Solvent-Minimized, Chromatography-Free, Diastereoselective Synthesis of Oxazolidine-Dispirooxindoles via oxa-1,3-Dipolar Cycloaddition of 3‑Oxindole

An efficient and diastereoselective decarboxylative oxa-1,3-dipolar cycloaddition between 3-oxindoles and diverse amino acids is developed to access novel oxazolidine-dispirooxindole skeletons bearing vicinal quaternary carbon centers. This protocol features operational simplicity, a broad substrate scope, and good to excellent chemical yields and diastereoselectivities. In particular, minimal solvent (1 mL/10 mmol) and chromatography-free purification render this synthetic process more efficient and environmentally benign in the context of green chemistry.