Condensation of 2-lithio-1-methyl-4-quinolone with methyl 2-(chloroformyl)benzoate gives 5-methylbenz[b]acridine-6,11-12-trione 3; addition of the anion of methyl 2-(1,3-dithian-2-yl)benzoate to 1-methoxycarbonyl-4-quinolone gives 5,5a-dihydro-11-hydroxy-5-methoxycarbonyl-12-oxaspiro{benz[b]acridine-6,2'(1',3'-dithiane)}7.