Reaction of 5,5-diphenyl-2-thiohydantoin with 1,2-dibromoethane.crystal and molecular structures of 2,3-dihydro-6,6-diphenylimi-dazo-[2,1-b]-thiazol-5(6h)-one and 2,3-dihydro-5,5-diphenylimi-dazo-[2,-1-b]-thiazol-6(5h)-one and their reactivity