Preparation and Characterization of Aryl or Heteroaryl(3-indolyl)methylium o-Benzenedisulfonimides

Abstract

An initial study has been accomplished into the synthetic feasibility of the preparation of diarylcarbenium salt via the direct coupling of aryl (or heteroaryl) aldehydes and arenes (or heteroaryl analogues) in the presence of a strong organic Brønsted acid. A number of stabilized aryl or heteroaryl(3-indolyl)carbenium ions, never previously prepared in the solid state, have been isolated in excellent yields as highly stable o-benzenedisulfonimide salts and have been fully characterized. Their purity has been proven by spectroscopic methods and chemical reduction with NaBH(4). An X-ray crystal structure analysis has been performed on one of the products: an azafulvenium species was shown to be the exclusive structure in the solid state.

Characterization of the Gene Cluster CYP264B1‐geoA from Sorangium cellulosum So ce56: Biosynthesis of (+)‐Eremophilene and Its Hydroxylation

“…In the salts 1 a – g the diarylcarbenium ion stabilizes the positive charge by resonance delocalization onto both the phenyl and the indole ring. The X‐ray crystal structure of the fully characterized 1 a has been described 19. The bond lengths obtained clearly agree with a resonance structure in which the charge is localized on the indole ring 28.…”

“…The stable nonsymmetric diarylmethylium ions 1 a – h (obtained as previously reported)19, 23 were selected for our investigations. Compound 1 a was taken as a model substrate in an organocatalytic alkylation promoted by different organocatalysts (Table 1), under various reactions conditions and with various additives.…”

“…On the other hand, the solubility of the salts under the reaction conditions also plays a decisive role, as extensive polymerization of the nucleophilic indole can result due to the strong acidic conditions in which the salts are obtained. In addition, the presence of the indole moiety is quite crucial for the stabilization of the carbenium ion, as other aromatic groups cannot be employed 19. 23…”

“…Aldehyde 2 c was prepared according to a literature procedure 30. Carbenium ions 1 a – h were prepared according to literature procedures 19. 20…”

Alkylideneindoleninium Ions and Alkylideneindolenines: Key Intermediates for the Asymmetric Synthesis of 3‐Indolyl Derivatives

“…The elimination process is similar to an E 1 process (elimination unimolecular), and hydrogen or aliphatic groups can be substituted at the nitrogen atom of the indole. Interestingly, stabilized aryl or heteroaryl(3‐indolyl)carbenium ions have been isolated as solids and fully characterized as highly stable o ‐benzenedisulfonamide salts 5…”