Isolation and biomimetic synthesis of (±)-calliviminones A and B, two novel Diels–Alder adducts, from Callistemon viminalis

(±)-Calliviminones A (1) and B (2), two Diels–Alder adducts of polymethylated phloroglucinol and myrcene with unprecedented spiro-[5.5] undecene skeleton, were isolated from the fruits of Callistemon viminalis. Structural elucidation was accomplished by NMR spectra studies, and the biomimetic synthesis of compounds 1 and 2 confirmed the pivotal role of Diels–Alder reaction in the plausible biosynthetic pathway. Compounds 1 and 2 were also the...