Gold(I)-Catalyzed\nReactions of <i>exo</i>-Glycals with Propargyl Esters toward\nC‑1 Alkenyl Spirocyclopropyl\nCarbohydrates

An atom-economic and diazo-free strategy\nfor the construction\nof\nnovel pseudo anomeric C-1 alkenyl spirocyclopropyl sugars is described.\nLeveraging the 1,2-migration pathway of propargyl esters under gold(I)\ncatalysis, easily available <i>exo</i>-glycals undergo β-selective\nalkenylcarbenoid insertion in moderate to excellent yields. Preferential\nactivation of propargyl moieties and concerted [2 + 1] insertion are\nboth favored through ligand choice and electron enrichment of esters.\nStereocontrol using conformational bias and rearrangement are also\ndemonstrated.