First example of a reaction of C- and N-styryltetrazoles with benzene in superacid CF3SO3H

Tetrazole derivatives are utilized in versatile spheres of human action [1]. Among the most promising compounds for the organic synthesis are Сand N-styryltetrazoles [2], yet they are the least studied. These compounds possessing a heteroaromatic system conjugated with a double carbon-carbon bond can be involved into chemical reactions at both these structural moieties. The reactions of Сand N-styryltetrazoles in superacids are especially interesting. These reactions are able to result in new, previously unavailable tetrazole derivatives of unusual structure and practically useful properties. However no information was published on the action of superacids on the styryltetrazoles. We report here on the investigation of the reactions between 2-methyl-5-[(E)-2-phenylethenyl]and 5-phenyl-2-[(E)-2-phenylethenyl]-2H-tetrazoles (Iа, Ib) and benzene in the superacid of Bronsted type CF3SO3H applied to the superelectrophilic activation of organic compounds [3]. The protonation in CF3SO3H of compounds Iа, Ib at the atom N4 of the tetrazole ring [4] and at the carbon atom of the С=С bond of the phenylvinyl substituent provides reactive dications А and B. These species are involved in the reaction of the electrophilic aromatic substitution with benzene at 20°С for 1–2 h and then are subjected to the treatment with aqueous alkali to destroy the superacid which leads to the formation of tetrazoles IIa, IIb in 70 and 67% yields respectively. We have demonstrated for the fi rst time that the conversion of both Сand N-styryltetrazoles in superacid proceeds chemoselectively exclusively at the С=С bond and does not affect the tetrazole ring. Ethenyltetrazoles Ia, Ib were prepared and character-