2-Trimethylsilyl-1,3-dithiane → 2-(6-{4-n-Propylcyclohexyl}spiro[3.3]hept-2-ylidene)[1,3]dithiane

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15.5 g (80.3 mmol) of 2-trimethylsilyl-1,3-dithiane are dissolved in 150 ml of THF, and 51 ml (80.3 mmol) of n-BuLi (15 percent in hexane) are rapidly added dropwise at −70° C. The batch is subsequently allowed to thaw to 0° C. over the course of 4 hours, stirred for 10 minutes without cooling and re-cooled to −70° C., and a solution of 17.0 g (72.5 mmol) of 6-(4-n-propylcyclohexyl)spiro[3.3]heptan-2-one 5 in 50 ml of THF is added drop-wise. The batch is left to stir overnight at room temperature, hydrolysed using saturated sodium hydrogencarbonate solution and extracted with dichloromethane. The combined organic phases are washed with water and dried over sodium sulfate. The solvent is removed under reduced pressure, and the crude product is recrystallised from n-heptane. The dithioacetal 6 is obtained as colourless flakes.

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