Catalytic cross-coupling reactions in biaryl synthesis

Fast, easy, clean chemistry by using water as a solvent and microwave heating: the Suzuki coupling as an illustration

Symmetrical biaryls are formed from arylboronic acids both under tetrakis(triphenylphosphine)palladium and under palladium(II) acetate catalysis. The principal mechanistic features of these self-couplings have been determined.

Palladium-Catalyzed Suzuki-Type Self-Coupling of Arylboronic Acids. A Mechanistic Study

A versatile method for the synthesis of complex, fused polycyclic aromatic systems in high chemical yield is described. Construction is achieved using a general two-step synthetic sequence. Pd-catalyzed Suzuki and Negishi type cross-coupling chemistries allow for the preparation of nonfused skeletal ring systems in yields consistently >80%. The critical ring-forming step, which generally proceeds in very high to quantitative yield, utilizes 4-alkoxyphenylethynyl groups and is induced by strong electrophiles such as trifluoroacetic acid and iodonium tetrafluoroborate. The reaction in essence produces phenanthrene moieties which are integrated into extended polycyclic aromatic structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepared utilizing this methodology. The scope of the described cross-coupling/cyclization chemistry including mechanistic insights and problematic side reactions are described.

http://web.mit.edu/tswager/Desktop/tswager/www/Papers/050-PolycyclicAromatics.pdf

Directed Electrophilic Cyclizations - Efficient Methodology for the Synthesis of Fused Polycyclic Aromatics

The aryl−aryl interchange reaction of ArPdL2I complex 1m was found to follow pseudo-first-order kinetics. A marked inhibition in the presence of excess phosphine and/or excess iodide was observed, suggesting that a dissociative pathway was involved, contrary to the analogous alkyl−aryl interchange reaction studied previously. Phosphine flooding experiments could not be performed due to a competing phosphonium salt formation reaction that occurred in the presence of excess phosphine. A deuterium labeling experiment indicated that the interchange reaction proceeded via the reductive elimination to form the phosphonium salt, suggesting that excess phosphine was acting as a trap for intermediate palladium(0) species preventing the generation of the interchanged palladium(II) complex. Substituent effect studies of the interchange reaction indicated that it was inhibited by electron-withdrawing groups on both the phosphine and palladium-bound aryl groups and by increased steric bulk on both the phosphine and pa...

Mechanistic Studies on the Aryl−Aryl Interchange Reaction of ArPdL2I (L = Triarylphosphine) Complexes

Palladium catalysed coupling of halobenzenes with arylboronic acids: Rôle of the triphenylphosphine ligand

Oxidation of the two DANA (2-deoxy-2,3-didehydro-N-acetylneuraminic acid) derivatives (3) and (4) by using several reagents has led to the isolation of the first sialic acid derivative (1) containing a γ-pyrone moiety.

David F. O'Keefe

Papers

Palladium catalysed coupling of halobenzenes with arylboronic acids: Rôle of the triphenylphosphine ligand

Synthesis of the First Sialic Acid Analogue Containing a y-Pyrone Moiety