Direct Access to 3,4‐Fused Spirooxindoles Through Visible‐Light‐Driven Diasterioselective [4+2] Cyclization of 3‐Methylene Oxindoles

Abstract A visible light‐mediated strategy has been developed to synthesize diastereoselective 3,4‐fused spirooxindoles via formal [4+2] cycloaddition of 3‐methylene oxindoles without the need of pre‐functionalization. The 3‐methylene oxindoles, when exposed to visible light in the presence of catalytic amount of CeCl 3 under alkaline conditions, afforded the complex 3,4‐fused spirooxindole framework with four contiguous chiral centers. The protocol proved to be highly chemo‐ and regio‐selective by affording 3,4‐fused spirooxindoles in moderatetogood yields. The protocol also works smoothly under the direct exposure of sunlight. It has been demonstrated that the method is also scalable on gram quantity.