Base-Assisted and Silica Gel-Promoted Indole-Substituted Indene Synthesis

Herein, we report for the first time a transition-metal-free and mild protocol that requires inexpensive K2CO3 and silica gel for direct access to polysubstituted indenes from readily obtainable starting precursors. Notably, sequential Michael addition, intramolecular cyclization, and silica gel-promoted nucleophilic substitution reactions afford the desired products. A broad range of indoles and other aromatic nucleophiles are well-tolerated, affording indenes in moderate to good yields. Gratifyingly, indene could be easily converted into synthetically useful 3-indole-substituted indanone and indanol. Nonetheless, the successful isolation of a reaction intermediate highlights the crucial role of methanol in this reaction.