Fixation of Natural Furanoeremophilane by Diels–Alder Reaction

Diels–Alder reaction of furanoeremophilan-6β-ol (petasalbin) and its synthetic analogue, 4-hydroxy-4,5,6,7-tetrahydrobenzofuran, was studied using N-ethyl- and N-phenylmaleimides as the dienophiles, affording corresponding adducts as mixtures of stereoisomers. The adduct of petasalbin and maleimide was also obtained when the latter compound was added to a crude extracted solution of Petasites japonicus var. giganteus. By using this method, it...