[CH3:1][CH:2]([CH3:6])[CH2:3][CH:4]=O.BrBr.[NH2:9][C:10]([NH2:12])=[S:11].C(O)C>O1CCOCC1>[NH2:12][C:10]1[S:11][C:3]([CH:2]([CH3:6])[CH3:1])=[CH:4][N:9]=12 ml (18.6 mmol) of 3-methylbutyraldehyde were dissolved in 15 ml of dioxane. 40.4 ml (18.6 mmol) of a solution 2% v/v of bromine in dioxane was dropped therein at 0° C. The mixture was maintained at room temperature under stirring for 2 hours, then 2.83 g (37.2 mmol) of thiourea and 5 ml of ethanol were added. After 6 hours at room temperature the solution was evaporated to dryness, the residue was dissolved in methylene chloride and the product extracted with 1M hydrochloric acid; the aqueous layer was made basic by using 30% ammonium hydrate and extracted again with methylene chloride. The organic phase was dried over sodium sulfate and evaporated under vacuum. The residue was chromatographed on a silica gel column, eluting with cyclohexane-ethylacetate to give 1.1 g (42% yield) of the title compound.
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