Reaction of the dicarboxylic acid (I) with thionyl chloride in hot toluene gives the di-acid chloride (II). Treatment of (II) with Cl2 in CH2Cl2 gives the sulfenyl chloride (III), which upon reaction with NH4OH affords the benzisothiazole (IV). Chlorination of (IV) in heat POCl3 yields the chlorobenzisothiazole (V). Reaction of (V) and piperazine (VI) in excess molten pipeazine gives the monosubstituted piperazine (VII). Reaction of (VII) with the dibromide (VIII) in refluxing ethanol yields the spiroquaternary (IX). Finally, BMY-13859-1 is obtained by treatment of (IX) with the glutarimide (X) in refluxing xylene followed by treatment with HCl in isopropanol.