Synthesis of Spiro Bis-Indanes via Domino Stetter-Aldol-Michael and Stetter-Aldol-Aldol Reactions: Scope and Limitations

The synthesis of spiro bis-indanes by means of N-heterocyclic carbene (NHC) catalysis is reported. The dimerization of various o-formylchalcone substrates or their combination with phthaldialdehyde derivatives under the catalysis of thiazolium-derived carbenes afforded Stetter-aldol-Michael products and Stetter-aldol-aldol products, respectively. The use of poor Michael acceptors in conjunction with an N-alkyltriazolium-derived catalyst furnished a variety of dibenzo[8]annulene products. This work highlights the interplay of a variety of factors affecting competing pathways in NHC-catalyzed domino reactions.