Chlorosulfates as Reagents in the Synthesis of Carboxylic Acid Esters Under Phase-Transfer Conditions

During a search for a satisfactory synthesis of chloromethyl esters 1 of certain β-lactam antibiotics, e.g. penicillanic acid sulfone, we discovered that chloromethyl chlorosulfate 1 ( 4 ) is an excellent reagent for this purpose. We also found that other alkyl chlorosulfates are useful reagents for the synthesis of the corresponding alkyl carboxylates.