Under argon, 11.5 g (0.03 mol) of 3-(9,10-didehydro-6-methyl-8α-ergolinyl)-1,1-diethylurea is dissolved in 300 ml of chloroform. At room temperature, 105 ml of ethyl formate and 5.4 ml of ethanedithiol are added in succession. Then 13.2 ml of titanium(IV) chloride in 150 ml of chloroform is added dropwise. The mixture is agitated for 3 days at room temperature. To work up the mixture, it is cooled in an ice bath and 75 ml of methanol and 600 ml of water are added in sequence dropwise to this mixture. The solution is rendered alkaline with 60 ml of 25% ammonia solution and extracted with methylene chloride. The organic phases are washed with water and dried over magnesium sulfate. The concentrated residue is chromatographed under pressure on silica gel with ethyl acetate/methanol 95:5, thus isolating 1.7 g of 3-[9,10-didehydro-2-(1,3-dithiolan-2-yl)-6-methyl-8α-ergolinyl]-1,1-diethylurea (12% yield).
