The reaction of 5(S)-methyl-3-phenyl-4,5-dihydro-3H-1,2,3-oxathiazol (VIII) with benzhydrylamine (IX) gives the sulfamic acid (X), which is deprotected by hydrogenation with H2 over Pd/C to yield N-(2(R)-aminopropyl-N-(2-pyridyl)sulfamic acid (XI). The hydrolysis of (XI) with 3N HCl affords N1-(2-pyridyl)propane-1,2(R)-diamine (XII). The cyclization of the intermediate dimesylate (VI) with sulfamic acid (XI) or diamine (XII) by means of K2CO3 and NaI in hot DMF or refluxing acetonitrile provides the disubstituted piperazine (XIII) (1), which is finally condensed with 4-cyanobenzoyl chloride (XIV) by means of K2CO3 in ethyl acetate to give the target benzamide (1,2).
The intermediate dimesylate (VI) can be obtained as follows: The condensation of 2,3-dihydro-1,4-benzodioxin-5-amine (I) with ethyl bromoacetate (II) by means of Hunig's base and NaI in refluxing toluene gives the tertiary amine (III), which is reduced by means of LiAlH4 in THF to yield the diethanolamine (IV). Finally, this compound is esterified by means of mesyl chloride (V) to provide the desired dimesylate intermediate (VI). Alternatively, the diethanolamine (IV) can be obtained by direct condensation of 2,3-dihydro-1,4-benzodioxin-5-amine (I) with 2-chloroethanol (VII) by means of Hunig's base.