Oxalyl chloride is a versatile twocarbon building block for synthesizing organic molecules. Carbon14 labeled oxalyl chloride should be a useful reagent for labeling many of these compounds. Unfortunately, its preparation suffers from low radiochemical yield and problems with stability, isolation and analysis. Because of these issues, the reagent is not a convenient or practical carbon14 label source. Synthetically, methyl 2chloro2oxoacetate reacts as an oxalyl chloride equivalent. This report describes a reliable and efficient twostep synthesis of carbon14 labeled methyl 2chloro2oxoacetate 14C1 from readily available carbon14 labeled dimethyl oxalate 14C2. The labeled oxalate was first treated with aqueous base to give the monopotassium salt of 2methoxy2oxoacetate 14C3, which was then reacted with oxalyl chloride to give 14C1as a solution in dichloromethane. The overall radiochemical yield for this process was essentially quantitative, and 14C1was found to be stable and easy to use in further synthetic manipulations. Copyright © 2009 John Wiley & Sons, Ltd.