A solution of 676 mg (5.49 mmol) of N,N-dimethylmethanesulphonamide in 10 ml of THF was admixed slowly at −78° C. with 3.43 ml (5.49 mmol) of 1.6M n-butyllithium solution in hexane versetzt. After 30 min at −78° C., the colourless solution obtained was added to a solution, cooled to −78° C. beforehand, of 500 mg (1.83 mmol) of the compound from Example 11A in 10 ml of THF. The reaction mixture was stirred at −78° C. for 30 min more and then slowly warmed to RT. After 30 min it was cooled to −20° C. again and the reaction was halted by addition of 5 ml of 10% strength aqueous ammonium chloride solution. The mixture was diluted with ethyl acetate and then washed twice with water and once with saturated aqueous sodium chloride solution. The organic phase was dried over sodium sulphate and freed from the solvent on a rotary evaporator. The residue was purified by preparative HPLC [Method 23]. The product fraction was freed from the solvent on a rotary evaporator. Drying of the residue in an HV gave 296 mg (41% of theory) of the title compound.
