Unusual Palladium-Catalyzed Cascade Arylation ofα,β-Unsaturated Phenyl Sulfones under Heck Reaction Conditions

Air Induced Phosphoryl Radical Mediated Stereoselective Hydrosulfonylation of Alkynes via Halogen Atom Transfer: Ingress of Z-Vinyl Sulfones

The phosphoryl radical is well-known to participate in addition reactions with alkenes/alkynes. Here, we report a novel reaction mode of the phosphoryl radical where it participates in halogen atom transfer (XAT) with electron deficient vinyl halides instead of a facile addition reaction. Nevertheless, in comparison with aryl and alkyl halides, the exploitation of vinyl halides into a carbon radical via XAT is quite rare. This protocol provides an opportunity for direct hydrosulfonylation of numerous internal as well as terminal alkynes to get various Z-vinyl sulfones under environmentally benign conditions. Generation of the phosphoryl radical in the open air, water as a solvent, excellent functional group compatibility, and exceptional chemoselectivity are the attractive features of the present methodology.

Intermolecular domino reaction of two aryl iodides involving two C-H functionalizations

A palladium-catalyzed intermolecular cross-coupling of two aryl iodides is reported, giving polycyclic ring systems with a high level of convergence and efficiency.

Palladium(II)-catalyzed C-H activation/C-C cross-coupling reactions: versatility and practicality

In the past decade, palladium-catalyzed C-H activation/C-C bond-forming reactions have emerged as promising new catalytic transformations; however, development in this field is still at an early stage compared to the state of the art in cross-coupling reactions using aryl and alkyl halides. This Review begins with a brief introduction of four extensively investigated modes of catalysis for forming C-C bonds from C-H bonds: Pd(II)/Pd(0), Pd(II)/Pd(IV), Pd(0)/Pd(II)/Pd(IV), and Pd(0)/Pd(II) catalysis. A more detailed discussion is then directed towards the recent development of palladium(II)-catalyzed coupling of C-H bonds with organometallic reagents through a Pd(II)/Pd(0) catalytic cycle. Despite the progress made to date, improving the versatility and practicality of this new reaction remains a tremendous challenge.

Understanding Sulfone Behavior in Palladium-Catalyzed Domino Reactions with Aryl Iodides

Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions takes place mainly by means of a four-component domino process, involving one unit of the alkene and three units of the aryl iodide, affording substituted 9-phenylsulfonyl-9,10-dihydrophenanthrenes. We report here the results of a computational study on the mechanism of this domino arylation reaction. Based on these results we can explain why vinyl sulfones, unlike other electron-deficient alkenes such as enones, preferentially follow this domino pathway instead of the usual Heck pathway. The key step is a C-H activation process in which a five-membered palladacycle is formed. The greater ability of vinyl sulfones, relative to enones, to reach the transition state that leads to the formation of the initial palladacycle makes the difference.