Homo‐ and Cross Coupling of C‐2 Propargyl Substituted Triterpenoic Acids: Synthesis of Novel Symmetrical and Unsymmetrical Triterpene 1,3‐Diynes

A synthesis of the first representatives of symmetrical and unsymmetrical triterpene 1,3‐diynes in which one or two triterpene cores are linked by a diyne spacer at the C‐2 position of ring A is described. The new triterpenoids are prepared by Cu‐ and Pd‐catalyzed acetylenic homo‐ and cross coupling of accessible C‐2 propynyl derivatives of betulinic, ursolic, and oleanolic acids. New potentially biologically active derivatives of triterpenoic acids bearing 1,3‐diyne moiety at C‐2 position of ring A were obtained by employing the methodology of Cu‐ and Pd‐catalyzed homo‐ and cross‐coupling of terminal alkynes. The resulting compounds can be used as important building blocks for future synthetic transformations due to the high unsaturation and abundant potential reactivity of the diyne carbon chain.