Catalytic [2 + 2 + 2] Cycloaddition of Benzothiophene Dioxides with α,ω-Diynes for the Synthesis of Condensed Polycyclic Compounds

Tf2O/2-Chloropyridine-Triggered Synthesis of Benzo[b]thiophene 1,1-Dioxides from Sulfonium α-Acyl Sulfonylmethylides

Triflic anhydride and 2-chloropyridine-comediated tandem activation, intramolecular aromatic electrophilic addition, and 1,2-sulfonyl shift via spirocyclic intermediates of sulfonium α-acyl sulfonylmethylides realize the efficient synthesis of 2-alkyl/arylthiobenzo[b]thiophene 1,1-dioxides. The deactivated sulfonyl group determines the site-selectivity of the electrophilic addition via the ipso-attack, while the following S-migration controls the regioselectivity. Some of 2-methylthiobenzo[b]thiophene 1,1-dioxides show fluorescence properties in the solid state and in their solutions.

Benzannulation and Hydrocarboxylation Methods for the Synthesis of a Neopentylene-Fused Analogue of Ibuprofen

Neopentylene ring fusions (ring-fused 4,4-dimethylcyclopentane polycycles) are found in many natural products, but they are largely absent from synthetic compound libraries and focused medicinal chemistry research. Here is reported a synthetic approach to one of the few non-natural product-based target compounds from medicinal chemistry that includes a neopentylene ring fusion: an analogue of ibuprofen referred to herein as "neoprofen". The approach features ring-opening fragmentation reactions of dimedone derivatives coupled with transition metal-catalyzed benzannulation and hydrocarboxylation methods.

Diastereoselective [2+2+1] Hydrative Annulation of Phenol-Linked 1,6-Enynes with Acetylenes Through Rhodium Catalysis: A Rapid Access to Cyclopenta[b]benzofuranols

An unprecedented [2+2+1] hydrative annulation of 1,6-enynes with terminal alkynes is achieved using catalytic cationic Rh(I). Thus, a modular assembly of cyclopenta[b]benzofuranols with two consecutive quarternary stereocenters is achieved from readily available alkynes. The reaction is proposed to go through a sequence of 5-membered rhoda-cycle formation, regioselective acetylene insertion, 1,5 H-shift, substrate controlled stereoselective addition of water molecule followed by 1,2-rhodium migration gave contracted rhoda-cycle D and reductive elimination. Necessary control/labelling experiments were conducted to gain insight in to the mechanism.

Rh(III)-Catalyzed Oxidative C-2 Coupling of N-Pyridinylindoles with Benzo[b]thiophene 1,1-Dioxides via C-H Bond Activation

An efficient Rh(III)-catalyzed cross-dehydrogenative coupling of N-pyridinylindoles with benzo[b]thiophene 1,1-dioxides has been developed through directing-group-assisted C-H activation. This transformation constructs a new C-C bond from two inert C-H bonds in a one-pot reaction. The present reaction is compatible with various functional groups with respect to indoles and benzothiophene[b] 1,1-dioxides. Furthermore, the emission properties of synthesized compounds have been explored.

Rh-Catalyzed [2 + 2 + 2] Cycloadditions with Benzoquinones: De Novo Access to Naphthoquinones for Lignan and Type II Polyketide Synthesis

The first examples of Rh-catalyzed [2 + 2 + 2] cycloadditions between diynes and benzoquinones are described. The method enables de novo and step-economical access to challenging naphthoquinones that are of relevance to lignan and type II polyketide synthesis. The value of the chemistry is demonstrated by a short total synthesis of justicidone.

Diels–Alder reaction of tetraarylcyclopentadienones with benzo[b]thiophene S,S-dioxides: an unprecedented de-oxygenation vs. sulfur dioxide extrusion

The Diels–Alder adduct, dihydrodibenzothiophene S,S-dioxides underwent aromatization either through de-oxygenation or extrusion of sulfur dioxide to furnish substituted dibenzothiophenes or benzenes.

Facile Synthesis of Dibenzotetracenedione Derivatives by Rhodium-Catalyzed [2+2+2] Cycloaddition/Spontaneous Aromatization

It has been established that a cationic rhodium(I)/SEGPHOS complex catalyzes the [2+2+2] cycloaddition of biphenyl-linked 1,7-diynes with 1,4-naphthoquinone and anthracene-1,4-dione. Conveniently, spontaneous aromatization proceeded upon removal of the rhodium complex by passing the reaction mixture through an alumina column, to give the corresponding dibenzotetracenediones and dibenzopentacenediones, respectively, in good yields. The obtained dibenzotetracenedione could be readily transformed into the corresponding dibenzotetracene in good yield. This dibenzotetracene showed blue fluorescence with a good quantum yield, which was significantly higher than those of tetracene, tetrabenzotetracene, and hexabenzotetracene.

Direct construction of 2,3-unsubstituted benzofurans and benzothiophenes via a metal-free catalyzed intramolecular Friedel–Crafts reaction

A highly effective and straightforward method for the construction of 2,3-unsubstituted benzofurans and benzothiophenes has been developed.

Double SO2 Insertion into 1,7-Diynes Leading to Functionalized Naphtho[1,2-c]thiophene 2,2-dioxides

A novel metal-free double SO₂ insertion/multicomponent bicyclization cascade of benzene-linked 1,7-diynes has been established by treatment with aryldiazonium tetrafluoroborates and DABCO-bis(sulfur dioxide) under redox-neutral conditions, providing a range of dual sulfone-containing naphtho[1,2-c]thiophene 2,2-dioxides with generally high stereoselectivity. The reaction pathway is proposed to proceed through the sequence of arylsulfonyl-radical-induced 6-exo-dig/5-endo-trig bicyclization, H-abstraction, and diazotization.

Rhodium-Catalyzed Asymmetric [2 + 2 + 2] Cycloaddition of α,ω-Diynes with Unsymmetrical 1,2-Disubstituted Alkenes

It has been established that a cationic rhodium(I)/axially chiral biaryl bisphosphine complex catalyzes the asymmetric [2 + 2 + 2] cycloaddition of α,ω-diynes with electron-rich and unstrained unsymmetrical 1,2-disubstituted alkenes to give chiral multicyclic compounds with good yields and ee values. Interestingly, enantioselectivity highly depends on the structures of α,ω-diynes used presumably due to the presence of two distinct reaction pathways.