The 5-thia-1, 8b-diazaacenaphthylenes (2 and its ester, 8) are new cyclazines, in which a paramagnetic ring is present in the peripheral 12π-electron ring system. Three convenient methods of preparing 8 have been developed. One involved thioglycolation of a new compound, 5-fluoroimidazo [1, 2-a] pyridine (6b), followed by the Duff reaction gave 8 in 64% yield without chromatographic purification.