Fully protected natural and unnatural N-acetylcysteine, dipeptide Cys–Gly, glutathione, and homoglutathione derivatives were synthesized by the Ugi four-component reaction using various benzylthio aldehydes and ketones as carbonyl building blocks. The scope and limitations of the method were investigated. Formation of imidazoline by-products in the Ugi reaction was discussed. 2, 2, 2-Trifluoroethanol was shown to be a superior reaction ...