Sulfonylisocyanates attack the arylaldehyde N,N-dialkylhydrazones 1-3 at the nitrogen or carbon of the azomethine function leading to the formation of the hexahydro-1, 3,5-triazine-2,4-diones 4-6 or arylglyoxylic acid sulfonamide-N, N-dialkylhydrazones 7-9 (scheame 1). Under equal experimental conditions the position of the electrophilic attack depends on the contribution of the dipolar structures