A mixture of the product of part (i) (20.0 g) and N,N-dimethylcarbamoyl chloride (6.80 g) in dichloromethane (250 ml) was stirred at room temperature for 2.5 days, giving a clear solution. Trimethylsilyl cyanide (6.35 g) was added and stirring was continued for a further 48 hours. Additional quantities of N,N-dimethylcarbamoyl chloride (1.30 g) and trimethylsilyl cyanide (1.30 g) were then added and the solution was stirred for a further 36 hours. The reaction was then washed successively with 10% potassium carbonate solution, brine and then dried (MgSO4). Evaporation of the solvent gave a solid which was stirred with ether and filtered to give the title compound, (19.2 g), m.p. 188°-189°.
