Gem-Difluorocyclopropenes as Versatile β-Monofluorinated Three-sp2 Carbon Sources for Cp*Rh(III)-Catalyzed [4 + 3] Annulation: Experimental Development and Mechanistic Insight

Regio- and Diastereoselective Hydrophosphination and Hydroamidation of gem-Difluorocyclopropenes

In this study, concise, efficient, and modular hydrophosphinylation and hydroamidation of gem-difluorocyclopropenes were disclosed in a mild and transition-metal-free pattern. Through this approach, phosphorus, and nitrogen-containing gem-difluorocyclopropanes were produced in moderate to good yields with excellent regio- and diastereoselectivity. Readily available gem-difluorocyclopropenes and nucleophilic reagents, along with inexpensive inorganic bases, were employed. Multiple synthetic applications, including gram-scale and derivatization reactions and modification of bioactive molecules, were subsequently elaborated.

Evolution of chemistry and selection technology for DNA-encoded library

DNA-encoded chemical library (DEL) links the power of amplifiable genetics and the non-self-replicating chemical phenotypes, generating a diverse chemical world. In analogy with the biological world, the DEL world can evolve by using a chemical central dogma, wherein DNA replicates using the PCR reactions to amplify the genetic codes, DNA sequencing transcripts the genetic information, and DNA-compatible synthesis translates into chemical phenotypes. Importantly, DNA-compatible synthesis is the key to expanding the DEL chemical space. Besides, the evolution-driven selection system pushes the chemicals to evolve under the selective pressure, i.e., desired selection strategies. In this perspective, we summarized recent advances in expanding DEL synthetic toolbox and panning strategies, which will shed light on the drug discovery harnessing in vitro evolution of chemicals via DEL.

Mask and Release Strategy-Enabled Diversity-Oriented Synthesis for DNA-Encoded Library

An ideal DNA-encoded library (DEL) selection requires the library to consist of diverse core skeletons and cover chemical space as much as possible. However, the lack of efficient on-DNA synthetic approaches toward core skeletons has greatly restricted the diversity of DEL. To mitigate this issue, this work disclosed a "Mask & Release" strategy to streamline the challenging on-DNA core skeleton synthesis. N-phenoxyacetamide is used as a masked phenol and versatile directing group to mediate diversified DNA-compatible C-H functionalization, introducing the 1st-dimensional diversity at a defined site, and simultaneously releasing the phenol functionality, which can facilitate the introduction of the 2nd diversity. This work not only provides a set of efficient syntheses toward DNA-conjugated drug-like core skeletons such as ortho-alkenyl/sulfiliminyl/cyclopropyl phenol, benzofuran, dihydrobenzofuran but also provides a paradigm for on-DNA core skeleton synthetic method development.

[3+2]-Cycloaddition Reactions of gem-Difluorocyclopropenes with Azomethine Ylides - Access to Novel Fluorinated Scaffolds

The introduction of fluorinated moieties into drugs as well as the increase of their overall three-dimensionality have become key strategies amongst medicinal chemists to generate sets of compounds with favorable drug-like properties. However, the introduction of fluorinated cyclopropane ring systems which combines both strategies is not widely exploited to date. This paper reports synthetic strategies exploiting the reactivity of gem-difluorocyclopropenes in dipolar cycloaddition reactions with azomethine ylides to afford sets of new fluorine-containing 3-azabicyclo[3.1.0]hexanes. In addition, the unexpected formation of complex trifluorinated scaffolds arising from proline esters and gem-difluorocyclopropenes is highlighted along with computational studies to elucidate the underlying mechanism. This study presents new avenues towards pharmaceutically relevant fluorinated 3-azabicyclo[3.1.0]hexanes that are accessible via robust and short synthetic sequences.

Enolate-Azide [3 + 2]-Cycloaddition Reaction Suitable for DNA-Encoded Library Synthesis

The DNA-encoded chemical library (DEL) is a powerful hit selection technique in either basic science or innovative drug discovery. With the aim to circumvent the issue concerning DNA barcode damage in a conventional on-DNA copper-catalyzed azide-alkyne cycloaddition reaction (CuAAC), we have successfully developed the first DNA-compatible enolate-azide [3 + 2] cycloaddition reaction. The merits of this DEL chemistry include metal-free reaction and high DNA fidelity, high conversions and easy operation, broad substrate scope, and ready access to the highly substituted 1,4,5-trisubstituted triazoles. Thus, it will not only further enrich the DEL chemistry toolbox but also will have great potential in practical DEL synthesis.

Rh(III)-catalyzed redox-neutral C-H alkenylation of benzamides with gem-difluorohomoallylic silyl ethers via β-H elimination

Fluorinated molecules are widely used in pharmaceutical and agrochemical industries. Herein we report the synthesis of 2-(3,3-difluoro-4-(silyloxy)but-1-en-1-yl)benzamides from the unprecedented rhodium(III)-catalyzed alkenylation of various benzamides with difluorohomoallylic silyl ethers. The practicability of this protocol is demonstrated by its broad substrate compatibility, good functional group tolerance, ready scalability and high regioselectivity. The oxygen in difluorohomoallylic silyl ethers makes β-H elimination feasible, which suppresses both the β-F elimination and dialkenylation of benzamides. This redox-neutral reaction proceeds efficiently via N-O bond cleavage without external oxidants and thus provides new opportunities for the synthesis of elaborate difluorinated compounds from readily available fluorinated synthons.

