Diastereoselective Intramolecular Aldol-Type Trapping of Zwitterionic Intermediates by Ketones for the Synthesis of Spiro[chroman-4,3′-oxindole] Derivatives

A simple, mild and efficient rhodium-catalyzed aromatic C–H functionalization of α-phenoxy ketones by 3-diazooxindoles for the synthesis of the spiro[chroman-4,3′-oxindole] ring system is described. A series of functionalized spiro[chroman-4,3′-oxindole] derivatives bearing two adjacent quaternary carbon centers have been attained in a highly diastereoselective manner with very good yields. Control experiments suggested the possibility of an intramolecular aldol-type trapping of zwitterionic intermediates after the C–H functionalization. Furthermore, the applicability of this method has been tested by a gram-scale synthesis. A facile treatment with base enabled the access to both syn- and anti-diastereomers via isomerization. (Figure presented.).