A highly stereoselective access to 3-sulfinyl-substituted isoindolinones has been achieved by a tandem organocatalytic addition/cyclization reaction of 2-carbobenzyloxy-N-tosylbenzylidenimine with thiols and succeeding diastereoselective oxidation with MCPBA. First, enantioenriched isoindolinone N,S-acetals have been obtained through a dynamic kinetic asymmetric transformation induced by a bifunctional chiral thiourea organocatalyst. In turn, the newly created carbon stereocenter enabled a high diastereocontrol in the subsequent sulfoxidation. Based on DFT calculations, a theoretical rationale for the stereoselectivity of the oxidation reaction is also provided.