In Situ Formation of Vilsmeier Reagents Mediated by Oxalyl Chloride: a Tool for the Selective Synthesis of N-Sulfonylformamidines

N‐Sulfonylformamidines were produced from sulfonamides or N‐acylated sulfonamides using Vilsmeier reagent obtained in situ from N,N‐disubstituted formamides and oxalyl chloride. Optically active substrates did not racemize during the process. The efficient and mild cleavage of N‐sulfonylformamidines can be achieved with hydrazine hydrate in ethanol. The entire procedure constitutes a simple method for protecting, and deprotecting, the sulfonamide moiety. A straightforward and efficient synthesis for N‐sulfonylformamidines by employment of various Vilsmeier reagents generated in situ is described. The reactions proceed under mild reaction conditions and tolerate several sensitive functional groups.