Rh(III)-Catalyzed C-H Functionalization/Annulation of 1-Arylindazolones: Divergent Synthesis of Fused Indazolones and Allyl Indazolones

Rh(III)-catalyzed C-H/N-H annulation and C-H allylation of phenylindazolones have been realized by employing 5-methylene-1,3-dioxan-2-one and 4-vinyl-1,3-dioxolan-2-one as scalable cross-coupling partners, delivering functionalized indazolone fused heterocycles and branched and linear allyl indazolones respectively in moderate to high yield. These divergent synthesis protocols showcase mild conditions, broad substrate scope, and high functional-group compatibility. In addition, scale-up synthesis and preliminary mechanistic exploratory were also accomplished.

Privileged heterocycles for DNA-encoded library design and hit-to-lead optimization

It is well known that heterocyclic compounds play a key role in improving drug activity, target selectivity, physicochemical properties as well as reducing toxicity. In this review, we summarized the representative heterocyclic structures involved in hit compounds which were obtained from DNA-encoded library from 2013 to 2021. In some examples, the state of the art in heterocycle-based DEL synthesis and hit-to-lead optimization are highlighted. We hope that more and more novel heterocycle-based DEL toolboxes and in-depth pharmaceutical research on these lead compounds can be developed to accelerate the discovery of new drugs.

Rh(i)-catalyzed dimerization of ene-vinylidenecyclopropanes for the construction of spiro[4,5]decanes and mechanistic studies

Rh(i) complex catalyzed dimerization of ene-vinylidenecyclopropanes took place smoothly to construct a series of products containing spiro[4,5]decane skeletons featuring a simple operation procedure, mild reaction conditions, and good functional group tolerance. In this paper, the combination of experimental and computational studies reveals a counterion-assisted Rh(i)-Rh(iii)-Rh(v)-Rh(iii)-Rh(i) catalytic cycle involving tandem oxidative cyclometallation/reductive elimination/selective oxidative addition/selective reductive elimination/reductive elimination steps; in addition, a pentavalent spiro-rhodium intermediate is identified as the key intermediate in this dimerization reaction upon DFT calculation.

Construction of heterocyclic rings from cyclopropenes

Heterocyclic rings are the fundamental building blocks of biological systems and have wide applications in synthetic chemistry and medicinal science. The development of novel synthetic methodology for heterocyclic skeletons from a variety of starting materials has made great progress in the past decades. Meanwhile, highly strained cyclopropenes as reactive reagents in organic transformations have drawn much attention from chemists. The rich chemical reactivity and reaction routes have been well investigated, and some review articles related to the reactivity of cyclopropenes and the construction of carbocycles and acyclic compounds have appeared in these years. Thus, this review mainly focuses on the progress in the construction of heterocyclic rings starting from various cyclopropenes including the reactions of commonly available stable cyclopropenes, in situ generated reactive cyclopropenes and cyclopropene precursors during this decade. Firstly, the transformations of common cyclopropenes into donor-type vinyl metal carbenes via transition metal induced ring opening, direct metalation of the CC bond of metal complexes, and cycloaddition reactions with 1,3-dipoles are described. Next, the annulation reactions of reactive cyclopropenes generated in situ with donor-acceptor reagents, intramolecular nucleophilic addition, and the cycloaddition reactions with 1,3-dipoles are introduced. Then, the transformation of cyclopropene precursors such as alkyl 1-chloro- or 1-alkoxy-2-aroylcyclopropanecarboxylates into five-membered heteroaromatic compounds is also mentioned. In addition, a brief outlook of the opportunity and challenges in the field of bio-orthogonal reactions related to cyclopropenes is given.

Copper-Catalyzed Ring-Opening Defluoroborylation of gem-Difluorinated Cyclobutenes: A General Route to Bifunctional 1,3-Dienes and Their Applications

The exploration of the reactivity of gem-difluorinated small-size rings has continuously drawn attention in recent years but is limited to three-membered carbocycles. Herein we report a copper-catalyzed reaction of gem-fluorinated cyclobutenes with bis(pinacolato)diboron (B₂pin₂). A sequence of defluoroborylation and a ring-opening process produces B,F-bifunctional 1,3-dienes in a stereoselective manner. The transformation together with the efficient downstream coupling of the boronate and the fluoride moieties collectively constitutes a modular route to highly functionalized and stereocontrolled 1,3-dienes.

A cascade indazolone-directed Ir(iii)- and Rh(iii)-catalyzed C(sp2)–H functionalization/[4 + 2] annulation of 1-arylindazolones with sulfoxonium ylides to access chemically divergent 8H-indazolo [1,2-a]cinnolines

An indazolone-directed chemoselective synthesis of 8H-indazolo [1,2-a]cinnolines has been realized via a cascade Cp*Ir(iii)- and Cp*Rh(iii)-catalyzed C–H activation/cyclization reaction of 1-arylindazolones with sulfoxonium ylides.

Rh(iii)-catalyzed simultaneous [3 + 3]/[5 + 1] annulation of 1-arylpyrazolidinones with gem-difluorocyclopropenes leading to fluorinated pyridopyrimidinone derivatives

Presented herein is an efficient and concise synthesis of fluorinated pyridopyrimidinone derivatives through formal [3 + 3]/[5 + 1] annulation of 1-arylpyrazolidinones with gem-difluorocyclopropenes.

Catalytic regio- and stereoselective silicon–carbon bond formations on unsymmetric gem-difluorocyclopropenes by capture of silyl metal species

A highly regioselective silylation of unsymmetric gem-difluorocyclopropenes was achieved by the capture of in-situ formed silyl metal intermediates, which gave structurally diverse silyldifluorocyclopropanes with good yields and stereoselectivity.