Unactivated CH3 groups in 2‐oxazolines are oxidized by inexpensive oxidants, such as tert‐butyl peroxyacetate and lauroyl peroxide, in the presence of a catalytic amount of Pd(OAc)2. Carboxylic anhydrides are essential for both the oxidation of the PdC bonds and regeneration of Pd(OAc)2. The use of [D6]Ac2O as the solvent shows that the acetyl group incorporated into the product is from acetic anhydride rather than the oxidant (see scheme).
A transition-metal-free method for the synthesis of C6 phenanthridine derivatives by arylative cyclization of 2-isocyanobiphenyls with arylamines in one pot was developed. Mechanistic studies suggest that electrophilic aromatic substitution (SEAr) of a nitrilium intermediate and homolytic aromatic substitution (HAS) of an imidoyl radical intermediate are two competitive reaction pathways involved in the annulation step.
Much attention has been paid to imidoyl radical-involved reactions in recent years. As a divergent reactive intermediate, imidoyl radicals are used for the synthesis of functionalized heterocycles, nitriles, imines, amines, etc. This review is intended to highlight some recent progress in the past decade.
A selective catalytic system for the dehydrogenation of primary alcohols to carboxylic acids using a facial ruthenium complex generated in situ from the [Ru(COD)Cl 2 ] n and a hybrid N-heterocyclic carbene (NHC)−phosphine− phosphine ligand (CPP) has been first reported. The facial coordination model was unveiled by NMR analysis of the reaction mixture. Such a fac-ruthenium catalyst system exhibited high catalytic activity and stability, and a high turnover number of 20 000 could be achieved with catalyst loading as low as 0.002 mol %. The exceedingly high catalyst stability was tentatively attributed to both the anchoring role of NHC and the hemi-lability of phosphines. The catalytic system also features a wide substrate scope. In particular, the facial coordination of CPP ligands was found to be beneficial for sterically hindered alcohols, and ortho-substituted benzylic alcohols and bulky adamantanyl methanol as well as cholesterol were all found to be viable dehydrogenation substrates.
The title reaction proceeds with acetylenic triflones and isocyanides under mild conditions using copper as a catalyst. This transformation provides an efficient access to (E)-N-alkyl trifluoromethyl alkynyl ketoimines, which are useful building blocks for the synthesis of CF3-containing N-heterocycles, propargylamines, etc.
A novel fluorescent probe based on the excited state intramolecular proton transfer mechanism for the detection of nitroxyl was developed for the first time.
A new strategy for the construction of phenanthridine and isoquinoline scaffolds, starting from arenes containing a pending isocyanide moiety under palladium catalysis, has been developed. This process involves sequential intermolecular isocyanide insertion to an aryl palladium(II) intermediate and intramolecular aromatic C-H activation as key steps. Alkyl palladium(II) intermediate lacking β-hydrogen is also applicable to this reaction, generating unique bisheterocyclic scaffolds with three C-C bonds being formed consecutively.
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