Sequential Selective C-H and C(sp3 )-+ P Bond Functionalizations: An Entry to Bioactive Arylated Scaffolds

Electroreductive carboxylation of benzylphosphonium salts with CO2 through the cleavage of the C(sp3)-P bond

Herein, a electroreductive carboxylation of benzylphosphonium salts was achieved by the cleavage of the C(sp3)-P bond, and various valuable arylacetic acids could be synthesized by this strategy. Also, based on control experiments and previous studies, a plausible reaction mechanism was proposed to explain the reaction process. The establishment of this procedure will provide a new paradigm for the functionalization of alkyl phosphonium salts.

The First Example of the Friedel-Crafts Cyclization Leading to (10-Hydroxy-9,10-dihydroanthr-9-yl)phosphonium Salts without the Expected Bradsher Dehydration

The reaction of (ortho-acetalaryl)arylmethanols with various phosphines PR1R2R3 (R1 = R2 = R3 = Ph; R1 = R2 = Ph, R3 = Me and R1 = R2 = Me, R3 = Ph) under acidic conditions (e.g., HCl, HBF4, TsOH) unexpectedly led to the formation of (10-hydroxy-9,10-dihydroanthr-9-yl)phosphonium salts instead of the corresponding anthryl phosphonium salts. The cyclization occurred according to the Friedel-Crafts mechanism but without the usually observed Bradsher dehydration, giving cyclic products in the form of cis/trans isomers and their conformers. In case of electron-rich and less-hindered dimethylphenylphosphine, all four stereoisomers were recorded in 31P{1H} NMR spectra, while for the other phosphines, only the two most stable cis/trans stereoisomers were detected. This study was supported by DFT and NCI calculations in combination with FT-IR analysis.

Sustainable Sulfonic Acid Functionalized Tubular Shape Mesoporous Silica as a Heterogeneous Catalyst for Selective Unsymmetrical Friedel-Crafts Alkylation in One Pot

The development of general and more sustainable heterogeneous catalytic processes for Friedel-Crafts (FC) alkylation reactions is a key objective of interest for the synthesis of pharmaceuticals and commodity chemicals. Sustainable heterogeneous catalysis for the typical FC alkylation of an easily accessible carbonyl electrophile and arenes or with two different arene nucleophiles in one-pot is a prime challenge. Herein, we present a resolution to these issues through the design and utilization of a mesoporous silica catalyst that has been functionalized with sulfonic acid. For the synthesis of sulfonic acid-functionalized mesoporous silica (MSN-SO3H), thiol-functionalized mesoporous silica was first synthesized by the co-condensation method, followed by oxidation of the thiol functionality to the sulfonic acid group. Sulfonation of mesoporous silica was confirmed by 13C CP MAS NMR spectroscopy. Further, the devised heterogeneous catalysis using MSN-SO3H has been successfully employed in the construction of diverse polyalkanes including various bioactive molecules, viz arundine, tatarinoid-C, and late-stage functionalization of natural products like menthol and Eugenol. Further, we have utilized this sustainable technique to facilitate the formation of unsymmetrical C-S bonds in a one-pot fashion. In addition, the catalyst was successfully recovered and recycled for eight cycles, demonstrating the high sustainability and cost-effectiveness of this protocol for both academic and industrial applications.

1-Hydroxyalkylphosphonium Salts-Synthesis and Properties

An efficient and convenient method for the synthesis of 1-hydroxyalkylphosphonium salts is described. Reactions were carried out at room temperature, in a short time, and without chromatography for product isolation. The properties of the obtained phosphonium salts were examined and discussed. In this paper, primary attention was paid to the stability of phosphonium salts, depending on the structure of the aldehydes used as substrates in their preparation. Other conditions such as the type of solvent, temperature, and molar ratio of the substrates were also investigated. Finally, the high reactivity of 1-hydroxyalkylphosphonium salts was demonstrated in reactions with amide-type substrates and (hetero)aromatic compounds. The developed step-by-step procedure (with the isolation of 1-hydroxyphosphonium salts) was compared to the one-pot protocol (in situ formation of such phosphonium salts).

