Collect. Czech. Chem. Commun. 1987, 52, 2508-2520

2-Isothiocyanatobenzyltriphenylphosphonium bromides – new type of functionalized heterocumulenes suitable for synthesis of indole derivatives

Jozef Gonda, Pavol Kristian and Ján Imrich

Department of Organic Chemistry, P. J. Šafárik University, 041 67 Košice


Reaction of 2-bromomethylphenyl isothiocyanates with triphenylphosphine afforded triphenyl-(2-isothiocyanatobenzyl)phosphonium salts. Their reaction with bases liberated the corresponding carbanions which on intramolecular addition to the N=C=S group gave substituted 3-triphenylphosphoniumindolyl-2-thiolates. These compounds did not react in the Wittig reaction but underwent electrophilic reactions on the sulfur atom or on the indol nitrogen atom. According to a detailed analysis of 1H, 13C, 31P NMR and mass spectra, the indole derivatives exist predominantly in the betaine form. X-Ray diffraction analysis of the unsubstituted betaine, 3-triphenylphosphoniumindolyl-2-thiolate, agrees well with the spectral results.