A wide array of aldehydes undergo smooth cross-coupling with 3-hydroxy-3-(4-hydroxybut-1-en-2-yl)-1-methylindolin-2-one in the presence of 10 mol% BF₃·OEt₂ at 0 °C in dichloromethane to afford the corresponding 2,3,5,6-tetrahydro-1′H-spiro[pyran-4,4′-quinoline]-2′,3′-dione derivatives in good yields with excellent diastereoselectivity. This is the first report on the synthesis of tetrahydro-1′H-spiro[pyran-4,4′-quinoline]-2′,3′-dione scaffolds through a cascade of Prins/pinacol reactions.