a Conditions: Acetal 2a or 5b (1.0 equiv), ZnBr2 or CuI (10 mol %), alkyne (1.0–1.3 equiv), Et3N (1.0–1.3 equiv), TMSOTf (1.1–1.2 equiv), Et2O or PhMe, rt, 12 h, unless otherwise noted. See Supporting Information for specific conditions. Yields in parentheses determined by 1H NMR analysis using 1,3,5-trimethoxybenzene as internal standard. b CH2Cl2 used as solvent.