N‐Heterocyclic Carbene‐Catalyzed Double Michael Addition: Stereoselective Synthesis of Spirofluorenes and Multisubstituted Indanes

Abstract The strong Brønsted basic character of N ‐heterocyclic carbenes (NHCs) has been used to promote the cascade double Michael addition between fluorenes and dienones. Under catalyst loadings of 1–5 mol% of NHC, fluorene reacts with divinyl ketones (DVKs) to afford anti‐spirofluorene compounds in high yields. However, when benzenedi(enones) were employed as Michael acceptors in the presence of 10 mol% of NHC, fluorene undergoes a different inter‐ and intramolecular cascade double Michael addition, providing multi‐substituted indanes in high yields with excellent diastereoselectivity. magnified image