The total syntheses of natural agelastatin A and agelastatin B were accomplished via a strategythat utilized an alkynyliodonium salt → alkylidenecarbene → cyclopentene transformation to converta relatively simple amino alcohol derivative to the functionalized core of the agelastatin system.Subsequent manipulations delivered debromoagelastatin, which served as a precursor to bothagelastatin A and agelastatin B. Alkylidenecarbene insertion chemoselectivity issues were exploreden route to the final targets.