S-(3-Chloro-2-methyl-3-oxopropyl) (S)-ethanethioate → Benzyl 3-(3-acetylthio-2-(S)-methyl-1-oxopropyl)-2,3-dihydro-5-phenyl-1,3,4-thiadiazole-2-carboxylate

3-Acetylthio-2-(S)-methylpropanoyl chloride (2.3 g) in dichloromethane (30 ml) was added over 5 minutes to a stirred mixture of the product of Example 1, step a) (3.6 g) and polyvinylpyridine (2.4 g) in dichloromethane (60 ml). The mixture was stirred at room temperature for 20 hours and 3-acetylthio-2-(S)-methylpropanoyl chloride (1.2 g) was then added. The mixture was stirred for a further 2 hours, filtered and the filtrate stirred with a saturated solution of sodium bicarbonate for 1 hour. The organic phase was separated, washed with water, dried and evaporated to a gum. The residue was purified by flash chromatography to give the sub-title product (4.4 g) as an oil.