Stereoselective Palladium‐Catalyzed Carboaminoxylations of Indoles with Arylboronic Acids and TEMPO

Indoles are not indolent : Various indoles react with arylboronic acids chemodivergently. C? H arylation of free indole and N‐methylindole gives the corresponding C(2)‐arylated indoles A whereas N‐acylated, N‐benzoylated, and N‐Boc‐protected indoles provide the corresponding arylcarboaminoxylated products B with excellent diastereoselectivity in good to excellent yields.

     

Transition‐Metal‐Catalyzed Synthesis of Hydroxylated Arenes

An overview of the recent bibliography in the transition‐metal‐catalyzed hydroxylation of aryl derivatives is presented. Two reaction protocols are considered: 1) C? H activation/hydroxylation and, 2) cross‐coupling hydroxylation of aryl halides. The achievements and limitations for both procedures are described taking into consideration different metal catalyst/oxidant combinations.     

Investigation and Comparison of the Mechanistic Steps in the [(Cp*MCl2)2] (Cp*=C5Me5; M=Rh,Ir)‐Catalyzed Oxidative Annulation of Isoquinolones with Alkynes

The mechanism of the [(Cp*MCl₂)₂] (M=Rh, Ir)‐catalyzed oxidative annulation reaction of isoquinolones with alkynes was investigated in detail. In the first acetate‐assisted C? H‐activation process (cyclometalated step) and the subsequent mono‐alkyne insertion into the M? C bonds of the cyclometalated compounds, both Rh and Ir complexes participated well. However, the desired final products, dibenzo[a,g]quinolizin‐8‐one derivatives, were only formed in high yield when the Rh species participated in the final oxidative coupling of the C? N bond. Moreover, a Rh^I sandwich intermediate was isolated during this transformation. The iridium complexes were found to be inactive in the oxidative coupling processes. All of the relevant intermediates were fully characterized and determined by single‐crystal X‐ray diffraction analysis. Based on this mechanistic study, a Rh^III→Rh^I→Rh^III catalytic cycle was proposed for this reaction.     

Ruthenium‐Catalyzed α‐(Hetero)Arylation of Saturated Cyclic Amines: Reaction Scope and Mechanism

Transition‐metal‐catalyzed sp³ C? H activation has emerged as a powerful approach to functionalize saturated cyclic amines. Our group recently disclosed a direct catalytic arylation reaction of piperidines at the α position to the nitrogen atom. 1‐(Pyridin‐2‐yl)piperidine could be smoothly α‐arylated if treated with an arylboronic ester in the presence of a catalytic amount of [Ru₃(CO)₁₂] and one equivalent of 3‐ethyl‐3‐pentanol. A systematic study on the substrate and reagent scope of this transformation is disclosed in this paper. The effect of substitution on both the piperidine ring and the arylboronic ester has been investigated. Smaller (pyrrolidine) and larger (azepane) saturated ring systems, as well as benzoannulated derivatives, were found to be compatible substrates with the α‐arylation protocol. The successful use of a variety of heteroarylboronic esters as coupling partners further proved the power of this direct functionalization method. Mechanistic studies have allowed for a better understanding of the catalytic cycle of this remarkable transformation featuring an unprecedented direct transmetalation on a Ru^II? H species.