A process for the preparation of compounds of formula (XI) wherein n is 0 or 1 and R 1 and R 2 , are independently selected in a group consisting of H, linear or branched (C 1 -C 6 ) alkyl, optionally substituted by one or more substituents selected from the group consisting of: halogen atoms, (C 3 -C 7 ) cycloalkyl, and linear or branched (C 2 -C 6 ) alkynyl, which process comprises: a) reacting a compound of formula (X) wherein n is 0 or 1, with a compound of formula (III) wherein X is selected from -NHSO 2 Me and -NO 2 and Z is selected from -OH, chlorine, bromine, linear or branched (C 1 -C 6 )alkoxy, aryloxy, arylalkoxy, (C 1 -C 6 )alkylcarbonyloxy, arylcarbonyloxy and aryl(C 1 -C 6 )alkylcarbonyloxy to obtain a compound of formula (XI) wherein n is 0 or 1 or a compound of formula (XII) wherein R1, R2 and n have the above reported meanings; and, when a compound of formula (XII) is obtained in step (a): b) reducing it to a corresponding compound of formula (XIII) wherein R1, R2 and n have the above reported meanings, and reacting it with methanesulfonyl halide to obtain a compound of formula (XI) wherein n has the above reported meanings; and wherein the compound of formula (X) in step (a) is obtained according to any one of the alternative steps (c1) or (c2) by: c1) oxidizing a compound of formula (XIV) wherein n is 0 or 1 to obtain a compound of formula (XV) wherein n is 0 or 1, and subsequently enantioselectively reducing it to obtain a compound of formula (X) wherein n has the above reported meanings; or c2) chromatographically separating a compound of formula (XIV) wherein n is 0 or 1, to obtain both a compound of formula (X) and a compound of formula (XVI) wherein n has the above reported meanings; and optionally oxidizing the compound of formula (XVI) obtained in step (c2) to a corresponding compound of formula (XV) to be subsequently reduced to a compound of formula (XIV) wherein n is 0 or 1 and reprocessed in the following chromatographic separation process; and wherein all of the compounds of formula (XI), (X), (XII), (XIII), (XIV), (XV) or (XVI) wherein n is 1 can be obtained by oxidizing the corresponding compounds wherein n is 0. a) reacting a compound of formula (X) wherein n is 0 or 1, with a compound of formula (III) wherein X is selected from -NHSO 2 Me and -NO 2 and Z is selected from -OH, chlorine, bromine, linear or branched (C 1 -C 6 )alkoxy, aryloxy, arylalkoxy, (C 1 -C 6 )alkylcarbonyloxy, arylcarbonyloxy and aryl(C 1 -C 6 )alkylcarbonyloxy to obtain a compound of formula (XI) wherein n is 0 or 1 or a compound of formula (XII) wherein R1, R2 and n have the above reported meanings; and, when a compound of formula (XII) is obtained in step (a): b) reducing it to a corresponding compound of formula (XIII) c1) oxidizing a compound of formula (XIV) wherein n is 0 or 1 to obtain a compound of formula (XV) wherein n is 0 or 1, and subsequently enantioselectively reducing it to obtain a compound of formula (X) wherein n has the above reported meanings; or c2) chromatographically separating a compound of formula (XIV) wherein n is 0 or 1, to obtain both a compound of formula (X) and a compound of formula (XVI) wherein n has the above reported meanings; and optionally oxidizing the compound of formula (XVI) obtained in step (c2) to a corresponding compound of formula (XV) to be subsequently reduced to a compound of formula (XIV) wherein n is 0 or 1 and reprocessed in the following chromatographic separation process; and wherein all of the compounds of formula (XI), (X), (XII), (XIII), (XIV), (XV) or (XVI) wherein n is 1 can be obtained by oxidizing the corresponding compounds wherein n is 0. <EOS>