The 1,3-dipolar addition of the unsaturated ester (I) with tertiary amine (II) by means of TFA gives the trans pyrrolidinecarboxylic acid methyl ester (III), which is hydrolyzed with NaOH to the corresponding racemic trans free acid (IV). The optical resolution of (IV) with (R)-alpha-methylbenzylamine affords the (2S,3S)-(IV), which is treated with SOCl2 in dichloromethane giving the acyl chloride (V). The reaction of (V) with ammonia yields the amide (VI), which is reduced with LiAlH4 in THF providing the aminomethyl pyrrolidine (VII). The protection of the primary amino group of (VII) with tert-butoxycarbonyl anhydride gives the carbamate (VIII), which is debenzylated by hydrogenolysis with H2 over Pd/C affording the pyrrolidine (IX). The condensation of (IX) with the protected quinolonecarboxylic acid (X) by means of triethylamine in DMSO gives the amino protected quinolone (XI), which is finally deprotected with trifluoroacetic acid as usual.