19β,28-Epoxy-18α-oleanan-3-one (I) when heated with sulfur in morpholine gives rise to 2-oxo derivative II, accompanied by a small amount of the starting ketone I. The reaction can be controlled to that 2-oxo derivative II is formed almost exclusively. Derivatives III-VII with a keto group and a further functional group in the position 2 and 3 also give 2-oxo derivative II. In the same manner 3-oxo-18α-oleanan-28→19β-olide (XVIII) was converted to 2-oxo derivative XIX. 1-Oxo derivative VIII and A-nor-ketone IX do not react under these conditions. An addition of vicinal diamine into the reaction mixture leads to the formation of compounds XIII, XV - XVII, XX with pyrazine cycle condensed with the ring A.
19β,28-环氧-18α-齐墩果烷-3-酮(I)在吗啡啉中加热与硫反应,生成2-酮衍生物II,伴随着少量的起始酮I。反应可以控制使得几乎只生成2-酮衍生物II。带有酮基和2、3位进一步官能团的衍生物III-VII也生成2-酮衍生物II。同样地,3-酮-18α-齐墩果烷-28→19β-酯(XVIII)被转化为2-酮衍生物XIX。1-酮衍生物VIII和A-去酮衍生物IX在这些条件下不发生反应。在反应混合物中加入邻二胺会导致形成带有吡嗪环与环A相接的化合物XIII、XV-XVII、XX。