(matrix presented) Reactivities of 10-propynyl-9(10H)-acridone toward various aldehydes in BF3·Et20-promoted hetero [2 + 2] cycloaddition reactions are described here. This electron deficient variant of ynamine is more stable and easier to handle than most ynamines but possesses comparable reactivity. These reactions lead to a highly stereoselective synthesis of trisubstituted alkenes. A mechanistic model based on the stereochemical assignment is also described here. 10-Propynyl-9(10H)-acridone is also reactive toward α,β-unsaturated aldehydes and ketones. It provides hetero [2 + 2] products in reactions with α,β-unsaturated aldehydes but gives only the inverse demand [4 + 2] cycloadduct in a reaction with methyl vinyl ketone.