Palladium-catalyzed one-pot phosphorylation of phenols mediated by sulfuryl fluoride

Facile Synthesis of H-Phosphinates from P(OR)3 or ClP(OR)2 via SiO2-Promoted Hydrolysis

H-Phosphinates represent a valuable class of organophosphorus building blocks and catalytic ligands. The existing synthetic approaches are generally associated with the use of strong acids, the need for meticulous treatment of intermediates, and the limitation of only P-aryl introductions. Following a comprehensive investigation into the unexpected SiO2-promoted hydrolysis observed during the chromatography workup of the crude R'P(OR)2 intermediates, we have developed an extremely simple and general synthetic route to H-phosphinates from commercially available Grignard reagents and P(OR)3. An alternative approach involved the use of ClP(OR)2 in place of P(OR)3, which proved to be a valuable strategy for the preparation of sterically hindered ArMgBr substrates bearing bulky ortho-substituted motifs. A library of 36 structurally diverse P-(cyclo)alkyl and P-(hetero)aryl H-phosphinates was thus obtained in moderate to high yields using this practical protocol. Furthermore, the CuCl2-mediated P(O)-H bond derivations were also examined, resulting in the formation of the corresponding EtOPhP(O)-X (X = O, N, S) compounds in nearly quantitative yields.

Palladium-Catalyzed Esterification of Aryl Fluorosulfates with Aryl Formates

An efficient palladium-catalyzed carbonylation of aryl fluorosulfates with aryl formates for the facile synthesis of esters was developed. The cross-coupling reactions proceeded effectively in the presence of a palladium catalyst, phosphine ligand, and triethylamine in DMF to produce the corresponding esters in moderate to good yields. Of note, functionalities or substituents, such as nitro, cyano, methoxycarbonyl, trifluoromethyl, methylsulfonyl, trifluoromethoxy, fluoro, chloro, bromo, methyl, methoxy, N,N-dimethyl, and [1,3]dioxolyl, were well-tolerated in the reactions, which could be kept for late-stage modification. The reactions employing readily available and relatively robust aryl fluorosulfates as coupling electrophiles could potentially serve as an attractive alternative to traditional cross-couplings with the use of aryl halides and pseudohalides as substrates.

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.

Visible light-enabled synthesis of phosphorylated indolizine and pyridoindole derivatives via HAT-mediated radical cascade cyclization

A visible light-enabled cascade cyclization strategy is disclosed with concomitant phosphorylation and heterocycle construction. It provides a novel and environmentally benign approach for accessing tetrahydroindolizine-containing phosphonates under metal-free conditions. Mechanistic studies revealed that phosphinoyl radicals were generated from H-phosphonates via a HAT process.

SO2F2-Mediated Fluorination of P(O)-H and P(O)-OH Compounds under Mild Conditions

With the increasing relevance of organophosphorus fluorine compounds in the pharmaceutical industry, their synthesis has attracted great attention. Herein, we report an efficient fluorination strategy for P(O)-H and P(O)-OH compounds using sulfuryl fluoride as the fluorination reagent. Avoiding the use of expensive or complex prepreparation reagents for fluoridation, this strategy could conveniently construct a variety of fluorophosphonates and phosphonofluoridates under mild conditions and without additional oxidants.

New Chemical Transformations Involving SO2 F2 -Mediated Alcohol Activation

Sulfuryl fluoride is a gas produced on a multi-ton scale for its use as a fumigant. In the last decades, it has gained interest in organic synthesis as a reagent with unique properties in terms of stability and reactivity when compared to other sulfur-based reagents. Sulfuryl fluoride has not only been used for sulfur-fluoride exchange (SuFEx) chemistry but also encountered applications in classic organic synthesis as an efficient activator of both alcohols and phenols, forming a triflate surrogate, namely a fluorosulfonate. A long-standing industrial collaboration in our research group drove our work on the sulfuryl fluoride-mediated transformations that will be highlighted below. We will first describe recent works on metal-catalyzed transformations from aryl fluorosulfonates while emphasizing the one-pot processes from phenol derivatives. In a second section, nucleophilic substitution reactions on polyfluoroalkyl alcohols will be discussed and the value of polyfluoroalkyl fluorosulfonates in comparison to alternative triflate and halide reagents will be brought to light.

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.

