Dibenzocycloheptanones construction through a removable P-centered radical: synthesis of allocolchicine analogues

Selective Synthesis of Mono- and Bis-Phosphorylated (Dihydro)pyrans via TMSCl-Mediated Cascade Phosphorylation Cycloisomerization of Enynones

A chlorotrimethylsilane (TMSCl)-mediated cascade phosphorylation and cycloisomerization of enynones with diphenylphosphine oxides is presented. This methodology enables the highly selective synthesis of monophosphorylated 2H-pyrans and bisphosphorylated dihydropyrans through precise solvent-reagent stoichiometry control. The strategy demonstrated excellent functional group compatibility and high yields (up to 96%), providing facile access to structurally diverse phosphorylated heterocycles with potential applications in medicinal chemistry and materials science.

Fused Seven-Membered Carbocycle Construction through Electrochemical Relay Cyclization

Seven-membered carbocycles, which are frequently associated with relevant biological activities, can be found in nature and drugs in ever-increasing numbers. Radical cascade addition of 1,n-enynes-like substrates is one of the most important and efficient strategies for the synthesis of this valuable skeleton with structural diversity and complexity. Herein, we describe an electrooxidative radical-mediated synthesis of dibenzocycloheptanes from ortho-ethynyl-substituted biaryls and tertiary C(sp3)-H containing reactants. The chemo- and regioselective addition of in situ generated carbon radical onto the alkynyl moieties triggers a desired reaction cascade, resulting in the formation of three new C-C bonds. This approach provides a step-economical regime for the facile assembly of a wide range of polycyclic products containing a 6-7-5 system. This green strategy features a good substrate scope, mild conditions, and high efficiency under ferrocene-mediated electrochemical oxidation conditions.

Synthesis of Seven- and Eight-Membered Rings by a Brønsted Acid Catalyzed Cationic Carbocyclization of Biphenyl Embedded Enynes

A Brønsted acid catalyzed cyclization of o-alkenyl-o'-alkynylbiaryls for the synthesis of biologically relevant dibenzo-fused medium-sized rings has been developed. The outcome of the cyclization is determined by the nature of the substituent at the alkyne, with arenes favoring seven-membered rings and alkyl substituents producing eight-membered rings. These reactions proceed via a vinyl cation, which is captured by water and, notably, by C-nucleophiles, such as electron-rich (hetero)arenes.

ipso-Cyclization of unactivated biaryl ynones leading to thio-functionalized spirocyclic enones

Ceric ammonium nitrate (CAN)-promoted oxidative ipso-cyclization of unactivated biaryl ynones with S-centered radicals (SCN/SCF3) to access spiro[5,5]trienones has been established. This approach displayed excellent regioselectivity towards spirocyclization and tolerated a variety of functional groups. Dearomatization of hitherto unknown aryl/heteroaryl groups is also disclosed. DMSO is employed as a low-toxicity, inexpensive solvent as well as a source of oxygen.

Electrooxidative tricyclic 6-7-6 fused-system domino assembly to allocolchicines by a removable radical strategy

Natural allocolchicine and analogues derived thereof a tricyclic 6-7-6-system have been found as key scaffold of various biologically relevant molecules. However, the direct preparation of the allocolchicine motif remains difficult to date. Herein, we report on an electrooxidative radical cyclization of biarylynones with various carbon- and heteroatom-centered radical precursors via a sequential radical addition/7-endo-trig/radical cyclization domino reaction. This approach provides a step-economical and strategically novel disconnection for the facile assembly of a wide range of carbocyclic 6-7-6 fused ring systems. Remarkably, the sulfonyl group on the products could be easily removed by photocatalysis at room temperature with high yields.

Synthesis of Seleno-Dibenzocycloheptenones/Spiro[5.5]Trienones by Radical Cyclization of Biaryl Ynones

We report herein an alternative method for the synthesis of seleno-dibenzocycloheptenones and seleno-spiro[5.5]trienones through the radical cyclization of biaryl ynones in the presence of diorganyl diselenides, using Oxone as a green oxidizing agent. The reactions were conducted using acetonitrile as the solvent in a sealed tube at 100 °C. The protocol is operationally simple and scalable, exhibits high regioselectivity, and allows the synthesis of 24 dibenzocycloheptenones/spiro[5.5]trienones in yields of up to 99%, 17 of which are unpublished compounds. Additionally, synthetic transformations of the prepared compounds, such as oxidation and reduction reactions, are demonstrated.

The synthesis of seven- and eight-membered rings by radical strategies

Radical strategies for preparation of seven- or eight-membered rings.

Construction of sulfonated spiro[5,5]trienones from sulfur dioxide via iron-catalyzed dearomative spirocyclization of biaryls

An iron-catalyzed dearomative spirocyclization of biaryl ynones with sodium metabisulfite and cycloketone oxime esters is developed. By using sodium metabisulfite as the source of sulfur dioxide, this approach enables the...