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.