Synthesis of Lupane Mono- and Bis-C19-(1,2,3-triazolyl)-triterpenoids by “Click” Reaction

A series of lupane C19-(1,2,3-triazolyl)-triterpenoids were obtained by “click” reaction of 3,28-diacetoxy-29-norlup- 20(30)-yne with different aromatic and sugar azides after screening of several copper-based catalytic systems. DFT calculations were performed (B3LYP/6.311 level of theory) and showed that the alkyne moiety is hindered by the triterpenoid skeleton, thus explaining its low reactivity and the requirement of a very active catalytic system. Ultimately, it was found that the dinuclear copper complex [Cu(μ-OH)(TMEDA)]2Cl2 is the most efficient catalyst. Moreover, for the first time, a bis-(triazolyltriterpenoid)-derivative was obtained by the reaction of lupane C19-alkyne with 1,4-bis(azidomethyl)benzene using the same catalyst.