Synthesis of (1R,4R)-2,5-diazabicyclo[2.2.1]heptane derivatives by an epimerization–lactamization cascade reaction

Abstract

An epimerization–lactamization cascade of functionalized (2S,4R)-4-aminoproline methyl esters is developed and applied in synthesizing (1R,4R)-2,5-diazabicyclo[2.2.1]heptane (DBH) derivatives. (2S,4R)-4-Aminoproline methyl esters are likely to undergo 2-epimerization under basic conditions, followed by an intramolecular aminolysis of the (2R)-epimer to form the bridged lactam intermediates. Key factors identified for this cascade reaction include the electron-withdrawal N-protective group in the substrates and a strong base as the promoter.