40012-82-6

High-valent cobalt carbene Co(OR)2(CPh2) (OR = OCtBu2Ph) undergoes reaction with various isocyanides CNR (CNR = 2,6-dimethylphenyl isocyanide, 4-methoxyphenyl isocyanide, 2-chloro-6-methylphenyl isocyanide, adamantyl isocyanide) to yield the corresponding ketenimine. The reaction is accompanied by the formation of cobalt bis(alkoxide) bis(isocyanide) complexes Co(OR)2(CNR)2, which were independently synthesized and characterized. DFT calculations suggest the mechanism proceeds through isocyanide binding to Co, followed by intramolecular insertion into the Co-carbene bond to form the ketenimine. We have also conducted an investigation of the catalytic formation of ketenimines at room temperature using mixtures of diazoalkanes (diphenyldiazomethane, methyl diazo(phenyl)acetate, and ethyl diazoacetate) and isocyanides (2,6-dimethylphenyl isocyanide, 4-methoxyphenyl isocyanide, adamantyl isocyanide, cyclohexyl isocyanide, and benzyl isocyanide). While no catalytic reactivity was observed for diphenyldiazomethane, ester-substituted diazoalkanes (diazoesters) demonstrate catalytic turnover. Relatively high yields are observed for the reactions involving bulkier aliphatic substrates adamantyl and cyclohexyl isocyanides. Mechanistic studies suggest that the lack of catalytic reactivity involving diphenyldiazomethane results from the inability of Co(OR)2(CNR)2 to undergo carbene formation upon reaction with N2CPh2. In contrast, facile reaction is observed between Co(OR)2(CNR)2 and diazoesters, which enables the overall catalytic reactivity.

Rhodium-catalyzed C-H activation/annulation reactions of ketenimines with N-methoxybenzamides furnished 3-aminoisoindolin-1-ones and 3-(diarylmethylene)isoindolin-1-ones. The synthesized 3-(diarylmethylene)isoindolin-1-ones exhibited aggregation induced emissions in aqueous tetrahydrofuran solution and strong green-yellow emissions in solids.

From readily available propargylic amines, 1,2,5-trisubstituted imidazoles are efficiently obtained through a cascade reaction catalyzed by AgOTf or promoted by molecular iodine. The AgOTf-catalyzed reaction involves nucleophilic addition of propargylic amine to ketenimine, a silver-catalyzed electrophilic cyclization reaction of alkyne, and a tautomerism/isomerism/metal-H exchange cascade. The iodine-mediated counterpart yields 5-formyl-1,2-disubtituted imidazoles, which presumably includes a cascade hydrolysis/oxidation reaction. Furthermore, the presented protocol can be scaled up and the resultant 1,2,5-trisubstituted imidazole can be converted into fused indeno[1,2-d]imidazole. 1,2,5-Trisubstituted imidazoles are efficiently prepared from readily available propargylic amines through a AgOTf-catalyzed or molecular iodine-promoted cascade reaction. The presented protocol can be scaled up and the resultant 1,2,5-trisubstituted imidazoles can be converted into fused indeno[1,2-d]imidazoles.

Ketenimines were conveniently synthesized from N-monosubstituted thioacetamides with dehydrating agents such as 2-chloro-1,3- dimethylimidazolinium chloride or 2-chloro-1-methylpyridinium iodide.