Large-scale synthesis of new cyclazines, 5-thia-1,8b-diazaacenaphthylene-3-carboxylic acid derivatives having the peripheral 12π-electron ring system

Abstract 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.