Synthesis of ¹³C‐labelled propylene oxide via ¹³C‐labelled 2‐chloropropionic acid and 2‐chloropropanol

1‐Methyl‐[2‐¹³C]ethylene oxide (I) is prepared in a four‐step synthesis, starting from [1‐¹³C]propionic acid. A method for an efficient α‐chlorination of low carboxylic acids is developed, 2‐chloropropionyl chloride being esterified without separation to give 72% of phenyl‐2‐chloro‐[1‐¹³C]propionate. The ester is hydrogenated with LiAlH₄ to give 95% yield of 2‐chloro‐[1‐¹³C]propan‐1‐ol which is then subjected to alkaline dehydrochlorination, giving 35% yield of the isolated product (I). This micro‐scale method is also suitable for syntheses of ¹⁴C‐labelled epoxides of low molecular weight.