Abstract: A convenient and straightforward synthesis of structurally diverse 2-methyl-N-[(3-phenylamino)oxetan-3-yl]-2-propanesulfinamide derivatives from 3-oxetan-3-tert-butylsulfinimine and substituted aromatic amines in methanol at 60 °C temperature is described. The corresponding diaminooxetane derivatives are obtained in good to excellent yield under optimized reaction conditions. The method presented herein was found to be advantageous for diaminooxetane derivatives as emerging building block for future drug discovery. The title diaminooxetanes should be considered as bioisosteric to isopropylidenediamines and urea derivatives rather than to gem-dimethyl and carbonyl groups, respectively.