Palladium-Catalyzed Cleavage of α-Allenylic Aryl Ether toward Pyrazolemethylene-Substituted Phosphinyl Allenes and Their Transformations via Alkenyl C–P(O) Cleavage

Pd/Brønsted Acid Co-catalyzed Dehydrative Coupling of Propargylic Alcohols with Diarylphosphine Oxides

An efficient dehydrative coupling of propargylic alcohols with diarylphosphine oxides to construct tetrasubstituted allenylphosphoryl compounds in the presence of a Pd/Brønsted acid co-catalyst has been developed. As a benefit from the use of a Brønsted acid, this reaction could perform under mild conditions with excellent yields, accommodating a wide range of functional groups. The potential utility of this method has also been demonstrated.

Efficient C(sp3)-P(V) bond cleavage and reconstruction of free α-aminophosphonates via palladium catalysis

Transition metal-catalyzed cleavage and reconstruction of the C-P bond provides a highly efficient and rapid method for the transformation of organophosphine compounds. In this study, a novel and general protocol for the palladium-catalyzed C(sp3)-P(V) bond cleavage of free α-aminophosphonates and subsequent functionalization via C-P bond recombination has been developed. The reaction exhibits high reactivity between the C(sp3)-P bond and halides, accommodating a wide range of substrates and enabling the rapid synthesis of aryl, alkenyl, and alkyl organophosphine molecules. Additionally, the synthetic utility is validated by gram-scale synthesis, and the reaction process is corroborated by mechanistic experiments.

Access Polyarylbipyrazoles via Palladium-Catalysis and Visible-Light-Driven C(sp3)-P(V) Cleavage Relay Strategy

An unprecedented palladium-catalyzed and visible-light-driven relay reaction of allenylphosphine oxide with in situ generated nitrile imines is presented for the direct synthesis of highly valuable polyarylbipyrazole skeletons. This one-pot strategy involves double 1,3-dipolar cycloaddition and C(sp3)-P(V) bond cleavage under photocatalyst-free and mild reaction conditions. The approach features simple operation, a high step economy, and a broad substrate scope, affording the corresponding products in moderate to excellent yields.

Visible-Light-Induced Palladium-Catalyzed Construction of Polyarylfuran Skeletons via Cascade Aryl Radical Cyclization and C(sp3)-P(V) Bond Cleavage

Herein, a novel and expedient method was established for the synthesis of polyarylfuran derivatives. The coupling of allenylphosphine oxide and bromophenol or bromonaphthol enabled by visible light and palladium catalysis directly furnishes polyarylfuran skeletons, which involves a radical tandem cyclization and cascade C(sp³)-P(V) bond cleavage. This protocol features easy operation, a broad substrate scope, and a high step economy, affording polyarylfurans in moderate to good yields.

Substituents Regulate the Cyclization of Conjugated Alkynes to Accurately Construct Cyclo-(E)-[3]dendralenes

Substituent-regulated cyclization of conjugated alkynes with acid catalysis was developed in this paper, and it provides a straightforward synthesis of cyclic-(E)-[3]dendralenes. Depending on the electronic effect of the aromatic ring pairing, a variety of phosphinyl quintuplet/hexa cyclo-[3]dendralenes with diverse substitution patterns are accessible, with good efficiency and high stereoselectivity. This self-cyclization process achieves the first precise construction of a phosphinylcyclo-(E)-[3]dendralene from conjugated alkynes to aromatization.

Transition-Metal-Free Multicomponent Approach to the Regioselective Synthesis of Highly Substituted N-Alkylpyrazoles

An efficient transition-metal-free multicomponent approach to the regioselective synthesis of highly substituted N-alkylpyrazoles through 1,6-addition of pyrazole (in situ generated from α,β-unsaturated aldehyde and hydrazide) to para-Quinone Methides has been developed. The N-alkylpyrazole containing triarylmethanes having several heteroaryl rings (quinoline, pyridine, thiophene) at the central methine carbon atom was developed. This chemical process may be used for large-scale synthesis and provides a novel way to produce triarylmethanes with diverse functional groups.

