A process for preparing a compound of formula wherein n is 0 or 1, which process comprises: a) reacting a compound of formula wherein n is 0 or 1, with a compound of formula wherein X is selected from -NHSO 2 Me and -NOz 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 wherein n is 0 or 1 or a compound of formula wherein n has the above reported meanings; and, when a compound of formula is obtained in step (a): b) reducing it to a corresponding compound of formula wherein n is 0 or 1, and reacting it with methanesulfonyl halide to obtain a compound of formula wherein n has the above reported meanings; and wherein the compound of formula is obtained according to step by: c3) reacting an intermediate of formula B" with an intermediate of formula D wherein R is a linear or branched (C 1 -C 6) alkyl group or a arylalkyl group and n has the above reported meanings, to obtain directly a compound of formula and subsequently enantioselectively reducing it to obtain a compound of formula wherein n has the above reported meanings; and wherein all of the compounds of formula,,, or wherein n is 1 can be obtained by oxidizing the corresponding compounds wherein n is 0. a) reacting a compound of formula wherein n is 0 or 1, with a compound of formula wherein X is selected from -NHSO 2 Me and -NOz 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 wherein n is 0 or 1 or a compound of formula wherein n has the above reported meanings; and, when a compound of formula is obtained in step (a): b) reducing it to a corresponding compound of formula wherein n is 0 or 1, and reacting it with methanesulfonyl halide to obtain a compound of formula wherein n has the above reported meanings; and wherein the compound of formula is obtained according to step by: c3) reacting an intermediate of formula B" with an intermediate of formula D wherein R is a linear or branched (C 1 -C 6) alkyl group or a arylalkyl group and n has the above reported meanings, to obtain directly a compound of formula and subsequently enantioselectively reducing it to obtain a compound of formula wherein n has the above reported meanings; and wherein all of the compounds of formula,,, or wherein n is 1 can be obtained by oxidizing the corresponding compounds wherein n is 0. b) reducing it to a corresponding compound of formula wherein n is 0 or 1, and reacting it with methanesulfonyl halide to obtain a compound of formula wherein n has the above reported meanings; and wherein the compound of formula is obtained according to step by: wherein n is 0 or 1, and reacting it with methanesulfonyl halide to obtain a compound of formula wherein n has the above reported meanings; and wherein the compound of formula is obtained according to step by: c3) reacting an intermediate of formula B" with an intermediate of formula D wherein R is a linear or branched (C 1 -C 6) alkyl group or a arylalkyl group and n has the above reported meanings, to obtain directly a compound of formula and subsequently enantioselectively reducing it to obtain a compound of formula wherein n has the above reported meanings; and wherein all of the compounds of formula,,, or wherein n is 1 can be obtained by oxidizing the corresponding compounds wherein n is 0.