January 2024

Herein, we report a regioselective cycloaddition strategy of N-aminopyridinium ylides with electron-deficient alkenes, in the presence of a hypervalent iodine reagent, PhI(OAc)2. A variety of multifunctionalized pyrazolo[1,5-a]pyridine architectures were smoothly afforded by the reactions of pyridine-, quinoline-, and isoquinoline-based N-ylides with diverse alkenes with or without a halogen atom adjacent to the electron-withdrawing group (EWG) under facile conditions.

We have revisited the imine-anion-mediated Smiles rearrangement for the synthesis of ortho-hydroxyphenyl arylketimines. Detailed examinations revealed that migration of various aromatic groups, previously considered to be unsuited to SNAr-type reactions, such as electron-rich or sterically hindered aromatic groups, can be accomplished by introducing bulky 9-anthryllithium as a nucleophile. Among the aromatic groups examined, naphthyl groups (1- and 2-naphthyl groups) exhibited an excellent performance, and their migration ability was well illustrated by the reaction with less bulky nucleophiles.

Control of radical reactivity is regarded as an important concern in the fields of catalysis and materials sciences. Radical species generated from monoruthenium acetylide complexes are, in general, highly reactive, and therefore structural characterization of these species has remained elusive. In this paper, a spectroscopic and structural characterization of the cationic radical species of a monoruthenium diacetylide bearing a Ru tetraphosphine fragment, [trans-(Ar–SC≡C)2Ru(dppe)2]SbCl6 ([1]+SbCl6) [Ar: p-t-BuC6H4; dppe: 1,2-bis(diphenylphosphino)ethane], is presented. The formation of the radical species [1]+ is supported by the vis-NIR, IR, and ESR studies. Furthermore, the solid-state structure of [1]+ reveals a significant contribution of the cumulenic Ru=C=C=S resonance structure. Remarkably, the thermal stability of [1]+ results from the incorporation of the electron-donating (arylsulfanyl)ethynyl ligands and the highly sterically demanding dppe ligands as compared with a monoruthenium complex with less-bulky and less-electron-rich derivatives.