Dimethoxyacetaldehyde‑<i>N</i>‑triftosylhydrazone:Preparation and Carbene Reactivity in Cyclopropanation and Doyle–KirmseReactions

Herein, we developed the new, powerful, and easy-to-handle chemical reagent, dimethoxyacetaldehyde-<i>N</i>-triftosylhydrazone (DMHz-Tfs), as a convenient in situ source of dimethoxydiazoethane under mild conditions. We demonstrate the carbene reactivity of DMHz-Tfs in iron-catalyzed cyclopropanation and Doyle–Kirmse reactions, providing access to diverse acetal functionalized cyclopropanes and homoallylic- and allenyl-sulfides at gram-scale with high stereoselectivity. DFT calculations elucidated the involvement of the most stable doublet spin state iron-carbene intermediate over other possible spin states.