Direct synthesis of spirobifluorenes by formal dehydrative coupling of biaryls and fluorenones.

A Tf2O-mediated, direct dehydrative coupling of (hetero)biaryls and fluorenones proceeds to form the corresponding spirobifluorenes in good to high yields. The reaction system allows the relatively simple nonhalogenated and nonmetalated starting substrates to be directly adopted in the spirocyclisation reaction. In addition, the double cyclisation reaction is easily performed, giving the highly spiro-conjugated aromatic compounds of potent interest in materials chemistry. The preliminary optoelectronic properties of some newly synthesised compounds are also demonstrated.

Direct Synthesis of Benzoselenophene and Benzothiophene Derivatives from 1,1-Diarylethenes and Biaryls by Chalcogen Cation-Mediated Successive Bond Formation.

A Tf2O-mediated sequential C-Se bond-forming reaction of 1,1-diarylethenes and biaryls with methaneselenic acid has been developed. Upon demethylation workup with ethanolamine, the corresponding benzoselenophene derivatives are obtained directly. The related synthesis of benzothiophene derivatives with sodium methanesulfinate is also possible with the unique assistance of the ball milling technique. The active species is considered to be a highly electrophilic chalcogen cation, which enables successive bond formation even at room temperature.

One-Step Synthesis of Benzophosphole Derivatives from Arylalkynes by Phosphenium-Dication-Mediated Sequential C-P/C-C Bond Forming Reaction.

A metal-free, phosphenium-dication-mediated sequential C-P and C-C bond forming reaction has been developed. This protocol can provide concise access to the (di)benzophosphole derivatives in one synthetic operation from the readily available and simple arylalkynes and phosphinic acids. Application to the multiple cyclization reaction and the fully intermolecular three-component-coupling-type reaction are also described.

Palladium-catalysed C-H arylation of benzophospholes with aryl halides.

A palladium-catalysed C-H arylation of benzophospholes with aryl halides has been developed. The reaction with aryl iodides and bromides proceeds well even under phosphine ligand-free Pd(OAc)2 catalysis whereas the Pd(PCy3)2 is effective for the coupling with less reactive aryl chlorides. The optimal conditions are also applicable to the double arylations with organic dihalides and annulation reaction with ortho-dihalogenated benzenes, making the corresponding benzophosphole-based acceptor-donor-acceptor-type molecules and highly condensed heteroacene-type molecules of potent interest in materials chemistry. Although there are many reports of catalytic C-H functionalisations of related benzoheteroles such as indoles, benzothiophenes, and benzofurans, this is the first successful example of the catalytic direct C-H transformation of benzophospholes, to the best of our knowledge. The preliminary optoelectronic properties of some newly synthesized benzophosphole derivatives are also investigated.

Direct Synthesis of Dibenzophospholes from Biaryls by Double C-P Bond Formation via Phosphenium Dication Equivalents.

We have developed a new strategy for the generation of phosphenium dication equivalents from readily available phosphinic acids and Tf2O. The in situ-generated dication equivalents can be readily coupled with simple (hetero)biaryls to form the corresponding dibenzophospholes directly. This protocol can also be applied to the concise synthesis of six- and seven-membered phosphacycles as well as the largely π-extended heteroacene derivatives, which are of great interest in the field of organic functional materials.

Synthesis of Dibenzophospholes by Tf2O-Mediated Intramolecular Phospha-Friedel-Crafts-Type Reaction.

A Tf2O-mediated intramolecular phospha-Friedel-Crafts-type reaction of secondary biarylphosphine oxides has been developed. The reaction is promoted simply by Tf2O to form the corresponding dibenzophospholes under metal-free conditions. The starting substrates are readily available and easy-to-handle phosphine oxides, and the regioselectivity is controlled by the innate electronic nature. Thus, this newly developed protocol can provide concise and complementary approach to the highly π-conjugated dibenzophospholes of potent interest in material chemistry.

Phosphenium-Cation-Mediated Formal Cycloaddition Approach to Benzophospholes.

A phosphenium-cation-mediated formal [3+2]-cycloaddition reaction of internal alkynes is reported. The reaction proceeds under metal-free conditions to give the corresponding C-P rearranged benzophospholes regioselectively, even when ortho- and para-substituted arylphosphine oxides are starting substrates. Mechanistic studies by 31 P{1 H} NMR analysis suggest an involvement of three-membered phosphirenium cation species and C-P rearrangement prior to a ring closure for benzophosphole skeleton formation.