Sesquiterpenoids from the Rhizome of <i>Ligularia virgaurea</i>

Abstract

Abstract Two novel sesquiterpene dimers, compounds 1 and 2 , were isolated from the rhizome of Ligularia virgaurea , together with the six known sesquiterpenoids 3 – 8 . Their structures were established by physico‐chemical and spectroscopic methods, especially by means of 1D‐ and 2D‐NMR as well as HR‐MS analyses. A mechanism based on a classical Diels–Alder cyclization is proposed for the formation of the dimer 1 from the precursors 8 and the quinone form of 6 ( Scheme ).