Csp3-H bond functionalization of amines via tunable iminium ions: divergent synthesis of trifluoromethylated arylamines

Trifluoromethylations of (Hetero)arenes and Polarized Alkenes Using Trifluoroacetic Anhydride under Photoredox Catalysis

A novel trifluoromethylation of (hetero)arenes and polarized alkenes using simple trifluoroacetic anhydride (TFAA) as the low price CF₃ source under photoredox catalysis was developed without using additives such as bases, hyperstoichiometric oxidant, or auxiliaries. The reaction showed excellent tolerance, including to some important natural products and prodrugs, even on the gram scale and extended to ketones. This simple protocol provides a practical utilization of TFAA. Several perfluoroalkylations and trifluoromethylation/cyclizations were successfully achieved under identical conditions.

Visible-Light-Induced Dual C(sp3)-H Bond Functionalization of Tertiary Amine via Hydrogen Transfer to Carbene and Subsequent Cycloaddition

Herein, we describe the dual C(sp³)-H bond functionalization of a tertiary amine through hydride-transfer-induced dehydrogenation, followed by cycloaddition, using an easily preparable diazoester as a new type hydride-acceptor precursor under mild, redox-neutral conditions. With carbene as a hydrogen acceptor, this method was demonstrated by the preparation of a broad range of functionalized isoxazoldines in moderate to good yields.

A One-Pot Approach for Bio-Based Arylamines via a Combined Photooxidative Dearomatization-Rearomatization Strategy

The synthesis of arylamines from renewable resources under mild reaction conditions is highly desired for the sustainability of the chemical industry, where the production of hazardous waste is a prime concern. However, to date, there are very few tools in chemists' toolboxes that are able to produce arylamines in a sustainable manner. Herein, a robust one-pot approach for constructing bio-based arylamines via a combined photooxidative dearomatization-rearomatization strategy is presented. The developed methodology enables the synthesis of structurally complex amines in moderate-to-good isolated yields using biomass-derived phenols, natural α-amino acids, and naphthols under remarkably mild reaction conditions. For the photooxygenation of phenols, a novel chrysazine-based catalyst system was introduced, demonstrating its efficiency for the synthesis of natural products - hallerone, rengyolone, and the pharmaceutically relevant prodrug DHED.

SmI2‑Mediated Intermolecular Addition-Elimination of Piperidine and Pyrrolidine N-α-Radicals with Arylacetylene Sulfones

An efficient approach to access α-arylacetylene substituted pyrrolidine and piperidine derivatives has been developed through a samarium diiodide mediated addition-elimination process of pyrrolidine and piperidine N-α-radicals with arylacetylene sulfones.

Condensation-Based Methods for the C-H Bond Functionalization of Amines

This review aims to provide a comprehensive overview of condensation-based methods for the C-H bond functionalization of amines that feature azomethine ylides as key intermediates. These transformations are typically redox-neutral and share common attributes with classic name reactions such as the Strecker, Mannich, Friedel-Crafts, Pictet-Spengler, and Kabachnik-Fields reaction, while incorporating a redox-isomerization step. This approach provides an ideal platform to rapidly transform simple starting materials into complex amines.

Synthesis of the Hexahydropyrrolo-[3,2-c]-quinoline Core Structure and Strategies for Further Elaboration to Martinelline, Martinellic Acid, Incargranine B, and Seneciobipyrrolidine

Natural products are rich sources of interesting scaffolds possessing a plethora of biological activity. With the isolation of the martinella alkaloids in 1995, namely martinelline and martinellic acid, the pyrrolo[3,2-c]quinoline scaffold was discovered. Since then, this scaffold has been found in two additional natural products, viz. incargranine B and seneciobipyrrolidine. These natural products have attracted attention from synthetic chemists both due to the interesting scaffold they contain, but also due to the biological activity they possess. This review highlights the synthetic efforts made for the preparation of these alkaloids and formation of analogues with interesting biological activity.

Metal-free C–H functionalization of pyrrolidine to pyrrolinium-based room temperature ionic liquid crystals

C–H functionalization of pyrrolidine-enabled synthesis of a new class of ionic liquid crystals

Formal α-Allylation of Primary Amines by a Dearomative, Palladium-Catalyzed Umpolung Allylation of N-(Aryloxy)imines

N-(Aryloxy)imines, readily accessible by condensation/tautomerization of (pseudo)benzylic primary amines and 2,6-di-tert-butyl-1,4-benzoquinone, undergo efficient allylation to afford a wide range of homoallylic primary amines following hydrolytic workup. Deprotonation of N-(aryloxy)imines generates a delocalized 2-azaallyl anion-type nucleophile that engages in dearomative C-C bond-forming reactions with allylpalladium(II) electrophiles generated from allylic tert-butyl carbonates. This reactivity umpolung enables the formal α-allylation of (pseudo)benzylic primary amines. Mechanistic studies reveal that the apparent regioselectivity of the desired bond-forming event is a convergent process that is initiated by unselective allylation of N-(aryloxy)imines to give several regioisomeric species, which subsequently rearrange via stepwise [1,3]- or concerted [3,3]-sigmatropic shifts, ultimately converging to provide the desired regioisomer of the amine products.

Stereocontrolled transformations of cyclohexadienone derivatives to access stereochemically rich and natural product-inspired architectures

The last two decades or so have witnessed an upsurge in defining the art of designing complex natural products and nature-inspired molecules. Throughout these decades, fundamental insights into stereocontrolled, step-economic and atom-economical synthesis principles were achieved by the numerous synthetic accomplishments particularly in diversity-oriented synthesis (DOS). This has empowered the visualization of the third dimension in synthetic design and thus has resulted in a dramatic increase with today's diversity-oriented synthesis (DOS) at the forefront enabling access to diverse scaffolds with a high degree of stereochemical and skeletal complexity. To this end, a starting material-based approach is one of the powerful tools utilized in DOS that allows rapid access to molecular architectures with a high sp3 content. Skeletal and stereochemical diversity is often paramount for the selective modulation of the biological function of a complementary protein in the biological space. In this context, stereocontrolled transformation of cyclohexadienone scaffolds has positioned itself as a powerful platform for the rapid generation of stereochemically enriched and natural product-inspired compound collections. In this review, we cover multidirectional synthetic strategies that utilized cyclohexadienone derivatives as pluripotent building blocks en route for the construction of novel chemical space.

Divergent synthesis of N-heterocyclic 1,6-enynes through a zinc-catalyzed decarboxylative A3 reaction

A zinc-catalyzed decarboxylative A³ reaction of cyclic amino acids, α,β-unsaturated aldehydes and terminal alkynes has been developed. A series of functionalized N-heterocyclic 1,6-enynes have been successfully obtained with excellent regioselectivities through this novel approach. In addition, the utility of this straightforward process is demonstrated by the preparation of a polycyclic nitrogen-containing heterocyclic compound.