Ruthenium(II)‐Catalyzed C−H/N−H Alkyne Annulation of Nonsymmetric Imidazoles: Mechanistic Insights by Computation and Photophysical Properties

Abstract

Imidazoles constitute an important class of heterocyclic compounds with extensive potential use, from pharmaceuticals to optoelectronics. However, synthetic methodologies capable of producing novel nonsymmetric imidazoles are still scarce. In a combined synthesis, photophysical and computational investigation, we show that ruthenium(II) catalysis enables C−H/N−H alkyne annulation of nonsymmetric imidazoles derived from naturally occuring β‐lapachone and nor‐β‐lapachone. This method provides an efficient and versatile tool for synthesizing fluorescent compounds with a broad application range.

DLPNO-CCSD(T) and DFT study of the acetate-assisted C–H activation of benzaldimine at [RuCl2(p-cymene)]2: the relevance of ligand exchange processes at ruthenium(ii) complexes in polar protic media

“…In particular, PCM and SMD solvation models have been successfully employed to investigate many ruthenium( ii )-catalyzed C–H activation and functionalization processes in almost all kinds of solvents (as 2-MeTHF, dioxane, toluene, DCE, acetonitrile, MeOH, TFE, tert -butanol, HFIP, or AcOH). 12–33 Nevertheless, the suitability of implicit solvent models for the study of ionic reactions that are performed in protic solvents is still controversial, as strong, specific, solvent–solute H-bonding interactions are seemingly ignored. These kinds of directed interactions are not captured by the CPCM and SMD models and this deficiency could compromise the accuracy of our results.…”

“…Most of the current knowledge of the mechanism of carboxylate-assisted C–H activations by ruthenium( ii ) complexes is based on computational evidence. 17 DFT studies covering the reactions of phenylpyrazoles, 18 benzylamines, 19 phenylpyridines, 20 N -aryl-oxazolidinones, 21 naphthols, 22 aryl carboxylic acids, 23 arylphosphonates, 24 arylacetamides, 16 d ,25 benzamides, 26 pyridylindoles, 27 phenylketones, 28 hydroxy-chromones 29 or phenylimidazoles 30 promoted by [RuCl 2 ( p -cymene)] 2 and acetate anions (or preformed Ru(OAc) 2 ( p -cymene)) support initial substrate ( A ) binding to the ruthenium precursor ( B ) followed by dissociation of a ligand (from C ) and creation of a key intermediate with a vacant site at which the M–C bond can form (see Scheme 2). Most of these electrophilic intermediates are cationic in nature ( D + ) 31 but alternative routes involving neutral intermediates equipped with two acetate ligands bound to the ruthenium ( F L ) and showing η 6 – η 2 slippage 32 or substitution of the arene co-ligand by solvent or a second substrate molecule 33 have been also reported.…”