Unexpected Reactivity of Acetylenic ω-Ketoesters toward TBAF and t-BuOK; New Cascade Reactions Affording Allene and Oxetane Derivatives^†

The reactivity of acetylenic ω-ketoesters toward tetra-n-butylammonium fluoride and potassium tert-butoxide was studied. These cascade reactions proceeded smoothly and afforded either electrophilic allene derivatives or highly functionalized oxetane derivatives in moderate to high yields.