Metal-Free Ring-Expansion Reaction of Six-membered Sulfonylimines with Diazomethanes: An Approach toward Seven-Membered Enesulfonamides.

A new metal-free, ring-expansion reaction of six-membered N-sulfonylimines with unstable diazomethanes, generated in situ from the N-tosylhydrazones, has been developed. This reaction delivers valuable seven-membered enesulfonamides by a Tiffeneau-Demjanov rearrangement and intramolecular proton transfer tautomerization process. Moreover, this ring-expansion reaction can be carried out in a one-pot fashion and scaled up to the gram scale by using aryl aldehydes, without the need to isolate the N-tosylhydrazone.