Tertiary Carbinamine Synthesis by Rhodium‐Catalyzed [3+2] Annulation of N‐Unsubstituted Aromatic Ketimines and Alkynes

A convenient and waste‐free synthesis of indene‐based tertiary carbinamines by rhodium‐catalyzed imine/alkyne [3+2] annulation is described. Under the optimized conditions of 0.5–2.5 mol % [{(cod)Rh(OH)}₂] (cod=1,5‐cyclooctadiene) catalyst, 1,3‐bis(diphenylphosphanyl)propane (DPPP) ligand, in toluene at 120 °C, N‐unsubstituted aromatic ketimines and internal alkynes were coupled in a 1:1 ratio to form tertiary 1H‐inden‐1‐amines in good yields and with high selectivities over isoquinoline products. A plausible catalytic cycle involves sequential imine‐directed aromatic C? H bond activation, alkyne insertion, and a rare example of intramolecular ketimine insertion into a Rh^I–alkenyl linkage.     

Rhodium(III)-Catalyzed Dehydrogenative Heck Reaction of Salicylaldehydes

Your CHOice! An efficient Rh(III) -catalyzed dehydrogenative Heck reaction (DHR) of salicylaldehydes with different classes of olefins extends the oxidative Heck reaction to aldehyde C?H bonds. Several structural motifs similar to natural products and bioactive molecules such as aurones, flavones, 2'-hydroxychalcones, and flavanones could be efficiently produced. Initial mechanistic studies give insight into the reaction mechanism.     

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.