Thioformylium methylide, which is readily generated from chloromethyl(trimethylsilyl)methyl sulfide by the action of fluoride, is used for the synthesis of spirocyclic derivatives from arylidene-azolones. Four types of the corresponding heterocycles have been studied. A series of 7-thia-3-azaspiro[4.4]nonan-4-ones was obtained with yields varying from 17 to 99%. The stereochemical study revealed selective formation of single either or stereoisomers, dependent on the heterocycle core used.