Hydrogen sulfide chemistry in continuous flow: Efficient synthesis of 2-oxopropanethioamide

David Cantillo^1,2, Phillip A. Inglesby³, Alistair Boyd³, Oliver Kappe^1,2

• ¹ Institute of Chemistry, University of Graz, NAWI Graz, Heinrichstrasse 28, 8010 Graz, Austria
• ² Research Center Pharmaceutical Engineering (RCPE), Inffeldgasse 13, 8010 Graz, Austria
• ³ AstraZeneca, Silk Road Business Park, Macclesfield, SK10 2NA, United Kingdom

A safe and scalable procedure for the synthesis of 2-oxopropanethioamide, an intermediate in the synthesis of a potent β-secretase (BACE-1) inhibitor, from the reaction of acetyl cyanide with hydrogen sulfide gas under continuous-flow conditions has been developed. The toxic gas could be accurately dosed using a mass-flow controller or a peristaltic pump. The reaction proceeded smoothly at room temperature in the presence of a small amount of triethylamine as basic catalyst. After a residence time of 15 min, excellent yield (96%) and purity (>99%) were obtained for the target compound. The high reaction selectivity permitted a simple workup procedure consisting of evaporation of all volatiles.

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