Allowing the direct interaction of N-aryl α-diimines with a high valent metal chloride: one-pot WCl₆-promoted formation of quinoxalinium salts

Abstract

The full potential of a high valent metal chloride as both a chlorinating and an oxidative agent was explored by allowing WCl to react with N-(2,6-diisopropylphenyl) α-diimines, in CHCl at room temperature. These α-diimines underwent unprecedented conversion to quinoxalinium cations via intramolecular C-N coupling.

Serendipitous Formation of a Zwitterionic Imidazolium Molecule from α‐Diimine with Glyoxal as Unusual Cyclization Agent

“…In the framework of our research on the coordination chemistry of α-diimines, [18][19][20][21] and in their derivatization with bioactive groups via esterification reactions, [22,23] we became interested in obtaining the α-diimine compound D1 bearing two 4-cyclohexanecarboxylic acid groups as nitrogen substituents. Using the classical procedure (see Scheme 1A), (1S,4S)-4-aminocyclohexanecarboxylic acid and glyoxal were refluxed in methanol in the presence of a catalytic amount of acetic acid.…”

Stable coordination complexes of α-diimines with Nb(v) and Ta(v) halides

“…20 The unclean NbCl 5 directed activation of DAD Dip produces, among the other products, the quinoxalinium salt 2 and, in this respect, matches the outcome of the reaction with WCl 6 . 25 The formation of 2 from DAD Dip presumably takes place via DAD Dip to Nb electron transfer, and release of one isopropyl group. The latter was detected by GC-MS as isopropyl chloride in the final reaction mixture; on the other hand, a variable temperature EPR study suggested the presence of minor amounts of the isopropyl radical, .…”

“…12,13,14,24 The first direct interaction (i.e., in the absence of further reactants) of α-diimines with a HVM halide (WCl 6 ) was recently reported by us, allowing the unusual conversion of the organic substrate into quinoxalinium cations (Scheme 1). 25 Scheme 1. WCl 6 -mediated conversion of α-diimine to quinoxalinium.…”

Cascade Reactions of α‐Phenylcinnamic Acid to Polycyclic Compounds Promoted by High Valent Transition Metal Halides

“…In particular, WCl 6 exhibits relatively weak W−Cl bonds, allowing the stoichiometric modification of simple molecules through unconventional pathways. Examples include the transformation of imines into aza‐2‐allenium and nitriulium cations, the former being generated via unusual N 2 elimination, and of α‐diimines into quinoxalinium salts . Also niobium pentahalides have been found to provide unique reactivity patterns to organic species,,, and their chemistry has witnessed a significant advance in the last years,, encouraged by their cheapness and the substantial non‐toxicity of the element niobium .…”

“…Examples include the transformation of imines into aza-2-allenium and nitriulium cations, [9] the former being generated via unusual N 2 elimination, and of α-diimines into quinoxalinium salts. [10] Also niobium pentahalides have been found to provide unique reactivity patterns to organic species, [1c,7,11] and their chemistry has witnessed a significant advance in the last years, [7,12] encouraged by their cheapness and the substantial non-toxicity of the element niobium. [13] Compared to WCl 6 , NbX 5 (X = F, Cl) are more inert to reduction processes, and comprise relatively strong niobium-halide bonds, [8] thus disfavouring halide/oxygen exchange reactions.…”