α,β-Unsaturated Carbonyls for One-Pot Transition-Metal-Free Access to 3,6-Dihydro-2H-pyrans

An efficient protocol has been developed for accessing mono-, di-, and trisubstituted 3,6-dihydro-2H-pyran derivatives by simply subjecting α,β-unsaturated carbonyls to the carefully optimized Corey-Chaykovsky reaction conditions. The strategy provides selectively substituted dihydropyran derivatives in good to excellent yields with a broad substrate scope under very mild reaction conditions. Easy transformation of the final 3,6-dihydro-2H-pyran to the valued 5,6-dihydro-2H-pyran-2-one and tetrahydro-2H-pyran derivatives expanded the scope of this methodology to diverse oxacycles. Further, the developed strategy also found application in a two-step route to racemic goniothalamin, which is widely studied for its cytotoxic behavior.

Synthesis of N-2(5H)-furanonyl sulfonyl hydrazone derivatives and their biological evaluation in vitro and in vivo activity against MCF-7 breast cancer cells

A series of (E)-N-2(5H)-furanonyl sulfonyl hydrazone derivatives have been rationally designed and efficiently synthesized by one-pot reaction with good yields for the first time. This green approach with wide substrate range and good selectivity can be achieved at room temperature in a short time in the presence of metal-free catalyst. The cytotoxic activities against three human cancer cell lines of all newly obtained compounds have been evaluated by MTT assay. Among them, compound 5 k exhibits high cytotoxic activity against MCF-7 human breast cancer cells with an IC₅₀ value of 14.35 μM. The cytotoxic mechanism may involve G2/M phase arrest pathway, which is probably caused by activating DNA damage. Comet test and immunofluorescence results show that compound 5 k can induce DNA damage in time- and dose-dependent manner. Importantly, 5 k also can effectively inhibit the proliferation of MCF-7 cells and angiogenesis in the zebrafish xenograft model. It is potential to further develop N-2(5H)-furanonyl sulfonyl hydrazone derivatives as potent drugs for breast cancer treatment with higher cytotoxic activity by modifying the structure of the compound.

Selective P-C(sp3 ) Bond Cleavage and Radical Alkynylation of α-Phosphorus Alcohols by Photoredox Catalysis

Herein the first P-C(sp³ ) bond cleavage and radical alkynylation of α-phosphorus alcohols to construct phosphonoalkynes is reported. The phosphorus radical is generated upon P-C bond cleavage reaction via the alkoxyl radical through photoredox catalysis with cyclic iodine(III) reagents. Various arylphosphinoyl-, alkylphosphinoyl-, phosphonate-, and phosphonic amide alcohols serve as radical phosphorus precursors to construct phosphonoalkynes for the first time.

Organobase catalyzed straightforward synthesis of phosphinyl functionalized 2H-pyran cores from allenylphosphine oxides and 1,3-diones

A cost-effective system is revealed here to construct polyfunctionalized 2H-pyran cores containing phosphinyl groups with an organobase as a catalyst.

Transition-metal-free radical cleavage of a hydrazonyl N–S bond: tosyl radical-initiated cascade C(sp3)–OAr cleavage, sulfonyl rearrangement and atropisomeric cyclopropanation

Combination of 1,10-phenanthroline and potassium carbonate enables a radical cleavage of a hydrazonyl N–S bond, allowing a coupling reaction of N-tosylhydrazone and phosphinyl allene via cascade C–O cleavage, sulfonyl rearrangement and atropisomeric cyclopropanation.

Expedited Route to Fully Substituted Amino-Pyrazole Building Blocks and Their Further Transformations

We report here an efficient and easily reproducible two-step approach to heterocycle-substituted amino-pyrazoles from heterocyclic acetonitriles and their unprecedented subsequent transformations to fully substituted pyrazoles. Such transformations include regioselective derivatization from polyamino derivatives, formation of tetracyclic compounds in up to 45% overall yield, and deaminative transformations through diazotization, followed by arylation through Suzuki-Miyaura cross-coupling and C-H activation, providing arylated pyrazoles in up to 71% yield over four steps. This strategy allows the swift introduction of significant molecular complexity to a range of scaffolds.