Synthesis of substituted pyridines with diverse functional groups via the remodeling of (Aza)indole/Benzofuran skeletons

Substituted pyridines with diverse functional groups are important structural motifs found in numerous bioactive molecules. Several methodologies for the introduction of various bio-relevant functional groups to pyridine have been reported, but there is still a need for a single robust method allowing the selective introduction of multiple functional groups. This study reports a ring cleavage methodology reaction for the synthesis of 2-alkyl/aryl 3-electron-withdrawing groups (esters, sulfones, and phosphonates) 5-aminoaryl/phenol pyridines via the remodeling of 3-formyl (aza)indoles/benzofurans. Totally ninety-three 5-aminoaryl pyridines and thirty-three 5-phenol pyridines were synthesized showing the robustness of the developed methodology. The application of this methodology further provided a privileged pyridine scaffold containing biologically relevant molecules and direct drug/natural product conjugation with ethyl 2-methyl nicotinate.

Metal-Free and Open-Air Arylation Reactions of Diaryliodonium Salts for DNA-Encoded Library Synthesis

A successful DNA-encoded library (DEL) will consist of diverse skeletons and cover chemical space as comprehensive as possible to fully realize its potential in drug discovery and chemical biology. However, the lack of versatile on-DNA arylation methods for phenols that are less nucleophilic and reactive poses a great hurdle for DEL to include diaryl ether, a privileged chemotype in pharmaceuticals and natural products. This work describes the use of "substrate activation" approach to address the arylation of DNA-conjugated phenols. Diaryliodonium salt, a highly electrophilic and reactive arylation reagent, is employed as Ar⁺ sources to ensure highly selective on-DNA arylation of phenols and oximes with both high yields and DNA fidelity. Notably, the new on-DNA arylation reaction can be applied to the late-stage modification of peptides containing tyrosine side-chain and to synthesize DNA-tagged analogues of existing drug molecules such as sorafenib, a known pan-kinase inhibitor. The new on-DNA diaryliodonium salts chemistry affords a greater flexibility in DEL design and synthesis.

C-P bond formation of cyclophanyl-, and aryl halides via a UV-induced photo Arbuzov reaction: a versatile portal to phosphonate-grafted scaffolds

A new versatile method for the C–P bond formation of (hetero)aryl halides with trimethyl phosphite via a UV-induced photo-Arbuzov reaction, accessing diverse phosphonate-grafted arenes, heteroarenes and co-facially stacked cyclophanes under mild reaction conditions without the need for catalyst, additives, or base is developed. The UV-induced photo-Arbuzov protocol has a wide synthetic scope with large functional group compatibility exemplified by over 30 derivatives. Besides mono-phosphonates, di- and tri-phosphonates are accessible in good to excellent yields. Mild and transition metal-free reaction conditions consolidate this method's potential for synthesizing pharmaceutically relevant compounds and precursors of supramolecular nanostructured materials.

UV-induced C–P bond formation of aryl halides via photo Arbuzov reaction: a versatile portal to phosphonate-grafted scaffolds.

Palladium-Catalyzed C-P Bond-Forming Reactions of Aryl Nonaflates Accelerated by Iodide

An iodide-accelerated, palladium-catalyzed C-P bond-forming reaction of aryl nonaflates is described. The protocol was optimized for the synthesis of aryl phosphine oxides and was found to be tolerant of a wide range of aryl nonaflates. The general nature of this transformation was established with coupling to other P(O)H compounds for the synthesis of aryl phosphonates and an aryl phosphinate. The straightforward synthesis of stable, isolable aryl nonaflates, in combination with the rapid C-P bond-forming reaction allows facile preparation of aryl phosphorus target compounds from readily available phenol starting materials. The synthetic utility of this general strategy was demonstrated with the efficient preparation of an organic light-emitting diode (OLED) material and a phosphonophenylalanine mimic.

Click Chemistry in Natural Product Modification

Click chemistry is perhaps the most powerful synthetic toolbox that can efficiently access the molecular diversity and unique functions of complex natural products up to now. It enables the ready synthesis of diverse sets of natural product derivatives either for the optimization of their drawbacks or for the construction of natural product-like drug screening libraries. This paper showcases the state-of-the-art development of click chemistry in natural product modification and summarizes the pharmacological activities of the active derivatives as well as the mechanism of action. The aim of this paper is to gain a deep understanding of the fruitful achievements and to provide perspectives, trends, and directions regarding further research in natural product medicinal chemistry.

The expanding reaction toolkit for DNA-encoded libraries

Over the past decade, DNA-encoded libraries (DELs) have emerged as a leading platform for small molecule drug discovery among pharmaceutical companies, biotech companies and academic drug hunters alike. This revolutionary technology has tremendous potential that is yet to be fully realized, as the exploration of therapeutically relevant chemical space is fueled by the ever-expanding repertoire of DNA-compatible reactions used to construct the libraries. Advances in direct coupling reactions, like photo-catalytic cross couplings, unique cyclizations such as the formation of 1,2,4-oxadiazoles, and new functional group transformations are valuable contributions to the DEL reaction toolkit, and indicate where future reaction development efforts should focus in order to maximize the productivity of DELs.