1,4-Difluoro-2,5-dimethoxybenzene as a Precursor for Iterative Double Benzyne−Furan Diels−Alder Reactions

Thermodynamically Stable o-Quinodimethane: Synthesis, Structure, and Reactivity

Thermal isomerization of cyclobutaphenanthrene to o-quinodimethane was investigated. Sterically congested substituents or electron-donating substituents on the four-membered ring promoted the ring-opening, affording o-quinodimethane in a relatively stable form. Isolation of the newly prepared o-quinodimethane allowed its structural elucidation and investigation of its potential reactivities. Dual [4+2] cycloaddition of an aryne and o-quinodimethane afforded tetrabenzopentacene, demonstrating the synthetic application of the isolated compound.

Anthranoxides as Highly Reactive Arynophiles for the Synthesis of Triptycenes

We report herein an efficient method to synthesize triptycenes by the reaction of benzynes and anthranoxides, which are electron-rich and readily prepared from the corresponding anthrones. Using this method, 1,9-syn-substituted triptycenes were regioselectively obtained employing 3-methoxybenzynes. This method was also applied to synthesize pentiptycenes. A DFT study revealed that the cycloaddition of lithium anthranoxide and benzyne proceeds stepwise.

Aryne-based strategy in the total synthesis of naturally occurring polycyclic compounds

This review has outlined the strategies and tactics of using arynes in the total syntheses of polycyclic natural products.

Synthesis of Octaaryl Naphthalenes and Anthracenes with Different Substituents

A synthesis of multiply arylated naphthalenes and anthracenes with eight different substituents has been accomplished. The key intermediates are tetraarylthiophene S-oxides, which are synthesized through a method involving sequential C-H arylation and cross-coupling from 3-methoxythiophene, followed by oxidation of the sulfur atom. The resulting tetraarylthiophene S-oxides can be converted into a tetraaryl benzynes or naphthalynes and then merged through [4+2] cycloaddition reaction with another tetraarylthiophene S-oxide, thereby resulting in the programmed synthesis of octaarylnaphthalenes and octaarylanthracenes.

Rapid access to substituted 2-naphthyne intermediates via the benzannulation of halogenated silylalkynes

A ZnCl₂-catalyzed, regioselective benzannulation of halogenated silylacetylenes provides access to 2-naphthyne precursors.

Aryne intermediates are versatile and important reactive intermediates for natural product and polymer synthesis. 2-Naphthynes are relatively unexplored because few methods provide precursors to these intermediates, especially for those bearing additional substituents. Here we report a general synthetic strategy to access 2-naphthyne precursors through an Asao-Yamamoto benzannulation of ortho-(phenylethynyl)benzaldehydes with halo-silylalkynes. This transformation provides 2-halo-3-silylnaphthalenes with complete regioselectivity. These naphthalene products undergo desilylation/dehalogenation in the presence of F^– to generate the corresponding 2-naphthyne intermediate, as evidenced by furan trapping experiments. When these 2-naphthynes are generated in the presence of a copper catalyst, ortho-naphthalene oligomers, trinaphthalene, or binaphthalene products are formed selectively by varying the catalyst loading and reaction temperature. The efficiency, mild conditions, and versatility of the naphthalene products and naphthyne intermediates will provide efficient access to many new functional aromatic systems.

Aryne multifunctionalization with benzdiyne and benztriyne equivalents

The applications of benzdiyne and benztriyne equivalents are summarized from the standpoint of synthetic organic chemistry as well as in the preparation of polycyclic aromatic functional frameworks.

Synthetic transformation of 1,3-diarylisobenzofuran-DMAD adducts: a facile preparation of tri-substituted α-naphthols

1,3-Diarylisobenzofuran-DMAD adducts upon reaction with BF₃·OEt₂ in DCM at room temperature underwent a regiospecific 1,2-aryl migration followed by the Krapcho decarboxylation to give tri-substituted α-naphthols in good yields.