Synthesis and Functionalization of Thiophosphonium Salts: A Divergent Approach to Access Thioether, Thioester, and Dithioester Derivatives

Herein, we report a straightforward practical method for efficiently obtaining a diverse range of thiophosphonium salts. This method involves the direct coupling of commercially available thiols and aldehydes with Ph3P and TfOH. The setup is simple and carried out in a metal-free manner. The synthetic utility of these salts is demonstrated through various examples of C-P bond functionalizations, enabling the synthesis of thioether, deuterated thioether, thioester, and dithioester derivatives. These products, which serve as valuable building blocks, are obtained in high yields.

Synthesis of triarylmethanes by silyl radical-mediated cross-coupling of aryl fluorides and arylmethanes

Although the cross-couplings of aryl halides with diarylmethanes are mostly achieved by transition-metal catalysis, aryl fluorides are rarely used as coupling partners owing to the high inertness of C-F bonds. Herein, we describe the efficient silylboronate-mediated cross-coupling reaction of aryl fluorides with arylalkanes under transition-metal-free, room-temperature conditions. The combination of silylboronate and KO ^t Bu is critical for driving a radical process via the cleavage of C-F and C-H bonds in two appropriate coupling precursors, resulting in a cross-coupling product. This practical cross-coupling protocol is applicable to a wide variety of aryl fluorides with a C(sp²)-F bond. This method can be extended to other coupling partners with a C(sp³)-H bond, including diarylmethanes, diarylethanes, and monoarylalkanes. Many di- and triarylalkanes with tertiary or quaternary carbon centers can be obtained easily in moderate to high yields. We believe that the developed silylboronate-mediated cross-coupling method is a valuable contribution to C-F and C-H activation chemistry.

Photoredox-Mediated Deoxygenative Radical Additions of Aromatic Acids to Vinyl Boronic Esters and gem-Diborylalkenes

A new method to access β-keto-gem-diborylalkanes, by direct deoxygenative radical addition of aromatic carboxylic acids to gem-dibortlalkenes, is described. The reaction proceeds under mild photoredox catalysis and involves the photochemical C-O bond activation of aromatic carboxylic acids in the presence of PPh₃ . It generates an acyl radical, which further undergoes an additional reaction with gem-diborylalkenes to form an α-gem-diboryl alkyl radical intermediate, which then reduces to the corresponding anion, which after protonation, affords the β-keto-gem-diborylalkane product. Moreover, the same scenario has been extended to the vinyl boronic esters, for example, gem-(Ar, Bpin)-alkenes, and gem-(Alkyl, Bpin)-alkenes. Importantly, this protocol provides a general platform for the late-stage functionalization of bio-active and drug molecules containing a carboxylic acid group.

Unified synthesis of multiply arylated alkanes by catalytic deoxygenative transformation of diarylketones

A deoxygenative transformation of diarylketones leading to multiply arylated alkanes was developed. Diarylketones were reacted with diphenylphosphine oxide resulting in a phospha-Brook rearrangement, followed by palladium-catalyzed cross-couplings or a Friedel-Crafts type alkylation to afford the corresponding multiply arylated alkanes. A variety of diarylketones can be converted to multiply arylated alkanes such as diarylmethanes, tetraarylethanes, and triarylmethanes by reduction, dimerization, and arylation in one pot. Furthermore, a one-pot conversion from arylcarboxylic acids to diarylmethanes and tetraarylethanes, and a synthesis of tetraarylmethane and triphenylethane using sequential coupling reactions are also presented.

DMSO-Promoted Difluoroalkylation of Organophosphonium Salts with Difluoroenol Silyl Ethers

An efficient method for the synthesis of β,β-di(hetero)aryl-α,α-difluorinated ketones using readily available organophosphonium salts and difluoroenol silyl ethers has been developed. This mild reaction features a good functional group tolerance, a scaled-up synthesis, and synthetic simplicity. By taking advantage of DMSO as a less-toxic promoter and solvent for the difluoroalkylation and C-P bond functionalization, the use of transition-metal catalysts and sensitive additives could be avoided.