Non-phosgene synthesis of benzyl chloroformate (CbzCl)

A novel synthetic method for benzyl chloroformate (CbzCl) using carbon monoxide or carbonyl sulfide as a carbonyl source was established. Benzyl chloroformate was successfully synthesized by the chlorination using sulfuryl chloride of S-methyl O-benzyl carbonothioate, which was prepared by the carbonylation of benzyl alcohol with carbon monoxide and sulfur (or carbonyl sulfide) in the presence of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) followed by esterification using methyl iodide.