Selective Halogen-Lithium Exchange of 1,2-Dihaloarenes for Successive [2+4] Cycloadditions of Arynes and Isobenzofurans

Successive [2+4] cycloadditions of arynes and isobenzofurans by site-selective halogen-lithium exchange of 1,2-dihaloarenes were developed, allowing the rapid construction of polycyclic compounds which serve as a useful synthetic intermediates for the preparation of various polyacene derivatives.

Synthetic Methods for the Generation and Preparative Application of Benzyne

Many methods have been developed for generating benzyne. Convenient and reliable precursors extensively studied so far involve benzenediazonium-2-carboxylate and o-dihalobenzenes such as 1,2-bromofluorobenzene and 1,2-dibromobenzene. Recently, in addition to the above precursors, o-(trimethylsilyl)phenyl triflate has been put into frequent use for benzyne reactions, in which benzyne is efficiently generated under mild conditions using fluoride ion. Furthermore, o-(trimethylsilyl)phenyliodonium triflate has been developed as a more efficient benzyne precursor. This mini-review focusses on recent progress in benzyne chemistry from the viewpoint of organic synthesis. The methods for generating benzynes are classified by the conditions into four categories: basic conditions using strong bases, mild conditions using fluoride ion, thermolysis, and oxidation.

Benzdiynes and Related Dehydroaromatics

Benzdiynes, which are more unsaturated than benzyne, were proposed as reactive intermediates in the pyrolyses of aromatic dianhydrides in 1966. The generation and direct observation of these highly unsaturated species has been an experimental challenge. More than 30 years later, the first direct observation of a benzdiyne, 1,4-bis(trifluoromethyl)-2,3,5,6-tetradehydrobenzene, was reported. We outline the progress in the generation and observation of benzdiynes as well as theoretical studies on the background of benzyne chemistry. Spectroscopic observation of the benzdiynes, in particular detection of an IR band due to the asymmetric stretching of the two triple bonds, in conjunction with quantum chemical computations reveals their multireference character. In connection with the studies for generating benzdiynes, the studies for generating bisarynes with extended π-systems and the most highly unsaturated cyclic C6 are briefly reviewed.

Simple molecule-based fluorescent sensors for vapor detection of TNT

1,4-Diarylpentiptycenes (1a-e) were synthesized from 1,4-dichloro- or 1,4-difluoro-2,5-diarylbenzene derivatives by double base-promoted dehydrohalogenation to give corresponding arynes, which in the presence of anthracene undergo cycloaddition providing 1,4-diarylpentiptycenes in moderate overall yields. The resulting 1,4-diarylpentiptycenes show fluorescence modulated by the 1,4-aryl residues. The fluorescence is quenched in the presence of vapors of nitroaromatic compounds suggesting potential application in sensing of explosives.

Iterative benzyne-furan cycloaddition reactions: studies toward the total synthesis of ent-Sch 47554 and ent-Sch 47555

[reaction: see text] 7-Fluoro-5,8-dimethoxy-1-naphthol, prepared from the lithiation and benzyne formation from 1,4-difluoro-2,5-dimethoxybenzene and Diels-Alder cycloaddition with furan, was sequentially C-glycosidated under Suzuki conditions and O-glycosidated using di-O-acetyl-L-rhamnal to provide the corresponding beta-naphthyl C,O-disaccharide. Further lithiation, benzyne formation, and cycloaddition with furan gave an oxa-bridged 1,4-dihydroanthracenyl C,O-disaccharide, a model compound relevant to the total synthesis of Sch 47555.

Highly Convergent Three Component Benzyne Coupling: The Total Synthesis of ent-Clavilactone B

The first total synthesis of (+)-clavilactone B, a potent antifungal agent and novel tyrosine kinase inhibitor, is described. The absolute configuration of clavilactones has been unambiguously established by using Sharpless asymmetric epoxidation to generate the enantiomerically pure substrate. The strategy highlights the use of a powerful and convergent three-component benzyne coupling with a methylallyl Grignard and a chiral epoxy-aldehyde to generate two C-C bonds and install the carbon skeleton of clavilactone. Oxidative lactonization, ten-membered ring construction by ring closing metathesis, and oxidation gave clavilactone B.