Reactions of triterpenoid ketones with sulfur and morpholine under the conditions of Willgerodt-Kindler reaction

Abstract

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.