Synthesis of chiral vicinal diamines by highly diastereoselective three-component phenolic Mannich reaction: temperature-dependent stereodivergency

reaction: see text] A diastereoselective three-component synthesis of chiral o-1,2-diaminoalkyl phenols from an electron-rich phenol, an amine, and a chiral alpha-N,N-dibenzylamino aldehyde is developed. The diastereoselectivity of this phenolic Mannich reaction is temperature-dependent,and either anti or syn diastereomer can be prepared by controlling the reaction conditions. Low reaction temperature (-20 degrees C) favors the formation of anti adduct 1, whereas higher temperature (60 degrees C) under otherwise identical conditions produces mainly the syn isomer.