Pd-Catalyzed cross-coupling synthesis of 4-aryl-3-formylcoumarins.

The threefold cross-coupling of triarylbismuth reagents with 4-chloro-3-formylcoumarins furnished the corresponding 4-aryl-3-formylcoumarins in a chemoselective manner with high yields under Pd-catalyzed conditions. This method was successfully applied to electronically different triarylbismuth reagents and 4-chloro-3-formylcoumarins preserving the 3-formyl group in the coumarin scaffold.

Rearrangement-Driven Molecular Diversity: Synthesis of Functionalized Pyrones, Orthoesters, and Xanthones from Spiroketals.

The reaction of tricyclic 5,5-benzannulated spiroketals with trifluoroacetic acid (TFA) and AlCl furnished benzopyranobenzopyrans, benzofuro-orthoesters, and benzofuroxanthones. Whereas the reaction of tricyclic 5,5-benzannulated spiroketals with TFA produced the pyrones, the reaction with AlCl furnished densely functionalized orthoesters and xanthones. The formation of these products was rationalized by fascinating mechanistic pathways involving semipinacol/α-ketol molecular rearrangements.

Copper-catalyzed synthesis of 1-(2-benzofuryl)-N-heteroarenes from -hydroxy--(dibromovinyl)benzenes and N-heteroarenes.

An efficient method for the synthesis of 1-(2-benzofuryl)-N-heteroarenes is developed from -hydroxy--(dibromovinyl)benzenes and N-heteroarenes under copper-catalyzed tandem reaction conditions. This methodology displayed a broad substrate scope and high yields in the preparation of a variety of 1-(2-benzofuryl)-N-heteroarenes. Further, 1-(2-benzofuryl)-N-heteroarenes were also applied in the synthesis of polycyclic benzofuro-indolo-pyridine scaffolds under palladium-catalyzed dehydrogenative coupling conditions.

Copper-catalyzed domino synthesis of ynamines.

The hitherto unexplored -alkynylation of electron-withdrawing or protecting group free N-heteroarenes such as indole, carbazole and pyrrole was developed using -dibromoalkenes to synthesize ynamines under ligand-free copper-catalyzed domino conditions. The development methodology of ynamines was also applied in the synthesis of enynamines, multi-coupled bis-ynamines, tris-ynamines, and the natural product peyonine, demonstrating its broad synthetic scope and applications.

De Novo Synthesis of Tricyclic 5,5-Benzannulated Spiroketals.

The synthesis of tricyclic 5,5-benzannulated spiroketal scaffolds was accomplished from 2'-hydroxyacetophenones and -dibromoalkenes involving a one-pot domino strategy. The hitherto unknown transformation afforded the tricyclic 5,5-benzannulated spiroketals as single diastereomers in high yields with a broad substrate scope.

Rh-Catalyzed aldehydic C-H alkynylation and annulation.

Novel Rh-catalyzed aldehydic C-H bond alkynylation and annulation for the in situ synthesis of chromones and aurones are described. It involves the sequential aldehyde C-H bond alkynylation of salicylaldehyde with in situ generated 1-bromoalkyne from 1,1-dibromoalkene followed by annulation. This protocol shows good functional group tolerance including aryl, alkenyl, alkyl and heteroaryl-1,1-dibromoalkenes.

Rh-Catalyzed domino synthesis of 4-hydroxy-3-methylcoumarins via branch-selective hydroacylation.

A Rh-catalyzed domino synthesis of 4-hydroxy-3-methylcoumarins via branch-selective hydroacylation of acrylates and acrylamides using salicylaldehydes is described. This protocol under phosphine-free Rh-catalyzed conditions provided 4-hydroxy-3-methylcoumarins in high yields with excellent functional group tolerance and high selectivity.

Rh-Catalyzed Deformylative Coupling of Salicylaldehydes with Acrylates and Acrylamides.

An unprecedented deformylative coupling of salicylaldehydes to acrylates and acrylamides under Rh-catalyzed conditions is reported. These deformylative couplings afforded o-hydroxycinnamates and o-hydroxycinnamamides with broad functional group tolerance and high chemoselectivity under milder reaction conditions.

Functional group manoeuvring for tuning stability and reactivity: synthesis of cicerfuran, moracins (D, E, M) and chromene-fused benzofuran-based natural products.

The protecting group manoeuvring as a strategy was applied for tuning the stability and reactivity of 4-(2,2-dibromovinyl)benzene-1,3-diol (12a) and 6-(2,2-dibromovinyl)-2,2-dimethylchroman-7-ol (22) in the domino synthesis of benzofuran-based natural products (1-8). The functional group demands and their impact on the reactivity driven by electronic effects were successfully managed by varying the protecting groups with substituted gem-dibromovinylphenols in domino couplings and triarylbismuth reagents under palladium-catalyzed conditions. This approach paved the way for the synthesis of moracin M (1) and cicerfuran (2), and the first time synthesis of moracin D (3) and moracin E (4) along with chromene-fused benzofuran-based natural products (5-8) in overall good yields.

Rapid regio- and multi-coupling reactivity of 2,3-dibromobenzofurans with atom-economic triarylbismuths under palladium catalysis.

A regio- and chemoselective cross-coupling study using 2,3-dibromobenzofurans and 2,3,5-tribromobenzofuran was achieved with sub-stoichiometric loadings of triarylbismuths as atom-economic reagents under Pd-catalyzed conditions. As part of this study, various 2,3-diaryl- and 2,3,5-triarylbenzofuran products were obtained in high yields, involving one-pot operations and short reaction times.

Transition-metal catalyzed C-C bond formation using organobismuth compounds.

Organobismuth(III) and organobismuth(V) compounds have been used in a variety of C-C bond forming reactions using transition-metal catalysis. Triarylbismuths are the most often used reagents among organobismuth reagents. All three aryl groups of triarylbismuths are potentially used in C-C bond formation, as shown in a number of reactions.

Pd-catalyzed domino synthesis of internal alkynes using triarylbismuths as multicoupling organometallic nucleophiles.

The domino coupling reaction of 1,1-dibromo-1-alkenes with triarylbismuth nucleophiles has been demonstrated to furnish disubstituted alkynes directly under catalytic palladium conditions. The couplings of triarylbismuths as multicoupling nucleophiles with 3 equiv of 1,1-dibromo-1-alkenes are very fast, affording high yields of alkynes in a short reaction time. Thus, an efficient domino process has been accomplished using 1,1-dibromo-1-alkenes as surrogates for internal alkyne synthesis in couplings with triarylbismuths in a one-pot operation.

Self-assembly of double stranded dinuclear titanium(IV)-Schiff base complexes and formation of intramolecular mu-oxo bridges.

The reaction of titanium isopropoxide with a Schiff base ligand containing an isobutenyl linker leads to double stranded dinuclear titanium(IV)-Schiff base complexes through self-assembly with concomitant formation of intramolecular mu-oxo bridges upon hydrolysis.