Sulfoxide-directed metal-free cross-couplings in the expedient synthesis of benzothiophene-based components of materials.

A metal-free approach combining sulfoxide-directed metal-free C-H cross-couplings with tuneable electrophile-mediated heterocyclizations and carbocyclative dimerizations, allows expedient access to benzothiophene-based systems that are components of important materials or are proven organic materials in their own right. As benzothiophene-based materials are typically prepared using Pd-catalyzed cross-coupling processes, our approach allows potential issues of metal cost and supply, and metal-contamination of products, to be avoided.

Sulfoxide-Directed Metal-Free ortho-Propargylation of Aromatics and Heteroaromatics.

A sulfoxide-directed, metal-free ortho-propargylation of aromatics and heteroaromatics exploits intermolecular delivery of a propargyl nucleophile to sulfur followed by an intramolecular relay to carbon. The operationally simple cross-coupling procedure is general, regiospecific with regard to the propargyl nucleophile, and shows complete selectivity for products of ortho-propargylation over allenylation. The use of secondary propargyl silanes allows metal-free ortho-coupling to form carbon-carbon bonds between aromatic and heteroaromatic rings and secondary propargylic centres. The 'safety-catch' nature of the sulfoxide directing group is illustrated in a selective, iterative double cross-coupling process. The products of propargylation are versatile intermediates and they have been readily converted into substituted benzothiophenes.

Palladium(II)-catalyzed oxidative arylation of quinoxalin-2(1H)-ones with arylboronic acids.

A straightforward palladium-catalyzed oxidative C-3 arylation of quinoxalin-2(1H)-ones with arylboronic acids is reported. This protocol is compatible with a wide range of functional groups and allows construction of various biologically important quinoxalin-2(1H)-one backbones.

Palladium-catalyzed direct arylation of polysubstituted benzofurans.

An efficient access to 2-substituted 3-arylbenzofurans through a palladium-catalyzed C3 direct arylation of 2-substituted benzofurans with aryl bromides is described. The scope and limitation of this reaction was studied. The method tolerates a variety of functional groups on the aryl halide and has been successfully extended to polysubstituted benzofurans to obtain the corresponding 3-arylbenzofurans with good to excellent yields.

Synthesis of 3-aryl-2-arylamidobenzofurans based on the Curtius rearrangement.

The synthesis of novel 3-aryl-2-arylamidobenzofurans has been accomplished via a Curtius rearrangement strategy in four steps from benzofuran-2-carboxylic acids. The requisite Suzuki-Miyaura cross-coupling, with benzyl 3-bromobenzofuran-2-ylcarbamate or 2-arylamido-3-bromobenzofurans, revealed an unusual reductive debromination process due to the presence of the free NH group. This dehalogenation can be suppressed by N-alkylation. DMAP is an efficient reagent for the one-pot conversion of benzyl benzofuran-2-ylcarbamates into the corresponding benzofuran-2-arylamides through aroylation, thus acting both as an acyl transfer reagent and a deprotecting agent of the Cbz group. A mechanism is postulated.