide attractive methods for the stereoselective introduction of C-N and C-O bonds across double bonds via high-valent palladium intermediates. To gain a deeper understanding of this "high-valent palladium strategy", systematic mechanistic studies were performed to illustrate the stereochemistry of aminopalladation and reductive elimination. These results are summarized in the final section and serve as a guide for further exploration of novel alkene transformation as well as in other areas, such as Pd-catalyzed C-H bond functionalization reactions.

Fluorination methods in drug discovery

Fluorination reactions of medicinal and biologically-active compounds will be discussed. Late stage fluorination strategies of medicinal targets have recently attracted considerable attention on account of the influence that a fluorine atom can impart to targets of medicinal importance, such as modulation of lipophilicity, electronegativity, basicity and bioavailability, the latter as a consequence of membrane permeability. Therefore, the recourse to late-stage fluorine substitution on compounds with already known and relevant biological activity can provide the pharmaceutical industry with new leads with improved medicinal properties. The fluorination strategies will take into account different fluorinating reagents, either of nucleophilic or electrophilic, and of radical nature. Diverse families of organic compounds such as (hetero)aromatic rings, and aliphatic substrates (sp(3), sp(2), and sp carbon atoms) will be studied in late-stage fluorination reaction strategies.

Peroxodisulfate-mediated selenoamination of alkenes yielding amidoselenide-containing sulfamides and azoles

A novel intermolecular selenoamination of alkenes has been successfully developed and a series of structurally diverse vicinal amidoselenides were effectively obtained under mild heating.