Carbon-14 labeled methyl 2-chloro-2-oxoacetate: a convenient carbon-14 labeled oxalyl chloride equivalent

Oxalyl chloride is a versatile two-carbon building block for synthesizing organic molecules. Carbon-14 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 carbon-14 label source. Synthetically, methyl 2-chloro-2-oxoacetate reacts as an oxalyl chloride equivalent. This report describes a reliable and efficient two-step synthesis of carbon-14 labeled methyl 2-chloro-2-oxoacetate ([C-14]-1) from readily available carbon-14 labeled dimethyl oxalate ([C-14]-2). The labeled oxalate was first treated with aqueous base to give the mono-potassium salt of 2-methoxy-2-oxoacetate ([C-14]-3), which was then reacted with oxalyl chloride to give [C-14]-1 as a solution in dichloromethane. The overall radiochemical yield for this process was essentially quantitative, and [C-14]-1 was found to be stable and easy to use in further synthetic manipulations.