Bicyclization of isocyanides with alkenoyl bis(ketene dithioacetals): access to 6,7-dihydro-1H-indol-4(5H)-ones.

The tandem [3 + 2] cycloaddition/intramolecular imidoyl anion trapping strategy has been successfully applied for the synthesis of 6,7-dihydro-1H-indol-4(5H)-ones from alkenoyl bis(ketene dithioacetals) and tosylmethyl isocyanide. The reaction proceeded smoothly under mild reaction conditions to afford bicyclization products in high to excellent yields in a single step.