A Convenient Synthesis of N‐Aryl Benzamides by Rhodium‐Catalyzed ortho‐Amidation and Decarboxylation of Benzoic Acids

The rhodium‐catalyzed amidation of substituted benzoic acids with isocyanates by directed C?H functionalization followed by decarboxylation to afford the corresponding N‐aryl benzamides is demonstrated, in which the carboxylate serves as a unique, removable directing group. Notably, less common meta‐substituted N‐aryl benzamides are generated readily from more accessible para‐ or ortho‐substituted groups by employing this strategy.     

Highly Regio‐ and Stereoselective Hydrosilylation of Alkynes Catalyzed by Tridentate Cobalt Complexes

Several cobalt complexes bearing tridentate (NNN) ligands were synthesized and served as precatalysts for alkyne hydrosilylation with Ph₂SiH₂. For terminal alkynes, the catalyst L2 b‐CoCl₂ was selected, and resulted in the corresponding α‐vinylsilanes with high (Markovnikov) regioselectivity and extensive functional‐group tolerance. For internal diaryl alkynes, the catalyst L2 c‐CoCl₂ exhibited the best activity, and afforded E‐selective vinylsilanes through syn‐addition in excellent yield under mild conditions.     

Inner-Sphere Oxygen Activation Promoting Outer-Sphere Nucleophilic Attack on Olefins

Alkoxylation and hydroxylation reactions of 1,5-cyclooctadiene (cod) in an iridium complex with alcohols and water promoted by the reduction of oxygen to hydrogen peroxide are described. The exo configuration of the OH/OR groups in the products agrees with nucleophilic attack at the external face of the olefin as the key step. The reactions also require the presence of a coordinating protic acid (such as picolinic acid (Hpic)) and involve the participation of a cationic diolefin iridium(III) complex, [Ir(cod)(pic)₂]⁺, which has been isolated. Independently, this cation is also involved in easy alkoxy group exchange reactions, which are very unusual for organic ethers. DFT studies on the mechanism of olefin alkoxylation mediated by oxygen show a low-energy proton-coupled electron-transfer step connecting a superoxide–iridium(II) complex with hydroperoxide–iridium(III) intermediates, rather than peroxide complexes. Accordingly, a more complex reaction, with up to four different products, occurred upon reacting the diolefin–peroxide iridium(III) complex with Hpic. Moreover, such hydroperoxide intermediates are the origin of the regio- and stereoselectivity of the hydroxylation/alkoxylation reactions. If this protocol is applied to the diolefin–rhodium(I) complex [Rh(pic)(cod)], free alkyl ethers ORC₈H₁₁ (R=Me, Et) resulted, and the reaction is enantioselective if a chiral amino acid, such as l -proline, is used instead of Hpic.     

Another characterization of homogeneous Poisson processes

For a general renewal process N (allowing delay, defect and multiple simultaneous arrivals) the independence of the first renewal epochs of the marked processes got from N by Bernoulli 0/1 thinning is characterized. This independence is well-known to hold true in the case of homogeneous Poisson processes; by way of corollary one obtains the interesting observation that, when coupled with some minimal extra conditions, it in fact already identifies them. The proof is analytic in character.     

Arene‐Limited Nondirected C−H Activation of Arenes

The nondirected C(sp²)−H activation of simple arenes has advanced significantly in recent years through the discovery of new catalyst systems that are able to perform transformations with the arene as the limiting reagent. Important developments in catalyst and ligand design that have improved reactivity and selectivity are reviewed.     

On methods for converting exhausters of positively homogeneous functions

In the paper we develop a method for converting a (not necessarily uniformly bounded) upper (lower) primal exhauster of a continuous positively homogeneous function to a lower (upper) primal exhauster of the same function. The method is based on representation of a continuous positively homogeneous function as a pointwise supremum (infimum) of an one-parameter monotone family of Lipschitz continuous positively homogeneous functions that is of independent interest.     

Copper‐Catalyzed Reaction Cascade of Thiophenol Hydroxylation and S‐Arylation through Disulfide‐Directed C−H Activation

Copper‐catalyzed thiophenol C?H activation is described. Through an initial attempt to conduct C‐arylation with arylboronic acid, a rather surprising sequential C?H activation and S‐arylation was discovered. Mechanistic investigation revealed the disulfide intermediate as the key component in directing C?H oxidation. The overall reaction proceeded under mild conditions with molecular oxygen as the oxidant. Discovery of disulfide as the directing group provides a potential new direction for catalytic C?H functionalization under mild conditions.     

Photomechanical Actuation of Ligand Geometry in Enantioselective Catalysis

A catalyst that couples a photoswitch to the biaryl backbone of a chiral bis(phosphine) ligand, thus allowing photochemical manipulation of ligand geometry without perturbing the electronic structure is reported. The changes in catalyst activity and selectivity upon switching can be attributed to intramolecular mechanical forces, thus laying the foundation for a new class of catalysts whose selectivity can be varied smoothly and in situ over a useful range by controlling molecular stress experienced by the catalyst during turnover. Forces on the order of 100 pN are generated, thus leading to measurable changes in the enantioselectivities of asymmetric Heck arylations and Trost allylic alkylations. The differential coupling between applied force and competing stereochemical pathways is quantified and found to be more efficient for the Heck arylations.