At room temperature under argon, 7 ml of ethyl formate and 3.6 ml (44 mmol) of ethanedithiol are added in succession to a solution of 6.8 g of 1,1-diethyl-3-(6-methyl-8α-ergolinyl)urea in 200 ml of chloroform. Thereafter 8.8 ml (80 mmol) of titanium(IV) chloride dissolved in 100 ml of chloroform is added gradually dropwise to the mixture. The latter is stirred for 20 hours at room temperature. Although the starting material is not as yet entirely converted at this point in time, the reaction mixture is worked up to avoid further formation of the disubstituted compound. For this purpose, the reaction mixture is cooled in an ice bath and combined, in sequence, dropwise with 50 ml of methanol and 40 ml of water. The mixture is then made alkaline with 25% ammonia solution and extracted with methylene chloride. The organic phases are washed with water and dried over magnesium sulfate. The evaporated residue is crystallized in boiling heat from methanol/ethyl acetate, thus obtaining 3.8 g of 1,1-diethyl-3-[2-(1,3-dithiolan-2-yl)-6-methyl-8α-ergolinyl]urea (42% yield).
