Solvent-Switched Benzylic Methylene Functionalization: Addition, Ring-Opening, Cyclization, and Unexpected Cleavage of C-O and C-C Bonds

Intermolecular benzylic methylene functionalization of exo-cyclic enol ethers has been achieved using imines as reagents and potassium tertbutoxide as the catalyst. Depending on the solvent used, the reaction proceeds by two pathways. In THF, an addition/elimination reaction of exo-cyclic enol ethers with imines provides dihydroisobenzofuran derivatives in good yield. In DMSO, an addition/ring-opening/cyclization cascade reaction occurs with unexpected cleavage of C-O and C-C bonds, affording isoquinolin-1(2H)-one products in high yield under ambient reaction conditions.