Methylation of Ylidene‐Triazenes: Insight and Guidance for 1,3‐Dipolar Cycloaddition Reactions

Abstract

Reaction of 1,3-dimesitylimidazolylidene (1) with p-functionalized phenyl azides 2 (a: H, b: OCH 3 , c: NO 2 ) afforded the respective imidazolylidene-triazenes 3 in good yields (65-99 %). Subsequent treatment with methyl iodide produced the corresponding methylated products 4 in near-quantitative yields (99 %). Analysis by NOESY 1D NMR spectroscopy and single-crystal X-ray diffraction revealed that the methylation reaction was regioselective and occurred at the nitrogen atom most distal from the heterocycle. Consistent with the formation of ionic salts, the 1 H NMR signals for the imidazole protons in 4 were shifted Ͼ 0.5 ppm downfield compared to 1, indicating the accumulation of positive charge.

5-Azido-4-dimethylamino-1-methyl-1,2,4-triazolium Hexafluoridophosphate and Derivatives

“…Organic azides were occasionally converted to triazenes, essentially by reaction with N-heterocyclic carbenes. Thus, a number of crystal structures of neutral aryl or alkyl triazenes have been reported [13][14][15][16][17][18][19][20]. The use of quaternary azidoazolium cations for this transformation resulted in cationic triazatrimethine cyanine dyes, but only one crystal structure of this type was reported, although with benzimidazole [21].…”

Covalent Capture of Nitrous Oxide by N‐Heterocyclic Carbenes

“…Single-crystal X-ray diffraction analyses were performed for both complexes [14] and graphical representations of the molecular structures are depicted in Figure 1. Crystallization was achieved by slow evaporation of CH 2 Cl 2 /n-hexane (for 1) or Et 2 O/n-hexane (for 2) solutions.…”

“…When 1 was added to a mixture of toluene and MeI (1:1) a solution formed which slowly turned red. [14] The data reveal the formation of a salt composed of a guanidinium-type cation and a triiodide anion. [23] After 5 hours, we were able to isolate the alkylation product 4 in 60 % yield (Scheme 3).…”

π‐Conjugated Triazenes and Nitriles: Simple Photoinduced Synthesis of Anilides Using Mild and Metal‐Free Conditions

“…Alternatively to the depicted proposed mechanism (Scheme ), it is important to consider that π‐conjugated triazenes can also act as nucleophiles, as previously reported by Bielawski, during S N 2 studies . This alternative mechanism could involve a direct attack from the aniline nitrogen of the triazene to a protonated nitrile.…”