N‐Аlkenyl thioureas, under the action of aryltellurium trichlorides, form the addition products N‐{2‐chloro‐3‐[dichloro(4‐alkoxyphenyl)‐tellanyl]propyl} thioureas or the intramolecular cyclization products 5‐{dichloro(4‐alkoxyphenyl)‐telluromethyl}‐2‐phenylamino‐4,5‐dihydro‐1,3‐thiazole hydrochlorides. The reaction route depends on the nature of the substituent in the thiourea. The Fukui function reactivity indexes identify the electrophilic/nucleophilic centers and explain the possible cyclization reaction in the case of phenyl substituted thioureas. In the case of other substituents, the calculated values of partial atomic charges clearly predict that the addition reaction is more possible.