A novel entry to functionalized benzofurans and indoles from furans in moderate to good yields has been developed. This protocol involves palladium(0)-catalyzed dearomatizing intramolecular arylation of the furan ring, formation of a π-allylic palladium complex, furan ring opening, and a β-hydride elimination sequence.
A facile and atom-economic method for the synthesis of 3a,6a-dihydro-furo[2,3-b]furan derivatives and polysubstituted furans starting from furylcarbionls has been developed. This protocol involved a domino Claisen rearrangement/dearomatizing electrocyclic ring-closure/aromatizing electrocyclic ring-opening sequence.
Three‐dimensional aliphatic fused and bridged rings are key pharmacophores in drugs and bioactive natural products. Here, we reported an organocatalytic visible‐light induced dearomative cycloaddition of (hetero)arenes, with organic light‐emitting diode material 4CzIPN or readily accessible thioxanthone as photocatalyst. A series of cyclobutane‐fused polycyclic structures and bridged bicyclo scaffolds were prepared in reasonable yields (27–99% yield) with medium to excellent diastereoselectivity (1.4:1 to>20:1 dr), predictable regioselectivity, good functional group compatibilities and broad substrate scopes. The combination of experimental and computational studies supported the energy transfer pathways.
When mono‐radical ipso‐cyclization of aryl sulfonamides tend to undergo Smiles‐type rearrangement through aromatization‐driven C−S bond cleavage, diradical‐mediated cyclization must perform in a distinct reaction pathway. It is interesting meanwhile challenging to tune the rate of C−S bond cleavage to achieve a chemically divergent reaction of (hetero) aryl sulfonamides in a visible‐light induced energy transfer (EnT) reaction pathway involving diradical species. Herein a chemically divergent reaction based on the designed indole‐tethered (hetero)arylsulfonamides is reported which involves a diradical‐mediated ipso‐cyclization and a controllable cleavage of an inherent C−S bond. The combined experimental and computational results have revealed that the cleavage of the C−S bond in these substrates can be controlled by tuning the heteroaryl moieties: a) If the (hetero)aryl is thienyl, furyl, phenanthryl, etc., the radical coupling of double dearomative diradicals (DDDR) precedes over C−S bond cleavage to afford cyclobutene fused indolines by double dearomative [2+2]‐cycloaddition; b) if the (hetero)aryl is phenyl, naphthyl, pyridyl, indolyl etc., the cleavage of C−S bond in DDDR is favored over radical coupling to afford biaryl products.
Dearomatization reactions are among the most efficient chemical processes, combining atom economy, stereospecificity and the ability to generate molecular complexity in a single step. Dearomative vinylation reactions provide a synthetic connection between readily available, simple aromatic starting materials and more unsaturated alkynes. The last decade has witnessed a steady increase in the development of transition metal-catalyzed dearomative vinylation methods of electron rich aromatic compounds with alkynes, providing new synthetic approaches to high-value building blocks and natural products. This review aims to serve as a comprehensive reference for work in transition metal-catalyzed dearomative vinylation reactions of electron rich aromatic compounds with alkynes.
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