Conventionally accessible 4-[(2-(3,4-dimethoxyphenyl)ethyl] -3-thiosemicarbazide .(2) was converted to new 1-substituted benzylidene/furfurylidene-4- [2-(3,4-dimethoxyphenyl)ethyl] -3-thiosemicarbazides (3) which furnished 2-(substituted benzylidene/furfurylidene)hydrazono-3-[2-(3,4-dimethoxyphenyl)ethyl]thiazolidin-4-ones (4) and 1-(substituted benzylidene/furfurylidene)-amino-3-[2-(3,4-dimethoxyphenyl)ethyl]-2-thioxo-4, 5-imidazolidinediones (5) on reaction with chloroacetic acid and oxalyl chloride, respectively. The structure of 5 was confirmed by X-ray diffraction performed on 5a. 4 and 5 were evaluated for their potentiating effects on pentobarbital induced hypnosis. Most of the compounds caused remarkable increases in pentobarbital sleeping time.